Source Characteristics of Two Underground Nuclear Explosions

SUMMARY Broadband seismic waveform data recorded in the distance range of 1-11 km from two underground explosions detonated at Pahute Mesa of the Nevada Test Site have been used to estimate the source time functions for the second-order moment tensors of these events. Data were available from eight three-component stations for the explosion Harzer and from 11 stations for the explosion Chancellor. Stable moment tensor estimates with a good signal-to-noise ratio were obtained in the frequency range of 0.2-5.0 Hz. The moment tensors are dominated by the diagonal elements, but a significant asymmetry is present, with vertical force couples being larger, having additional low-frequency energy in the 0.3-0.4 Hz range, and having a different time dependence in the 0.5-2.5s range than the horizontal force couples. Considerable evidence points to the possibility that this asymmetry is related to spall processes taking place in the depth interval between the explosion and the free surface. When the isotropic parts of the moment tensors are interpreted as reduced displacement potentials, the results are in reasonable agreement with theoretical and empirical models, except that the characteristic times are about three times those predicted by published scaling relationships. This difference is most likely due to the effects of spall, but the fact that the explosions were detonated in unsaturated materials may also be a contributing factor.

[1]  Brian W. Stump,et al.  Constraints on explosive sources with spall from near-source waveforms , 1985 .

[2]  John R. Murphy,et al.  Seismic source functions and magnitude determinations for underground nuclear detonations , 1977, Bulletin of the Seismological Society of America.

[3]  L. Johnson,et al.  Two-dimensional array measurements of near-source ground accelerations , 1983 .

[4]  H. C. Rodean,et al.  Nuclear-explosion seismology , 1971 .

[5]  W. Silva.  Body waves in a layered anelastic solid , 1976 .

[6]  T. Wallace,et al.  EVIDENCE OF TECTONIC RELEASE FROM UNDERGROUND NUCLEAR EXPLOSIONS IN LONG-PERIOD S WAVES , 1985 .

[7]  Lane R. Johnson,et al.  The effects of unconsolidated sediments upon the ground motion during local earthquakes , 1981 .

[8]  David G. Harkrider,et al.  Surface waves in multilayered elastic media. I. Rayleigh and Love waves from buried sources in a multilayered elastic half-space , 1964 .

[9]  H. C. Rodean,et al.  Inelastic Processes in Seismic Wave Generation by Underground Explosions , 1981 .

[10]  N. A. Haskell.  The Dispersion of Surface Waves on Multilayered Media , 1953 .

[11]  T. Lay,et al.  The effects of tectonic release on short-period P waves from NTS explosions , 1984 .

[12]  John R. Murphy,et al.  P Wave Coupling of Underground Explosions in Various Geologic Media , 1981 .

[13]  E. Flynn,et al.  Effects of source depth on near‐source seismograms , 1988 .

[14]  L. Johnson,et al.  Near-field source characterization of contained nuclear explosions in tuff , 1984 .

[15]  B. Stump.  Mathematical representation and physical interpretation of a contained chemical explosion in alluvium , 1987 .

[16]  R. Kind,et al.  The reflectivity method for a buried source , 1977 .

[17]  Brian W. Stump,et al.  The determination of source properties by the linear inversion of seismograms , 1977, Bulletin of the Seismological Society of America.

[18]  Thorne Lay,et al.  Modeling Near-Field and Teleseismic Observations From the Amchitka Test Site , 1984 .

[19]  W. J. Carr,et al.  Interpretation of gravity data in a complex volcano‐tectonic setting, southwestern Nevada , 1984 .

[20]  A. S. Alekseev,et al.  The solution of dynamic problems of elastic wave propagation in inhomogeneous media by a combination of partial separation of variables and finite-difference methods , 1980 .

[21]  Velocity structure of Silent Canyon Caldera, Nevada Test Site , 1987 .

[22]  Hadley,et al.  Seismic source functions and attenuation from local and teleseismic observations of the NTS Events Jorum and Handley. Quarterly technical report, 22 November 1978-31 January 1979 , 1981 .

[23]  David von Seggern,et al.  Source Time Functions and Spectra for Underground Nuclear Explosions , 1972 .

[25]  T. Lay,et al.  Reply to “Comments on ‘Average Q and yield estimates from the Pahute mesa test site’” , 1987 .

[26]  John R. Murphy,et al.  Seismic characteristics of underground nuclear detonations Part I. Seismic spectrum scaling , 1971 .

[27]  N. A. Haskell.  Analytic Approximation for the Elastic Radiation from a Contained Underground Explosion , 1967 .

[28]  J. Theodore Cherry,et al.  Surface waves from underground explosions with spall: analysis of elastic and nonlinear source models , 1983 .