CAJ | 학술논문

利用2008-2013年青海东南部数字地震波资料，采用 Pg、Sg 最大振幅比及 CAP 方法反演得到92个 ML 2．5～4．9中小地震震源机制解。统计结果表明该区中小地震震源类型以走滑为主，应力轴接近水平，兼有一定量正断层类型，逆冲类型较少；利用格点尝试法求出研究区平均现代构造应力场是以处于近 NE-SW 方向的水平压应力和近 NW-SE 方向的水平张应力为特征；进一步分析了研究区正断层小震产生的背景，初步认为这些正断层类型小震可能主要源自高海拔地形产生的重力滑塌作用。
이용2008-2013년청해동남부수자지진파자료，채용 Pg、Sg 최대진폭비급 CAP 방법반연득도92개 ML 2．5～4．9중소지진진원궤제해。통계결과표명해구중소지진진원류형이주활위주，응력축접근수평，겸유일정량정단층류형，역충류형교소；이용격점상시법구출연구구평균현대구조응력장시이처우근 NE-SW 방향적수평압응력화근 NW-SE 방향적수평장응력위특정；진일보분석료연구구정단층소진산생적배경，초보인위저사정단층류형소진가능주요원자고해발지형산생적중력활탑작용。
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.