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Long-term behaviour of Australian Stable Continental Region (SCR) faults
Abstract
Australia boasts arguably the richest Late Neogene to Quaternary faulting record in stable continental region (SCR) crust anywhere in the world. Variation in fault scarp length, vertical displacement, proximity to other faults and relationship to topography permits division of the continent according to fault character. Six onshore “neotectonic domains” are recognised, with an additional offshore domain proposed by analogy with the eastern United States. Each domain relates to a distinct underlying crustal type and architecture, broadly considered to represent cratonic, non-cratonic and extended environments. In general, greater topographic expression associated with faults occurring in extended crust relative to non-extended crust suggests a higher rate of seismic activity in the former setting, consistent with observations worldwide. Using the same reasoning, non-cratonic crust might be expected to have a higher rate of seismic activity than cratonic crust. This distinction, together with the variation in fault character between domains, should be recognised in attempts to identify analogous systems worldwide.
... Intraplate seismicity can take place in stable continental regions (SCR) where great earthquakes are not common, and the strain rates are low, making faults' seismic cycles very different from those of interplate regions (e.g., Johnston, 1996;Tregoning et al., 2013;Talwani, 2017). Therefore, the behaviour of intraplate seismicity is unclear, and the hazard assessment challenging (e.g., Crone et al., 2003;Clark et al., 2012;Villamor et al., 2012;Calais et al., 2016;Talwani, 2017;King et al., 2019). Specific characteristics of intraplate seismicity can be summarised as follows: 1) seismicity is often located in previous reactivated structures (e.g., Schulte and Mooney, 2005;Talwani, 2014Talwani, , 2017Mazzotti and Gueydan, 2018). ...
... 2) Intraplate earthquakes are unexpected or "unanticipated" . 3) They typically affect faults with low strain rates and long quiescence periods (10,000-100,000 years), with scarce morphotectonic expression, and showing episodic seismicity (Crone et al., 2003;Stein et al., 2009;Clark et al., 2012;Calais et al., 2016). 4) Intraplate seismicity is often remarkably clustered (Holbrook et al., 2006;Rockwell et al., 2009;Mörner, 2005). ...
... 4) Intraplate seismicity is often remarkably clustered (Holbrook et al., 2006;Rockwell et al., 2009;Mörner, 2005). 5) Seismicity often migrates, and the activity is transferred between neighbouring faults, a process known as roaming (Clark et al., 2012;Calais et al., 2016;King et al., 2019;Stein et al., 2009;Liu et al., 2011). 6) The location and distribution of intraplate seismicity is also complex, which has been attributed to the fact that most intraplate seismicity (M ≥ 4.5) is located in old rift structures (52%) (Schulte and Mooney, 2005) and at craton boundaries (Talwani, 2014(Talwani, , 2017Mazzotti and Gueydan, 2018). ...
Despite that earthquakes in stable continental regions (SCR) often cause more damage than interplate seismicity, they remain poorly understood. This is mainly because of the lower rate of intraplate seismicity and because of its different behaviour compared to the better-known seismicity at the plate boundary. Understand the characteristics of the intraplate seismicity is a challenge for the seismic risk studies. We study and characterise an SCR (NW
Iberian Peninsula), which not only registers moderate instrumental intraplate seismicity, but also important historic seismicity and paleoseismic activity. To tackle some of the difficulties posed by intraplate seismicity, we analyse a wide and multidisciplinary data set (e.g., geological structures, seismicity, focal mechanisms, and geophysical data). Seismicity in this region is not associated with an old rift, but with inherited faults widely distributed throughout the region with a great variety of orientations. The reactivation kinematics of these faults are coherent with the current regional stresses. Instrumental seismicity is not associated with the large active faults nor with crustal limits. Seismicity is mainly clustered in swarms and sequences. Although seismic swarms present lower magnitudes, they are the most common. Based on swarms’ characteristics (high b-values, upward spatiotemporal migration), reported mantellic CO2 in some thermal springs, and the reactivation of inherited steeply-dipping faults, we propose the migration of deep fluids through steeply-dipping fractured areas as the cause of the intraplate seismicity. These processes could increase the pore pressure and decrease the stresses necessary for the fault rupture in a fault-valve behaviour. In general, in intraplate context, the important control in the seismicity of the inherited fault systems favourable oriented under the current stress tensor is observed, and also the need for mechanisms that can decrease the effective stress for the fault ruptures. Mechanisms as hydrothermal fluids in arterial faults with fault-valve processes has been identified as an effective driver of intraplate seismicity, playing an important role in stability of tectonic faults. The large number and variety of these faults, that share the low strain rates in intraplate polyorogenic context, may explain the different characteristics of these intraplate regions compared with the interplate regions, as the “unanticipated” behaviour, variety of kinematics, the long quiescence periods without seismicity associated and erosion obliterating their morphotectonic expression.
... However, neotectonic faulting and historical surface-rupturing earthquakes have occurred throughout Australia's cratons (Clark et al., 2012;King et al., 2019;Quigley et al., 2010;Yang et al., 2021). Repeated surface-rupturing earthquakes on a single fault may enable fault lengthening through lateral propagation and linkage (Cowie and Scholz, 1992) and can accumulate displacements that can be quantified through analyses of neotectonic features, e.g. ...
... The 200,000 km 2 surface of the Nullarbor Plain is covered by 100s-meter-thick limestones (Scheib et al., 2016) that are deformed by linear scarps attributed to reverse faulting on inherited bedrock structures (Clark et al., 2012). The typically broad wavelength nature of the scarps and absence of clear surface breaks suggests most of them are fault-propagation fold scarps; henceforth referred to as 'neotectonic traces' in this paper. ...
... The arid climate in this region has helped preserve these neotectonic traces from surface erosion (Sandiford and Quigley, 2009). Previous paleo-earthquake studies in the Nullarbor Plain have revealed that some neotectonic traces are >100 km long (Clark et al., 2012). Rupturing along the entire length would produce an earthquake of Mw ≈ 7.3 to 7.5, according to the empirical relationships between surface rupture length (L) and Mw: log10(L)=0.5Mw-1.93 for reverse faulting earthquakes in stable continents (Yang et al., 2021). ...
Plain Language Summary
Stable cratons on the Earth are generally considered to be immune from large earthquakes. Historical seismic quiescence and a paucity of evidence for geologically recent activity on large intraplate faults can result in an absence or low level of seismic hazard awareness, though intraplate earthquakes have caused more fatalities than interplate earthquakes. Long recurrence intervals commonly obscure evidence for paleo‐earthquakes because surface erosional processes may erode or bury surface ruptures and other neotectonic deformational features. Finding an ideal place that can provide sufficient observations of intracontinental active faults is challenging but pivotal for unraveling intracontinental fault dynamics and seismic hazard assessment. The nearly flat Nullarbor Plain in South‐Central Australia is covered by 100s‐m‐thick limestone, which is cut by reactivated reverse faults propagating upward from the Precambrian basement. The limestone has been exposed to the surface since the mid‐Miocene. The arid climate in this region has helped preserve these neotectonic features from surface erosion. Fault traces with high displacements can be well correlated with patches with high electrical conductivities, which are sensitive to fluids in the lithosphere. With co‐located seismic reflection profiles, gravity, and magnetic maps, we propose that enhanced neotectonic activity is associated with fluids ascending from deeper parts of the lithosphere.
... This paper explores different conceptual aspects and implications of previous research work (e.g., Tokarev et al., 1999;Hill et al., 2003;Tokarev, 2003;Micklethwaite and Cox, 2004;Clark, 2010;Quigley et al., 2010;Clark et al., 2011;Clark et al., 2012;Morris et al., 2018;Clark and Edwards, 2018;González-Álvarez et al., 2020b;González-Álvarez et al., 2020c;King et al., 2021;Kelka et al., 2022;González-Álvarez et al., 2022), and presents a novel and comprehensive data set on the stratigraphy, petrography and geochemistry of the only drill hole (CDP008) within a ~70 km radius that interests cover and basement rocks in the central region of the Nullarbor Plain in southern Australia. We used the drilling information collected to model geochemical dispersion processes through ~500 m of cover in this region. ...
... Primarily north-northwest/south-southeast to north-northwest to northeast-southwest trending fault scarps occur within the Coompana area ( Fig. 6; Clark et al., 2011;). The scarps typically show less than 10 m displacement (Clark et al., 2012) and are interpreted to preserve a neotectonic record, reflecting the long-term tectonic stability of the underlying Proterozoic basement terranes (Clark et al., 2012). ...
... Primarily north-northwest/south-southeast to north-northwest to northeast-southwest trending fault scarps occur within the Coompana area ( Fig. 6; Clark et al., 2011;). The scarps typically show less than 10 m displacement (Clark et al., 2012) and are interpreted to preserve a neotectonic record, reflecting the long-term tectonic stability of the underlying Proterozoic basement terranes (Clark et al., 2012). ...
Detection of mineral system footprints in regions under thick cover is challenging. The difficulties are enhanced in regions with low-relief landscapes that are deeply weathered. This research examines how information from a single drill hole in an underexplored region can deliver a significant amount of information to assist in greenfields exploration. This study describes the geochemical dispersion processes through >500 m of cover based on observations from drill hole CDP008, and explores the possibility of recognising landscape features that link basement features with the surface.
Our study revealed that: (1) the lower fluvial sandstone package contains a geochemical footprint of the underlying basement rocks, produced by vertical and lateral geochemical dispersion; whereas (2) the overlying sediments do not record any footprint of the basement rocks; and (3) the top limestone units are a chemical barrier for vertical geochemical dispersion due to their lack of permeability.
Basement features identified from magnetic data are mimicked by linear surface landscape features that lie above them, which may potentially be associated with vertical geochemical dispersion processes, linking the basement with the surface. Hence from the point of view of mineral exploration, surface geochemical sampling should target these particular neotectonic/reactivation-associated features of the landscape.
We suggest that in areas of deep cover, neotectonics/reactivation surface landscape features have the highest prospectivity to detect deep basement geochemical signatures at surface. The findings from this study may therefore impact approaches to mineral exploration under cover in similar landscape contexts around the world, such as regions in West Africa, India, China and Brazil.
... Alternatively, for comparison, we conduct the same analysis considering a single Tantabiddi time-stratigraphic marker of marine isotope stage (MIS) 5e age as previously interpreted by other authors (e.g., Clark et al., 2011Clark et al., , 2012McPherson et al., 2013; Whitney and Hengesh, 2015a). Again, the warping rate changes with time, however, variations in rates are within the same order of magnitude. ...
... This is anchored on the paradigm that "the Western Australian margin is assumed to have been tectonically stable at a level <0.01 mm/year (1 m/ glacial cycle)" (Lambeck et al., 2012, p. 4). Recently, a series of tectonic geomorphological, paleoseismological, and geophysical investigations have revealed active late Quaternary tectonic deformation along an ∼2000-km-long section of western Australia's former passive margin (e.g., Clark et al., 2011;Whitney and Hengesh, 2015b;Hengesh and Whitney, 2016) passing through and including the Cape Range anticline (Clark et al., 2012;McPherson et al., 2013;Whitney and Hengesh, 2015a;Whitney et al., 2015). These studies alter the previously held paradigm of this region's tectonic stability and by extension have highlighted the importance of understanding the tectonic contribution to paleoshoreline positions when using marine limit features to assess global paleo-sea levels under the a priori assumption of tectonic stability. ...
... Sandstrom et al. (2020) attempt to reconstruct the vertical displacement of the Cape Range and conclude that "the most recent interglacial shoreline [MIS 5e] has undergone <1.3 m of vertical warping, suggesting minimal deformation since deposition." The authors repeatedly assert that their results are in contrast to, and significantly lower than, published tectonic uplift rates (e.g., Clark et al., 2012;Whitney and Hengesh, 2015a). However, their rates are not uplift rates and are not comparable to any published rates due to the issues discussed in this comment. ...
Sandstrom et al. (2020) present new elevation and age data for a flight of four marine terraces preserved along the western limb of the Cape Range anticline in western Australia. Their interpretation of these data provides an alternative estimate for the amount of tectonic deformation that has occurred since terrace formation. They conclude that less tectonic uplift has occurred in the region than previously reported and posit
that their study provides a template for reducing the uncertainty associated with last interglacial paleoshoreline reconstructions.
