In the process of using the NGA models for probabilistic hazard analysis (PSHA), there is a need to add a component of epistemic (“model to model”) uncertainty that is not necessarily captured by the use of multiple NGA West models. There is currently no consensus epistemic uncertainty model to use with the NGA models, though several have been used in the past like the one used by the USGS in the 2008 update of the National Seismic Hazard Maps. This task will develop a consensus-based epistemic uncertainty model for the NGA models that can be used by all users of these models. This will provide broader community consensus and acceptance, especially from those who are concerned about the relatively low median estimates of ground motion from large-magnitude earthquakes.
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