Quantifying the Epistemic Uncertainty in the Probabilistic Seismic Hazard from Two Major Faults in Western Nevada

Abstract

The probabilistic seismic hazards in the larger cities of western Nevada are dominated by the Mount Rose and Carson Range faults. These are normal faults; Reno and Carson City are on the hanging wall. This paper finds the sensitivity of the hazard posed by these faults to epistemic uncertainty of dip, slip rate, magnitude, and choice of ground motion prediction equation (GMPE) for an earthquake that ruptures the length of each fault. SA(0.01 s) with exceedance probability of 2% in 50 years was determined for each branch of a logic tree for those properties. This paper uses tools of probability theory to characterize this logic tree distribution with a lognormal distribution function, and to suggest an estimate of uncertainty in the mean hazard. In this case, which should not be considered general, on the hanging wall, the uncertainties in fault dip and the choice of the GMPE are the dominant contribution to the standard deviation of the lognormal distribution function. Elsewhere nearby, uncertainties in fault slip rate dominate, while at larger distances uncertainties in the magnitude dominate.