We have three principal comments regarding the methodology and data interpretation
presented in Sandstrom et al. (2020). First, their method for measuring deformation is neither a measurement of, nor a proxy for, tectonic uplift. Second, their method for calculating deformation rates is internally inconsistent. Third, their interpretation of the upper and lower Tantabiddi notches as two independent time-stratigraphic units together with their age assignment for the upper notch generate warping rates that are untenable. These shortcomings individually and collectively lead to an erroneous conclusion
regarding the region’s tectonic stability
and could lead future paleo–sea-level researchers
to underappreciate the tectonic component
of land-level changes that are ongoing and well
documented in the region. The purpose of this
comment is to highlight these issues and their
implications for sea-level studies.
... Alternatively, for comparison, we conduct the same analysis considering a single Tantabiddi time-stratigraphic marker of marine isotope stage (MIS) 5e age as previously interpreted by other authors (e.g., Clark et al., 2011Clark et al., , 2012McPherson et al., 2013; Whitney and Hengesh, 2015a). Again, the warping rate changes with time, however, variations in rates are within the same order of magnitude. ...
... This is anchored on the paradigm that "the Western Australian margin is assumed to have been tectonically stable at a level <0.01 mm/year (1 m/ glacial cycle)" (Lambeck et al., 2012, p. 4). Recently, a series of tectonic geomorphological, paleoseismological, and geophysical investigations have revealed active late Quaternary tectonic deformation along an ∼2000-km-long section of western Australia's former passive margin (e.g., Clark et al., 2011;Whitney and Hengesh, 2015b;Hengesh and Whitney, 2016) passing through and including the Cape Range anticline (Clark et al., 2012;McPherson et al., 2013;Whitney and Hengesh, 2015a;Whitney et al., 2015). These studies alter the previously held paradigm of this region's tectonic stability and by extension have highlighted the importance of understanding the tectonic contribution to paleoshoreline positions when using marine limit features to assess global paleo-sea levels under the a priori assumption of tectonic stability. ...
... Sandstrom et al. (2020) attempt to reconstruct the vertical displacement of the Cape Range and conclude that "the most recent interglacial shoreline [MIS 5e] has undergone <1.3 m of vertical warping, suggesting minimal deformation since deposition." The authors repeatedly assert that their results are in contrast to, and significantly lower than, published tectonic uplift rates (e.g., Clark et al., 2012;Whitney and Hengesh, 2015a). However, their rates are not uplift rates and are not comparable to any published rates due to the issues discussed in this comment. ...
Sandstrom et al. (2020) present new elevation and age data for a flight of four marine terraces preserved along the western limb of the Cape Range anticline in western Australia. Their interpretation of these data provides an alternative estimate for the amount of tectonic deformation that has occurred since terrace formation. They conclude that less tectonic uplift has occurred in the region than previously reported and posit that their study provides a template for reducing the uncertainty associated with last interglacial paleoshoreline reconstructions.
... Waikato; Villamor et al. 2024) and beyond (e.g. Australia; Clark et al. 2012; the USA's Basin and Range Province; Pérouse and Wernicke 2017; Korean Peninsula; . ...
... ). There are, however, increasing examples of paleoseismic records that indicate temporal earthquake clustering at 1-1000 kyr timescales, particularly for low slip rate (<1 mm/yr) faults in stable continental regions(Clark et al. 2012;Calais et al. 2016), slowly deforming plate boundariesGoodall et al. 2021;Martín-Banda et al. 2021) or, like the Settlement Fault, at the peripheral edge of plate boundaries (Pérouse and Wernicke 2017). ...
... Understanding fault activity within intraplate regions presents a persistent challenge, particularly as the interevent times on low slip-rate faults can display a range of patterns-quasi-periodic, Poisson, or clustered (Styron, 2019;Salditch et al., 2020;Morell et al., 2020;Walton et al., 2021). Intraplate earthquakes are often unanticipated and caused by active faults that have long quiescence periods (10,000-100,000 yr; Calais et al., 2016;Stein et al., 2009;Clark et al., 2012;Nicol et al., 2016;Liu and Stein, 2016;Griffin et al., 2020;Stevens and Avouac, 2021;Martín-González et al., 2023). In slow-deforming regions, tectonic loading seems to be distributed among multiple faults of similar strength, with each fault remaining stable for long periods and activating briefly. ...
... Recent studies compiling historical and instrumental records of earthquakes from different intraplate areas indicate that seismic activity migrates between fault systems over distances that exceed their rupture lengths. The slow tectonic loading in the intraplate region appears to be shared by many faults of similar strength (Stein et al., 2009;Liu et al., 2011;Clark et al., 2012;Calais et al., 2016;Martín-González et al., 2023). With these challenges, crustal deformation in intraplate regions is commonly accommodated by broadly distributed complex fault systems. ...
The Yangsan fault is the most prominent NNE-SSW−striking active right-lateral strike-slip fault crossing the Korean Peninsula, with a continuous trace of ∼200 km. It can likely generate large earthquakes; however, the paleoseismic information on slip per event, slip rate, and timing of past ruptures along this fault remains sparse. To explore these parameters for the Yangsan fault, we excavated trenches across the central segment of the fault, which showed evidence for at least five surface-rupturing earthquakes preserved in Quaternary fluvial deposits. The timing of these earthquakes is discussed based on luminescence and radiocarbon ages. A close examination of three-dimensional trench exposures revealed that the most recent event(s) occurred during or slightly after the third century CE (one-event interpretation) or sixth to eighth century CE (two-event interpretation), and it was associated with 4.5 m to 5.3 m of lateral displacement of a paleochannel. The observed lateral displacement indicates that large earthquakes with a magnitude of around Mw 7 have taken place in the recent past, which is the first-ever direct evidence of large-magnitude earthquakes along the Yangsan fault. The penultimate event occurred after 17 ± 1 ka, whereas an earlier late Quaternary event occurred in the late Pleistocene, suggesting a recurrence interval in the range of 10,000 yr, and a consequent slip rate on the order of 0.5 mm/yr. The oldest observed ruptures are preserved below an erosional unconformity that probably dates back to the last interglacial period, based on infrared stimulated luminescence ages. An unknown number of ruptures may have occurred between the unconformity and subsequent sedimentation during the latest Pleistocene to Holocene period. Historical earthquake records indicate clustered behavior of moderate and large earthquakes along the Yangsan fault. Past faulting events and implied recurrence intervals constrain the long-term faulting behavior along the Yangsan fault and will contribute to a better seismic hazard assessment in the southeastern part of the Korean Peninsula.
... It is used in the "Global Neotectonic Fault and Fold Database", and Australia's "Neotectonic characteristics database". [23,33,34] Quaternary active fault ...
... In a Stable Continental Region (SCR) like Australia and central-eastern North America, where paleo-earthquake studies show that the activity of most faults is characterized by long recurrence intervals (>100,000 years), low slip rates (<0.01 mm/yr), and horizontal compressive stress field [105], both late Quaternary and Holocene active faults can only encompass a small fraction of faults with possible Holocene movement. In these cases, the term "neotectonic fault" will be the most appropriate [23,33]. ...
Active faults are generally defined as faults that have moved in the past and will continue to be active in the future. They are expected to cause deformation and potential disasters if they are localized close to human activities. The definition and classification of active faults are important bases for evaluating the risk. This paper summarizes and compares the history, status, and progress of their definition and classification schemes used in representative countries and regions, as well as in some relevant standards, in active fault mapping, in the construction of spatial databases, and in some other aspects. It is concluded that the current geodynamic setting, existing technical means, geological operability, application purpose, and social acceptability of active faulting hazard in a specific area comprehensively determine the selection of the definition and classification. The key parameter in defining active faults is the time limit. It usually involves four time scales, i.e., Neotectonic (post-Neogene), Quaternary, Late Quaternary, and Holocene. The definition using a short time scale, such as Late Quaternary and Holocene, is usually suitable for the plate boundary zone, which has a high strain rate, but active faults in the intraplate deformation region and stable continental region should be defined with a long time scale, such as the Quaternary and Neotectonics. In addition, the magnitude standard can determine the activity intensity of active faults, which most generally includes three classes, namely, M ≥ 5.0 damaging earthquakes, M ≥ 6.0 strong earthquakes, and M ≥ 6.5 earthquakes that may produce surface displacement or deformation. The M ≥ 5.0 earthquake is generally applicable to regional earthquake prevention and risk mitigation in many countries or regions, but the M ≥ 6.5 earthquake magnitude benchmark is generally used as the standard in rules or regulations regarding active fault avoidance. The most common classification schemes in many countries or regions are based on fault activity, which is reflected mainly by the fault slip rate and fault recurrence interval (FRI), as well as by the last activation time. However, when determining the specific quantitative parameters of the different activity levels of faults, it is necessary to comprehensively consider the differences in activity and ages of the faults in the study region, as well as the amount and validity of existing data for the purpose of classifying different active levels of faults effectively.
... Thus, M o can be considered an upper limit of the magnitude of a quake generated by the formation of the fault scarp. It is not unprecedented for meter-scale structural relief to be generated on thrust fault scarps from ruptures generated by single seismic events, particularly with intraplate earthquakes like those that have occurred in Western Australia (Clark et al. 2012). A value of G of 100 MPa is assumed for the nearsurface lunar regolith, which is based on characterization of the mechanical properties of a lunar regolith simulant (He et al. 2013). ...
... intraplate earthquakes like those in Western Australia are potential analogs to lunar SMQs. The relatively low relief (tens of centimeters to meters) of some of the thrust fault scarps of Western Australia (Clark et al. 2012) suggest that there may be another scale of lunar thrust fault scarps (see Figure 5), a population that may not be easily detected even in LROC NAC images with optimum lighting conditions and that may only be clearly recognized in ground surveys by robotic and human exploration. ...
The lunar south pole regions are subjected to global stresses that result in contractional deformation and associated seismicity. This deformation is mainly expressed by lobate thrust fault scarps; examples are globally distributed, including polar regions. One small cluster of lobate scarps falls within the de Gerlache Rim 2 Artemis III candidate landing region. The formation of the largest de Gerlache scarp, less than 60 km from the pole, may have been the source of one of the strongest shallow moonquakes recorded by the Apollo Passive Seismic Network. The scarp is within a probabilistic space of relocated epicenters for this event determined in a previous study. Modeling suggests that a shallow moonquake with an M w of ∼5.3 may have formed the lobate thrust fault scarp. We modeled the peak ground acceleration generated by such an event and found that strong to moderate ground shaking is predicted at a distance from the source of at least ∼40 km, while moderate to light shaking may extend beyond ∼50 km. Models of the slope stability in the south polar region predict that most of the steep slopes in Shackleton crater are susceptible to regolith landslides. Light seismic shaking may be all that is necessary to trigger regolith landslides, particularly if the regolith has low cohesion (on the order of ∼0.1 kPa). The potential of strong seismic events from active thrust faults should be considered when preparing and locating permanent outposts and pose a possible hazard to future robotic and human exploration of the south polar region.
... It is used in the "Global Neotectonic Fault and Fold Database", and Australia's "Neotectonic characteristics database". [23,33,34] Quaternary active fault ...
... In a Stable Continental Region (SCR) like Australia and central-eastern North America, where paleo-earthquake studies show that the activity of most faults is characterized by long recurrence intervals (>100,000 years), low slip rates (<0.01 mm/yr), and horizontal compressive stress field [105], both late Quaternary and Holocene active faults can only encompass a small fraction of faults with possible Holocene movement. In these cases, the term "neotectonic fault" will be the most appropriate [23,33]. ...
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Special Issue Information
Dear Colleagues,
We are pleased to invite you to contribute a paper to an upcoming Special Issue entitled "Active Tectonics and Earthquakes".
In a widely accepted definition, active tectonics is a discipline approaching the study of those tectonic processes that produce the deformation of the Earth’s crust on a time scale of significance to society. Active faults and in general active structures (e.g., active folding or wide-scale warping) can be responsible for processes likely to cause damage to societies within a timespan of decades to hundred years. However, a full understanding of an active tectonic process requires a time span of hundreds of thousands to millions of years. The study of a specific geological structure or a specific active tectonic region, aimed at deducing its evolution, can contribute to the knowledge of related geological hazards and consequently to assessing and reducing their risk.
