Time‐Series Analysis of Volume Change at Brady Hot Springs, Nevada, USA, Using Geodetic Data From 2003–2018

Abstract

Brady Hot Springs geothermal field has exhibited subsidence, as measured by interferometric synthetic aperture radar (InSAR). Previous studies have examined both the temporal evolution of the deformation from 2004 through 2016 and the spatial extent of the deformation, directly relating the observed subsidence to volumetric changes below the surface. We extend the modeling at Brady to analyze a data set of interferometric pairs spanning from the end of 2003 through 2018. We examine spatial and temporal trends in the observed deformation by time-series analysis of each of the 1,656 cubic voxels in a parameterized elastic dislocation model to identify areas where the subsurface volume changes as a function of time. Joint time-series analysis of Global Positioning System and InSAR pairs confirm significant changes in rates of volume change during time intervals when well operations were varied. The rate of subsidence increases with increased injection, consistent with the identification of thermal contraction of the rock matrix as the dominant driving mechanism. Conversely, the modeled volume increases when pumping ceases, suggesting thermal expansion of the rock matrix.

On the role of thermal stress and fluid pressure in triggering seismic and aseismic faulting at the Brawley Geothermal Field, California.

“…1c) and surface rupture, which were not observed in the nearby Salton Sea geothermal field [Barbour et al, 2016]. Fault reactivation can thus add to the effect of pressure depletion [e.g., Barbour et al, 2016] and thermal contraction [e.g., Reinisch et al, 2020a] that are generally observed at geothermal fields. All three mechanisms are actually mechanically coupled and probably contribute jointly in general to the observed surface deformation [Im et al, 2021].…”

“…Thermal and pressure effects have been shown to be significant factors of surface deformation in geothermal fields [e.g., Im et al, 2017;Fialko and Simons, 2000;Reinisch et al, 2020a] and can contribute to fault reactivation [Gan and Elsworth, 2014] and seismicity rate changes [Im et al, 2021]. It is therefore probable that both thermal and pressure effects contributed to the surface deformation at Brawley, and to the triggering of the 2012 swarms.…”

Advancing the Limits of InSAR to Detect Crustal Displacement from Low-Magnitude Earthquakes through Deep Learning

“…We perform our analysis similar to previous studies [52][53][54]. In order to account for the relative nature of InSAR measurements, we assign GPS station RG09 as a reference station and treat RG10 as being within a deforming region.…”

Spatio-temporal analysis and volumetric characterization of interferometric synthetic aperture radar-observed deformation signatures related to underground and in situ leach mining

“…Instead, we perform a validation analysis at a proxy site that is both actively deforming due to subsurface processes and that has GPS data available to measure such deformation to determine the uncertainty that we have in Sentinel-1 InSAR-observed deformation due to underground processes. We choose Brady Hot Springs geothermal field in Nevada, a site that has been used in previous studies to validate InSAR measurements within an actively deforming region due to subsurface processes, 16 , 32 for such analysis. This site is an ideal choice due to the existence of a continuous GPS station (BRDY) in a non-deforming region as well as a continuous GPS station (BRD1) located in the middle of the subsiding region, courtesy of a 2016 field study led by the University of Wisconsin in support of a US Department of Energy’s Geothermal Technologies Office project 33 .…”

“…We conduct our validation similar to previous works, 16 , 32 using data from Sentinel-1’s track T144 (s^=[0.65,−0.11,0.75]) to compute our pairs. To address the relative nature of displacement measured by InSAR, we treat BRDY as a baseline for deformation and difference InSAR-measured range change around BRD1 from range change measured around BRDY to estimate InSAR-observed range change within the deforming region relative to BRDY.…”