A large mafic dyke from the NNW-trending dyke swarms in the Eastern Block of the North China Craton was dated by SHRIMP U-Pb age analysis. This dyke occurs near Mt. Taishan in Shandong Province; it cuts Neoarchean tonalite, adamellite and diorite plutons. Two types of zircons were found in the dyke. Type 1 zircons were inherited from the host rocks and gave a SHRIMP U-Pb age of 2544±24 Ma with a weighted mean 207Pb/206Pb age of 2523±18 Ma. Type 2 zircons were crystallized from the dyke magma and yielded a concordant SHRIMP U-Pb age of 1830±17 Ma with a weighted mean 207Pb/206Pb age of 1837±18 Ma, indicating that the large dyke at Taishan was emplaced at ∼1830 Ma. The mafic dyke swarm provides evidence of a phase of extension in the Eastern Block of the North China Craton at ∼1.8 Ga. This dyke has a similar age to dyke swarms in the Western Block and in the Central Orogen Belt of the North China Craton. This lithospheric extension, led to the opening of the Yanliao and Zhongtiao aulacogens. The similar ages and orientations of ∼1.8 Ga dyke swarms throughout the North China Craton demonstrate that at that time the Eastern and Western blocks were united and that the amalgamated craton experienced widespread extension.
The Neoarchean Nellore greenstone belt, located along the eastern margin of the Eastern Dharwar Craton, was the site for younger igneous activity. The timing of this magmatism and the host metabasalt, critical for constraining extensional events along the deformed southeast margin of the Eastern Dharwar Craton, was conducted by the Sm–Nd method.Samples from the large differentiated gabbroic Kandra igneous complex, a subset Kandra group a, define an isochron age of 1926 ± 110 Ma, Ndi = 0.51006 ± 12, MSWD = 0.98 (n = 5), εNd = −1.7, and the Kandra group b subset yielded a Model 3 isochron age of 1882 ± 120 Ma, Ndi = 0.50994 ± 14, MSWD = 1.8 (n = 4), εNd = −5.1. Whereas the three samples from north Pamuru gabbro-anorthosite yielded an isochron age of 1882 ± 160, Ndi = 0.51012 ± 18, MSWD = 0.064, εNd = −1.7, the Kandra group a and north Pamuru samples regressed together yielded a preferred isochron age of 1911 ± 88 Ma, Ndi = 0.51008 ± 10, MSWD = 0.62 (n = 8), εNd = −1.6, for the emplacement of gabbros. In contrast host greenstone belt metabasalt from Chundi yielded a Sm–Nd isochron age of 2693 ± 94 Ma, Ndi = 0.50920 ± 8, MSWD = 1.4 (n = 4), εNd = +1.2, whereas regressing the Chaganam and Chundi samples yielded an isochron age of 2654 ± 100 Ma, Ndi = 0.50923 ± 9, MSWD = 1.5 (n = 11), εNd = +0.7. Basal metapelite, underlying the metabasalt yields old Nd model ages between 2888 and 3054 Ma.The results of this study show that the ∼2.7 Ga Nellore greenstone belt was intruded by enriched MORB-type gabbros at ∼1911 Ma. It is proposed that this Palaeoproterozoic magmatism formed in response to a major extensional event along the Eastern Dharwar Craton margin that likely initiated breakup from the southeastern margin of the North China Craton. This exposed craton margin later evolved as the site for collisional events during the Late Palaeoproterozoic to Early Mesoproterozoic.
Was the abrupt climate cold reversal called the Younger Dryas (YD) a global climate excursion? This study presents the first evidence for YD glacial advances on the Tibetan Plateau, derived from 10Be, 26Al, and 21Ne exposure ages of two erratics with a weighted mean age of about 11,600 years bp from a moraine at the eastern margin of the Tibetan Plateau. This implies that the YD climate signal, commonly thought to be initiated by decreased North Atlantic Deep Water Formation and transferred by ocean circulation, was even recorded at the inner-continental, high-altitude site of Tibet, implying atmospheric transport and thus a global character for this abrupt climatic change.
