New Magnetotelluric Response Functions for Geothermal Applications

Abstract

As geothermal reservoirs usually occur in geologically complex zones, where the physical properties of the rocks have complicated geometrical distributions, the traditional 2-D TE-TM approach for magnetotelluric interpretation severely limits the use of the available information. 3-D inversion using the full tensor information is so far too expensive for standard use, mainly because both the number of model parameters and the number of response functions are too large. In this work we use a new approach, the series and parallel transformation, which transforms the tensor into two complementary impedances and two angular response functions. This new representation of MT responses is valid regardless of dimensionality and, unlike the tensor elements do not depend on rotations of the measuring reference system. The series and parallel impedances play the roll of the TE and TM modes in 2-D situations. In addition, our approach could be an alternative to reduce the number of response functions used in 3-D interpretation. We present applications to field data from Las Tres VÌrgenes geothermal field in Mexico.