Topographic Effects and Correction in Electromagnetic Surveys
Yutaka Sasaki
Kyushu University, Department of Earth Resources Engineering, Japan.
Contacts: sasaki@mine.kyushu-u.ac.jp (Yutaka Sasaki)
Abstract
The effects of topography on electromagnetic (EM) surveys have not been reported in the literature for a long time. One reason is that topographic responses are considered small compared with those from conductive targets such as massive sulfide ores. However, as the geotechnical and geological applications increase, there are many cases in which topographic effects should be important. I use a staggered-grid finite-difference method to simulate the frequency-domain EM responses to topography in three dimensions. The modeling examples include both ground and airborne EM surveys. Results show that a hill produces significant anomalies over the ridge and the slope changes. To reduce these effects, a simple correction procedure is presented and tested on synthetic data. Although the correction is helpful in suppressing topographic effects, the corrected data do not reproduce the effects of the actual resistivity structure accurately enough to permit the quantitative interpretation assuming a flat-earth model. The most accurate approach to interpreting EM data with topographic effects is to incorporate topography into the forward-modeling part in the inversion. A 3-D inversion method is successfully tested on synthetic data.
raeg2003@tansa.kumst.kyoto-u.ac.jp
Last modified: Mon Nov 11 12:25:12 2002