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Title:: Velocity Structure Tomography in Southern California Area Based on Local Earthquakes P-wave Travel-time

Author(s):: ZHOU Xixi; CHEN Qiang; ZHANG Yijun; HUANG Xiaomei; (Faculty of Geosciences and Environmental Engineering,Southwest Jiaotong University,Chengdu 611756,Sichuan,China)

Keywords:: Southern California; P-wave travel-times; three-dimensional crustal velocity structure; seismic tomography

摘要:: 采用2015—2018年南加州地区密集分布的宽频带地震台站记录的505个近震事件,利用AIC准则拾取了35 600个初至P波到时,应用FMTOMO软件进行走时层析成像,获得了该地区0～40 km深度的三维P波地壳速度结构,其分辨率达0.5°×0.5°×5 km。不同深度的速度结构表明:南加州地区P波速度不仅随深度的变化而变化,且该地区地壳具有明显的横向不均匀性。反演结果显示:中地壳以上的速度结构与地壳岩层和断层系统密切相关,下地壳以下的速度结构存在大范围低速区,呈现横向不均匀性。

Abstract:: In this study,basing on 505 local-seismic events recorded by densely distributed broadband seismic stations in Southern California between Jan.,2015 and Dec.,2018,we pick up 35 600 first-arrival travel-time of P-waves by adopted the AIC method.Then using the FMTOMO software,we obtained a three-dimensional P-wave crust velocity structure with a depth range of 0～40 km in this area through travel-time tomography,and the resolution of the velocity structure can reach 0.5°×0.5°×5 km.The velocity structure at different depth revealed that the P-wave velocity in Southern California changed with the depth,and the crust in this region had obvious lateral heterogeneity.The inversion results show that the velocity structure above the mid-crust is closely related to the rock formations and fault systems,and that below the lower crust has a large area of low-speed,showing lateral heterogeneity.