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

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.

Structural, lithological, and geodynamic controls on geothermal activity in the Menderes geothermal Province (Western Anatolia, Turkey)

“…In others words, fault-controlled circulation of meteoric fluids is the dominant mechanism to explain the migration of mantle volatiles from the ductile-brittle transition zone to the near-surface ( Fig. 12b) (Mutlu et al 2008;Jolie et al 2016). Brittle fault systems are thus probably connected at depth with ductile shear zones (Fig.…”

Pinpointing Deep Geothermal Upflow in Zones of Complex Tectono‐Volcanic Degassing: New Insights from Aluto Volcano, Main Ethiopian Rift

“…Major faults in the East African Rift System are controlled by tectonic and volcanic mechanisms. Surface gas release and hydrothermal fluid circulation in active rift systems not only are related to its volcanic heat source but also reflect local and regional tectonic controls in the subsurface (Brune et al, ; Goerner et al, ; Jolie et al, ). Increased degassing along fracture zones outlines deep‐rooted permeable segments of active faults and points to major upflow and outflow zones of hydrothermal fluids.…”

“…In Tule Moye, a comparable site to Aluto, faults channel magmatic fluids from a depth of ~14 km to the surface (Samrock et al, ). Fault segments with strong gas emissions are characterized by increased slip and dilation tendencies (Jolie, Moeck, et al, ; Jolie et al, ). Analyses of a variety of soil gases have proven their suitability for assessing the tectonic and volcanic controls on geothermal systems (Hunt et al, ; Jolie, Klinkmueller, et al, ; Jolie et al, ; Lee et al, ).…”

“…Fault segments with strong gas emissions are characterized by increased slip and dilation tendencies (Jolie, Moeck, et al, ; Jolie et al, ). Analyses of a variety of soil gases have proven their suitability for assessing the tectonic and volcanic controls on geothermal systems (Hunt et al, ; Jolie, Klinkmueller, et al, ; Jolie et al, ; Lee et al, ). These gases provide vital information for the exploration of geothermal fields and help in targeting wells in the most permeable structures with the greatest flow rates of high‐temperature hydrothermal fluids.…”

“…Tectono‐volcanic interactions have an effect on soil degassing within the Aluto volcanic complex and result in more intense gas emissions. Our approach consists of a combination of systematic alpha‐spectroscopic measurements as well as CO 2 efflux measurements based on an area‐wide, regular grid (Jolie, Klinkmueller, et al, ; Jolie et al, ). Results illustrate that substantial information on permeable subsurface structures and lateral outflows can be obtained by the analysis of surface degassing.…”