2019年6月17日长宁MS6.0地震前后b值时空变化分析  

Spatial and Temporal Variation of b value before and after the Changning MS6.0 Earthquake on June 17,2019

作　　者：曾宪伟[1] 龙锋[2] 任家琪[1] 蔡新华[1] 李文君 ZENG Xian-wei;LONG Feng;REN Jia-qi;CAI Xin-hua;LI Wen-jun(Earthquake Agency of Ningxia Hui Autonomous Region,Yinchuan 750001,China;Sichuan Earthquake Agency,Chengdu 610041,China)

机构地区：[1]宁夏回族自治区地震局,宁夏银川750001 [2]四川省地震局,四川成都610041

出　　处：《地震》2020年第3期1-14,共14页Earthquake

基　　金：地震科技星火计划项目(XH18053Y);宁夏自然科学基金项目(NZ17221);国家自然科学基金(41604015);强震危险性研究创新团队(CX2019-4)。

摘　　要：选取2014年1月至2019年8月宜宾地区(28.0°N^28.5°N,104.6°E^105.1°E)记录的地震资料,利用最大似然法估算b值,得到了宜宾地区b值的时空变化特征。结果显示:①2019年长宁M_S6.0地震前5个月,b值出现加速下降变化,震后快速回升。这一现象很可能反映了地震孕育中的应力积累集中到地震发生后的应力释放过程。②长宁地震前震中区及附近地区一直存在低b值异常(≤0.85),震前5个月,震中附近出现了b值下降,尤其是长宁地震西偏北方向出现了b值显著下降,后续珙县发生的3次M_S5地震正位于该异常区及边缘。③b值空间低值异常可用于判定未来中强地震发生的危险区域,而b值的下降可用于判定强余震的可能发生地点。④分析地震危险性时,更应关注低b值背景下的b值下降,即高应力集中区域的地震危险性增强。Based on the earthquakes recorded in Yibin area(28.0°N^28.5°N,104.6°E^105.1°E),Sichuan Province,from January 2014 to August 2019,we estimated the b values in the studied area by the maximum likelihood method and obtained their temporal and spatial characteristics.The results show that,firstly,the b value decreased rapidly five months before the Changning M_S6.0 earthquake and recovered quickly after that.This phenomenon is likely to reflect the process of stress accumulation during earthquake preparation and stress release after the earthquake.Secondly,before the Changning earthquake,there was always a low b value anomaly(≤0.85)in the epicenter and its vicinity.Five months before the earthquake,a further decrease of b value occurred near the epicenter,especially in the northwest of Changning,where following three M_S5 earthquakes taking place in Gongxian were just located in this abnormal region and its edge area.Thirdly,the spatial distribution of low b value anomalies indicates the risk area of medium and strong earthquakes in the future.And,the fast decrease region in b value can be used to determine the possible location of strong aftershocks.Fourthly,when analyzing the seismic risk,we should pay more attention to the b value decrease under the background of long-term low b value,which illustrates the increasing seismic risk in high stress concentration area.

关 键 词：长宁地震 B值 最大似然法 地震危险性 

分 类 号：P315.7[天文地球—地震学]