Magnetotelluric Survey in Extremely Noisy Environment at the Pohang Low-Enthalpy Geothermal Area, Korea

Abstract

Korea is one of the most difficult countries in the world from the point of view of magnetotelluric (MT) data acquisition. This is because the natural MT signals are often completely contaminated by artificial electromagnetic noises from power lines and other various man-made sources. We conducted MT measurements in the Pohang area, southeastern Korea, in 2002 and 2003, as one of the initial surveys for the development of low-enthalpy geothermal resources in the area. We applied a very far remote reference by setting a remote site in southwestern Japan, which is approximately 500 km away from the Pohang area. Very strong artificial noise was observed at a frequency band from 0.1 Hz to 100 Hz. The remote reference processing successfully removed most of these noises. Although the resultant MT impedance was not of very high quality at most sites as compared with the clean data obtained in calm areas in other countries, these data are of sufficient quality for further interpretation. We carried out 3D inversion of the MT data and compared with geological and drilling data in the area. In this paper, we present the remote referenced results and the 3D resistivity models of the Pohang geothermal area.