The background concentrations of 13 soil trace elements, copper (Cu), lead (Pb), zinc (Zn), cadmium (Cd), nickel (Ni), chromium (Cr), mercury (Hg), arsenic (As), selenium (Se), cobalt (Co), vanadium (V), manganese (Mn), and fluorine (F), from approximately 205 pedons in Tibet, China are reported here for the first time. The 13 trace element concentrations follow an approximately log–normal distribution. While the mean concentrations of Hg and Se are lower and As is higher than the average concentration for all of China, concentrations of the other trace elements are similar to the national average. Trace element concentrations are related to vegetation and human activity also played a notable role on the contents of trace elements in Tibet. The parent material relationship for all 13 soil trace element concentrations follows the pattern: shale>sandstone≅igneous rock≅limestone>alluvial sediment>glacial deposits>lake sediments; while for vegetation and human activity the concentration pattern is farmland=shrub>forests>meadow>prairie>marsh and others. The soil trace element concentrations on the Tibetan Plateau are related primarily to the parent material, but were also affected by vegetation and human activity.
Variations of orbital-driven insolation, ice volume, and greenhouse gas effects have been proposed as major controlling factors in determining the timing and amplitude of Quaternary cyclic climate changes. However, it remains to be determined how the internal feedback in the tropical atmosphere and ocean and the coupling between the low- and high-latitude systems may have produced instability or non-cyclic changes in the long-term climate evolution. Such “abnormalities” have been reported increasingly from paleoclimatic reconstructions in East Asia and the western Pacific for a prolonged warm and humid climate interval during marine isotope stage (MIS) 13–15, ∼475–610 kya. To better address the climate abnormality in MIS 13–15 that has been observed in the western Pacific, here we report high-resolution late Quaternary planktic foraminifer faunal abundance and faunal sea surface temperature (SST) records from the International Marine Past Global Change (IMAGES) program core MD972142, which was retrieved from the southeastern South China Sea (SCS). Our results indicate that the faunal assemblages and SSTs in the southeastern SCS express a substantially prolonged, unusual warm interglacial-type climate condition in MIS 13–15. The climate was abnormally warm during the cold MIS 14. Our study also suggests a lowering of sea surface salinity (SSS) during MIS 13–15. While the western Pacific climate experienced a persistently warm and humid period at MIS 14, a “normal” cooling (∼2 °C) condition on the surface of the eastern equatorial Pacific existed concomitantly. While assessing possible interpretations of this “abnormal” climate interval in MIS 13–15, our study indicates that an enhanced interhemispheric and/or longitudinal temperature gradient across the basin-wide Pacific cannot be ruled out. A change in the sensitivity of the East Asian Monsoon (EAM) that controlled temperature and precipitation patterns in East Asia and the western Pacific is probably also important or responsible for this climate abnormality. Based on our evidence, we suggest that the tropical dynamics would have played a role in the climate abnormality in MIS 13–15, through maintaining or even increasing the longitudinal SST gradient in the equatorial Pacific, which may have intensified the low-latitude trade winds in the eastern component of the Walker Circulation that drove a longer duration and/or stronger intensity of the summer vs. winter EAM.
An earthquake of Mw 5.1 occurred on March 14, 2005, in the seismically active Koyna–Warna region in western India, the site known for the largest reservoir triggered seismicity (RTS) in the world. For more than four decades, earthquakes with M ⩾ 4.0 have occurred in this region at regular intervals. Impoundment of reservoirs and changes in lake levels can trigger earthquakes by two processes of stress modifications, namely direct loading effect of the reservoir and diffusion through various faults and fractures. In this paper we analysed the reservoir water level data at Koyna and Warna reservoirs prior to the occurrence of the March 14, 2005 earthquake, to explain the dominant mechanism behind its occurrence and its correlation with the observed coseismic changes. We conclude that the diffusion process, not the reservoir load effect, is the dominating mechanism triggering earthquakes in the region. The coseismic changes in deep well water levels sensitive to earth tides are found to be to the order of 1–12 cm.
