西安地裂缝的新活动及其机制的初步研究

本文给出了西安地裂缝的新活动图象(1985—1989)井进行了分析,指出了西安地裂缝的构造特征及人文特征。对于构造特征,本文提出了不仅有构造的几何控制作用,而且有构造的力学控制作用。前者直观地表现在地裂缝的空间几何分布规律上,而后者则既表现在地裂缝的形成过程中,又表现在地裂缝活动与地震活动的时间特征上。人类活动主要是过量抽取地下承压水所导致的地面不均匀沉降,这是地裂缝运动速率比构造运动速率高一个数量级的原因。按照地裂缝的主运动即垂直差异运动速率,本文将地裂缝分为三个等级(A级≥20毫米/年,5毫米≤B级<20毫米/年,C级<5毫米/年)。西安地裂缝的活动度分级图较好地反映了地裂缝的多因迭加机制。

A PRELIMINARY DISCUSSION ON EVOLUTION OF XI'AN GROUND FISSURE (1985-1989) AND ITS MECHANISM

The active pictures of XGF (Xi''an Ground Fissures) are given and analysed. Both tectonic characteristics and artificial characteristics of XGF are shown. The tectonic control functions on XGF appear not only geometrical but also mechanical, the former can be seen from space distribution feature and geometrical pattern of XGF, the latter can be seen from its formation process, as well as the time feature of earthquakes and XGF. The human activities, mainly overextraction of piezometrie ground water, result in land subsidence in Xi''an. The ununiform land subsidence is responsible for high rate of the movement of XGF, which is about ten times higher than the rate of tectonic movement. According to the major rate(the rate of vertical slip), XGF is classified into three grades. The map of XGF classification well reflects its multiplicate cause mechanism.