Canada's 6th Generation Seismic Hazard Model, as prepared for the 2020 National Building Code of Canada

Canada's 6th Generation seismic hazard model has been developed to generate seismic design values for the 2020 National Building Code of Canada (NBCC2020). The model retains most of the seismic source model from the 5th Generation, but updates the earthquake sources for the deep inslab earthquakes under the Straits of Georgia and adds the Leech River - Devil’s Mountain fault near Victoria. The rates of magnitude ~9 Cascadia earthquakes are also increased to match new paleoseismic information. Two major changes in the ground motion model (GMM) are A) replacement of most of the three-branch representative suite used in 2015 by suites of weighted GMMs, and B) use and adaptation of various GMMs to directly calculate hazard on various site classes with representative Vs30 values, rather than providing hazard values on a reference Class C site and applying F(T) factors as in 2015. Computations are now also being performed with the OpenQuake engine, which has been validated through the replication of the 5th Generation results. Seismic design values (on various Soil Classes) for PGA, and for Sa(T) for T = 0.2, 0.5, 1.0, 2.0, 5.0, and 10.0 s are proposed for NBCC2020 mean ground shaking at the 2% in 50-year probability level. The paper discusses chiefly the change in Site Class C values relative to 2015 in terms of the changes in the seismic source model and the GMMs, but the changes in hazard at other site classes that arise from application of the direct-calculation approach are also illustrated.