Ground-motion models for the 6th Generation Seismic Hazard Model of Canada

The 6th Generation seismic hazard model of Canada is being developed to generate seismic design values for the 2020 National Building Code of Canada (NBCC2020). Ground-motion models (GMMs) from the Next Generation Attenuation (NGA)-West 2 and NGA-East programs are used and epistemic uncertainty in ground-motion models is captured through the use of a classical weighted logic tree framework. For the first time, seismic hazard is computed directly on primary (e.g. A-E) seismic site classes from their time-averaged shear wave velocities in the upper 30 m of the crust (VS30). This approach simplifies the way end users will determine seismic design values for a given location and site class, while having other technical advantages such as capturing epistemic uncertainty in site amplification models. It will remove the need for separate site amplification look-up tables in the building code, enabling users to simply supply their location and site class to determine seismic design values. In general, the new ground- motion models predict higher hazard in most Canadian localities due to a variable combination of changes in median ground motions, site amplification and aleatory uncertainty.