Evidence for Liquefaction Identified in Peeled Slices of Holocene Deposits along the Lower Columbia River, Washington

Takada, Keita

doi:10.1785/0120020152

Cited by 47 publications

(25 citation statements)

References 30 publications

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“…Paleoseismic evidence for Cascadia megathrust earthquakes chiefly includes stratigraphic sequences of organic‐rich soils and sediment of coastal wetlands suddenly buried by tidal mud and sand [e.g., Darienzo et al ., ; Atwater and Hemphill‐Haley , ; Witter et al ., ], with matching sudden changes in vascular plant fossils and microfossil assemblages [e.g., Atwater and Yamaguchi , ; Guilbault et al ., ; Hughes et al ., ], sometimes accompanied by tsunami‐laid sand [e.g., Clague et al ., ; Kelsey et al ., ; Nelson et al ., ], and/or liquefaction caused by strong shaking [ Atwater , ; Takada and Atwater , ]. Radiocarbon dating of plant fossils in coastal stratigraphic sequences suggests recurrence intervals from less than a century to as much as a millennium, with an average of about 300–600 years [ Atwater et al ., ; Kelsey et al ., ; Nelson et al ., ].…”

Section: Paleoseismic Estimates Of Cascadia Coseismic Coastal Subsidencementioning

confidence: 99%

Heterogeneous rupture in the great Cascadia earthquake of 1700 inferred from coastal subsidence estimates

et al. 2013

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Past earthquake rupture models used to explain paleoseismic estimates of coastal subsidence during the great A.D. 1700 Cascadia earthquake have assumed a uniform slip distribution along the megathrust. Here we infer heterogeneous slip for the Cascadia margin in A.D. 1700 that is analogous to slip distributions during instrumentally recorded great subduction earthquakes worldwide. The assumption of uniform distribution in previous rupture models was due partly to the large uncertainties of then available paleoseismic data used to constrain the models. In this work, we use more precise estimates of subsidence in 1700 from detailed tidal microfossil studies. We develop a 3‐D elastic dislocation model that allows the slip to vary both along strike and in the dip direction. Despite uncertainties in the updip and downdip slip extensions, the more precise subsidence estimates are best explained by a model with along‐strike slip heterogeneity, with multiple patches of high‐moment release separated by areas of low‐moment release. For example, in A.D. 1700, there was very little slip near Alsea Bay, Oregon (~44.4°N), an area that coincides with a segment boundary previously suggested on the basis of gravity anomalies. A probable subducting seamount in this area may be responsible for impeding rupture during great earthquakes. Our results highlight the need for more precise, high‐quality estimates of subsidence or uplift during prehistoric earthquakes from the coasts of southern British Columbia, northern Washington (north of 47°N), southernmost Oregon, and northern California (south of 43°N), where slip distributions of prehistoric earthquakes are poorly constrained.

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Section: Paleoseismic Estimates Of Cascadia Coseismic Coastal Subsidencementioning

confidence: 99%

Heterogeneous rupture in the great Cascadia earthquake of 1700 inferred from coastal subsidence estimates

et al. 2013

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“…1d). We used geo-slicers, consisting of a 3 m-long sample tray and a shutter plate that are driven by a weighted vibrator (Takada et al, 2002;Takada and Atwater, 2004). The obtained slice samples are 10 cm wide, 3 cm thick, and range from 1.2 m to 2.9 m in length.…”

Section: Sampling Survey At Numanohama In Miyako Citymentioning

confidence: 99%

Historical tsunami and storm deposits during the last five centuries on the Sanriku coast, Japan

et al. 2015

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“…The shallowest fluidization features were directly correlated to the last Cascadia megathrust rupture, based on the correlation of sand venting and coseismic subsidence in the Columbia River estuary. Some of the larger clastic dikes and sills were investigated for the geotechnical properties of subsurface sand deposits that could have contributed to the paleoliquefaction [23]- [26]. Recent dating of exposed channel bank deposits in the lower Columbia River [27] [28] shows that most of the cutbank sequences were just old enough to have recorded the last Cascadia event at 0.3 ka, but not the older megathrust events >1.0 ka [6].…”

Section: Introductionmentioning

confidence: 99%

Large-Scale Fluidization Features from Late Holocene Coseismic Paleoliquefaction in the Willamette River Forearc Valley, Central Cascadia Subduction Zone, Oregon, USA

Peterson¹,

Kristensen²,

Minor³

2014

OJER

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A search of Willamette River cutbanks was conducted for the presence of late Holocene paleoliquefaction records in the Willamette forearc valley, located 175 ± 25 km landward from the buried trench in the central Cascadia subduction zone. Eight cutbank sites are reported that show evidence of large-scale fluidization features (≥10 cm width) including clastic sand dikes and intruded sand sills in Holocene overbank mud deposits. The targeted alluvial sequences, and hosted paleoliquefaction records, are of late Holocene age, as based on radiocarbon dating, flood silt thickness (≤4 m thickness), and minimal consolidation of dike sand (~1.5 ± 0.5 kg•cm −2 unconfined compressive strength). Two of the paleoliquefaction sites, which are separated by 150 km distance, overlap in age (175 -500 yr BP) with the last great megathrust rupture (Mw 8.5 -9.0) in the Cascadia margin, dated at AD 1700. The scarcity of exposed late Holocene paleoliquefaction sites in the Willamette River cutbanks motivated subsurface searches for thick basal sand deposits and overlying fluidization features, using floodplain geomorphological analyses, ground penetrating radar, and remote pole-camera scans of deep trench walls (3 -4 m depth). The onset of large-scale fluidization features occurred in overbank mud deposits (2 -3 m thickness) above unconsolidated sand bodies (≥2 m thickness) with unconfined compressive strengths of ~1.5 ± 0.5 kg•cm −2 . We recommend geomorphically-targeted subsurface explorations rather than traditional cutbank searches for evidence of coseismic paleoliquefaction in high-gradient river valley systems.

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Evidence for Liquefaction Identified in Peeled Slices of Holocene Deposits along the Lower Columbia River, Washington

Cited by 47 publications

References 30 publications

Heterogeneous rupture in the great Cascadia earthquake of 1700 inferred from coastal subsidence estimates

Heterogeneous rupture in the great Cascadia earthquake of 1700 inferred from coastal subsidence estimates

Historical tsunami and storm deposits during the last five centuries on the Sanriku coast, Japan

Large-Scale Fluidization Features from Late Holocene Coseismic Paleoliquefaction in the Willamette River Forearc Valley, Central Cascadia Subduction Zone, Oregon, USA

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