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Anisotropy, repeating earthquakes, and seismicity associated with the 2008 eruption of Okmok volcano, Alaska

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journal contribution
posted on 10.02.2021, 22:07 by J Johnson, S Prejean, Martha SavageMartha Savage, John TownendJohn Townend
We use shear wave splitting (SWS) analysis and double-difference relocation to examine temporal variations in seismic properties prior to and accompanying magmatic activity associated with the 2008 eruption of Okmok volcano, Alaska. Using bispectrum cross-correlation, a multiplet of 25 earthquakes is identified spanning five years leading up to the eruption, each event having first motions compatible with a normal fault striking NE-SW. Cross-correlation differential times are used to relocate earthquakes occurring between January 2003 and February 2009. The bulk of the seismicity prior to the onset of the eruption on 12 July 2008 occurred southwest of the caldera beneath a geothermal field. Earthquakes associated with the onset of the eruption occurred beneath the northern portion of the caldera and started as deep as 13 km. Subsequent earthquakes occurred predominantly at 3 km depth, coinciding with the depth at which the magma body has been modeled using geodetic data. Automated SWS analysis of the Okmok catalog reveals radial polarization outside the caldera and a northwest-southeast polarization within. We interpret these polarizations in terms of a magma reservoir near the center of the caldera, which we model with a Mogi point source. SWS analysis using the same input processing parameters for each event in the multiplet reveals no temporal changes in anisotropy over the duration of the multiplet, suggesting either a short-term or small increase in stress just before the eruption that was not detected by GPS, or eruption triggering by a mechanism other than a change of stress in the system. © 2010 by the American Geophysical Union.

History

Preferred citation

Johnson, J., Prejean, S., Savage, M. & Townend, J. (2010). Anisotropy, repeating earthquakes, and seismicity associated with the 2008 eruption of Okmok volcano, Alaska. Journal of Geophysical Research, 115(9), 1-21. https://doi.org/10.1029/2009JB006991

Journal title

Journal of Geophysical Research

Volume

115

Issue

9

Publication date

01/01/2010

Pagination

1-21

Publisher

American Geophysical Union (AGU)

Publication status

Published

Contribution type

Article

Online publication date

11/09/2010

ISSN

2169-9313

eISSN

2169-9356

Article number

B00B04

Language

en