The Longgang volcanic field, located in northeastern China, is volcanically active with a number of eruptions during the Quaternary but the chronology of the eruptions is poorly defined. Some tephra layers are well preserved in the annually laminated sediments of maar lakes in the region, and facilitate the construction of a much improved chronological framework for the volcanic history of the area. The results of our investigations reveal that three basaltic explosive eruptions occurred at AD 460, 11460 cal yr BP and 14000 cal yr BP, respectively. The largest explosive basaltic eruption (AD 460) produced a thick black scoria layer in the Longgang volcanic field, including lakes. The tephra distribution and chronological data suggest that this eruption is likely to be from the Jinlongdingzi volcano. Two basaltic flood eruptions occurred at Jinlongdingzi. The earlier basaltic eruption produced a lava flow that spread over a forest and encased standing trees. Two radiocarbon ages obtained from charcoal samples collected from the burned remains of these trees are 1828–1989 cal yr BP and 2164–2359 cal yr BP. In the most recent stage of volcanism, the lava flow extended only ca. 2 km, and flowed into Lake Dalongwan. From the present status of the forest ecosystem, which has not yet reached the fully mature successional stage, we estimate that this lava is very young (ca. a few hundreds years old). Jinlongdingzi is a potentially dangerous volcano. Monitoring and assessment of the potential hazards in the Longgang volcanic field should be carried out in the future.
The Dauki Fault, which is inferred to go through the southern margin of the Shillong Plateau, is an E–W trending reverse one inclined towards the north. The Dauki Fault was believed to be active during the Late Quaternary time by the geomorphic features of the Shillong Plateau, the gravity anomaly data, and uplifted Tertiary and Quaternary deposits on the southern foothills of the Shillong Plateau. However, previous studies did not show any specific evidence that the Dauki Fault is active, since active fault survey such as satellite photo interpretation and trench investigation was not performed hitherto. We carried out CORONA satellite photo interpretation and trench investigation across the Dauki Fault at Gabrakhari Village for the first time. Consequently small fault strands and clear unconformity accompanied with faulting were confirmed in the trench. However, these small fault strands may be secondary ones branched from a main fault which may be concealed under the trench. The time of seismic event, which is inferred from unconformity, is dated back to A.D. 1500–1630. The seismic event during A.D. 1500–1630 may correspond with the 1548 earthquake which is currently a first recorded large earthquake in Bangladesh. Furthermore, sand dikes due to paleo-liquefaction, which reach near the ground surface, were confirmed at the trench. According to radiocarbon age, the sand dikes were formed during the 1897 Ms. 8.0 Great Assam earthquake.Highlights► We conducted active fault survey on the southern margin of the Shillong Plateau. ► The Dauki Fault was first confirmed by trench investigation. ► The Dauki Fault has ruptured during 16th century. ► The seismic event may correspond with the 1548 earthquake.
Seismo-electromagnetic phenomena refers to the electric and magnetic field perturbations that may be caused due to geophysical activities like earthquakes and volcanic eruptions. Due to the existence of such phenomena before earthquakes they may be regarded as short term precursors to earthquakes. Keeping in mind the in situ measurements for detection of such phenomena, the satellite based techniques are of great interest because they keep a constant track of the seismically active zones globally. With the objective of detecting the electromagnetic emissions in the ionosphere, the DEMETER satellite has been launched on 29th June 2004 from Baikonour in order to study the ionospheric perturbations associated with seismic activities. In this paper, we discuss some interesting results of electromagnetic emissions that are observed before a series of recent Indonesian earthquakes in the Jawa region with a major shock measuring 7.7 magnitude on Richter scale which occurred on 17 July 2006. The emissions have been observed in the Ultra Low Frequency (ULF)/Extremely Low Frequency (ELF) range of electromagnetic spectra.
