Uncertainties in Probabilistic Seismic Hazard Analysis for a Poisson Earthquake Occurrence Model

Yuehua Zeng, & Mark D. Petersen

Published August 13, 2018, SCEC Contribution #8477, 2018 SCEC Annual Meeting Poster #049

We revisit the theory for the probabilistic seismic hazard analysis (PHSA) and solve for the standard errors of the rate and probability of exceedance. We show that the PSHA defined by the probability of one or more ground motion exceedances over a time period is equivalent to the mean probability of exceedance for a Poisson earthquake occurrence model. We apply a California seismic hazard model to evaluate the standard errors of the rate and probability of exceedances. We find that the range of values between the lower and upper limits are very high for the following cases: (1) rate/probability of exceedance for fixed ground motion and (2) ground motions with a fixed probability of exceedance. These uncertainties for probability/rate of exceedance and ground motions are both correlated with the relative earthquakes rate uncertainties on faults across the region. For example, at a fixed 2% in 50-year PGA probability of exceedance, the uncertainties in probability caused by the Poisson rate calculation are highest over less active faults and lower over the San Andreas Fault (SAF). Overall the standard error of the probability of exceedances are often higher than the mean and can span a factor of 2 to 10. On the other hand, the uncertainties in probability of exceedance for fixed ground motions is highest over the SAF and lower near the less active faults. The results also show that the average ground motion uncertainties across the state are about 70%. In general, the uncertainties in the rate/probability of exceedance are much higher than many people have assessed in previous analyses and are comparable in size to the uncertainties in ground motions, often a factor of two or more. The results suggest that in places where seismic hazards are low, the risk could be higher because of the high uncertainties.

Key Words
Probabilistic Seismic Hazard Analysis, Uncertainties

Citation
Zeng, Y., & Petersen, M. D. (2018, 08). Uncertainties in Probabilistic Seismic Hazard Analysis for a Poisson Earthquake Occurrence Model. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)