ADVANCED SEISMIC HAZARDS ASSESSMENT USE IN CALIFORNIA

Recent developments in earthquake forecasting and ground motion prediction equations have generally lowered seismic hazard input for strong ground shaking in seismic risk assessment application in the State of California that have a short return interval (10% in 50 year interval) and a short period (~0.2 to 1.0 seconds). The two main drivers of this breakthrough were the time dependent version of the Uniform California Earthquake Rupture Forecast (UCERF II) and the Next Generation Attenuation (NGA) equations. During their development the United States Geological Survey and the California Geological Survey played active roles in the evaluation of both UCERF II and NGA. During their development a loss modeling company representative monitored and provided input and in some cases actively participated in issues related to both projects. The final products of UCERF II and NGA were assessed by loss modeling companies supporting the California Earthquake Authority, which is required under state law to use best available science to help establish residential earthquake insurance rates. During the development of UCERF II the United States Geological Survey monitored developments that helped it update the California portion of the National Seismic Hazard Map within a few weeks of the release of the UCERF II final report in the spring of 2008. NGA final report products were reviewed and utilized by several loss modelers in updating their loss models. Within 18 months after the release of both UCERF II and the NGA final deliverable products all three loss modeling companies had integrated the appropriate information and data into their loss models. This effort has had the effect of reducing epistemic uncertainty in estimating recurrence intervals on known faults in California and also in general lowering strong ground motion for earthquakes that have a short return interval and a short period similar to those used in estimating strong ground motion in residential earthquake insurance applications for buildings three stories of less in height.