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Coseismic subsidence in the 1700 great Cascadia earthquake; coastal estimates versus elastic dislocation models

Lucinda J. Leonard, Roy D. Hyndman and Stephane Mazzotti
Coseismic subsidence in the 1700 great Cascadia earthquake; coastal estimates versus elastic dislocation models
Geological Society of America Bulletin (June 2004) 116 (5-6): 655-670

Abstract

Seismic hazard assessments for a Cascadia subduction zone earthquake are largely based on the rupture area predictions of dislocation models constrained by geodetic and geothermal data; this paper tests the consistency of the models for the 1700 great Cascadia earthquake with compiled coastal coseismic subsidence as estimated from paleoelevation studies. Coastal estimates have large uncertainties but show a consistent pattern. Greatest coseismic subsidence ( approximately 1-2 m) occurred in northern Oregon/southern Washington; subsidence elsewhere was approximately 0-1 m. Elastic dislocation models constrained by interseismic geodetic and thermal data are used to predict the coseismic subsidence for two likely strain accumulation periods of (i) 800 and (ii) 550 yr of plate convergence and for uniform megathrust slip of 10, 20, 30, and 50 m. The former two models provide a better and equally good fit; predicted subsidence is in broad agreement with marsh estimates. Discrepancies exist, however, at the ends of the subduction zone. In the south, misfit may be due to breakup of the Gorda Plate. The discrepancy in the north may be explained if the 1700 event released only part of the accumulated strain there, consistent with long-term net uplift in excess of eustatic sea-level rise. The coseismic slip magnitude, estimated by comparing uniform slip model predictions with marsh coseismic subsidence estimates, is consistent with the M 9 earthquake indicated by Japanese tsunami records. The coseismic slip was greatest in northern Oregon/southern Washington, declining to the north and south.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 116
Serial Issue: 5-6
Title: Coseismic subsidence in the 1700 great Cascadia earthquake; coastal estimates versus elastic dislocation models
Affiliation: University of Victoria, School of Earth and Ocean Sciences, Victoria, BC, Canada
Pages: 655-670
Published: 200406
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 91
Accession Number: 2004-054253
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2004076; Geol. Surv. Can., Publ. No. 2002281
Illustration Description: illus. incl. sects., 1 table, sketch maps
N42°00'00" - N46°19'60", W124°34'60" - W116°34'60"
N48°30'00" - N51°00'00", W128°30'00" - W123°30'00"
N45°30'00" - N49°00'00", W124°45'00" - W116°55'00"
Secondary Affiliation: Geological Survey of Canada, CAN, Canada
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200416
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