怀来盆地的构造应力场  

Tectonic stress field in Huailai Basin

作　　者：许向彤[1] 陈运泰[1] 王培德[1] 

机构地区：[1]国家地震局地球物理研究所

出　　处：《地震地磁观测与研究》1997年第1期1-8,共8页Seismological and Geomagnetic Observation and Research

摘　　要：１９９５年７月２０日在北京西北的怀来盆地发生了一次ＭＬ＝４．１地震。在此主震之后该地区小震活动变得十分活跃。在１９９５年７月１日至１９９６年６月３０日期间，中－欧合作怀来数字地震台网记录并精确定位了这个地震序列的４５０多个地震。余震的震源分布表明，余震主要分布在两个共轭的断层上。在盆地南部边缘的余震震源位于走向５０°、倾向南东，倾角８０°的断层上，而盆地北部边缘的余震震源则位于走向１５０°、几乎竖直的断层上。用Ｐ波初动符合资料得到了主震的震源机制解。根据余震震源的分布，确定走向３７°、倾角４０°、滑动角－１５４°的节面为主震的断层面，另一节面走向２８７°、倾角７４°、滑动角－５３°。利用怀来数字地震台网的记录资料，分析了怀来地区近期地震活动性和构造应力场。结果表明，怀来盆地的主压应力轴的方位角为２３６°，倾角４８°，与主压应力轴近水平、北东东向的华北地区的构造应力场一致，表明了ＭＬ（＝４．１地震序列是在怀来盆地北东东向挤压、北北西向拉张的构造应力作用下发生的。处于上述两条共轭断层文汇处的怀来县城附近地区近期小震活动较少，表现出断层闭锁区的特征。怀来盆地潜在的地震危险性应予以特别关注，但其近期的微震活动并未显?On July 20, 1995, an earthquake of ML= 4.1 occurred in Huailai basin, northwest of Beijing, Following the main shock , seismicity sharply increased in the basin. Over 450 earth- quakes of the ML= 4.1 sequence were recorded and well located in the period July 1 , 1995 through June 30, 1996 by the Sino-European Cooperative Huailai Digital Seismograph Net- work(HDSN ) , and the hypocenters of the aftershocks suggest activities on two conjugate faulcs. The hypocenters of the aftershocks at the south-edge of the basin lie on a northeastern trending fault (strike 50°, dip 85° , and those of the aftershocks at the north-edge of the basin , on a nearly vertical and northwestern trending fault (strike 150°), The fault-plane solu- tion of the main shock was obtained using P-wave first motion data. One of the nodal plane has strike 37°, dip 40°and rake - 154° This plane was selected as fault plane of the main shock based on the hypocentral distribution of the aftershocks at the south-edge of the basin. The alternate nodal plane has strike 287°, dip 74°, and rake - 53°, Using the data from the HDSN , we analyzed recent seismicity and tectonic stress field in the Huailai basin , The com- pression axis in the Huailai basin (azimuch 236°and plunge 48°) orients in the same azimuth as the compression axis . close to herizontal and oriented NEE , of the tectontic stress field in North China area. This suggests that the occurrence of the ML= 4.1 earthquake sequence is tectonically driven by the NEE-SWW compression and NNW-SSE tension in the Huailai basin. Low seismicity in the Huailai county area , which is located at the intersection of the above-mentioned two conjugate faults , is of the characteristics for a locked portion of a fault, While the potential earthquake hazard in the Huailai basin is worthy of particular note , recent activity of microearthquakes in the basin appears no visible anomaly related to the forthcoming of a major earthquake in short-tern. or month scale.

关 键 词：构造应力场 震源机制 怀来盆地 盆地 

分 类 号：P554[天文地球—构造地质学] P315.2[天文地球—地质学]