华北中部重力场的动态变化及其强震危险含义

基于绝对和相对重力观测获得的区域重力场时、空动态变化,结合区域GPS测量资料与活动构造分析,本文研究了华北中部地区2009-2011年的重力场变化特征,讨论了该区域重力场动态变化的强震危险含义.结果主要表明:(1)华北中部的活动地块边界及部分重要活动断裂带两侧存在较大差异的重力场空间变化;其中,以山西断陷带北东段所在的晋冀蒙交界地区为中心,形成较大面积的重力负值变化区,且沿该区西北缘的NE向岱海-黄旗海断裂带以及东南缘的NNE向太行山山前断裂带附近分别形成重力变化的高梯度带,可能反映这些部位近年的构造或断裂活动显著.(2)不同时段的重力场差分动态演化图像可能反映了近年山西断陷带北东段(京西北盆-岭构造区)及其附近的重力场整体经历了"准均匀→非均匀→断陷带北段侧向显著变化→局部"硬化"的演化过程.(3)研究区重力场的时间累积变化图像可用"区域应力场增强→区域断裂与断块差异运动及变形增强→局部运动受阻"的过程进行解释.(4)研究区的一些重力异常部位存在中-长期强震危险背景.

Dynamic variation of the gravity field in middle North China and its implication for seismic potential

Based on the spatial-temporal dynamic variation of the regional gravity field from absolute and relative gravity measurements, combined with GPS data and active tectonic analysis, this paper studies the change characteristics of the gravity field in middle north China for the period from 2009 to 2011, and discusses the implication of the dynamic change of the regional gravity field for seismic strong earthquakes. The results show that: (1) The spatial distribution of the gravity field is very different on either side of active block boundaries and some major active faults in middle North China. In the northern portion of the Shanxi graben zone that is centered at the border region among Shanxi, Hebei and Inner Mongolia,the gravity variation shows a great area of negative anomalies, and on the northwestern margin and the southeastern margin of the region, two gradient zones with high gravity differences are present along the NE-trending Daihai-Huangqihai fault zone and the NNE-trending Taihang mountain front fault zone, respectively, apparently suggesting that tectonic activity or active faulting in these two margin areas are significant. (2)The dynamic evolution patterns of the gravity differences of the northern segment of the Shanxi graben zone ( or in the basin-and-range province northwest of Beijing) for various periods in the recent years seem to have displayed such a process that the total change of the gravity field may be in the order: quasi-homogeneous-non-homogeneous-significantly various on the bilateral sides of the northern segment of the Shanxi graben zone-locally'hardening’(or changing little). (3) The patterns of the cumulated gravity variation with time can be explained by such a process: strengthening of the regional stress field-strengthening of active faulting and movement or deformation between fault-blocks-the movement being locked somewhere. (4) In the study region, those places with significant gravity anomalies would be localities with mid- and long-term risks of major earthquakes in the future.