Epistemie Uncertainty for NGA-West2 Models

The development of the NGA-West2 ground motion prediction equations (GMPEs) is a collaborative effort with many interactions and exchange of ideas among the developers. The NGA-West2 developers indicate that additional epistemic uncertainty needs to be incorporated into the median ground motion estimation from each of the five NGA-West2 GMPEs in order to more fully represent an appropriate level of epistemic uncertainty. A proposed minimum additional epistemic uncertainty is evaluated based on statistical estimates of the uncertainty in the median predictions of each GMPE. The proposed additional epistemic uncertainty model is distance-independent but depends on magnitude, style of faulting (SOF), and spectral period. The epistemic uncertainty in the median predictions from each GMPE is then modeled using a three-point discrete approximation to a normal distribution.