Structure of Long Valley caldera, California, from a seismic refraction experiment

Journal Article · Tue Feb 10 04:00:00 EST 1976 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB081i005p00745· OSTI ID:7365729

Hill, D P

Two seismic refraction profiles crossing the Long Valley caldera in approximately east and north directions indicate that the crystalline basement with P wave velocities of 6.0 +- 0.4 km/s has been downdropped by 2.5-3 km across normal faults along the north and northwest sides of the caldera and 1-2 km along the south and east sides. Basement depths beneath the caldera floor range from between 3 and 4 km in the north and east sections to about 2 km in the central and south sections. Relief on the basement within the caldera suggests that the caldron block was partially disrupted during collapse, although a steplike offset in the eastern part of the basement may be due in part to precollapse displacement along the Hilton Creek fault. The distribution of P wave velocities in the caldera fill suggests that the Glass Mountain rhyolite and Bishop tuff have velocities of 4.0-4.4 km/s and the postcollapse rhyolite, rhyodacite, and basalt flows have velocities of 2.7-3.4 km/s. Domelike relief on the 4.0- to 4.4-km/s horizon indicates that postcollapse resurgence elevated the west central part of the caldera by about 1 km. Evidence for the roof of the magma chamber is contained in later arrivals tentatively identified as reflections from a low-velocity horizon at a depth of 7-8 km. Evidence for anomalous scattering or absorption properties associated with the region of shallow hydrothermal alteration and hot spring activity is contained in relative attenuation of high frequencies in a guided wave propagating through this region.

• Research Organization: Geological Survey, Menlo Park, CA
• OSTI ID: 7365729
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 81:5; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150201 -- Geology & Hydrology of Geothermal Systems-- USA-- (-1989)
150301* -- Geothermal Exploration & Exploration Technology-- Geophysical Techniques & Surveys
CALIFORNIA
GEOLOGIC FAULTS
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
IGNEOUS ROCKS
LONG VALLEY
MAGMA
NORTH AMERICA
RHYOLITES
ROCKS
SEISMIC P WAVES
SEISMIC SURVEYS
SEISMIC WAVES
TUFF
USA
VOLCANIC ROCKS
WESTERN REGION