EVALUATION OF TOPOGRAPHIC EFFECTS ON P-WAVES AND S-WAVES OF EXPLOSIONS AT THE NORTHERN NOVAYA-ZEMLYA TEST SITE USING 3-D NUMERICAL SIMULATIONS

Using a 3-D finite difference simulation, we calculated the effects of surface topography on the amplitudes and waveforms of seismic waves generated by a hypothetical nuclear explosion at the northern Novaya Zemlya test site (Matochkin Shar). The simulation shows substantial azimuthal variations in the amplitude of the downgoing P waveform at shallow depths beneath the source, caused by variations in the amplitude of pP. However, these azimuthal amplitude variations diminish as the wavefront propagates deeper in the crust. Based on these results, we estimate that the topographic scarp considered here produces a maximum azimuthal variation of +/-0.05 magnitude units for m(b) determined from teleseismic P-waves. The sloping topography causes substantial SH motion for azimuths along the strike of the scarp.