Numerical Modeling on Transient Electromagnetic Responses of a 3-D Electric Dipole Source on 2-D Polarizable Earth Surface

Abstract

Numerical modeling on transient electromagnetic responses of a 3-D electric dipole source on 2-D earth model is an important basic work in computation geophysics. In electromagnetic method of the geophysical exploration, when the dipole-dipole array is used, and response on the polarizable earth surface is studied in time domain, it is called time spectral resistivity method (TSR). In this paper, 2.5-dimensional numerical algorithm for TSR is established, whose characters are as following: (1) A 2-D finite element method is adopted in which two diagonal lines are increased in each rectangular net to form triangular networks. Unknown variable at central node of the rectangular net is eliminated by the Gauss elimination. So complex 2-D geoelectric section can be modeled more exactly but computation quantity is much less than that in rectangular network. (2) A new algorithm of computing secondary field directly is founded, which only needs computing two components of electric and magnetic primary field. Not only the computation accuracy is high, but also the computation time is not increasing much. (3) The new G-S inverse Laplace transform method based on the delay theorem of Laplace transform is used for the rapid calculation of the transient electromagnetic response with dense samples. (4) The algorithm can be used for computing the transient electromagnetic response on the conductive and polarizable earth.