This Special Issue invites contributions from a wide range of disciplines such as structural geology, seismology, geomorphology, geodynamics, field geology, and seismic hazard assessment, linked by a common key: active tectonics and its relationship to earthquakes. Contributions are encouraged that approach different techniques, such as classical geological field studies, space geodesy (e.g., InSAR and GNSS), seismology, geochemistry, stratigraphy, paleoseismology, stress field analyses, and analog and numerical modeling. Work based on new and novel methods is welcome.
Submissions can include original research articles or comprehensive reviews relating to the title/description above. Each submission will undergo a formal peer review process, and acceptance or rejection of the submitted article will be evaluated upon reception of the reviews.
Dr. Bruno Massa
Dr. Daniela Di Bucci
Prof. Dr. Zhonghai Wu
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Keywords
active tectonics
seismotectonics
earthquake geology
fault
surface deformation
Published Papers
This special issue is now open for submission
... The criteria used to determine if a fault is "active" vary between regional active fault databases . For example, only faults with evidence for displacement within the last 125 ka are included in New Zealand Active Fault Database (Langridge et al., 2016), while in the USA, the equivalent criteria are evidence for displacement in the Quaternary (i.e., the last 2.6 million years; Machette et al., 2004), and in Australia, which is a stable continental region, displacements within the last 5 million years (D. Clark et al., 2012). Using an age-based criteria for determining fault activity is further complicated as (a) faults capable of hosting future earthquakes will not necessarily preserve chronostratigraphic evidence for relatively recent earthquakes (Cox et al., 2012;King et al., 2019;Nicol et al., 2016;Perea et al., 2006), and (b) even in regions with well-developed active fault databases, in situ chronostratigraphic data are not available for most faults (T. ...
... New paleoseismic and chronostratigraphic data would help resolve which onshore faults in the MAFD have been active in the recent (i.e., Quaternary) geologic past. However, in low strain rate regions like Malawi, faults can go through very long periods (∼50-100 ka) of quiescence (D. Clark et al., 2012;Pérouse & Wernicke, 2017;Taylor-Silva et al., 2020), during which evidence for past earthquakes may be buried or eroded away (Hodge et al., 2020;Nicol et al., 2016). Alternatively, a fault may have hosted earthquakes that did not rupture to the surface (Hecker et al., 2013;Wells & Coppersmith, 1993), a possibility that is increased in Malawi because of its thick seismogenic layer. ...
We present the Malawi Active Fault Database (MAFD), an open‐access (https://doi.org/10.5281/zenodo.5507190) geospatial database of 113 fault traces in Malawi and neighboring Tanzania and Mozambique. Malawi is located within the East African Rift's (EAR) Western Branch where active fault identification is challenging because chronostratigraphic data are rare, and/or faults are buried and so do not have a surface expression. The MAFD therefore includes any fault that has evidence for displacement during Cenozoic East African rifting or is buried beneath the rift valley and is favorably oriented to the regional stresses. To identify such faults, we consider a multidisciplinary data set: high‐resolution digital elevation models, previous geological mapping, field observations, seismic reflection surveys from offshore Lake Malawi, and aeromagnetic and gravity data. The MAFD includes faults throughout Malawi, where seismic risk is increasing because of population growth and its seismically vulnerable building stock. We also investigate the database as a sample of the normal fault population in an incipient continental rift. We cannot reject the null hypothesis that the distribution of fault lengths in the MAFD is described by a power law, which is consistent with Malawi's relatively thick seismogenic layer (30–40 km), low (<8%) regional extensional strain, and regional deformation localization (50%–75%) across relatively long hard‐linked border faults. Cumulatively, we highlight the importance of integrating onshore and offshore geological and geophysical data to develop active fault databases along the EAR and similar continental settings both to understand the regional seismic hazard and tectonic evolution.
... Therefore, identifying basement structures that may be associated with mineral deposit formation has become an important part of exploration protocols and prospectivity assessments (Porwal et al. 2010). South Australia possesses widespread basement structures, many of which have been reactivated by neotectonic activity (Clark et al. 2012;Preiss 2019). This may have important implications for landscape evolution, and also on the efficiency of vertical geochemical dispersion processes through the cover. ...
... However, direct observation based surface lineament mapping has been widely applied in geoscience (e.g. Wise 1982;Boucher 1997;Koch and Mather 1997;Sahoo et al. 2000;Tiren 2010;Clark et al. 2012;Elmahdy et al. 2012;Elmahdy and Mohamed 2014). The identification of lineaments has been improved by the increasing availability of high-resolution satellite images, as well as DEM datasets (Fig 6). ...
... régions à fort taux de déformation, montrent un comportement beaucoup plus complexe. En effet, dans la plupart des systèmes tectoniques actifs, on observe que les grands séismes ont lieu plus souvent en clusters regroupés dans le temps, alternant avec des intervalles de quiescence longs et variables (Wallace, 1987 ;Sieh et al., 1989 ;Agnon, 2014 ;D. Clark, McPherson et Van Dissen, 2012 ;D. Clark, McPherson, T. Allen et al., 2014 ;Ratzov et al., 2015 ;Salditch et al., 2020 ;. Cette distribution des séismes en Escalier du Diable (Mandelbrot, 1982 ;Turcotte, 1997) est une caractéristique des systèmes dynamiques complexes. Cela suggère donc que ces motifs particuliers d'occurrence sismique manifestent le comportement de sys ...
... (King et al., 2019) Par conséquent, assigner un label « actif/inactif» à une faille (ou segment(s) de faille) dans ces zones continentales intraplaques, basé sur l'occurrence (ou la non occurrence) d'un séisme dans les quelques derniers milliers d'années n'est pas un indicateur robuste de futur potentiel sismogénique (D. Clark et Mcpherson, 2011 ;D. Clark, McPherson et Van Dissen, 2012 ;Boncio et al., 2018). ...
La compréhension des mécanismes qui gouvernent l'occurrence et la distribution de la sismicité faible à modérée des régions continentales stables est entravée par les capacités limitées des algorithmes utilisés à détecter les petits séismes dans des environnements anthropisés, malgré le déploiement intensif des réseaux de stations. Cette thèse développe une procédure de détection automatique des séismes de faible magnitude à travers SeisComP3 et le Calcul de Haute Performance. Cette nouvelle procédure réduit la contamination des séismes détectés par du bruit sismique en tenant compte des niveaux de bruit enregistré aux stations, de la géométrie du réseau de stations et du milieu de propagation des ondes sismiques. En incorporant un algorithme d’apprentissage machine supervisé, elle discrimine efficacement les séismes détectés, des tirs de carrière et des faux événements associés à du bruit. Les résultats sont prometteurs : 50% de séismes de magnitude inférieure à 1.2 sont détectés en plus. Ce travail vise à une plus large exploration de l’apprentissage machine dans les observatoires sismologiques.
... The future activity level of a fault can be described at multiple directions. For example, based on the time of the last earthquake that displaced the surface, the active faults were divided into neotectonic faults, early Pleistocene faults, middle Pleistocene faults, late Pleistocene faults, and Holocene faults [26,[32][33][34][35][36][37][38]. Worldwide, several works have mapped faults and developed databases that integrate and organize structural-geological information from published and unpublished sources to support seismotectonic studies. ...
Fault displacement hazard, along with ground shaking hazard and earthquake-induced geohazard, are the primary forms of disaster in major earthquakes. Buildings located on areas of strong seismic surface displacement are likely to be damaged if anti-displacement design is not carried out. Therefore, a reasonable and targeted active fault classification scheme is helpful for avoidance and anti-displacement hazard of active fault in engineering construction. However, the existing classification schemes are rough, and some have no quantitative classification basis, which makes it difficult to apply these classification schemes in actual work. Also, they did not specify whether all active faults should be avoided. In this paper, considering the physical mechanism of earthquakes, using two activity parameters of active faults, “strong earthquake recurrence period” (TRP) and “strong earthquake elapsed time ratio” (Ret), and referring to the probabilistic seismic hazard analysis method (PSHA), the maximum magnitude of potential earthquake on the fault under different exceedance probabilities (EP) is calculated, and was divided into six levels. The fault displacement hazard level under different exceedance probabilities may be different. For buildings with different importance levels, we recommend six hazard classification schemes with different exceedance probabilities. Standard buildings should avoid active faults with a fault displacement hazard level of Ⅰ ~ Ⅲ (faults that can generate earthquakes of magnitude m0 and above under a 4% exceedance probability over 100 years). Special buildings and key buildings should avoid active faults with a fault displacement hazard level of Ⅰ ~ Ⅳ (faults that can generate earthquakes of magnitude m0-0.5and above under a 1% exceedance probability over 100 years). The fault displacement hazard classification scheme given in this paper takes into account the physical mechanism of earthquake occurrence and the importance of buildings, which makes this classification scheme both scientific and practical, helps provide technical support for the design and construction of buildings. This study is still quite preliminary, and there are many issues that need further study.
... While our method has general application across diverse geological settings, we focus on low activity-rate reverse faults because a number of studies have demonstrated significant aperiodicity in the recurrence times of large earthquakes on these faults (similar observations have been made in extensional settings, e.g., Friedrich et al., 2003Friedrich et al., , 2004Wallace, 1987). Such behavior has variously been described as clustered, episodic or "Wallace-type" earthquake recurrence (e.g., Clark et al., 2012Clark et al., , 2015Crone et al., 1997Crone et al., , 2003Friedrich et al., 2003;Taylor-Silva et al., 2020). This episodic behavior contrasts with the weakly-to moderately-quasiperiodic recurrence more typically observed for active faults globally Moernaut, 2020;Williams et al., 2019). ...
Long recurrence intervals of large earthquakes relative to the historical record mean that geological data are often utilized to inform forecasts of future events. Geological data from any particular fault may constrain the timing of past earthquakes (paleoearthquake data), or simply the time period over which a certain amount of fault displacement has occurred due to one or more earthquakes. These data are typically subject to large uncertainties, and available records often only constrain the timing of a few events. Variability in earthquake inter‐event times (aperiodicity) has been observed for many faults, particularly in low seismicity regions, further hampering the utilisation of small data sets for developing forecasts. A challenge for earthquake forecasting therefore concerns how best to utilize all of the limited available data while fully considering uncertainties. Here we present a concise Bayesian model for developing time‐dependent earthquake forecasts from geological data. Using the additive property of the Brownian passage time distribution, we make inference on the model parameters jointly from paleoearthquake and fault displacement data. Monte Carlo Markov Chain methods are used to sample the posterior distribution of model parameters, which is subsequently used to forecast future earthquake probabilities. The method incorporates data uncertainties and does not rely on a priori assumptions of quasiperiodic earthquake recurrence, allowing application in a wide range of tectonic settings. We demonstrate the method using data from two reverse faults in Otago, southern Aotearoa New Zealand, a region in which aperiodic earthquake recurrence has previously been observed.
... For example, in the Ordos and Sichuan Basins, the stable regions with thick sediment cover and small-scale strike-slip faults have no earthquakes ( Figs. 2A and 10A). Another example is the Australian stable continental region, where more than half of the instrumented global cratonic earthquakes occurred (Clark et al., 2012 Yang et al., 2021a). We found that in these stable regions, the sediment thickness above the basement is usually less than 1000 m ( Fig. 11; Allen and Allen, 2013). ...
