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Phase-velocity filtering is a technique by which seismic arrivals having a certain phase velocity are eliminated from the record. The main application is considered to be in refraction exploration areas where overlapping arrivals are a problem in interpretation. Filtering action is accomplished by use of a receiver array at each receiver site and a particular way of combining the signals from the elements of the array. The array consists of two receivers on a line which includes the shotpoint.

The two ways of combining the signals are called the time-delay method and the signal-gradient method. In the former, the signal from the receiver nearest the shot is delayed prior to being subtracted from the signal of the farthest receiver. In the latter method, the gradient or instantaneous difference signal of the two receivers depends inversely upon phase velocity. The difference signal is referred to the sum signal of the array to obtain filtering. Experiments with seismic models show that both methods are effective. The time-delay method requires the least data manipulation, so it is considered the better method for field applications.

The field use of phase-velocity filtering will require only minor changes in field procedure and conventional magnetic-recording and data-processing equipment. In the laboratory tests it was noted that nonuniform receiver coupling in an array was a problem. Nonuniformity of receiver plant may also present a problem in field application.

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