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Seismic investigation of magmatic unrest beneath Mammoth Mountain, California, USA

Guoqing Lin
Seismic investigation of magmatic unrest beneath Mammoth Mountain, California, USA
Geology (Boulder) (June 2013) 41 (8): 847-850


I present a reinvestigation of the seismic activity during an 11-mo-long seismic swarm between 1989 and 1990 beneath Mammoth Mountain in eastern California (United States). This swarm, believed to be the result of a shallow intrusion of magma beneath Mammoth Mountain, was followed by the emission of magmatic CO (sub 2) gas, resulting in tree die-off in 1990 and posing a significant human health risk around Mammoth Mountain. In this study, I apply a state-of-the-art approach to estimate the ratio of compressional- to shear-wave velocity (Vp/Vs) within similar event clusters using differential times from waveform cross-correlation. A high-resolution three-dimensional seismic velocity model and a precise earthquake location catalog are obtained to complement the analysis of the in situ Vp/Vs ratios. The majority of the relocated seismicity below sea level is distributed in an anomalous body with low Vp and high Vp/Vs, consistent with the seismic expression of the magma body that triggered the seismic swarm. Abrupt changes in Vp/Vs ratios, with lower values for the shallow depths, are observed near sea level, indicating the source of the 1989 CO (sub 2) flux is a shallow CO (sub 2) reservoir instead of the hypothesized basaltic magma at mid-crustal depths of 10-25 km. From sea level to the surface, low Vp/Vs ratios in a near-vertical zone suggest involvement of fluid in the upward-migration of the seismicity.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 41
Serial Issue: 8
Title: Seismic investigation of magmatic unrest beneath Mammoth Mountain, California, USA
Author(s): Lin, Guoqing
Affiliation: University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL, United States
Pages: 847-850
Published: 20130606
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 20
Accession Number: 2013-054275
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. geol. sketch map
N37°37'60" - N37°37'60", W119°01'60" - W119°01'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201333
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