Tectonic controls on magmatism and geothermal resources in the Geysers-Clear Lake region, California: Integration of new geologic, earthquake tomography, seismicity, gravity, and magnetotelluric data

Stanley, William D.; Benz, H.; Walters, Mark; Rodriguez, Brian D.

doi:10.3133/ofr9795

Cited by 3 publications

(1 citation statement)

References 25 publications

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“…The single station recordings for profiles MT1 to MT4 are reported in Williams and Rodriguez (2000;2001a) and Williams and others (200la;2001b;2001c) along with the vertical magnetic field recordings at stations 12A to 28A, 1, 11, 14, 71, 77, 79 to 89, 98, 108, and 109. Sampling this frequency range in other areas of widely varying geology has allowed us to probe the crust from depths of hundreds of meters to depths of tens of kilometers (Eberhart-Phi Hips and others, 1990;Stanley and others, 1991;1997;Rodriguez and others, 1996a;1996b). The recorded time-series data were transformed to the frequency domain and processed to determine a two-dimensional apparent resistivity and phase tensor at each site.…”

Section: Magnetotelluric Surveysmentioning

confidence: 99%

Resistivity structure across the Humboldt River basin, north-central Nevada

Rodriguez¹,

Williams²

2002

Open-File Report

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Magnetotelluric data collected along five profiles show deep resistivity structures beneath the Battle Mountain-Eureka and Carlin gold trends in north-central Nevada, which appear consistent with tectonic breaks in the crust that possibly served as channels for hydrothermal fluids. It seems likely that gold deposits along these linear trends were, therefore, controlled by deep regional crustal fault systems.Two-dimensional resistivity modeling of the magnetotelluric data generally show resistive (30 to 1,000 ohm-m) crustal blocks broken by sub-vertical, two-dimensional, conductive (1 to 10 ohmm) zones that are indicative of large-scale crustal fault zones. These inferred fault zones are regional in scale, trend northeast-southwest, north-south, and northwest-southeast, and extend to mid-crustal (20 km) depths. The conductors are about 2-to 15-km wide, extend from about 1 to 4 km below the surface to about 20 km depth, and show two-dimensional electrical structure. By connecting the locations of similar trending conductors together, individual regional crustal fault zones within the upper crust can be inferred that range from about 4to 10-km wide and about 30-to 150-km long. One of these crustal fault zones coincides with the Battle Mountain-Eureka mineral trend. The interpreted electrical property sections also show regional changes in the resistive crust from south to north. Most of the subsurface in the upper 20 km beneath Reese River Valley and southern Boulder Valley are underlain by rock that is generally more conductive than the subsurface beneath Kelly Creek Basin and northern Boulder Valley. This suggests that either elevated-temperature or high-salinity fluids, alteration, or carbonaceous rocks are more pervasive in the more conductive area (Battle Mountain Heat-Flow High), which implies that the crust beneath these valleys is either more fractured or has more carbonaceous rocks than in the area surveyed along the 41st parallel.

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Section: Magnetotelluric Surveysmentioning

confidence: 99%

Resistivity structure across the Humboldt River basin, north-central Nevada

Rodriguez¹,

Williams²

2002

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Seismic imaging of reservoir heterogeneity using a network with high station density at The Geysers geothermal reservoir, CA, USA

Gritto

Jarpe²,

Hartline³

et al. 2023

GEOPHYSICS

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We have developed the results of high-resolution seismic imaging at The Geysers geothermal reservoir in northern California, USA, using a dense seismic network to image the spatial heterogeneity of the reservoir structure and flow paths. The project uses 92 seismic stations spaced at approximately 500 m over a 5 km × 5 km study area. Microseismic data for more than 17,000 earthquakes were acquired over a period of 13 months and automatically processed for P- and S-wave phase arrival times. The data were subsequently inverted using a joint inversion approach to image the spatial heterogeneity of the reservoir including the 3D P- and S-wave velocity structure, VP/ VS ratio, and to locate earthquake hypocenters. The resulting tomographic images were appraised by integration into The Geysers’ 3D reservoir model and by a spatial correlation to the injection and production wells. Spatial correlation of P-wave velocity images to water injection and steam production wells reveal higher velocities below injection wells, due to higher water saturation, and lower velocities in the vicinity of steam-producing wells, due to the presence of steam in the surrounding reservoir rocks. The spatial correlation of VP/ VS to steam in the reservoir indicates decreased estimates in the vicinity of steam production wells. In contrast, the VP/ VS ratio reveals high values in the reservoir for regions near water injection wells and along the potential flow path of water through the reservoir. The estimates of the shear modulus indicate high values in a region of competent graywacke, which is known for a lack of fractures and steam production, and low values in a region that is dominated by water flow, suggesting that fractured rock created a pathway for the water through the reservoir. The heterogeneity observed in the S-wave velocities indicates a compartmentalized reservoir, which correlates spatially with the fault projections in the 3D reservoir model.

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Publications of the Volcano Hazards Program 1997

Nathenson¹

1998

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Tectonic controls on magmatism and geothermal resources in the Geysers-Clear Lake region, California: Integration of new geologic, earthquake tomography, seismicity, gravity, and magnetotelluric data

Cited by 3 publications

References 25 publications

Resistivity structure across the Humboldt River basin, north-central Nevada

Resistivity structure across the Humboldt River basin, north-central Nevada

Seismic imaging of reservoir heterogeneity using a network with high station density at The Geysers geothermal reservoir, CA, USA

Publications of the Volcano Hazards Program 1997

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