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TitleThermal state of the Explorer segment of the Cascadia subduction zone: Implications for seismic and tsunami hazards
AuthorGao, D; Wang, K; Davis, E E; Jiang, Y; Insua, T L; He, J
SourceGeochemistry, Geophysics, Geosystems (G3) vol. 18, issue 4, 2017 p. 1569-1579,
Alt SeriesEarth Sciences Sector, Contribution Series 20160434
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formatpdf
ProvinceWestern offshore region
NTS103B; 103C; 103F; 103G; 102I; 102O; 102P; 103A; 103H; 93A; 93B; 93C; 93D; 93E; 93F; 93G; 93H; 92
AreaCascadia Subduction zone
Lat/Long WENS-132.0000 -119.0000 53.0000 47.5000
Subjectsearthquakes; subduction zones; health hazards; heat flow; structural analysis; thermal analyses; tsunami; megathrust; convergence; rupture zone
Illustrationslocation maps; graphs; schematic diagrams
ProgramAssessing Earthquake Geohazards, Public Safety Geoscience
AbstractThe Explorer segment of northernmost Cascadia is an end-member "warm" subduction zone of very young incoming plate and slow convergence rate. Understanding the megathrust earthquake potential of this type of subduction zone is of both geodynamic and societal importance. Available GNSS geodetic observations indicate that the subduction megathrust of the Explorer segment is currently locked to some degree, but the downdip extent of the fault area that is potentially seismogenic is not known. Here we develop finite element models to estimate the thermally allowed megathrust seismogenic zone, using available knowledge of regional plate kinematics, structural data, and heat flow observations as constraints. Despite ambiguities in plate interface geometry constrained by hypocenter locations of low-frequency earthquakes beneath Vancouver Island, the thermal models suggest a potential rupture zone of ~60 km downdip width and located offshore. Using dislocation modeling, we further illustrate that a rupture zone of this size, even with a conservative assumption of ~100 km strike length, can cause significant tsunami-genic deformation. Future seismic and tsunami hazard assessment in northern Cascadia must take the Explorer segment into account.
Summary(Plain Language Summary, not published)
In assessing hazard in western Canada, a knowledge gap is the potential of the Explorer segment of the Cascadia subduction to produce large megathrust earthquakes. Seismic and geodetic observations are very limited in this area. We developed a thermal model and use the model-predicted temperature along the megathrust to assess the seismogenic potential. We find that the subduction zone is cold enough to allow seismic rupture, despite the very young age (5 Ma) of the subducting plate and slow subduction rate (2 cm/yr). If we assume the rupture is limited by a temperature of 450 C, then the maximum downdip width of the potential rupture zone is about 60 km, entirely offshore.