Experimental study of instant variations in velocity and attenuation of seismic waves in a friable medium in situ under a pulse dynamic load

Instant variations in velocity and attenuation of seismic waves in a friabl e medium subjected to dynamic loading have been studied by new experimental techniques using a powerful seismic vibrator. The half-space below the ope rating vibrator baseplate was illuminated by high-frequency elastic waves, and the recorded fluctuations were exposed to a stroboscopic analysis. The variations in seismic velocities and attenuation are synchronous with the e xternal pulsatory loading but are out of phase with the latter and with eac h other. Instant variations in the studied parameters depend on the magnitu de and absolute, rate of deformation, which always reduces elastic-wave vel ocities. Some weak seismic boundaries have shown a high sensitivity to the presence of dynamic disturbance in the, medium.