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TitleSeismic hazard in western Canada from GPS strain rates versus earthquake catalog
AuthorMazzotti, S; Leonard, L J; Cassidy, J F; Rogers, G C; Halchuk, S
SourceJournal of Geophysical Research vol. 116, B12310, 2011 p. 1-17, (Open Access)
Alt SeriesEarth Sciences Sector, Contribution Series 20110036
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia; Alberta; Western offshore region
NTS82; 83; 92; 93; 102; 103
AreaCanada; United States
Lat/Long WENS-134.0000 -110.0000 56.0000 46.0000
Subjectsgeophysics; mathematical and computational geology; seismic risk; strain; earthquakes; analyses; earthquake magnitudes; earthquake catalogues; earthquake risk; earthquake studies; seismic zones; statistical analyses; statistical methods; probability distributions; faults; subduction zones; global positioning system
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
Released2011 12 17
AbstractProbabilistic seismic hazard analyses (PSHA) are commonly based on frequency - magnitude statistics from 50 - 100 year-long earthquake catalogs, assuming that these statistics are representative of the longer-term frequency of large earthquakes. We test an alternative PSHA approach in continental western Canada, including adjacent areas of northwestern U.S.A., using regional strain rates derived from 179 Global Positioning System (GPS) horizontal velocities. GPS strain rates are converted to earthquake statistics, seismic moment rates, and ground shaking probabilities in seismic source zones using a logic-tree method for uncertainty propagation. GPS-based moment rates and shaking estimates agree well with those derived from earthquake catalogs in only two zones (Puget Sound and mid-Vancouver Island). In most other zones, GPS-based moment rates are 6 - 150 times larger than those derived from earthquake catalogs, and shaking estimates are 2 -5 times larger. This discrepancy may represent an under-sampling of long-term moment rates and shaking probabilities by earthquake catalogs in some zones; however a systematic under-sampling is unlikely over our entire study area. Although not demonstrated with a high confidence level, long-term regional aseismic deformation may account for a significant part of the GPS / catalog discrepancy and, in some areas, represent as much as 80 - 90% of the total deformation budget. In order to integrate GPS strain rates in PSHA models, seismic vs. aseismic partitioning of long-term deformation needs to be quantified and understood in terms of the underlying physical and mechanical processes.