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Active convergence between the Lesser and Greater Caucasus in Georgia: Constraints on the tectonic evolution of the Lesser–Greater Caucasus continental collision
Abstract
We present and interpret newly determined site motions derived from GPS observations made from 2008 through 2016 in the Republic of Georgia, which constrain the rate and locus of active shortening in the Lesser–Greater Caucasus continental collision zone. Observation sites are located along two ∼160 km-long profiles crossing the Lesser–Greater Caucasus boundary zone: one crossing the Rioni Basin in western Georgia and the other crossing further east near the longitude of Tbilisi. Convergence across the Rioni Basin Profile occurs along the southern margin of the Greater Caucasus, near the surface trace of the north-dipping Main Caucasus Thrust Fault (MCTF) system, and is consistent with strain accumulation on the fault that generated the 1991 MW6.9 Racha earthquake. In contrast, convergence along the Tbilisi Profile occurs near Tbilisi and the northern boundary of the Lesser Caucasus (near the south-dipping Lesser Caucasus Thrust Fault), approximately 50–70 km south of the MCTF, which is inactive within the resolution of geodetic observations (<±0.5 mm/yr) at the location of the Tbilisi Profile. We suggest that the southward offset of convergence along strike of the range is related to the incipient collision of the Lesser–Greater Caucasus, and closing of the intervening Kura Basin, which is most advanced along this segment of the collision zone. The identification of active shortening near Tbilisi requires a reevaluation of seismic hazards in this area.
... Most of the works listed above which disputed the existence of large nappes on the southern slope of the Greater Caucasus, were published many years ago, moreover, only in Russian. This is apparently the reason why in some of the latest publications concerning the structure of the Greater Caucasus and its formation, the existence of large tectonic nappes on its southern slope is generally ignored (Forte et al. 2013;Sharkov et al. 2015;Sokhadze et al. 2018;Vasey et al. 2020 and others). Some of these authors pay main attention to the Main Caucasian fault (thrust), which is indeed a very important fault, but, according to all data, this has an insignificant horizontal component (Gudjabidze and Gamkrelidze, 2003;Gamkrelidze et al. 2015;Gamkrelidze and Maisadze, 2016;Mauvilly et al. 2015;Mauvilly et al. 2016;Mosar et al. 2019Mosar et al. , 2022. ...
... Quite remarkable are GPS data obtained by R. Reillinger et al. (2006), A. Karakhanyan et al. (2013) and G. Sokhadze et al. (2018). These data indicate movement of the Earth's crust to the north-northeast in the territory of both Western and Eastern Georgia including the Greater Caucasus and they indicate that the principal convergence between the Lesser and Greater Caucasus in Eastern Georgia occurs along the northern boundary of the Lesser Caucasus. ...
... These data indicate movement of the Earth's crust to the north-northeast in the territory of both Western and Eastern Georgia including the Greater Caucasus and they indicate that the principal convergence between the Lesser and Greater Caucasus in Eastern Georgia occurs along the northern boundary of the Lesser Caucasus. G. Sokhadze et al. (2018) suggest that the southward offset of convergence along the strike of the ridge is associated with the onset of the collision of the Lesser and Greater Caucasus and the closure of the intermediate Kura foreland basin, which, together with the Lesser Caucasus, is the most advanced (with higher velocities of displacement on average, about 8 mm per year, compared with velocities within the Greater Caucasus -about 5 mm per year) in this segment of the collision zone. Thus, it is quite obvious that the subduction both of its footwall and hangingwall are displaced to the north, but the footwall is ahead of the movement of the hangingwall thereby causing its subduction under the Greater Caucasus. ...
In the region of the Caucasus considered herein two large structural complexes have been identified: an autochthone, including the Gagra-Java zone (GJZ) of the Greater Caucasus fold-and-thrust belt, the Kura foreland basin (KFB), and an allochthone consisting of the Utsera-Pavleuri, Alisisgori-Chinchvelta, Sadzeguri- Shakhvetila, Zhinvali-Pkhoveli nappes and Ksani-Arkala parautochthone. The nappes are established on the basis of paleogeographic reconstructions, structural data, as well as drilling and geophysical data. The leading mechanism for the nappe formation is the advancement to the north and the underthrusting of the autochthone under the Greater Caucasus (A-type subduction). The nappes were formed mainly in the Late Alpine time (Late Eocene–Early Pliocene) and include only the sedimentary cover of the Earth’s crust (thin-skinned nappes). However the basal detachment (décollement) of the nappes, according to seismic data, penetrates deeply and cuts the pre-Jurassic crystalline basement, and even the entire Earth’s crust representing thick-skinned deformation. The total horizontal displacement of the flysch nappes of the southern slope of the Greater Caucasus in their eastern (Kakhetian) part is 90–100 km. While, considering the folding of the entire Greater Caucasus, the total transverse shortening of the Earth‘s crust within its limits is equal to 190–200 km.
... Most of the works listed above which disputed the existence of large nappes on the southern slope of the Greater Caucasus, were published many years ago, moreover, only in Russian. This is apparently the reason why in some of the latest publications concerning the structure of the Greater Caucasus and its formation, the existence of large tectonic nappes on its southern slope is generally ignored (Forte et al. 2013;Sharkov et al. 2015;Sokhadze et al. 2018;Vasey et al. 2020 and others). Some of these authors pay main attention to the Main Caucasian fault (thrust), which is indeed a very important fault, but, according to all data, this has an insignificant horizontal component (Gudjabidze and Gamkrelidze, 2003;Gamkrelidze et al. 2015;Gamkrelidze and Maisadze, 2016;Mauvilly et al. 2015;Mauvilly et al. 2016;Mosar et al. 2019Mosar et al. , 2022. ...
... Quite remarkable are GPS data obtained by R. Reillinger et al. (2006), A. Karakhanyan et al. (2013) and G. Sokhadze et al. (2018). These data indicate movement of the Earth's crust to the north-northeast in the territory of both Western and Eastern Georgia including the Greater Caucasus and they indicate that the principal convergence between the Lesser and Greater Caucasus in Eastern Georgia occurs along the northern boundary of the Lesser Caucasus. ...
... These data indicate movement of the Earth's crust to the north-northeast in the territory of both Western and Eastern Georgia including the Greater Caucasus and they indicate that the principal convergence between the Lesser and Greater Caucasus in Eastern Georgia occurs along the northern boundary of the Lesser Caucasus. G. Sokhadze et al. (2018) suggest that the southward offset of convergence along the strike of the ridge is associated with the onset of the collision of the Lesser and Greater Caucasus and the closure of the intermediate Kura foreland basin, which, together with the Lesser Caucasus, is the most advanced (with higher velocities of displacement on average, about 8 mm per year, compared with velocities within the Greater Caucasus -about 5 mm per year) in this segment of the collision zone. Thus, it is quite obvious that the subduction both of its footwall and hangingwall are displaced to the north, but the footwall is ahead of the movement of the hangingwall thereby causing its subduction under the Greater Caucasus. ...
In the region of the Caucasus considered herein two large structural complexes have been identified: an autochthone, including the Gagra-Java zone (GJZ) of the Greater Caucasus fold-and-thrust belt, the Kura foreland basin (KFB), and an allochthone consisting of the Utsera-Pavleuri, Alisisgori-Chinchvelta, Sadzeguri- Shakhvetila, Zhinvali-Pkhoveli nappes and Ksani-Arkala parautochthone. The nappes are established on the basis of paleogeographic reconstructions, structural data, as well as drilling and geophysical data. The leading mechanism for the nappe formation is the advancement to the north and the underthrusting of the autochthone under the Greater Caucasus (A-type subduction). The nappes were formed mainly in the Late Alpine time (Late Eocene–Early Pliocene) and include only the sedimentary cover of the Earth’s crust (thin-skinned nappes). However the basal detachment (décollement) of the nappes, according to seismic data, penetrates deeply and cuts the pre-Jurassic crystalline basement, and even the entire Earth’s crust representing thick-skinned deformation. The total horizontal displacement of the flysch nappes of the southern slope of the Greater Caucasus in their eastern (Kakhetian) part is 90–100 km. While, considering the folding of the entire Greater Caucasus, the total transverse shortening of the Earth‘s crust within its limits is equal to 190–200 km.
... This area absorbs a considerable amount (about 15-20 %) of the strain associated with the Arabia-Eurasia collision (Reilinger et al., 2006), as testified by GPS vectors indicating an anticlockwise motion relative to stable Eurasia, with northward motion increasing from about 2 mm/yr in the Rioni Basin close to the Black Sea coast to 12 mm/yr in the Kura Basin close to the Caspian Sea coast (Forte et al., 2013;Reilinger et al., 2006). Most deformation in the Caucasian region is accommodated in the domain comprised between the Greater and the Lesser Caucasus (named Transcaucasus; Karakhanyan et al., 2013;Sokhadze et al., 2018). ...
... The study area is tectonically active. GPS vectors in the eastern Adjara-Trialeti FTB are N/NNE-oriented and indicate velocities in the order of 4-6 mm/yr, decreasing to the north in the Kura Basin to 2-4 mm/yr (Reilinger et al., 2006;Sokhadze et al., 2018). Historical earthquakes in the study area are of moderate intensity, with the last major event recorded in 2002 in the surroundings of Tbilisi (Fig. 2) yielding a magnitude of 4.5 (Tibaldi et al., 2020). ...
... At this time the area was characterized by the convergence between the Greater and Lesser Caucasus (Nemčok et al., 2013). We propose that strike-slip tectonics could have caused such a subsidence pulse just before the uplift of the area, based on (i) paleomagnetic and structural data (Avagyan et al., 2005;Meijers et al., 2017;Rolland, 2017) suggesting oroclinal bending accompanied by strike-slip deformation in the Lesser Caucasus/Transcaucasus during the Cenozoic; (ii) present-day GPS vectors indicating anticlockwise rotation of the Arabian Plate and in the Kura Basin (Forte et al., 2014;Reilinger et al., 2006); (iii) earthquake focal mechanisms suggesting transpression/transtension in the eastern Transcaucasus (Ismail-Zadeh et al., 2020;Sokhadze et al., 2018;Tibaldi et al., 2020); (iv) fault patterns likely associated to the structural inversion of strike-slip (transtensional) faults imaged in seismic profiles in the eastern Adjara-Trialeti fold-and-thrust belt (see cross-section of Fig. 7 and Tari et al., 2021), and (v) the high subsidence rates evidenced in the modelling results (Fig. 10). Additional field-based structural studies are needed to test this hypothesis. ...
... White boxes highlight the locations of the seven detrital samples analyzed for zircon (U-Th)/He used in this study, and labels are keyed to Figure (c) Gray swath shows maximum, minimum, and mean topography within the swath in (a). Red swath is smoothed convergence between the Lesser Caucasus and southern margin of the Greater Caucasus as measured by GPS (Kadirov et al., 2012;Reilinger et al., 2006;Sokhadze et al., 2018). Details of the calculation of convergence are discussed in Forte et al. (2014) and Forte et al. (2022). ...
... This estimate was confirmed and slightly refined in a larger, regional compilation of paleomagnetic data and plate reconstruction for the Mediterranean region by van Hinsbergen et al. (2019). Decadal scale GPS data show an order of magnitude along-strike eastward increase from <2 mm/yr to >14 mm/yr of NE-SW Lesser Caucasus motion with respect to stable Eurasia, driven by counter-clockwise rotation of the Lesser Caucasus block (Figure 1c, e.g., Kadirov et al., 2012;Reilinger et al., 2006;Sokhadze et al., 2018). In part, the slow rates of geodetic convergence paired with the high topography of the western GC led to the suggestion that additional sources of uplift, for example, isostatic response to slab detachment, were necessary to explain the topography of the western portion of the range, but critically assumed this velocity gradient present in the GPS data to be a long-lived pattern . ...
... The majority of modern LC motion appears to be accommodated via shortening along the southern flank of the GC, but with noticeable departures near the center of the range, where significant fractions of shortening are accommodated in the interior or along the northern edge ( Figure 1; Forte et al., 2014). This shift in locus of shortening within the range may relate to the ongoing collision of the LC and GC structural systems in the center of the range (e.g., Alania, Beridze, et al., 2021;Banks et al., 1997;Forte et al., 2014;Nemčok et al., 2013;Sokhadze et al., 2018). It is unclear how far back in time these convergence gradients, either the broad counter-clockwise LC motion or the partitioning between shortening on the southern versus northern flank of the GC, can be extrapolated. ...
The Greater Caucasus (GC) Mountains within the central Arabia‐Eurasia collision zone are an archetypal example of a young collisional orogen. However, the mechanisms driving rock uplift and forming the topography of the range are controversial, with recent provocative suggestions that uplift of the western GC is strongly influenced by an isostatic response to slab detachment, whereas the eastern half has grown through shortening and crustal thickening. Testing this hypothesis is challenging because records of exhumation rates mostly come from the western GC, where slab detachment may have occurred. To address this data gap, we report 623 new, paired zircon U‐Pb and (U‐Th)/He ages from seven different modern river sediments, spanning a ∼400 km long gap in bedrock thermochronometer data. We synthesize these with prior bedrock thermochronometer data, recent catchment averaged ¹⁰Be cosmogenic exhumation rates, topographic analyses, structural observations, and plate reconstructions to evaluate the mechanisms growing the GC topography. We find no evidence of major differences in rates, timing of onset of cooling, or total amounts of exhumation across the possible slab edge, inconsistent with previous suggestions of heterogeneous drivers for exhumation along‐strike. Comparison of exhumation across timescales highlight a potential acceleration, but one that appears to suggest a consistent northward shift of the locus of more rapid exhumation. Integration of these new datasets with simple models of orogenic growth suggest that the gross topography of the GC is explainable with traditional models of accretion, thickening, and uplift and does not require any additional slab‐related mechanisms.
... White boxes highlight the locations of the seven detrital samples analyzed for zircon (U-Th)/He used in this study, and labels are keyed to Figure (c) Gray swath shows maximum, minimum, and mean topography within the swath in (a). Red swath is smoothed convergence between the Lesser Caucasus and southern margin of the Greater Caucasus as measured by GPS (Kadirov et al., 2012;Reilinger et al., 2006;Sokhadze et al., 2018). Details of the calculation of convergence are discussed in Forte et al. (2014) and Forte et al. (2022). ...
... This estimate was confirmed and slightly refined in a larger, regional compilation of paleomagnetic data and plate reconstruction for the Mediterranean region by van Hinsbergen et al. (2019). Decadal scale GPS data show an order of magnitude along-strike eastward increase from <2 mm/yr to >14 mm/yr of NE-SW Lesser Caucasus motion with respect to stable Eurasia, driven by counter-clockwise rotation of the Lesser Caucasus block (Figure 1c, e.g., Kadirov et al., 2012;Reilinger et al., 2006;Sokhadze et al., 2018). In part, the slow rates of geodetic convergence paired with the high topography of the western GC led to the suggestion that additional sources of uplift, for example, isostatic response to slab detachment, were necessary to explain the topography of the western portion of the range, but critically assumed this velocity gradient present in the GPS data to be a long-lived pattern . ...
... The majority of modern LC motion appears to be accommodated via shortening along the southern flank of the GC, but with noticeable departures near the center of the range, where significant fractions of shortening are accommodated in the interior or along the northern edge ( Figure 1; Forte et al., 2014). This shift in locus of shortening within the range may relate to the ongoing collision of the LC and GC structural systems in the center of the range (e.g., Alania, Beridze, et al., 2021;Banks et al., 1997;Forte et al., 2014;Nemčok et al., 2013;Sokhadze et al., 2018). It is unclear how far back in time these convergence gradients, either the broad counter-clockwise LC motion or the partitioning between shortening on the southern versus northern flank of the GC, can be extrapolated. ...
... White boxes highlight the locations of the seven detrital samples analyzed for zircon (U-Th)/He used in this study, and labels are keyed to Figure (c) Gray swath shows maximum, minimum, and mean topography within the swath in (a). Red swath is smoothed convergence between the Lesser Caucasus and southern margin of the Greater Caucasus as measured by GPS (Kadirov et al., 2012;Reilinger et al., 2006;Sokhadze et al., 2018). Details of the calculation of convergence are discussed in Forte et al. (2014) and Forte et al. (2022). ...
... This estimate was confirmed and slightly refined in a larger, regional compilation of paleomagnetic data and plate reconstruction for the Mediterranean region by van Hinsbergen et al. (2019). Decadal scale GPS data show an order of magnitude along-strike eastward increase from <2 mm/yr to >14 mm/yr of NE-SW Lesser Caucasus motion with respect to stable Eurasia, driven by counter-clockwise rotation of the Lesser Caucasus block (Figure 1c, e.g., Kadirov et al., 2012;Reilinger et al., 2006;Sokhadze et al., 2018). In part, the slow rates of geodetic convergence paired with the high topography of the western GC led to the suggestion that additional sources of uplift, for example, isostatic response to slab detachment, were necessary to explain the topography of the western portion of the range, but critically assumed this velocity gradient present in the GPS data to be a long-lived pattern . ...
... The majority of modern LC motion appears to be accommodated via shortening along the southern flank of the GC, but with noticeable departures near the center of the range, where significant fractions of shortening are accommodated in the interior or along the northern edge ( Figure 1; Forte et al., 2014). This shift in locus of shortening within the range may relate to the ongoing collision of the LC and GC structural systems in the center of the range (e.g., Alania, Beridze, et al., 2021;Banks et al., 1997;Forte et al., 2014;Nemčok et al., 2013;Sokhadze et al., 2018). It is unclear how far back in time these convergence gradients, either the broad counter-clockwise LC motion or the partitioning between shortening on the southern versus northern flank of the GC, can be extrapolated. ...
