fan shooting

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fan shooting A simple seismic refraction method used for delineating subsurface geologic features (e.g. salt domes, buried valleys, and back-filled mineshafts) by contrasting their seismic velocities with those of the surrounding materials. Geophones are set out around a segment of arc in a fanlikearray centred on one or more shot locations. A base line of geophones is used in relation to one of the shot locations to provide a time—distance curve where no subsurface feature is present, thus calibrating the travel times for a given range. Using the fan arrays, travel times of refracted rays are measured to each detector; any ray encountering a zone of anomalously high or low velocity will arrive ahead of or behind the expected travel time for that shot-to-geophone range.