The Longmenshan-Longriba region is located on the eastern edge of the Tibetan Plateau, and is an ideal place to study the eastward extrusion and uplift mechanism of the plateau. Previous studies on this area mainly fo...The Longmenshan-Longriba region is located on the eastern edge of the Tibetan Plateau, and is an ideal place to study the eastward extrusion and uplift mechanism of the plateau. Previous studies on this area mainly focused on tectonic activity and seismic hazard, with few studies giving its overall deformation characteristics and dynamic mechanism. This paper uses the latest dense GPS data, combined with precise Leveling data to analyze the kinematic characteristics and deformation mode of the Longmenshan fault zone (LMSF) and the Longriba fault zone (LRBF). The results show that both the Longmenshan fault zone and the Longriba fault zone have certain right-lateral strike-slip and thrusting, indicating that they play an important role in adjusting strain distribution and absorbing tectonic deformation;The strain-rate field on the Longriba fault zone is broadly distributed, suggesting that the deformation field is at least partially coupled;while the strain-rate field on the Longmenshan fault zone presents a non-uniform distribution, indicating different dynamic sources acting on segments. The high strain rate areas revealed in this study points us to the high-risk area for future earthquakes. The present-day vertical motion velocity field in the region obtained from Leveling and GPS data shows a mismatch between the regional deformation field and active tectonics, which can be explained by the incomplete coupling of deformation between the lower and upper crust.展开更多
Little attention had been paid to the intracontinental strike-slip faults of the Tibetan Plateau. Since the discovery of the Longriba fault using re-measured GPS data in 2003, an increasing amount of attention has bee...Little attention had been paid to the intracontinental strike-slip faults of the Tibetan Plateau. Since the discovery of the Longriba fault using re-measured GPS data in 2003, an increasing amount of attention has been paid to this neglected fault. The local relief and transverse swath profile show that the Longriba fault is the boundary line that separates the high and flat tomography of the Tibet plateau from the high and precipitous tomography of Orogen. In addition, GPS data shows that the Longriba fault is the boundary line where the migratory direction of the Bayan Har block changed from eastward to southeastward. The GPS data shows that the Longriba fault is the boundary fault of the sub-blocks of the eastern Bayan Har block. We built three-dimensional models containing the Longriba fault and the middle segment of the Longmenshan fault, across the Bayan Har block and the Sichuan Basin. A nonlinear finite element method was used to simulate the fault behavior and the block deformation of the Eastern Tibetan Plateau. The results show that the low resistivity and low velocity layer acts as a detachment layer, which causes the overlying blocks to move southeastward. The detachment layer also controls the vertical and horizontal deformation of the rigid Bayan Har block and leads to accumulation strain on the edge of the layer where the Longmenshan thrust is located. After a sufficient amount of strain has been accumulated on the Longmenshan fault, a large earthquake occurs, such as the 2008 Wenchuan earthquake. The strike slip activity of the Longriba fault, which is above the low resistivity and low velocity layer, partitions the lateral displacements of the Bayan Har block and adjusts the direction of motion of the Bayan Har block, from the eastward moving Ahba sub-block in the west to southeastward moving Longmenshan sub-block in the east. Four models with different depths to the Longriba fault were constructed： （1） a shallow fault with a depth of only 4 km, （2） a deeper fault that is half as deep as the Longmenshan fault, （3） a deep fault that is 2 km shallower than the low resistivity and low velocity layer, and （4） a fault that is as deep as the low resistivity and low velocity layer. The activity and influence of the Longriba fault with different development stage under this tectonic system were shown： in one Earthquake recurrence period, the rupture region of the fault increases with the depth of the fault, and the lateral slip partition by the fault also changes with the fault depth. It suggests that the Longriba fault is a newly generated fault that developed after the quick uplift in Late Cenozoic along this tectonic setting and gradually extended from the northwest to southeast. The calculations provide the characteristic of block deformation and fault behaviors of intra-continental strike-slip fault and major boundary thrust faults in the eastern margin of the Tibet plateau. Although the low resistivity and low velocity layer controls the deformation of the Bayan Hat block and the uplift of the Longmenshan thrust, the partition of the Longriba fault has an important influence on the intra-plate deformation and modern geomorphic evolution.展开更多