... By combining this zircon U-Pb age dataset with published stratigraphy for the three sampled sections, we find evidence for coarsening and shallowing foreland basin deposition leading to erosional conditions, derivation of sediment from deeper crustal levels in the orogen, and establishment of an axial drainage network in the foreland basin. We combine the timing of these stratigraphic changes with published thermochronometric , geodetic (Reilinger et al., 2006;Kadirov et al., 2012Kadirov et al., , 2015Sokhadze et al., 2018), and paleomagnetic (Austermann and Iaffaldano, 2013;van der Boon et al., 2018) records to correlate sedimentary changes such as the transition to erosional conditions in the basin with distinct stages of the transition from soft to hard collision ( Fig. 6.1). In doing so, we develop a framework for the stratigraphic record of collision that may be applicable to interpreting the stratigraphic archives of other collisional orogens. ...
... The Kura Basin and the Lesser Caucasus are on the lower plate of this subduction system ( Fig. 6.2b). There are no deep earthquakes beneath the western Greater Caucasus (Mumladze et al., 2015) and GPS convergence rates in the western Greater Caucasus are 3-4 mm/yr (Reilinger et al., 2006;Kadirov et al., 2015;Sokhadze et al., 2018), suggesting that subduction in the western part of the range has ceased and this part of the range is colliding with the Lesser Caucasus, which is located immediately to the south. At the locus of collision, elevated topography is contiguous between the Greater and Lesser Caucasus ( Fig. 6.2c). ...
... The orogen is inferred from geological and geophysical data to be in the process of transitioning from subduction to collision (Mumladze et al., 2015;Cowgill et al., 2016, Tye et al., submitted). Deep earthquakes suggest the presence of a subducting slab beneath the Eastern Greater Caucasus ( Fig. 7.1a;Mellors et al., 2012;Mumladze et al., 2015) and geodetic convergence rates indicate that 10-12 mm/yr of shortening is accommodated in the Eastern Greater Caucasus, while 4 mm/yr is accommodated in the western part of the orogen ( Fig. 7.1a;Reilinger et al., 2006;Kadirov et al., 2012Kadirov et al., , 2015Sokhadze et al., 2018). These deep earthquakes and geodetic convergence rates have been interpreted to suggest that collision has begun in the western part of the orogen while active subduction continues in the Eastern Greater Cauacasus (Mumladze et al., 2015). ...
The distribution of strain in continents is of primary importance in determining Earth's topography, the distribution of Earth resources, and hazards. This dissertation explores several records of continental deformation on timescales from thousands to millions of years and spatial scales from single faults to whole orogens. Many of these records are influenced by a complex set of factors and have limited sampling, so I develop and use new Bayesian statistical approaches in order to rigorously quantify uncertainties in data and interpretations. The dissertation work is broadly centered on three themes. First, a novel Bayesian statistical method for modeling and comparing detrital zircon U-Pb age distributions is developed (Chapters 2, 3). It is shown that this method can be used to accurately infer uncertainties on population age distributions inferred from samples, leading to more robust interpretations of geologic processes from detrital geochronology datasets. In addition, the new method is shown to permit robust quantitative inferences of mixing and dilution between detrital zircon populations. Second, the potential to infer paleoseismic slip histories from bedrock fault scarp rock properties including strength and roughness is explored using bedrock scarps of the Hebgen Fault, Montana, and the Pleasant Valley Fault, Nevada (Chapters 4, 5). It is demonstrated that on bedrock normal fault scarps, Schmidt hammer strength measurements and microtopographic roughness are distributed in a stepwise pattern up-scarp, suggesting that these physical properties reflect exposure of patches of the scarp during successive earthquakes. The number and timing of paleoseismic events inferred from bedrock scarp strength and microtopography are consistent with available independent constraints on paleoseismic slip history for the analyzed scarps. Third, the structural and stratigraphic effects of the transition from subduction to continental collision are investigated using the Greater Caucasus as a natural laboratory (Chapters 6, 7). A structural and thermochronometric investigation of the Eastern Greater Caucasus, where subduction is active, reveals that pervasive out-of-sequence folding in the core of the range plays a significant role in thickening the accretionary wedge as it grows in order to maintain a critical taper. Detrital zircon provenance of three foreland basin stratigraphic sections distributed along strike of the orogen reveals a detailed picture of the changes in source exposure and sediment routing that accompany the transition from subduction to collision. Initial entrance of tapered lower plate continental lithosphere into the subduction zone occurred between 15 and 8 Ma in the Caucasus, 3 - 10 Myrs before plate kinematic and exhumational effects of collision began at 5 Ma. Inferred collision-related slowing of plate convergence and acceleration of exhumation in the Caucasus coincided with the development of erosive conditions in the foreland basin between the two colliding continents and the concomitant formation of an axial drainage network that transported sediment laterally within the foreland basin. The chapters of the dissertation are unified in their exploration of how continental deformation at different temporal and spatial scales is preserved in the geologic record. Because of the complexity of many of these records and the uncertainties inherent in their interpretation, Bayesian statistical methods offer a promising way to increase the reliability of quantitative geological interpretations, as documented in several of the chapters. In addition, the dissertation makes a significant contribution to our understanding of the transition from subduction to collision.
... ≥ 5 It is known that large earthquakes (M ) are prepared for quite a long time, which means that the process of tectonic stress accumulation takes a long time in any seismically active region. For this reason, it is essential that these active regions are simultaneously monitored using the space geodetic techniques of Global Navigation Satellite System (GNSS) permanent networks, which have the potential to identify anomalous regions of high tectonic stress accumulation (Banks et al., 1997;Reilinger et al., 2006;Khamidov, 2017;Khazaradze et al., 2019;Sokhadze et al., 2018Sokhadze et al., , 2020Elshin and Tronin, 2020). In Transcaucasia, including Georgia, these type of observations have been conducted in collaboration with scientists from the United States since the end of the last century (Reilinger et al., 2006;Sokhadze et al., 2018Sokhadze et al., , 2020. ...
... For this reason, it is essential that these active regions are simultaneously monitored using the space geodetic techniques of Global Navigation Satellite System (GNSS) permanent networks, which have the potential to identify anomalous regions of high tectonic stress accumulation (Banks et al., 1997;Reilinger et al., 2006;Khamidov, 2017;Khazaradze et al., 2019;Sokhadze et al., 2018Sokhadze et al., , 2020Elshin and Tronin, 2020). In Transcaucasia, including Georgia, these type of observations have been conducted in collaboration with scientists from the United States since the end of the last century (Reilinger et al., 2006;Sokhadze et al., 2018Sokhadze et al., , 2020. ...
... In this study, new GPS observations are presented for the period of 2008 to 2016 for 21 surveymode sites and nine continuous stations. The GPS observations are primarily aligned along two roughly range-perpendicular profiles that crossed the Lesser and Greater Caucasus boundary zone (Figure 1, it is the Figure 2 of Sokhadze et al., 2018). The objectives of the study were to determine the rate of active deformation across these two segments of the boundary and use the observed deformation and elastic fault models to constrain the locations and character of active structures in this portion of the Arabia-Eurasia collision zone (Figure 1). ...
It is widely known that very low frequency/ low frequency (VLF/LF) radiation has been recorded prior to large earthquakes in several seismically active countries of the world. The networks employed to detect this radiation consist of stationary transmitters and receivers. However, there are reported cases of existing networks being unable to detect any electromagnetic radiation prior to large earthquakes. In this study, we determined the optimal arrangement of a mobile VLF/LF electromagnetic radiation network to ensure the detection of an upcoming earthquake precursor. We considered the possible arrangements of the VLF/LF mobile network based on certain physical considerations, and developed a relatively simple arrangement that is completely different from the existing stationary networks. The suggested design will significantly increase the number of detected/ predicted earthquakes by using the relevant electromagnetic radiation receivers strategically placed in regions of increased tectonic and seismic activity.
... During the late Cenozoic, in response to collision between Arabia and Eurasian plates and their subsequent deformations, convergence between the LC and GC orogens took place in far-field zone (e.g. Adamia et al. 2010;Alania et al. 2017a;Banks et al. 1997;Nemcok et al., 2013;Sokhadze et al. 2018). Between the two opposite verging chains of the LC and the GC, the Rioni and Kura foreland basins (KFB) are located (Adamia et al. 2010(Adamia et al. , 2011aAlania et al. 2017a;Banks et al. 1997;Cowgill et al. 2016;Forte et al. 2014;Sokhadze et al. 2018;T arietal. ...
... Adamia et al. 2010;Alania et al. 2017a;Banks et al. 1997;Nemcok et al., 2013;Sokhadze et al. 2018). Between the two opposite verging chains of the LC and the GC, the Rioni and Kura foreland basins (KFB) are located (Adamia et al. 2010(Adamia et al. , 2011aAlania et al. 2017a;Banks et al. 1997;Cowgill et al. 2016;Forte et al. 2014;Sokhadze et al. 2018;T arietal. 2018;Tibaldi et al. 2017). ...
... Currently available structural models considerably differ from each other (e.g. Adamia et al. 2010;Alania et al. 2017a;Banks et al. 1997;Basheleishvili 1985;Gamkrelidze 1976;Nemcok et al. 2013;Papava 1967;Sokhadze et al. 2018;Sosson et al. 2013Sosson et al. , 2016. According to one group of authors, the frontal part of the western KFB in the study area is overthrusted on the frontal part of the LC (Basheleishvili 1984;Gamkrelidze 1976;Papava 1967), while another group believes that frontal part of LC is represented by a triangle zone, and the south-vergent thrust is a passive-backthrust formed as a result of the northward displacement of a duplex (Alania et al. 2017a;Banks et al. 1997;Nemcok et al. 2013;Sosson et al. 2013Sosson et al. , 2016. ...
Abstract The thrust front of the central Lesser Caucasus and southern part of the
Greater Caucasus orogens is one of the key regions of an apparent convergence
zone between two orogens. The formation of the complex structure of the Lesser
Caucasus-Greater Caucasus convergence zone is governed by the northward and
southward-directed thrusting. Here we show the structural style of deformation of
a convergence zone between Lesser Caucasus retro-wedge and Greater Caucasus
pro-wedge based on seismic reflection profiles. Seismic profiles reveal the transition
between convergence and the initial collision zone within the study area. The frontal
part of the Lesser Caucasus retro-wedge is represented by a shallow triangle zone
and north-vergent structural wedge. The thrust front of Greater Caucasus pro-wedge
is represented by south-vergent fault-related folds. Between the Lesser Caucasus
and Greater Caucasus frontal parts, the undeformed Kura foreland basin is located.
... According to GPS data, the rate of this convergence is up to 30 mm/year [37,[46][47][48]. The convergence rate across the Lesser Caucasus is up to 10 mm/year, while in the Greater Caucasus, it reaches values up to 4 mm/year [35,37,49]. The rate of convergence between the Lesser and Greater Caucasus increases from approximately 4 mm/year in the Rioni basin to about 14 mm/year in the Kura Basin [35,37,37,40,[49][50][51][52][53]. ...
... The convergence rate across the Lesser Caucasus is up to 10 mm/year, while in the Greater Caucasus, it reaches values up to 4 mm/year [35,37,49]. The rate of convergence between the Lesser and Greater Caucasus increases from approximately 4 mm/year in the Rioni basin to about 14 mm/year in the Kura Basin [35,37,37,40,[49][50][51][52][53]. The Enguri area, situated in western Georgia, is characterized by three main tectonic units, each with distinct geological development structures. ...
A spectral analysis of the time dynamics of seismicity occurring in the Enguri area of Georgia from 1978 to 2021 is performed by means of Schuster’s spectrum analysis, periodogram analysis, and empirical mode decomposition. The results of our analysis suggest that earthquakes around the reservoir (within a 50 km radius from the center of the dam) may be due to changes in water level, featured by the yearly cycle of loading and unloading operations of the reservoir. It is observed that the impacts of water fluctuations are more pronounced in shallower strata (down to 10 km) than deeper ones (down to 20 km); this could indicate that earthquakes occurring at deeper levels may primarily result from tectonic forces, whereas those at shallower depths may be predominantly triggered by reservoir-induced factors.
... The compression is attenuated to the east and west from the central segments of the Caucasus like butterfly wings. According to the seismological, paleoseismological, and GPS data, convergence between the Eurasian and African-Arabian plates is still active, causing deformation within the mountain belt and in surrounding regions (Adamia et al. 2017;Alizadeh et al. 2016;Allen et al. 2004;Avagyan et al. 2010;Jackson et al. 1997;Kadirov et al. 2008Kadirov et al. , 2015Kadirov et al. , 2012Koçyigit et al. 2001;Pasquarè et al. 2011;Rebai et al. 1993;Reilinger et al. 2006;Sokhadze et al. 2018;Tan and Taymaz 2006;Tibaldi et al. 2017aTibaldi et al. , b, 2018bTsereteli et al. 2016b). Based on the GPS data, the convergent rate is up to 30 mm/year (DeMets et al. 1990(DeMets et al. , 1994Reilinger et al. 2006;Triep et al. 1995). ...
... Although the induced tectonic stress by the northward motion of the Arabian plate is mainly absorbed in the Periarabian Ophiolitic Suture Zone and in the Zagros fold-thrust belts, the stress is propagated towards the Central Caucasus and causes crustal shortening and causes the convergent rate of up to 10 mm/year and 4 mm/year across the Lesser Caucasus and Greater Caucasus, respectively. The rate of convergence between the Lesser and Greater Caucasus, in fact, decreases from about 14 mm/year in the Kura Basin to about 4 mm/year in the Rioni basin (Aktug et al. 2013;Guliev et al. 2002;Kadirov et al. 2012;Mcclusky et al. 2000;Reilinger et al. 1997Reilinger et al. , 2006Shevchenko et al. 1999;Sokhadze et al. 2018). The major geodynamic activity of the region results in the occurrence of frequent moderate to strong earthquakes. ...
In the frame of the DAMAST (Dams and Seismicity) project, we deployed a dense high-fidelity seismological real-time network to investigate in detail the spatio-temporal seismicity distribution around the Enguri high dam, situated in the greater Caucasus in western Georgia. We aim at recording the weak seismicity in a 10 km distance around the dam structure. To lower the detection threshold by reducing the ambient background noise, we installed four seismic stations in shallow (ca. 20 m) and deep boreholes. From these stations, KIT1 with a depth of ca. 250 m is the deepest seismological station in Georgia. In this paper, we characterize the seismicity recorded by the local seismic network from October 2020 to July 2022. To have a better historical picture of the seismic activity, especially since the dam construction and initial operations, re-processing of the old seismological catalogs was carried out. This required digitizing the paper-only catalog copies prior to relocation. We finally obtain a uniform catalog for the Enguri region to characterize the seismicity and start investigating its possible relationship with the exploitation of the dam reservoirs.
... Alania et al., 2021;Tari et al., 2021). Based on geodetic measurements, the ATFTB currently absorbs 3-6 mm/yr of the convergence rate between the eastern Anatolian Plateau and Eurasia (Reilinger et al., 2006;Sokhadze et al., 2018). Total shortening along the northern frontal structures was estimated at $ 15 km (Bazhenov and Burtman, 2002); northward advancement of these frontal structures has progressively deformed the southern margins of the Rioni-Kartli foreland basin (Alania et al., 2017;Banks et al., 1997;Nemčok et al., 2013). ...
... The GPS velocity field indicates an anticlockwise motion relative to stable Eurasia, with northward motion increasing from $ 2 mm/yr in the Rioni Basin close to the Black Sea coast to 12 mm/yr in the Kura Basin close to the Caspian Sea coast (Forte et al., 2013;Reilinger et al., 2006). Most deformation in the Caucasian region is accommodated in the domain comprised between the Greater and the Lesser Caucasus (named Transcaucasus; Karakhanyan et al., 2013;Sokhadze et al., 2018). ...
... Geodetic observations suggest that the majority of Arabia-Eurasia shortening at the latitude of the Greater Caucasus is being accommodated on structures within the Greater Caucasus Mountains (e.g., Philip et al., 1989;Jackson, 1992;Allen et al., 2004;Reilinger et al., 2006), which root into a shallowly north-dipping fault beneath the range (Sokhadze et al., 2018). Meanwhile, structural observations from the region suggest that faults within the core of the orogen are steeply dipping and thus are not favorably oriented to accommodate active tectonic shortening (e.g., Somin, 2000). ...
... A broad array of new data sets from the Greater Caucasus has been published in recent years, including low-temperature thermochronology to constrain exhumation timing and magnitude (e.g., Avdeev and Niemi, 2011;Vincent et al., 2011Vincent et al., , 2020Vasey et al., 2020), sediment provenance analysis to constrain paleogeography (e.g., Morton et al., 2003;Vincent et al., 2014;Cowgill et al., 2016;Tye et al., 2021), and investigation of geomorphic indices of uplift (e.g., Forte et al., 2014) and geodetic data (e.g., Reilinger et al., 2006;Kadirov et al., 2012;Sokhadze et al., 2018) to constrain modern deformation patterns. Structural and tectonic studies (e.g., Alania et al., 2020aAlania et al., , 2020bTibaldi et al., 2018Tibaldi et al., , 2020Vasey et al., 2020) are often localized and do not report regionally distributed structural data from the core of the range, which are critical for establishing a tectonic framework in which to interpret the new data sets in the context of active orogenic uplift and evolution. ...
Although the Greater Caucasus Mountains have played a central role in absorbing late Cenozoic convergence between the Arabian and Eurasian plates, the orogenic architecture and the ways in which it accommodates modern shortening remain debated. Here, we addressed this problem using geologic mapping along two transects across the southern half of the western Greater Caucasus to reveal a suite of regionally coherent stratigraphic packages that are juxtaposed across a series of thrust faults, which we call the North Georgia fault system. From south to north within this system, stratigraphically repeated ~5–10-km-thick thrust sheets show systematically increasing bedding dip angles (<30° in the south to subvertical in the core of the range). Likewise, exhumation depth increases toward the core of the range, based on low-temperature thermochronologic data and metamorphic grade of exposed rocks. In contrast, active shortening in the modern system is accommodated, at least in part, by thrust faults along the southern margin of the orogen. Facilitated by the North Georgia fault system, the western Greater Caucasus Mountains broadly behave as an in-sequence, southward-propagating imbricate thrust fan, with older faults within the range progressively abandoned and new structures forming to accommodate shortening as the thrust propagates southward. We suggest that the single-fault-centric “Main Caucasus thrust” paradigm is no longer appropriate, as it is a system of faults, the North Georgia fault system, that dominates the architecture of the western Greater Caucasus Mountains.
