The Vibroseis Source - Volume 3

Approximately 50% of all seismic surveys on land are performed using a seismic vibrator as a source.

To obtain an accurate image of the earth, one needs to know the input signal to remove its effect on the seismogram.

One of the main advantages of the Vibroseis source over impulsive sources like dynamite is the control one has over the emitted signal.

To establish which signal on the vibrator needs to be monitored for this purpose (feedback signal), both the behaviour of the earth and of the vibrator must be understood.

Discussion in the literature on the choice of feedback signal started in the 1980's, when Lerwill (1981) and Sallas and Weber (1982) raised this issue.This book presents a sound theoretical foundation to evaluate existing and new methods of signal control, and compares theoretical results with real data.

Another slightly more theoretical issue discussed in the literature is the general problem of a plate (or disk) vibrating on the earth. The most famous paper in this respect is by Miller and Pursey (1954). The non-uniform distributions of traction and displacement under the plate that are measured in the field have never been included before, but this volume presents new models which account for this non-uniformity. One of these new models includes the bending of the baseplate. The behaviour of the vibrator can only be understood when vibrator and earth are coupled. Usually, either the earth model is very simple (e.g. a spring-dashpot model), or the vibrator model is very simple (e.g. uniform traction under the plate), or both. Included are accurate models for both vibrator and earth, and results for the coupled earth-vibrator model.Most articles on marine vibroseis only deal with the problem of smearing of the data due to the movement of the source and receiver through the water. Many other aspects of the marine vibrator (for example far field relations, power output, feedback signal) are considered in this volume.