A Study on Magnetotelluric Characteristics of Magmatic Geothermal Systems

The Magnetotelluric (MT) method is a widely used and effective method of exploring geothermal resources because it can reveal geological information at a great depth and is cost effective. In order to further improve the reliability and rationality of MT data interpretation, MT responses for a typical hydrothermal system and a hot dry rock (HDR) and partial melting system are investigated by a finite-element (FE) forward modeling approach based on unstructured tetrahedral grids that can handle with complex-shaped geothermal systems. These two geothermal models, designed by the 3ds Max software, are comprised of a clay cap, a reservoir, and a heat source, and are discretized into tetrahedral elements by TetGen software. The results show that the apparent resistivities at the broadband of frequencies are mainly affected by the shallow low-resistivity clay cap due to its strong shielding effects, and the induction arrows effectively reflect the boundary of the clay cap. The conductive heat-conducting path and heat source (1 S/m) considered in the models of the HDR and partial melting system could cause significant changes in the apparent resistivities and induction arrows at low frequencies. It suggests that in addition to the apparent resistivities, the induction arrows should be taken into consideration in MT data processing and inversion for better lateral resolution when exploring geothermal resources.