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TitleComparing felt intensity patterns for deep intraslab earthquakes in the Cascadia and Chilean subduction zones, offshore British Columbia, United States, and Chile
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorRutherford, J; Cassidy, J FORCID logo
SourceGeological Survey of Canada, Open File 8899, 2022, 24 pages, Open Access logo Open Access
PublisherNatural Resources Canada
Documentopen file
Mediadigital; on-line
File formatpdf
ProvinceBritish Columbia
NTS92; 93A; 93B; 93C; 93D; 102; 103A; 103B; 103C
AreaVancouver; Vancouver Island; Washington State; Oregon; Pacific Ocean; Canada; United States of America; Chile
Lat/Long WENS-134.0000 -120.0000 53.0000 38.0000
Lat/Long WENS -84.0000 -65.0000 -16.0000 -48.0000
Subjectstectonics; geophysics; Science and Technology; Nature and Environment; Health and Safety; tectonic setting; subduction zones; downgoing slab; seismology; earthquakes; earthquake magnitudes; Cascadia Subduction Zone; Chilean Subduction Zone; Juan de Fuca Plate; North American Plate; Pacific Plate; Nazca Plate; South American Plate; Antarctic Plate; ANSS Comprehensive Earthquake Catalog (ComCat) Documentation; Natural hazards; Methodology; Citizen participation; Databases
Illustrationsblock diagrams; location maps; geoscientific sketch maps; screen captures; plots; tables
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2022 06 29
AbstractIn this study, we utilize US Geological Survey citizen science earthquake felt intensity data to investigate whether deep, intraslab earthquakes in the Chilean Subduction Zone show similar, 'felt intensity' distributions to events of the same magnitude and depths within the Cascadia Subduction Zone (Quitoriano & Wald, 2020; USGS Earthquake Hazards Program, 2020). In a companion article (Rutherford & Cassidy, 2022) we examine crustal earthquake intensity patterns for the Chile and Cascadia subduction zones. One goal of this comparison is to determine whether felt intensity information from several recent large (M8-8.8) subduction earthquakes in Chile can be applied to Cascadia (where no subduction earthquakes have been felt since 1700). This will provide a better understanding of shaking intensity patterns for future subduction earthquakes in Cascadia - critical information for scientists, engineers, and emergency management organizations.
For this research, we utilized 20 years of catalogued 'Did You Feel It?' (DYFI) citizen science data from the US Geological Survey's (USGS) earthquake online catalogue, the ANSS Comprehensive Earthquake Catalog (ComCat) Documentation (USGS Earthquake Hazards Program, 2021). In total, we compared intensity patterns from five earthquakes in Cascadia (M4.8, M5.0. M6.7 & M6.8) to the intensity patterns from 157 earthquakes in Chile, with the same magnitudes as the Cascadia events (M4.8-M6.8).
Our analysis involved plotting and fitting the Chile and Cascadia earthquakes' DYFI responses in order to compare the intensity patterns for the two subduction zones. Overall, we find good agreement between felt patterns in Chile and Cascadia. For example, all plots show the expected downward trend for intensity with distance; and there is generally a similar intensity clustering of responses around 50 to 300 km hypo-central distance. These results provide confidence that we can use Chilean intensity data for megathrust earthquakes in Cascadia.
Summary(Plain Language Summary, not published)
In this study we collect and compare felt intensity information for deep (oceanic plate) earthquakes in the Cascadia and Chile subduction zones. We collected felt information on earthquakes of magnitude 4.8-6.8 over the past ~20 years. By comparing these felt intensity patterns (which we found to be very similar) we have confidence in using felt intensity data for much larger subduction earthquakes recorded in Chile to apply to the Cascadia subduction zone (where subduction earthquakes occur, but not for more than 322 years). The use of Chilean felt intensity information for better assessing the effects of subduction earthquakes in Cascadia is valuable for engineers, scientists and emergency managers.

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