Response of a small Oregon estuary to coseismic subsidence and postseismic uplift in the past 300 years

The Sixes River estuary, south coastal Oregon, sits above the locked portion of the Cascadia subduction zone, which intermittently releases in subduction-zone earthquakes. One such Cascadia earthquake ∼300 years ago caused subsidence and a tsunami at the Sixes estuary. The subsidence raised the rive...

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Bibliographic Details
Published in:Geology (Boulder) 1998-03, Vol.26 (3), p.231-234
Main Authors: Kelsey, Harvey M, Witter, Robert C, Hemphill-Haley, Eileen
Format: Article
Language:English
Subjects:
absolute age
algae
biostratigraphy
C-14
carbon
Cascadia subduction zone
Cenozoic
clastic sediments
coseismic processes
Curry County Oregon
dates
diatoms
Earthquakes
estuaries
fluvial features
Geochronology
Geology
grain size
Holocene
isotopes
landform evolution
Oregon
overbank sediments
paleoseismicity
paleosols
Plantae
postseismic processes
Quaternary
Quaternary geology
radioactive isotopes
Rivers
roots
Sediments
Sixes River
southwestern Oregon
structural controls
subsidence
terraces
unconformities
United States
uplifts
upper Holocene
vertical movements
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Summary:The Sixes River estuary, south coastal Oregon, sits above the locked portion of the Cascadia subduction zone, which intermittently releases in subduction-zone earthquakes. One such Cascadia earthquake ∼300 years ago caused subsidence and a tsunami at the Sixes estuary. The subsidence raised the river's base level, resulting in an ∼3 km upstream shift of the head of tide of the estuary. At the upper end of the expanded estuary, more than 4 m of overbank sediment was deposited in the first decades or century after subsidence. Subsequent incision through the overbank deposits accompanied the gradual emergence of the estuary, and attendant downstream shift of the head of tide, as relative sea level fell in response to interseismic uplift.
ISSN:0091-7613
1943-2682
DOI:10.1130/0091-7613(1998)026<0231:ROASOE>2.3.CO;2