Pre‐drilling data review and synthesis for the Long Valley Caldera, California

Goldstein, N.E.

doi:10.1029/88eo00034

Cited by 7 publications

(8 citation statements)

References 30 publications

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“…The depth range placed on the possible locations of the scattering material agrees well with the low-velocity anomaly located between 9 and 20 km depth as imaged by Dawson et al [1988] (see also Goldstein [1988]). Candidate features include molten or partially molten material, small intrusions, or major fault zones, all of which are expected in this area of large and recent volcanism.…”

Section: [1982] Present a Detailed Analysis Of Much Of The Seismicitysupporting

confidence: 74%

An S‐to‐P converted phase recorded near Long Valley/Mono Craters Region, California

Ammon¹,

Zucca²,

Kasameyer³

1989

J. Geophys. Res.

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We examine and model the arrival time of a large secondary seismic arrival recorded in the Long Valley/Mono Craters region of east central California. Zucca et al. (1987) and Peppin (1987) both previously reported on different features of this same arrival. Using both arrays of sources and receivers, we demonstrate that the arrival in an S‐to‐P converted phase as first suggested by Lewis and Peppin (1988). Back projection of the observed travel times allows us to constrain the location of the converting material to somewhere within a southeast dipping zone between 7 and 16 km depth and within 5 km on either side of the northwest topographic margin of the caldera. The analysis demonstrates the power of source and receiver array combinations when analyzing seismic arrivals in complicated environments.

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Section: [1982] Present a Detailed Analysis Of Much Of The Seismicitysupporting

confidence: 74%

An S‐to‐P converted phase recorded near Long Valley/Mono Craters Region, California

Ammon¹,

Zucca²,

Kasameyer³

1989

J. Geophys. Res.

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“…where the most recent volcanism has occurred and, apparently, where many workers feel that the geothermal potential is highest (Wollenberg et a1.,1987;Suemnicht, 1987;Goldstein, 1988). This paper reports constraints on the structure of the caldera boundaries in that area.…”

Section: Of Particular Importance Is a Recent Surge Of Interest In Stmentioning

confidence: 82%

“…This is a typical assumption in using this method (e.g. Hermance at al., 1984;1988) potentially suffers from the same oversimplification of what is undoubtedly a much more complicated geological situation. Third, we assume that we can represent the local distortion as being due to a circularly shaped basin having approximately the same radius of curvature as the local curvature of the actual caldera itself.…”

Section: Refined Modelling Of the Caldera Boundarymentioning

confidence: 99%

Evidence for multiple boundary faults beneath the northwest moat of Long Valley Caldera: Magnetotelluric results

Hermance¹,

Neumann²

1988

Geophysical Research Letters

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The boundaries of Long Valley Caldera, in Eastern California, are sharply delineated by steeply dipping normal faults which, for the most part, are buried and obscured by recent volcanic and sedimentary cover. The only evidence for their presence is from their geophysical signatures on regional gravity, seismic and electromagnetic surveys. Recently, a surge of interest has focused studies in the western moat, where the volcanism is most recent, and where many workers feel that the geothermal potential is highest. A detailed, narrow‐band (20–80 s) magnetotelluric profile in that area has delineated a parallel set of buried high angle normal faults which have virtually no expression at the surface. The outermost fault has a throw of approximately 500 m, while the innermost has a throw of approximately 2 km; neither has an expression in the surface morphology. Moreover, based on a relatively low resistivity contrast between the basement and the basin fill, we infer a relatively high fracture porosity in the Sierran basement, which suggests that there may be considerable lateral and vertical migration of meteoric water; a result which has considerable significance to understanding the regional hydrology.

