Abstract

A seismic method is described by which depth to bedrock in valleys can be estimated without the need to traverse the valley surface with conventional refraction or reflection techniques. A short detector array on rock outcrop on one side of the valley is used to measure compressional waves from a shot on outcrop on the opposite side, and to measure the seismic velocity of the rock. The shortest travel-time path across the valley follows the bedrock overburden interface, and when the bedrock velocity is known, the length of the path can be computed. The ratio of the length of the bedrock path to the direct distance between source and receiver is a function of the depth to bedrock at the valley center. The success of the method requires that certain valley-shape configurations be reasonably predictable and that the bedrock velocity be uniform throughout. Depth calculations for several field examples have been made using graphical techniques.

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