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
The East Kunlun active fault zone, which lies in the valley of the Kunlun Mountains above an elevation of 4,000 meters, is an important active fault zone in the Northeast Qinghai-Xizang (Tibet) Plateau. The 1937, the ...The East Kunlun active fault zone, which lies in the valley of the Kunlun Mountains above an elevation of 4,000 meters, is an important active fault zone in the Northeast Qinghai-Xizang (Tibet) Plateau. The 1937, the Tosonhu lake M_S7.5 earthquake occurred in the eastern segment of the East Kunlun active fault zone. Four field investigations were launched on this seism in 1963, 1971, 1980, and between 1986 and 1990. However, due to different extents of the investigations, four different conclusions have been gained. Concerning the length aspect of the surface rupture zone of this earthquake, the unanimous consensus is that its eastern end lies in the west side of the main Ridge of the A'nyêmaqên Mountains, but opinions about the western end and the location of the macro-epicenter are different. Based on investigation and comprehensive study, a series of scientific problems like geometric and kinetic characteristics, the length of the rupture zone, the maximum sinistral horizontal displacement and the macro-epicenter were re-evaluated. We believe that the total length of this earthquake's surface deformation zone is at least 240km; the western end of the zone is at the west of Wusuwuwoguole; the maximum sinistral horizontal displacement is 8m to the west of Baerhalasha gully on the east side of Sanchakou; the maximum vertical displacement is 3.5m in the south of Sanchakou and the macro-epicenter is in Sanchakou.展开更多
The Kunlun Fault,an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks,is one of the major left lateral strike-slip faults in the Tibetan Plateau.Previous research has not reached a consensus on...The Kunlun Fault,an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks,is one of the major left lateral strike-slip faults in the Tibetan Plateau.Previous research has not reached a consensus on agreeable slip rates along much of its length and the slip rate gradient along the eastern part,both of which play critical roles in a range of models for the eastward extrusion and thickened crust of the Tibetan Plateau.New slip rates have been determined at sites along the eastern part of the Kunlun Fault by dating deposits and measuring atop displaced fluvial terrace risers.Field investigations and interpretation of satellite images reveal geometrical features of the fault and the late Quaternary offset,new earthquake ruptures and surface-rupturing segmentation,from which long-term slip rates and earthquake recurrence intervals on the fault are estimated.The tectonic geomorphology method has determined that the long-term horizontal slip rates on the Tuosuohu,Maqin and Maqu segments from west to east are 11.2±1,9.3±2,and 4.9±1.3 mm/a while their vertical slip rates are 1.2±0.2,0.7±0.1,and 0.3 mm/a in the late Quaternary.Results indicate that the slip rates regularly decrease along the eastern ～300 km of the fault from >10 to <5 mm/a.This is consistent with the decrease in the gradient such that at the slip rate break point is at the triple point intersection with the transverse fault,which in turn is transformed to the Awancang Fault.The vector decomposition for this tectonic transformation shows that the western and eastern branches of the Awancang Fault fit the slip-partitioning mode.The slip rate of the southwestern wall is 4.6 mm/a relative to the northeastern wall and the slip direction is 112.1°.The mid-eastern part of the Kunlun Fault can be divided into three independent segments by the A'nyêmaqên double restraining bend and the Xigongzhou intersection zone,which compose the surface rupture segmentation indicators for themselves as well as the ending point of the 1937 M7.5 Tuosuohu earthquake.The average recurrence interval of the characteristic earthquakes are estimated to be 500-1000 a,respectively.The latest earthquake ruptures occurred in AD 1937 on the western Tuosuohu segment,as compared to ～514-534 a BP on the Maqin segment,and ～1055 to 1524 a BP on the Maqu segment.This may indicate a unidirectional migration for surface rupturing earthquakes along the mid-eastern Kunlun Fault related to stress triggered between these segments.Meanwhile,the long-term slip rate is obtained through the single event offset and the recurrence interval,which turn out to be the same results as those determined by the offset tectonic geomorphology method,i.e.,the decreasing gradient corresponds to the geometrical bending and the fault's intersection with the transverse fault.Therefore,the falling slip rate gradient of the mid-eastern Kunlun Fault is mainly caused by eastward extension of the fault and its intersection with the transverse fault.展开更多
