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Coastal subsidence in Oregon, USA during the giant Cascadia earthquake of AD 1700

July 12, 2011

Quantitative estimates of land-level change during the giant AD 1700 Cascadia earthquake along the Oregon coast are inferred from relative sea-level changes reconstructed from fossil foraminiferal assemblages preserved within the stratigraphic record. A transfer function, based upon a regional training set of modern sediment samples from Oregon estuaries, is calibrated to fossil assemblages in sequences of samples across buried peat-mud and peat-sand contacts marking the AD 1700 earthquake. Reconstructions of sample elevations with sample-specific errors estimate the amount of coastal subsidence during the earthquake at six sites along 400 km of coast. The elevation estimates are supported by lithological, carbon isotope, and faunal tidal zonation data. Coseismic subsidence at Nehalem River, Nestucca River, Salmon River, Alsea Bay, Siuslaw River and South Slough varies between 0.18 m and 0.85 m with errors between 0.18 m and 0.32 m. These subsidence estimates are more precise, consistent, and generally lower than previous semi-quantitative estimates. Following earlier comparisons of semi-quantitative subsidence estimates with elastic dislocation models of megathrust rupture during great earthquakes, our lower estimates for central and northern Oregon are consistent with modeled rates of strain accumulation and amounts of slip on the subduction megathrust, and thus, with a magnitude of 9 for the AD 1700 earthquake.

Citation Information

Publication Year 2011
Title Coastal subsidence in Oregon, USA during the giant Cascadia earthquake of AD 1700
DOI 10.1016/j.quascirev.2010.11.017
Authors A. D. Hawkes, B. P. Horton, A. R. Nelson, C. H. Vane, Y. Sawai
Publication Type Article
Publication Subtype Journal Article
Series Title Quaternary Science Reviews
Series Number
Index ID 70003468
Record Source USGS Publications Warehouse
USGS Organization Geologic Hazards Science Center

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