地震工程学报Issue(2)：372-379,8.DOI:10.3969/j.issn.1000-0844.2014.02.0372
青海东南部应力场特征及正断层小震现象的初步研究
Research on Stress Field Characteristics and Normal Fault Small Earthquakes of Southeastern Qinghai
摘要
Abstract
Digital seismic waves recorded by Qinghai and Gansu digital networks from January 2008 to August 2013 are used to obtain 92 focal mechanism solutions of 4.9 ≥ M L≥ 2.5 moder-ate and small earthquakes in southeastern Qinghai by using the methods of P-wave and S-wave maximum amplitude ratio and cut and paste (CAP).The focal mechanism solutions of 3.9 ≥ M L≥ 2.5 are retrieved by the former method,and the other larger earthquakes are retrieved by the latter.Moreover,analysis of these focal mechanism solutions by means of statistics and systematic cluster analysis reveals that the predominant distributions of the plunge of T-and P-axes are less than 45°and that a few have a high plunge of P.These results indicate that the moderate and small earthquakes in this region are mostly strike-slip and that a certain number of normal fault earthquakes are present;however,small thrust fault earthquakes are rarely seen.The distributions of all of the azimuths of the P-axis are widely scattered,which may be attributed to the fact that the small earthquakes are more happenstance than tectonic earthquakes;however,the distribu-tions of the P-axis azimuth of M L≥ 3.0 are so regular that it is easy to see the predominant dis-tributions.By using focal mechanism solutions of M L≥ 3.0 by the grid test method,the mean re-gional stress field is obtained.The tectonic stress field is primarily represented by NE-SW hori-zontal compressive stress and NW-SW horizontal tensile stress in the southeastern Qinghai prov-ince,and the mean contradictory ratio is 0.32.These results are the same as those in previous re-search.Furthermore,it is determined that the small normal fault earthquakes are mainly distribu-ted in the eastern part of the Kunlun active fault(Maqin-Maqu)and in the southern part of the Elashan Mountain fault.This paper analyses the mechanism in which small normal fault earth-quakes are produced.The southeastern region of Qinghai province still belongs to the inner Qing-hai-Tibet block,and the significant differences in elevation could create many small pull-apart basins in some area,such as the eastern part of the Kunlun active fault(Maqin-Maqu)In this re-gion,the small normal fault earthquakes have a certain proportion;therefore,it is suggested that these small normal fault earthquakes may be attributed to gravity slumping because of the high al-titude.关键词
青海东南部/震源机制解/构造应力场/正断层地震Key words
the southeast of Qinghai/focal mechanism solutions/tectonic stress field/normal fault earthquakes分类
天文与地球科学引用本文复制引用
马辉青,姚家骏,马建新,李玮杰,袁伏全..青海东南部应力场特征及正断层小震现象的初步研究[J].地震工程学报,2014,(2):372-379,8.基金项目
2014年星火计划青年项目（XH14050Y）；2014年度震情跟踪青年课题 （）
