On April 14, 2010 at 07:49 (Beijing time), a catastrophic earthquake with MS7.1 occurred at the central Qinghai-Tibetan Plateau. The epicenter was located at Yushu county, Qinghai Province, China. A total of 2036 land...On April 14, 2010 at 07:49 (Beijing time), a catastrophic earthquake with MS7.1 occurred at the central Qinghai-Tibetan Plateau. The epicenter was located at Yushu county, Qinghai Province, China. A total of 2036 landslides were determined from visual interpretation of aerial photographs and high resolution remote sensing images, and verified by selected field investigations. These landslides covered a total area of about 1.194km2. Characteristics and failure mechanisms of these landslides are listed in this paper, including the fact that the spatial distribution of these landslides is controlled by co-seismic main surface fault ruptures. Most of the landslides were small scale, causing rather less hazards, and often occurring close to each other. The landslides were of various types, including mainly disrupted landslides and rock falls in shallows and also deep-seated landslides, liquefaction induced landslides, and compound landslides. In addition to strong ground shaking, which is the direct landslide triggering factor, geological, topographical, and human activity also have impact on the occurrence of earthquake triggered landslides. In this paper, five types of failure mechanisms related to the landslides are presented, namely, the excavated toes of slopes accompanied by strong ground shaking; surface water infiltration accompanied by strong ground shaking; co-seismic fault slipping accompanied by strong ground shaking; only strong ground shaking; and delayed occurrence of landslides due to snow melt or rainfall infiltration at sites where slopes were weakened by co-seismic ground shaking. Besides the main co-seismic surface ruptures, slope fissures were also delineated from visual interpretation of aerial photographs in high resolution. A total of 4814 slope fissures, with a total length up to 77.1km, were finally mapped. These slope fissures are mainly distributed on the slopes located at the southeastern end of the main co-seismic surface rupture zone, an area subject to strong compression during the earthquake.展开更多
On May 12th, 2008, the Mw7.9 Wenchuan earthquake ruptured the Beichuan, Pengguan and Xiaoyudong faults simultaneously along the middle segment of the Longmenshan thrust belt at the eastern margin of the Tibetan platea...On May 12th, 2008, the Mw7.9 Wenchuan earthquake ruptured the Beichuan, Pengguan and Xiaoyudong faults simultaneously along the middle segment of the Longmenshan thrust belt at the eastern margin of the Tibetan plateau. Field investigations constrain the surface rupture pattern, length and offsets related to the Wenchuan earthquake. The Beichuan fault has a NE-trending rightlateral reverse rupture with a total length of 240 km. Reassessment yields a maximum vertical offset of 6.5±0.5 m and a maximum right-lateral offset of 4.9±0.5 m for its northern segment, which are the largest offsets found; the maximum vertical offset is 6.2±0.5 m for its southern segment. The Pengguan fault has a NE-trending pure reverse rupture about 72 km long with a maximum vertical offset of about 3.5 m. The Xiaoyudong fault has a NW-striking left-lateral reverse rupture about 7 km long between the Beichuan and Pengguan faults, with a maximum vertical offset of 3.4 m and left-lateral offset of 3.5 m. This pattern of multiple co-seismic surface ruptures is among the most complicated of recent great earthquakes and presents a much larger danger than if they ruptured individually. The rupture length is the longest for reverse faulting events ever reported.展开更多
Re-measured GPS data have recently revealed that a broad NE trending dextral shear zone exists in the eastern Bayan Har block about 200 km northwest of the Longmenshan thrust on the eastern margin of the Qinghai-Tibet...Re-measured GPS data have recently revealed that a broad NE trending dextral shear zone exists in the eastern Bayan Har block about 200 km northwest of the Longmenshan thrust on the eastern margin of the Qinghai-Tibet Plateau. The strain rate along this shear zone may reach up to 4-6 mm/a. Our interpretation of satellite images and field observations indicate that this dextral shear zone corresponds to a newly generated NE trending Longriba fault zone that has been ignored before. The northeast segment of the Longriba fault zone consists of two subparallel N54°±5°E trending branch faults about 30 km apart, and late Quaternary offset landforms are well developed along the strands of these two branch faults. The northern branch fault, the Longriqu fault, has relatively large reverse component, while the southern branch fault, the Maoergai fault, is a pure right-lateral strike slip fault. According to vector synthesizing principle, the average right-lateral strike slip rate along the Longriba fault zone in the late Quaternary is calculated to be 5.4±2.0 mm/a, the vertical slip rate to be 0.7 mm/a, and the rate of crustal shortening to be 0.55 mm/a. The discovery of the Longriba fault zone may provide a new insight into the tectonics and dynamics of the eastern margin of the Qinghai-Tibet Plateau. Taken the Longriba fault zone as a boundary, the Bayan Har block is divided into two sub-blocks: the Ahba sub-block in the west and the Longmenshan sub-block in the east. The shortening and uplifting of the Longmenshan sub-block as a whole reflects that both the Longmenshan thrust and Longriba fault zone are subordinated to a back propagated nappe tectonic system that was formed during the southeastward motion of the Bayan Har block owing to intense resistance of the South China block. This nappe tectonic system has become a boundary tectonic type of an active block supporting crustal deformation along the eastern margin of the Qinghai-Tibet Plateau from late Cenozoic till now. The Longriba fault zone is just an active fault zone newly-generated in late Quaternary along this tectonic system.展开更多
