Topographic responses in magnetometric resistivity modeling

Abstract

The magnetometric resistivity (MMR) topographic responses due to earth topography were simulated using a finite‐element method. An algorithm was developed and the computer program was verified by comparison with analytic responses for half‐space and contact models. The topographic responses for different rugged surfaces were computed, and the model results indicate topographic effects can affect MMR sounding interpretation. In general, MMR topographic responses do depend on surface form; the more rugged the ground surface is, the larger the MMR topographic anomaly will be. These topographic effects will decrease as the distance between the source (and/or receiver) position and the high relief area is increased. We only address the problem of determining MMR anomalies over a two‐dimensional (2-D) topography. A numerical example illustrates an effective means of reducing the terrain effects for a 45‐degree dipping fault model incorporating a 45‐degree ramp surface, suggesting that the finite‐element modeling technique does provide a means of determining topographic correction for MMR sounding data.