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Testing the use of microfossils to reconstruct great earthquakes at Cascadia

S. E. Engelhart, B. P. Horton, A. R. Nelson, A. D. Hawkes, R. C. Witter, K. Wang, P. L. Wang and C. H. Vane
Testing the use of microfossils to reconstruct great earthquakes at Cascadia
Geology (Boulder) (July 2013) 41 (10): 1067-1070


Coastal stratigraphy from the Pacific Northwest of the United States contains evidence of sudden subsidence during ruptures of the Cascadia subduction zone. Transfer functions (empirical relationships between assemblages and elevation) can convert microfossil data into coastal subsidence estimates. Coseismic deformation models use the subsidence values to constrain earthquake magnitudes. To test the response of foraminifera, the accuracy of the transfer function method, and the presence of a pre-seismic signal, we simulated a great earthquake near Coos Bay, Oregon, by transplanting a bed of modern high salt-marsh sediment into the tidal flat, an elevation change that mimics a coseismic subsidence of 0.64 m. The transplanted bed was quickly buried by mud; after 12 mo and 5 yr, we sampled it for foraminifera. Reconstruction of the simulated coseismic subsidence using our transfer function was 0.61 m, nearly identical to the actual elevation change. Our transplant experiment, and additional analyses spanning the A.D. 1700 earthquake contact at the nearby Coquille River 15 km to the south, show that sediment mixing may explain assemblage changes previously interpreted as evidence of pre-seismic land-level change in Cascadia and elsewhere.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 41
Serial Issue: 10
Title: Testing the use of microfossils to reconstruct great earthquakes at Cascadia
Affiliation: University of Rhode Island, Department of Geosciences, Kingston, RI, United States
Pages: 1067-1070
Published: 20130730
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 28
Accession Number: 2013-069356
Categories: Quaternary geologySeismology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2013295
Illustration Description: illus. incl. geol. sketch map
N42°00'00" - N46°19'60", W124°34'60" - W116°34'60"
Secondary Affiliation: Rutgers, the State University of New Jersey, USA, United StatesU. S. Geological Survey, USA, United StatesUniversity of North Carolina at Wilmington, USA, United StatesGeological Survey of Canada, CAN, CanadaNational Taiwan University, TWN, TaiwanBritish Geological Survey, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201341
Program Name: USGSOPNon-USGS publications with USGS authors
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