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The 1998 Earthquake Sequence South of Long Valley Caldera, California: Hints of Magmatic Involvement

Hough, S. E. and Dollar, R. S. and Johnson, P. (2000) The 1998 Earthquake Sequence South of Long Valley Caldera, California: Hints of Magmatic Involvement. Bulletin of the Seismological Society of America, 90 (3). pp. 752-763. ISSN 0037-1106. doi:10.1785/0119990109.

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A significant episode of seismic and geodetic unrest took place at Long Valley Caldera, California, beginning in the summer of 1997. Activity through late May of 1998 was concentrated in and around the south moat and the south margin of the resurgent dome. The Sierran Nevada block (SNB) region to the south/southeast remained relatively quiet until a M 5.1 event occurred there on 9 June 1998 (UT). A second M 5.1 event followed on 15 July (UT); both events were followed by appreciable aftershock sequences. An additional, distinct burst of activity began on 1 August 1998. The number of events in the August sequence (over the first week or two) was similar to the aftershock sequence of the 15 July 1998 M 5.1 event, but the later sequence was not associated with any events larger than M 4.3. All of the summer 1998 SNB activity was considered tectonic rather than magmatic; in general the SNB is considered an unlikely location for future eruptions. However, the August sequence—an “aftershock sequence without a mainshock”—is suggestive of a strain event larger than the cumulative seismotectonic strain release. Moreover, a careful examination of waveforms from the August sequence reveals a small handful of events whose spectral signature is strikingly harmonic. We investigate the waveforms of these events using spectral, autocorrelation, and empirical Green's function techniques and conclude that they were most likely associated with a fluid-controlled source. Our observations suggest that there may have been some degree of magma or magma-derived fluid involvement in the 1998 SNB sequence.

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Hough, S. E.0000-0002-5980-2986
Additional Information:© 2000 by the Seismological Society of America. Manuscript received 29 July 1999. The authors are indebted to IRIS/PASSCAL for their prompt response to our instrument request and exemplary technical/field support throughout the course of our experiment. We also gratefully acknowledge the fieldwork and/or organizational contributions of David Hill, Peter Malin, Bruce Julian, Yehuda BenZion, Emily Brodsky, Nano Seeber, Chris Farrar, Dan Lyster, Josh Feinberg, Robert Drake, Robert Brooks, Scott Roripaugh, Juli Baldwin, Paul Slice, and Joshua Slice. We also thank Emily Brodsky, Kerry Sieh, Ken Hudnut, Nano Seeber, Steve McNutt, Lee Steck, and David Hill for reviews that were thorough and unfailingly constructive in their criticism.
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Official Citation:S. E. Hough, R. S. Dollar, and P. Johnson The 1998 Earthquake Sequence South of Long Valley Caldera, California: Hints of Magmatic Involvement Bulletin of the Seismological Society of America, June 2000, v. 90, p. 752-763, doi:10.1785/0119990109
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48059
Deposited By: Ruth Sustaita
Deposited On:06 Aug 2014 17:08
Last Modified:10 Nov 2021 18:03

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