Seismic Magnitudes of Underground Nuclear Explosion Signals and Their Uses

Session: Explosion Seismology Advances
Type: Oral
Date: 4/29/2020
Time: 08:30 AM
Room: 240
Description: 

We have re-analyzed observations of body waves and surface waves for well-recorded underground nuclear explosions (UNEs) conducted in the Balapan sub-region of the Semipalatinsk Test Site (STS) in Kazakhstan.

First, we present a new magnitude-yield relation for UNEs at STS, namely m_b = 4.55 + log Y (yield Y in kilotons), which uses a recent carefully-assigned teleseismic m_b based on data from a fixed network of global stations (Peacock et al., GJI, 2017). This relation gives an remarkably good fit to yield information announced by the Russian Federation in the early 1990s and demonstrates the importance of using a method to assign m_b values that is stable over decades.

Second, to reconcile differences between body-wave and surface-wave amplitudes, we solve for a scaling factor between vertical and horizontal dipoles in an explosion model. These dipoles do not need to be the same size, as in the traditional isotropic model. We infer that vertical forces are typically stronger than horizontal forces for shallow UNEs, tending toward equality (isotropy) for increasing scaled depth of burial, for the subset of UNEs at Balapan that have published depths. Such variations in force scaling influence surface-wave excitation, and data suggests that recorded surface-wave amplitudes are significantly affected by UNE burial depth as well as by previously recognized tectonic release.

Our work is pertinent to an understanding of: the m_b — M_s discriminant and to the low quality of yield estimates inferred from M_s values.

Presenting Author: Paul G. Richards

Authors