3D Numerical Modeling of Tectonic Strain Release from Explosions

We perform calculations of an explosion in 3D prestress field and examine the effects on near-field data, regional data, surface waves, and far-field body waves. We specifically model the nuclear explosion Shoal, which had anomalous near-field ground motion. The calculation of Shoal shows that tectonic strain release consistent with the local stress state can generate near-field and regional signals, including long-period surfacewaves, similar to those observed. We find that tectonic release causes small changes to the far-field P-wave waveform but has very little effect on far-field P-wave amplitudes. It does generate SH waves not present in the calculation without tectonic release. This implies that whereas tectonic release may significantly affect M-s, the effect on m(b) is small. Nonlinear effects above the explosion have a stronger effect on body waves than tectonic release, with the main effect being a reduction in the pP amplitude.