... Geodetic data indicate that the ATFTB is tectonically active and accommodates 3-6 mm/yr of the present convergence rate between the eastern Anatolian Plateau and Eurasia (Reilinger et al., 2006;Sokhadze et al., 2018) (Fig. 2). The major earthquakes within the fold-and-thrust belt are characterized by transpressive focal mecha nisms (Sokhadze et al., 2018;Tsereteli et al., 2016). ...
... Geodetic data indicate that the ATFTB is tectonically active and accommodates 3-6 mm/yr of the present convergence rate between the eastern Anatolian Plateau and Eurasia (Reilinger et al., 2006;Sokhadze et al., 2018) (Fig. 2). The major earthquakes within the fold-and-thrust belt are characterized by transpressive focal mecha nisms (Sokhadze et al., 2018;Tsereteli et al., 2016). Seismicity is higher in the Rioni-Kartli-Kura foreland basin to the north (Adamia et al., 2017a;Tibaldi et al., 2017) where fault-plane solution data indicate ongoing north-south-oriented compression and convergence rates can reach 12 mm/yr (Forte et al., 2014(Forte et al., , 2013Karakhanyan et al., 2013;Reilinger et al., 2006). ...
The 350 km-long Adjara-Trialeti fold-and-thrust belt of southwestern Georgia is the result of the structural inversion of a continental back-arc basin developed in the Paleogene on the upper (Eurasian) plate of the northward subducting northern branch of the Neotethys. Low-temperature thermochronological data [fission- track and (U-Th)/He analyses on apatite] from sedimentary and plutonic rocks provide robust constraints on the tectonic evolution of the Adjara-Trialeti orogenic belt. Fission-track central ages range from the Middle Eocene to the Middle Miocene (46–15 Ma); helium ages are clustered in the Late Miocene-Pliocene (10–3 Ma). Time-temperature paths obtained integrating thermochronologic, stratigraphic, and radiometric data show that the volcanosedimentary basin fill of the Adjara-Trialeti back-arc basin underwent progressive burial heating prior to final cooling/exhumation in the late Middle Miocene-Pliocene. These new data show that the Adjara- Trialeti back-arc basin was inverted and developed as a fold-and-thrust belt starting at 14–10 Ma, in tune with widespread Middle-to-Late Miocene shortening and exhumation across wide areas of the Middle East, from the eastern Pontides of NE Turkey to the Lesser Caucasus in northern Armenia and NW Azerbaijan, and the Talysh and Alborz ranges in northern Iran. Such a supraregional tectonism is interpreted as a far-field effect of the Arabia-Eurasia collision along the Bitlis suture ca. 400 km to the south of the study area.
... In the beginning of Tortonian, the uplit of the Carpathians isolated the CP from the rest of the Paratethys and transformed it into the Lake Pannon (ter Borgh et al., 2014). In the terminal Bessarabian, uplift of the Caucasus and the closure of the Transcaucasian Strait took place (Cavazza et al., 2024;Mosar et al., 2010;Nemčok et al., 2013;Sokhadze et al., 2018). During the Khersonian, a series of sudden high-amplitude water level drops in the Eastern Paratethys not only disconnected its subbasins (including the Caspian Basin) but also provoked a near-total extinction of all faunal groups (Paramonova, 1994;Popov et al., 2010;Gol'din and Startsev, 2017;Maissuradze and Koiava, 2011). ...
The hydrological connectivity of semi-isolated basins with the global ocean drives remarkable ecosystem turnover and regional climate shifts, making palaeoenvironmental and palaeohydrological studies of the epicontinental basins of high relevance. During the late Middle–Late Miocene, the Paratethys Sea, which occupied vast areas of the West Eurasian Interior, underwent a notable hydrological isolation from the global ocean. Between 12.65 and 7.65 Ma, the Paratethys experienced significant water level fluctuations and eventually near-total ecosystem collapse. The causes and timing of these hydrological and biotic changes remain unclear, especially in the understudied Caspian Sea region. Our study presents an integrated stratigraphic framework of the 136-m-thick Karagiye section on the east coast of the Caspian Sea (Mangystau region, Kazakhstan). The fauna-rich deposits document the pre- (Konkian), syn- (Volhynian, Bessarabian and Khersonian) and post-isolation (Maeotian) phases of Paratethys evolution at its eastern margin. We reconstruct the palaeoenvironmental history of the Caspian Basin by combining palaeomagnetic dating with biostratigraphic analyses of microfauna, molluscs, marine vertebrates and calcareous nannoplankton. Our key findings in the studied section include: 1. Konkian (incomplete): Open lagoonal environments with restricted connectivity to the global ocean in the early Konkian followed by a middle Konkian faunal influx and establishment of normal marine environments; 2. Volhynian (incomplete, 12.3–12.05 Ma): Onset of Paratethys hydrological isolation with marginal lagoonal environments, new endemic species, plus rare surviving Konkian taxa; 3. Bessarabian (12.05–9.9 Ma): Transgression and offshore setting at ~12.05 Ma with maximum flooding at 11.6 Ma and Intra-Bessarabian Carbonate Surge at ~10.7 Ma, followed by upper Bessarabian (10.7–9.9 Ma) carbonate platform interior settings; 4. Khersonian (9.9–7.65 Ma): Khersonian Ecological Crisis, carbonate platform to backshore environments with hiatus between 9.5 and ~8.0 Ma representing an extreme lowstand. 5. Maeotian (incomplete 7.65–7.0 Ma): Transgression at 7.65 Ma, followed by a delayed invasion of Maeotian faunas at 7.5 Ma, linked to the reconnection of the Caspian Basin with the rest of the Eastern Paratethys. The well-dated biotic record of Karagiye enhances understanding of Paratethyan hydrological and ecological events in the Caspian Basin and provides a foundation for further palaeoclimatic and palaeobiogeographic studies across Eurasia.
... Tbilisi is the capital of Georgia, and its adjacent territory is located within the Adjara-Trialeti fold-thrust mountain belts in the intermountain (Mtkvari) depression which is notably narrow in that place. In the Tbilisi area, the (submeridional) N-S shortening through the Greater and Lesser Caucasus is mainly localized within the Lesser Caucasus [32]. There are several active faults around Tbilisi; two of them are parallel with the latitudinal strike and are located along the northern and southern borders of the Adjara-Trialeti zone with reverse motion dipping to the south and north, respectively ( Figure 2). ...
The attenuation of high-frequency seismic waves was investigated in the crust beneath Tbilisi and the surrounding territory by analysing 225 local earthquakes that occurred from 2008 to 2020 and were recorded by eight seismic stations. The quality factors of coda waves QC and direct P and S waves, QP and QS, were estimated using the single backscattering model and the extended coda normalization method, respectively. The separation of intrinsic quality factors Qi from scattering quality factor QSC was fulfilled by Wennerberg’s method. Observed results show that all evaluated attenuation parameters are frequency-dependent in the frequency range of 1-32 Hz and increase with increasing frequency. Coda QC values increase also with increasing lapse time window from 20 s to 50 s and vary from 91±5 at 1.5 Hz to 1779±108 at 24 Hz, respectively. P waves attenuate slightly faster than S waves, and the ratio of QS/QP is more than unity and varies in a range of 1.5-1.8. The intrinsic and scattering quality factors are expressed by the following power laws: Qi=77±4f0.930±0.046 and QSC=219±6f0.924±0.050. The results show that Qi is close to QC, but QSC is larger than Qi, which means that intrinsic attenuation has a dominant role compared with the scattering effect. Our results were compared with those obtained in two other seismically active regions of Georgia, as well as with regions of the world. In general, the observed quality factors and their frequency-dependent relationships follow a similar trend, characterizing seismically active regions with complex tectonics. The calculated attenuation parameters characterize the entire earth’s crust under Tbilisi and the surrounding area. The results obtained will be useful in future seismological studies since the Q parameters are estimated for the first time for the given region.
... Inset simplifies major regional tectonic faults and representative GPS velocity relative to stable Eurasia. et al., 2003;Avdeev & Niemi, 2011;Cowgill et al., 2016;Forte, 2012;Forte et al., 2010Forte et al., , 2013Forte et al., , 2014Forte et al., , 2015Sokhadze et al., 2018;Sukhishvili et al., 2021;Tibaldi et al., 2017;Trexler et al., 2020;Trifonov, 1978). In contrast, few studies have utilized paleoseismic trenching to examine faults in the Greater Caucasus (Ovsyuchenko et al., 2014;Rogozhin et al., 2004). ...
Here we present the results of the first paleoseismic study of the Kura fold‐thrust belt in Azerbaijan based on field mapping, fault trenching, and Quaternary dating. Convergence at rates of ∼10 mm/yr between the Arabian and Eurasian Plates is largely accommodated by the Kura fold‐thrust belt which stretches between central Azerbaijan and Georgia along the southern front of the Greater Caucasus (45–48°E). Although destructive historic earthquakes are known here, little is known about the active faults responsible for these earthquakes. A paleoseismic trench was excavated across a 2‐m‐high fault scarp near Agsu revealing evidence of two surface rupturing earthquakes. Radiocarbon dating of the faulted sediments limits the earthquake timing to AD 1713–1895 and AD 1872–2003. Allowing for uncertainties in dating, the two events likely correspond to historical destructive M ∼ 7 earthquakes near Shamakhi, Azerbaijan in AD 1668 and 1902. A second trench 60 km west of Agsu was excavated near Goychay also revealing evidence of at least one event that occurred 334–118 BC. Holocene shortening and dip‐slip rates for the Kura fold‐thrust belt are ∼8.0 and 8.5 mm/yr, respectively, based on an uplifted strath terrace west of Agsu. The only known historical devastating (M > ∼7) earthquakes in the Kura region, west of Shamakhi, occurred in 1139 and possibly 1668. The lack of reported historical ruptures from the past 4–8 centuries in the Kura, in contrast with the numerous recorded destructive earthquakes in Shamakhi, suggests that the Kura fold‐thrust belt may have accumulated sufficient strain to produce a M > 7.7 earthquake.
... GNSS measurements in the Caucasus, which were started in the 1990s [Reilinger et al., 1997;Shevchenko et al., 1999], are of high interest. Now, they have almost a thirty-year history [Ismail-Zadeh et al., 2020;Karapetyan et al., 2020;Mironov et al., 2021;Reilinger et al., 2006;Sokhadze et al., 2018;Tibaldi et al., 2021]. Measurements of recent crustal movements in the Caucasus are very heterogeneous, as a large number of scientific groups have worked in these regions [Tibaldi et al., 2021]. ...
There are numerous methods for modeling velocity fields of the Earth's crust. However, only a few of them are capable of modeling data beyond the contour of the geodetic network (extrapolating). Spatial modeling based on a neural network approach allows for the adequate modeling of the field of recent crustal movements and deformations of the Earth's crust beyond the geodetic network contour. The study extensively examines the hyperparameter settings and justifies the applicability of the neural network model for predicting crustal movement fields using the Ossetian geodynamic polygon as an example. The presented results, when compared to classical modeling methods, demonstrate that the neural network approach confidently yields results no worse than classical methods. The results of modeling for the Ossetian polygon can be used for geodynamic zoning, identification zones of extension and compression, computing the tectonic component of stresses, and identifying areas of high-gradient displacements.
... The recent structure of the orogen developed in the Late Cenozoic (in the last 10 million years), but it is still evolving as a result of the northwards movement of the African and Arabian plates at a velocity of 20-30 mm/yr (Reilinger and Barka, 1997). In fact, GPS and seismic data indicate that the convergence between the Eurasian and the African-Arabian plates is still ongoing (Kadirov et al., 2008(Kadirov et al., , 2012Avagyan et al., 2010;Adamia et al., 2017;Sokhadze et al., 2018). As a result, the Greater Caucasus and the Lesser Caucasus are still tectonically active, with vertical and horizontal components of displacement that result in present-day, active orogenic processes (Koçyigit et al., 2001;Allen et al., 2004;Reilinger et al., 2006;Tan and Taymaz, 2006;Pasquaré Mariotto et al., 2011;Kadirov et al., 2015;Tibaldi et al., 2017aTibaldi et al., , 2017bTibaldi et al., , 2020. ...
... Integrated since an initiation age of~30 Ma, the minimum shortening of 130-200 km we report implies a minimum average shortening rate of at least 4.3 mm/yr along the Enguri transect and at least 6.7 mm/yr along the Aragvi/Terek transect. Such minimum rates, particularly along the Aragvi/Terek transect, are at the high end or greater than those determined from geodetic data, which provide a modeled active convergence rate of 3-5 mm/yr in the western GC (Sokhadze et al., 2018). ...
The Greater Caucasus orogen forms the northern edge of the Arabia-Eurasia collision zone. Although the orogen has long been assumed to exhibit dominantly thick-skinned style deformation via reactivation of high-angle extensional faults, recent work suggests the range may have accommodated several hundred kilometers or more of shortening since its ~30 Ma initiation, and this shortening may be accommodated via thin-skinned, imbricate fan-style deformation associated with underthrusting and/or subduction. However, robust shortening estimates based upon surface geologic observations are lacking. Here we present line-length and area balanced cross sections along two transects across the western Greater Caucasus that provide minimum shortening estimates of 130-200 km. These cross sections demonstrate that a thin-skinned structural style provides a viable explanation for the structure of the Greater Caucasus, and highlight major structures that may accommodate additional, but unconstrained, shortening.
... The RFFTB system consists of several major anticlines and is represented mainly by fault-propagation folds detached along the basal thrust which soles within the Late Jurassic evaporates [2][3][4][5][6][7][8][9][10]. Recent GPS and earthquake data indicate that the RFFTB is still tectonically active [11][12][13]. ...
Our study is focused on the structural geometry of the outer Rioni foreland fold-and-thrust belt disposed in western Georgia. The structural architecture of the outer Rioni foreland fold-and-thrust belt has been interpreted using a seismic reflection profile. The interpreted seismic profile shows that the compressional structures are represented by Tsaishi fault-propagation fold and duplexes. The seismic profile reveals the occurrence of normal faults within the pre-orogenic sedimentary strata. Normal faults are inherited from the Middle Jurassic-Paleogene and represented by four sets of extensional faults separated by detachment levels. The origin of extensional faults is related to the Jurassic-Paleogene evolution of the outer Greater Caucasus marginal basin. © 2023 Bull. Georg. Natl. Acad. Sci. Rioni foreland fold-and-thrust belt, seismic profile, fault-propagation fold, duplex, normal fault The Rioni foreland fold-and-thrust belt (RFFTB) is one of the main oil-bearing and hydrothermal provinces of the west Georgia [1, 2]. Many structural studies mainly based on seismic data, were undertaken in the RFFTB during the past decade. They were predominantly focused on the study of compressional structures and kinematic evolution of the RFFTB that are exposed on the seismic lines [2-6]. To understand the evolution of the extensional basin during the Jurassic-Eocene time, we used a seismic reflection profile from the outer RFFTB. In this paper, the extensional faults identified in the seismic profile reflect that these normal faults are related to four extensional sets.
... Based on apatite fission-track data, the exhumation process in the GC started in the Oligocene and reached its highest rate in the Miocene-Pliocene (Avdeev, 2011;Avdeev and Niemi, 2011;Vincent et al., 2007Vincent et al., , 2011. GPS and seismic data indicate that the convergence between the Eurasian and the African-Arabian plates is ongoing (Reilinger et al., 2006;Kadirov et al., 2008Kadirov et al., , 2012Avagyan et al., 2010;Adamia et al., 2017;Alizadeh et al., 2016;Sokhadze et al., 2018). As a result, the GC and the Lesser Caucasus are still tectonically active, with vertical and horizontal components of motions that imply ongoing mountain building processes (Rebai et al., 1993;Jackson and Ambraseys, 1997;Koçyiğit et al., 2001;Allen et al., 2004;Reilinger et al., 2006;Tan and Tayemaz, 2006;Pasquarè et al., 2011;Kadirov et al., 2015;Tibaldi et al., 2017a,b). ...
This work contributes to depict the current seismicity, fault kinematics, and state of stress in the Greater Caucasus (territories of Georgia, Azerbaijan and Russia). We merged and homogenized data from different earthquake catalogues, relocated~1000 seismic events, created a database of 366 selected focal mechanism solutions, 239 of which are new, and performed a formal stress inversion. Preferential alignments of crustal earthquake foci indicate that most seismic areas are located along the southern margin of the belt and in the northeastern sector. This is consistent with the presence of dominant active WNW-ESE faults, parallel to the mountain range. In the entire Greater Caucasus, a dominant NNE-SSW-oriented greatest principal stress (σ 1) controls the overall occurrence of earthquakes of minor and major magnitude. Main earthquakes are characterized by a vertical least principal stress (σ 3), corresponding to reverse kinematics. Reverse slip is more common along the southwestern and northeastern foothills of the Greater Caucasus, although in these areas there are also scattered strike-slip events. This suggests the presence of local stress fields with horizontal σ 1 and σ 3. In the central-southern part of the mountain belt, in correspondence of the local collision between the Lesser and the Greater Caucasus, σ 1 rotates to NNW-SSE. The strike-slip events, instead, dominate along the southern flank of the central-eastern mountain range; this is interpreted as the effect of the collision that promotes eastward escape of the tectonic blocks located to the east.