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“…Long Valley is an attractive prospect because it is one of the most extensively studied Quaternary magmatic systems in the world (Bailey et al, 1976;Hill et al, 1985;Rundle and Hill, 1988). Intense seismicity, contemporary resurgence, high heat flow, low density, and seismic delay zones have been suggested to signify the possibility of magma in the middle crust of the west-central portion of the caldera (Goldstein, 1987a;Dawson et al, 1990). If present, magma and its associated high-temperature hydrothermal system could be important as deep, but high-enthalpy, geothermal resources.…”

mentioning

confidence: 99%

“…If present, magma and its associated high-temperature hydrothermal system could be important as deep, but high-enthalpy, geothermal resources. An energy exploration hole has been initiated to a target depth near 6 km to assess these resources (Goldstein, 1987a;Finger and Eichelberger, 1990). The primary purpose of the MT profile is to discern any potential midcrustal melt zone or hydrothermal system through their influence on the electrical resistivity (Olhoeft, 1981;Wannamaker, 1986).…”

mentioning

confidence: 99%

Magnetotelluric transect of Long Valley caldera: Resistivity cross‐section, structural implications, and the limits of a 2-D analysis

et al. 1991

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Twenty-four magnetotelluric (MT) soundings have been collected in an east-west profile across the center of Long Valley caldera. The average station spacing is approximately I km and appears adequate to sample the important features of the upper crustal and deeper resistivity structures. Additional control on the shallowest resistivity is provided by a continuous profile of time domain electromagnetic soundings coincident with the western portion of the MT line. Our MT data set reveals numerous resistivity structures which illuminate the evolution and present state of the Long Valley system. Many of these have been quantified through two-dimensional (2-D) finite element modeling emphasizing the transverse magnetic (TM) mode. Important structural components include low-resistivity layers 0.5-1.5 km deep under the eastern half of the caldera, beneath the axial graben of the resurgent dome, and under the west caldera moat. Most of this layering appears to lie in post-caldera Early Rhyolite tuffs, and the uppermost unwelded Bishop Tuff. These rhyolite units have been observed to be porous and highly altered and to commonly contain Pleistocene intercalated lacustrine clays. The remainder and majority of the Bishop Tuff appears highlyresistive. A low resistivity layer also occurs below the axial graben near the base of the Bishop Tuff (1.5 km). Hydrothermal fluids or alteration in precaldera volcanic strata or, less likely, carbonaceous metasediments may be the cause of this. Resistive, probably crystalline basement at high levels is apparent beneath the center of resurgence. Low resistivities are modeled at a depth around 5 km below the entire west moat and central graben and may represent a zone of hydrothermal fluids released from magma crystallization, with potential magmatic contributions at greater depths. The correspondence between this low resistivity and teleseismic delay and low density zones found in other studies is quite striking. A subtle anomaly in the transverse electric (TE) mode impedance is weakly suggestive of a midcrustal conductive axis centered beneath the central graben and resurgent dome. However, it cannot be simulated by two-dimensional transverse electric calculations and requires a full three-dimensional evaluation to ensure that the anomaly does not represent resistivity complexity in just the upper few kilometers. A fundamental, caldera-wide 3-D effect is documented by comparison of observed and computed TE impedance and vertical magnetic field data. The abrupt termination of conductive caldera sediments less than 10 km north and south of our profile greatly depresses the observed TE apparent resistivity and vertical magnetic field relative to the model calculations for periods greater than 0.3 s for the central and eastern caldera. Analysis of the TE mode data also suggests that a similar finite-strike effect lies in the response at periods greater than 3 s due to the mid-crustal west moat conductor. The TM mode measurements are judged to also contain some large-scale departure from the ...

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Pre‐drilling data review and synthesis for the Long Valley Caldera, California

Cited by 7 publications

References 30 publications

An S‐to‐P converted phase recorded near Long Valley/Mono Craters Region, California

An S‐to‐P converted phase recorded near Long Valley/Mono Craters Region, California

Evidence for multiple boundary faults beneath the northwest moat of Long Valley Caldera: Magnetotelluric results

Magnetotelluric transect of Long Valley caldera: Resistivity cross‐section, structural implications, and the limits of a 2-D analysis

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