Ð During the period from 1975 to 1979, the former Soviet Union conducted a series a six nuclear explosions in a water-®lled cavity in salt which was created in 1968 by a tamped 27 kt explosion at a depth of 597 m at the Azgir test site at the north end of the Caspian Sea. Broadband, near-regional seismic data recorded from these tests have been processed and analyzed in an attempt to characterize the seismic source characteristics of these explosions and assess their relevance to the cavity decoupling evasion scenario. The results of these analyses indicate that the explosions in the water-®lled cavity were not decoupled, but rather show evidence of enhanced seismic coupling with respect to that which would be expected from tamped explosions of the same yields in salt. Theoretical ®nite dierence simulations of these tests have been conducted in which the complex, nonlinear interactions between the shock eects in both the water and surrounding salt medium have been explicitly modeled. The results of these simulations indicate that the most prominent yield dependent features of the observed seismic source functions can be largely explained by the dynamic interactions between the expanding and contracting steam bubbles generated by the explosions in water and the shock-wave re¯ections from the cavity wall. More speci®cally, it has been found that the shock-wave re¯ection from the cavity wall retards the expansion of the steam bubble in a yield dependent fashion relative to that expected in the open ocean, resulting in a smaller maximum bubble radius and a shorter bubble oscillation period.
A summary of information is presented for 122 Soviet peaceful nuclear explosions (PNE) detonated during the 1965 to 1988 time period. The data presented include detonation times, locations, explosion yields, and depths of burial, as well as summary information regarding the explosion configurations and source emplacement media. This summary is intended to provide a concise reference for use in research studies of the seismic data recorded from this unique set of explosion sources.
A new seismic discriminant based on spectral differences of regional phases from earthquakes and explosions recorded at a single station has been tested and found to work remarkably well. The test data consisted of a well-constrained set of 30 Nevada Test Site (NTS) explosions and 21 earthquakes located within about 100 km of NTS which were recorded on short-period seismographs at the Tonto Forest Observatory in central Arizona at an epicentral distance averaging 530 km. The events in the data set cover a magnitude range from 3.3 to 4.8 (mb) for which Pn, Pg, and Lg phases have been analyzed.
We found that, although Lg phases from earthquakes are typically more prominent than for explosions with comparable P-wave amplitude levels, simple time-domain Lg/P amplitude ratios do not result in a separation of the earthquake and explosion samples consistent enough to provide reliable discrimination. However, spectral analyses of the data over the frequency band from 0.5 to 5.0 Hz revealed significant differences in the spectra of certain regional phases which proved to be a quite reliable discriminant. In particular, both the Pg and Lg spectra from earthquakes have been found to be richer in high-frequency content than corresponding explosion spectra. A discriminant measure, defined as the ratio of average Lg spectral amplitude level in the 0.5- to 1.0-Hz passband to that in the 2.0- to 4.0-Hz passband, provides good separation of earthquake and explosion populations.
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