Sensitivity of Experimental Dynamic Stiffness of the Vibrator-Earth System

The dynamics of the vibrator-earth system is driven by the properties of both the vibrator and the earth. Using a model for the dynamics of this system, we determine theoretically the dynamic stiffness curves that describe the system. In order to define them we need to specify the ground force and the acceleration at the surface of the earth. In our case we use a simplified model of the vibrator to determine the ground force and then assuming that the vibrator baseplate is properly coupled to the surface of the earth (that is very close to the reality due to the hold down force) we use the acceleration of the baseplate to extract these characteristic dynamic stiffness curves of the system. Then we examine, using experimental data, the effect of location, and vibration polarity in dynamic stiffness curves of the system. The sensitivity analysis showed that at low frequencies there is no effect but at medium and high frequencies these curves are very sensitive to the variations. This work is a starting point for the determination of effective earth properties through dynamic stiffness.