The eastern margin of the Tibetan Plateau is bounded by a N–S-trending active fault zone, including the Zemuhe Fault, which is an important tectonic boundary in studies of continental dynamics and deformation modes. Here, we present the kinematic mechanism and deformation features of co-seismic surface ruptures caused by a large historic earthquake that occurred upon the Zemuhe Fault. Field investigations and interpretations of aerial photographs reveal a NNW–SSE-trending surface rupture zone, less than 100 m wide, defined by en echelon fractures, mole tracks, and fault scarps over a length of 60 km. Trench excavations and radiocarbon age data confirm that the surface rupture zone was produced by the 1850 M 7.5 Xichang earthquake. Gullies preserved on the youngest alluvial fans and the lowest terrace risers in the area record systematic left-lateral offsets of 1.4–6.0 m and vertical offsets of 0.2–0.65 m resulting from the 1850 earthquake. Topographic and geologic evidence reveals that the spatial distribution of the 1850 co-seismic surface rupture was controlled by pre-existing geological structures of the Zemuhe Fault. The present results confirm that the Zemuhe Fault plays an important role as a major strike-slip fault in the southeastward motion of the southeastern Tibetan Plateau, and that the southern segment of the Zemuhe Fault has high seismic potential.
During a 42 year period (1893–1935), the Swedish explorer Sven Hedin led and co-ordinated four expeditions to remote and inhospitable parts of Central Asia (Tibet, Xinjiang, Pamir). Along with collaborators he collected a diverse collection of just under 3100 petrological specimens. Petrographic examples of high pressure metamorphic blueschists, mantle peridotites and serpentinites, granitoids, K-rich alkaline lavas, mylonites, and a range of clastic and fossil rich carbonate sedimentary rocks are present. This collection is a major asset for scientists studying the history of continental collision between India and Asia, and the uplift of the Tibetan plateau.A spreadsheet listing all the samples collected during Hedin's first three expeditions into Tibet (commencing 1893, 1899, 1906) includes a brief description and location of each specimen, with additional information on the availability of thin sections. Samples are cross-referenced with the geographical position of Hedin's campsites indicated on maps published with his extensive reports. Most samples, and a number of thin sections, are available for loan from the Swedish Museum of Natural History, Stockholm. We also describe a smaller collection of specimens and thin sections from Hedin's fourth (1927–35, Sino-Swedish) expedition, currently housed at the Institute of Earth Sciences, Uppsala University. Hedin's career as an explorer, highlighting the geological significance of his work and the reasons that it has remained largely ignored by the majority of Himalayan and Central Asian researchers for so many years, is outlined.
The earthquakes of November 1951 constitute the most destructive seismic episode in the recorded history of the Longitudinal Valley, eastern Taiwan. However, information about their source parameters is sparse. To understand the relationship between the 1951 ruptures and new interpretations of the regional neotectonic architecture of the Longitudinal Valley, we re-evaluated the November 1951 ruptures by analyzing old documents, reports and photographs, and by interviewing local residents who experienced the earthquake. As a result, we have revised significantly the rupture map previously published. We divide the surface ruptures from south to north into the Chihshang, Yuli, and Rueisuei sections. The first shock of the 1951 series probably resulted from the Chihshang rupture, and the second shock probably resulted from the Yuli and Rueisuei ruptures. The lengths of these ruptures indicate that the two shocks had similar magnitudes. The Chihshang and Rueisuei ruptures are along segments of the Longitudinal Valley fault, a left-lateral oblique fault along which the Coastal Range thrusts westward over the Longitudinal Valley. The Yuli rupture, on the other hand, appears to be part of a separate, left-lateral strike-slip Yuli fault, which traverses the middle of the Longitudinal Valley. The complex behavior of these structures and interaction between them are important in understanding the future seismic hazard of the area.
The 80-km-long surface rupture of the Chelungpu fault in the 21 September 1999, Chichi, Taiwan Mw=7.6 earthquake resulted in a surface scarp with vertical throws of 2–9 m, and horizontal heaves of 4–8 m. Few major thrust faults have broken the surface in the past century, and the Chelungpu surface rupture is of interest in that it provides a morphological template for the identification of paleo-surface thrusts in similar neotectonic environments such as the Himalaya. The toe of the thrust is found emplaced gently over underlying hanging-wall materials, partly by prograde hanging-wall rotation and partly by simple shear, leaving few overt clues as to the total amount or sense of slip. Despite the large surface slip near the toe of the Chelungpu thrust its emplacement appears to have been relatively slow. MSK (the Medvedev–Sponheuer–Karnik 1981 revision of the Seismic Intensity Scale MSK81 supersedes the Mercalli Intensity scale for the description of acceleration-induced damage to modern buildings) Intensity VIII accelerations were imposed on buildings on the hanging-wall, and Intensity VII on the footwall, decaying in both directions by perhaps one intensity unit a few hundred meters from the rupture. The somewhat moderate amplitude of these accelerations, for a rupture with several meters of slip, is attributed to non-linear dissipative deformation near the toe of the rupture. The partitioning of thrusting into basal slip and hillside steepening in some locations on the Chelungpu fault suggests that the estimation of paleoseismic slip from the offset of piercing points crossing historic thrust faults elsewhere may result in underestimates of fault slip.
