Amplification of earthquake ground motion by steep topographic irregularities

The problem of amplification of seismic waves by surface topographic irregularities is addressed through analytical and numerical investigations. First, a closed-form expression for estimating the fundamental vibration frequency of homogeneous triangular mountains is obtained, using Rayleigh's method. Subsequently, numerical modelling based on the spectral element approximation is used to study the 3D seismic response of several real steep topographic irregularities excited by vertically propagating plane S-waves. A topographic amplification factor is obtained for each case, by a suitable average of the ratio of acceleration response spectra of output vs input motion. The 3D amplification factors are then compared with those derived by 2D analyses as well as with the topographic factors recommended in Eurocode 8 for seismic design. Copyright (C) 2002 John Wiley Sons, Ltd.