A comparison of seismic-hazard and risk deaggregation

The deaggregation of seismic hazard is an effective way to identify scenario events that contribute to a selected seismic-hazard level. Depending on the use of the deaggregation results, the contribution may be defined as equal to or exceeding the selected hazard level. The deaggregation of seismic hazard should consider all uncertainty, aleatory uncertainty, and epistemic uncertainty. The identified scenario events can be used to check the responses of structures such as buildings. However, structures are constructed to provide service rather than just sustain environmental disturbances, and the seismic-risk assessment is at least as important and valuable as the seismic-hazard assessment for emergency preparedness planning and for the financial industry. Therefore, the notion of the deaggregation of seismic hazard is extended to that of seismic risk in the present study. Other issues investigated in this study are the impact of approximate treatment of epistemic uncertainty and the Cascadia subduction events on the deaggregation, and the differences in the identified scenario events from the deaggregation of seismic hazard and seismic risk. Numerical results suggest that the contribution of the uncertainty in attenuation relations to the deaggregation results can be very significant, and that the identified scenario events by deaggregating seismic hazard and seismic risk are somewhat different. Also, the elapsed time since the last major event for source zones whose earthquake occurrence is modeled as a renewal process can affect the deaggregation results significantly.