TIME-DEPENDENT EARTHQUAKE HAZARD CONSTRAINTS FROM A CALIFORNIA-WIDE PALEOSEISMIC DATABASE

Time-dependent seismic source hazard-models endeavor to predict earthquake likelihood from elapsed time since a prior event. We compile 34 Oxcal-calibrated paleoseismic event records from across California to analyze the regularity of earthquake inter-event times. Inter-event times distributions from long paleoseismic records (n≥10 events) are well fit by the Weibull distribution, indicating that the likelihood of earthquake rupture at a paleoseismic site increases as a power-law of time since the previous event. The exponent of this power-law hazard function is typically one or less, suggesting that hazard rises rapidly immediately after the prior event, contrary to the expectation from an elastic rebound-type process. By aggregating ratios of inter-event times from shorter paleoseismic records from across California, we show that hazard exponents are generally less than one. This finding shows that irregular patterns of earthquake rupture extent and timing are the norm, which should be factored into time-dependent earthquake forecasts.