REMOVAL OF THE DETECTOR-GROUND COUPLING EFFECT IN THE VERTICAL SEISMIC PROFILING ENVIRONMENT

In a 'controlled' experiment with the Gulf VSP tool, the detector-ground coupling was measured and removed from the recorded signal using the Washburn-Wiley algorithm. Repeat measurements were made at a common detector depth with two coupling configurations, the first to permit the true ground motion to be recorded and the second to ensure that a coupling resonance existed within the seismic frequency band. The algorithm removed the distortion of the body-wave portion of the seismogram caused by the coupling resonance for the second configuration and recovered true ground motion. However, lowering the coupling resonance into the seismic band also caused the tool to become sensitive to tube waves. This observation is helpful in evaluating current VSP tools; it implies that any VSP tool that is sensitive to tube waves has a coupling resonance within the seismic frequency band, and that the signal recorded with such a tool does not measure true ground motion.