RHEOLOGICAL EXPERIMENTS OF A DUAL-WAX MEDIUM FOR ANALOG MODELING OF 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 squeeze-box model in an attempt to yield quantifiable data with respect to the flow of material as it encounters a fault asperity. Fault surfaces are generally non-planar and irregular with fault asperities at a wide range of scales (from mm- to km-scale). Understanding the kinematics of the material adjacent to these asperities is critical for understanding fault behavior at the first order. We have designed and built a new analog modeling rig that utilizes a dual-wax analog material. One constituent is spherical wax particles that have been embedded in a differently-colored matrix wax. Deformation of the analog material is facilitated by heating elements lining the underside and exterior walls of the squeeze-box reservoir.

We examine the rheological properties of our dual-wax medium using a modified Portable Rock-Analog Deformation Apparatus (PRADA, NSF award: EAR-135206; PI: Phil Skemer). The PRADA was modified such that the temperature of the wax can be controlled during the experiment. Constant stresses were applied through a series of weights. As has been described for a single phase paraffin wax, our wax demonstrates a typical creep deformation behavior. As described by Mancktelow (1988) and Rossetti et al. (1999), our wax medium has a temperature dependence with regard to the power-law exponent, n, as can be seen in the varying slopes of the trend lines within the strain rate versus stress log-log plots. This is similar to experimentally determined n-values from quartz aggregates (e.g., Gleason & Tullis, 1995).

The preliminary results from this new deformation rig demonstrate deformation features consistent with those observed in nature, including fault localization, conjugate faults, slickenlines, listric backthrusts, brecciation, cataclastic flow, grain fracture, grain boundary sliding, veining, and pressure shadows. The results of this type of modeling provide unique information about fault kinematics in a poly-phase system for a variety of physical conditions within the Earth’s crust, both within the brittle, seismogenic crust as well as within the deeper, plastically-deforming crustal environments.