The eastern margin of Tibetan Plateau is one of the most active zones of tectonic deformation and seismicity in China. To monitor strain buildup and benefit seismic risk assessment, we constructed 14 survey-mode globa...The eastern margin of Tibetan Plateau is one of the most active zones of tectonic deformation and seismicity in China. To monitor strain buildup and benefit seismic risk assessment, we constructed 14 survey-mode global position system （GPS） stations throughout the northwest of Longmenshan fault. A new GPS field over 1999-2011 is derived from measurements of the newly built and pre-existing stations in this region. Sequentially, two strain rate fields, one preceding and the other following the 2008 MwT.9 Wenchuan earthquake, are obtained using the Gausian weighting approach. Strain field over 1999-2007 shows distinct strain partitioning prior to the 2008 MwT.9 Wenchuan earthquake, with compression spreading over around Longmenshan area. Strain fieldderived from the two measurements in 2009 and 2011 shows that the area around Longmenshan continues to be under striking compression, as the pattern preceding the Wenchuan earthquake, implying a causative factor of the sequent of 2013 Mw6.7 Lushan earthquake. Our GPSderived dilatation shows that both the Wenchuan and Lushan earthquakes occurred within the domain of pro- nounced contraction. The GPS velocities demonstrate that the Longriba fault underwent slight motion with the faultnormal and -parallel rates at 1.0 -4- 2.5 mm and 0.3 4-2.2 mm/a; the Longmenshan fault displayed slow activity, with a fault-normal rate at 0.8 ± 2.5 mm/a, and a fault-parallel rate at 1.8 4- 1.7 mm/a. Longriba fault is on a par with Longmenshan fault in strain partitioning to accommodate the southeastward motion of eastern margin of the Tibetan Plateau. Integrated analysis of principal strain tensors, mean principal stress, and fast directions of mantle anisotropy shows that west of Sichuan is characterized as mechanically strong crust-mantle coupling.展开更多
1研究背景2022年6月10日在四川阿坝藏族羌族州马尔康市发生M_(S) 6.0震群,其中6月10日00时03分09秒发生M_(S) 5.8(M_(L) 6.3)地震,相隔1 h 25 min 25 s发生M_(S) 6.0(M_(L) 6.5)地震,又相隔1 h 58 min 26 s发生M_(S) 5.2(M_(L) 5.6)地...1研究背景2022年6月10日在四川阿坝藏族羌族州马尔康市发生M_(S) 6.0震群,其中6月10日00时03分09秒发生M_(S) 5.8(M_(L) 6.3)地震,相隔1 h 25 min 25 s发生M_(S) 6.0(M_(L) 6.5)地震,又相隔1 h 58 min 26 s发生M_(S) 5.2(M_(L) 5.6)地震。由此可见,在3.5小时内连续发生3次5级以上地震,多次震级相近地震的间隔时间相当短,给震群中每次较强地震发生后的趋势研判增加了难度。展开更多
文摘The Longmenshan-Longriba region is located on the eastern edge of the Tibetan Plateau, and is an ideal place to study the eastward extrusion and uplift mechanism of the plateau. Previous studies on this area mainly focused on tectonic activity and seismic hazard, with few studies giving its overall deformation characteristics and dynamic mechanism. This paper uses the latest dense GPS data, combined with precise Leveling data to analyze the kinematic characteristics and deformation mode of the Longmenshan fault zone (LMSF) and the Longriba fault zone (LRBF). The results show that both the Longmenshan fault zone and the Longriba fault zone have certain right-lateral strike-slip and thrusting, indicating that they play an important role in adjusting strain distribution and absorbing tectonic deformation;The strain-rate field on the Longriba fault zone is broadly distributed, suggesting that the deformation field is at least partially coupled;while the strain-rate field on the Longmenshan fault zone presents a non-uniform distribution, indicating different dynamic sources acting on segments. The high strain rate areas revealed in this study points us to the high-risk area for future earthquakes. The present-day vertical motion velocity field in the region obtained from Leveling and GPS data shows a mismatch between the regional deformation field and active tectonics, which can be explained by the incomplete coupling of deformation between the lower and upper crust.
