唐山地震序列的构造过程

The Tectonic Process of the Tangshan Earthquake Sequence

本文采用地质构造、地震活动图象、震源机制资料综合分析方法,对唐山地震序列主要的构造过程进行研究。其结果表明,唐山地震序列是一个由多条断裂参加并逐次活动的复杂构造过程。先后显示活动的断裂及其错动性质是:唐山断裂带右旋剪切、蓟运河断裂左旋剪切、滦县—乐亭断裂右旋剪切、卢龙断裂右旋剪切。北西向蓟运河断裂与唐山断裂带构成一对共轭剪切构造。沿唐山断裂带的主震破裂面由初始阶段的北北东向北东—北东东和南西方向扩展,形成不对称的“S”形曲面。与现代地壳应力场最大剪切应力方向不完全一致的先存断裂的活动和地震破裂面转向扩展,是序列震源机制解P、T轴取向离散的主要原因之一。

In this paper, the main tectonic process of the Tangshan earthquake sequence was studied by comprehensive analysis of geological structures, seismicity pattern and focal mechanism data. The result shows that the process in which many faults involved were active. The faults which displayed activities early or late were the Tangshan fault zone with right lateral distortion, the Jiyunhe fault with left lateral distortion, the Luanxian-leting fault with right lateral distortion, and the Lulong fault with right lateral distortion. Furthermore,the rupture plane of the main shock along the Tangshan fault zone was extended in the directim of NE-NEE and SW instead of the original NNE direction, forming an unsym-metric 'S' shaped curved surface. It was one of the important reasons of dispersive orientation of the P and T axes of the focal mechanism solutions of the sequence that the rupture plane changed the direction of exeensim and the Preexisted fault activity was not completely consistent with the maximum shear stress direction of recent crustal stress field. The NW Jiyunhe fault displayed activity in various stages of the sequence development and it formed a pair of conjugate earthquake structures together with the Tangshan fault zone.