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Multiple sources for late-Holocene tsunamis at Discovery Bay, Washington State, USA

Holocene

By:
, ,
DOI: 10.1191/0956683605hl784rp

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Abstract

Nine muddy sand beds interrupt a 2500-yr-old sequence of peat deposits beneath a tidal marsh at the head of Discovery Bay on the south shore of the Strait of Juan de Fuca, Washington. An inferred tsunami origin for the sand beds is assessed by means of six criteria. Although all the sand beds contain marine diatoms and almost all the beds display internal stratification, the areal extent of the oldest beds is too limited to confirm their origin as tsunami deposits. The ages of four beds overlap with known late-Holocene tsunamis generated by plate-boundary earthquakes at the Cascadia subduction zone. Diatom assemblages in peat deposits bracketing these four beds do not indicate concurrent change in elevation at Discovery Bay. Diatoms in the peat bracketing a tsunami bed deposited about 1000 cal. yr BP indicate a few decimeters of submergence, suggesting deformation on a nearby upper-plate fault. Other beds may mark tsunamis caused by more distant upper-plate earthquakes or local submarine landslides triggered by earthquake shaking. Tsunamis from both subduction zone and upper-plate sources pose a significant hazard to shoreline areas in this region.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Multiple sources for late-Holocene tsunamis at Discovery Bay, Washington State, USA
Series title:
Holocene
DOI:
10.1191/0956683605hl784rp
Volume
15
Issue:
1
Year Published:
2005
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
60
Last page:
73
Number of Pages:
14