CONSTRUCTING A GEOLOGICAL SQUEEZEBOX TO MODEL FAULT ASPERITY KINEMATICS

The geological squeezebox has been used to model deformation in analogue materials (usually sand and/or clay) ever since Henry Cadell’s experiments in 1888. We have modified the basic squeezebox model in an attempt to yield quantifiable data with respect to the flow of material as it encounters a deep fault asperity. We have chosen a viscoplastic analog material of spherical wax beads in order to record the kinematics of the ductile deformations associated with fault motion. These wax spheres are themselves “cemented” by a lower melting temperature wax matrix.

Our deformation rig consists of an aluminum framed box with a movable push-plate at one end. A modified trailer jack is attached to the push-plate which receives a constant displacement from a stepper motor. Heating coils line the exterior of the aluminum box to provide the requisite heat to facilitate plastic deformation. The bottom of the squeezebox is fitted with a removable aluminum asperity. Additional overburden can be simulated with the addition of water bladders on top of the deforming wax.

A single experiment includes three successive runs with the squeezebox. At the end of an experiment, the cooled wax is sectioned in order to preform strain analysis on the deformed wax beads. Strain measurements are taken from three mutually perpendicular sections and combined to yield three-dimensional strain ellipsoids.

We anticipate that the strain distributions will incorporate large amounts of material flow perpendicular to the compression direction and that the deforming material within the fault system will need to compensate for this material flow by transmitting strain to material farther from the fault surface. We hypothesize that the strains associated with irregularities along fault surfaces are the major contributing factors in whether a fault continues to be active versus the initiation of a new fault.