新丰江水库三维速度结构和震源参数的联合反演

本文对ACH方法做简化处理,先以一个地震为单元形成子矩阵,并将慢度扰动用一平均量来代替;在修正参数时,震源部分按常规进行,对慢度部分则利用代数重建技术将其分配到各个块体上.数值模拟结果表明,该方法能很好地反演震源位置和速度结构.运用新丰江遥测台网的数据进行研究,表明地震强活动区位于大坝附近,特别是在人字石断裂和高寨断裂的交汇处,震源集中沿罗坑-双下、葫芦凹-燕岩和黄竹蒿3条地震带,呈密集的高倾角分布,地震活动主要与北北西向构造和东西向构造有关,而与地表甚为发育的北东东向构造关系不大.速度图像中的低速区对应地表的破碎区,即地震带区域,也是该区重磁异常急剧变化的区域;而高速区内地震较少.上述特征同水的渗透作用有密切关系.

THE JOINT INVERSION OF 3-D VELOCITY STRUCTURE AND SOURCE PARAMETERS IN XINFENGJIANG RESERVOIR

In this paper some simplifications in ACH method have been made, first, we decompose the big part deviation matrix into a small one, which is made up of one earthquake only, as the same time we use the mean slowness disturbance to replace all that related with this earthquake, so that in each earthquake there are four parameters only, three of them relate with source and one relates with velocity. Second, the calculation for each earthquake consists of two iteration stepes in which SVD method is applied to construct inverse matrix and then a particalar treatment for speeding up calculation is adopted according to binomial theorem. Third, the term relating with source parameter is modified directly and the slowness correction is performed to corresponding blocks by Algebraic Reconstruction Technique. Repeating above procedure for each earthquake in turn, iterative process can be formed. Numerical modelling shows that this method has good quality in inversion. Applicating the present method and using those recordings obtained from the local telemetering stations in Xinfengjiang reservoir, the result shows some interesting features. It is found out that the area with strong seismicity is near the dam, particular in the intersection portion between Rengzisi fault and Gaozai fault, most earthquakes distribute along with three seismic belts of Ruokeng-Shuangxia, Huluou-Yanyan and Huang zhusong. It is also worthwhile to point out that seismic activity has certain relationship with NNW and EW tectonic structures, rather than NNE tectonics which are dominant on the surface. The velocity map indicates that low velocity zones are corresponding to some fractured zones where the gravitational and aeromagnetical anormalies show obvious change, while very few earthquakes occur in the high velocty zone. It is inferred that these characteristics are contributed to the penetration of water.