Finite-difference modelling for P-pulse propagation in elastic media with arbitrary polygonal surface
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The applicability of the finite-difference methods has been limited in most cases to simple geometric shapes. The problem of introducing boundary conditions into the scheme has usually restricted the models to structures in which the boundaries are parallel to the coordinates. Recently, several investigators have studied the effect of prominent topographic features on seismic signals. Most deal with SH waves. The behaviour of a P-SV pulse in media with prominent irregular surfaces is yet almost unknown. The difficulty of the last problem relative to the SH case lies in the vectorial form of the equation of motion and the more complicated boundary conditions. In the present work a technique is proposed for simulating the P-SV wave propagation in a two-dimensional half-space with an arbitrary polygonlike topography. This technique has been applied to compute seismograms due to a P-pulse on surfaces of ridges and canyons. The incident pulse is amplified at the crest of mountains and at the upper corners of canyons. The magnitude of amplification is a function of the steepness of the topographic structure and can increase by 50 % compared to a flat surface under the same conditions. The maximum attenuation computed at the bottom of a canyon was 25 %. It can be concluded that the influence of prominent topographic features on the incident P-pulse is similar to that on incident SH waves, which was computed in previous investigations.
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