3.1.5. Seismic Choice
Recreating results similar to those felt by an earthquake would be achieved by recreating the waves that impact the surface of the Earth's crust. The study of the various types of seismic waves has led to the conclusion that the surface/shear waves are the waves that must be recreated. These waves create effects in multiple degrees of motion, but due to our design and cost constraints, or team must determine a method in recreating the earthquake motion in one degree of freedom. Recreating a shear wave will be the most promising method in recreating earthquake motion in only one degree of freedom.
A shear wave is created when the crust of the earth is sheared by the motion of the seismic waves. A shear wave laterally shifts the crust of the earth from the bedrock that lies underneath it. This motion can be compared to a shear dislocation in a material structure. Figure 3.5 below helps to explain the process and principle of a shear dislocation. The forces from the seismic waves force the lateral separation of the relatively thin crust and soil that lies above the bedrock.