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

Journal of Geophysical Research B: Solid Earth

By:
, , , , , ,
DOI: 10.1002/jgrb.50101

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Abstract

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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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Heterogeneous rupture in the great Cascadia earthquake of 1700 inferred from coastal subsidence estimates
Series title:
Journal of Geophysical Research B: Solid Earth
DOI:
10.1002/jgrb.50101
Volume
118
Issue:
5
Year Published:
2013
Language:
English
Publisher:
AGU
Contributing office(s):
Geologic Hazards Science Center
Description:
14 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Geophysical Research B: Solid Earth
First page:
2460
Last page:
2473
Country:
United States;Canada
State:
British Columbia;Washington;Oregon;California
Other Geospatial:
Cascadia