Stable intraplate cratonic blocks usually have less structural deformation and fewer earthquakes than other locations on Earth, but with strong compressional deformation around their periphery. Investigating how and why this different deformation occurred is beneficial for understanding why the cratonic block is so stable and how the intraplate in-plane stress is transmitted. In this work, we first investigated the structural deformation changes from the margin to the interior of the western Ordos block (one of the most tectonically stable areas in China) via seismic data. The results show abrupt structural deformation changes from the margin to the interior of the Ordos block in terms of the deformation strength (from strong to weak), structural orientation (high-angle oblique relationships), and kinematics (from compression to wrenching). Our investigation also shows that such phenomena are widespread in cratonic blocks worldwide. The abrupt changes are probably induced by special in-plane stress transfer inside the cratonic block: When far-field stress is transmitted into continental interiors from active plate margins, the weak belt around the cratonic block filters and accommodates the in-plane stress. Consequently, this decreases the stress, changes the stress direction, and transmits the in-plane stress along a shallower layer (probably less than 1500 m). Furthermore, the compressional stress from the plate margin is converted into shear stress within the cratonic block. This stress transmission manner makes reactivation of deep preexisting faults difficult under far-field horizontal plate-boundary stresses in the cratonic block without vertical forces from the mantle, guaranteeing long-term stability and low seismicity. This understanding can provide a new perspective for the interpretation of earthquakes in stable continental regions. It can also be applied to appraise the long-term stability of sites for the storage of CO2.
... A variety of processes are proposed to explain SCR seismicity: from mantle dynamics or lithosphere heterogeneities acting on geological time scales, to glacial isostatic adjustment or erosion pulses on thousandyear time scales (Mazzotti, 2007;Calais et al., 2010;Ghosh et al., 2019). This uncertainty in the steady-state or transient nature of the forcing mechanisms results in ongoing debates on the spatial and temporal distribution, clustering, and recurrence of large SCR earthquakes (Clark et al., 2012;Page and Hough, 2014;Calais et al., 2016). Another peculiarity is that large SCR ruptures appear biased to shallow (0-10 km) depths (Klose and Seeber, 2007;Jackson and McKenzie, 2022). ...
The causes of seismicity in stable continental regions (SCRs) remain an open question, in particular with respect to (1) the transient or steady-state nature of the forcing mechanisms and (2) the bias toward shallow seismicity. In this study, we test the impact of long-term localized erosion on crustal stresses and the promotion or inhibition of seismicity in SCRs. We subject numerical models with various geotherms and rheologies to typical SCR erosion rates (4–200 m/m.y.) over 10 m.y. to estimate the lithosphere mechanical response and the associated stress perturbations. In all models, the lithosphere deformation and stresses due to long-term localized erosion are close, but not identical, to those predicted by a simple elastic plate model. In specific cases with relatively high geotherm or weak crust, upper mantle or lower crust viscous flow can significantly impact the upper crust stress perturbations. Overall, erosion-induced horizontal tension is maximum in the upper crust (0–10 km depth) and much smaller in the mid- and lower crust. These stress perturbations reach a few tens of megapascals to a few megapascals over a few million years. Depending on the erosion patterns and regional state of stress, they can promote fault instability and seismicity for all faulting styles. Our results suggest that erosion-induced stresses can contribute to explaining the bias toward shallow seismicity in SCRs.
... In intraplate settings, recognizing active structures and quantifying their deformation rates for seismic hazard can be challenging when seismicity is diffuse and infrequent, with long periods of quiescence spanning 10 5-6 years (e.g., Clark et al., 2012). The recognition and documentation of moderate earthquakes with surface rupture, like that of the 2020 Sparta M w 5.1 earthquake, has increased recently (e.g., King et al., 2019;Ritz et al., 2020), likely due to the increasing knowledge and availability of remote sensing methods. ...
... The identification of a cluster of major fault scarps in a fairly small area could be interpreted as evidence that this area may be deforming more rapidly than other parts of Namibia and southern Africa. Studies in Australia and north China have found evidence for clustering and migration of SCR seismicity whereby a group of faults experiences a concentrated period of deformation before becoming inactive and the locus of seismicity shifts to another fault system (Clark et al., 2012;Liu et al., 2011), and it is possible that a similar process may occur in our study area. ...
Four previously unrecognized neotectonic fault scarps in southwest Namibia are described. These relatively straight, simple but segmented structures are 16–80 km long and have measured vertical separations of 0.7–10.2 m. We estimate that each is capable of producing earthquakes of Mw 6.4 or greater, indicating that large earthquakes may occur despite limited cumulative displacement. There is strong evidence that some of these scarps were formed by repeated earthquakes. Comparison with aeromagnetic and geological maps reveal that the normal faults reactivate major crustal weaknesses that are orientated north‐south and northwest‐southeast and perpendicular to the local gravitational potential energy gradient. The presence of these structures in an area with a limited record of instrumental seismicity suggests that the Mmax of this region may be much larger than generally assumed. They highlight the necessity of incorporating information from fault studies into probabilistic seismic hazard assessments in this region, in a similar way to other stable continental regions such as Australia. The fact that such major structures have gone hitherto unrecorded suggests significant further research is needed to characterize these sources of hazard. The identification of an apparent cluster of large magnitude neotectonic earthquakes in the area may be related to the exceptional preservation potential of scarps rather than indicating an area of comparatively rapid deformation. If this interpretation is correct, then these scarps represent an important indication of the potential seismic hazard across the region, and the occurrence of infrequent large‐magnitude seismicity on similar structures should be considered throughout southwestern Africa.
... In contrast to aftershocks, earthquakes in the three remaining situations chiefly release long-term strain, yet they have different implications for long-term seismic hazard. Intraplate seismicity often clusters in space and time (e.g., Clark et al., 2012). Therefore, ETSZ events could represent a naturally active phase of strain release in what is a broadly uniform long-term stress and thus strain-rate field (here, "stress" refers to the deviatoric component of the tensor sum of forces responsible for fault loading, or strain accrual). ...
The eastern Tennessee seismic zone (ETSZ) experiences the second highest rates of natural seismicity in the central and eastern United States (CEUS), following the New Madrid area, yet the cause of elevated earthquake rates is unknown. We probe the origin of ETSZ seismicity using geomechanically constrained stress inversions of earthquake focal mechanisms from 57 earthquakes, including 24 newly derived here and five from the recent events not used in the previous stress studies. Highly oblique northwest–southeast (NW–SE) extension that is unique in the CEUS dominates the ETSZ—central Alabama to southeastern Kentucky—and preferentially reactivates normal to strike-slip faults in the northeast (NE) and southwest (SW) quadrants (strikes 018°–086° or 196°–272° and dips 55°–90°). This extension cannot be explained by the compressive tectonic plate-boundary tractions that cause oblique NE–SW contraction elsewhere in the CEUS. Although our analyses do not uniquely determine the origin of the anomalous stress, we favor isostatic disequilibrium, due to anything from surface processes to crust–mantle interactions, as the possible cause. Increased long-term seismic hazard in the ETSZ may be controlled by and confined to the spatial extent of this anomalous seismotectonic state.
... Plate boundaries are known as seismically active regions on Earth. The Australian continent, which is thought to be stable, is situated in the middle of a tectonic plate far away from an active plate boundary and has a large number of neotectonic (late Neogene to Quaternary) faults (Quigley et al., 2010;Clark et al., 2012Clark et al., , 2014. Earthquakes occurring in stable continental regions like Australia are called intraplate earthquakes because they occur within the tectonic plates instead of the plate boundaries. ...
The Australian Seismometers in Schools (AuSIS) network operates 50 broadband seismic stations across Australia that are hosted at schools. The instruments augment the Australian National Seismograph Network providing valuable data from urban and regional Australia. The network coverage is quite sparse, but these vital records of rare, moderate Australian earthquakes can improve our understanding of the deformation within the stable continental region of Australia, especially for events with no surface rupture. In this study, we present the feasibility of identifying the fault plane of moderate earthquakes on the Australian continent, using data from the AuSIS network. We examine the fault plane of the September 2021 Mw 5.9 Woods Point earthquake that occurred about 130 km northeast of the Melbourne metropolitan area. We estimate the hypocenter and the centroid moment tensor (CMT) to identify the fault plane from the auxiliary plane in the focal mechanism. We explore a range of 1D models and a 3D Earth model to simulate seismic arrivals and full waveform data. The hypocenter is resolved using P- and S-wave arrivals in a probabilistic framework and the CMT is derived from full waveform modeling through grid search over a set of trial points around the hypocenter. Our solution suggests the mainshock ruptured the depth of 15 ± 4 km, with a strike-slip mechanism striking 348° north on a nearly vertical plane. The high double-couple percentage of this event indicates a simple rupture that propagated from the south (hypocenter) toward the north (centroid) and remained subsurface. This indicates that the causative fault had a deeper structure than the previously known shallow, northwest–southeast-striking faults of the region. The P and T axes deduced from our fault model are notably aligned with the maximum horizontal crustal stress in the region.
... Hence, our stress measurement results strongly support the mechanical origin and action mechanism of faults in this region. Moreover, even the variability in the σ H direction among stress provinces is roughly identical to that in neotectonic features, which further validates that the current stress pattern is a main controlling factor of the deformation process throughout the continental plate [58]. Through the above analysis, a certain linkage between the stress field and geological structure exists in the study area, which is not just an accidental phenomenon. ...
Full knowledge of the current tectonic stress state is crucial for assessing open-pit mine slope stability and regional tectonic evolution and geodynamic processes. Overcoring, hydraulic fracturing, and acoustic emission in situ stress measurement techniques were adopted to determine the 3D stress tensor in an iron mine district, North China, and 25 sets of stress data ranging from 56 to 490 m were measured. Accordingly, the current tectonic stress state and its relationship to regional geological tectonics were investigated. The results indicated that the stress condition seemed to favor thrust and strike-slip faulting, and the stress field was particularly controlled by the horizontal tectonic stress. A high horizontal tectonic stress considerably influenced the stability of high and steep slopes in this mine district, which requires great attention. The stress directions derived from different methods were almost similar, indicating a dominant NEE–SWW stress field direction or near-E–W direction, comparable to the direction revealed by focal mechanism solutions and other stress indicators around the mine district. According to geological structure analysis, the present-day stress field in this district generally inherited the third-stage tectonic stress field while partially retaining the characteristics of the second-stage tectonic stress field, which is the result of dynamic action and tectonic movement during different geological periods, and the maximum principal stress direction of the tectonic stress field that affects the modern tectonic activity in this area is the NEE–EW direction.
... Large areas within SCRs are devoid of contemporary seismicity, while others may host low-to moderate-magnitude earthquakes that exhibit spatiotemporal clustering with migratory and transient characteristics (Calais et al., 2006;Clark et al., 2007Clark et al., , 2012. It is typically challenging to attribute seismicity to crustal faults with surface expressions. ...
Analysis of TanDEM‐X and Shuttle Radar Topography Mission (SRTM) data reveals geomorphic evidence for 292 fault‐propagation fold scarps across the Miocene Nullarbor and Pliocene Roe Plains in south‐central Australia. Vertical displacements (VD) are determined using topographic profiling of a subset (n=48) of the fold traces. Fault dips (mean = 44+16/‐14o at 1σ) are estimated from seismic reflection data; the mean dip is assigned to faults with unknown dip and combined with VD to estimate net displacements (ND) average net displacements (AD) for each fault. AD exceeds single event displacements estimated from fault‐length scaling regressions, indicating the identified faults have hosted multiple earthquakes. Combining AD with (i) faulted surface ages (Nullarbor ~10‐5 Ma, Roe ~2.5 Ma), (ii) ages of faulted erosional‐depositional features (e.g. relic late Miocene dune‐fields and Pliocene paleochannels), (iii) onset of the neotectonic regime in Australia at ~10 Ma yields average slip rates from <0.1m Myr‐1 to >17m Myr‐1 (mean=1.1m Myr‐1). Summation of displacements across faults yields crustal horizontal shortening rates lower than geodetically‐detectable resolution (≤0.01mm yr‐1) since the Late Miocene. The ca. 10 Myr long record of neotectonic faulting on the Nullarbor Plain provides important insights into earthquake spatial‐temporal behaviours in a slowly deforming intraplate continental region.
... The depth of antecedent topography, and ultimately the base of Holocene reef growth, may be controlled by active geological structures (e.g., faults) in underlying basement (Chappell and Polach, 1976;Gischler and Hudson, 2004;Ota and Chappell, 1999;Purdy et al., 2003). Studies on the effect of structural control on modern subsidence in the GBR are rare as the eastern margin of Queensland occupies an intraplate setting and seismicity is limited in the region, but remains understudied (Clark et al., 2012). Hence, the GBR has been considered to have relatively little neotectonic activity (e.g., Quigley et al., 2010). ...
