SUBSURFACE MOTION FROM A CONFINED UNDERGROUND DETONATION. PART I
Particle motion measurements were made within the mesa adjacent to Rainier shot on both a horizontal and a vertical radius. Principal information was derived from radial component acceleration data. Long-base strain gages on both radii provided some data of limited value. Horizontal radius data were obtained from 100 to 1355 feet from the source; vertical radius data were obtained from 366 feet to the surface at 896 feet. Most of the accelerometers were given set ranges below the actual peak accelerations produced by Rainier. A consequence of this was that many records required use of a nonlinear calibration prccedure snd a few included peaks truncated by saturation of the recording system. All acceleration data were integrated to Particle velocity and displacement information. Peaks were added to truncated records to produce velocity-time data which implied return to zero velocity at a reasonable time after initial motion. Peak horizontal accelerations decay inversely as the fourth power of radial range to about 5g at 500 feet, then progressively as the inverse second and first powers. Peak vertical accelerations decrease as the inverse second power up to the base of the welded tuff (rhyolite) cap rock. Above that point peak accelerations increase, presumably as a result of reflection phenomena in a medium of decreasing seismic impedance as the surface is approached. Vertical acceleration and velocity data indicate development of at least three horizontal partings by a mechanism analogous to spalling and generation of a 1-second oscillation of a massive section of the mesa at least 530 feet thick above Rdinier. This oscillation appears to be related to a 1- second surface wave which is propagated with a velocity of abcut 3000 feet per second outward to 3240 feet, as recorded by strong motion seismographs. Long- base strain gage data were limited on the horizontal radius by early mechanical failure caused by spalling of the tunnel walls. Strain gages in the vertical radius were limited to compressive strains by the method of mounting on steel cables. (auth)
- Research Organization:
- Sandia Corp., Albuquerque, N. Mex.
- NSA Number:
- NSA-15-024636
- OSTI ID:
- 4024379
- Report Number(s):
- WT-1529
- Country of Publication:
- United States
- Language:
- English
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