广西北流地震震源区短周期密集台阵背景噪声成像  

Seismic image of ambient noise beneath the focal area of the Guangxi Beiliu earthquake from dense short-period array

作　　者：黄强强 沈旭章 王文天 许小伟 周启明 黄河 黄柳婷 吕晋妤 余占洋 HUANG QiangQiang;SHEN XuZhang;WANG WenTian;XU XiaoWei;ZHOU QiMing;HUANG He;HUANG LiuTing;LV JinYu;YU ZhanYang(School of Earth Sciences and Engineering,Sun Yat-sen University,Guangdong Province Key Laboratory of Geodynamics and Geological Hazards,Guangzhou 510275,China;Guangdong Laboratory of Southern Ocean Science and Engineering(Zhuhai),Zhuhai Guangdong 519082,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,广州510275 [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：《地球物理学报》2022年第8期2917-2930,共14页Chinese Journal of Geophysics

基　　金：国家自然基金项目(41874052和41730212);广东省防震减灾协同创新(2018B020207011);广东省引进人才创业创新团队(2017ZT07Z066和2016ZT06N331);国家重点研发计划(2017YFC1500103);第二次青藏高原综合科学考察研究(2019QZKK0701)联合资助.

摘　　要：作为构造上较为稳定的华南地块,其地震活动相对中国西部明显偏低,但也发生过多次中强地震.华南中强地震震源区深部结构对于深入研究华南板内地震成因具有重要科学意义.2019年发生在两广交界的北流5.2级地震是近年来华南最大的一次中强地震,该次地震的发生也为我们研究华南地震震源区深部结构提供了理想场所.本文基于120个短周期地震仪组成的密集台阵背景噪声资料,通过互相关提取了1~5 s高频面波频散信号,然后采用面波直接反演法,对北流地震震源区进行地下6 km深度范围内浅层地壳速度结构成像.结果显示:浅层地壳剪切波速度横向变化强烈,速度分布不均匀;低速异常主要分布于三条断裂带周围;研究区存在NNW-SSE向的高速异常,该高速异常与震中区高速异常相交在水平方向上呈“L”形环绕分布于石窝断裂南东侧;震中上方为上凸形态的高速异常,这些高速异常可能为中生代花岗岩基,结合研究区现今NW-SE向的构造应力场分析:石窝断裂南西盘向南东方向运动时受到“L”形高速体阻挡,可能导致应力积累,进而引发地震.此外,这种局部异常高速体可能是华南“马赛克”结构中微陆块在上地壳中的延伸,上地壳结构的不均匀性和大尺度构造相互作用,会在局部区域导致应力积累,从而引发中强地震,这也可能是华南板内地震发生的一种重要成因机制.As a structurally stable block,the seismicity of South China is significantly weaker than that of western China,but there have been still some medium-strength earthquakes in history.The deep structure of the earthquake source area in south China is helpful to understand the mechanism of earthquakes in the south China block.The Beiliu earthquake in 2019 was the largest medium-strength earthquake in south China recent years,and the earthquake also provided an ideal opportunity to carry out the deep structure of the earthquake source area in southern China.Based on the ambient noise data of 120 short-period seismometers,we extracted the high-frequency surface wave dispersion signal with 1~5 s period,and then imaged the shallow crustal velocity structure in the depth range of 6 km underground by the direct inversion method of surface wave.The results show that the velocity of shallow crust shear wave has strong lateral heterogeneous,the low velocity anomaly is mainly distributed around the three fault zones,the high velocity anomaly along the NNW-SSE direction exists in the study area,and it intersects with another high velocity anomaly beneath the focal area with“L”shape which is distributed around the south and east side of the Shiwo fault.The high velocity anomaly exhibits convex shape above the epicenter,which may be related to the middle-generation granite base.Combined with the analysis of the current tectonic stress field with NW-SE direction in the research area,we deduced that the south-eastward disk of the Shiwo fault has been blocked by the“L”-shaped high velocity zone,which may lead to the accumulation of stress and then trigger the earthquake.In addition,this local high velocity abnormalities may be the extension of micro-land blocks in the"mosaic"structure in southern China in the upper crust,the unevenness of the upper crust structure and the interaction of large-scale structures,will lead to stress accumulation in the local area,thus triggering medium-strength earthquakes,which maybe a typical

关 键 词：广西北流地震 短周期密集台阵 背景噪声成像 高速异常 华南板内地震 

分 类 号：P315[天文地球—地震学]