Geophysical Surveys of The Milford, Utah, FORGE Site: Gravity and Tem

Hardwick, Christian; Hurlbut, Will; Gwynn, Mark

doi:10.34191/mp-169-f

Cited by 8 publications

(5 citation statements)

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“…We note that estimated sensitivity kernels of H/V ratios (Lin et al., 2014) in the period range of 5–10 s using the regional 1D reference velocity model (Arabasz et al., 2005) place the depth sensitivity of our ellipticity measurements between 0 and 5 km below the surface (Figure 7). Given this sensitivity, we find the H/V values consistent with surface geology and basin depth estimations based on gravity data and well logs (Hardwick et al., 2018). We note that while the lowest H/V ratios are as low as 0.5, these values are only found on the edges of our study area and are associated with higher uncertainty.…”

Section: Resultssupporting

confidence: 87%

“…There are also multiple active hot springs and sources of geothermal heat on the surface (Hardwick et al., 2018), as well as a series of mapped Pliocene to Quaternary volcanic deposits indicating geologically young volcanism, from 6 Ma to present, but concentrated in the last 2.5 Ma (Johnsen et al., 2010; Rowley et al., 2013; Sine et al., 2008). As a result, the greater region is classified as the Sevier geothermal resource area (Hardwick et al., 2018; Olson & Smith, 1976; Rowley et al., 2013). As at Coso, there are active geothermal power plants coincident with the locations of the higher heat flux (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

“…Some of these features are similar to those found in Coso: some areas have hot, solid granitic bodies as basement rock (Moore et al., 2020) and the region has measurably higher surface heat flux than surrounding regions (Blackwell et al., 2011; Edwards & Chapman, 2013). There are also multiple active hot springs and sources of geothermal heat on the surface (Hardwick et al., 2018), as well as a series of mapped Pliocene to Quaternary volcanic deposits indicating geologically young volcanism, from 6 Ma to present, but concentrated in the last 2.5 Ma (Johnsen et al., 2010; Rowley et al., 2013; Sine et al., 2008). As a result, the greater region is classified as the Sevier geothermal resource area (Hardwick et al., 2018; Olson & Smith, 1976; Rowley et al., 2013).…”

Section: Introductionmentioning

confidence: 99%

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Combining Dense Seismic Arrays and Broadband Data to Image the Subsurface Velocity Structure in Geothermally Active South‐Central Utah

et al. 2022

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South‐central Utah is characterized by Quaternary volcanism, current geothermal activity, and unusually high surface heat flux across the region. Additionally, there are three operating geothermal power plants in this region, known as the Sevier thermal area. This setting is very similar to that found in the Coso geothermal area. However, the source and lateral extent of subsurface heat in Utah is poorly understood. We use temporally separated geophone arrays combined with regional broadband data to perform ambient noise seismic tomography to study the subsurface shear velocity structure in the region. We find good recovery of ocean‐seism excited Rayleigh wave signals between the periods of 5 and 10 s. For each period, we measure the Rayleigh wave phase velocity and ellipticity across the region using the beamforming methodology and horizontal to vertical (H/V) amplitude ratio. Finally, we combine spline‐based 1D shear velocity models inverted using Rayleigh wave phase velocity and H/V measurements on a 2D, beamforming discretized grid to construct a final 3D model. The final 3D model has many similarities to imaged velocity models at the Coso geothermal area. We find a strong correlation between low velocity anomalies and high surface heat flux and geothermal activity. Additionally, we find a laterally continuous low‐velocity anomaly between 5 and 15 km depth, which may represent elevated temperature of hundreds of degrees Celsius, partial melt, and/or the presence of water, and a common heat source across the region which likely originates from the mantle.

