2022年9月5日四川泸定MS6.8地震序列重定位研究

Study on Relocation of the September 5, 2022 Luding MS6.8 Earthquake

摘要:

利用2022年9月5—12日震相报告中的P波和S波到时资料,采用双差定位方法对四川泸定M_S6.8地震序列的主震和余震进行重定位。重新定位后地震序列较重新定位之前震中分布更加集中,线性趋势更加明显。余震主要分布在鲜水河断裂以西地区,总体沿着鲜水河断裂呈NW向展布,余震区长轴约为65km。根据重定位结果,发震断层为鲜水河断裂磨西—石棉段,该断裂走向为331°～340°,倾角较陡。受SW向海螺沟段断裂影响,余震区具有明显的分段特征,总体上呈现北浅南深的特征。随时间的演化,余震区中南段震源深度逐渐变浅,且地震频次逐渐衰减,而北段震源深度变化不大,频次也未明显减弱。不同时段的余震活动表明,本次地震的初始破裂方向为SE向,该破裂随后触发了与主断裂共轭的SW向分支断裂,余震沿这两个方向逐步扩展,最后达到稳定状态。

Abstract:

The main shock and aftershocks of the Luding M_S6.8 earthquake in Sichuan Province were relocated by applying the double-difference location algorithm using P-wave and S-wave arrival times from the catalog reports from September 5 to September 12,2022. Compared with the previous result,the earthquake sequence after the relocation is more concentrated and the linear trend is more obvious. The aftershocks which are mainly located in the west of the Xianshuihe fault generally distributed along the Xianshuihe fault in an NW direction with a long axis of about 65km. Based on the relocation results,the seismogenic fault is the Moxi-Shimian segment of the Xianshuihe fault,which the strike of this fault is 331°～340° with the steep dip angle. Affected by the Hailuogouduan faults in the SW direction,the aftershock zone has obvious segmentation characteristics,i.e. generally shallow in the northern section and deep in the southern section. With the evolution of time,the focal depth of the aftershocks in the central and southern sections gradually became shallower as the frequency of earthquakes attenuated,while the focal depth in the northern section did not change much as the frequency did not attenuate significantly. The activities of aftershocks at different periods show that the initial rupture direction of the event is in the SE direction,which then triggers an SW branch fault conjugated with the main fault. The aftershocks expand along these two faults till reaching a steady state.