On the Interpretation of Conditional Ground-Motion Models

ABSTRACT Recently, a number of conditional ground-motion models (CGMMs) have been developed for intensity measures (IMs) other than pseudospectral acceleration (PSA) values that are particularly useful for geotechnical earthquake engineering problems. In a CGMM, a non-PSA IM is conditioned on PSA IMs, and other earthquake parameters (e.g., magnitude Mw, rupture distance Rrup) as well as site conditions (e.g., the time-averaged shear-wave velocity in the top 30 m VS30). Even though CGMMs are useful in engineering practice, their interpretation in the context of traditional (non-CGMM) has not been discussed to the authors’ best knowledge. In this study, we provide an interpretation of CGMMs in terms of the scaling difference between the spectral and nonspectral IMs used in the formulation of a CGMM and the coefficient of correlation of these spectral and nonspectral IMs. In addition, the interpretation can derive into an alternative procedure for calculating correlation coefficients between PSA IMs and non-PSA IMs, which is illustrated.