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Section: Resultssupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Combining Dense Seismic Arrays and Broadband Data to Image the Subsurface Velocity Structure in Geothermally Active South‐Central Utah

et al. 2022

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“…Thus, the rotated fault is not expected to influence the development and growth of the FORGE EGS reservoir. Seismic reflection and gravity data [17,18] indicate the contact between the basin fill and the basement dips approximately 20° to 35° to the west on the east side of Milford Valley. This contact is interpreted to represent the eroded foot wall side of a steeply dipping basin-bounding fault that was tilted eastward during uplift and exhumation of the Mineral Mountains block [19][20][21].…”

Section: Geological Review Of Forge Sitementioning

confidence: 99%

In-Situ Stress Measurements at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE) Site

2020

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A scientific injection campaign was conducted at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE) site in 2017 and 2019. The testing included pump-in/shut-in, pump-in/flowback, and step rate tests. Various methods have been employed to interpret the in-situ stress from the test dataset. This study focuses on methods to interpret the minimum in-situ stress from step rate, pump-in/extended shut-in tests data obtained during the stimulation of two zones in Well 58-32. This well was drilled in low-permeability granitoid. A temperature of 199 °C was recorded at the well’s total depth of 2297 m relative to the rotary Kelly bushing (RKB). The lower zone (Zone 1) consisted of 46 m of the openhole at the toe of the well. Fractures in the upper zone (Zone 2) were stimulated between 2123–2126 m measured depths (MD) behind the casing. The closure stress gradient variation depended on the depth and the injection chronology. The closure stress was found to increase with the pumping rate/volume. This stress variation could indicate that poroelastic effects (“back stress”) and the presence of adjacent natural fractures may play an important role in the interpretation of fracture closure stress. Further, progressively increasing local total stresses may, consequently, have practical applications when moderate volumes of fluid are injected in a naturally fractured or high-temperature reservoir. The alternative techniques that use pump-in/flowback tests and temperature signatures provide a valuable perspective view of the in-situ stress measurements.

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“…The broader Sevier Desert region (white dashed lines, Fig. 1A ) is also distinguished from surrounding regions by relatively high heat flow, low lithospheric thickness, and shallow Late Cenozoic intrusions 57 58 .…”

Section: Modes Of Extension In West-central Utahmentioning

confidence: 99%

Late Quaternary faulting in the Sevier Desert driven by magmatism

Stahl

Niemi

2017

Sci Rep

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Seismic hazard in continental rifts varies as a function of strain accommodation by tectonic or magmatic processes. The nature of faulting in the Sevier Desert, located in eastern Basin and Range of central Utah, and how this faulting relates to the Sevier Desert Detachment low-angle normal fault, have been debated for nearly four decades. Here, we show that the geodetic signal of extension across the eastern Sevier Desert is best explained by magma-assisted rifting associated with Plio-Pleistocene volcanism. GPS velocities from 14 continuous sites across the region are best-fit by interseismic strain accumulation on the southern Wasatch Fault at c. 3.4 mm yr−1 with a c. 0.5 mm yr−1 tensile dislocation opening in the eastern Sevier Desert. The characteristics of surface deformation from field surveys are consistent with dike-induced faulting and not with faults soling into an active detachment. Geologic extension rates of c. 0.6 mm yr−1 over the last c. 50 kyr in the eastern Sevier Desert are consistent with the rates estimated from the geodetic model. Together, these findings suggest that Plio-Pleistocene extension is not likely to have been accommodated by low-angle normal faulting on the Sevier Desert Detachment and is instead accomplished by strain localization in a zone of narrow, magma-assisted rifting.

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Geophysical Surveys of The Milford, Utah, FORGE Site: Gravity and Tem

Cited by 8 publications

References 0 publications

Combining Dense Seismic Arrays and Broadband Data to Image the Subsurface Velocity Structure in Geothermally Active South‐Central Utah

Combining Dense Seismic Arrays and Broadband Data to Image the Subsurface Velocity Structure in Geothermally Active South‐Central Utah

In-Situ Stress Measurements at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE) Site

Late Quaternary faulting in the Sevier Desert driven by magmatism

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