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TitleSeismic hazard in western Canada from global positioning system vs. earthquake catalogue data
AuthorMazzotti, S; Leonard, L J; Cassidy, J C; Rogers, G; Halchuk, S
Source2010 Annual Seismological Society of America Meeting, Abstracts; Seismological Research Letters vol. 81, no. 2, 2010 p. 364
Alt SeriesEarth Sciences Sector, Contribution Series 20100153
Meeting2010 Annual Seismological Society of America Meeting; Portland; US; April 21-23, 2010
Mediapaper; on-line; digital
ProvinceAlberta; British Columbia
Subjectsgeophysics; earthquakes; earthquake catalogues; earthquake studies; global positioning system
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
LinksOnline - En ligne
AbstractProbabilistic seismic hazard analyses are principally based on frequency-magnitude statistics of historical and instrumental earthquake catalogues. This method assumes that return periods of large damaging earthquakes (100s - 1000s yr) can be extrapolated from 50-100 yr statistics of small and medium earthquakes. The method has obvious limitations when applied to areas of low-level seismicity where the earthquake statistics may be poorly constrained. In this study, we test an alternative approach to assess seismic hazard in Western Canada. We use horizontal velocities at ~250 Global Positioning System (GPS) sites in BC and Alberta to calculate strain rates and earthquake statistics within seismic source zones. GPS-based strain rates are converted to seismic moment, earthquake frequency-magnitude statistics, and seismic hazard using a logic-tree method. The GPS-based earthquake statistics and seismic hazard are then compared to those derived from the earthquake catalogue. In one zone (Puget Sound), the GPS seismic hazard estimates are in good agreement with those from earthquake statistics. In nearly all other zones (e.g., most of BC and Alberta), the GPS seismic hazard estimates are significantly larger than those from the earthquake catalogue by one or two orders of magnitude. This discrepancy could indicate that the earthquake catalogue significantly under predicts long-term seismic hazard in areas of low-level seismicity. Alternatively, significant aseismic deformation may occur over long time-scales, which would imply that the GPS strain rates over predict the true seismic hazard. We discuss the nature and limitations of both methods in light of our results for Western Canada, with the goal of defining a methodology to incorporate GPS strain rate data into probabilistic seismic hazard assessments.