We summarize the structural characteristics of the surface ruptures of the 1999 Mw 7.6 Chi-Chi earthquake in western Taiwan and discuss the geological interaction of the Chelungpu fault with adjacent faults. Based on geological investigations, seismological analyses, and GPS measurements of surface co-seismic displacements, we describe the regional 3-D fault plane and slip distribution of the Chi-Chi earthquake and compare these to the geological features of the Chelungpu fault. We find that one key feature of the Chelungpu fault is the stratigraphy-controlled slip surface: at the level of the uppermost few kilometers, the Chelungpu fault slip plane generally follows the bedding plane of the Pliocene Chinshui shale. The second key feature of the Chelungpu fault is the difference in structurally geometric configuration between its northern and southern segments. The northern Fengyuan segment shows a bedding-parallel thrust fault within east-dipping strata in both footwall and hanging wall. In contrast, the southern Tsaotun segment exhibits east-dipping strata are overthrust onto flat-lying recent alluvial deposits. These two features not only explain a hinterland imbricate thrusting on the hanging-wall of the Fengyuan segment, but also explain the change in strike of the Chi-Chi surface ruptures at the northern end. The southern end of the 1999 Chi-Chi rupture is interpreted to be linked to a series of NW-trending strike-slip faults. In particular, we propose that the Luliao strike-slip fault served as the lateral ramp of the Chelungpu fault, and the Gukeng strike-slip fault acted as a barrier to end the southern propagation of the 1999 rupture. Geomorphic features and paleoseismological data indicate that the range-front Chelungpu fault has generated large earthquakes during the last several thousand years. Alternatively, in the Miaoli area to the north and the Chiayi area to south, historical earthquakes as well as active geomorphic features are not restricted on the range-front thrust faults. Instead, more complicated structures, including tightly spaced folds, duplex structures, and strike-slip faults are involved in seismogenic processes. A more detailed investigation of regional structural characteristics is needed for mitigation against the seismic hazards in the 300-km-long active fold belt in western Taiwan, where several damaging large earthquakes have been documented during the last century.
The 21 September 1999 earthquake (MW 7.6) produced a surface rupture that extended for 100-km in a general north–south direction in front of the Western Foothills, central Taiwan. The study area, located in a segment of the fold–thrust belt of central Taiwan, provides an important natural laboratory to study the relationship between active thrust deformation and fluvial terrace development. We recognize, from west to east, three subparallel thrusts, the Sanyi, Houli, and Shihkang faults in the northern part of the earthquake disaster area. The 1999 earthquake rupture occurred only along the Shihkang fault, whereas the other two faults were inactive. Along the Tachia River in the hanging wall of the Shihkang fault, eight well-developed terrace levels are observed, and can be subdivided into lateritic (Lt5–Lt1) and non-lateritic terraces (Ft3–Ft1). Five levels of lateritic terrace (Lt5–Lt1) are located in the hanging wall of the Houli fault, and a lateritic terrace (Lt5) is present in the hanging wall of the Sanyi fault. Stratigraphic and elevation correlations between these well-developed fluvial terraces in relationship to nearby geologic structures show that the Sanyi fault is the oldest structure. Lateritic terraces of at least 10,000 yr bp, for example, overlie the Sanyi fault, but correlative terraces associated with the Houli fault are offset. These types of terrace correlations allow us to define the progressive development of the thrust system within the Western Foothills.
