Analog modeling of fault asperity kinematics using a modified squeeze-box design and wax media

Abstract

Fault movement is strongly influenced by the physical characteristics of the fault surfaces. Fault surfaces are generally nonplanar and have a certain amount of roughness to them, which manifests as fault asperities. In order for a fault to continue moving along its preexisting surface, the asperities must either move past each other, which involves moving a large volume of rock around these obstacles, or create new fractures that “decapitate” and pulverize these asperities, ultimately leading to a smoother fault surface. We explore a new way to investigate fault asperity kinematics using a squeeze-box analog deformation rig. The more typical and classic squeeze-box model uses sand and/or clay to demonstrate fault and fold deformations. We have designed and built a new analog modeling rig that uses a dual-wax analog material. One constituent is white spherical wax particles that have been embedded in a lower-melting-temperature black matrix wax. Deformation of the analog material is facilitated by the addition of heating elements lining the underside and exterior walls of the squeeze-box reservoir. An aluminum asperity is secured to the floor of the reservoir. Additional overburden is simulated with lead shot that rests on the top surface of the wax block during deformation. Once the experiment is completed, the wax block can be finely sectioned, polished, and scanned in preparation for analysis. Here, we present the first results from this new deformation rig where we were able to generate realistic looking deformation features at different strain rate conditions. The results of this type of modeling provide unique information about fault localization, the role of fluids, and fault asperity kinematics in a polyphase system for a variety of physical conditions within the earth’s crust. These conditions are difficult to model with other analog or numerical techniques or to derive from field or seismic investigations.