... The convergence rate increases systematically from ∼4 mm=yr in the west, near the Black Sea coast, to ∼14 mm=yr in the east, along the Caspian Sea coast (Reilinger et al., 2004). In general, the Greater Caucasus accommodates more of this relative plate motion than the Lesser Caucasus (Kadirov et al., 2012;Forte et al., 2014), although locally in the Tbilisi region shortening appears to be localized within the Lesser Caucasus (Sokhadze et al., 2018). ...
... The tectonic setting of the Greater Caucasus varies along strike (Figure 2a; Forte et al., 2014). The western Greater Caucasus accommodates 4 mm/yr convergence (Reilinger et al., 2006;Sokhadze et al., 2018), is characterized structurally by coherent macro-scale thrust sheets of 2-10 km thickness (Trexler et al., 2022), and has earthquake depths of <20 km (Mumladze et al., 2015). In contrast, the eastern Greater Caucasus is accommodating convergence rates of 10-12 mm/yr (Figure 2a; Kadirov et al., 2012Kadirov et al., , 2015Reilinger et al., 2006) and earthquake depths of up to >100 km have been recorded north of the range (Burmin et al., 2019;Gunnels et al., 2021;Mellors et al., 2012;Mumladze et al., 2015). ...
Orogenic wedges are common at convergent plate margins and deform internally to maintain a self‐similar geometry during growth. New structural mapping and thermochronometry data illustrate that the eastern Greater Caucasus mountain range of western Asia undergoes deformation via distinct mechanisms that correspond with contrasting lithologies of two sedimentary rock packages within the orogen. The orogen interior comprises a package of Mesozoic thin‐bedded (<10 cm) sandstones and shales. These strata are deformed throughout by short‐wavelength (<1 km) folds that are not fault‐bend or fault‐propagation folds. In contrast, a coeval package of thick‐bedded (up to 5 m) volcaniclastic sandstone and carbonate, known as the Vandam Zone, has been accreted and is deformed via imbrication of coherent thrust sheets forming fault‐related folds of 5–10 km wavelength. Structural reconstructions and thermochronometric data indicate that the Vandam Zone package was accreted between ca. 13 and 3 Ma. Following Vandam Zone accretion, thermal modeling of thermochronometric data indicates rapid exhumation (∼0.3–1 mm/yr) in the wedge interior beginning between ca. 6 and 3 Ma, and a novel thermochronometric paleo‐rotation analysis suggests out‐of‐sequence folding of wedge‐interior strata after ca. 3 Ma. Field relationships suggest that the Vandam Zone underwent syn‐convergent extension following accretion. Together, the data record spatially and temporally variable deformation, dependent on both the mechanical properties of deforming lithologies and perturbations such as accretion of material from the down‐going to the overriding plate. The diverse modes of deformation are consistent with the maintenance of critical taper.
... Recent GPS and earthquake data indicate that the RFFTB is still tectonically active and the earthquakes focal mechanisms are mainly thrust faults (e.g., Adamia et al., 2004;Tsereteli et al., 2016, Adamia et al., 2017Sokhadze et al., 2018;Tibaldi et al., 2020, Tibaldi et al., 2021. ...
The Rioni foreland fold-and-thrust belt is part of the Greater Caucasus pro-wedge and is one of the most important examples of the collision-driven far-field deformation of the Arabia-Eurasia convergence zone. Here we show the deformation structural style of the Rioni foreland fold-and-thrust belt based on seismic reflection profiles and regional balanced cross-section. The main style of deformation within the Rioni foreland fold-and-thrust belt is represented by a set of fault-propagation folds, duplexes, and triangle zone. The regional balanced cross-section shows that fault-propagation folds above the upper detachment level can develop by piggyback and break-back thrust sequences. Formation of fault-bend fold duplex structures above the lower detachment is related to piggyback thrust sequences. A balanced section restoration of compressional structures across the Rioni foreland fold-and-thrust belt provides a minimum estimate of shortening of −40%, equivalent −42.78 km. The synclines within the Rioni foreland fold-and-thrust belt are filled by the Middle Miocene-Pleistocene shallow marine and continental syn-tectonic sediments, forming a series of typical thrust-top basins. Fault-propagation folds and duplex structures formed the main structure of the thrust-top basin. The evolution of the thrust-top basins was mainly controlled by the kinematics of thrust sequences. Using end-member modes of thrust sequences, the thrust-top basins are divided into: 1) Type I-piggyback basin, 2) Type II-break-back basin, and 3) Type III—formation of thrust-top basin characterized by bi-vergent geometry and related to combined, piggyback and piggyback back thrust sequences.
... the Central Iranian Block and the Eurasian Plate. South of the Lesser Caucasus, the North Tabriz and GSKF (Siahcheshmeh) fault systems in Iran have an average slip rate of 8 mm/yr (Nilforoushan et al., 2003;Vernant et al., 2004;Masson et al., 2006;Reilinger et al., 2006;Djamour et al., 2011;Raeesi et al., 2017;Sokhadze et al., 2018;Khorrami et al., 2019). Apparently, the well-constrained strain along the North Tabriz fault in Iran broadens towards the west in the Çaldıran fault zone of eastern Turkey; this is consistent with crustal shortening and associated thrust faulting observed in the Lake Van area (Fielding et al., 2013;Dogan and Karakaş, 2013). ...
We present the source mechanisms and rupture processes for the damaging 23 February 2020 earthquake doublet of Mw 5.8 and Mw 5.9 that occurred near the Turkish-Iranian border regions of Qotur-Goharan-Mir'Omar-Ravian (NW Iran), extending towards Saray and Bas¸kale (Eastern Turkey), as obtained from seismological waveform analysis and space geodesy imaging. Seismotectonic characteristics of the sequence highlight the role of indentation tectonics developed within regional-scale compressional environment where the Arabian microplate collides with the Eurasian plate. Here we report optimal finite-fault slip distribution patterns of the 2020 Qotur-Ravian earthquake doublet revealing complex co-seismic rupture propagation along the fault planes with maximum displacements ranging from 20 to 50 cm, stretching from the hypocentre to the surface. Analysis of aftershocks based on 3.5 months-long seismicity confirms distributed deformation. This energetic earthquake sequence demonstrates the distinct rupture characteristics illuminating differences in seismogenic properties and seismic hazard. Coulomb stress transfer modelling predicts triggering of the second event of Mw 5.9 by the first event of Mw 5.8. The zone of Coulomb stress changes attributed to varying pore pressure linking to geothermal water resources in the region as a driving force, may have an impact on the nucleation of triggered faulting. Evaluation of Interferometric Synthetic Aperture Radar (InSAR) data reveals the activated faults with evident co-seismic slip. Specifically, (1) we detected a rare case in earthquake-induced ground deformation where there is overlapping surface deformation due to sequential shallow events located closely in the crust, (2) the initial event ruptured a normal fault located towards W-NW of the latter inferred strike-slip fault and (3) the conjugate system of faults is closely placed at a few km apart. The frequent Sentinel-1 interferograms enhanced our imaging abilities of geometry and kinematics of shallow moderate-size M < 6.0 earthquakes and to trace seismogenic structures in remote and mountainous earthquake prone regions.
... the Central Iranian Block and the Eurasian Plate. South of the Lesser Caucasus, the North Tabriz and GSKF (Siahcheshmeh) fault systems in Iran have an average slip rate of 8 mm/yr (Nilforoushan et al., 2003;Vernant et al., 2004;Masson et al., 2006;Reilinger et al., 2006;Djamour et al., 2011;Raeesi et al., 2017;Sokhadze et al., 2018;Khorrami et al., 2019). Apparently, the well-constrained strain along the North Tabriz fault in Iran broadens towards the west in the Çaldıran fault zone of eastern Turkey; this is consistent with crustal shortening and associated thrust faulting observed in the Lake Van area (Fielding et al., 2013;Dogan and Karakaş, 2013). ...
We present the source mechanisms and rupture processes for the damaging 23 February 2020 earthquake doublet of Mw 5.8 and Mw 5.9 that occurred near the Turkish-Iranian border regions of Qotur-Goharan-Mir'Omar-Ravian (NW Iran), extending towards Saray and Başkale (Eastern Turkey), as obtained from seismological waveform analysis and space geodesy imaging. Seismotectonic characteristics of the sequence highlight the role of indentation tectonics developed within regional-scale compressional environment where the Arabian microplate collides with the Eurasian plate. Here we report optimal finite-fault slip distribution patterns of the 2020 Qotur-Ravian earthquake doublet revealing complex co-seismic rupture propagation along the fault planes with maximum displacements ranging from 20 to 50 cm, stretching from the hypocentre to the surface. Analysis of aftershocks based on 3.5 months-long seismicity confirms distributed deformation. This energetic earthquake sequence demonstrates the distinct rupture characteristics illuminating differences in seismogenic properties and seismic hazard. Coulomb stress transfer modelling predicts triggering of the second event of Mw 5.9 by the first event of Mw 5.8. The zone of negative Coulomb stress changes attributed to varying pore pressure linking to geothermal water resources in the region as a driving force, may have an impact on the nucleation of triggered faulting. Evaluation of Interferometric Synthetic Aperture Radar (InSAR) data reveals the activated fault with evident post-seismic slip. Specifically, (1) we detected a rare case in earthquake-induced ground deformation where there is overlapping surface deformation due to sequential shallow events located closely in the crust, (2) the initial event ruptured a fault located towards W-NW of the latter inferred fault and (3) the conjugate system of faults is closely placed at a few km apart. The frequent Sentinel-1 interferograms enhanced our imaging abilities of geometry and kinematics of shallow moderate-size M < 6.0 earthquakes and to trace seismogenic structures in remote and mountainous earthquake prone regions.
... In the Greater Caucasus, shortening is accommodated primarily by reverse faulting and folding, and topography is supported by a thickened crustal root (Forte et al., 2014;2016;Mumladze et al., 2015;Cowgill et al., 2016;Vincent et al., 2016;Gunnels et al., 2021;Tye et al., 2021). In contrast, the down-going plate (i.e. the Lesser Caucasus-Eastern Pontides; LCEP; Fig. 4.1) is a more enigmatic orogen where fundamental questions regarding the structure, recent tectonic and topographic histories, and nature of support for high topography remain unanswered Cowgill et al., 2016;Sokhadze et al., 2018;Gusmeo et al., 2021). ...
Continental lithosphere exhibits complex deformation across broad regions, challenging simplistic tectonic models of how plate boundaries behave. As geologists develop models to explain observed patterns of deformation, they have proposed a wide array of geodynamic mechanisms and material properties that may control the rates, styles, and magnitudes of continental deformation. In most study areas, we now have an excess of hypothesized controls and a dearth of data with which to test competing models of deformation. This dissertation presents three field studies of continental deformation that apply a diverse set of investigative approaches to characterize deformation, then link that deformation to the most likely geodynamic causes. Two studies are from the Basin and Range extensional province, addressing debates around the relative role of plate boundary stresses and internal gravitational potential energy gradients in driving extensional tectonism over the Cenozoic. In Chapter 2, I use field mapping, stratigraphy, detrital zircon geochronology, and structural observations to build a basin history for the Titus Canyon Formation, one of the earliest syn-extensional deposits in the central Basin and Range. Our results from the Titus Canyon Formation suggest that it records extension related to a ~40 Ma slowdown in plate convergence along western North America. In Chapter 3, I apply multiple low-temperature thermochronometers to a suite of Jurassic plutons in the northern Basin and Range to decipher their exhumational histories. My data support a major phase of extension in the Miocene, and also reveal changes in Cretaceous-Paleogene exhumation that may be related to contractional tectonism of the Sevier orogeny and construction of the Nevadaplano. Chapter 4 examines the recent tectonic history of the down-going plate in the Caucasus collisional orogen. I apply low-temperature thermochronology to measure the tectonic response to the initiation of collision at 5 Ma with the goal of understanding the partitioning of strain between the two colliding plates. The results indicate that the collision is highly asymmetric, with the majority of shortening in the down-going plate being accommodated by strike-slip faulting, in contrast with deformation in the overriding plate which is accommodated primarily by reverse faulting and folding. Together these studies illustrate the rich complexity of continental deformation and the wide variety of geodynamic mechanisms that must be considered when building models of how deformation evolves in old continental lithosphere.
... Convergence between the Lesser and Greater Caucasus is the difference between these velocities along-strike. Our results are similar to prior estimates (Forte et al., 2014), but incorporate updated GPS velocities (Sokhadze et al., 2018). ...
Hypothesized feedbacks between climate and tectonics are mediated by the relationship between topography and long-term erosion rates. While many studies show monotonic relationships between channel steepness and erosion rates, the degree of nonlinearity in this relationship varies by landscape. Mechanistically explaining controls on this relationship in natural settings is critical because highly nonlinear relationships imply low sensitivity between climate and tectonics. To this end, we present a coordinated analysis of cosmogenic ¹⁰Be concentrations in river sands paired with topographic, hydroclimatic, and tectonic data for the Greater Caucasus Mountains where topography is invariant along-strike despite large gradients in modern precipitation and convergence rates. We show that spatial patterns in erosion rates largely reflect regional tectonics with little sensitivity to mean precipitation or runoff. The nonlinearity in the erosion rate – steepness relationship may arise from very low runoff variability, which we attribute to the large contribution from snowmelt. Transitioning from rainfall- to snowmelt-driven runoff as mean elevation increases is common to many mid-latitude mountain ranges. The associated decrease in runoff variability may represent important, unrecognized dynamics inhibiting the sensitivity of tectonics to climate more broadly.
... Recent apatite fissiontrack and (U-Th)/He data have refined its age of inception, which occurred in the Middle Miocene [10,11]. Recent GPS and earthquakes data indicate that the ATFTB is tectonically active [13][14][15]. ...
This paper presents a new structural model for the frontal part of the eastern Achara-Trialeti fold-and-thrust belt based on the interpretation of a seismic reflection profile across the retro-wedge of the Lesser Caucasus orogen. The structural details from the interpreted seismic reflection profile provide new data on the deep structure of the frontal part of the eastern Achara-Trialeti fold-and-thrust belt. The seismic reflection profile crosses, from south to north, the Varketili anticline, the Ormoiani syncline, and a south-directed imbricate thrust system. Seismic interpretation is constrained by surface geology, exploration wells, and application of theoretical models on fault-related folding. Seismic reflection data interpretation reveals the interaction between south-and north-vergent fold-thrust structures and north-vergent duplexes at depth. The duplexes are well imaged on the seismic profile and constituted by a lower and an upper duplex system. The lower duplex involves the Cretaceous-Middle Eocene sequence, whereas the upper duplex affects the Upper Eocene strata. © 2021 Bull. Georg. Natl. Acad. Sci. Achara-Trialeti fold-and-thrust belt, seismic reflection profile, duplex The structural interpretation of the deep architecture of the frontal sector of the eastern Achara-Trialeti fold-and-thrust belt (ATFTB) has significantly changed following the interpretation of progressively new seismic data [1-3]. A robust reconstruction of the subsurface derived only from surface geology and borehole data is fairly hard to obtain [4, 5], consequently the reliability of such models is doubtful. It should be mentioned that previous studies for particular sectors of the eastern
... Given the modern advances in geodetic, geotectonic, and earthquake surveys, some changes need to be made in their solution capabilities, and the research phases should therefore be as follows: § 1. Seismic risk assessment 1.1. To detect geotectonic anomalies in seismically active regions (countries), it is necessary continuously to conduct geodetic surveys using GPS and GNSS methods [22], as well as quantitatively to estimate the earthquake preparation area. For example, a geotectonic anomaly identified by studies near Tbilisi has the following appearance ( Fig. 1) [28]: where R is the strain radius in km and M is earthquake magnitude 1.3. ...
A large earthquake is still considered to be a natural catastrophic event that not only
causes immeasurably great material damage to seismically active regions and countries
but also takes the lives of thousands of people.That is why the assessment of seismic risk
is one of the most important issues, and research in this area is now in one of the first
places in all countries. However, despite the high level of research, the practical results
of the seismic risk do not provide great protection guarantees from disaster. Based
on recent studies of earthquake prediction possibility, the offered article presents a
completely different view on the possibilities of seismic risk assessing and reducing the
accumulated tectonic stress in the large earthquake focus.
... The Greater Caucasus Mountains host the highest topography in Europe and are the main locus of active convergence at their longitude within the Arabia-Eurasia continental collision zone (Figure 1g; Jackson, 1992;Reilinger et al., 2006;Sokhadze et al., 2018). West of 45°E, the axis of the range is defined by a Paleozoic crystalline core, which is separated from Mesozoic-Cenozoic strata of the Caucasus Basin to the south by the north-dipping Main Caucasus Thrust (Dotduyev, 1986;Mosar et al., 2010;Saintot et al., 2006;Vasey et al., 2020). ...
Extension within a continental back‐arc basin initiates within continental rather than oceanic lithosphere, and the geochemical characteristics of magmatic rocks within continental back‐arcs are poorly understood relative to their intraoceanic counterparts. Here, we compile published geochemical data from five exemplar modern continental back‐arc basins—the Okinawa Trough, Bransfield Strait, Tyrrhenian Sea, Patagonia plateau, and Aegean Sea/Western Anatolia—to establish a geochemical framework for continental back‐arc magmatism. This analysis shows that continental back‐arcs yield geochemical signatures more similar to arc magmatism than intraoceanic back‐arcs do. We apply this framework to published data for Triassic‐Jurassic magmatic rocks from the Caucasus arc system, which includes a relict continental back‐arc, the Caucasus Basin, that opened during the Jurassic and for which the causal mechanism of formation remains debated. Our analysis of ⁴⁰Ar/³⁹Ar and U‐Pb ages indicates Permian‐Triassic arc magmatism from ∼260 to 220 Ma due to subduction beneath the Greater Caucasus and Scythian Platform. Late Triassic (∼220–210 Ma) collision of the Iranian block with Laurasia likely induced trench retreat in the Caucasus region and led to migration of the Caucasus arc and opening of the Caucasus Basin. This activity was followed by Jurassic arc magmatism in the Lesser Caucasus from ∼180 to 140 Ma and back‐arc spreading in the Caucasus Basin from ∼180 to 160 Ma. Trace element and Sr‐Nd isotopic data for magmatic rocks indicate that Caucasus Basin magmatism is comparable to modern continental back‐arcs and that the source to the Lesser Caucasus arc became more enriched at ∼160 Ma, likely from the cessation of back‐arc spreading.
