Vibration response and evaluation of oil shale mine openings to the Rio Blanco event

Project Rio Blanco was designed to further study the economic and technical feasibility of the commercial development of natural gas, using underground nuclear explosions to stimulate production. Simultaneous detonation of the three, 30 kt devices took place on May 17, 1973, at 10:00:00.12 hours +-0.01 second, M.D.T. The initial compressional impulse was evident on all data channels at the Colony, Anvil Points and Dutch Creek No. 1 Mines. Other phases were not readily identifiable due to the complexity of the seismic signals. Recorded particle velocity and acceleration were, in general, near that predicted for the event. Particle velocity was directly recorded from all station points. Acceleration was directly recorded only from selected stations for comparative purposes. Displacement was derived for all station points from recorded particle velocity and/or acceleration. Propagation velocity was calculated to be 13,950 feet/second to the Colony Mine and 15,800 feet/second to the Anvil Points Mine. In view of the fact that both mines lie very nearly on a common line to ground zero, a higher velocity to the Anvil Points mine is unique. This may indicate the presence, at depth, of a high velocity refraction layer through which the seismic wave to both mines was transmitted. Loss of the transmitted time signal at the Dutch Creek No. 1 mine station prevents calculation of the propagation velocity