Construction of a Ground-Motion Logic Tree through Host-to-Target Region Adjustments Applied to an Adaptable Ground-Motion Prediction Model: An Addendum

ABSTRACT Boore et al. (2022; hereafter, Bea22) described adjustments to a host-region ground-motion prediction model (GMPM) for use in hazard calculations in a target region, using Chiou and Youngs (2014; hereafter, CY14) as the host-region model. This article contains two modifications to the Bea22 procedures for the host-to-target adjustments, one for the source and one for the anelastic attenuation function. The first modification is to compute logic-tree branches for the source adjustment variable ΔcM given in Bea22 assuming that the host- and target-region stress parameters are uncorrelated, instead of the implicit assumption in Bea22 that they are perfectly correlated. The assumption of uncorrelated stress parameters makes little difference for the example in Bea22 because the standard deviation of the host-region stress parameter is much less than that of the target-region stress parameter. However, this might not be the case in some future applications. The second modification is to the host-to-target anelastic attenuation path adjustment. The adjustment in Bea22 involves a distance-independent change in the γ variable that controls the rate of anelastic attenuation in the CY14 GMPM. This article proposes a method to account for a distance dependence in the adjustment. Such a dependence is needed for short-period ground-motion intensity measures (GMIMs) at distances greater than 100 km, with the importance increasing with distance. For the example in Bea22, the ratio of GMIMs computed with the revised and the previous adjustment to γ is less than about a factor of 1.05 at distances within about 100 km, but it can exceed a factor of 2 at 300 km for short-period GMIMs.