陈安国,
高原^,,
石玉涛
中国地震局地震预测研究所(地震预测重点实验室), 北京 100036

基金项目: 国家重点研发计划重点专项课题(2017YFC1500304)资助


详细信息

作者简介: 陈安国, 男, 1991年生, 在读研究生, 主要从事地壳剪切波分裂研究.E-mail:18733672676@163.com

通讯作者: 高原, 男, 1964年生, 研究员, 主要从事地震各向异性和深部构造等研究.E-mail:qzgyseis@163.com

中图分类号: P315

收稿日期:2018-05-24
修回日期:2018-07-06
上线日期:2019-08-05

Seismic anisotropy and its variation in the upper crust beneath the Longmen Shan fault zone

CHEN AnGuo,
GAO Yuan^,,
SHI YuTao
Key Laboratory of Earthquake Forecasting, Institute of Earthquake Forecasting, China Earthquake Administration, Beijing 100036, China



More Information

Corresponding author: GAO Yuan,E-mail:qzgyseis@163.com

MSC: P315

--> Received Date: 24 May 2018
Revised Date: 06 July 2018
Available Online: 05 August 2019


摘要
摘要:龙门山断裂带上发生了2008年汶川8.0级和2013年芦山7.0级地震，为了研究芦山地震前后该区域地壳各向异性的空间分布和变化，以及较大地震对快剪切波偏振方向造成的影响，本文运用剪切波分裂系统分析方法，结合固定地震台网（2010-01—2017-10）和川西流动地震台阵（2006-10—2009-07）的小震波形数据，得到了龙门山断裂带及邻近地区上地壳各向异性参数.结果表明，慢剪切波时间延迟主要分布在0.65~7.39 ms·km^-1之间，横向上具有不均匀性，地壳20 km以上的介质对各向异性的贡献较大.快剪切波优势偏振方向主要为NW或NWW和NE向，具有明显的分区特性.位于龙门山断裂带附近台站的快剪切波偏振方向自北向南由NWW转变为NW、NE向，在南段又变为NWW、NE向，指示了龙门山断裂带的分段特性是其构造属性.根据得到的有效事件数据，本文使用的49个台站中有19个台站的各向异性参数与反方位角、深度、震级和路径长度等显示出一定的相关性.研究区内的芦山地震及其他较大地震可能影响了局部快剪切波偏振方向.研究表明，更多的有效事件数据将有益于定量分析局部构造应力场和断裂属性的变化情况，从而有益于断裂带地震学特性及地震预测研究.
关键词: 龙门山断裂带/
剪切波分裂/
快剪切波偏振/
慢剪切波时间延迟/
区域主压应力方向与变化/
芦山地震

Abstract:Both the Wenchuan M_S8.0 earthquake in 2008 and the Lushan M_S7.0 earthquake in 2013 occurred on the Longmen Shan fault zone.The purpose of this work is to study the spatial distribution and variation of seismic anisotropy in the upper crust beneath this area before and after the Lushan earthquake and the influence of major templors on polarization direction of fast shear waves. Using the systematic analysis method for shear-wave splitting and data from the permanent seismic stations from January 2010 to October 2017 and the Western Sichuan Seismic Array from October 2006 to July 2009, we obtain anisotropic parameters of upper crust in the study area. The results show that the time delay of slow shear-waves ranges from 0.65 to 7.39 ms·km^-1, implying obvious lateral inhomogeneity. Media above depth 20 km has major contribution to the anisotropy.Dominant polarization directions of fast shear-waves (FPS) are NW, NWW and NE, showing an obvious zoning pattern.Dominant FPS from north to south along the Longmen Shan fault zone changes from NWW to NW or NE direction.However, it is in NWW or NE direction in the south part.Tectonically it indicates segmentation of the Longmen Shan fault zone.Based on data of effective events available, seismic parameters of 19 of 49 stations show some correlations with the back-azimuth, source depth, magnitude and ray paths.The Lushan earthquake and the other major earthquakes in the study area might have influenced locally polarization directions of fast shear-waves.This paper indicates more effective data will be helpful to quantitatively analyze variations of the local tectonic stress field and fault attributions, furthermore beneficial to study seismic features of fault zones and earthquake prediction.
Key words:Longmen Shan fault zone/
Shear-wave splitting/
Polarization of fast shear-wave/
Time delay of slow shear-wave/
Direction and variation of regional principal compressive stress/
Lushan earthquake



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