科研之友
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摘要
Based on the concept of active blocks, we analyze the major active faults and secondary faults, historical earthquakes, field geological investigation, and other data, then divide the eastern segment of Bayan Har block and its adjacent regions into four first grade blocks: Bayan Har block(I), South China block(II), Sichuan-Yunnan block(III), and West Qinling block(IV). According to GPS velocities, data of geophysical fields and geomorphological features, we further divide the Bayan Har block into three subblocks, Aba (I-1), Maerkang (I-2), and Longmenshan (I-3), and divide the Xiqinling block into two subblocks, Minxian (IV1) and Lixian (IV2), and then check the relative independence among those blocks by F-test. The modern translation and rotation rates of those blocks were calculated using the GPS data from the Crustal Motion Observation Network of China between 1999 and 2007. The results show that besides the eastward or southeastward translation the subblocks also rotate around the Euler pole; the slip rates for the eastern Kunlun fault, Ganzi-Yushu fault, and the Xianshuihe fault are much higher than that for the Longmenshan fault; the faults trending northwest or northwest-west show apparently left-lateral strike-slip and with a tensile characteristic, and those faults trending northeast show obviously right-lateral strike-slip and compression characteristics, except for the Chengxian-Taibai fault which shows left-lateral and compression characteristics. The eastward motion of Bayan Har block is accommodated mainly by the Longriba fault and Minjiang fault, and the right-lateral horizontal component of Longriba fault is obviously similar to 4.8+/-1.6 mm/a, and this may indicate that the eastward motion of Bayan Har block is discontinuous. The Longmenshan fault was divided into three segments by Maerkang subblock, Longmenshan subblock and Minxian subblock. The strain rate on the middle part of the Longmenshan fault is smaller than that on the southern part, and the deformation northwest of the fault shows that near the fault the strain rate becomes smaller, it maybe imply that high strain energy had accumulated before the earthquake, which promoted the surface rupture. The change from thrust motion to thrust and right strike-slip motion revealed by the surface ruptures and focal mechanism of aftershocks of Wenchuan earthquake may be related to the change of the stress on the middle part of the Longmenshan fault from southwest to northeast. The low velocity of Maerkang, Longmenshan, and Minxian subblocks relative to the South China block, the low strain rate and the tightly locked character of Longmenshan fault may determine the low slip rate of the Longmenshan fault.
- 出版日期2013-12
- 单位中国地震局; 中国地震局地震预测研究所
