2018年3月20日阳江新湖水库M_L4.2级震群发震机理分析

Seismological Mechanism Analysis of M_L4.2 Earthquake Swarm on March 20^(th) in Xinhu Reservoir,Yangjiang

2018年3月20日,阳江新湖水库发生了M_L4.2级震群活动。为研究该次震群的发震构造及机理,采用CAP、初动及振幅比方法反演了3次M_L3.0级以上地震的震源机制,采用双差定位方法对震群序列进行了重新定位,并计算了这3次地震之间的静态库仑应力触发效应。结果表明:主震震源机制为走向311°、倾角65°、滑动角-61°,破裂性质为正断兼左旋走滑,震源破裂类型与余震空间展布符合较好,且与NW向左旋正断型的洋边海断裂相吻合。该次震群活动是洋边海断裂北延线在区域构造应力场作用下破裂的结果。静态库仑应力计算结果显示:3次地震之间应力触发效应明显, 2018年2月18日M_L3.2级地震触发了2018年3月17日M_L3.5级地震,这两次地震又联合显著触发了2018年3月20日M_L4.2级地震。

On the March 20th,2018,a significant M_L4.2 earthquake swarm occurred in Xinhu reservoir,YangJiang.To systematically analyze the seismological mechanism of this swarm,the paper firstly inversed the focal mechanisms of three earthquakes with M_L≥3.0 by using CAP method and polarity and SV/P amplitude ratio method.Secondly,the paper relocated the sequence by using HypoDD method.At last,in order to study earthquake triggering effect in thisswarm,the paper calculated static coulomb stress triggering effect betweenthese three earthquakes with M_L≥3.0.The result shows:the M_L4.2 main shock is a significant normal fault with small left lateral components,which has a strike 311°,dip 65°and rake-61°.Considering the well agreement of this focal mechanism among with the relocated earthquake distributionand the Yangbian sea active fault,the paper suggests that this M_L4.2 earthquake swarm is fractured on northwest extension of Yangbian sea active fault guided by reginal tectonic stress.The static coulomb stress change among these three earthquakes show that these three earthquakes have been triggered by each other.The M_L3.5 earthquake on March 17th,2018 has been triggered by the M_L3.2 earthquake on February 18th by 0.016 Bar,and The M_L4.2 earthquake on March 20 th has been significantly triggered by the two former events by 0.119 Bar.