层状介质中三维大地电磁模拟

MAGNETOTELLURIC MODELLING OF THREE-DIMENSIONAL BODIES IN LAYERED EARTHS

本文发展了积分方程法用于层状介质中三维不均匀体的大地电磁模拟算法(简称MT).分为二个步骤:第一步,异常体用等效的散射电流代替,通过层状介质中的格林函数,建立以散射电流为未知参数的积分方程;第二步,把求得的散射电流乘上相应的格林函数,即得地面上的二次电磁场,由此而计算出各种MT响应. 文中采用了数值滤波与插值、群变换以及格林矩阵带状化三个方面的数值处理方法,提高了计算效率.通过与已发表的三维MT计算结果对比及格林函数互易性检验,表明了该算法的正确性.在此基础上,进行了数值模拟,初步讨论了三维MT曲线的畸变特点.

In this paper, we have developed an algorithm based on the method of integral equations to simulate the MT responses of three-diemsional bodies in layered earths. It has two steps. First is to compute the equivalent scatter current distribution in inhomogeneous midia. The 3-D bodies are replaced by an equivalent current which is approximated by pulse basis funtions. The integral equations of unknown electrical fields in 3-D bodies are constructued using the tensor Green's funtions appropriate to layered earths. Second step is to find the scattered fields on he surface of earth by integration electric and magnetic tensor Green's funtions over the scattering currents.In order to reduce computation cost and storage, three kinds of processing methods are adopted. They are linear filtering and interpolation, group transformation, and sparse tensor Green's matrix.A comparision of our responses over a 3-D body in uniform half space with that reported in literatures and reciprocity of Green's funtions have verified our program. The distortions of 3-D MT curves are preliminarily discussed with some new conclusions.