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 Science Foundation (Grant No.40474037) and by the Special Programfor Early-stage Investigation of National Major Basic Research of the Ministry of Science and Technology,China (Grant No.JC200016)
文摘The East Kunlun active fault zone, which lies in the valley of the Kunlun Mountains above an elevation of 4,000 meters, is an important active fault zone in the Northeast Qinghai-Xizang (Tibet) Plateau. The 1937, the Tosonhu lake M_S7.5 earthquake occurred in the eastern segment of the East Kunlun active fault zone. Four field investigations were launched on this seism in 1963, 1971, 1980, and between 1986 and 1990. However, due to different extents of the investigations, four different conclusions have been gained. Concerning the length aspect of the surface rupture zone of this earthquake, the unanimous consensus is that its eastern end lies in the west side of the main Ridge of the A'nyêmaqên Mountains, but opinions about the western end and the location of the macro-epicenter are different. Based on investigation and comprehensive study, a series of scientific problems like geometric and kinetic characteristics, the length of the rupture zone, the maximum sinistral horizontal displacement and the macro-epicenter were re-evaluated. We believe that the total length of this earthquake's surface deformation zone is at least 240km; the western end of the zone is at the west of Wusuwuwoguole; the maximum sinistral horizontal displacement is 8m to the west of Baerhalasha gully on the east side of Sanchakou; the maximum vertical displacement is 3.5m in the south of Sanchakou and the macro-epicenter is in Sanchakou.
基金supported by National Natural Science Foundation of China (Grant Nos. 40821160550 and 40974057)International Scientific Joint Project of China (Grant No. 2009DFA21280)
文摘The Kunlun Fault,an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks,is one of the major left lateral strike-slip faults in the Tibetan Plateau.Previous research has not reached a consensus on agreeable slip rates along much of its length and the slip rate gradient along the eastern part,both of which play critical roles in a range of models for the eastward extrusion and thickened crust of the Tibetan Plateau.New slip rates have been determined at sites along the eastern part of the Kunlun Fault by dating deposits and measuring atop displaced fluvial terrace risers.Field investigations and interpretation of satellite images reveal geometrical features of the fault and the late Quaternary offset,new earthquake ruptures and surface-rupturing segmentation,from which long-term slip rates and earthquake recurrence intervals on the fault are estimated.The tectonic geomorphology method has determined that the long-term horizontal slip rates on the Tuosuohu,Maqin and Maqu segments from west to east are 11.2±1,9.3±2,and 4.9±1.3 mm/a while their vertical slip rates are 1.2±0.2,0.7±0.1,and 0.3 mm/a in the late Quaternary.Results indicate that the slip rates regularly decrease along the eastern ～300 km of the fault from >10 to <5 mm/a.This is consistent with the decrease in the gradient such that at the slip rate break point is at the triple point intersection with the transverse fault,which in turn is transformed to the Awancang Fault.The vector decomposition for this tectonic transformation shows that the western and eastern branches of the Awancang Fault fit the slip-partitioning mode.The slip rate of the southwestern wall is 4.6 mm/a relative to the northeastern wall and the slip direction is 112.1°.The mid-eastern part of the Kunlun Fault can be divided into three independent segments by the A'nyêmaqên double restraining bend and the Xigongzhou intersection zone,which compose the surface rupture segmentation indicators for themselves as well as the ending point of the 1937 M7.5 Tuosuohu earthquake.The average recurrence interval of the characteristic earthquakes are estimated to be 500-1000 a,respectively.The latest earthquake ruptures occurred in AD 1937 on the western Tuosuohu segment,as compared to ～514-534 a BP on the Maqin segment,and ～1055 to 1524 a BP on the Maqu segment.This may indicate a unidirectional migration for surface rupturing earthquakes along the mid-eastern Kunlun Fault related to stress triggered between these segments.Meanwhile,the long-term slip rate is obtained through the single event offset and the recurrence interval,which turn out to be the same results as those determined by the offset tectonic geomorphology method,i.e.,the decreasing gradient corresponds to the geometrical bending and the fault's intersection with the transverse fault.Therefore,the falling slip rate gradient of the mid-eastern Kunlun Fault is mainly caused by eastward extension of the fault and its intersection with the transverse fault.