The Great Barrier Reef is generally considered a passive tectonic setting, however the effect of antecedent topography and local geological structures on Holocene reef development is poorly understood. Offshore reefs along the central shelf were recently hypothesized to have grown continuously through a possible small Holocene sea level fall, in response to greater local subsidence, in contrast to reefs immediately to the north and south, which experienced synchronous turnoff phases. We tested this hypothesis by isolating four map zones along the GBR shelf and using: (1) a geomorphic reef type classification applying perceived evolutionary “age” as juvenile, mature, and senile domains based on geomorphology; (2) analysis of bathymetry data to understand the role of antecedent topography on the spatial distribution of reef type domains and general sea floor depths; and (3) the distribution of earthquake epicentres as an indication of possible active geological structures (i.e., faults). The results reveal that juvenile reefs (42.25 %) are more abundant in the central shelf, whereas mature-2 (40 %) and senile (31 %) reefs are more abundant in the northern zone. In the south-central zone, mature-2 reefs are prevalent, while the southern zone includes a mixture of juvenile and mature to senile domains with a sharp internal boundary. These results support the hypothesis that the central zone may have experienced greater active subsidence during the Holocene. Bathymetric data support greater regional subsidence in both central and south-central zones, but reefs are less abundant and cover a lesser percentage area of their antecedent platforms in the central zone, consistent with greater subsidence there. The boundaries between the central zone and adjacent zones are the sites of clusters of recent earthquakes, consistent with the occurrence of active geological faults bounding the zone of greater Holocene subsidence. Combined, our data support the occurrence of a tectonically defined region of active greater subsidence in the central GBR shelf that has affected the geomorphology and growth history of reefs through the Holocene. Knowledge of such spatial partitioning of reef behaviour may allow reef managers to better suite their efforts to local conditions, especially in regard to predicted sea level rise, while highlighting potential seismic risks over longer time frames.
... In intraplate settings, recognizing active structures and quantifying their deformation rates for seismic hazard can be challenging when seismicity is diffuse and infrequent, with long periods of quiescence spanning 10 5-6 years (e.g., Clark et al., 2012). The recognition and documentation of moderate earthquakes with surface rupture, like that of the 2020 Sparta M w 5.1 earthquake, has increased recently (e.g., King et al., 2019;Ritz et al., 2020), likely due to the increasing knowledge and availability of remote sensing methods. ...
At 8:07 a.m. EDT on 9 Aug. 2020 a Mw 5.1 earthquake located ~3 km south of Sparta, North Carolina, USA, shook much of the eastern United States, producing the first documented surface rupture due to faulting east of the New Madrid seismic zone. The co-seismic surface rupture was identified along a 2-km-long traceable zone of predominantly reverse displacement, with folding and flexure generating a scarp
averaging 8–10-cm-high with a maximum observed height of ~25 cm. Widespread deformation south of the main surface
rupture includes cm-dm–long and mm-cm– wide fissures. Two trenches excavated across the surface rupture reveal that this earthquake propagated to the surface along a preexisting structure in the shallow bedrock, which had not been previously identified as an active fault. Surface ruptures by faulting are rarely reported for M <6 earthquakes, and hence the Sparta earthquake provides an opportunity
to improve seismic hazard knowledge associated with these moderate events. Furthermore, this earthquake occurred in a very low strain rate intraplate setting, where earthquake surface deformation, regardless
of magnitude, is sparse in time and rare to observe and characterize.
... Earthquakes in stable continental regions (SCRs) such as Namibia are relatively uncommon, and faults in these areas have recurrence intervals of thousands to hundreds of thousands of years (Clark et al. 2012;Calais et al. 2016). SCRs do however experience large earthquakes, in some cases leading to major losses of human life (Maurer & Oblitas 2001). ...
This study explores the geomorphological expression and geological context of a normal fault scarp in a stable continental region (SCR) which we interpret as having failed in large (Mw >7) earthquakes. Records of such large normal faulting events in an SCR (or even in more rapidly deforming regions) are extremely rare, and so understanding this feature is of international interest. The scarp is exceptionally well-preserved due to the extensive calcrete/silcrete cementation. In areas where this cementation is reduced or absent the scarp is more diffuse, as expected for a feature formed by one or more paleoearthquakes. The exceptional preservation aids comparison with data sets based on scarps which have formed more recently. Our analysis is based on a high-resolution digital elevation model of the Hebron Fault scarp in southern Namibia using pan-sharpened Worldview-3 satellite stereophotos (0.31 m resolution). We make scarp height measurements at 160 locations providing improved estimates of the average displacement (5.9 m), maximum displacement (10.1 m), and the minimum fault length (45 km). No consistent evidence of lateral displacements in water courses or alluvial fan margins were found implying predominantly normal displacement. A newly described section in the northwest has en-echelon scarps consistent with a component of strike-slip motion that may be explained by its difference in strike from the central section. Most channels crossing the fault show a single knick-point. The displacement varies smoothly as it crosses a number of different generations of alluvial fan surfaces. No evidence of a multiscarp or a composite scarp were observed. We have therefore found no evidence for a mutiple-event origin for the scarp, although, this lack of evidence does not conclusively demonstrate a single-event origin. Published regressions, based on the limited data available for SCRs, suggest that the mean expected average displacement () for a faults of this length is 1.2–3.1 m implying that the scarp is likely to have formed in 2–5 events with an expected Mw = ∼7.1 though displacements in individual events may exceed these average values. Comparison with the regional geology and aeromagnetic data sets suggests that the fault reactivates a Mesoproterozoic ductile structure, the Nam Shear Zone, and that the location, orientation and segmentation of the scarp is controlled by the alignment of pre-existing structurally weak zones with the present-day stress regime. The fault has undergone repeated brittle reactivation, accumulating ∼110 m of vertical offset since the deposition of the Ediacaran-to-Cambrian Nama Group. This is less than expected from global compilations of total displacement and fault length data, suggesting that the fault rapidly attained its current length by recruiting an existing weak zone and is expected to accumulate displacement at a relatively constant length in the future.
... Large earthquakes in mid-continents such as Australia, Eastern United States, North China and Northwestern Europe show complex patterns in time and space that do not fit existing seismotectonic models (Clark et al., 2012;Calais et al., 2016;. Individual faults tend to fall into thousands of years quiescence following a cluster of Figure 11.6 Focal depths and magnitudes of the earthquakes in Figure 11.2 projected into a profile perpendicular to the postglacial Stuoragurra Fault Complex. ...
Glacially triggered faulting describes movement of pre-existing faults caused by a combination of tectonic and glacially induced isostatic stresses. The most impressive fault-scarps are found in northern Europe, assumed to be reactivated at the end of the deglaciation. This view has been challenged as new faults have been discovered globally with advanced techniques such as LiDAR, and fault activity dating has shown several phases of reactivation thousands of years after deglaciation ended. This book summarizes the current state-of-the-art research in glacially triggered faulting, discussing the theoretical aspects that explain the presence of glacially induced structures and reviews the geological, geophysical, geodetic and geomorphological investigation methods. Written by a team of international experts, it provides the first global overview of confirmed and proposed glacially induced faults, and provides an outline for modelling these stresses and features. It is a go-to reference for geoscientists and engineers interested in ice sheet-solid Earth interaction.
... Episodic earthquake recurrence in Otago is consistent with observations from many low activity rate faults globally (e.g. Clark et al. 2012), particularly for reverse faults, and is not easily explained by the standard earthquake cycle model of regular strain accumulation and release (Calais et al. 2016;Griffin et al. 2020b). Developing a better understanding of the variability of earthquake inter-event times on faults within Otago, and whether episodic recurrence is a ubiquitous feature within the system, has important implications for seismic hazard assessment (e.g. ...
We present the first paleoseismic investigation of the Hyde Fault, one of a series of north-east striking reverse faults within the Otago range and basin province in southern New Zealand. Surface traces of the fault and associated geomorphology were mapped using a lidar digital elevation model and field investigations. Trenches were excavated at two sites across fault scarps on alluvial fan surfaces. The trenches revealed stratigraphic evidence for four surface-rupturing earthquakes. Optically stimulated luminescence dating constrains the timing of these events to around 47.2 ka (37.5–56.7 ka at 95% confidence), 34.6 ka (24.7–46.4 ka), 23.5 ka (19.7–27.3 ka) and 10.5 ka (7.9–13.1 ka). We obtain a mean inter-event time of 12.4 kyr (2.3–23.9 kyr at 95% confidence) and the slip rate is estimated to be 0.22 mm/yr (0.15–0.3 mm/yr). We do not find evidence to suggest that earthquake recurrence on the Hyde Fault is episodic, in contrast to other well-studied faults within Otago, suggesting diverse recurrence styles may co-exist in the same fault system. This poses challenges for characterising the seismic hazard potential of faults in the region, particularly when paleoearthquake records are limited to the most recent few events.
... Craig and Calais, 2014], in Australia [e.g. Clark et al., 2012], as well as in South Africa [e.g. Saria et al., 2013]. ...
The macroseismic and instrumental observations accumulated by the Bureau Central Sismologique Français and other national agencies over the last 100 years show that the northwestern part of metropolitan France is affected by an apparently diffuse and moderate intraplate seismicity. Far from any plate boundary, well-documented inherited structures, such as the Armorican shear zone network, the Sillon Houiller, and the normal faults related to the Atlantic ocean margin, likely exert significant control on the regional seismicity pattern. However, in the absence of a clearly measurable strain field, processes other than far-field tectonic stress loading such as erosion, gravitational potential energy, and/or hydraulic loadings can co-exist, but their respective influence on the current seismicity is debated and remains to be fully addressed. Reliable detection/location of low-to-moderate magnitude events is one of the most important challenges in the near future to better understand the processes that control this intraplate seismicity. As shown here for a limited region, this issue can be achieved positively, thanks to the new Résif-Epos network, in conjunction with sophisticated algorithms for both earthquakes’ detection and discrimination.
Field and desktop mapping studies were conducted for the stable continental region in the Western Cape Province of South Africa to characterize fault activity of four fault systems, including the Worcester, Groenhof, Piketberg-Wellington, and Colenso faults. The geologic studies presented here were in support of a Probabilistic Seismic Hazard Analysis (PSHA) for a nearby nuclear power facility site. Previous studies performed by the South African Council for Geoscience in the region suggested evidence of near-surface co-seismic deformation (De Beer, 2004; De Beer et al., 2008). The goal of this study is to re-assess the prior interpretations of these four faults and gather the required data for including them in a seismic source model for use in a PSHA. The primary aspects to include in the characterization are the recency of movement, slip rate, kinematics, and geometry. To improve the interpretation and target sites, the study used a satellite-derived digital elevation model and aerial imagery for six areas, totaling over 900 km2 of data. Limited Quaternary cover, or other late Cenozoic deposits that overlie the Precambrian and Paleozoic bedrock structures, resulted in difficulty constraining the recency of faulting. The new observations presented in this study suggest that reactivation and surface rupture along pre-Cenozoic faults of the four fault systems have not occurred in at least the last 10 ka. Further, the lack of youthful tectonic geomorphology and deformation of Quaternary stratigraphy indicate that surface faulting has not occurred in the late to middle Quaternary along any of these four structures.
Precariously balanced rocks (PBRs) and other fragile geologic features have the potential to constrain the maximum intensity of earthquake ground shaking over millennia. Such constraints may be particularly useful in the eastern United States (U.S.), where few earthquake-source faults are reliably identified, and moderate earthquakes can be felt at great distances due to low seismic attenuation. We describe five PBRs in northern New York and Vermont—a region of elevated seismic hazard associated with historical seismicity. These boulders appear to be among the most fragile PBRs in the region, based on reports from hobbyists. The PBRs are glacial erratics, best evidenced by glacial striations on bedrock pedestals. The pedestals themselves are locally high knobs, often situated on regionally high topography; this setting limits soil development and indicates that any outwash deposits were likely ephemeral. As a result, PBR ages can be reliably established by the retreat of the last continental ice sheet, ∼15–13 ka. To quantify the fragility of the PBRs, we surveyed them with ground-based light detection and ranging and calculated geometric parameters from the point clouds, field observations, and seismic responses. Preliminary validation of the 2023 time-independent U.S. National Seismic Hazard Model (NSHM) shows that the existence of PBRs is generally consistent with the median site-specific hazard curves. Only the Blue Ridge Road site suggests a modest reduction in hazard. To visualize the ensemble of data, we mapped the minimum permissible distance to potential source faults around each PBR site as a function of source magnitude by using the ground-motion models from the 2023 NSHM. Viewed in this manner, our data are consistent with potential M∼6.5 earthquake-source faults in many parts of the Lake Champlain Valley and northern Adirondack Mountains. Our work illustrates a potential pathway for better constraining earthquake-source faults in regions of cryptic faults.
