Contributions to the investigation of the geothermal system of the Azufral volcano in Colombia through 2D magnetotelluric models

Abstract

This work presents the modeling of the resistive structure of the subsoil for the geothermal area of the Azufral Volcano. The structure was adapted according to magnetotelluric soundings (MT) and from the information processing acquired in 140 MT stations, whose average recording times were 24 hours. These allowed to obtain data from 10⁴ to 10^-2 Hz and 39 transient soundings (TDEM) have also been carried out to control the displacement of static shift. 2D inversions have made possible to determine that the resistive structure of the area is characterized by focus of conductive anomalies between 1-10 Ω·m, intermediate between 10-100 Ω·m and resistive zones with values >100 Ω·m. The superficial resistive anomalies with thicknesses of 200 to 500 m were associated with unaltered pyroclastic deposits and the deep ones with thicknesses of more than 4 km to the basement, which in the research area would correspond to the Diabasic group. The zones of conductive anomalies, which extend laterally throughout the study area with an approximate thickness of 2 km are associated with clayey layers that would form the seal of the geothermal system. The anomalies with intermediate values may be due to variations in the temperature of the geothermal system, creating minerals of different conductivity such as Illite, biotite, and chlorite, among others.