用接收函数方法研究汶川和芦山地震之间未破裂段的地壳结构  

The crust structure of the unruptured segment between Wenchuan and Lushan Earthquakes revealed by Receiver Functions

作　　者：何富君[1] 梁春涛[1,2] 杨宜海[1] 房立华[3] 苏金蓉[4] 

机构地区：[1]地球探测与信息技术教育部重点实验室(成都理工大学),成都610059 [2]地质灾害防治与地质环境保护国家重点实验室(成都理工大学),成都610059 [3]中国地震局地球物理研究所,北京100081 [4]四川省地震局,成都610041

出　　处：《地球物理学报》2017年第6期2130-2146,共17页Chinese Journal of Geophysics

基　　金：国家自然科学基金(41340009;41674059;U1262206);成都理工大学地质灾害防治与地质环境保护国家重点实验室自主课题基金;成都理工大学四川盆地及周边地震活动性研究创新团队联合资助

摘　　要：芦山与汶川地震之间存在约40 km的地震空区.震源区和地震空区的深部构造背景的研究对深入了解中强地震的深部孕育环境及地震空区的地震活动性具有重要科学意义.利用本小组布设的15个临时观测地震台以及21个芦山科考台站和21个四川省地震局固定台站记录的远震数据,用H-K叠加方法得到各个台站的地壳厚度和平均泊松比,并构建了接收函数共转换点(CCP)偏移叠加图像以及反演得到台站下方的S波速度模型.我们的结果揭示了震源区和地震空区地壳结构特征差异:(1)汶川震源区的地壳平均泊松比为~0.28;芦山震源区为~0.29;而地震空区处于泊松比变化剧烈的区域;(2)汶川地震与芦山地震的震源区以西下方的Moho面呈现深度上的突变(这与前人的研究成果基本一致),分别从~44 km突变到~59 km,~40 km突变到~50 km,而地震空区地壳平均厚度呈现渐变性变化;(3)地震空区Moho面下凹且具有低速的上地壳.综合一维S波速度结构和H-k以及CCP的初步结果,这可能显示汶川地震的发震断裂在深部方向上向西倾斜并形成切割整个地壳的大型断裂;芦山地震则可能是由于上、下地壳解耦引起的;而地震空区处于两种地震形成机制控制区域的过渡带中.A seismic gap with a horizontal distance of 40 km exists between Wenchuan and Lushan earthquakes. Study on the deep tectonic setting of the area near strong earthquakes and seismic gap may shed lights on the seismogenic environment in these areas. Using teleseismic data from 15 temporary observation stations deployed by our research group and 21 stations deployed by the Scientific Exploration of Lushan earthquake team （China Earthquake Administration） and 21 permanent stations from Seismological Bureau of Sichuan Province, we apply the H-κ stacking method to estimate the crustal thickness and average Poisson＇s ratio beneath each station, then build the receiver function common conversion point （CCP） images and the S-wave velocity model below seismic stations obtained by linear inversion. Our results reveal sharp contrast of crustal structure between source area of large earthquakes and seismic gap： （1） the average Poisson＇s ratio of the crust in the source region of Wenchuan earthquake is ~0.28, and ~0.29 in the source area of Lushan earthquake; the Poisson＇s ratio in the seismic gap varies dramatically;（2） below the source area of the Wenchuan earthquake and the Lushan earthquake, Moho depth deepens gradually westward （this is consistent with many other results）, the Moho depth jumps from ~44 km to ~59 km and ~40 km to ~50 km in the west of Lushan and Wenchuan earthquakes, respectively; but the crustal thickness along the cross-section passing the seismic gap is relatively flat; （3） the seismic gap is characterized as a Moho depression and a low velocity in upper crust. Integrated 1-D S wave velocity structure and results of H-κ and CCP stacking indicate that the fault of Wenchuan earthquake may cut through the entire crust and tilt westward; the Lushan earthquake may be caused by a low-velocity zone in middle crust to decouple the deformation between the upper and lower crust; and the seismic gap may be in the transition zone of the two regions controlled by the two seismogenic

关 键 词：汶川地震 芦山地震 地震空区 速度结构 接收函数 

分 类 号：P315[天文地球—地震学]