接收函数和面波频散联合反演广西北流M_(S)5.2级地震震源区地壳速度结构  

Crust Structures Beneath M_(S)5.2 Beiliu Earthquake Focal Region in Guangxi Province Constrained by Receiver Functions and Surface Wave Dispersion

作　　者：范盼 沈旭章 黄强强 FAN Pan;SHEN Xuzhang;HUANG Qianqiang(Guangdong Provincial Key Lab of Geodynamics and Geohazards,School of Earth Sciences and Engineering,Sun Yat-sen University,Zhuhai 519082,Guangdong,China;Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519082,Guangdong,China)

机构地区：[1]中山大学地球科学与工程学院,广东省地球动力作用与地质灾害重点实验室,广东珠海519082 [2]南方海洋科学与工程广东省实验室(珠海),广东珠海519082

出　　处：《大地构造与成矿学》2022年第3期633-644,共12页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(U1701641,41730212,41874052);国家重点研发计划(2017YFC1500103);广东省引进人才创新创业团队项目(2017ZT07Z066,2016ZT06N331);第二次青藏高原综合科学考察研究项目(2019QZKK0701);广东省防震减灾协同创新中心项目(2018B020207011)联合资助。

摘　　要：华南陆块属于比较稳定的陆块,地震活动不论是强度还是频度都比西部和华北地区弱很多,2019年在广西北流与广东化州交界处发生的M_(S)5.2中强地震为探讨华南板内中强地震成因提供了理想场所。本文计算了北流地震震源区布设的7个宽频带流动地震台站、120个短周期流动台站和4个固定台站的远震P波接收函数,结合前人在该区域的面波频散曲线,采用线性阻尼最小二乘反演算法联合反演了研究区地壳三维S波速度结构。得到如下结果:①研究区S波速度具有明显横向不均匀性,上下地壳速度在断裂附近存在明显差异性,新丰断裂南侧及东侧上地壳整体S波速度较高;②石窝断裂附近存在一条NW向连续性较好的低速带,震中区位置10 km深处存在明显局部高速异常,并随着深度减小异常逐渐增加,在浅处其与焦林断裂和新丰断裂附近的高速异常汇聚成一条NNE向连续异常带;③结合研究区地质调查结果和余震分布,震中区的局部高速异常可能是NW向石窝断裂南西盘发生右行走滑,并受到新丰断裂高速体的限制和互相作用发生了应力积累,从而引发此次中强地震;④地壳厚度泊松比反演结果显示研究区存在NE向明显地壳增厚(26~30 km),结合华南地区应力场分析,地壳增厚可能与中下地壳局部的NE向挤压作用相关。The South China block is one of the most stable blocks in China,however,its seismic activity is much weaker than those of the west and north China in terms of intensity and frequency.A moderate strong earthquake with M_(S)5.2 that occurred at the border of Beiliu,Guangxi and Huazhou,Guangdong in 2019 has important significance for the exploration of the earthquake genesis in South China.Here,we isolated the teleseismic P wave receiver functions beneath 7 broadband temporary seismic stations,120 short-period nodal seismometers and 4 permanent stations in the earthquake focal region.Combining with the surface wave dispersion from previous results and receiver functions,we perform a joint inversion by means of the linear damped least—squares method to get the 3D S-wave velocity structure of the crust and upper mantle beneath the earthquake focal region.The results are as follows:(1)The S-wave velocity has lateral inhomogeneity.The velocity distribution in the upper and lower crust is different near the fault.The S-wave velocity in the south and east sides of the Xinfeng fault is higher in the upper crust.(2)A continuous low velocity zone along the NW direction exists near the Shiwo fault,and a local high-velocity anomaly is at a depth of 10 km near the epicenter of the Beiliu earthquake,which gradually merged with the high velocity anomaly near the surface beneath the Jiaolin and Xinfeng faults,forming a NNE trend continuous high velocity anomaly zone.(3)In combination with the current geological investigations and aftershock distribution in the study area,we deduced that the local high velocity anomaly may be from the blocked southeast wall of the NW-trending Shiwo fault with dextral strike-slip by the Xinfeng fault,which triggered the medium-strong earthquake by accumulation of stress.(4)Study of the crustal thickness and Possion ratio shows an obvious crustal thickening(26-30 km)along NE direction,which may be related to the compression process during the tectonic evolution in South China.

关 键 词：北流地震 密集台阵 接收函数 面波频散 联合反演 三维S波速度结构 

分 类 号：P67[天文地球—海洋地质]