Regional Seismic Observations from NTS Explosions
- Steven R. Taylor,
- Howard J. Patton and
- Paul G. Richards
Published Online: 18 MAR 2013
Copyright 1991 by the American Geophysical Union.
Explosion Source Phenomenology
How to Cite
Taylor, S. R. (1991) Regional Seismic Observations from NTS Explosions, in Explosion Source Phenomenology (eds S. R. Taylor, H. J. Patton and P. G. Richards), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM065p0185
- Published Online: 18 MAR 2013
- Published Print: 1 JAN 1991
Print ISBN: 9780875900315
Online ISBN: 9781118663820
- Underground nuclear explosions—Detection—Congresses;
The compilation of seismograms from a large number of NTS explosions recorded on a four-station broadband seismic network operated by the Lawrence Livermore National Laboratory has proven useful for a number of verification studies, most notably an assessment of discrimination and yield estimation capabilities. A major component of these studies has been the examination of anomalous explosions that present technical problems. From these studies, it is apparent that our understanding of the supposedly “simple” explosion source is murky at best. Detailed analysis of spectral ratio observations has demonstrated that complicated factors such as spall and the dynamic material response to the expanding explosion shock wave can have a significant effect on radiated seismic spectra. Depending on the physical scaling relationships, spall may affect certain portions of the spectrum in a complicated manner. Large variations in spectral content that are a function of depth of burial and material response are evident in the data. Probably a dominant factor affecting the radiated seismic spectrum is the dynamic material response to the expanding explosion shock wave. This is supported by comparing observations of close-in strong ground motion data with far-field seismic data. Analysis of the NTS explosion QUESO points out the importance of upgoing energy on the generation of regional phases from explosions.
In light of these observations, we have begun to develop a quasi-empirical explosion source model that simultaneously fits the explosion spectral-ratio data from both the U.S. and Soviet Union relative to earthquakes in each of the respective regions. The key to the model is the shape of the pressure-time history acting at the elastic radius which is strongly controlled by the physical state of the material in the near-source volume. Explosions in high-strength rocks produce narrow source pulses with short rise times resulting in high corner frequencies and low rates of high-frequency decay. For explosions detonated in weak, porous rock, the radiated shock wave divides into a two-wave system consisting of an elastic precursor followed by a plastic wave that has the effect of introducing a rise time into the pressure-time history and broadening the pulse width. This results in a lower corner frequency and rapid rates of high-frequency decay.