SUA: A computer program to compute regolith site-response and estimate uncertainty for probabilistic seismic hazard analyses

The presence of soils, geological sediments and weathered rock (collectively known as regolith) can amplify the level of ground shaking experienced during an earthquake. Consequently, including the affect of regolith on earthquake ground shaking is an important component of any seismic hazard analysis. This manuscript provides a detailed and comprehensive description of equivalent linear site-response analysis, a technique for modelling the amplification of seismic waves due to propagation through regolith. The description includes a theoretical solution of the wave equation, derivation of a transfer function relating bedrock acceleration to surface acceleration, calculation of a response spectral acceleration and computation of an amplification factor.This paper also presents a simple approach for estimating the level of uncertainty in the modelled amplification factors due to variations in regolith thickness and velocity structure. A suite of MATLAB routines referred to as SUA are provided to implement an equivalent linear site-response analysis with the option of including an assessment of uncertainty. An example from Sydney, Australia demonstrates the techniques ability to successfully estimate site-response and associated uncertainties.