... The divisions among the Adjara-Trialeti, Baiburt-Karabakh and Artvin-Bolnisi Units have been drawn after Yilmaz et al. (2000). The MCTF (Main Caucasus Thrust Fault) and the LCTF (Lesser Caucasus Thrust Fault) have been drawn after Sokhadze et al. (2018). Dark grey areas indicate the present Kvemo-Kartli administrative region. ...
This archaeometric study deals with seven samples of prehistoric pottery and, for the first time in Georgian studies, thirteen samples of glazed medieval pottery. All specimens were collected at Samshvilde, the most remarkable archaeological complex in southern Georgia and believed to represent locally-manufactured products. Two additional samples of raw materials composed of clay, silt, and sand were collected near the site and used to compare composition. Several analytical techniques were applied: Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA), X-ray Diffraction (XRD) and X-ray Fluorescence (XRF). The results allowed to build a complex scenario in terms of exploitation of raw materials and technological choices. The raw materials indicate a volcanic environment and correspond to the geological settings of the territory of Samshvilde. The glazed ceramics were characterised as alkali, low alkali – low lead, lead, high lead and tin-opacified mixed-alkaline lead glazes. The compositional comparisons extend from east to west and place these ceramics in the wider framework of Islamic ceramics.
This report describes a new Probabilistic Seismic Hazard Assessment (PSHA) developed for Azerbaijan. This includes the compilation and processing of a new and improved earthquake catalogue, which was used along existing active fault studies to develop the seismic source characterization. Broadband ground motion simulations were carried out to inform the selection and weighting of ground motion models (GMMs) that reflect the attenuation characteristics in eastern Caucasus. The resulting PSHA output is presented in the form of national hazard maps as well as hazard curves, uniform hazard spectra, and hazard deaggregations for major urban areas in Azerbaijan.
According to daily visible-band and 7-2-1 MODIS images obtained from Terra and Aqua satellites from 2000 to 2018, a significant number of mesoscale single-cell cyclones have been identified in the middle Caspian Sea and on the eastern side of the Caucasus Mountains, mainly during the cold seasons. To investigate the formation mechanism of these cyclones, the ECMWF ERA5 were used to examine mean sea level pressure, geopotential, temperature, vorticity, vertical velocity, and 10-m wind field patterns. The study of the 10-m wind field charts revealed a tendency for the establishment of a westerly current, directed from the southwestern slope (upwind side) of the Caucasus mountains toward their northeastern slope (lee side) and a southerly wind component along with counter-clockwise cyclonic circulation in the middle Caspian Sea. The stream pattern at 850 hPa also confirmed a southerly flow. The analysis of relative vorticity and vertical velocity (as dynamic quantities) at 500 hPa and 850 hPa showed the formation of positive relative vorticity and upward motions on the leeside of the Caucasus Mountains. According to the law of conservation of mass, this disruption of the mass balance on the leeward side of the Caucasus Mountains leads to the forced upward motion of air mass, which results in the stretching of air mass at the lower to middle levels of the troposphere. By strengthening cyclonic relative vorticity, these conditions eventually lead to the formation of a secondary low-pressure lee cyclone over the middle Caspian Sea. This phenomenon is likely to be related to moisture injection from the warm Caspian Sea and cloud formation in the lower layers of the troposphere, and the wind induced increased evaporation potential in the area. The higher frequency of the cyclones during the cold months can be attributed to the dominance of southerly wind in the area during these months and also due to the maximization of the thermal contrast between the sea water and the overlying air. The most important result of this study was the identification of the source of cyclogenesis in the northeastern slopes (leeside) of the Caucasus Mountains. Given the synergistic roles of the Caucasus Mountains and the Caspian Sea toward the formation of these cyclones, they were named Caucasus-Caspian cyclones.
The authors present the results of developing a library designed for GNSS deformation measurement upshot analysis in the Python 3 environment and their visualization in the QGIS 3 geographic information system. Development of global navigation satellite systems (permanent networks, data publications, creation of software for processing satellite measurement results) has led to increase in the number of researches in the field of studying modern crustal movements. Deformation analysis is a key component in exploring modern crustal and earth’s surface movements. Despite the large number of commercial and freely distributed software for the declared goal, the problem of integrating calculation results into the environment of freely distributed geoinformation systems is still relevant. The presented PyGeoStrain library includes some sets of corresponding subprograms, created QGIS 3 styles for visualizing deformation parameters, original test data, and a control GIS project for the example territory of the Caucasus. For deformation analysis, PyGeoStrain uses the classical geodetic approach to determining the components of the deformation tensor. The use of PyGeoStrain is an adequate replacement for analogue programs due to open access to the source.
To download: PyGeoStrain: A software package for calculation crustal strain (v1.0). 2023. Zenodo. https://doi.org/10.5281/zenodo.7948241
To investigate the recent landscape evolution of the orogenic Turkish–Iranian Plateau (TIP) and the Lesser/Greater Caucasus ranges, we perform a quantitative analysis of topography and drainage networks at a regional scale. This analysis focuses on climatic–topographic swath profiles, local relief distribution, longitudinal river profiles, normalized channel steepness index ( k sn ), paleo‐river profile, and chi analysis ( χ ). In general, we find that the evolution of topographic relief and river networks are locally controlled by Late Cenozoic volcanism, contrasts in rock strength, and neotectonic activity along regional tectonic structures. However, our results show that the influence of these factors on the landscape evolution of the Greater Caucasus is significantly different from the Lesser Caucasus and TIP. This study shows that a combination of enhanced aridity, rapid uplift of orographic barriers along the TIP margins, and exposure of resistant rock types associated with the regional volcanic activity resulted in low‐relief plateau and the Lesser Caucasus surfaces that are preserved in the upper/middle Kura–Arax and Qezel‐Owzan river catchments. High local relief in the flanks of the Greater Caucasus and west Alborz, downstream increase in channel steepness, and perturbations in the χ plots of the three main rivers indicate that the topography is in a transient state.
We reconstruct the paleo‐river profiles from the relict section of the upper Kura–Arax and Qezel‐Owzan rivers and show that the last drastic fall of the Caspian base‐level, which occurred during the Late Miocene–Early Pliocene, can explain the incision of ~500–1000 m gorges (i.e., Amardos) below major knickpoints. Furthermore, local cross‐divide differences of the χ parameter reveal that disequilibrium in the plan‐form geometry of the drainage networks, attributed to the upstream migration of the regional knickpoints towards the plateau interior and integration of plateau areas into the external fluvial system.
Convergent margins play a fundamental role in the construction and modification of Earth's lithosphere and are characterized by poorly understood episodic processes that occur during the progression from subduction to terminal collision. On the northern margin of the active Arabia‐Eurasia collision zone, the Greater Caucasus Mountains provide an opportunity to study a protracted convergent margin that spanned most of the Phanerozoic and culminated in Cenozoic continental collision. However, the main episodes of lithosphere formation and deformation along this margin remain enigmatic. Here, we use detrital zircon U–Pb geochronology from Paleozoic and Mesozoic (meta)sedimentary rocks in the Greater Caucasus, along with select zircon U–Pb and Hf isotopic data from coeval igneous rocks, to link key magmatic and depositional episodes along the Caucasus convergent margin. Devonian to Early Carboniferous rocks were deposited prior to Late Carboniferous accretion of the Greater Caucasus crystalline core onto the Laurussian margin. Permian to Triassic rocks document a period of northward subduction and forearc deposition south of a continental margin volcanic arc in the Northern Caucasus and Scythian Platform. Jurassic rocks record the opening of the Caucasus Basin as a back‐arc rift during southward migration of the arc front into the Lesser Caucasus. Cretaceous rocks have few Jurassic‐Cretaceous zircons, indicating a period of relative magmatic quiescence and minimal exhumation within this basin. Late Cenozoic closure of the Caucasus Basin juxtaposed the Lesser Caucasus arc to the south against the crystalline core of the Greater Caucasus to the north and led to the formation of a hypothesized terminal suture. We expect this suture to be within ~20 km of the southern range front of the Greater Caucasus because all analysed rocks to the north exhibit a provenance affinity with the crystalline core of the Greater Caucasus.
Continental collision zones form at convergent plate boundaries after the negatively buoyant oceanic lithosphere subducts entirely into the Earth’s mantle. Consequently, orogenesis commences, and the colliding continents are sutured together. During the collision, plate convergence and motion of the sutured boundary towards the overriding plate are manifest in its deformation, as is the case for the long term (∼50 Ma) and nearly constant convergence rate at the India-Eurasia collisional zone that hosts the Himalaya. However, despite the long history of modelling subduction-collision systems, it remains unclear what drives this convergence, especially in models where subduction is driven solely by buoyancy forces. This paper presents dynamic self-consistent buoyancy-driven 2D whole-mantle scale numerical models of subduction-and-collision processes to explore variations in density and rheological stratification of the colliding continent and overriding plate (OP) viscosity (a proxy for OP strength) that facilitate post-collisional convergence and collisional boundary migration. In models with a moderately buoyant indenting continent, the collisional boundary advance is comparatively low (0.1-0.6 cm/yr), and convergence is driven by the dense continental lithospheric mantle that continues to subduct as it decouples from its deforming crust. Conversely, models with a highly buoyant indenting continent show sustained indentation at 0.5-1.5 cm/yr until the slab detaches. Furthermore, models with a weaker OP and lower backarc viscosity show an enhanced propensity for indentation by a positively buoyant continent. These models additionally highlight the role of whole mantle flow induced by the sinking of the detached slab in the lower mantle as it sustains slow convergence at an average rate of 0.36 cm/yr for ∼25 Myrs after break-off as well as prevents the residual slab from educting. In previous buoyancy-driven partial mantle depth models such eduction does generally occur, given that free-sinking of the detached slab in the mantle is not modelled. Although these findings widen the understanding of the long-term convergence of indenting continents, the lower post-collisional advance rates (0.3-1.5 cm/yr) compared to India’s approximate 1000-2000 km of northward indentation during the last 50 Myrs attest to the need for 3D models.
Structural interference along the boundaries of adjacent tectonic domains generates complex subsidence and exhumation patterns. In this paper we study a key segment of the convergence zone between the interfering south-verging Greater Caucasus and north-verging Lesser Caucasus retro-wedge. The study area comprises the along-strike transition between the Paleogene Adjara-Trialeti back-arc basin and the Oligocene-Neogene Kura foreland basin of eastern Georgia. During the Neogene, despite their difference in age and subsidence mechanisms, both basins have been progressively inverted to various extent within the overall context of the Arabia-Eurasia continental collision. Thermal modelling of borehole data from the Adjara-Trialeti basin allowed to reconstruct two phases of rapid subsidence, late Paleocene-Early Eocene and Middle-Late Eocene, respectively correlated to flexural loading by the Lesser Caucasus retro-wedge and continental rifting. Integration of thermal modelling, apatite fission-track statistical inverse modelling, and seismic interpretation detected a third subsidence phase in the Early Miocene, possibly related to strike-slip tectonics. Thermal maturity data dictate that 1.0-1.3 km of the Adjara-Trialeti sedimentary succession has been eroded since the onset of structural inversion in the mid-Miocene. The burial history of the western Kura Basin outlines intermittent and asymmetrical episodes of flexural subsidence from the Oligocene to the Late Miocene, due to competing loading by the Lesser Caucasus, the Adjara-Trialeti fold-and-thrust belt and the Greater Caucasus. Finally, during latest Miocene times southward propagation of deformation from the Greater Caucasus induced an additional tectonic loading (1.3-1.8 km) due to the emplacement of thin-skinned thrust sheets, mostly eroded during the Plio-Quaternary.
The article presents an overview of the structural structure of the Rioni Forland Fold-and-thrust Belt. The structures are mainly represented by folds and duplexes associated with south-vergent faults. The synclines are overlaid by Middle Miocene-Pleistocene syntectonic sediments and are represented by piggy-back basins. Faultrelated folds are mainly represented by growing fault-propogation folds. The kinematic evolution of the Rioni Forland Basin in the Late Alpine period is related to the structural wedge (or duplexes) of the Caucasus foundation moving southwards, and its modern structure is represented by a thin-skinned fold-and-thrust belt.
Fault characterization is a critical step toward improving seismic hazard assessment in the Georgian Greater Caucasus but is largely absent from the region. Here, a paleoseismic trench near the capital city of Tbilisi revealed evidence for recurring surface rupture on a shallowly north-dipping thrust fault. The fault has broken through the overturned forelimb of a fault-propagation anticline that folds a sequence of soils and deposits. Stratigraphic relationships and radiocarbon dating of terrestrial gastropod shells corrected for “old carbon” age anomalies loosely constrain three surface-deforming earthquakes on this fault between ∼40 and ∼3 ka, with variable dip-slip displacements ranging between 0.35 and ∼3 m, and a cumulative displacement of 6.5 ± 0.85 m. Single event slips and recurrence intervals (11, 25, and 3 ka open interval) at this site demonstrate apparent slip rate variations of 3−7× over the last two earthquake cycles on the fault, which we attribute to possible rupture complexity involved in crustal thrust fault earthquakes. This study provides a structural and geochronologic template for future paleoseismic investigations in the Greater Caucasus while highlighting some of the challenges of conducting seismic source characterization in this region.
Thermal history reconstructions can help to better characterise the geological history of areas that experienced a polyphase tectonic evolution. The integration of published stratigraphic/structural data with new and pre- existing data on thermal maturity (clay mineralogy, Raman spectroscopy, vitrinite reflectance, and pyrolysis) of both surface and subsurface sedimentary successions of a wide region of Georgia including -north to south- the southern Greater Caucasus, the western Kura Basin, and the Adjara-Trialeti fold-and-thrust belt (FTB) provides cogent constraints on its late Mesozoic-Cenozoic tectono-sedimentary evolution.
Overall, thermal maturity spans from the low diagenesis (60–80 ◦C) in the Upper Miocene section of the Kura Basin to anchizone-epizone (about 400 ◦C) in the central Greater Caucasus axial zone. In more detail, different maturity trends and thermal histories point to the existence of two domains formed by positive tectonic inver- sion: (i) the Adjara-Trialeti FTB from an Eocene rift basin and (ii) the Greater Caucasus from a Mesozoic rift basin. Multiple thermal indicators, along with stratigraphic/structural evidence, show that the Paleocene section of the Adjara-Trialeti basin fill reached the upper oil window (ca. 115 ◦C) during maximum sedimentary burial and that the whole basin was then exhumed starting from the late Middle Miocene. A positive correlation be- tween thermal maturity and stratigraphic age points to a limited thermal effect of tectonic loading. In the southern Greater Caucasus, thermal maturity increases progressively with stratigraphic age, from ca. 100 ◦C (Upper Eocene) to 400 ◦C (Lower Jurassic), in broad agreement with the reconstructed thickness of the basin-fill succession, thus indicating that most of the thermal maturity was again induced by sedimentary burial.
As to the flexural western Kura Basin, its Maikopian (Oligocene-Early Miocene) section reached the oil window (up to ca. 110 ◦C) whereas the Middle-Late Miocene one is immature. The Kakheti ridge -a highly tectonised portion of the Kura Basin- reached immature to early mature conditions.
Paper presents a new view of seismic risk and tectonic stress reduction in the earthquake focus
Hypothesized feedbacks between climate and tectonics are mediated by the relationship between topography and long-term erosion rates. While many studies show monotonic relationships between channel steepness and erosion rates, the degree of nonlinearity in this relationship varies by landscape. Mechanistically explaining controls on this relationship in natural settings is critical because highly nonlinear relationships imply low sensitivity between climate and tectonics. To this end, we present a coordinated analysis of cosmogenic 10Be concentrations in river sands paired with topographic, hydroclimatic, and tectonic data for the Greater Caucasus Mountains where topography is invariant along-strike despite large gradients in modern precipitation and convergence rates. We show that spatial patterns in erosion rates largely reflect regional tectonics with little sensitivity to mean precipitation or runoff. The nonlinearity in the erosion rate – steepness relationship may arise from very low runoff variability, which we attribute to the large contribution from snowmelt. Transitioning from rainfall- to snowmelt-driven runoff as mean elevation increases is common to many mid-latitude mountain ranges. The associated decrease in runoff variability may represent important, unrecognized dynamics inhibiting the sensitivity of tectonics to climate more broadly.
