1989年10月和1991年3月大同地震的活动断裂

Active faults of the Datong Earthquakes of October 1989 and March 1991

中国地震局地球物理研究所在 1 989年 1 0月 5.8级和 1 991年 3月 5.5级大同地震之后使用由数字地震仪组成的小孔径流动台网对其余震进行了流动观测。通过利用多道地震数据分析软件正确地确定震相 ,修改地壳速度模型等方法 ,高精度地确定了部分余震的震源位置。两次大同地震部分余震的震中分布表明 ,大同地震的主干断裂是北北东走向的断裂 ,同时伴随北西走向的分支断裂的活动。盆地的速度结构可以以双层速度结构模拟 ,其上层为 P波速度为3.1 km/s的沉积层 ,符合大同盆地为火山喷发堆积物的实际情况。

Both after the October,1989 M S=5 8 and the March,1991 M S=5 5 Datong Earthquakes,The Institute of Geophysics,CSB deployed a mobile network consisted by digital seismograph in the epicenter area for aftershock observation.The multiply trace processing program is used for correct phase picking up.Try and error method is used for finding the right velocity structure.Under the bases of the right structure,we got high accurate hypocenter location.The distribution of hypocenter of aftershocks shows that the fault of the main shock is a northeast striking fault.And the northwest striking sub branch faults are active also.The velocity structure of the Datong basin could be simulated by two layers model.The P wave velocity in the upper layer is 3 1 km/sec.This is consisted with the actual situation in which the upper layer of the basin is disposed by volcano fragmentary and ash.