Velocity steps across four orders of magnitude to investigate the effect of fault roughness on the stability of slip

Abstract:

The conditions that lead to stick slip as opposed to aseismic sliding are of great interest both in the realms of natural as well as induced seismicity. With this in mind, tectonic faults have been shown to have rougher patches that are stronger, and control earthquake nucleation and co-seismic slip. Indeed, in general, rougher faults seem to have a greater tendency to slip aseismically. However, while the influence of roughness on earthquake nucleation has been recognized, it has not yet been well explored and characterized. Using the High Strain TEmperature Pressure Speed (HighSTEPS) low to high velocity biaxial friction apparatus located at the EPFL in Switzerland, the effect of fault roughness on the stability of slip during velocity steps has been investigated.

The investigation concerns gabbro samples with customized roughness and Hrms ranging from 3 to 115 microns under normal stresses ranging from 10 to 40 MPa. Velocity steps from 10 microns/sec to 100, 1000, and 10000 microns/sec were performed, reaching higher velocities in comparison to previous related studies. Rate and state friction parameters have also been identified along with their trends in relation to relevant variables. It is generally found that increasing roughness and decreasing normal stress both stabilize slip. Additional velocity stepping experiments are also performed on Westerly Granite, lending support to previous investigations in the literature as well as to the fidelity of the novel HighSTEPS apparatus.