In this paper we present GPS observations of crustal deformation in the Africa- Arabia-Eurasia zone of plate interaction, and use these observations to constrain broad-scale tectonic processes within the collision zone of the Arabian and Eurasian plates. Within this plate te ctonics context, we examine deformation of the Caucasus syste m (Lesser and Greater Caucasus and intervening Caucasian Isthmus) and show that most crus- tal shortening in the collision zone is accommodated by the Greater Caucasus Fold-and-Thrust Belt (GCFTB) along the southern edge of the Gr eater Caucasus Mountains. The eastern GCFTB appears to bifurcate west of Baku, with one branch following the accurate geometry of the Greater Caucasus, turning towards the south and traversing the Neftchala Peninsula. A second branch (or branches) may extend directly into the Caspian Sea south of Baku, likely connecting to the Central Caspian Seismic Zone (CCSZ). We model deformation in terms of a locked thrust fault that coincides in general with the main surface trace of the GCFTB. We consid- er two end-member models, each of which tests the likelihood of one or other of the branches being the dom- inant cause of observed deformation. Our models indicate that strain is actively accumulating on the fault along the ~200 km segment of the fault west of Baku (approximately between longitudes 47-49°E). Parts of this segment of the fault broke in major earthquakes historically (1191, 1859, 1902) suggesting that signif i- cant future earthquakes (M~6-7) are likely on the central and western segment of the fault. We observe a sim- ilar deformation pattern across the eastern end of the GCFTB along a profile crossing the Kur Depression and Gre ater Caucasus Mountains in the vicinity of Baku. Along this eastern segment, a branch of the fault chang- es from a NW-SE striking thrust to an ~ N-S oriented strike-slip fault (or in multiple splays). The similar de- formation pattern along the eastern and central GCFTB segments raises the possibility that major earthquakes may also occur in eastern Azerbaijan. However, the eastern segment of the GCFTB has no record of large his- toric earthquakes, and is characterized by thick, highly saturated and over-pressured sediments within the Kur Depression and adjacent Caspian Basin that may inhibit elastic strain accumulation in favour of fault creep, and/or distributed faulting and folding. Thus, while our analyses suggest that large earthquakes are likely in central and western Azerbaijan, it is still uncertain whether significant earthquakes are also likely along the eastern segment, and on which structure. Ongoing and future focused studies of active deformation promise to shed further light on the tectonics and earthquake hazards in this highly populated and developed part of Az erbaijan.
The structure and geological history of the Caucasus are largely determined by its position between the stillconverging Eurasian and Africa-Arabian lithospheric plates, within a wide zone of continental collision. During the Late Proterozoic-Early Cenozoic, the region belonged to the Tethys Ocean and its Eurasian and Africa-Arabian margins where there existed a system of island arcs, intra-arc rift s, back-arc basins characteristic of the pre-collisional stage of its evolution of the region. The region, along with other fragments that are now exposed in the Upper Precambrian- Cambrian crystalline basement of the Alpine orogenic belt, was separated from western Gondwana during the Early Palaeozoic as a result of back-arc rift ing above a south-dipping subduction zone. Continued rift ing and seafloor spreading produced the Palaeotethys Ocean in the wake of northward migrating peri-Gondwanan terranes. The displacement of the Caucasian and other peri-Gondwanan terranes to the southern margin of Eurasia was completed by ~350 Ma. Widespread emplacement of microcline granite plutons along the active continental margin of southern Eurasia during 330-280 Ma occurred above a north-dipping Palaeotethyan subduction zone. However, Variscan and Eo-Cimmerian-Early Alpine events did not lead to the complete closing of the Palaeozoic Ocean. The Mesozoic Tethys in the Caucasus was inherited from the Palaeotethys. In the Mesozoic and Early Cenozoic, the Great Caucasus and Transcaucasus represented the Northtethyan realm - the southern active margin of the Eurasiatic lithospheric plate. The Oligocene-Neogene and Quaternary basins situated within the Transcaucasian intermontane depression mark the syn- and post-collisional evolution of the region; these basins represented a part of Paratethys and accumulated sediments of closed and semiclosed type. The final collision of the Africa-Arabian and Eurasian plates and formation of the present-day intracontinental mountainous edifice of the Caucasus occurred in the Neogene-Quaternary period. From the Late Miocene (c. 9-7 Ma) to the end of the Pleistocene, in the central part of the region, volcanic eruptions in subaerial conditions occurred simultaneously with the formation of molasse troughs. The geometry of tectonic deformations in the Transcaucasus is largely determined by the wedge-shaped rigid Arabian block intensively indenting into the Asia Minor-Caucasian region. All structural-morphological lines have a clearly-expressed arcuate northward-convex configuration reflecting the contours of the Arabian block. However, farther north, the geometry of the fold-thrust belts is somewhat different - the Achara-Trialeti fold-thrust belt is, on the whole, W-E-trending; the Greater Caucasian fold-thrust belt extends in a WNW-ESE direction.
The Eurasia-Arabia continental collision region, including surrounding areas of eastern Turkey, the Caucasus, and the Iranian plateau, is one of Earth's most seismically active and rapidly deforming continental regions. The wide range of deformation processes occurring in this relatively confined region makes the eastern Mediterranean region a unique place in which to improve our understanding of the complexities of continental collision, including strike-slip faulting and crustal extension, as well as the associated seismicity and volcanism. The Arabia-Eurasia continental collision mainly forms fold belts along major thrust faults in southeastern Anatolia and in the Caucasus, while originating major strike-slip faults in eastern Anatolia and northwestern Iran capable of generating major destructive earthquakes. The Arabia plate is moving northerly at a rate of similar to 18 mm/yr, whereas there is a shortening of 6-10 mm/yr along the Caucasus. However, it is not certain how much of this shortening by seismic activity is due to the insufficient time of observations and the lack of reliable data. In addition, the continental collision in eastern Anatolia and the northward subduction of the Africa plate beneath western Turkey and the Aegean region are causing extension of the continental crust in the overlying Aegean extensional province. Eastern Turkey is experiencing crustal shortening and thickening due to northward motion of the Arabia plate relative to Eurasia. Although the interplay between dynamic effects of the relative motions of adjoining plates controls large-scale crustal deformation and the associated earthquake activity on the major fault zones in the region, a few large earthquakes have occurred since the 1960s, and many great earthquakes have been reported in historical records. The source mechanisms and rupture histories of the earthquakes that occurred in the Caucasus and surrounding regions are estimated from teleseismic long-period and broadband body waveform (P- and SH-waves) data recorded by worldwide seismograph networks. We have studied twenty earthquakes and compiled the other reported twenty-four earthquakes' source parameters to correlate with the regional tectonic process under way. In general, the dip angles of the thrust faulting in the Caucasus are shallow, and the depths of the events are no more than 20 km, which indicates seismogenic thickness. Contrary to previous studies, the sources of the earthquakes in the region do not have complex rupture properties. The north-south seismic deformation in the Lesser and Greater Caucasus was found to be similar to 1 mm/yr from moment summation of the events. The slip vectors indicate that the northward plate motion changes its direction not only in the Caucasus but also on the Northeast Anatolian fault.
The Greater Caucasus Mountains contain the highest peaks in Europe and define, for over 850 km along strike, the leading edge of the second-largest active collisional orogen on Earth. However, the mechanisms by which this range is being constructed remain disputed. Using a new database of earthquake records from local networks in Georgia, Russia, and Azerbaijan, together with previously published hypocenter locations, we show that the central and eastern Greater Caucasus Mountains are underlain by a northeast-dipping zone of mantle seismicity that we interpret as a subducted slab. Beneath the central Greater Caucasus (east of 45°E), the zone of seismicity extends to a depth of at least 158 km with a dip of ∼40°NE and a slab length of ∼130–280 km. In contrast, beneath the western GC (west of 45°E) there is a pronounced lack of events below ∼50 km, which we infer to reflect slab breakoff and detachment. We also observe a gap in intermediate-depth seismicity (45–75 km) at the western end of the subducted slab beneath the central Greater Caucasus, which we interpret as an eastward-propagating tear. This tear coincides with a region of minimum horizontal convergence rates between the Lesser and Greater Caucasus, as expected in a region of active slab breakoff. Active subduction beneath the eastern Greater Caucasus presents a potentially larger seismic hazard than previously recognized and may explain historical records of large magnitude (M 8) seismicity in this region.
The Greater Caucasus Mountains, due to their youth (~5 Ma), provide an opportunity for insight into the early stages of orogen development during continent-continent collision. However, their recent tectonic evolution and first-order architecture remain unclear. Here we investigate the evolution of the orogen by integrating new observations of the fluvial geomorphology and neotectonics of the range with prior work on seismicity, geodetic strain, bedrock geology and foreland-basin structure. We find that the range contains four zones along strike that differ in structural architecture, topography, and first-order tectonic history. In particular, two south-directed, singly-vergent zones at the western and eastern tips of the orogen are separated by both a central doubly-vergent zone that is dominated by north-directed deformation, and an eastern doubly-vergent zone in which south-directed thrusting dominates. We hypothesize that the along-strike changes in vergence and locus of deformation reflects different stages in the development of a doubly-vergent orogen, with the tips of the range preserving an early, singly-vergent form and the center recording a more advanced orogen. The differences between the two-doubly vergent zones seem to be driven by the initial stages of collision between the structurally thickened crust of the Greater and Lesser Caucasus orogens, which initiated at ~5 Ma.
The potential for large, shallow earthquakes and their associated seismic hazard in the eastern Caucasus, an area of dense population and sensitive industrial infrastructure, remains speculative based on historical precedent and current geologic and seismologic observations. Here we present updated and expanded results from a GPS network between the northern edge of the Lesser Caucasus and Greater Caucasus, providing geodetic constraints to the problem. A significant strain rate is observed in a profile over a distance of about 150 km across the Kura Basin. We attribute this to inter-seismic strain accumulation on buried fault structures and present simple elastic dislocation models for their plausible geometry and slip rate based on the known geology, seismicity and the GPS velocities. Due to the close proximity of the strain anomaly to Baku, further observations are needed to determine whether observed contraction is due to inter-seismically locked faults and, if so, implications for the seismic hazard in the region.
Crystallization and thermal histories of two plutons in the west-central
Alborz (also Elburz, Elburs) Mountains, northern Iran, are combined with
crosscutting relations and kinematic data from nearby faults to
determine the Cenozoic tectonic evolution of this segment of the
youthful Euro-Arabian collision zone. U/Pb,
40Ar/39Ar, and (U-Th)/He data were obtained from
zircon, biotite, K-feldspar, and apatite. The Akapol pluton intruded at
56 ± 2 Ma, cooled to ˜150 °C by ca. 40 Ma, and stayed
near that temperature until at least 25 Ma. The nearby Alam Kuh granite
intruded at 6.8 ± 0.1 Ma and cooled rapidly to ˜70 °C
by ca. 6 Ma. These results imply tectonic stability of the west-central
Alborz from late Eocene to late Miocene time, consistent with Miocene
sedimentation patterns in central Iran. Elevation-correlated (U- Th)/He
ages from the Akapol suite indicate 0.7 km/m.y. exhumation between 6 and
4 Ma, and imply ˜10 km of Alborz uplift that was nearly
synchronous with rapid south Caspian subsidence, suggesting a causal
relation. Uplift, south Caspian subsidence and subsequent folding,
reversal of Alborz strike-slip (from dextral to sinistral) and(?)
eastward extrusion of central Iran, coarse Zagros molasse deposition,
Dead Sea transform reorganization, Red Sea oceanic spreading, and(?)
North and East Anatolian fault slip all apparently began ca. 5 ±
2 Ma, suggesting a widespread tectonic event that we infer was a
response to buoyant Arabian lithosphere choking the Neo-Tethyan
subduction zone.
We extend the Bayesloc seismic multiple-event location algorithm for application to global arrival time data sets. Bayesloc is a formulation of the joint probability distribution spanning multiple-event location parameters, including hypocenters, travel time corrections, pick precision, and phase labels. Stochastic priors may be used to constrain any of the Bayesloc parameters. Markov Chain Monte Carlo sampling is used to draw samples from the joint probability distribution, and the posteriori samples are summarized to infer conventional location parameters such as the hypocenter. The first application of the broad area Bayesloc algorithm is to a data set consisting of all well-recorded events in the Middle East and the most well-recorded events with 5° spatial sampling globally. This sampling strategy is designed to provide the ray coverage needed to determine lithospheric-scale P wave velocity structure in the Middle East using the complementary ray geometry provided by regional (subhorizontal) and teleseismic (subvertical) raypaths and to determine a consistent, albeit lower-resolution, image of global mantle structure. The data set consists of 5401 events and 878,535 P, Pn, pP, sP, and PcP arrivals recorded at 4606 stations. Relocated epicenters are an average of 16 km from bulletin locations. The data set included events that are known to an accuracy of 1 km (a.k.a. GT1) based on nonseismic information. The average distance between GT1 epicenters and our relocated epicenters is 5.6 km. For arrivals labeled P, Pn, and PcP, ˜92%, ˜90%, and 96% are properly labeled with probability >0.9, respectively. Incorrect phase labels are found to be erroneous at rates of 0.6%, 0.2%, 1.6%, and 2.5% for P, Pn, PcP, and depth phases (pP and sP), respectively. Labels found to be incorrect, but not erroneous, were reassigned to another phase label. P and Pn residual standard deviation with respect to ak135 travel times are dramatically reduced from 3.45 s to 1.01 s. The differences between travel time residuals for nearly reciprocal raypaths are significantly reduced from the input event locations, suggesting that Bayesloc relocation improves data set consistency. The reciprocity tests suggest that the dominant contribution to travel time residuals calculated from information provided in global bulletins is location and picks errors, not travel time prediction errors due to 3-D structure. Modeling the whole multiple-event system results in accurate locations and an internally consistent data set that is ideal for tomography and other travel time calibration studies. Simmons et al. (2011) (companion paper) use the Bayesloc-processed data set to develop a 3-D tomographic image, which further reduces residual standard deviation to 0.50 s.
The Alborz range of N Iran provides key information on the spatiotemporal evolution and characteristics of the Arabia-Eurasia continental collision zone. The southwestern Alborz range constitutes a transpressional duplex, which accommodates oblique shortening between Central Iran and the South Caspian Basin. The duplex comprises NW-striking frontal ramps that are kinematically linked to inherited E-W-striking, right-stepping lateral to obliquely oriented ramps. New zircon and apatite (U-Th)/He data provide a high-resolution framework to unravel the evolution of collisional tectonics in this region. Our data record two pulses of fast cooling associated with SW-directed thrusting across the frontal ramps at ~ 18–14 and 9.5-7.5 Ma, resulting in the tectonic repetition of a fossil zircon partial retention zone and a cooling pattern with a half U-shaped geometry. Uniform cooling ages of ~ 7–6 Ma along the southernmost E-W striking oblique ramp and across its associated NW-striking frontal ramps suggests that the ramp was reactivated as a master throughgoing, N-dipping thrust. We interpret this major change in fault kinematics and deformation style to be related to a change in the shortening direction from NE to N/NNE. The reduction in the obliquity of thrusting may indicate the termination of strike-slip faulting (and possibly thrusting) across the Iranian Plateau, which could have been triggered by an increase in elevation. Furthermore, we suggest that ~ 7-6-m.y.-old S-directed thrusting predated inception of the westward motion of the South Caspian Basin.
Orogens formed by a combination of subduction and accretion are featured by a short-lived collisional history. They preserve crustal geometries acquired prior to the collisional event. These geometries comprise obducted oceanic crust sequences that may propagate somewhat far away from the suture zone, preserved accretionary prism and subduction channel at the interplate boundary. The cessation of deformation is ascribed to rapid jump of the subduction zone at the passive margin rim of the opposite side of the accreted block. Geological investigation and 40Ar/39Ar dating on the main tectonic boundaries of the Anatolide–Tauride–Armenian (ATA) block in Eastern Turkey, Armenia and Georgia provide temporal constraints of subduction and accretion on both sides of this small continental block, and final collisional history of Eurasian and Arabian plates. On the northern side, 40Ar/39Ar ages give insights for the subduction and collage from the Middle to Upper Cretaceous (95–80Ma). To the south, younger magmatic and metamorphic ages exhibit subduction of Neotethys and accretion of the Bitlis–Pütürge block during the Upper Cretaceous (74–71Ma). These data are interpreted as a subduction jump from the northern to the southern boundary of the ATA continental block at 80–75Ma. Similar back-arc type geochemistry of obducted ophiolites in the two subduction–accretion domains point to a similar intra-oceanic evolution prior to accretion, featured by slab steepening and roll-back as for the current Mediterranean domain. Final closure of Neotethys and initiation of collision with Arabian Plate occurred in the Middle-Upper Eocene as featured by the development of a Himalayan-type thrust sheet exhuming amphibolite facies rocks in its hanging-wall at c. 48Ma.
A field study of the neotectonics of the Georgian Caucasus is combined with geophysical, geodetic and geological information in order to obtain a mechanical model of actual deformation.The analysis of satellite photos together with topographical and geological maps shows that the Great Caucasus is bisected by a NNE-trending sinistral strike-slip fault zone. The western Great Caucasus is thrusted to the south over the Rioni basin; while, on the other hand, its northern flank is a monocline that descends gently into the Russian Platform. Active volcanism is present from Elbruz to Kazbeg. The eastern Great Caucasus is limited by thrusts to the north and to the south, and intermediate structures are disposed in a fan-like shape. No recent volcanism is observed. The eastern limit of the chain is a NNW-trending dextral strike-slip fault zone.Seismicity from a local network illustrates the activity of the thrusts and gives evidence for the strike-slip faults. Microtectonic data confirm the recent activity and the sinistral character of the Borjomi-Kazbeg strike-slip fault.The strike-slip faults bordering the eastern Caucasus may be seen as the limits of a plastic wedge in front of the Arabian Plate, at an early stage of continental collision.
Dedicated to the memory of three pioneers, İhsan Ketin, Sırrı Erinç and Melih Tokay, and a recent student, Aykut Barka, who burnt himself out in pursuit of the mysteries of the North Anatolian Fault. ▪ Abstract The North Anatolian Fault (NAF) is a 1200-km-long dextral strike-slip fault zone that formed by progressive strain localization in a generally westerly widening right-lateral keirogen in northern Turkey mostly along an interface juxtaposing subduction-accretion material to its south and older and stiffer continental basements to its north. The NAF formed approximately 13 to 11 Ma ago in the east and propagated westward. It reached the Sea of Marmara no earlier than 200 ka ago, although shear-related deformation in a broad zone there had already commenced in the late Miocene. The fault zone has a very distinct morphological expression and is seismically active. Since the seventeenth century, it has shown cyclical seismic behavior, with century-long cycles beginning in the east and progressing westwa...
