Land-level changes from a late Holocene earthquake in the northern Puget Lowland, Washington
- 1Department of Geology, Humboldt State University, Arcata, California 95521, USA
- 2U.S. Geological Survey, Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195-1310, USA
- 3U.S. Geological Survey, Pacific Science Center, 1156 High Street, Santa Cruz, California 95064, USA
- 4U.S. Geological Survey, 600 4th Street, St. Petersburg, Florida 33701, USA
Abstract
An earthquake, probably generated on the southern Whidbey Island fault zone, caused 1–2 m of ground-surface uplift on central Whidbey Island ∼2800–3200 yr ago. The cause of the uplift is a fold that grew coseismically above a blind fault that was the earthquake source. Both the fault and the fold at the fault's tip are imaged on multichannel seismic refection profiles in Puget Sound immediately east of the central Whidbey Island site. Uplift is documented through contrasting histories of relative sea level at two coastal marshes on either side of the fault. Late Holocene shallow-crustal earthquakes of Mw = 6.5–7 pose substantial seismic hazard to the northern Puget Lowland.
Footnotes
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↵GSA Data Repository item 2004081, Figure DR1, survey data, and Table DR1, radiocarbon ages, is available online at http://www.geosociety.org/pubs/ft2004.htm, or on request from editing{at}geosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA.
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- Accepted February 17, 2004.
- Received November 25, 2003.
- Revision received February 4, 2004.
- Geological Society of America
