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TitleProbabilities of significant ground shaking due to Cascadia Subduction aftershocks
AuthorSeeman, M; Onur, T; Cassidy, J
SourceAssociation of American Geographers annual meeting, abstracts volume; 2011, 1 pages
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20110033
MeetingAssociation of American Geographers annual meeting; Seattle, WA; US; April 10-16, 2011
Mediaon-line; digital
ProvinceWestern offshore region
Subjectsgeophysics; tectonics; earthquakes; earthquake studies; earthquake risk; earthquake mechanisms; subduction; aftershocks; seismic interpretations; seismicity; seismic risk; Cascadia Subduction Zone
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
AbstractGreat (M>8.0) subduction interface earthquakes, or megathrust earthquakes, are typically followed by hundreds if not thousands of aftershocks, some of which may exceed M7.0. Owing to the number, proximity to urban centres, and strength of these aftershocks, they can be more damaging than the main shock itself and therefore pose a significant threat to regional communities. Additionally, as these aftershocks follow a large main shock, they strike areas which have recently experienced strong and/or prolonged ground shaking and therefore not only impact already compromised structures, but also inhibit on-going response and recovery efforts.
While a great deal of research exists regarding megathrust earthquakes in the Cascadia subduction zone off the west coast of North America, little attention has been given to quantifying and assessing the subduction aftershock activity and its potential impact on local communities. Based on an analysis of recorded aftershock sequences at similar subduction zones around the Pacific ocean, this paper offers estimates of ground shaking probabilities resulting from aftershock activity following a Cascadia megathrust earthquake. Ground shaking probabilities are provided for 22 communities across the Pacific Northwest. Calculations estimate the likelihood of an aftershock exceeding each of three ground shaking intensity levels (MMI V - widely felt; MMI VI - threshold for non-structural damage; and, MMI VII - threshold of structural damage). Results are offered to profile the full scope of the Cascadia subduction earthquake threat (i.e. beyond the initial megathrust event), and to provide quantitative hazard information on which to base sound funding and policy decisions.