Palynological and sedimentological studies of a series of slimes collected from a 284 m-long drill-well from the Kathmandu Basin reveal paleoclimatic records and environmental changes within the Kathmandu Valley during the last 2.5 myr. The slimes are composed of fluvio-deltaic and lacustrine sediments comprising sand beds of 66.3 m and mud beds of 218 m in length. Pollen analyses show Quercus and Cyclobalanopsis are predominant, with frequencies exceeding 70%. Pinus, Alnus and Gramineae are the next dominant taxa. Three fossil pollen zones were discriminated; each zone reflects major climatic change: Zone I, the oldest stage, indicates a cool and rather wet climate during 400 kyr from ca. 2.5 to 2.1 Ma; Zone II, the middle stage, reflects a warm and relatively dry climate without remarkable fluctuation; Zone III is characterized by seven cycles of warm-and-wet and cold-and-dry climate, which reflect the alternation of glacial and interglacial periods. The last cold maximum, 11 m deep, corresponds to the last glacial age around 20 kyr bp, judging from the 14C dating of the uppermost part of the lacustrine sediments.The Paleo-Kathmandu Lake is likely to have been initiated at around 2.1 Ma and to have been filled with black organic mud, the Kalimati Clay. The top of the Kalimati Clay is eroded and was overlain by fluvial sand after the last glacial age. The abrupt appearance of a 4 m-thick fossiliferous sand bed at the top of the middle member suggests a lowering of water level at around 1 Ma.
We investigated the characteristics of the precursory seismicity changes associated with the M=6.8 Nemuro Peninsula earthquake, January 28, 2000 by applying the RTL (Region–Time–Length) algorithm to the earthquake catalogue of the Japan Meteorological Agency (JMA). The RTL parameters at the epicentre indicated that a seismic quiescence started in 1995 and reached its minimum during October 1996. An activation stage with a duration of about eight months followed. Our detailed investigations indicated that the RTL anomaly around 1996 was not an artificial effect due to the changes of the model parameters, the upgrade of the JMA seismic network or the process of aftershock elimination. The spatial distribution of quiescence in 1996 revealed a significant anomaly in a broad region around the epicentre of the Nemuro Peninsula earthquake. Following the quiescence stage, an activation zone, which was on the order of the rupture length of this earthquake, was obtained around the epicentre during October 1996–July 1997. The consistency of the rupture region and the anomalous activation zone that appeared after the seismic quiescence stage may provide useful information for determining the future risk zones. This study may strengthen the understanding of the seismogenic process of strong earthquakes.
In this paper, we examine pre-earthquake ionospheric anomalies by the total electron content (TEC) derived from a ground-based receiver of the global positioning system (GPS). A network of eight GPS receivers is used to construct daily latitude-time-TEC (LTT) plots to monitor the crest of equatorial ionization anomaly (EIA) in the Taiwan area. Three parameters of the strength, location, and formation time of the EIA crest are extracted. A 15-day running medians of the three parameters and the associated upper and lower quartiles are utilized as the references for identifying abnormal signals for all of the 150 M ≧ 5.0 earthquakes in the Taiwan area during 2001–2007. Results show that the EIA crest significantly moves equatorward (poleward) and appears in an earlier (later) time of the afternoon period a few days before (after) the earthquakes along the Taiwan longitude. The two parameters of the EIA crest location and occurrence time can be employed to detect ionospheric earthquake precursors. The results further imply that atmospheric electric fields generated around the epicenter of a forthcoming earthquake during the preparation period are essential.
Mistakenly perceived as safe from the hazards of tsunami, Malaysia faced a rude awakening by the 26 December 2004 Andaman tsunami. Since the event, Malaysia has started active research on some aspects of tsunami, including numerical simulations of tsunami and the role of mangrove as a mitigation measure against tsunami hazards. An in-house tsunami numerical simulation model TUNA has been developed and applied to the 26 December 2004 Andaman tsunami to simulate the generation, propagation and inundation processes along affected beaches in Malaysia. Mildly nonlinear bottom friction term in the deeper ocean is excluded, as it is insignificant to the simulation results, consistent with theoretical expectation. On the other hand, in regions with shallow depth near the beaches, friction and nonlinearity are significant and are included in TUNA. Simulation results with TUNA indicate satisfactory performance when compared with COMCOT and on-site survey results.
