Evidence of tectonic release in long-period S waves from underground nuclear explosions at the Novaya Zemlya test sites

Evidence of tectonic release produced by underground nuclear explosions at Novaya Zemlya is present in teleseismic, long-period S waves. SH waveforms from representative events at the Southern and Northern Novaya Zemlya test sites were modeled to determine the SH radiation patterns. Long-peded P and SV waves were also investigated to further constrain the equivalent double-couple orientation of the tectonic release. Events within each test site have similar faulting mechanisms, but there are definite differences in the tectonic release orientation between the two sites. The southem test site double-couple orientation is either vertical strike slip or 45°-dipping thrust, while the northem test site has an oblique-normal dip slip orientation. The limited resolution of SH signals and complexity of the observed SV waveforms, along with uncertainties in the absolute explosion source strengths and t*, prevent unique solutions for both test sites. Assuming a strike slip orientation, the 27 October 1973 Southem Novaya Zemlya event has the largest tectonic release moment (1.6 x 1024 dyne-cm) and 14 October 1969 northern event has the smallest moment (0.9 x 10" dyne-cm) of the 12 events studied. The ratio of tectonic release moment to explosion strength varies by as much as a factor of 3 at the northem test site and by a factor of 2 at the southern site. The variability of the tectonic release orientation and strength at the two test sites allows us to address the question of whether tectonic release affects yield estimation