Empirical ground-motion models adapted to the intensity measure ASA 40

Relative average-spectral-acceleration (ASA40), a recently developed intensity measure, is defined as the average spectral pseudo-acceleration on the probable interval of evolution of the fundamental frequency of a structure. This article presents two ground motion prediction equations (GMPEs) appropriate for the prediction of ASA40, using a pan-European strong motion database. Taking advantage of the strong correlation between the new intensity measure ASA40 and the spectral pseudo-acceleration (SA), existing GMPEs predicting SA can be adapted to predict ASA40. The first GMPE used in this study is the modified version of a new generation ground motion model, ASB13. In order to decrease the high aleatory uncertainty (sigma) that accompanies predictions when using this modified model, a new model is developed for the prediction of ASA40. Its range of applicability is for magnitudes Mw from 5.5 to 7.6 and distances out to 200 km, it includes site amplification and it is applicable for a range of periods between 0.01 and 4 s. The proposed model decreases the aleatory uncertainty by almost 15 % with respect to the uncertainty of the modified ground motion model