基于短周期密集台阵的北川地区浅层地壳结构研究  

Shallow structure of Beichuan area from a dense,short-period seismic array

作　　者：陈辛平 李红谊[1] 张玉婷 黄雅芬 葛慧颖 卫志杰 管勇[2] CHEN XinPing;LI HongYi;ZHANG YuTing;HUANG YaFen;GE HuiYing;WEI ZhiJie;GUAN Yong(School of Geophysics and Information Technology,China University of Geosciences(Beijing),Beijing 100083,China;Sichuan Earthquake Administration,Chengdu 610041,China)

机构地区：[1]中国地质大学(北京)地球物理与信息技术学院,北京100083 [2]四川省地震局,成都610041

出　　处：《地球物理学报》2022年第11期4311-4325,共15页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(U1939203);中国地震科学实验场专项(2019CSES0113)联合资助.

摘　　要：北川地区位于龙门山中央断裂带的中北段,2008年M_(S)8.0汶川地震发震断裂(映秀—北川断裂)穿北川老县城而过,对当地造成了毁灭性的破坏.除北川老县城以外,北川县内多处为汶川地震极震区,汶川地震摧毁了县内多个镇落.本研究在北川地区布设了由242台短周期地震仪组成的一条一维长测线和一个小孔径的二维面状密集台阵,进行了22天的连续记录.利用这些数据分别开展了背景噪声层析成像和水平垂直向谱比法(HVSR)研究,最终得到了北川地区浅层地壳结构.首先我们从背景噪声连续数据中提取了0.1~1 Hz的瑞利面波信号,然后反演得到了研究区的三维浅层横波速度结构,结果显示研究区存在三个低速区,其中汶川地震的地表破裂带附近存在深约2 km的低速区.同时我们提取了各台站的HVSR曲线,结果显示位于地表破裂带附近的台站HVSR曲线具有双峰特征,而远离地表破裂带台站的HVSR曲线总体呈现单峰特征,研究区沉积层最厚可达200 m.Beichuan is located in the central and northern section of the Longmen Shan central fault zone.The 2008 M_(S)8.0 Wenchuan earthquake seismogenic fault(Yingxiu-Beichuan fault)passed through the Beichuan old town,causing devastating damage.Besides the Beichuan old town,the earthquake destroyed many other villages in this county.In this study,a linear array crossing the surface rupture and a two dimensional dense array with a small aperture comprising 242 short-period seismic stations,were deployed in Beichuan for 22 days.Ambient noise tomography and horizontal vertical spectral ratio method(HVSR)are used to study the shallow crustal structure in Beichuan area.Firstly,we measured Rayleigh waves dispersion curves between 0.1~1 Hz from the continuous ambient noise data by cross-correlation,and then the three-dimensional shallow shear wave velocity structure was inverted from Rayleigh wave dispersion.The results show that there are three low-velocity zones in the study area,among which there is a low-velocity zone with a depth of~2 km near the surface rupture trace of the Wenchuan earthquake.Meanwhile,we computed the HVSR curves of each station.Our results reveal that the HVSR curves of stations near the surface rupture exhibit double peaks,while stations far away from the surface rupture trace are featured with a single peak.The maximum thickness of the sedimentary layer in the study area can reach~200 m.

关 键 词：龙门山中央断裂带 北川地区 背景噪声 HVSR 

分 类 号：P315[天文地球—地震学]