Linking gas fluxes at Earth’s surface with fracture zones in an active geothermal field

The percolation of fluids is of utmost relevance for the utilization of underground resources; however, the location and occurrence of fractures are not always known, and important characteristics of faults, such as stress state and permeability, are commonly uncertain. Using a case study at the Brady’s geothermal field in Nevada (USA), we demonstrate how permeable fractures can be identified and assessed by combining fault stress models with measurements of diffuse degassing and emanations at Earth’s surface. Areas of maximum gas emissions and emanations correspond to fault segments with increased slip and dilation tendency, and represent a fingerprint of the geothermal system at depth. Thus, linking gas fluxes with fault stress models serves as a measure of the connectivity between surface and subsurface.