k(0): The role of Intrinsic and Scattering Attenuation

Knowledge of the acceleration spectral shape is important for the prediction of ground motion. At high frequencies, the rapid decrease of the spectral amplitude, which controls the peak values, has been modeled by the spectral decay factor k, allowing an estimate of the apparent attenuation and which currently constitutes a basic input parameter for the generation of stochastic ground motion and the calibration of ground-motion prediction equations. Based on numerical simulations of ground motion, we investigate the role of intrinsic and scattering attenuation in determining the high-frequency decay of earthquake-induced ground motion. We show that the attenuation term related to scattering depends nonlinearly on the intrinsic term, meaning that the commonly used explanation for the high-frequency decay spectrum parameter might not be appropriate when analyzing signal windows of several seconds' width.