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Geologic-Geodetic Block Modeling of Northwestern North America for Seismic Hazard Assessment of Western Canada

Description: 

The northwestern plate margin of North America is complex, alternating between subduction and transform configurations, and with distributed crustal faulting extending for hundreds of kilometers inboard of the margin. Data to characterize faulting and earthquake occurrence in the region is unevenly distributed, and sparse in large swaths. Though this presents challenges to seismic hazard analysis, recent work documenting Quaternary paleoearthquakes in southwestern British Columbia demonstrates the need to create a fault-based seismic hazard model for western Canada and the vicinity. In order to build this model, we first create a database of probable active faults in Canada, with ~50 fault traces, as well as similar databases for Alaska and the northwestern contiguous US. Then, we build a block model upon the fault data that inverts geologic slip rates and GNSS velocities to find internally-consistent fault slip rates for all faults in the databases, as well as spatially-variable partial locking on the Cascadia and Aleutian megathrusts. The preliminary model predicts deformation rates of significance for seismic hazard (i.e., ~1 mm/a) on faults throughout western Canada with lengths suitable for generating large-magnitude crustal earthquakes, including the Rocky Mountain Trench and frontal thrusts, as well as the Fraser and Thompson River faults. Faults closer to the Cascadia subduction zone (and metro Vancouver) may have higher slip rates. However, when fitting the GNSS data there is a substantial tradeoff between permanent strain the model allocates to crustal faults and interseismic strain accumulation on the subduction interface, and the model may not be finding the most accurate solution; more geologic slip rate data would help resolve this. Slip rates throughout the US Cascadia region are generally slower, as strain is distributed on a large number of closely-spaced faults. Fault database and model refinements are ongoing, and a preliminary fault-based hazard model is forthcoming.

Session: Crustal Deformation and Seismic Hazard in Western Canada, Cascadia and Alaska

Type: Oral

Date: 4/20/2023

Presentation Time: 08:15 AM (local time)

Presenting Author: Richard H. Styron

Student Presenter: No

Invited Presentation: 

Authors