Regional short-term and long-term risk and loss assessment under sequential seismic events

A framework for building-portfolio risk and loss assessment under mainshock-aftershock earthquake sequences is presented. The temporary increase in seismic hazard after a large-magnitude mainshock coupled with the reduction in the structural capacity under sequential ground motions are considered in the framework. For the inventory of reinforced concrete frames located in Los Angeles County, the annual rate of complete (HAZUS) damage and expected annual losses are, on average, 10% and 25% higher, respectively, when aftershocks are incorporated in the risk assessment procedure. A short-term risk and loss analysis after a hypothetical scenario mainshock on the Puente Hills fault showed a substantial increase in the seismic risk within one week after the mainshock. The aftershock-induced losses during the same period were estimated at approximately 30% of the losses due to the mainshock.