A Model for Vertical-to-Horizontal Response Spectral Ratios for Europe and the Middle East

In the framework of probabilistic seismic hazard analysis, the preferred approach for obtaining the response spectrum of the vertical component of motion is to scale the horizontal spectrum by vertical-to-horizontal (V/H) spectral ratios. In order to apply these ratios to scenario or conditional mean spectra, the V/H ratios need to be defined as a function of variables such as magnitude, distance, and site classification. A new model for the prediction of V/H ratios for peak ground acceleration and spectral accelerations from 0.02 to 3.0 s is developed from the database of strong-motion accelerograms from Europe and the Middle East. A simple functional form, expres- sing the V/H ratios as a function of magnitude, style of faulting, distance, and site class, is found to be appropriate, and the associated aleatory variability is found to be at least as low as that obtained in other studies using more complex models. The predicted ratios from the new European model are found to be in broad agreement with recent models derived from predominantly western North America data.