Forensic PSHA: Benchmarking Canada’s 5th Generation Seismic Hazard Model using the OpenQuake-engine

This paper explores the implementation of the Natural Resources Canada’s 5th Generation national seismic hazard model as developed for the National Building Code of Canada (NBCC), within the OpenQuake-engine. It also describes the reconciliation of the differences in hazard estimates relative to the published NBCC values, calculated using GSCFRISK. Source and ground-motion input models developed for the GSCFRISK software were translated to the OpenQuake-engine format for the hazard comparison. In order to successfully undertake this process, several adjustments to the OpenQuake code were needed to mimic the behavior of GSCFRISK. This required the development of new functions for earthquake rupture scaling and ground-motion interpolation. Hazard values estimated using the OpenQuake-engine are generally in good agreement with the 2015 NBCC national-scale hazard values, with differences less than 2-3% typically achieved. Where larger differences arise, they can be rationalized in terms of differences between the behaviours of the two software engines with respect to earthquake rupture length uncertainty and maximum ground-motion integration distance.