利用背景噪声研究2021年云南漾濞M_(S)6.4地震同震及震后波速变化  

Using ambient noise to study the co-seismic and post-seismic velocity changes of the 2021 Yangbi M_(S)6.4 earthquake in Yunnan

作　　者：安艳茹 王伟涛[1,3] 杨微[1,3] 蒋海昆 杨军[4] 李孝宾 潘睿[1,3] AN YanRu;WANG WeiTao;YANG Wei;JIANG HaiKun;YANG Jun;LI XiaoBin;PAN Rui(Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;China Earthquake Networks Center,Beijing 100045,China;Key Laboratory of Earthquake Source Physics,China Earthquake Administration,Beijing 100081,China;Dali Center,China Seismic Experimental Site,Dali Yunnan 671000,China)

机构地区：[1]中国地震局地球物理研究所,北京100081 [2]中国地震台网中心,北京100045 [3]中国地震局震源物理重点实验室,北京100081 [4]中国地震科学实验场大理中心,云南大理671000

出　　处：《地球物理学报》2023年第8期3185-3201,共17页Chinese Journal of Geophysics

基　　金：国家重点研发计划(2018YFC150330502);中国地震局地球物理研究所基本科研业务费专项(DQJB22Z01-06);国家自然科学基金(41974069)联合资助。

摘　　要：通过测量地震波速度变化可分析地下介质应力状态的变化,加深对地震物理过程的认识.本文利用2021年5月21日漾濞MS6.4地震震中50 km范围内16个地震台站2021年的三分量连续记录,通过背景噪声干涉方法研究了漾濞MS6.4地震同震波速变化及震后恢复过程.结果表明,在1~4 Hz的频带范围内,台站对间的相对波速在主震后明显降低,dv/v_(pair)的幅度为-0.29%~-0.02%,随台站间距增大而降低.由线性回归获得的各台站的相对波速变化dv/v_(station)的幅度为-0.16%~-0.02%,总体随震中距增大而减小.分析表明,测量得到的同震波速变化主要来自于浅层(≤2km)介质,受静态应变和动态应变的共同影响,主要由强地面运动引起的岩石破碎和应力大规模调整控制.远离主震的北部台站波速变化较大,对应力扰动敏感性高,推测与台站下方的热流体分布相关.波速变化测量结果指示漾濞地震周边地震波速度在震后几天内达到最低值,而在8月份前后逐渐恢复到震前的水平,表征了介质的愈合过程.研究表明利用背景噪声干涉可对同震及震后恢复过程的波速变化进行有效测量,漾濞地震的同震波速变化受断裂带破碎程度、动态应变和流体作用等多种因素的共同控制.Seismic velocity change is a good indicator reflecting the stress state variation of the underground media.Therefore,seismogenic process could be effectively revealed by the velocity change calculation.Based on the seismic ambient noise interferometry,we study the co-seismic velocity change and post-seismic recovery process of the 21 May 2021 M_(S)6.4 Yangbi earthquake using the continuous records from 16 stations within 50km of the epicenter.The results show that the relative velocity changes between the station pairs(dv/v_(pair))decrease significantly after the mainshock.The amplitude ranges from-0.29%to-0.02%and decreases with the increase of station spacing.The relative velocity changes of each station(dv/v_(pair))obtained by linear regression range from-0.16%to-0.02%,and are generally negatively correlated with the epicenter distance.It is notable that the measured co-seismic velocity changes are mainly originated from the shallow media(≤2 km).Such changes are considered to be caused by both static and dynamic strain,but the primary controlling factor is rock fragmentation and large-scale adjustment of stress produced by strong ground motion.In addition,dv/v_(station) located at the northern stations far from the epicenter have the largest drop values,demonstrating that they are more sensitive to stress disturbances.This may be related to the distribution of thermal fluids below these stations.The results of velocity changes indicate that around the study area the seismic velocity reached its minimum value within a few days after the mainshock.The value then gradually recovered,reaching the pre-seismic level around August,which characterizes the healing process of broken rocks.In this study,ambient noise interferometry has been effectively applied to measure the velocity changes during and after the Yangbi earthquake,and the results show that co-seismic velocity changes are jointly controlled by various factors including the fracture degree of the fault zone,dynamic strain,and the existence of fluids.

关 键 词：漾濞6.4级地震 背景噪声 同震波速变化 震后恢复 

分 类 号：P315[天文地球—地震学]