Modeling Teleseismic SV Waves from Underground Explosions with Tectonic Release: Results for Southern Novaya Zemlya

摘要

Detailed forward modeling of long-period shear waves for 2 large underground explosions at the Southern Novaya Zemlya test site indicates that the appropriate equivalent double-couple orientation for the tectonic release radiation is vertical strike-slip. Previous studies of observed teleseismic SH waveforms and SV amplitudes for the 27 Oct 1973 and 2 Nov 1974 events using geometric theory could not distinguish between vertical strike-slip and 45 deg-dipping thrust geometries. Either mechanism can match the observed four-lobed SH radiation pattern, and the two-lobed SV amplitude pattern can be produced by interference with an appropriate size explosion pS signal. However, the complexity of the observed SV waveforms arising from Sp conversions near the receiver, diffracted Sp, and shear-coupled PL phases is not accounted for in the ray theory synthetics. Incorporating more realistic Green's functions using Baag and Langston's WKBJ spectral method allows more complete modeling of the SV signals. Due to differences in frequency content between the explosion and double-couple SV waveforms, constructive interference occurs more efficiently than destructive interference when the two signals are linearly superimposed. As a result, using tectonic release moments determined from the SH waves and the optimum F factors required to match the SV amplitude patterns, the waveforms produced by the strike-slip and thrust orientations differ substantially at some azimuths. (EDC)