Measurement and Characterization of Fault Asperities on Hand Samples

Abstract:

Fault roughness has emerged as a central issue in earthquake physics. Principal slip surfaces in faults have measurable roughness that is generated during slip, with the final geometry preserving information about the scale-dependent strength of the material. Over the past decade, scanning with ground-based LiDAR, laboratory laser profilometers and other optical scanning methods has enabled higher-precision, high-density measurements of exhumed fault surfaces.

One of the most intriguing applications of roughness is understanding asperities. Well-defined, persistent asperities are often invoked as a key element of earthquake physics, yet their physical origin remains elusive. While it is difficult to measure asperities on active faults, a statistical approach that uses observed roughness from different exhumed faults could connect the distribution of asperities to commonly observed features of earthquake populations like the Gutenberg-Richter distribution and source function scaling.

We have built a laser profilometer with a wide field of view, allowing the measurement of large hand samples of up to 25 x 25 cm at 15 micron voxel resolution. We use this profilometer to measure surfaces recovered from faults to compare the sensitivity of different characterization metrics. In addition, we explore the effect of surface corrections in order to probe the relevant scale of asperities for earthquakes.