2014年鲁甸M_S6.5地震及其强余震序列重定位

Relocation of the 2014 Ludian M_S6.5 earthquake and its large aftershock sequence

本文采用云南测震台网的观测报告数据,利用双差定位方法对2014年鲁甸M_S6.5地震及其强余震序列进行了重定位,获得了3 658个地震事件的震源参数。重定位后地震序列的震中分布显示,余震分布存在两个优势方向,分别为近EW向和SES向,呈共轭型分布,近EW向条带展布长度为30 km,SES向条带展布长度为20 km;震源深度的分布显示,地震序列总体表现为主震附近震源较深,沿近EW向和SES向逐渐变浅,地震序列的震源深度主要分布在4—20 km范围内。截至2017年2月28日,鲁甸M_S6.5地震震源区共发生(同一天发生的一组地震算一次)MS≥4.5强余震4次。重定位后的鲁甸4次强余震序列震中分布存在差异:2014年9月10日和10月27日两次强余震序列的展布特征与主震相同,而2016年和2017年另外两次强余震的后续余震仅分布在强余震的周边,与主震序列明显不同。综合重定位后余震序列分布、震源区地质调查资料以及前人研究认为,鲁甸地震的4次强余震序列是区域应力场和主震引发的震源区应力场共同作用的结果,2014年9月10日和10月27日的两次强余震序列主要受主震引发的震源区应力场的影响;而2016年和2017年两次强余震序列则主要受区域应力场的影响。

We use catalog data recorded by Yunnan seismic network to relocate the 2014 Ludian MS6.5 earthquake and its aftershock sequence with double-difference location algorithm,and obtain focal parameters of 3 658 earthquakes. The results show that the relocated epicenter distribution of Ludian MS6.5 earthquake sequence exhibits two predominant directions,approximately EW and SES,and conjugated to each other. The length of the EW strip is about 30 km,while the length of SES strip is about 20 km. The Ludian earthqucke sequence mainly distributed between 4-20 km in depth. It is deeper around the mainshock and becomes shallower along the strips. There are four MS≥4.5 large aftershocks（the earthquakes that occurred on the same day counts as one） occurred in the Ludian MS6.5 earthquake source region till February28,2017. The distributions of four strong aftershock sequences are different from each other after relocation. The distributions of aftershock sequences of MS4.7 occurred in September 10 and MS4.6 occurred in October 27 are similar with the mainshock sequence,while the aftershock sequences located around 2016 MS4.7 earthquake and 2017 MS4.9 earthquake are different from the mainshock sequence. Synthesizing the distribution of relocated Ludian MS6.5 earthquake sequence,geologic data in studied area and previous researches,we draw the following conclusion：the distribution of four strong aftershock sequences are resulted from combined action of regional stress field and source stress field caused by the mainshock,the strong aftershock sequences occurred in September 10 and October 27 in 2014 are mainly influenced by source stress field induced by the mainshock,while the strong aftershock sequences occurred in 2016 and 2017 are mainly influenced by regional stress field.