Bringing Faults to the Lab: 3D Printing Natural Faults for Rock Friction Experiments
Julia Baumgarte, McGill University
James Kirkpatrick, McGill University
Multiple aspects of fault slip, including earthquake rupture propagation and frictional sliding, are influenced by the roughness of fault surfaces. This roughness is evident in ancient, exhumed faults that contain non-planar slip surfaces, and can be measured at a wide range of length scales (nanometers to kilometers). Fault roughness is well described by a power law, in which roughness scales according to the Hurst exponent (usually 0.6 and 0.8 in the slip-parallel and slip-perpendicular direction, respectively). However, realistic fault roughness is rarely used in rock friction experiments; rather, plates with "teeth" usually grip experimental material for shearing. The mechanical effects of the characteristics of fault roughness on frictional behavior are therefore largely unexplored. Here, we use 3D printing methods to recreate naturally rough surfaces and conduct friction experiments using these fault replicas as shearing plates. One method of 3D printing, termed stereolithography, uses a UV laser to harden resin layer by layer into a designated topography. Stereolithography preserves micron-scale details, and current work seeks to minimize the warping associated with printing thin plates. These plates will be sheared in a triaxial deformation apparatus to study the transition from localized shear to distributed shear in gouge between increasingly rough surfaces. Another type of 3D printing, fused deposition modelling (FDM), works by strategically laying down melted strands of plastic such that layers and strips fuse together. This method is faster and allows for larger models. Casts of fault surfaces will be printed using FDM, then filled with cement with various sized aggregates to create lime "conglomerates." These concrete conglomerates will be sheared in a large direct shear apparatus to investigate the dependence of wear and friction on clast size. Results from these sets of experiments will improve understanding of how laboratory friction experiments apply to natural faulting.
Session 1: Fault Zones from Top to Bottom