Modifications to Existing Ground-Motion Prediction Equations in Light of New Data

We compare our recent ground-motion prediction equations (GMPEs) for western North America (WNA; Boore and Atkinson, 2008 [BA08]) and eastern North America (ENA; Atkinson and Boore, 2006 [AB06]; Atkinson, 2008 [A08]) to newly available ground-motion data. Based on these comparisons, we suggest revisions to our GMPEs for both WNA and ENA. The revisions for WNA affect only those events with M <= 5.75, while those for ENA affect all magnitudes. These are simple modifications to the existing GMPEs that bring them into significantly better agreement with data. The wealth of new data clearly demonstrates that these modifications are warranted; we therefore recommend the use of the updated equations for seismic hazard analyses and other applications. More detailed studies are under way by many investigators (including ourselves) to develop a new generation of ground-motion models in both WNA and ENA from scratch, through a comprehensive reevaluation of source, path, site, and modeling issues. In time, those more complete models will replace those proposed in this study. However, as the new models will be several years in development, we recommend using the modified models proposed herein, labeled BA08' (for WNA), AB06' (for ENA), and A08' (for ENA, to replace A08), as interim updates to our existing models. The proposed models are in demonstrable agreement with a rich database of ground motions for moderate-magnitude earthquakes in both WNA and ENA and are constrained at larger magnitudes by the BA08 magnitude and distance scaling.