Seismic vibrator control and the downgoing P-wave

Abstract

While the need for phase compensation is well established, the best method to measure the seismic vibrator output is not. Phase control of the force exerted by a seismic vibrator upon the earth’s surface (ground force) is shown to be useful in producing consistent downhole P-wave signatures. Experimental results are presented which compare the downhole correlation wavelets produced by phase‐locking to ground force; reaction mass acceleration and baseplate acceleration as changes in vibrator type, sweep bandwidth, drive level, and coupling medium are made. The empirical results support earlier theoretical work which predicts with suitable assumptions that ground force and far‐field particle displacement are in phase except for a time delay.