Eastern Queensland (Australia) was struck by a major earthquake at ≈04:14 a.m. local time on 7 June 1918. Most previous studies have suggested that the epicenter of this earthquake lies off the coast of Bundaberg, between the port cities of Gladstone and Rockhampton. This epicentral location was based upon instrumental observations from the Riverview College observatory in Sydney. However, this epicenter lies ≈250 km to the northeast of an inland region that experienced both the strongest shaking effects and numerous felt aftershocks. We revisited available macroseismic data from 224 geographic locations and surviving instrumental observations for the 1918 Queensland earthquake to show that the most likely epicentral location was inland at ≈24.93°S and ≈150.88°E in the Banana Shire and North Burnett region. The re-estimated instrumental magnitude of Mw 6.0 ± 0.3 (1σ) makes it one of the largest onshore earthquakes in eastern Australia in the past century. Our observations also offer support for a viewpoint proposed in 1935 by an eminent Queensland geologist, Walter Heywood Bryan, that the 1918 earthquake was inland. Our study highlights the benefit of the critical evaluation of primary source materials, both archival and seismological, to study historical earthquakes in Australia that are relevant for modern seismic hazard analysis.
The Australian continent, being void of active plate boundaries, is often perceived as seismically quiescent. However, earthquakes of moderate magnitude (M6+) occur on the continent around once per decade. Such intra-plate activity can pose a significant risk as these earthquakes can occur along fault lines that are either unknown or considered inactive, are often non-periodic, and poorly understood. Within Australia, the spatial distribution of intraplate seismicity is non-uniform, instead tending to concentrate along certain weak zones of increased activity. One such region is the eastern margin of
the Gawler Craton in South Australia, one of the oldest building blocks of the continent. Recently, several new temporary seismic arrays have been deployed in the region, transforming data coverage across southern Australia. In total, 139 new local earthquakes have been recorded, most of which went undetected by the national seismic network. Following relocation, the pattern of earthquakes becomes more localised and appears to coincide with the edge of the Gawler Craton. Further, a spatial association was found between earthquakes and mound springs, which act as the discharge point for groundwater migrating from the Great Artesian Basin. Enhanced fluid pressures (mantle-degassing) within permeable crustal scale fault systems, responding to a regional contractional strain field, appear to be a key driver of seismicity in the area.
Mass transport deposits have long been known on the Exmouth Plateau, offshore NW Australia, identified in 2D and 3D industry seismic lines. The expedition SO257 in 2017 collected 30 high-resolution, shallow seismic lines along targeted transects on the northern Australian margin. Many of these imaged mass transport deposits, with the top 700-800m of the section captured in detail not available with industry seismic. We present 9 new high resolution seismic lines from 3 separate areas of the North West Shelf. Slides in the Roebuck Basin show complex anastomosing ductile extensional mechanisms, with multiple slip surfaces and no headscarps or adjacent faults. Slides on the Exmouth Plateau have fault control, with surface fault offsets of up to 300m, indicating seismicity as a likely triggering mechanism. Slumps along the western margin of Western Australia are more limited in extent, associated with surface notches, with indications of previous activity at depth. All areas show a repeated history of mass transport deposits. The area of the active landslide province offshore of NW Australia is far larger than the individual slides recognized on the Exmouth Plateau.
This article explores several area-based tests of long-term seismic hazard forecasts for the Australian continent. Using the observed seismicity, ShakeMaps are calculated for earthquakes that are expected to have generated moderate-to-high levels of ground shaking within continental Australia in the past 50 years (January 1972 through December 2021). A “composite ShakeMap” is generated that extracts the maximum peak ground acceleration “observed” in this 50-year period for any site within the continent. The fractional exceedance area of this composite map is compared with four generations of Australian seismic hazard maps for a 10% probability of exceedance in 50 years (~1/500 annual exceedance probability) developed since 1990.
In general, all these models appear to forecast higher seismic hazard relative to the ground motions that are estimated to have occurred in the last 50 years, with the most recent hazard model yielding a fractional exceedance area most similar to the target 1/500 annual exceedance probability. The sensitivity of these results to various modeling assumptions was tested by exploring an alternative ground-motion characterization model that forecasts higher overall ground-shaking intensities. The sensitivity of these results is also tested with the interjection of a rare scenario earthquake with an expected regional recurrence of approximately 8700 years. While these area-based analyses do not provide a robust assessment of the performance of the candidate seismic hazard for any specific location given the limited independent data, they do provide—to the first order—a guide to the performance of the respective maps at a continental scale.
The Mabian fault zone, distanced ∼200 km to the east of the Xianshuihe-Xiaojiang fault system, is located in the western vicinity of the relatively stable South China Block. Since 1917, about 54 M > 4.7 earthquakes, including the 1974 Ms = 7.1 Mabian event have occurred around this fault zone, suggesting that significant strain is localized within the Mabian fault zone. Here, we built a three-dimensional finite element model to investigate the main parameters that possibly control strain localization around the Mabian fault zone averaged over the active deformation timescale. In the model, the Xianshuihe-Xiaojiang fault system is specified as a discontinuous contact interface for its motion governed by a Coulomb-friction law, and the crustal rheology is simplified as a frictional upper crust underlain by a viscoelastic lower crust. In addition, Global Positioning System (GPS) data are used to mimic the horizontal tectonic loading, and the model base is supported by a hydrostatic pressure. Numerical results show that with the weak fault strength and the low viscosity contrast between the Tibetan plateau and the South China Block, strain rates from motion of the southeastern Tibetan plateau could be propagated across the Xianshuihe-Xiaojiang fault system more widely within the Mabian fault zone. Constrained by the estimates on slip rates of the faults and on rheological structures of the crust, our optimal model predicts the effective friction coefficient of the Xianshuihe-Xiaojiang fault of 0.05 - 0.1. Under this condition, relative motion across the Xianshuihe-Xiaojiang fault system is largely partitioned by the geometric bend near the center of the fault system, resulting in a relatively high strain rate of 2.1 - 3×10–8 yr–1 accumulating around the Mabian fault zone. Keeping the weak strength of the fault, numerical results also show that if the middle portion of the Xianshuihe-Xiaojiang fault system follows the Daliangshan fault, strain accumulation around the Mabian fault zone could be significantly reduced. It thus can be concluded that the strain partitioning from the weak strength and the special geometry of the Xianshuihe-Xiaojiang fault system must play a crucial role in active deformation around the Mabian area out of the Tibetan plateau deformation domain. This in turn means that in the Xianshuihe-Xiaojiang fault system, the Anninghe-Zemuhe fault is still the main boundary between the southeastern Tibetan plateau and the South China Block.
The Nullarbor Plain is underlain by a thick cratonic lithospheric mantle, which is thought to have a paucity of neotectonic faults and seismicity. Based on the analysis of high-resolution digital elevation models, identified neotectonic fault traces on the nearly flat karst landscape locally extend >100 km long, suggesting potential for hosting large (>7.3 to 7.5) moment magnitude earthquakes. The measured cumulative along-strike maximum displacement Dmax for each trace is not proportional to surface rupture length (L) but is correlated with the occurrence of crust-scale electrical conductors identified in magnetotelluric surveys. Two major conductors penetrate from the upper crust to the topmost mantle along crustal scale shear zones. The conductivity value in the topmost mantle is much higher than in the cratonic mantle, indicating serpentinization of the mantle with the addition of fluids. Lithospheric fluid localization may have weakened pre-existing faults and enhanced neotectonic faulting in the Nullarbor plain.
The Australian territory is just over 400 km from an active convergent plate margin with the collision of the Sunda–Banda Arc with the Precambrian and Palaeozoic Australian continental crust. Seismic energy from earthquakes in the northern Australian plate-margin region are channeled efficiently through the low-attenuation North Australian craton (NAC), with moderate-sized (Mw≥5.0) earthquakes in the Banda Sea commonly felt in northern Australia. A far-field ground-motion model (GMM) has been developed for use in seismic hazard studies for sites located within the NAC. The model is applicable for hypocentral distances of approximately 500–1500 km and magnitudes up to Mw 8.0. The GMM provides coefficients for peak ground acceleration, peak ground velocity, and 5%-damped pseudospectral acceleration at 20 oscillator periods from 0.1 to 10 s. A strong hypocentral depth dependence is observed in empirical data, with earthquakes occurring at depths of 100–200 km demonstrating larger amplitudes for short-period ground motions than events with shallower hypocenters. The depth dependence of ground motion diminishes with longer spectral periods, suggesting that the relatively larger ground motions for deeper earthquake hypocenters may be due to more compact ruptures producing higher stress drops at depth. Compared with the mean Next Generation Attenuation-East GMM developed for the central and eastern United States (which is applicable for a similar distance range), the NAC GMM demonstrates significantly higher short-period ground motion for Banda Sea events, transitioning to lower relative accelerations for longer period ground motions.
Glacially triggered faulting describes movement of pre-existing faults caused by a combination of tectonic and glacially induced isostatic stresses. The most impressive fault-scarps are found in northern Europe, assumed to be reactivated at the end of the deglaciation. This view has been challenged as new faults have been discovered globally with advanced techniques such as LiDAR, and fault activity dating has shown several phases of reactivation thousands of years after deglaciation ended. This book summarizes the current state-of-the-art research in glacially triggered faulting, discussing the theoretical aspects that explain the presence of glacially induced structures and reviews the geological, geophysical, geodetic and geomorphological investigation methods. Written by a team of international experts, it provides the first global overview of confirmed and proposed glacially induced faults, and provides an outline for modelling these stresses and features. It is a go-to reference for geoscientists and engineers interested in ice sheet-solid Earth interaction.
Glacially triggered faulting describes movement of pre-existing faults caused by a combination of tectonic and glacially induced isostatic stresses. The most impressive fault-scarps are found in northern Europe, assumed to be reactivated at the end of the deglaciation. This view has been challenged as new faults have been discovered globally with advanced techniques such as LiDAR, and fault activity dating has shown several phases of reactivation thousands of years after deglaciation ended. This book summarizes the current state-of-the-art research in glacially triggered faulting, discussing the theoretical aspects that explain the presence of glacially induced structures and reviews the geological, geophysical, geodetic and geomorphological investigation methods. Written by a team of international experts, it provides the first global overview of confirmed and proposed glacially induced faults, and provides an outline for modelling these stresses and features. It is a go-to reference for geoscientists and engineers interested in ice sheet-solid Earth interaction.
Glacially triggered faulting describes movement of pre-existing faults caused by a combination of tectonic and glacially induced isostatic stresses. The most impressive fault-scarps are found in northern Europe, assumed to be reactivated at the end of the deglaciation. This view has been challenged as new faults have been discovered globally with advanced techniques such as LiDAR, and fault activity dating has shown several phases of reactivation thousands of years after deglaciation ended. This book summarizes the current state-of-the-art research in glacially triggered faulting, discussing the theoretical aspects that explain the presence of glacially induced structures and reviews the geological, geophysical, geodetic and geomorphological investigation methods. Written by a team of international experts, it provides the first global overview of confirmed and proposed glacially induced faults, and provides an outline for modelling these stresses and features. It is a go-to reference for geoscientists and engineers interested in ice sheet-solid Earth interaction.
