If the UCERF earthquake rupture forecasting model is used, the uncertainty of the source model is considered in UCERF. For OpenQuake ERF, uncertainty is typically considered with logic trees. However, logic trees are not implemented in R2D now. After earthquake scenarios are generated, R2D uses empirical ground motion prediction equations to generate ground motion intensity measure fields. The uncertainty of GMPEs is considered by modeling the IMs as random fields with distributions as specified in the spatial correlation models. Hope this answers your questions.

Best,

Jinyan