The shallow Longmenshan crustal S-velocity structure of the fault zone using ambient noise tomography of a seismic dense array  

作　　者：Dandan Li Gaochun Wang Ruihua Lin Kai Deng Xiaobo Tian 

机构地区：[1]State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China [2]University of Chinese Academy of Sciences,Beijing 100049,China [3]Sinosteel Tianjin Geological Academy LTD,Tianjin 300181,China [4]College of Geophysics,Chengdu University of Technology,Chengdu 610059,China [5]CAS Center for Excellence in Tibetan Plateau Earth Sciences,Beijing 100101,China

出　　处：《Earthquake Science》2019年第5期197-206,共10页地震学报（英文版）

基　　金：the National Key R&D Program of China(No.2016YFC0600301);the National Natural Science Foundation of China.(No.41974053).

摘　　要：The Longmenshan fault zone(LMSF),characterized by complex structures and strong seismicity,is located at the junction between the eastern margin of the Tibetan Plateau and the north-western Sichuan basin.Since the Wenchuan earthquake on May 12,2008,abundant studies of the formation mechanism of earthquakes along the LMSF were performed.In this study,a short-period dense seismic array deployed across the LMSF was applied by ambient noise tomography.Fifty-two 3-D seismic instruments were used for data acquisition for 26 days.We calculated the empirical Green's functions(EGFs)between different station-pairs and extracted 776 Rayleigh-wave dispersion curves between 2 and 7 s.And then,we used the direct-inversion method to obtain the fine shallow crustal S-wave velocity structure within 6 km depth in the middle section of the Longmenshan fault zone and nearby areas.Our results show that the sedimentary layer(>5 km)exists in the northwest margin of Sichuan Basin with a low S-wave velocity(~1.5-2.5 km/s)which is much thicker than that beneath the Longmenshan fault zone and the Songpan-Garze block.The high-velocity structures with clear boundaries below the middle of Longmenshan fault zone(~2-4 km)and the Songpan-Garze block(~4.5-6 km)probably reveal the NW-SE distribution patterns of both the Pengguan complex and the high-density belt hidden in the northwest of the Pengguan complex.And the obviously high-velocity anomalies observed at the depth of^1-2 km in the southeastern margin of the Songpan-Garze block can be considered as the Laojungou granites.Our results provide a high-resolution shallow velocity structure for detailed studies of the Longmenshan fault zone.

关 键 词：Longmenshan fault zone ambient noise tomography S-wave velocity structure short-period dense seis-mic arrays 

分 类 号：P315[天文地球—地震学]