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TitleHeterogeneous rupture in the great Cascadia earthquake of 1700 inferred from coastal subsidence estimates
AuthorWang, P -L; Engelhart, S E; Wang, K; Hawkes, A D; Horton, B P; Nelson, A R; Witter, R C
SourceJournal of Geophysical Research vol. 118, issue 5, 2013 p. 2460-2473, (Open Access)
Alt SeriesEarth Sciences Sector, Contribution Series 20120185
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS92C; 92E; 92F
AreaCanada; United States
Lat/Long WENS-128.0000 -124.0000 50.0000 40.0000
Subjectsgeophysics; tectonics; earthquakes; earthquake mechanisms; earthquake studies; faults, slip; subsidence; subduction zones; subduction
Illustrationslocation maps; tables; plots; models
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
Released2013 05 15
AbstractPast 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.