基金the project of National Natural Science Foundation of China (Grant No.41004037 and 41202235)
文摘Little attention had been paid to the intracontinental strike-slip faults of the Tibetan Plateau. Since the discovery of the Longriba fault using re-measured GPS data in 2003, an increasing amount of attention has been paid to this neglected fault. The local relief and transverse swath profile show that the Longriba fault is the boundary line that separates the high and flat tomography of the Tibet plateau from the high and precipitous tomography of Orogen. In addition, GPS data shows that the Longriba fault is the boundary line where the migratory direction of the Bayan Har block changed from eastward to southeastward. The GPS data shows that the Longriba fault is the boundary fault of the sub-blocks of the eastern Bayan Har block. We built three-dimensional models containing the Longriba fault and the middle segment of the Longmenshan fault, across the Bayan Har block and the Sichuan Basin. A nonlinear finite element method was used to simulate the fault behavior and the block deformation of the Eastern Tibetan Plateau. The results show that the low resistivity and low velocity layer acts as a detachment layer, which causes the overlying blocks to move southeastward. The detachment layer also controls the vertical and horizontal deformation of the rigid Bayan Har block and leads to accumulation strain on the edge of the layer where the Longmenshan thrust is located. After a sufficient amount of strain has been accumulated on the Longmenshan fault, a large earthquake occurs, such as the 2008 Wenchuan earthquake. The strike slip activity of the Longriba fault, which is above the low resistivity and low velocity layer, partitions the lateral displacements of the Bayan Har block and adjusts the direction of motion of the Bayan Har block, from the eastward moving Ahba sub-block in the west to southeastward moving Longmenshan sub-block in the east. Four models with different depths to the Longriba fault were constructed： （1） a shallow fault with a depth of only 4 km, （2） a deeper fault that is half as deep as the Longmenshan fault, （3） a deep fault that is 2 km shallower than the low resistivity and low velocity layer, and （4） a fault that is as deep as the low resistivity and low velocity layer. The activity and influence of the Longriba fault with different development stage under this tectonic system were shown： in one Earthquake recurrence period, the rupture region of the fault increases with the depth of the fault, and the lateral slip partition by the fault also changes with the fault depth. It suggests that the Longriba fault is a newly generated fault that developed after the quick uplift in Late Cenozoic along this tectonic setting and gradually extended from the northwest to southeast. The calculations provide the characteristic of block deformation and fault behaviors of intra-continental strike-slip fault and major boundary thrust faults in the eastern margin of the Tibet plateau. Although the low resistivity and low velocity layer controls the deformation of the Bayan Hat block and the uplift of the Longmenshan thrust, the partition of the Longriba fault has an important influence on the intra-plate deformation and modern geomorphic evolution.
基金supported by the National Natural Science Foundation of China (Nos. 41174004, 41461164004, 41491240265)International Science & Technology Collaborative Program of China (No. 2010DFB20190)+2 种基金the project of Far Eastern Federal University, Russia (14-08-01-05_m)State Key Basic Research Development and Programming Project of China (No. 2008CB425704)Basic Research Program of the Institute of Earthquake Science, CEA (No. 2014IES010102)
文摘The eastern margin of Tibetan Plateau is one of the most active zones of tectonic deformation and seismicity in China. To monitor strain buildup and benefit seismic risk assessment, we constructed 14 survey-mode global position system （GPS） stations throughout the northwest of Longmenshan fault. A new GPS field over 1999-2011 is derived from measurements of the newly built and pre-existing stations in this region. Sequentially, two strain rate fields, one preceding and the other following the 2008 MwT.9 Wenchuan earthquake, are obtained using the Gausian weighting approach. Strain field over 1999-2007 shows distinct strain partitioning prior to the 2008 MwT.9 Wenchuan earthquake, with compression spreading over around Longmenshan area. Strain fieldderived from the two measurements in 2009 and 2011 shows that the area around Longmenshan continues to be under striking compression, as the pattern preceding the Wenchuan earthquake, implying a causative factor of the sequent of 2013 Mw6.7 Lushan earthquake. Our GPSderived dilatation shows that both the Wenchuan and Lushan earthquakes occurred within the domain of pro- nounced contraction. The GPS velocities demonstrate that the Longriba fault underwent slight motion with the faultnormal and -parallel rates at 1.0 -4- 2.5 mm and 0.3 4-2.2 mm/a; the Longmenshan fault displayed slow activity, with a fault-normal rate at 0.8 ± 2.5 mm/a, and a fault-parallel rate at 1.8 4- 1.7 mm/a. Longriba fault is on a par with Longmenshan fault in strain partitioning to accommodate the southeastward motion of eastern margin of the Tibetan Plateau. Integrated analysis of principal strain tensors, mean principal stress, and fast directions of mantle anisotropy shows that west of Sichuan is characterized as mechanically strong crust-mantle coupling.
文摘1研究背景2022年6月10日在四川阿坝藏族羌族州马尔康市发生M_(S) 6.0震群,其中6月10日00时03分09秒发生M_(S) 5.8(M_(L) 6.3)地震,相隔1 h 25 min 25 s发生M_(S) 6.0(M_(L) 6.5)地震,又相隔1 h 58 min 26 s发生M_(S) 5.2(M_(L) 5.6)地震。由此可见,在3.5小时内连续发生3次5级以上地震,多次震级相近地震的间隔时间相当短,给震群中每次较强地震发生后的趋势研判增加了难度。
