CHARACTERISTICS OF RAYLEIGH WAVE IN THE EPICENTRAL ZONE OF SHALLOW EARTHQUAKE

Abstract

The surface waves have more damage potential to both the surface and sub-surface long-span structures as compared to body waves since they can generate large strain in long-span structures in addition to the load reversal. So, there is an urgent need of quantification of characteristics of Rayleigh waves in terms of epicentral distance and focal-depth. In order to fulfill the above identified scientific gaps, the SV-wave responses of a homogeneous half-space model with a sufficient bandwidth in the source time functions (STF) (i.e. Gabor and Ricker wavelets) and various focal depths were simulated and analyzed. Further, the effects of Poisson's ratio and duration of the STF on the characteristics of the generated Rayleigh waves were also studied. The variation of % amount of incident SV-wave energy converted in to the Rayleigh wave energy with focal depth is also quantified. The analysis of simulated responses revealed generation of Rayleigh wave at the critical distance. The obtained decrease of spectral amplitude and frequency content in the generated Rayleigh waves with an increase of focal depth may be the decrease of curvature of the wave front of the SV-wave. The largest spectral amplitude for unit amplitude of incident SV-wave at the critical distance was obtained in that wavelength for which the ratio of focal depth to wavelength of Rayleigh wave was around 0.63. Further, there is almost exponential decrease of spectral amplitude of Rayleigh wave departing from this constant