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Tsunamis in the Salish Sea; recurrence, sources, hazards

Carrie Garrison-Laney and Ian Miller
Tsunamis in the Salish Sea; recurrence, sources, hazards (in From the Puget Lowland to east of the Cascade Range; geologic excursions in the Pacific Northwest, Ralph A. Haugerud (editor) and Harvey M. Kelsey (editor))
Field Guide (Geological Society of America) (January 2017) 49


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.

ISSN: 2333-0937
EISSN: 2333-0945
Serial Title: Field Guide (Geological Society of America)
Serial Volume: 49
Title: Tsunamis in the Salish Sea; recurrence, sources, hazards
Title: From the Puget Lowland to east of the Cascade Range; geologic excursions in the Pacific Northwest
Author(s): Garrison-Laney, CarrieMiller, Ian
Author(s): Haugerud, Ralph A.editor
Author(s): Kelsey, Harvey M.editor
Affiliation: University of Washington at Seattle, Department of Earth and Space Sciences, Seattle, WA, United States
Affiliation: U. S. Geological Survey, Seattle, WA, United States
Published: 201701
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
ISBN: 978-0-8137-5649-3
ISBN: 978-0-8137-0049-6
Number of pages: 67-78
References: 53
Accession Number: 2018-014477
Categories: SeismologyQuaternary geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. geol. sketch maps
N47°00'00" - N48°00'00", W124°00'00" - W122°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 2018
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