Constraining the timing of onset and rates of deformation within the Greater Caucasus mountains is key to understanding their role in accommodating deformation across the Arabia-Eurasia orogen. We present new low-temperature thermochronometric constraints on the Cenozoic thermal evolution of the central Greater Caucasus that elucidate a three-phase cooling history. Between 50 and 30 Ma, cooling within the range was negligible. In Oligocene time, cooling rates throughout the range increased to ∼4°C/Myr. These rates remained constant until the early Pliocene time, when they increased again, reaching ∼25°C/Myr along the axial part of the range. Rates and timing of Oligocene exhumation are consistent with previous results from the western Greater Caucasus and are proposed to result from onset of subduction of the Greater Caucasus back-arc basin. Rapid exhumation of the Greater Caucasus, beginning in Pliocene time, contrasts with previously reported thermal histories for other portions of the range. Pliocene exhumation of the central Greater Caucasus appears to be tectonically driven and coincides with widespread evidence for a major reorganization of the Arabia-Eurasia plate boundary. We hypothesize that this exhumation, and regionally observed plate reorganization, results from the collision of the Lesser Caucasus with Eurasia, completing the subduction of oceanic lithosphere across this segment of the Arabia-Eurasia plate boundary.
The 1991, Ms = 7.0 Racha earthquake is the largest ever recorded in the Caucasus Mountains. Approxi-mately three months after this thrust-faulting earth-quake, a GPS network was set up to measure postseis-mic surface deformation. We present an analysis of these data, which indicate accelerated postseismic motions at several near-field sites. We model this deformation as either afterslip on the rupture surface or viscoelastic re-laxation of the lower crust. We find that the postseis-mic motions are best explained by shallow afterslip on the earthquake rupture plane. The minimum postseismic moment release is estimated at 6.0 × 10 18 N m, which is over 200 times the moment released by aftershocks in this same period and about 20% of the coseismic moment. We also show that the effective viscosity of the lower crust in the western Greater Caucasus region exceeds 10 18 Pa s.
Over the past decade, many Global Positioning System (GPS) networks have been installed to monitor tectonic motions around the world. Some of these networks contain hundreds of sites spread across active tectonic margins where the differences in velocities across the network can be 50–100mm/year. For networks that have been running for a number of years, the uncertainty in the velocity estimates can be less than 1mm/year. In some cases the vertical motions can also be significant and of importance. Often, the time series of the motions of the GPS sites show complex non-linear behavior, and in all cases the statistical model of the time series is more complex than simple white noise. In this article, we describe a set of Matlab tools developed for use with the GAMIT/GLOBK GPS data analysis system (King 2002; King and Herring 2002) that allow interactive viewing and manipulation of GPS velocities and time series with a Matlab-based graphical user interface (GUI). The formats of the data files used by the tools are specific to GAMIT/GLOBK, but they are simple ASCII files that can be generated from other file formats. The tools are referred to as GGMatlab.
We Present a GPS-derived velocity field 1988-2005 for the zone of
interaction of the Arabian African Nubian and Somalian and Eurasian
plates The Velocity field indicates counterclockwise motion of a broad
area of the Earth s surface that includes the Arabian plate adjacent
parts of the Zagros and Central Iran Turkey and the Aegean at rates in
the range of 20 -- 30 mm yr This relatively rapid motion occurs within
the framework of the slow-moving 5 mm yr relative motions Eurasian
Nubian and Somalian plates The circulatory pattern of motion increases
in rate towards the Hellenic trench system suggesting that subduction in
the eastern Mediterranean is the dominant process responsible for
regional deformation Using seismic and other geophysical and geological
information we develop an elastic block model and use the GPS velocity
field to estimate relative block motions This model provides a
reasonable fit to the observed motions with the principal block
boundaries corresponding to known seismically active faults e g Sinai
and Marmara regions The GPS observations for Sinai imply that the Sinai
Peninsula and Levant region comprise a separate sub-plate sandwiched
between the Arabian and Nubian plates
The Alpine geodynamics of the Caucasus and adjacent areas is discussed. Palinspastic reconstructions are given on the basis of new geologic, paleomagnetic and paleobiogeographic data. The dynamic unity of extension and compression processes is shown to take place within the central segment of the Mediterranean belt. The closure of the Paleotethys oceanic basin coincides approximately with the opening of the Mesotethys. Owing to this the opening between Afro-Arabia and Eurasia persists, as is confirmed by paleomagnetic and other data. The closure of the Mesozoic Tethys is, on the whole, synchronous with the opening of the Central and South Atlantic. The formation of the present structure of the Caucasus and adjacent areas is connected with the unidirectional compression of this area and the rotation of the compressional axis from a northeastern to a sub-meridional direction in the course of the Cimmerian-Alpine cycle.
A complete suite of closed analytical expressions is presented for the surface displacements, strains, and tilts due to inclined shear and tensile faults in a half-space for both point and finite rectangular sources. These expressions are particularly compact and free from field singular points which are inherent in the previously stated expressions of certain cases. The expressions derived here represent powerful tools not only for the analysis of static field changes associated with earthquake occurrence but also for the modeling of deformation fields arising from fluid-driven crack sources.
Our analysis of Global Positioning System (GPS) site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal and 4 mm for vertical, with some sites at twice these amplitudes. Power spectrum analysis confirms that GPS time series also contain significant power at annual harmonic frequencies (with spectral indices 1 < α < 2), which indicates the presence of repeating signals. Van Dam et al. [2001] showed that a major annual component is induced by hydrological and atmospheric loading. Unless accounted for, we show that annual signals can significantly bias estimation of site velocities intended for high accuracy purposes such as plate tectonics and reference frames. For such applications, annual and semiannual sinusoidal signals should be estimated simultaneously with site velocity and initial position. We have developed a model to calculate the level of bias in published velocities that do not account for annual signals. Simultaneous estimation might not be necessary beyond 4.5 years, as the velocity bias rapidly becomes negligible. Minimum velocity bias is theoretically predicted at integer-plus-half years, as confirmed by tests with real data. Below 2.5 years, the velocity bias can become unacceptably large, and simultaneous estimation does not necessarily improve velocity estimates, which rapidly become unstable due to correlated parameters. We recommend that 2.5 years be adopted as a standard minimum data span for velocity solutions intended for tectonic interpretation or reference frame production and that we be skeptical of geophysical interpretations of velocities derived using shorter data spans.
Comparison of plate convergence with the timing and magnitude of upper-crustal shortening in collisional orogens indicates both shortening deficits (200-1700 km) and significant (10-40%) plate deceleration during collision, the cause(s) for which remain debated. The Greater Caucasus Mountains, which result from post-collisional Cenozoic closure of a relict Mesozoic back-arc basin on the northern margin of the Arabia-Eurasia collision zone, help reconcile these debates. Here we use U-Pb detrital zircon provenance data and the regional geology of the Caucasus to investigate the width of the now-consumed Mesozoic back-arc basin and its closure history. The provenance data record distinct southern and northern provenance domains that persisted until at least the Miocene. Maximum basin width was likely ~350-400 km. We propose that closure of the back-arc basin initiated at ~35 Ma, coincident with initial (soft) Arabia-Eurasia collision along the Bitlis-Zagros suture, eventually leading to ~5 Ma (hard) collision between the Lesser Caucasus arc and the Scythian platform to form the Greater Caucasus Mountains. Final basin closure triggered deceleration of plate convergence and tectonic reorganization throughout the collision. Post-collisional subduction of such small (102-103 km wide) relict ocean basins can account for both shortening deficits and delays in plate deceleration by accommodating convergence via subduction/underthrusting, although such shortening is easily missed if it occurs along structures hidden within flysch/slate belts. Relict-basin closure is likely typical in continental collisions in which the colliding margins are either irregularly shaped or rimmed by extensive back-arc basins and fringing arcs, such as those in the modern South Pacific.
The Greater Caucasus Mountains are a young (~5 m.y. old) orogen within the Arabia-Eurasia collision zone that contains the highest peaks in Europe and has an unusual topographic form for a doubly vergent orogen. In the east-central part (45°E–49°E), the range is nearly symmetric in terms of prowedge and retrowedge widths and the drainage divide is much closer to the southern margin of the range (prowedge side) than it is to the north- ern margin (retrowedge side). Moreover, the divide does not coincide with the topographic crest, but rather the crest is both shifted northward by as much as 40 km and traversed by several large north-flowing rivers. Both the topographic crest and drainage divide appear to coincide with zones of active rock uplift, because they are characterized by bands of high local relief and normalized channel steepness values (>300). This uplift pattern could result from a synchronous initiation of the two uplift zones or propagation of deformation either northward or southward. The two propagating scenarios differ fundamentally in their predictions for the relative ages of topographic features; northward propagation predicts that the topographic crest is younger than the drainage divide, and the southward scenario predicts the converse. Because available geologic and topographic data are consistent with both propagation directions, we use a landscape evolution model to test all three scenarios. Model results indicate that the current topography and drainage network is best explained by a northward propagation of deformation from the south flank into the interior of the east-central Greater Caucasus. Such propagation implies recent out-of-sequence deformation within the Greater Caucasus due to reactivation or development of new structures within the core of the orogen. It remains unclear if such deformation is a transient response to an accretion cycle or stems from a fundamental change in the structural architecture of the orogen.
A complete set of closed analytical expressions is presented in a unified manner for the internal displacements and strains due to shear and tensile faults in a half-space for both point and finite rectangular sources. Several practical suggestions to avoid mathematical singularities and computational instabilities are presented. -from Author
Strike slip on various scales and on faults of diverse orientations is one of the most prominent modes of deformation in continental convergence zones. Extreme heterogeneity and low shear strength of continental rocks are responsible for creating complex 'escape routes' from nodes of constriction along irregular collision fronts toward free faces formed by subduction zones. The origin of this process is poorly understood. The 2 main models ascribe tectonic escape to buoyancy forces resulting from differences in crustal thickness generated by collision and to forces applied to the boundaries of the escaping wedges. Escape tectonics also creates a complicated geological signature, whose recognition in fossil examples may be difficult. We examine the Neogene to present tectonic escape-dominated evolution of Turkey both to test the models devised to account for tectonic escape and to develop criteria by which fossil escape systems may be recognized.-from Authors
This chapter describes the geology of Georgia and the Georgian part of the Black Sea. It is based on geological maps and seismic interpretation, integrated with well data and outcrop studies. The geology of Georgia consists of two major thrust belts: the Greater Caucasus and the Achara-Trialet belt, separated by two foreland basins (Rioni and Kartli) with an intervening basement culmination, the Dziruli Massif. The Achara-Trialet belt comprises a thick Upper Cretaceous and Paleogene sequence that restores to a rift and postrift basin of probable Paleocene age, connecting to the Eastern Black Sea. The basin began to close by the Oligocène. Structures are detached at Aptian and Oligocène levels and are large and open. The Rioni Basin developed mainly during the Oligocène and the Miocene through loading by the Achara-Trialet belt folds. It dies out into the Eastern Black Sea as the foreland basin megasequence merges with the postrift fill of the latter. North of the Rioni Basin, the major thrust front is a large south-dipping monocline, in front of which there are extensive salients detached in Upper Jurassic evaporites. The Kartli Basin passes into the Kura Basin to the east, where the foreland basin is deformed by the Greater Caucasus south-vergent thrust structures.
[1] The Greater Caucasus are the northernmost extent of the Arabia-Eurasia collision and are thought to represent the main locus of shortening within the central portion of the collision zone between 40° and 48°E. Recent work suggests that in detail, since the Plio-Pleistocene, much of the shortening in the eastern portion of the Caucasus system has been focused within the Kura fold-thrust belt along the southeastern margin of the Greater Caucasus. Here we present new field mapping and stratigraphic investigations of the eastern termination of the Kura fold-thrust belt in Azerbaijan to better constrain the structural geometries, magnitude of shortening, and initiation age for this portion of the fold-thrust belt. Our work suggests that this area of the fold-thrust belt exhibits significant along-strike variations in structural style and evolution and can effectively be divided into two distinct domains at ~48°E. The western domain is characterized by a subcritical median surface slope and isolated folds and thrusts propagating out of sequence, whereas the eastern domain is dominated by a single duplex structure and a history of in-sequence development in a critically tapered wedge. We hypothesize that these variations result from changes in relative rates of syn-tectonic sedimentation, erosion, and convergence velocity along strike. We find that within the western domain, the fold-thrust belt has accommodated ~12 km of total shortening. An unconformity within the western domain brackets the initiation age of this portion of the fold-thrust belt to between 1.8 and 0.88 Ma yielding permissible average shortening rates of between 6.7 and 13.6 mm/yr. Comparison of these average shortening rates to the geodetically measured shortening rate of 8 mm/yr indicates that since initiation, the fold-thrust belt has accommodated 83–100% of convergence between the Greater and Lesser Caucasus at this longitude.
Earthquake moment tensors reflecting seven years of global seismic activity (2004–2010) are presented. The results are the product of the global centroid-moment-tensor (GCMT) project, which maintains and extends a catalog of global seismic moment tensors beginning with earthquakes in 1976. Starting with earthquakes in 2004, the GCMT analysis takes advantage of advances in the mapping of propagation characteristics of intermediate-period surface waves, and includes these waves in the moment-tensor inversions. This modification of the CMT algorithm makes possible the globally uniform determination of moment tensors for earthquakes as small as MW = 5.0. For the period 2004–2010, 13,017 new centroid-moment tensors are reported.
It is possible to use the waveform data not only to derive the source mechanism of an earthquake but also to establish the hypocentral coordinates of the 'best point source' (the centroid of the stress glut density) at a given frequency. Thus two classical problems of seismology are combined into a single procedure. Given an estimate of the origin time, epicentral coordinates and depth, an initial moment tensor is derived using one of the variations of the method described in detail by Gilbert and Dziewonski (1975). This set of parameters represents the starting values for an iterative procedure in which perturbations to the elements of the moment tensor are found simultaneously with changes in the hypocentral parameters. In general, the method is stable, and convergence rapid. Although the approach is a general one, we present it here in the context of the analysis of long-period body wave data recorded by the instruments of the SRO and ASRO digital network. -Authors
An intermediate-depth earthquake is confirmed at a depth of 158 +/- 4 km under the northern foothills of the Greater Caucasus. Separate methods were used to confirm the depth: data from local and regional networks, teleseismic depth phases, and examination of waveforms. Additional examination of global catalogs suggests the presence of a (perhaps remnant) northeast-dipping subduction zone under the Greater Caucasus. The most likely explanation appears to be subduction of oceanic crust with the interface at the northern edge of the Kura Basin. Events at depths of 30-50 km in the Kura Basin may be related to underthrusting by the South Caspian basin rather than subduction in the Greater Caucasus.
New tectonic uplifts south of the Salt Range Thrust and Himalayan Front Thrust (HFT) represent an outward step of the plate boundary from the principal tectonic displacement zone into the Indo-Gangetic Plain. In Pakistan, the Lilla Anticline deforms fine-grained overbank deposits of the Jhelum River floodplain 15 km south of the Salt Range. The anticline is overpressured in Eocambrian non-marine strata. In northwest India south of Dehra Dun, the Piedmont Fault (PF) lies 15 km south of the HFT. Coalescing fans derived from the Himalaya form a piedmont (Old Piedmont Zone) 15–20 km wide east of the Yamuna River. This zone is uplifted as much as 15–20 m near the PF, and bedding is tilted 5–7° northeast. Holocene thermoluminescence-optically-stimulated luminescence dates for sediments in the Old Piedmont Zone suggest that the uplift rate might be as high as several mm/a. The Old Piedmont Zone is traced northwest 200 km and southeast another 200 km to the Nepal border. These structures, analogous to protothrusts in subduction zones, indicate that the Himalayan plate boundary is not a single structure but a series of structures across strike, including reactivated parts of the Main Boundary Thrust north of the range front, the HFT sensu stricto, and stepout structures on the Indo-Gangetic Plain. Displacement rates on all these structures must be added to determine the local India-Himalaya convergence rate.
This paper examines how active faulting in the Turkey-Iran-Caucasus region accommodates the Arabia-Eurasia collision and the velocity field observed by GPS. The overall shortening across the zone is, in general, spatially separated (“partitioned”) into right-lateral strike slip in the Turkish-Iranian Plateau and thrusting in the Greater Caucasus. A band of counterclockwise rotating NW-SE right-lateral strike-slip faults accommodates a NW-SE gradient in NE directed velocity (relative to Eurasia) between the Black and Caspian seas. A NNW-SSE band of previously unrecognized oblique normal faults is present on the Turkey-Iran border. We estimate the offsets on faults from geomorphological features and show that these offsets can be achieved in 5 ± 2 Ma at present rates. This implies a reorganization of deformation in the collision zone at that time, after the initial collision at ∼12 Ma, probably in response to mantle-induced dynamic uplift.
Although fault-bounded thrust sheets are common in the geological record, seismic evidence for their motion is sparse. The April 29, 1991, Racha earthquake (M(sub S) = 7.0), the largest instrumentally recorded earthquake in the Greater Caucasus, is one of the largest recent earthquakes in continental thrust belts and provides evidence on mechanisms of thrust sheet motion. Using data from a deployment of Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL) digital seismographs and various other instruments, we locate 1952 aftershocks occurring between May 7 and June 30, 1991. The aftershocks form a zone approximately 70 km long and 10-25 km wide striking E-W, following the Racha ridge at the southern boundary of the Greater Caucasus thrust system. Teleseismic body waves are inverted for source parameters of the mainshock and the two largest aftershocks. The solutions show thrust faulting with centroid depths of 3-10 km, comparable to depths of locally recorded aftershocks (approximately 2-12 km). The shallow-dipping nodal plane, the aftershock distribution, and surface geology demonstrate that the main event was caused by faulting on a thrust system dipping NNE at 20 deg- 31 deg bounding the southern slope of the Greater Caucasus. This fault system thrusts the Greater Caucasus structures south over the Dzhirula basement massif. The inferred fault geometry suggests that the active fault is either a detachment between sediments and Dzhirula basement or cuts through the basement at shallow depths. The 1500-m-high Racha ridge overlies the aftershock zone and is a likely consequence of repeated similar earthquakes. Hence the 1991 earthquake sequence shows that the western Greater Caucasus is accommodating plate convergence at a rate possibly comparable to the eastern Greater Caucasus (a few millimeters per year).
