基于地震活动性和震源机制解研究渭河-运城盆地主要断裂带的特征及应力场分布  

THE CHARACTERISTICS OF MAJOR FAULTS AND STRESS FIELD IN WEIHE-YUNCHENG BASIN CONSTRAINED BY SEISMIC ACTIVITY AND FOCAL MECHANISM SOLUTIONS

作　　者：余占洋 沈旭章 梁浩 郑文俊 刘旭宙 YU Zhan-yang;SHEN Xu-zhang;LIANG Hao;ZHENG Wen-jun;LIU Xu-zhou(Provincial Key Lab of Geodynamics and Geohazards,School of Earth Sciences and Engineering,Sun Yat-Sen University,Guangzhou 510275,China;Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519082,China;Gansu Earthquake Agency,Lanzhou 730000,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),珠海519082 [3]甘肃省地震局,兰州730000

出　　处：《地震地质》2022年第2期395-413,共19页Seismology and Geology

基　　金：国家重点研发计划项目(2017YFC1500103);国家自然科学基金(41874052,41730212);“珠江人才计划”引进创新创业团队(2016ZT06N331,2017ZT07Z066);第2次青藏高原综合科学考察研究(2019QZKK0701);广东省防震减灾协同创新中心项目(2018B020207011)共同资助。

摘　　要：文中选取2009年1月1日—2018年6月30日渭河-运城盆地地区的震相报告资料,共包括14381个地震事件,剔除其中地震信息不完整和台站记录过少的地震事件,剩余11856个地震事件。由于研究区域较大,为减少不同区域结构影响,将渭河-运城盆地划分成3个较小的区域,分别使用双差定位法进行重定位,定位过程中使用52个台站的数据,得到了8106个地震事件的重定位结果。采用格点尝试法反演震源机制解,通过最小空间旋转角将其与前人使用其他方法得到的震源机制解结果进行定量比较,发现两者基本一致。此外,文中确定了区域内346个M_(L)≥2地震事件的震源机制解,经分析可知,正断型和走滑型地震事件分布广泛,占全部地震事件的60%以上,且大多集中在断裂带附近。根据震源机制解和应力张量阻尼反演方法使用MSATSI程序包反演得到了渭河-运城盆地地区1°×1°网格的地壳应力场,并垂直断层截取了一定数量的深度剖面进行分析。结果显示:与定位前的分布相比,重定位后的地震事件分布更集中,在平面上基本沿断裂走向分布,在垂向上沿断层面密集分布。山西地堑带内部及周边地震活动频繁,但震级普遍较小;而渭河断陷带内地震活动性相对较弱。重定位前震源深度集中分布在5~10km,重定位后震源深度的分布发生了明显改变,集中分布在10~25km范围内,总体上震源深度集中在20km以内,小部分地震发生在25~35km深度处。盆地内部的震源深度相对较浅,以5~15km为主,盆地两端震源深度有加深的趋势,最深约达30km,与前人的研究结果较为一致。对截取的深度剖面进行分析,结果显示,研究区域内大部分断层面的倾角较大,与地表产状相近,有的断层面甚至接近直立状态。断裂构造的运动性质和震源机制解指示研究区内断层性质以正断和走滑为主;应力场反演结果显示,除东南缘部分地区的R值�In this paper,the seismic phase bulletin of 14381 earthquakes from January 1,2009 to June 30,2018 in the Weihe-Yuncheng Basin and its adjacent region were selected and analyzed.After removing the records with incomplete event information and insufficient station information,11856 seismic events remained.A basic requirement for the double difference location method is that the distance between the pairs of seismic events is much smaller than the distance between the events and the stations and the linear scale of the velocity inhomogeneous body on the wave propagation path,so that the travel time difference between two earthquakes and the same station is only determined by the relative position between the two seismic events and the velocity of the seismic wave.In this case,the error caused by insufficient understanding of crustal structure can be effectively reduced and the result of relocation can be more accurate.Due to the large area,the whole study region was divided into three smaller parts for relocation of the events in order to reduce the influences of local structures.8106 seismic events recorded by 52 stations were relocated using the double-difference location algorithm.It is found that the results constrained by the grid searching method are basically consistent with those obtained by other methods.The reliability of focal mechanism is affected by the number of initial motion and the azimuth distribution of the station.Therefore,when inversion of focal mechanism solution is carried out,earthquakes with more than 10 clear initial motion phases are selected,and the maximum azimuth gap between two stations with clear initial motion is required to be less than 90°.The azimuth coverage of the initial motion on the source sphere was measured according to azimuth and take-off angle distributions,and the focal mechanism solutions with poor coverage were eliminated.The contradiction ratio of focal mechanism solutions is less than 0.2.The average difference of b-axis of the best fitting solutions is less than

关 键 词：双差定位法 震源机制解 渭河-运城盆地 构造应力场 

分 类 号：P315.2[天文地球—地震学]