Geophysical Investigation of the Shallow Structure of El Tatio Geotermal Field

El Tatio geothermal field, located in the north of Chile, is the largest geothermal field in the southern hemisphere and the third largest in the world, comprising more than one hundred active geothermal manifestations, including geysers, perpetual spouters, fumaroles and nonerupting springs. Since most of the existing studies are commercial, in scientific terms there are still several key questions about the processes that control the different manifestations. This study presents one of the first geophysical studies in the region aiming to detect dominant subsurface structures and to understand their influence on the existence/development of the great variety of geothermal manifestations. El Tatio geothermal field is characterized for a lineament of geysers in NE direction in the Upper Basin where a normal fault have been inferred, while the Middle Basin has a lineament of perpetual spouters in NW direction. This suggest a structural difference between these two zones that allow the differences between the existent superficial manifestations.

The subsurface electrical structure was obtained using Transient Electromagnetic (TEM) data along five profiles, in order to identify different structures controling the different domains of geothermal manifestations. In total, fifty TEM soundings were collected. The derived models image the presence of fluids and subsurface structures which may influence the permeability of the rock and control de fluid upflow within the hydrothermal system. 2D models have been developed starting from 1D inversion, to estimate the effect of posible 2D structures. The derived electrical resistivity sections indicate zones of very low resistivity (0.5-1 Ω-m) that are related to the presence of hydrothermal fluids in their hosting rocks, with varying thicknesses depending on the area.