Bad weather conditions usually limit the acquisition of optical remote sensing images, while all day and all weather synthetic aperture radar (SAR) shows the ability of providing timely remote sensing data for emergency response and rescue works after earthquake. Because SAR is sensitive to the surface changes caused by earthquake, the modified electromagnetic behaviour by geological disasters and the collapse of buildings can be recorded in SAR images as backscattering intensity changes. Absolute radiometric calibration was performed to SAR products to derive backscattering coefficient sigma nought from image digital number (DN). Based on change detection methods, Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) data and TerraSAR-X data acquired for the Ms 8.0 Wenchuan earthquake were used to extract earthquake damage information. This study revealed that landslides showed stronger backscattering and barrier lakes showed lower backscattering in post-earthquake 10 m ALOS PALSAR images comparing to pre-earthquake, and collapsed buildings showed lower backscattering compared to un-collapsed buildings in 1 m TerraSAR-X image. Results showed that SAR data with different spatial resolutions are useful for different earthquake damage information extraction: medium spatial resolution SAR data, e.g. 10 m ALOS PALSAR data, were efficient for secondary geological disaster extraction; high-resolution SAR data, e.g. 1 m TerraSAR-X data, with the help of ancillary GIS data or high-resolution optical data, could be used to extract building collapse information in urban areas. This study indicates that SAR remote sensing data can provide earthquake damage information at early emergency stage and assist the field surveying, further damage assessment and post-earthquake reconstruction.
The Ms 8.0 Wenchuan earthquake of May 12, 2008 is one of the most disastrous earthquakes in China. The earthquake triggered tens of thousands of landslides over a broad area, including shallow, disrupted landslides, rock falls, deep-seated landslides, and rock avalanches, some of which buried large sections of some towns and dammed the rivers. The purpose of this study is to investigate correlations between the occurrence of landslides with geologic and geomorphologic conditions, and seismic parameters. Over 56,000 earthquake-triggered landslides, with a total area of 811 km2, are interpreted using aerial photographs and remote sensing images taken following the earthquake. The spatial distribution of these landslides is analyzed statistically using both landslide-point density (LPD), defined as the number of landslides per square kilometer, and landslide-area density (LAD), the percentage of the area affected by landslides, to determine how the occurrence of landslides correlates with distance from the epicenter, distance from the major surface rupture, seismic intensity and peak ground acceleration (PGA), slope angle, slope aspect, elevation, and lithology. It is found that both LAD and LPD have strong positive correlations with slope steepness, distance from the major surface rupture and seismic intensity, and that Pre-Sinian schist, and Cambrian sandstone and siltstone intercalated with slate have the most concentrated landslide activities, followed by the Permian limestone intercalated with shale, and Devonian limestone. Statistical analyses also indicate that the major surface rupture has influence on the spatial distribution of landslides, because LAD and LPD are relatively higher on the hanging wall than on the footwall. However, the correlation between the occurrence of landslides with distance from the epicenter of the earthquake is complicated, rather than a relatively simple negative correlation as found from other reported cases of earthquakes. This is possibly due to complicated rupture processes of the earthquake.
The May 12, 2008, Mw 7.9 Wenchuan earthquake was induced by failure of two of the major faults of the Longmen Shan thrust fault zone along the eastern margin of Tibet Plateau. Our study focused on trenches across the Yingxiu–Bichuan fault, the central fault in the Longmen Shan belt that has a coseismic surface break of more than 200 km long. Trenching excavation across the 2008 earthquake rupture on three representative sites reveals the styles and amounts of the deformation and paleoseismicity along the Longmen Shan fault. Styles of coseismic deformation along the 2008 earthquake rupture at these three sites represent three models of deformation along a thrust fault. Two of the three trench exposures reveal one pre-2008 earthquake event, which is coincident with the pre-existing scarps. Based on the observation of exposed stratigraphy and structures in the trenches and the geomorphic expressions on ground surface, we interpret the 2008 earthquake as a characteristic earthquake along this fault. The interval of reoccurrence of large earthquake events on the Central Longmen Shan fault (the Yingxiu–Beichuan fault) can be inferred to be about 11,000 years according to 14C and OSL dating. The amounts of the vertical displacement and shortening across the surface rupture during the 2008 earthquake are determined to be 1.0–2.8 m and 0.15–1.32 m, respectively. The shortening rate and uplift rate are then estimated to be 0.09–0.12 mm/yr and 0.18–0.2 mm/yr, respectively. It is indicated that the deformation is absorbed mainly not by shortening, but by uplift along the rupture during the 2008 earthquake.
