Inversion of magnetotelluric data for the characterization of geothermal structures in the Paucarani zone, Tacna, Peru

Abstract

The region of Paucarani zone, Tacna (Peru) is formed mainly by mountains, hills, and volcanoes, in addition to wetlands. It is mainly composed of dasitic and andesitic rocks from the Holocene. The regional structural geology is characterized by fault planes in the NW–SE direction, which correspond to the fault system of Apurimac-Caylloma-Maure. This research work presents models of the geoelectrical structure after the analysis, processing, inversion, and interpretation of magnetotelluric data collected in the geothermal area of Paucarani, in order to determine areas of high electrical conductivity that are generally associated with anomalous temperatures, which are of great interest for the possible generation of geothermal energy. The data were acquired by the Instituto Geológico Minero Metalúrgico of Perú in the 2017 campaign covering an area of 120 km2. Forty-three longband MT soundings with frequencies ranging from 10-3 Hz to 103 Hz were processed and distributed in 9 NE–SW profiles. The distribution of soundings was conditioned by the varied topography. Data processing required several steps, such as the determination of apparent impedances, dimensionality analysis using the WALDIM method, strike analysis from geological (regional faults) and geophysical (magnetic prospecting) information. After processing the raw data, the 2D inversion was performed using the WinGlink software. This program builds a geoelectric model from data inversion by iterative processes and smoothness constraints from an initial model that is composed of a mesh with a given resistivity. As a product of all these steps, geoelectrical sections were generated capable of identifying resistivity variations throughout the study area. The results indicate that the most conductive zones, of greatest interest for the study of geothermal sources, are located in the western part of the study area.