Delineation of spall zone from pre/post shot reflections studies: Preliminary results from BEXAR. Los Alamos Source Region Project
- Los Alamos National Lab., NM (United States)
- Kansas Univ., Lawrence, KS (United States)
In order to delineate the lateral and depth extent of spall from a buried nuclear explosion, we have performed a high-resolution pre- and post-shot seismic reflection survey from BEXAR. Although the data quality were marginal due to poor wave propagation through the volcanic tuffs of Pahute Mesa, a number of interesting differences are observed on the pre- and post-shot surveys. On the pre-shot survey, a reflector (reflector `` 1 ``) is observed at 250 ms (or about 150 m depth) using a stacking velocity of 1300 m/s. On the post-shot survey two reflectors are observed and a stacking velocity of 1150 m/s was used representing a 12% reduction in compressional velocity. With this stacking velocity, reflector `` 1 `` is recorded at 290 ms (still at about 150 m depth) and a new reflector ``2`` is observed at 210 ms (or about 100 m depth). These stacking velocities correspond well with available uphole travel times collected in U19ba and nearby U19ax (BEXAR and KEARSARGE emplacement holes, respectively). The cause for the differences observed in the pre- and post-shot surveys may be due to one of two reasons. First, it is possible that the near-surface rocks were damaged as part of the spallation process (thus reducing the in situ velocities) and reflector ``2`` represents a spall detachment surface. However, analysis of acceleration data collected close to the reflection line suggests that the ground motions were probably inadequate to damage the tuffs. Also, no evidence of actual spallation was actually observed. The second hypothesis is that the near-surface velocities of the tuffs were altered by the change in saturation state due to extensive rains occurring between the pre- and postshot surveys. Although the dependence of seismic velocity on saturation state is controlled by a number of complex factors, it cannot be ruled out.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 10183455
- Report Number(s):
- LA-UR-92-1158; ON: DE93040502
- Resource Relation:
- Other Information: PBD: [1992]
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION
UNDERGROUND EXPLOSIONS
SEISMIC DETECTION
NUCLEAR EXPLOSIONS
TUFF
ROCK MECHANICS
WAVE PROPAGATION
BOREHOLES
NUCLEAR EXPLOSION DETECTION
SPALLATION
VELOCITY
GROUND MOTION
DETONATION WAVES
RHYOLITES
SEISMIC P WAVES
450300
350300
VERIFICATION