2015年新疆皮山6.5级地震序列震源机制特征分析

Analysis of the Focal Mechanism of the 2015 Pishan,Xinjiang,MS6.5 Mainshock and Aftershok Sequences

摘要:

利用新疆区域数字地震台网波形资料，采用CAP方法反演了2015年7月3日新疆皮山6.5级地震主震及部分M_S≥3.6余震的震源机制解和距心深度。研究结果显示，皮山6.5级地震主震最佳双力偶解节面I：走向290°/倾角55°/滑动角96°；节面Ⅱ：走向101°/倾角35°/滑动角82°，最佳矩心深度16km，表明该地震是一次逆冲型事件。通过反演部分M_S≥3.6余震的震源机制解发现，早期余震的破裂方式与主震较为一致，随着时间的推移余震震源机制出现走滑型和正断型，表明早期余震的破裂受主震影响较大，随着序列的发展变化，后期震源区应力场可能出现一定程度的调整。统计皮山6.5级地震序列P轴方位发现，优势方位为NNE向，与该区域构造应力场方向较为一致。结合地震序列的震源机制及他人精定位结果和震源区地质构造情况，初步解释了导致此次地震的原因。

Abstract:

On the basis of the digital broadband seismic data recorded by the Xinjiang Digital Seismic Network,we obtained focal mechanism mainshock and M_S ≥ 3.6 aftershocks of the July 3 Pishan,Xinjiang M_S6.5 earthquake by using the Cut and Paste method. The results shown that the best results of the focal mechanism of Pishan M_S6.5 mainshock had the nodal plane Ⅰ with strike 286°/dip 52°/rake 91° and the nodal plane Ⅱ with strike 105°/dip 38°/rake 89°. The centroid depth moment magnitude was calculated to be 19km and M_W6.22,indicating that the earthquake is a thrust event. The results show that the early aftershocks are similar to those of the main shock,but the latter part of the activities were affected by the deep fracture control and stress changes in the source area changes. The dominant position of the P-axis was NNE,which is consistent with the background stress field of the region. Combined with the focal mechanism of the earthquake sequence,the results of other people's precise location and the geological structure of the source region,the causes of the earthquake are preliminarily explained.