The plate motion model NUVEL-1 (De Mets et al., 1990) predicts a strongly oblique component to the convergence between Arabia and Eurasia at the longitude of the Caucasus. Earthquake focal mechanisms suggest that this oblique convergence is partitioned into pure right-lateral strike-slip motion in eastern Turkey and pure shortening by thrusting in the Greater Caucasus. Such partitioning offers an explanation for the apparent eastward continuation of the right-lateral faulting of the North Anatolian fault from Turkey into Iran. From a summation of seismic moment tensors between 1911 and 1991 it appears that most of the right-lateral strike-slip motion in eastern Turkey is accommodated by faulting in large earthquakes, while most of the shortening in the Caucasus appears to occur aseismically.
Anatolian Plateau-Caucasus-Caspian region is an area of complex structure accompanied by large variations in seismic wave velocities. Despite the complexity of the region little is known about the detailed lithospheric structure. Using data from 29 new broadband seismic stations in the region, a unified velocity structure is developed using teleseismic receiver functions and surface waves. Love and Rayleigh surface waves dispersion curves have been derived from event-based analysis and ambient-noise correlation. We jointly inverted the receiver functions with the surface wave dispersion curves to determine absolute shear wave velocity and important discontinuities such as sedimentary layer, Moho, lithospheric-asthenospheric boundary. We combined these new station results with Eastern Turkey Seismic Experiment results (29 stations). Caspian Sea and Kura basin underlained by one of the thickest sediments in the world. Therefore, short-period surface waves are observed to be very slow. The strong crustal multiples in receiver functions and the slow velocities in upper crust indicate the presence of thick sedimentary unit (up to 20 km). Crustal thickness varies from 34 to 52 km in the region. The thickest crust is in Lesser Caucasus and the thinnest is in the Arabian Plate. The lithospheric mantle in the Greater Caucasus and the Kura depression is faster than the Anatolian Plateau and Lesser Caucasus. This possibly indicates the presence of cold lithosphere. The lower crust is slowest in the northeastern part of the Anatolian Plateau where Holocene volcanoes are located.
A unique broadband data set is combinedLithospheric velocity structure in the Caucasus region is estimatedReceiver functions and surface waves are used for the estimation
Although the geometry and kinematics of the first-order structures accommodating Arabia-Eurasia convergence are relatively well known in Turkey and Iran, major shortening structures remain poorly understood within the central portion of the collision zone, in eastern Anatolia and the Caucasus. New remotely sensed neotectonic mapping, synthesis of regional geologic and stratigraphic data, and balanced cross sections suggest that the Kura fold-thrust belt has accommodated the majority of Arabia-Eurasia convergence since the early Pliocene between the longitudes of ~45°E and ~49°E. This belt lies southeast of the N80°W-striking Greater Caucasus Mountains and forms an eastwardnarrowing band of elevated topography that roughly parallels the range front for ~400 km along strike. The belt is separated from the Greater Caucasus to the north by the 10 to 25-km-wide Alazani Basin and comprises a series of predominantly south-verging folds deforming Eocene-Quaternary flysch and molasse. To document structural geometries within the Kura fold-thrust belt, we have used the Real-time Interactive Mapping System (RIMS) software to analyze Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), visible to near-infrared (VNIR), and digital elevation model (DEM) data. This neotectonic mapping indicates an along-strike, eastward decrease in both structural complexity and the degree to which deformed geomorphic surfaces are dissected. Existing geologic maps indicate a corresponding eastward decrease in the depth of exposure. By integrating the structural geometries determined in our analysis of remote-sensing data with existing geologic data, we have constructed two balanced cross sections, which suggest these systematic along-strike variations result from a west-to-east decrease in total shortening within the Kura fold-thrust belt. We interpret this variable shortening to stem from eastward propagation of the Kura fold-thrust belt. Comparison of our preliminary total shortening estimates with those predicted by current plate motions suggest that the Kura fold-thrust belt has accommodated ~30%-40% (~25 km) of total Arabia-Eurasia convergence since 5 Ma, and thus forms a first-order structural system within the central portion of the collision zone.
The ITRF2008 velocity field is demonstrated to be of higher quality and
more precise than past ITRF solutions. We estimated an absolute tectonic
plate motion model made up of 14 major plates, using velocities of 206
sites of high geodetic quality (far from plate boundaries, deformation
zones and Glacial Isostatic Adjustment (GIA) regions), derived from and
consistent with ITRF2008. The precision of the estimated model is
evaluated to be at the level of 0.3 mm/a WRMS. No GIA corrections were
applied to site velocities prior to estimating plate rotation poles, as
our selected sites are outside the Fennoscandia regions where the GIA
models we tested are performing reasonably well, and far from GIA areas
where the models would degrade the fit (Antarctica and North America).
Our selected velocity field has small origin rate bias components
following the three axis (X, Y, Z), respectively 0.41 ± 0.54,
0.22 ± 0.64 and 0.41 ± 0.60 (95 per cent confidence
limits). Comparing our model to NNR-NUVEL-1A and the newly available
NNR-MORVEL56, we found better agreement with NNR-MORVEL56 than with
NNR-NUVEL-1A for all plates, except for Australia where we observe an
average residual rotation rate of 4 mm/a. Using our selection of sites,
we found large global X-rotation rates between the two models
(0.016°/Ma) and between our model and NNR-MORVEL56 of 0.023°/Ma,
equivalent to 2.5 mm/a at the Earth surface.
We present the 1998–2009 GPS-derived velocity field for the Armenia region based on a survey-mode observation network of 31 GPS sites. We combine our results with previous GPS studies of the region to better assess the deformation of the Lesser Caucasus and Kura basin region. The results show that the Kura basin and the Lesser Caucasus regions are two different blocks, and that the main fault (Pambak–Sevan–Sunik) between these two regions has a right-lateral slip rate of 2 ± 1 mm/yr. This is consistent with morphotectonic estimates and suggests a fairly constant slip rate over the last 120–300 ka. The right-lateral slip rate on one of the southern branch of the Pambak–Sevan–Sunik fault is lower than 1 mm/yr and the good agreement with a geologically estimated slip rate suggests a constant slip rate over the last 1.4 Myr. The Sardarapat and Akhurian faults experience some shortening. This shortening is consistent with some independent geological estimates and shows the Arabian push. However, NNW-SSE-orientated faults have an extensional fault normal component instead of the expected shortening due to the Arabia–Eurasia convergence. This substantial extensive strain, and the sharp azimuth change of the velocity vectors between the Arabia promontory and the Lesser Caucasus suggest that processes other than “extrusion”, possibly related to old subduction or delamination, contribute to the geodynamics of the region.
The Arabia-Eurasia collision has been linked to global cooling, the slowing of Africa, Mediterranean extension, the rifting of the Red Sea, an increase in exhumation and sedimentation on the Eurasian plate, and the slowing and deformation of the Arabian plate. Collision age estimates range from the Late Cretaceous to Pliocene, with most estimates between 35 and 20 Ma. We assess the consequences of these collision ages on the magnitude and location of continental consumption by compiling all documented shortening within the region, and integrating this with plate kinematic reconstructions. Shortening estimates across the orogen allow for similar to 350 km of Neogene upper crustal contraction, necessitating collision by 20 Ma. A 35 Ma collision requires additional subduction of similar to 400-600 km of Arabian continental crust. Using the Oman ophiolite as an analogue, ophiolitic fragments preserved along the Zagros suture zone permit similar to 180 km of subduction of the Arabian continental margin plus overlying ophiolites. Wholesale subduction of this more dense continental margin plus ophiolites would reconstruct similar to 400-500 km of postcollisional Arabia-Eurasia convergence, consistent with a ca. 27 Ma initial collision age. This younger Arabia-Eurasia collision suggests a noncollisional mechanism for the slowing of Africa, and associated extension.
We use drainage patterns, geological markers and geomorphological features to determine a right-lateral offset of ∼50 km, and possibly as much as ∼70 km, on the Main Recent Fault in NW Iran. This fault trends NW–SE and forms the NE border of the Zagros mountains. It accommodates the strike-slip component of the N–S convergence between Arabia and Eurasia, with the NE–SW shortening component being accommodated in the Zagros Fold Belt. Its ∼50 km strike-slip offset implies a shortening of ∼50 km in the fold belt and ∼70 km total N–S convergence accommodated in the NW Zagros. This is a substantial fraction of the 85–140 km overall Arabia–Eurasia convergence expected over the last 3–5 Ma. If the Main Recent Fault initiated at that time, as seems likely from geological arguments, it has a horizontal slip rate of at least 10–17 mm yr−1 and should be the source of frequent earthquakes of Ms 6–7, as has been seen in the 20th century and the earlier historical record. The similarity of the offsets and probable ages of the North Anatolian and Main Recent Faults suggests that they have been active as an almost continuous zone of right-lateral shear on the north edge of the Arabian and Anatolian plates since the early Pliocene.
The Racha-Dzhava earthquake (Ms = 7.0) that occurred on 1991 April 29 at 09:12:48.1 GMT in the southern border of the Great Caucasus is the biggest event ever recorded in the region, stronger than the Spitak earthquake (Ms = 6.9) of 1988. A field expedition to the epicentral area was organised and a temporary seismic network of 37 stations was deployed to record the aftershock activity. A very precise image of the aftershock distribution is obtained, showing an elongated cloud oriented N105°, with one branch trending N310° in the Western part. The southernmost part extends over 80 km, with the depth ranging from 0 to 15 km, and dips north. The northern branch, which is about 30 km long, shows activity that ranges in depth from 5 to 15 km. The complex thrust dips northwards. A stress-tensor inversion from P-wave first-motion polarities shows a state of triaxial compression, with the major principal axis oriented roughly N-S, the minor principal axis being vertical. Body-waveform inversion of teleseismic seismograms was performed for the main shock, which can be divided into four subevents with a total rupture-time duration of 22 s. The most important part of the seismic moment was released by a gentle northerly dipping thrust. The model is consistent with the compressive tectonics of the region and is in agreement with the aftershock distribution and the stress tensor deduced from the aftershocks. The focal mechanisms of the three largest aftershocks were also inverted from body-wave records. The April 29th (Ms = 6.1) and May 5th (Ms = 5.4) aftershocks have thrust mechanisms on roughly E-W-oriented planes, similar to the main shock. Surprisingly, the June 15th (Ms = 6.2) aftershock shows a thrust fault striking N-S. This mechanism is explained by the structural control of the rupture along the east-dipping geometry of the Dzirula Massif close to the Borzhomi-Kazberg strike-slip fault... (D'après résumé d'auteur)
Examination of more than 100 fault plane solutions for earthquakes within the Alpide belt between the Mid-Atlantic ridge and Eastern Iran shows that the deformation at present occurring is the result of small continental plates moving away from Eastern Turkey and Western Iran. This pattern of movement avoids thickening the continental crust over much of Turkey by consuming the Eastern Mediterranean sea floor instead. The rates of relative motion of two of the small plates involved, the Aegean and the Turkish plates, are estimated, but are only within perhaps 50 per cent of the true values. These estimates are then used to reconstruct the geometry of the Mediterranean 10 million years ago. The principal difference from the present geometry is the smooth curved coast which then formed the southern coast of Yugoslavia, Greece and Turkey. This coast has since been distorted by the motion of the two small plates. Similar complications have probably been common in older mountain belts, and therefore local geological features may not have been formed by the motion between major plates.
A curious feature of several of the large shocks for which fault plane solutions could be obtained for the main shock and one major after-shock was that the two often had different mechanisms.
Over 80 new fault plane solutions, combined with satellite imagery as well as both modern and historical observations of earthquake faulting, are used to investigate the active tectonics of the Middle East between western Turkey and Pakistan.
The deformation of the western part of this region is dominated by the movement of continental material laterally away from the Lake Van region in eastern Turkey. This movement helps to avoid crustal thickening in the Van region, and allows some of the shortening between Arabia and Eurasia to be taken up by the thrusting of continental material over oceanic-type basement in the southern Caspian, Mediterranean, Makran and Black Sea. Thus central Turkey, bounded by the North and East Anatolian strike-slip faults, is moving west from the Van region and overrides the eastern Mediterranean at two intermediate depth seismic zones: one extending between Antalya Bay and southern Cyprus, and the other further west in the Hellenic Trench. The motion of northern Iran eastwards from the Van region is achieved mainly by a conjugate system of strike-slip faults and leads to the low angle thrusting of Iran over the southern Caspian Sea. The seismicity of the Caucasus shows predominantly shortening perpendicular to the regional strike, but there is also some minor elongation along the strike of the belt as the Causcasus overrides the Caspian and Black Seas.
The deformation of the eastern part of this region is dominated by the shortening of Iran against the stable borders of Turkmenistan and Afghanistan. The north-east direction of compression seen in Zagros is also seen in north-east Iran and the Kopet Dag, where the shortening is taken up by a combination of strike-slip and thrust faulting. Large structural as well as palaeomagnetic rotations are likely to have occurred in NE Iran as a result of this style of deformation. North-south strike-slip faults in southern Iran allow some movement of material away from the collision zone in NE Iran towards the Makran subduction zone, where genuinely intermediate depth seismicity is seen.
Within this broad deforming belt large areas, such as central Turkey, NW Iran (Azerbaijan), central Iran and the southern Caspian, appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200-300 km wide. The motion of these blocks can usefully be described by poles of rotation. The poles presented in this paper predict motions consistent with those observed and also predict the opening of the Gulf of Iskenderun NE of Cyprus, the change within the Zagros mountains from strike-slip faulting in the NW to intense thrusting in the SE, and the relatively feeble seismicity in SE Iran (Baluchistan). This description also explains why the north-south structures along the Iran-Afghanistan border do not cut the east-west ranges of the Makran.
Within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation, even though motions at the surface may be concentrated on faults. The evolution of fault systems within the active zones is controlled by geometric constraints, such as the requirement that simultaneously active faults do not, in general, intersect.
Many of the active processes discussed in this paper, particularly large-scale rotations and lateral movement along the regional strike, are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them.
We review the geological and geophysical structural framework of the deep Black Sea and Caspian Sea basins. Based on seismic evidence and subsidence history, we conclude that the deep basins have an oceanic crust formed in a marginal sea environment. We propose that the present deep basins are remnants of a much greater marginal sea formed during three separate episodes during the Mesozoic: in the Middle Jurassic, Upper Jurassic and Late Cretaceous. A tentative sketch of the geologic evolution of the area is presented. The marginal sea reached its greatest extent in the Early Tertiary when it was about 900 km wide and 3000 km long. The central part of the marginal sea has since disappeared during the collision between the Arabian promontory and the Eurasian margin.
Teleseismic and geological observations of the continent-continent collision zone in the Greater Caucasus mountains of the southwestern Soviet Union indicate that the range is presently being underthrust primarily from the south. Since the onset of Alpide deformation, tectonic activity has been concentrated along the southern slope of the mountains, but ongoing deformation along the northern slope in the eastern part of the range may be associated with thrusting of the mountains northward over the Scythian platform in this area. To understand the present-day plate interactions in the Caucasian region and the mode of compensation of the Greater Caucasus mountains, we analyze Bouguer gravity anomaly data using both spectral (coherence and admittance calculations) and traditional spatial domain forward modeling techniques. As a whole, the range appears to be in regional isostatic equilibrium with compensation by flexure of an elastic plate of approximately 40 km thickness (D = 6×1023Nm) loaded strongly from the bottom as well as the top. Subsurface loads corresponding to stacking of thrust sheets, uplifts of basement rocks, active volcanic zones, and thick sequences of basin sediments play an important role in improving the fit between observed and calculated Bouguer values. Closer examination of the individual tectonic provinces which make up the range yields results consistent with support by a 40–50 km thick plate in the eastern and central parts of the Greater Caucasus mountains and by a plate with no flexural rigidity in the western part of the range. Coupled with the active volcanism and the relative lack of seismicity in the western part of the Greater Caucasus region, these results indicate the presence of hot, thermally-altered lithosphere in this area contrasting to the colder, more brittle, and more elastic lithosphere of the seismically active eastern region.
Backstripping a representative stratigraphic column from the northwest of the South Caspian basin shows that 2.4 km of tectonic subsidence has occurred since ca. 5.5 Ma, at 1.5–10 times the rate recorded in typical foreland basins. Roughly half the basin's sedimentary thickness of 20 km has accumulated in this time, while the upper part of the succession has begun to deform by buckle folding. The South Caspian basement appears to be either thick oceanic crust, or thinned, high-velocity continental crust. Seismicity and gravity data indicate that the basement is in the initial stages of subduction under the middle Caspian region to the north. We propose that basement subduction began ca. 5.5 Ma to create the major Pliocene-Quaternary subsidence. Subduction may have been triggered by a regional reorganization in the Arabia-Eurasia collision at that time, possibly following the construction of the Turkish-Iranian Plateau.
The application of the F-ratio test, a standard statistical technique, to the results of relative plate motion inversions has been investigated. The method tests whether the improvement in fit of the model to the data resulting from the addition of another plate to the model is greater than that expected purely by chance. This approach appears to be useful in determining whether additional plate boundaries are justified. Previous results have been confirmed favoring separate North American and South American plates with a boundary located beween 30 N and the equator. Using Chase's global relative motion data, it is shown that in addition to separate West African and Somalian plates, separate West Indian and Australian plates, with a best-fitting boundary between 70 E and 90 E, can be resolved. These results are generally consistent with the observation that the Indian plate's internal deformation extends somewhat westward of the Ninetyeast Ridge. The relative motion pole is similar to Minster and Jordan's and predicts the NW-SE compression observed in earthquake mechanisms near the Ninetyeast Ridge.