Geophysical characterization of the Cerro Machin geothermal area using three dimensional seismic and resistivity models

The volcanic complex of Cerro Machín is located on the eastern flank of Colombia’s Cordillera Central. It exhibits complex geological and geothermal features indicative of a significant subsurface geothermal reservoir. This study proposes the first joint interpretation of passive 3D seismic tomography and magnetotelluric resistivity modeling to characterize the geothermal potential of the Cerro Machín area. Seismic data recorded from 1998 to 2019 are used to generate P wave velocity and Vp/Vs ratio models down to 8 km below sea, level (b.s.l.), Additionally, statistical analysis of the seismicity is used to refine the data interpretation. Magnetotelluric data acquired in 2019, are used to generate a high-resolution resistivity model to depths of 5.1 km. The results are then combined to propose an integral model where a high resistivity sealing cup is topping a vertically elongated low Vp, low Vp/Vs and low resistivity body beneath the Cerro Machín Volcano. These bodies reach depths of ∼2 km b.s.l., providing useful information about the lateral and vertical extension of a potential geothermal reservoir. Additionally, a high Vp body identified at 2–3 km b.s.l. is compatible with the expression of a magmatic heat source that possibly is feeding the system. The distribution of seismic clusters, b-values, and resistivity patterns further delineates fluid pathways, likely controlled by fault zones or the volcanic domes conduits. These findings provide key insights on the structure of an ongoing state of the Cerro Machin volcanic complex that can be used for future exploration and support for the Colombia’s geothermal energy initiatives.