Microseismic Monitoring of a Longwall Coal Mine. Volume II - Determination of Seismic Velocity

摘要

This report is volume 2 of a three-volume report dealing with the microseismic monitoring of a longwall coal mine. The report describes the evaluation of a number of different field techniques and the seismic velocity data obtained at the Greenwich Collieries, Barnesboro, PA., mine site where the microseismic studies were carried out. Three different methods were employed to evaluate seismic velocities; namely, surface refraction, downhole, and transmission. In all cases the seismic sources were either located on surface (mechanical impact) or near-surface (explosive charges). It was found that a mechanical source could be conveniently utilized to determine shallow velocities and make bedrock-regolith interface depth determinations. For deeper velocity determinations suitable explosive charge sources were required. In general, refraction data did not always plot in a linear manner and some subjective interpretation was necessary. The downhole method was useful for incremental vertical velocity evaluation; however, the transmission method provided the most consistent average vertical velocity data.