Canada’s 5th Generation Seismic Hazard Model: 2015 Hazard Values and Future Model Updates

Abstract eng:
The Geological Survey of Canada (GSC) has contributed earthquake hazard information for the National Building Code of Canada (NBCC) since the 1953 edition. The 2015 national hazard model update yields many important advances on its predecessors, including: probabilistic treatment of the Cascadia subduction zone; reconfigured seismic source zones and special consideration of rare large eastern earthquakes; explicit definition of crustal fault sources in the Yukon Territory and offshore western margin faults (north of Cascadia) based on GPS observations and paleoseismic slip rates; catalogue magnitudes expressed consistently in terms of moment magnitude for improved magnitude-frequency statistics; and the use of a suite of representative backbone ground-motion models. Seismic design values (on Soil Class C defined at V S30 = 450 m/s) are calculated for PGA and PGV, as well as spectral acceleration Sa at nine periods between 0.05 and 10 s. For locations in eastern Canada, the estimated seismic hazard at long periods has generally increased while the seismic hazard at short periods has decreased – in some places significantly. For locations in western Canada, the seismic hazard at long periods has increased significantly for areas affected by great Cascadia interface earthquakes. In Haida Gwaii (formally the Queen Charlotte Islands) and the Yukon, the explicit inclusion of fault sources has also raised the modelled hazard. The GSC is now working towards the 2020 building code cycle with a view of rethinking the fundamental scientific questions and building on the advances made for the 2015 hazard model. In particular, we will: evaluate and adopt new hazard computation software; evaluate catalogue declustering techniques; examine, in more detail, the rationale for groundmotion model selection in specific tectonic environments; consider hazard from induced earthquakes; and explore the utility of risk-targeted ground motions for design.

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