北天山中段地壳三维速度结构与地震重定位  

THREE-DIMENSIONAL SEISMIC VELOCITY STRUCTURE OF THE MIDDLE PART OF NORTH TIANSHAN MOUNTAINS,XINJIANG BASED ON SEISMIC RELOCATION AND LOCAL SEISMIC TOMOGRAPHY

作　　者：张志斌[1] 梁晓峰[3] 周贝贝 刘代芹[1] 唐明帅[1] ZHANG Zhi-bin;LIANG Xiao-feng;ZHOU Bei-bei;LIU Dai-qin;TANG Ming-shuai(Earthquake Agency of Xinjiang Uygur Autonomous Region,Urumqi 830011,China;Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]新疆维吾尔自治区地震局,乌鲁木齐830011 [2]中国地震局地球物理研究所,北京100081 [3]中国科学院地质与地球物理研究所,北京100029

出　　处：《地震地质》2021年第5期1292-1310,共19页Seismology and Geology

基　　金：国家自然科学基金(41674063,41574056);中国地震局三结合项目(3JH-202001096);新疆天山青年计划基金(2017Q010);新疆维吾尔自治区自然科学基金(2021D01A131)共同资助。

摘　　要：天山作为世界上最大、最活跃的板内造山带之一,在新近纪以来经历了显著的地壳缩短和隆升,其地壳变形和结构一直受到研究者的高度关注。前人对天山地区的深部结构开展了诸多研究,但受限于地震台站的分布,较为精细的地壳三维速度结构结果尚比较缺乏。文中利用新疆测震台网在新疆北天山中段架设的14个固定宽频带地震台站近10a的观测数据及4个流动台站的观测资料进行了近震走时层析成像,获得了地壳的三维速度结构,并利用三维速度结构对该区域的近震事件进行了重新定位。反演结果显示,新疆天山中段的速度结构呈现出明显的纵向不均匀性:天山浅层为高速带,准噶尔盆地一侧为低速带;在10km深度处,研究区基本以高速异常为主;在20km深度处,区内在昌吉附近呈现近SN向的高速异常,在准噶尔南缘断裂带附近也表现为高速异常;在中下地壳,区内以准噶尔南缘及博格达弧形断裂附近的低速异常为主,该低速带可能是区域内大型韧性剪切系统所致。地震重定位结果显示,在盆山结合处,特别是博格达弧形构造附近,中下地壳地震时有发生,震源深度较大的特征指示该区域的地温梯度较低,同时该区域的波速比和P波波速均相对较低,构造变形强烈。此外,2016年呼图壁M_(S)6.2地震的余震重定位分布特征显示,呼图壁地震发生在准噶尔南缘断裂带上,余震分布形态指示该断裂可能为S倾,倾角约为50°;同时震源位于高速异常区,这为地震的孕育和发生创造了条件。As one of the largest and most active intraplate orogenic belts in the world,Tianshan has experienced significant crustal shortening and uplift since the Neogene.Its crustal deformation and structure have been deeply concerned by researchers.The predecessors carried out many studies on the deep structure of the Tianshan area,but limited by the distribution of stations,the relatively fine three-dimensional crustal velocity structure is still lacking.The middle section of North Tianshan is the most concentrated area of population and economy in Xinjiang.There are a series of active faults in the piedmont,causing frequent occurrence of strong earthquake in the region.Due to the lack of targeted research on the deep structure of the region,it is difficult to understand the mechanism of earthquakes in the region.In this study,we used the observations of 14 fixed stations and 4 temporary stations set up in the middle section of north Tianshan Mountains in Xinjiang to obtain the three-dimensional velocity structure of the crustal by using local seismic tomography and relocated the local seismic events in the area using the three-dimensional velocity structure.The seismic events used in the inversion were recorded by at least 5 stations,and the azimuth coverage was greater than 180°.Finally,629 seismic events were obtained,including 5238 P-wave traveltimes and 2144 S-wave traveltimes.The time-distance curve indicates that there are some seismic events with deeper focal depths in the study area.After relocation,the residual is stable at about 0.52,the theoretical deviation of the source position is about 0.5km,the root mean square of the residual is reduced from 0.8 seconds to 0.5 seconds,and the positioning accuracy is obviously improved.The inversion of the three-dimensional velocity structure shows that the velocity structure in the middle section of the Tianshan Mountains in Xinjiang shows obvious longitudinal inhomogeneity.At a depth of 5km,the shallow layer shows high-velocity zone beneath Tianshan and low-velocity

关 键 词：新疆北天山中段 近震层析成像 速度结构 呼图壁地震 

分 类 号：P315.2[天文地球—地震学]