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Tsunamis in the Salish Sea: Recurrence, sources, hazards

Carrie Garrison-Laney
Carrie Garrison-Laney
Department of Earth and Space Sciences, University of Washington, Johnson Hall Rm-070, Box 351310, 4000 15th Avenue NE, Seattle, Washington 98195-1310, USA, and Washington Sea Grant, University of Washington, 3716 Brooklyn Avenue NE, Box 355060, Seattle, Washington 98105-6716, USA
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Ian Miller
Ian Miller
Washington Sea Grant, University of Washington, 1502 E. Lauridsen Boulevard #82, Port Angeles, Seattle, Washington 98362, USA
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January 01, 2017
20 July 2017


A tidal marsh at the head of Discovery Bay contains the longest record of tsunami deposits in Washington State. At least nine tsunami deposits dating back 2500 yr are preserved as fine sand layers in peaty tidal marsh deposits. Discovery Bay is a setting that amplifies tsunami waves, has an abundant sediment source, and a tidal marsh that traps and preserves tsunami deposits. The youngest deposit, bed 1, is probably from the 1700 A.D. Cascadia earthquake. Bed 2 has a newly revised age of 630–560 cal yr B.P. (1320–1390 A.D.), an age range that overlaps with the ages of tsunami deposits from Vancouver, British Columbia, and northern Oregon, as well as evidence for strong shaking in the region including submarine and sublacustrine slope failures. However, there is no geologic evidence for a late fourteenth-century earthquake or tsunami in any of the southwest Washington estuaries that record seven Cascadia earthquakes in the last 3500 yr. Discovery Bay bed 2 and similar-aged evidence in the region may represent a short rupture on the Cascadia subduction thrust, possibly centered west of the Strait of Juan de Fuca, that did not cause significant coastal subsidence. Other possible sources considered for bed 2 include a crustal fault earthquake, a tsunamigenic slope failure, or a transoceanic tsunami. Older tsunami deposits beds 3–9, which outnumber the number of Cascadia earthquakes in the last 2500 yr, are likely from a combination of Cascadia and non-Cascadia sources. Additional radiocarbon dating of beds 3–9 will improve age ranges and constrain potential sources.

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GSA Field Guides

From the Puget Lowland to East of the Cascade Range: Geologic Excursions in the Pacific Northwest

Ralph A. Haugerud
Ralph A. Haugerud
U.S. Geological Survey c/o Department of Earth and Space Sciences University of Washington, Box 351310 Seattle, Washington 98195, USA
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Harvey M. Kelsey
Harvey M. Kelsey
Geology Department Humboldt State University 1 Harpst Street Arcata, California 95521, USA
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Geological Society of America
ISBN electronic:
Publication date:
January 01, 2017



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