The cratonic shield system of central and western Australia, with its lithosphere up to 200 km thick, is geologically similar to other ancient, stable continental interiors. But since 1968 it has experienced a number of moderate-sized (Mw 5.0–6.6) earthquakes characterised by the extreme shallowness of their sources (the deepest is 8 km and most are shallower than 4 km). At least 11 of these have produced co-seismic faulting, often very long compared to their depth, with typically no evidence of previous movement on those faults in either the local geomorphology or paleoseismological trenching. Other earthquakes show that cratonic Australia, like other shield regions, has a seismogenic layer about 30–40 km thick, but the intense very shallow seismicity in the region of thickest lithosphere stands out and is unusual. A clue to the origin of these shallow earthquakes lies in their association with some of the largest continental gravity anomalies outside the forelands of young orogenic belts, yet in essentially flat topography. The wavelength of the gravity anomalies (∼240 km) is large compared with the seismogenic thickness (∼30 km) of the lithosphere, and their amplitude is ∼50 mGals. These anomalies need stresses to support them, which can be estimated by a simple model of a flexed elastic plate that reproduces the essential features of the earthquakes, including their focal mechanisms and shallow depth limit. The model shows that the maxima of the compressive stress occur beneath the maxima and minima of the gravity, on the upper and lower boundaries of the layer respectively. Perhaps surprisingly, the magnitude of such stresses is considerably greater than most estimates of the regional stress within plates. The maxima of the shear stress occur on planes with dips of 45°. The locations and mechanisms of the earthquakes show the same features. We conclude that the earthquakes release stored elastic stresses in an exfoliation process, perhaps activated by a reduction in strength through weathering, erosion or some other process.
The spatial and temporal distribution of earthquakes inside continental interiors, where tectonic loading rate is negligible, is much more complicated than plate boundary regions. On 30 March 1986, the moment magnitude (Mw) 5.7 Marryat Creek earthquake occurred in the Musgrave Block of central Australia. Subsequent earthquakes include the1989 Ml 5.6 Uluru, 2012 Mw 5.2 Pukatja, 2013 Mw 5.6 Mulga Park, and 2016 Mw 6.0 Petermann earthquakes. In this study, I explore whether coseismic and viscoelastic Coulomb stress changes following the 1986 Marryat Creek earthquake could have played a role in influencing the basic spatiotemporal characteristics of this earthquake sequence. I find that coseismic stress change does not successfully explain earthquake triggering in the area. I then explore this issue using a viscoelastic stress change model with a range of rheology parameters. In some models, the magnitude of viscoelastic stress change is higher than coseismic stress changes and may be of sufficient magnitude to be considered within an earthquake triggering context. Moreover, I also hypothesize that these earthquakes may have occurred due to dynamic stress triggering or other processes such as fluid migration, nonlinear friction, and/or aseismic deformation, which due to the small distribution of seismic networks across the area I have not been able to investigate in detail. However, I cannot dismiss the possibility that these earthquakes occurred randomly, with no identifiable stress triggering relationships among them.
The spatial distribution of large earthquakes in slowly deforming continental regions (SDCR) is poorly documented and, thus, has often been deemed to be random. Unlike in high strain regions, where seismic activity concentrates along major active faults, earthquakes in SDCR may seem to occur more erratically in space and time. This questions classical fault behavior models, posing paramount issues for seismic hazard assessment. Here, we investigate the M7, 1967, Mogod earthquake in Mongolia, a region recognized as a SDCR. Despite the absence of visible cumulative deformation at the ground surface, we found evidence for at least 3 surface rupturing earthquakes during the last 50,000 years, associated with a slip-rate of 0.06 ± 0.01 mm/year. These results show that in SDCR, like in faster deforming regions, deformation localizes on specific structures. However, the excessive length of return time for large earthquakes along these structures makes it more difficult to recognize earthquake series, and could conversely lead to the misconception that in SDCR earthquakes would be randomly located. Thus, our result emphasizes the need for systematic appraisal of the potential seismogenic structures in SDCR in order to lower the uncertainties associated with the seismogenic sources in seismic hazard models.
We have discovered hundreds of planar, nearly vertical sand- and gravel-filled dikes that we interpret to have been caused by earthquake-induced liquefaction in the Wabash Valley of Indiana- Illinois. These dikes range in width from a few cm to as much as 2.5 m. The largest dikes are centered about the general area of Vincennes, Indiana; they decrease in size and abundance to the north and south of this area. Preliminary studies indicate the high possibility that many, if not all, of the dikes were formed by a single large earthquake that took place in the Vincennes area sometime between 2,500 and 7,500 years ago. The severity of ground shaking required to have formed the dikes far exceeds the strongest level of shaking of any earthquake in the central United States since the 1811–12 New Madrid earthquakes.
On March 30, 1986, an earthquake of surface-wave magnitude (Ms) 5.8 generated about 13 km of surface ruptures in the remote northern part of South Australia. This earthquake is significant because it occurred in the interior of the tectonically stable Precambrian shield (craton) of the Australian plate, about 2000 km from the nearest plate margin. The source parameters of the earthquake are described and their implications discussed. Investigations of the historical faulting at Marryat Creek, Tennant Creek, and Meckering in Australia and palaeoseismologic data from the Meers fault in the United States all suggest that intraplate faults may have long repeat times for surface rupturing. Based on these observations, it is suggested that the concept of recurrence intervals may not be appropriate for faults in stable continental interiors. -from Authors
Within 12 hours on January 22, 1988, three major earthquakes with surface-wave magnitudes (Ms) of 6.3, 6.4 and 6.7 struck the Tennant Creek area, Northern Territory, Australia. The earthquakes produced surface ruptures along two major fault strands that have a total length of about 32km. Individual ruptures are 6.7 to 16.0km long and are characterized by north- and south-directed folds and reverse fault scarps. The earthquakes occurred in the interior of the tectonically stable Precambrian shield of the Australian plate, about 1500km from the nearest plate margin. These earthquakes join a group of only nine other historic intraplate earthquakes in the world that have produced documented surface ruptures in stable continental interiors. Investigations suggest that faults in this kind of tectonic setting have long time intervals between surface ruptures. Therefore, the concept of recurrence intervals may not be appropriate in describing these faults. Perhaps hazard assessments in stable continental interiors should be based on a random earthquake that can occur at any time on a suitably oriented fault rather than only on faults having demonstrable Quaternary movement. -from Authors
The Barmah-Millewa forest has excited the curiosity of two generations of earth scientists. This triangle of forest has developed on a low-angle alluvial fan formed by an an anabranching network of channels. The Barmah-Millewa forest exists because of the limited hydraulic capacity of the present channel of the Murray River. The result is that flood flows leave the Murray and spread through the forest via a complex network of effluents. The extent and position of those effluents is, in turn, controlled by the fan of palaeo-levees associated with late Quaternary channels of larger size, and coarser sediment load. The morphology of the Rarmah-Millewa fan is thus indirectly a product of the rise of the Cadell Fault block, but directly the result of a sequence of channel avulsions. The most enigmatic of six distinct avulsions is the most recent which has taken the river to the south. In a few thousand years the river will make its next avulsion, this time returning to its more natural, northerly, path along the Edward River, to the north of the Cadell Fault block. In this light, the present path of the Murray, via Echuca, could be described as a short-term southern excursion for Australia's iconic river.
Four emerged, marine erosion terraces are preserved on the western flank of the Cape Range Anticline. From oldest to youngest they are named the Muiron, Milyering, Jurabi, and Tantabiddi Terraces. The related old shoreline cliffs are named Muirion, Milyering, Jurabi, and Tantabiddi Scarps,and the respective terrace deposits are named the Muiron and Milyering Members of the Exmouth $andstone and the Jurabi and Tantabiddi Members of the Bundera Calcarenite. The terraces, which are distinctly warped, are believed to have formed during Quaternary interglacial high sea-level stands. The warping indicates signiflcant Quaternary tectonism in the Cape Range area.
Two emergent marine erosion terraces and terrace deposits, now at 2 to 4 m and 7 m above Mean Low Water Springs level, occur along the east shores of Lake MacLeod. Two similar terraces and deposits occur on the coast at Cape Cuvier and Red Bluff, where there elevations are 1 to 3 m higher.
Correlation with Cape Range and Shark Bay units indicates that the terraces and terrace deposits are of Pleistocene age.
Late Quaternary tectonism is indicated in the area by the fact that the terraces and marine deposits are folded alomg the Cape Cuvier Anticline. In addition the terraces are at higher elevations than those on the east side of Lake MacLeod. This together with previous work indicates that the West Australian coast between North West Cape and Shark Bay has been tectonically unstable during the Quaternary.
The elevation of shoreline features and distribution of marine deposits indicate that the Lake MacLeod Pleistocene embayment extended over an area 50 per cent greater than Lake MacLeod, and was open to the ocean at both its southern and northern ends. This configuration allowed normal marine oceanic salinities to exist in the embayment, and permitted the growth of corals that mark the shoreline benches.
A regional seismic interpretation ot the on shore Otway Basin has been completed and used to determine the basin's structural history.Sedimentation commenced in the Tithonian-Berriasian with the deposition of the volcanogenic Casterton Formation and continued into the Berriasian-Barremian with the deposition in elongate half graben, of thick fluviolacustrine sediments of the Crayfish Group, typically thickening dramatically towards the bounding faults. The NW to W trend of Crayfish Group depocentres and their major bounding faults suggest that the initial extension direction was N-S to NE-SW in the Late Jurassic-Early Cretaceous. Dextral transtensional movement occurred along the Trumpet Fault in the west of the basin and was complemented by sinistral transtension on the major NNE striking faults of the Torquay Sub-basin in the east during this period.The dip direction of the pre-Barremian bounding faults changes a number of times along the northern margin of the basin. These changes occur across transfer/accommodation zones of complex faulting and folding, not over discrete transfer faults.Faulting and related uplift resulted in partial erosion of the Crayfish Group from a number of structural highs, prior to the Aptian. The half graben faults are overlain by Eumeralla Formation indicating that active rifting had ceased by the Aptian in the onshore Otway Basin. Further erosion occurred following post-Albian faulting and uplift prior to the Paleocene, in particular within the eastern part of the basin.During deposition of the Sherbrook Group in the Late Cretaceous, fault reactivation produced minor, shallow grabens within the older half graben systems. Major movement also continued along the Tartwaup Fault Zone, resulting in basin deepening toward the SW. This fault activity continued into the Paleocene-Early Eocene during deposition of the Wangerrip Group. In the Eocene, the Southern Ocean spreading rates changed from slow to fast, resulting in the late-Early Eocene deltaic sediment of the Upper Wangerrip Group covering some of the earlier extension faults. Compression, resulting in right-lateral wrenching and inversion of previous faults, occurred during the Miocene-Recent. Pliocene-Holocene volcanic activity occurred along zones of weakness related to these fault systems.
Paleoseismic studies of two historically aseismic Quaternary faults in Australia confirm that cratonic faults in stable continental regions (SCR) typically have a long-term behavior characterized by episodes of activity separated by quies- cent intervals of at least 10,000 and commonly 100,000 years or more. Studies of the approximately 30-km-long Roopena fault in South Australia and the approxi- mately 30-km-long Hyden fault in Western Australia document multiple Quaternary surface-faulting events that are unevenly spaced in time. The episodic clustering of events on cratonic SCR faults may be related to temporal fluctuations of fault-zone fluid pore pressures in a volume of strained crust. The long-term slip rate on cratonic SCR faults is extremely low, so the geomorphic expression of many cratonic SCR faults is subtle, and scarps may be difficult to detect because they are poorly pre- served. Both the Roopena and Hyden faults are in areas of limited or no significant seismicity; these and other faults that we have studied indicate that many potentially hazardous SCR faults cannot be recognized solely on the basis of instrumental data or historical earthquakes. Although cratonic SCR faults may appear to be nonhaz- ardous because they have been historically aseismic, those that are favorably oriented for movement in the current stress field can and have produced unexpected damaging earthquakes. Paleoseismic studies of modern and prehistoric SCR faulting events provide the basis for understanding of the long-term behavior of these faults and ultimately contribute to better seismic-hazard assessments.
