Abstract

Ground‐motion models (GMMs) and ground‐motion adjustment factors developed using the hybrid empirical method (HEM) are used in seismic‐hazard analyses throughout the world as an alternative to GMMs developed from the more traditional empirical and simulation methods. The HEM uses the ratio of stochastic ground‐motion simulations between a target and host region to adjust empirical GMMs from the host region to use in the target region. The HEM is used primarily in regions where strong‐motion data are sparse or exist only for small‐magnitude earthquakes. The most common application of the HEM has been in the development of GMMs for eastern North America (ENA), two of which were used in the 2008 U.S. national seismic‐hazard maps, but the method also has been used to develop or adjust GMMs in many other regions of the world. A comparison of four ENAGMMs developed using the HEM and a fifth developed using the closely related referenced empirical approach show that they fall into three distinct groups based on differences in the methods, models, and parameters used to calculate the host‐to‐target adjustment factors, and on differences in the selection of the host empirical ground‐motion models. A different set of groups are implied from the aleatory variability models. General guidance is provided to aid the user in the selection and weighting of the five GMMs for application in seismic‐hazard analysis.

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