基金sponsored by the National Natural Science Foundation,China(40821160550),supported by the National Natural Science Foundation of China (41202235 )the Basic Scientific Fund of the Institute of Geology, China Earthquake Administration (IGCEA1215)
文摘On April 14, 2010 at 07:49 (Beijing time), a catastrophic earthquake with MS7.1 occurred at the central Qinghai-Tibetan Plateau. The epicenter was located at Yushu county, Qinghai Province, China. A total of 2036 landslides were determined from visual interpretation of aerial photographs and high resolution remote sensing images, and verified by selected field investigations. These landslides covered a total area of about 1.194km2. Characteristics and failure mechanisms of these landslides are listed in this paper, including the fact that the spatial distribution of these landslides is controlled by co-seismic main surface fault ruptures. Most of the landslides were small scale, causing rather less hazards, and often occurring close to each other. The landslides were of various types, including mainly disrupted landslides and rock falls in shallows and also deep-seated landslides, liquefaction induced landslides, and compound landslides. In addition to strong ground shaking, which is the direct landslide triggering factor, geological, topographical, and human activity also have impact on the occurrence of earthquake triggered landslides. In this paper, five types of failure mechanisms related to the landslides are presented, namely, the excavated toes of slopes accompanied by strong ground shaking; surface water infiltration accompanied by strong ground shaking; co-seismic fault slipping accompanied by strong ground shaking; only strong ground shaking; and delayed occurrence of landslides due to snow melt or rainfall infiltration at sites where slopes were weakened by co-seismic ground shaking. Besides the main co-seismic surface ruptures, slope fissures were also delineated from visual interpretation of aerial photographs in high resolution. A total of 4814 slope fissures, with a total length up to 77.1km, were finally mapped. These slope fissures are mainly distributed on the slopes located at the southeastern end of the main co-seismic surface rupture zone, an area subject to strong compression during the earthquake.
基金supported by the National Basic Research Program of China(Grant No.2004CB418401)National Science Foundation of China(grant No.40841007)
文摘On May 12th, 2008, the Mw7.9 Wenchuan earthquake ruptured the Beichuan, Pengguan and Xiaoyudong faults simultaneously along the middle segment of the Longmenshan thrust belt at the eastern margin of the Tibetan plateau. Field investigations constrain the surface rupture pattern, length and offsets related to the Wenchuan earthquake. The Beichuan fault has a NE-trending rightlateral reverse rupture with a total length of 240 km. Reassessment yields a maximum vertical offset of 6.5±0.5 m and a maximum right-lateral offset of 4.9±0.5 m for its northern segment, which are the largest offsets found; the maximum vertical offset is 6.2±0.5 m for its southern segment. The Pengguan fault has a NE-trending pure reverse rupture about 72 km long with a maximum vertical offset of about 3.5 m. The Xiaoyudong fault has a NW-striking left-lateral reverse rupture about 7 km long between the Beichuan and Pengguan faults, with a maximum vertical offset of 3.4 m and left-lateral offset of 3.5 m. This pattern of multiple co-seismic surface ruptures is among the most complicated of recent great earthquakes and presents a much larger danger than if they ruptured individually. The rupture length is the longest for reverse faulting events ever reported.
基金the National Basic Research Program of China (Grant No. 2004CB418401)the National Natural Science Foundation of China (Grant No. 40474037)
文摘Re-measured GPS data have recently revealed that a broad NE trending dextral shear zone exists in the eastern Bayan Har block about 200 km northwest of the Longmenshan thrust on the eastern margin of the Qinghai-Tibet Plateau. The strain rate along this shear zone may reach up to 4-6 mm/a. Our interpretation of satellite images and field observations indicate that this dextral shear zone corresponds to a newly generated NE trending Longriba fault zone that has been ignored before. The northeast segment of the Longriba fault zone consists of two subparallel N54°±5°E trending branch faults about 30 km apart, and late Quaternary offset landforms are well developed along the strands of these two branch faults. The northern branch fault, the Longriqu fault, has relatively large reverse component, while the southern branch fault, the Maoergai fault, is a pure right-lateral strike slip fault. According to vector synthesizing principle, the average right-lateral strike slip rate along the Longriba fault zone in the late Quaternary is calculated to be 5.4±2.0 mm/a, the vertical slip rate to be 0.7 mm/a, and the rate of crustal shortening to be 0.55 mm/a. The discovery of the Longriba fault zone may provide a new insight into the tectonics and dynamics of the eastern margin of the Qinghai-Tibet Plateau. Taken the Longriba fault zone as a boundary, the Bayan Har block is divided into two sub-blocks: the Ahba sub-block in the west and the Longmenshan sub-block in the east. The shortening and uplifting of the Longmenshan sub-block as a whole reflects that both the Longmenshan thrust and Longriba fault zone are subordinated to a back propagated nappe tectonic system that was formed during the southeastward motion of the Bayan Har block owing to intense resistance of the South China block. This nappe tectonic system has become a boundary tectonic type of an active block supporting crustal deformation along the eastern margin of the Qinghai-Tibet Plateau from late Cenozoic till now. The Longriba fault zone is just an active fault zone newly-generated in late Quaternary along this tectonic system.
