Continuous Electromagnetic Monitoring Network in the Mexicali Rift, Mexico

Abstract

The use of electromagnetic exploration methods as a monitoring tool for the evaluation of geothermal fields is relatively new. However, the first results have generated promising results. In México we are starting the installation of electromagnetic monitoring stations to register natural electromagnetic field in the Mexicali rift. Our plan is to have a network consisting of 15 continuous monitoring stations, installed in strategic locations of the Mexicali valley around the Cerro Prieto geothermal field. The aim is to improve our understanding of permeability changes and fluid dynamics in the area. Natural varying electromagnetic fields may provide information about temporal variations of the electrical properties of the ground, likely linked to changes in permeability and geothermal fluids flow. With this propose, long period magnetotelluric stations were designed and built in CICESE. They use 25-meters length electrical dipoles to measure the variation of the horizontal electric field (Ex, Ey) and a triaxial fluxgate magnetometer to register the variation of the natural magnetic field (Hx, Hy, Hz). The first station was installed in May 2013, and data were registered and processed in a regular time basis. In this paper we show preliminary results in terms of apparent resistivity curves for different times.