Abstract
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.
Highlights
Degassing and emanation processes at Earth’s surface occur as a result of fluids ascending along fault zones, for example from magmatic intrusions, metamorphic or plutonic basement rocks, and deep-seated mantle sources
Maximum possible tendency for slip and dilation occurs along north-south–oriented fault segments (007° ± 2°), steeply dipping westward
The subsurface structure of the study area has been visualized by a 3-D fault model, which provides the basis for fault stress analyses (Jolie et al, 2015a)
Summary
Degassing and emanation processes at Earth’s surface occur as a result of fluids ascending along fault zones, for example from magmatic intrusions, metamorphic or plutonic basement rocks, and deep-seated mantle sources. Tracing such gases and emanations into the subsurface provides significant information about major fault structures and subterranean dynamics. Our results enable a three-dimensional (3-D) reproduction of potential permeability structures along fault zones that facilitate fluid circulation These structures correspond to fault segments with an increased tendency to slip and dilate as well as to increased gas emissions and emanations at the surface.
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