1987年8月10日灵武5.5级地震前后小震活动图象及震区应力场特征

THE ACTIVE PATTERN OF SMALL EARTHQUAKES AND THE FEATURES OF FOCAL REGION STRESS FIELD BEFORE AND AFTER THE LINGWU EARTHQUAKE OF Ms5.5 ON AUG. 10, 1987

摘要:

本文对1987年8月10日灵武5.5级地震进行了综合研究。其地震序列属前震-主震-余震型,前震和余震沿该区两条主要断裂分布,主震位于两条断裂交汇部位。震前形成了明显的小震活动空区。这次地震的发震构造走向为322°,长16km。震区应力场主压应力方向为268°。本文还指出,强烈的水平和垂直差异运动是灵武地区频繁多震的主要原因。

Abstract:

The Lingwu earthquake of Ms 5.5 on Aug. 10, 1987 is studied comprehensively. Before the seism, the direction of the principal compressional stress axis of the regional stress field is 268°. The strike of the structure where the earthquake occurred is 322°, it is 16km long. The seismic sequence belongs to the foreshock-mainshock-aftershock type. Foreshocks and aftershocks are distributed along two main active structure zones in Lingwu area. The mainshock is located at place where the two structures cross. The seismic gap appeared before the earthquake. The mechanical reason that a lot of seisms frequently took place in this region is due to the strong horizontal and vertical different motion.