Earthquake recurrence models for faults: the crucial role of intermediate magnitude earthquakes in seismic hazard assessment

Titre du congrès :STASEIS Workshop Ville du congrès :Kanagawa Date du congrès :09/01/2006

Seismic hazard results (levels and scenarios) obtained for a site located close to a potentially active fault segment of the Durance fault system, southeast France, depend strongly on the assumed seismicity rates of intermediate magnitude events. We consider here three time-independent recurrence models: Gutenberg-Richter, Young-Coppersmith and Maximum Earthquake for the probability density function on magnitude and different slip rate estimates and historical seismicity to estimate the earthquake occurence rates. We only consider M>=5 events in hazard calculations. The model producing the highest rate of intermediate magnitude events leads systematically to higher hazard levels and lower magnitude scenarios. The integration of the aleatory variability of ground motion prediction equations in the hazard calculation leads naturally to this result. Additional geological criteria indicative of the earthquake frequency-size potential of faults is necessary in order to reduce uncertainty in the modeling of intermediate magnitude events, potentially important contributors to seismic hazard estimates close to faults.