玉树地震序列重新定位及其地震构造研究

Relocation of the Yushu Ms7.1earthquake sequence and investigation on its seismotectonics

对玉树地震序列自2010年4月11日至9月15日由台网记录到的1 832个地震采用双差地震定位法进行重新定位,获得了1 670个地震重新定位的震源参数。重新定位后的震源深度主要分布在15km以内。重新定位后的Ms7.1级主震发生在无地表破裂段,余震活动向两侧破裂扩展。余震沿地表破裂带基本呈线性分布,剖面上显示为近垂直的结构面,在北西端无地表破裂出露处,出现近垂直于断裂方向较宽的北东向地震密集带。震源机制解显示的主压应力方向斜交地表破裂带,地表破裂与震源破裂都表现为纯左旋走滑的错动性质,而在北西端主压应力方向偏转为近垂直于断裂带的方向,此处较宽的北东向地震密集带可能由近东西与南北两个方向的共轭破裂所组成。余震的后期活动与发展并不局限于主震形成的破裂带内,更多的受局部应力调整被触发而产生新的破裂。

We investigated the seismotectonics of the Yushu Ms7.1 earthquake by relocating the 1670 earthquakes in its sequence from April 11to September 15,2010 using the double difference algorithm.Most of the relocated hypocentral depths are between 0 and 15 km.The relocated Ms7.1 mainshock occurred at the segment without surface rupture,while the aftershocks distribute along the surface rupture zone to its two sides in a linear pattern.At the northwestern end of the seismic belt without surface rupture,the aftershocks formed a wide fault nearly perpendicular to the main seismic belt.The seismic source rupture process delineated by the aftershocks is to be the bilateral rupture propagation contrast to the result of seismic rupture inversion as the unilateral rupture.The focal mechanism solutions of the mainshock and some large aftershocks suggest that the seismic faulting along the segment with surface rupture to be pure sinistral strike slip,whereas to the northwestern end,the rupture mechanism might be different from that of the mainshock,the wide seismic belt there might be formed by a conjugate rupture.It can be concluded that the aftershocks occurred after a time period were triggered in the process of stress adjustment,and not constrained inside the rupture zone created by the mainshock.