基于近场强震记录和同震位移的汶川地震破裂过程

doi:10.3969/j.issn.0253-4967.2018.03.014

摘要/Abstract

摘要： 基于方位角覆盖较均匀的近场宽频带强震记录和同震位移资料，采用非负最小二乘法和多时间视窗技术，反演了2008年汶川地震破裂过程。从运动学的角度，对北川断层南段、彭灌断层和小鱼洞断层可能的破裂顺序进行了分析，同时探讨了北川断层南段浅部高倾角部分起始破裂的时间。得到如下结论：1）通过近场记录波形拟合残差结合同震位移资料得到，只有北川断层南段在与小鱼洞断层相交处发生双侧破裂，断层西南侧台站合成记录才符合观测记录，同时不会在彭灌断层南段近地表处产生远大于观测值的位错。得到1种可能的破裂方式为：主震从北川断层南段深部低倾角部分开始，造成浅部的彭灌断层破裂，彭灌断层往北侧破裂传播触发小鱼洞断层，进而引起北川断层南段浅部高倾角部分与小鱼洞断层相交处发生双侧破裂。2）通过分析断层西南侧台站合成记录的第2个波包波形拟合的结果，发现北川断层南段高倾角部分起始破裂可能有8s的"停滞"。从时间上来说，相互平行的北川断层南段和彭灌断层在破裂时可能存在先后顺序，北川断层南段浅部区域的破裂可能滞后于彭灌断层。同时，北川断层南段可能存在多点破裂的情况。3）断层面上滑动速度较大的区域，滑动速率的值与周边台站有较好的对应关系。断层面上产生较大滑动速率的区域，其周边台站往往有较大的PGV产生。

关键词: 汶川地震, 近场强震记录, 同震位移资料, 小鱼洞断层, 破裂顺序

Abstract: Based on the extensive near field broadband strong-motion records with uniform azimuthal coverage and coseismic displacements, the rupture process of 2008 Wenchuan earthquake is inversed by the non-negative least square method and multiple-time window technique. The possible rupture sequence among southern Beichuan Fault, Pengguan Fault and Xiaoyudong Fault and the initial rupture time of high dip angle part of southern Beichuan Fault are analyzed from kinetic aspects, which have been seldom focused on. The results indicate that:(1) The near field waveform fitting residuals and the coseismic displacements show that only a bilateral rupture occurs on the intersection between the southern Beichuan Fault and Xiaoyudong Fault can the synthetic records of the stations located near the southwestern end of the Beichuan Fault conform to the observed ones, and meanwhile, the Pengguan fault cannot generate large slips on its southwestern part. The possible rupture sequence is that the earthquake started at the low dip angle part of Beichuan Fault and propagates to the Pengguan Fault in the shallow area, the Xiaoyudong Fault is triggered by the Pengguan Fault, and then producing bilateral rupture on the high dip angle part of Beichuan Fault at the intersection with the Xiaoyudong Fault. (2) Through analysis of the synthetic second packet records of stations at the southwest area of the fault, we obtain the initial rupture time on the high dip angle part of Beichuan Fault may have a 8s stagnation. In terms of timing, there may be rupture sequence between the southern Beichuan Fault and Pengguan Fault which are parallel to each other. The rupture of the southern shallow part of Beichuan Fault with high dip angle may lag behind the Pengguan Fault. At the same time, there may be a multipoint rupture in the southern section of the Beichuan Fault. (3) There is a good correspondence between the area on the fault with larger slip rate and the surrounding stations with larger PGV. In areas where slip rate on the fault plane is large, the stations tend to have larger peak ground velocities.

Key words: Wenchuan earthquake, near field strong-motion records, coseismic displacements, Xiaoyudong Fault, rupture sequence

中图分类号:

P315

尹得余, 刘启方, 刘畅, 季鑫洋. 基于近场强震记录和同震位移的汶川地震破裂过程[J]. 地震地质, 2018, 40(3): 698-717.

YIN De-yu, LIU Qi-fang, LIU Chang, JI Xin-yang. ESTIMATING THE WENCHUAN EARTHQUAKE RUPTURE PROCESS USING NEAR FIELD STRONG MOTION RECORDS AND COSEISMIC DISPLACEMENTS[J]. SEISMOLOGY AND GEOLOGY, 2018, 40(3): 698-717.

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