Seismic image of the Mount Spurr magmatic system |
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| Authors: | J A Power A Villaseñor H M Benz |
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| Institution: | (1) U.S. Geological Survey, Alaska Volcano Observatory, 4200 University Drive, Anchorage, AK 99508, USA e-mail: jpower@usgs.gov Fax: +907 786 7525, US;(2) U.S. Geological Survey, Box 25046, MS-966, Denver, CO 80225, USA, US |
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| Abstract: | The three-dimensional P-wave velocity structure of Mount Spurr is determined to depths of 10 km by tomographic inversion
of 3,754 first-arriving P-wave times from local earthquakes recorded by a permanent network of 11 seismographs. Results show
a prominent low-velocity zone extending from the surface to 3–4 km below sea level beneath the southeastern flank of Crater
Peak, spatially coincident with a geothermal system. P-wave velocities in this low-velocity zone are approximately 20% slower
than those in the shallow crystalline basement rocks. Beneath Crater Peak an approximately 3-km-wide zone of relative low
velocities correlates with a near-vertical band of seismicity, suggestive of a magmatic conduit. No large low-velocity zone
indicative of a magma chamber occurs within the upper 10 km of the crust. These observations are consistent with petrologic
and geochemical studies suggesting that Crater Peak magmas originate in the lower crust or upper mantle and have a short residence
time in the shallow crust. Earthquakes relocated using the three-dimensional velocity structure correlate well with surface
geology and other geophysical observations; thus, they provide additional constraints on the kinematics of the Mount Spurr
magmatic system.
Received: 4 December 1997 / Accepted: 27 February 1998 |
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| Keywords: | Mount Spurr Crater Peak Alaska Three-dimensional structure Hydrothermal system Magmatic conduit |
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