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Title:: Focal Mechanism Analysis of the Recent Earthquakes in Tangshan Seismic Region of M7.8 in 1976

作者:: 张宏志¹; 刁桂苓²; 陈祺福³; 胡新亮²; 王晓山²; 张跃刚²; (1.中国地震局地球物理研究所,北京 100081; 2.河北省地震局,石家庄 050021; 3.中国地震局地震预测研究所,北京 100036)

Author(s):: ZHANG Hong-zhi¹; DIAO Gui-ling²; CHEN Qi-fu³; (1.Institute of Geophysics,CEA,Beijing 100081,China)(2.Earthquake Administration of Hebei Province,Shijiazhuang 050021,China)(3.Institute of Earthquake Science,CEA,Beijing 100036,China)

Keywords:: Tangshan earthquake; focal structure; accurate locating; focal mechanism; long term activity of earthquake

摘要:: 利用首都圈数字地震台网记录,采用双差定位法对1976年唐山地震震区近年来发生的中小地震重新定位,获得1 998个高精度结果,据此将震区划分为中、东、西3个分布特征不同的区。唐山7.8级主震所在的中区南部地震分布走向NNE,主震震中北部转为NE向; 滦县7.1级余震所在的东区地震分布呈“丁”字形; 宁河6.9级余震所在的西区地震分布没有明显优势方向。反演得到198个地震的震源机制解,对进一步划分的5个子区分别给出平均解的应力轴取向,并结合震源位置讨论了唐山地震序列的震源构造。

Abstract:: Based on the records recorded by Digital Seismic Network in Capital Area,1998 accurate relocating results for the mid-small earthquake occurred in Tangshan seismic region in 1976 are obtained with Double-Difference Method.According to the characteristics,the seismic region can be divided into 3 sub-regions.The southern part of middle region with NNE strike,where the M7.8 main shock located,and turns to NE strike in the northern part.The eastern part shows a T shape where the Luanxian M7.1 earthquake located.There is no preponderant strike in the western part,where the M6.9 earthquake located.198 focal mechanisms are obtained by inversion,and the direction of mean stress axis is given respectively for the 5 divided sub regions.The focal structure of Tangshan earthquake series is discussed with hypocenter locations.