Stratigraphic relations and radiocarbon ages of deposits exposed in several trenches and excavations help to establish the timing, sense of slip, and style of the deformation that resulted from late Holocene surface faulting on the Meers fault in southwestern Oklahoma. The eastern half of the scarp is formed on relatively ductile Permian Hennessey Shale and Quaternary alluvium, whereas the western half is formed on well-lithified, relatively brittle Permian Post Oak Conglomerate in the Slick Hills. At Canyon Creek on the eastern half of the scarp, the shale and alluvium in two trenches are deformed mainly by monoclinal warping. These trenches contain stratigraphic evidence of one surface-faulting event that produced about 3 m of throw. At this site, the amount of throw in middle Holocene and middle Pleistocene deposits is similar. Lateral displacement is difficult to detect in these trenches, most likely because of plastic deformation in the shale and alluvium. In contrast, trenches and excavations on the western half of the scarp show that the Holocene surface faulting produced at least as much lateral as vertical displacement. At two sites, the scarp has dammed small gullies and ponded fine-grained alluvium upslope from the scarp. The channels of the gullies at these ponded-alluvium sites have been separated 3-5 m left-laterally since they were dammed. The lateral displacement on the gullies is 3.3 to 1.6 times as much as the vertical displacement. In a pit excavated into the colluvium on the downthrown side of the scarp, subhorizontal striae on conglomerate clasts along the fault plane provide evidence of nearly pure strike-slip movement. The age of the striae is unknown, but they are believed to be Quaternary in age because it is unlikely that such delicate striae could be preserved in soluble carbonate rock in a near-surface weathering environment for many hundreds of thousands of years. Multiple radiocarbon ages of soil-humus samples from the Canyon Creek trenches and the ponded-alluvium sites show that the last surface faulting occurred 1,200-1,300 yr ago. Limited geologic evidence, however, indicates a long-term recurrence interval on the order of 100,000 yr or more. The youthful surface faulting compared to the apparently long recurrence interval presents a difficult problem for regional seismichazard assessments. Hazard assessments that rely on the long-term slip rate might seriously underestimate the hazard if the behavior of the fault is characterized by a temporal clustering of events, and if the late Holocene surface faulting signals the beginning of a period of frequent faulting. Conversely, if strain accumulates steadily on the Meers fault and is released regularly over time intervals of 100,000 yr or more, then the hazard may be low because much of the stored strain was released only about 1,000 yr ago. Improved earthquake-hazard assessments in much of the central United States and in stable intraplate settings worldwide require a better understanding of the long-term and short-term behavior of seismogenic intraplate faults.
Along the present southwest Australian margin, in the Perth and Carnarvon Basins, the wholly nonmarine Permian, Triassic, and Jurassic sedimentary rocks of the southern Perth Basin pass northwards into paralic and marine equivalents of the Carnarvon Basin, which additionally contains marine Silurian, Devonian, and Carboniferous rocks. These contrasts are interpreted in terms of the re-assembly of Australia in Gondwanaland: the southern Perth Basin lay alongside India in the interior of Gondwanaland, and the northern Carnarvon Basin faced a gulf of Tethys.According to this model, southwest Australia was arched in the Late Carboniferous, and the arch collapsed by rifting in the Permian, Triassic, and Jurassic, with the accumulation of thick nonmarine (in the south) to paralic and marine sediments (in the north). Rupture from India was marked by the eruption of basalt in the earliest Cretaceous, and dispersal of India and Australia was marked by rapid marginal subsidence in the Late Cretaceous. This model, derived from stratigraphical and faciological data, is supported by the ridge-and-rift structure of southwest Australia.
The Reelfoot Lake basin, Tennessee, is structurally complex and of great interest seismologically because it is located at the junction of two seismicity trends of the New Madrid seismic zone. To better understand the structure at this location, a 7.5-km-long seismic reflection profile was acquired on roads along the southern margin of Reelfoot Lake. The seismic line reveals a westerly dipping basin bounded on the west by the Reelfoot reverse fault zone, the Ridgely right-lateral transpressive fault zone on the east, and the Cottonwood Grove right-lateral strike-slip fault in the middle of the basin. The displacement history of the Reelfoot fault zone appears to be the same as the Ridgely fault zone, thus suggesting that movement on these fault zones has been synchronous, perhaps since the Cretaceous. Since the Reelfoot and Ridgely fault systems are believed responsible for two of the main-shocks of 1811-1812, the fault history revealed in the Reelfoot Lake profile suggests that multiple mainshocks may be typical of the New Madrid seismic zone.
The Ridgely fault zone consists of two northeast-striking faults that lie at the base of and within the Mississippi Valley bluff line. This fault zone has 15 m of post-Eocene, up-to-the-east displacement and appears to locally control the eastern limit of Mississippi River migration. The Cottonwood Grove fault zone passes through the center of the seismic line and has approximately 5 m of up-to-the-east displacement. Correlation of the Cottonwood Grove fault with a possible fault scarp on the floor of Reelfoot Lake and the New Markham fault north of the lake suggests the Cottonwood Grove fault may change to a northerly strike at Reelfoot Lake, thereby linking the northeast-trending zones of seismicity in the New Madrid seismic zone.
The Murray Basin extends over 300 000 km 2 of inland southeastern Australia, is flanked by subdued mountain ranges, and forms a low-lying saucer-shaped basin with thin flat-lying Cainozoic sediments. Beneath the Murray Basin, geophysical and borehole evidence indicates that folded and partly metamorphosed Proterozoic and Lower Palaeozoic basement is block-faulted, and that the Cainozoic sequence is locally underlain by poorly defined infrabasins preserved in graben-like troughs. These contain thick sequences of Devonian to Lower Carboniferous sedimentary rock and discontinuous, erosional remnants of Upper Carboniferous, Permian, Triassic and Cretaceous platform-cover sediments. The Cainozoic succession of the Murray Basin forms an extensive blanket of sediment, with a maximum thickness of about 600 m preserved in the deeper, central-western parts of the basin. The main emphasis of the study is on improving our understanding of the geological context of groundwater and surface discharge in the Murray Basin, but it also includes reference to other mineral resources. These include Cainozoic limestone, alluvial gold, kaolin, heavy minerals, gypsum and halite deposits. -from Authors
Fault-plane solutions determined for earthquakes in northwestern Australia (6 may 1978), central Australia (25 November 1978) and southeastern Australia 4 July 1977) each indicate nearly horizontal axes of maximum compressive stress. However, the azimuths of these are different from the azimuths of maximum stress axes determined previously for earthquakes in each area. This may be the result of a combination of warped stress fields at the junction of geologically different crustal blocks, and faulting in weakened zones of these blocks where the strike is oblique to the regional direction of maximum stress. Results in northwestern Australia can be explained by such effects.-Authors compressive stress warped stress fields faulting Australia
The Taranaki Basin has undergone a complex sedimentary and tectonic history since the late Oligocene, reflecting the impingement of deformation associated with the evolving Pacific and Australian convergent plate boundary. At various times through the Neogene, elements of a passive continental margin, retro-arc foreland basin, foreland fold and thrust belt, inverted subbasin, back-arc rift and back-arc contractional basin have been variously displayed within the Taranaki Basin. -from Authors
A study of the Bass Basin using a basin-wide integration of seismic data, well logs, biostratigraphy and seismic/sequence stratigraphy has resulted in the identification of six basin phases and related megasequences/ supersequences. These sequences correlate to three periods of extension and three subsidence phases. The complex nature of facies relationships across the basin is attributed to the mostly terrestrial setting of the basin until the Middle Eocene, multiple phases of extension, strong compartmentalisation of the basin due to underlying basement fabric, and differential subsidence during extension and early subsidence phases. The Bass Basin formed through upper crustal extension associated with three main regional events:rifting in the Southern Margin Rift System;rifting associated with the formation of the Tasman Basin; and,prolonged separation, fragmentation and clearance between the Australian and Antarctic plates along the western margin of Tasmania.The final stage of extension was the result of far-field stresses that were likely to be oblique in orientation. The late Early Eocene to Middle Eocene was a time of rifttransition and early subsidence as the effects of intra-plate stresses progressively waned from east to west. Most of the coaly source rocks now typed to liquid hydrocarbon generation were deposited during this rift-transition phase. Biostratigraphic studies have identified three major lacustrine episodes during the Late Cretaceous to Middle Eocene. The lacustrine shales are likely to be more important as seal facies, while coals deposited fringing the lakes are the principal source rocks in the basin.
The 16 December 1954 Dixie Valley (MS 6.8) earthquake followed the Fairview Peak (MS 7.2) earthquake by only 4 min and 20 sec. A three-dimensional model of the two dip-slip fault systems based on recent detailed field studies shows the ruptures were separated by a 6-km step in surface trace. A boundary-element approach shows that the static stress changes imposed by rupture of the Fairview Peak earthquake are in the correct sense to explain the northward propagation of faulting along four distinct faults that comprise the Fairview Peak earthquake and the subsequent triggering of the Dixie Valley earthquake. The location of rupture end points at sites where static stresses change sign is also used to suggest that static stress changes may play a role in controlling the extent of fault ruptures. We also observe that the largest coseismic surface displacements tend to correlate with those sections of the faults showing the largest positive stress change from preceding ruptures.
The North West Cape area in the Exmouth Sub-basin was the site of the first onshore oil flow in Australia at Rough Range-1 in 1953. Subsequently, exploration focused on two large surface anticlines, Cape Range and Rough Range. By 1984, 30 unsuccessful wells had made it clear that the subsurface was far more complex than indicated by the surface mapping and limited seismic data. A detailed reappraisal of the subsurface structure and stratigraphy was needed.A joint venture group operated by Ampol Exploration began a new phase of exploration by recording over 1200 km of seismic data, both regional and detailed, between 1985 and 1989. An integrated interpretation of seismic data, well information and Landsat imagery has improved the understanding of structural and stratigraphic complexities and has given direction to the current exploration effort.Five of the most significant tectonic episodes to affect the North West Cape area have been recognised. They are Late Carboniferous and Early Jurassic (Sinemurian) rifting phases, Callovian-Oxfordian and Berriasian-Valanginian syn-rift pulses related to break-up and, finally, structural inversion in the Late Miocene. Each of these episodes is associated with characteristic structural styles and stratigraphic sequences.Significant lateral displacement along transfer faults during Sinemurian rifting and again during the Berriasian- Valanginian syn-rift pulse has resulted in the formation of tear faults that swing westward and merge with the plane of the transfer faults. Fault-block rotation and uplift associated with these tear faults provide potential structural and stratigraphic traps. The influence that transfer faults have on the hydrocarbon prospectivity of the North West Cape area has been recognised, including their role in the distribution of reservoir and source rocks.These tectono-stratigraphic concepts have provided a sound framework for future exploration in the North West Cape area, and may have implications for hydrocarbon prospectivity in other parts of the North West Shelf and on passive margins elsewhere.
The Riverine Plain links the glaciated uplands of SE Australia with the arid inland western plains. Dated river, lake and dune deposits indicate three distinct and climatically-controlled phases of fluvial activity since ca 30 000 BP; with little modification of relict river channels during the past 10 000 years. -Editors
Knowledge of the in situ stress field of the Australian continent has increased greatly since compilation of the World Stress Map in 1992, principally by analysis of borehole breakouts and drilling-induced tensile fractures in petroleum wells. Stress orientations are variable across the Australian continent as a whole. However, within 15 of 16 individual stress provinces defined in the Australian continent (of one to a few hundred kilometres scale), mean stress orientations are statistically significant. The stress provinces, and stress trajectory mapping, reveal that there are systematic, continental-scale rotations of stress orientation within Australian. Unlike many other continental areas, stress orientations do not parallel the direction of absolute plate motion. Nonetheless, the regional pattern of stress orientation is consistent with control by plate boundary forces, if the complex nature of the convergent northeastern boundary of the Indo-Australian plate, and stress focusing by collisional segments of the boundary, is recognized.
Evidence from earthquake focal mechanisms, in situ stress measurements, and surface deformations indicate that the Australian continent is in a state of substantial horizontal compression. Reliable focal mechanism determinations are now available from eight earthquakes that have occurred in several parts of the continent since 1967. Each of these mechanisms indicates that the faulting associated with the earthquakes was caused by compressive stress acting close to horizontal. In situ measurements made in mines and tunnels, and close to the surface in quarry floors or on rock outcrops, also indicate horizontal compressive stress in all areas.-Authors