New Insights into the Explosion Source from SPE

Abstract:

Phase I of the Source Physics Experiments (SPE) is a series of chemical explosions at varying depths and yields detonated in the same emplacement hole on Climax stock, a granitic pluton located on the Nevada National Security Site. To date, four of the seven planned tests have been conducted, the last in May 2015, called SPE-4P, with a scaled depth of burial of 1549 m/kt^1/3 in order to localize the source in time and space. Surface ground motions validated that the source medium did not undergo spallation, and a key experimental objective was achieved where SPE-4P is the closest of all tests in the series to a pure monopole source and will serve as an empirical Green’s function for analysis against other SPE tests. A scientific objective of SPE is to understand mechanisms of rock damage for generating seismic waves, particularly surface and S waves, including prompt damage under compressive stresses and “late-time” damage under tensile stresses. Studies have shown that prompt damage can explain ~75% of the seismic moment for some SPE tests. Spallation is a form of late-time damage and a facilitator of damage mechanisms under tensile stresses including inelastic brittle deformation and shear dilatancy on pre-existing faults or joints. As an empirical Green’s function, SPE-4P allows the study of late-time damage mechanisms on other SPE tests that induce spallation and late-time damage, and I’ll discuss these studies. The importance for nuclear monitoring cannot be overstated because new research shows that damage mechanisms can affect surface wave magnitude Ms more than tectonic release, and are a likely factor related to anomalous mb-Ms behavior for North Korean tests.