Seismotectonic study by relocation of the Wench uan M_S 8.0 earthquake sequence
Seismotectonic study by relocation of the Wench uan M_S 8.0 earthquake sequence
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发表时间：
2009
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通讯作者：
Cheng Jiu
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作者：
Cheng Jiu
综合利用川西流动地震台阵观测数据和震后应急地震观测台站的震相数据，采用双差地震定位方法对汶川地震的余震序列进行了精确重新定位，并对汶川地震的地震构造进行了深入研究.本文还对地震构造变形和破裂过程进行了研究。结果表明，汶川地震序列起始于彭关地块南缘，向东北方向延伸约350 km，宽度20-30 km。余震的空间分布具有明显的不均匀性，可以划分为小的扇形区。坚硬的彭关地块控制着地震序列的分布和复杂的破裂过程。以松潘—甘孜地块中地壳低速层顶部为底边界，余震主要分布在4~24 km深度范围内的龙门山东缘上地壳高速层内.余震的深度分布表明，映秀-北川断裂、灌县-江油断裂和文川-茂文断裂在20-22 km深度处合并成一条剪切带。从小鱼洞到礼县方向存在一条垂直于龙门山走向的余震分布带，其长度超过60 km。结合强余震震源机制和主震破裂过程的研究结果，可以推断：彭关地块下部在地震过程中经过长期的应力积累而发生了破裂，这可能是此次大震发生的主要原因。
Accurate relocation of the Wenchuan earthquake sequence is obtained by using the double difference relocation algorithm from the integrated travel time data recorded at the Western Sichuan movable seismic array and the earthquake emergency response stations. In this presentation, the seismotectonic deformation and rupture process is also investigated. The results show that the Wenchuan earthquake sequence begins from the south margin of the Pengguan Massif and extends northeastward for about 350 km within a width of 20-30 km. The spatial distribution of the aftershocks exhibits obvious inhomogeneity which can be divided into small sectors. The rigid Pengguan Massif controls the distribution of the earthquake sequence and the complex rupture process. The aftershocks occurred mainly in the depth ranging from 4 to 24 km inside the high velocity layer of the upper crust in the eastern border of the Longmen Shan and above the low velocity zone in the middle crust. Depth distributions of the aftershocks across the sections show clearly that the Yingxiu-Beichuan, Guanxian-Jiangyou and the Wenchuan-Maowen faults merge into a shear belt at the depth of 20-22 km. There exists an aftershock distribution belt from Xiaoyudong to the direction of Lixian, which is perpendicular to the strike of the Longmen Shan and longer than 60 km. Consulting with the results of the focal mechanism of strong aftershocks and the rupture process of the main shock, it could be inferred that the lower part of the Pengguan Massif has been broken up during the earthquake after long term stress accumulation, which would be the main reason why such a great earthquake occurred.