Finite Difference Simulations of Rayleigh Wave Scattering by 2-D Rough Topography.
TELEDYNE GEOTECH ALEXANDRIA VA
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Rayleigh waves normally incident upon 2 D simple or rough topographic structures are simulated by the linear finite difference method to study the attenuation, transmission, and reflection of Rayleigh waves and to measure the Rayleigh-to-P and -SV bodywave conversion. For simple ramp structures, transmission, reflection, and scattering depend on the sign of change of slope of the topographic feature, as well as the ratio of the ramp height to the wavelength, hlambda. Simple ramp structures produce back-scattered body-waves h lambda, and forward-scattered body-waves for h lambda. The radiation patterns of P and S bodywaves are roughly consistent with the model of equivalent point forces along the free surface. More complicated topographic features generated by random Markov sequences have been characterized by the Rayleigh wave spatial Qf. As expected, rougher topography attenuates Rayleigh waves more than smooth topography. P and S amplitudes ratios are consistent with radiation from equivalent point forces near the surface, but distribution of slownesses generated is greater than from the simple ramp structures. Reflection of Rayleigh waves by topographic slopes and by random topography is an inefficient process and the bulk of the energy that is not transmitted as Rayleigh waves is converted to bodywaves. Fundamental Rayleigh-to-Lg scattering and generation of teleseismic P coda by short period Rayleigh should be observable.