A new method is presented in this paper for modeling the 3-D terrain effect that, in turn, can be approximately removed by applying a terrain correction to resistivity surveys. First, the 3-D electrical boundary value problem is transformed into an integral equation problem by use of Green's theorem. Then the boundary element method is used to solve the integral equation. The ground surface and the boundary of the anomalous body are divided into triangular elements. Linear variation of quantities is assumed within each element and a Gaussian quadrature formula is used to calculate the integral. In this way. the integral equation is converted into a set of linear equations. The potential field value on the ground surface is obtained by solving the linear equation system with Gaussian elimination.

本文提出一种反演非均匀的海山磁性的新方法——虚源法，海山的磁化强度由均匀和不均匀两部分组成。将均匀磁化强度J0看作位于无穷远处的虚磁源在海山中产生的场，非均匀磁化强度J'看作位于海山外部一组虚磁源在海山中产生的场和和。用电优化的方法使剩余异常取极小来反演J0和J'。模型研究表明，虚源法反演得到的均匀磁化强度J0与海山的主磁化方向很接近。

This paper uses the boundary element methodto solve the problem of the effect of two-dimensional terrain with point current source on resistivity surveys. First, the 3-D boundary value problem of the electric field of a point source on 2-d terratin is converted in to a 2-D boundary value problem using a Fourer trans form. Then, the 2-D boundaryvalue poroblem is transformed into a boundary integral equation by means of Green's formula. The boundary element method is used to solve the integral equation. Finally, using an inverse Fourier inverse transform, we get the electric potential in 3-D space. Examples calculated for two terrain models show that the resultsform this method compare well with those from analytic andfinite elemont mothod. If the terrain has a clear strike, this method can be used for terrain corrections for resistivity surveys. An example of a terrain correction for electric sounding is given. This method can be run on a personal computer and takes a few minutes to correct a profile of data on an IBM AT-grade computer.

倾度法电气探查にぉはゐ2次元地形の地形楠正法み境界要素法み用いて導出てた。倾度法电气探查にぉいては，信号源み水平方向の一样电场と考えるこがでをる。2次元境界值问题をケリンの定理な用いて分方程式に变换し，境界要素法に基づいて，地表面の电位な数值计算の可能を式ょして導いた。式の变形过程は，すぺて输文中に明记した。2次元地形をそっ比抵抗p0の均质大地の见挂比抵抗を上记の方法で计算してptopょする。测定さゎに见挂比抵抗pobaをptop/poでわったそのを地形補正见挂比抵抗pcorょ定义する。2次阮地形を有する均质大地内に比抵抗异常体をわいた场合の见挂比抵抗ょ，异常体の无い场合の见挂比抗を计算して，そわぞわpobsょptopょわき，上记の方法で地形補正した结果，地形の无い场合の见挂比抵抗ょ非常に近い见挂比抵抗が得ちわるこょを示した。ケーススタラィょして，安山岩质の母岩中に，金を伴ち高比抵抗の石英脈石が存在する地域の比抵抗探查ラータを用いて，本手法にょり地形補正を行った。補正后のラータに对してslop法にょり推定した埋设深度け12mでめった。试锥にょり确答ざぉた12.9mでめった。本手法けぺーソナルュンピュータで1～2秒の计算时间で简便に计算でさゐので，倾度法の地形補正法ょして极めて便利な方法あゐ。

Using the boundary element method, thenumerical modeling problem of three-dimensional terrain effect on magnetotelluric (MT) field is solved. This modeling technique can be run on PC in the case of adopting special net divison. The result of modeling test for 2-D terrain hy this modeling technique isbasically coincident with that by 2-D modeling technique, but there is a great difference between the results of 3-D and 2-D modeling for 3-D terrain.