利用反射地震剖面探查隐伏同震破裂——以2018年台湾海峡南部M_(S)6.2地震为例  

THE BURIED CO-SEISMIC RUPTURE EXPLORATION USING SEISMIC REFLECTION PROFILE:A CASE STUDY OF THE M_(S)6.2 SOUTH TAIWAN STRAITS EARTHQUAKE IN 2018

作　　者：王笋[1] 丘学林[2,3] 赵明辉 姚道平[1,4] 张艺峰 闫培[1] 金震 WANG Sun;QIU Xue-lin;ZHAO Ming-hui;YAO Dao-ping;ZHANG Yi-feng;YAN Pei;JIN Zhen(Xiamen Marine Seismic Station,Fujian Earthquake Agency,Xiamen 361021,China;Key Laboratory of Ocean and Marginal Sea Geology,Innovation Academy of South China Sea Ecology and Environmental Engineering,South China Sea Institute of Oceanology,Chinese Academy of Sciences,Guangzhou 511458,China;Institute of Deep-sea Science and Engineering,Guangzhou 511458,China;Xiamen Institute of Marine Seismology,China Earthquake Administration,Xiamen 361021,China)

机构地区：[1]福建省地震局海洋地震观测中心,厦门361021 [2]中国科学院边缘海与大洋地质重点实验室,中国科学院南海生态环境工程创新研究院,中国科学院南海海洋研究所,广州511458 [3]南方海洋科学与工程广东省实验室,广州511458 [4]中国地震局厦门海洋地震研究所,厦门361021

出　　处：《地震地质》2022年第1期188-204,共17页Seismology and Geology

基　　金：中国地震局地震科技星火计划项目(XH19022Y);国家自然科学基金(41774104);福建省地震局科技基金(SF202104)共同资助。

摘　　要：调查浅源地震在地表附近产生的同震破裂对研究地震发震构造、防御地震灾害具有重要意义。常规的地形地貌和探槽调查方法易受到盖层复杂多变的影响,在海域更是难以应用。为此,文中提出参考石油工业中时移地震的思路,用分别采集于地震发生前、后的2期反射地震剖面来识别隐伏同震破裂。2018年台湾海峡南部发生了M_(S)6.2地震,文中基于福建省地震局于地震发生前、后(2017年和2019年)在宏观震中西侧分别采集的2期多道地震资料,筛选出噪声残留、照明度、速度场、偏移算法等成像条件完全一致的2期数据体并进行互均化。经对比,同频段(20~50Hz)剖面的主要强反射波组相位相同且基本重合,满足检测地层变化的要求。对比发现,在宏观震中以西约25km、震源机制解反演得到的地震断层与反射地震剖面交叉处,断层F_(1)的形态在地震发生后无显著变化,但400m以下深度与之接触的各反射波组形态发生了显著变化,表现为标志层的极性反转、界面形态变化和基底反射波组移位。结合研究区的地质构造特征,推测此处断层的封闭性在地震发生时发生了快速改变(即同震滑动),孔隙流体沿断层面快速运移导致地层波阻抗剧烈变化。文中研究证明虽然以反射地震剖面的分辨率难以直接识别垂向同震位移,但隐伏同震破裂引起的流体运移可能使断层面附近地层的波阻抗发生显著变化,而在时移地震剖面上可以可靠地识别出这种变化。与传统的地表类调查方法相比,时移地震方法可以克服盖层对同震变形的吸收影响,扩展同震破裂的可识别范围。该方法为判别浅源地震的发震构造、滑动分布提供了新思路,对通常缺少地质调查和地表形变资料的海域地震研究尤为重要。Co-seismic near-surface rupture is one of the keys to the recognition of earthquake fault and the defense to seismic hazard.However,conventional investigation methods such as outcrop mapping and trenching,are often disturbed by the variation of capping formation.Besides,it’s difficult to apply these methods under the sea water.Drawing on the idea of time-lapse seismic techniques in the petroleum industry,we suggest identifying the buried co-seismic ruptures using two reflection seismic data sets acquired before and after earthquake,respectively.In this paper,a case study is presented.On Nov.26^(th),2018,a M_(S)6.2 earthquake occurred in the south Taiwan Straits.The focal mechanism of this event is dextral strike slip with a slight dip-slip component,and the aftershock distribution is E-W oriented.West of the epicenter,multi-channel seismic profiling was carried out twice under the direction of Fujian Earthquake Agency in 2017 and 2019.To avoid the influence of the difference in acquisition conditions,before comparing we reprocessed and cross-equalized the two data sets with the same de-noise method,illumination,migration algorithm and velocity field.The profile correlation in 20~50Hz shows that the dominant reflecting wave groups are coincident with the time-lapse ones,which means the two sections are in phase.The comparison results show that:at about 25km west of the epicenter,the reflection profile met the earthquake fault inferred by focal mechanism,and the morphology of Fault F_(1) did not change significantly after the earthquake,but at depths greater than 400m,the remarkable reflections near the strike-slip fault plane changed significantly.From 2017 to 2019,the strongest reflection in the hanging wall reduced in amplitude and shifted from near horizontal to a jagged fold in shape,besides,the polarity of two remarkable reflections reversed,and a piece of the basement reflection in the heading wall close to the fault plane subsided about 8milliseconds measured in two-way travel time.The remarkable reflecti

关 键 词：同震破裂 时移地震 浅源海域地震 孔隙流体运移 

分 类 号：P315.2[天文地球—地震学]