A Mw 6.3 magnitude earthquake occurred on October 6, 2008 in southern Damxung County within the N–S trending Yangyi graben, which forms the northern section of the Yadong-Gulu rift of south-central Tibet. The earthquake had a maximum intensity of IX at the village of Yangyi (also Yangying) (29°43.3′N; 90°23.6′E) and resulted in 10 deaths and 60 injured in this sparsely populated region. Field observations and focal mechanism solutions show normal fault movement occurred along the NNE-trending western boundary fault of the Yangyi graben, in agreement with the felt epicenter, pattern of the isoseismal contours, and distribution of aftershocks. The earthquake and its tectonic relations were studied in detail to provide data on the seismic hazard to the nearby city of Lhasa.
This study attempts to analyse paleoceanographic changes in the Central Indian Ocean (Deep Sea Drilling Project Site 237), linked to monsoon variability as well as deep-sea circulation during the Plio-Pleistocene. We used factor and cluster analyses of census data of the 34 most dominant species of benthic foraminifera that enabled us to identify five biofacies: Astrononion umbilicatulum–Uvigerina proboscidea (Au–Up), Pullenia bulloides–Bulimina striata (Pb–Bs), Globocassidulina tumida–Nuttallides umbonifera (Gt–Nu), Gyroidinoides nitidula–Cibicides wuellerstorfi (Gn–Cw) and Cassidulina carinata–Cassidulina laevigata (Cc–Cl) biofacies. Knowledge of the environmental preferences of modern deep-sea benthic foraminifera helped to interpret the results of factor and cluster analyses in combination with oxygen and carbon isotope values. The biofacies indicative of high surface productivity, resulting from a stronger South Equatorial Current (Au–Up and Pb–Bs biofacies), dominate the early Pliocene interval (5.6–4.5 Ma) of global warmth. An intense Indo-Pacific ‘biogenic bloom’ and strong Oxygen Minimum Zone extended to intermediate depths (∼1000–2000 m) over large parts of the Indian Ocean in the early Pliocene. Since 4.5 Ma, the food supply in the Central Indian Ocean dropped and fluctuated while deep waters were corrosive (biofacies Gt–Nu, Gn–Cw). The Pleistocene interval is characterized by an intermediate flux of organic matter (Cc–Cl biofacies).
This work deals with 2D thermal modeling in order to delineate the crustal thermal structure of central India along two Deep Seismic Sounding (DSS) profiles, namely Khajuriakalan–Pulgaon and Ujjan–Mahan, traversing the Narmada-Son-Lineament (NSL) in an almost north–south direction. Knowledge of the crustal structure and P-wave velocity distribution up to the Moho, obtained from DSS studies, has been used for the development of the thermal model. Numerical results reveal that the Moho temperature in this region of central India varies between 500 and 580 °C. The estimated heat flow density value is found to vary between 46 and 49 mW/m2. The Curie depth varies between 40 and 42 km and is in close agreement with the Curie depth (40±4 km) estimated from the analysis of MAGSAT data. Based on the present work and previous work, it is suggested that the major part of peninsular India consisting of the Wardha–Pranhita Godavari graben/basin, Bastar craton and the adjoining region of the Narmada Son Lineament between profiles I and III towards the north and northwest of the Bastar craton are characterized with a similar mantle heat flow density value equal to ∼23 mW/m2. Variation in surface heat flow density values in these regions are caused by variation in the radioactive heat production and fluid circulation in the upper crustal layer.