Resistivity imaging of the Santa Maria sector and the Northern zone of Las Pailas geothermal area, Costa Rica, using joint 1D inversion of TDEM and MT data

Abstract

In this geophysical research work, data from MT and TDEM surveys are processed, inverted and discussed to explain the electrical resistivity of the subsurface of two specific areas located north and east of Las Pailas geothermal field in Costa Rica. The static shift problem of MT data is solved by inverting jointly both TDEM and MT data. Seven profiles are analysed, based on 1D models from 22 MT and 19 TDEM soundings. Resistivity cross-sections and isoresistivity maps were compiled from the 1D models of the inverted TDEM and MT data. The main idea was to analyse the subsurface resistivity structure of those areas and also to compare the results with a discontinuity known as NF7, trying to see if the existing MT and TDEM data could reveal a more detailed model of the zone that can be of use in future expansion of the production field. The main result of the survey is the probable confirmation of the NF7 structure on the northern side of the survey area and in the Santa María sector. Another important fact was the appearance of a low-resistivity body (deep conductor) in the northern part of the study area and in the Santa María sector, interpreted as a possible heat source.