Abstract

The factors which influence the efficiency of generation of seismic energy by a falling weight-coupler system have been investigated both theoretically and experimentally using model techniques. Two media, sand and clay-silt-sand, were used. Source conditions were changed by 1) varying the mass of the falling weight, 2) varying the drop-height, and 3) embedding various bodies (couplers) at the impact point. The results showed that for compressional waves: 1) A alpha M 2 / 3 V c where A is the amplitude of the seismic signal, M the mass of the coupler, and V c the maximum speed of the coupler; 2) the seismic energy is not proportional to the source energy; 3) in general, for a given source energy, the larger the falling mass the more efficient is the generation of seismic energy; 4) the coefficient of restitution between the falling mass and coupler can be determined from seismic-wave amplitudes; 5) complex waves can be generated when the mass of the falling weight is greater than that of the product of the mass of the coupler and the coefficient of restitution; 6) the wave shape depends on the coupler mass and the elastic properties, and the degree of compaction of the medium; and 7) the stacking of suitable masses on the coupler can increase the seismic efficiency by a factor of nearly 4. The results of this study have important implications in the practical application of the weight-drop method used in seismic exploration and in other related energy coupling studies.

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