Frictional anisotropy of 3D-printed fault surfaces

TL;DR

This study uses 3D-printed synthetic fault surfaces based on real field data to investigate how surface anisotropy influences static friction, revealing significant directional dependence and stress-related wear effects.

Contribution

It demonstrates the application of 3D-printing to model fault surface anisotropy and quantifies its impact on static friction in a controlled laboratory setting.

Findings

Friction coefficient along fault striations is 3-4 times smaller than perpendicular.

Frictional anisotropy decreases with increasing normal stress.

Surface wear reduces overall static friction and anisotropy.

Abstract

The surface morphology of faults controls the spatial anisotropy of their frictional properties, and hence their mechanical stability. Such anisotropy is only rarely studied in seismology models of fault slip, although it might be paramount to understand the seismic rupture in particular areas, notably where slip occurs in a direction different from that of the main striations of the fault. To quantify how the anisotropy of fault surfaces affects the friction coefficient during sliding, we sheared synthetic fault planes made of plaster of Paris. These fault planes were produced by 3D-printing real striated fault surfaces whose 3D roughness was measured in the field at spatial scales from millimeters to meters. Here, we show how the 3D-printing technology can help for the study of frictional slip. Results show that fault anisotropy controls the coefficient of static friction, with the friction coefficient along the striations being three to four times smaller than the friction coefficient along the direction perpendicular to the striations. This is true both at the meter and the millimeter scales. The anisotropy in friction and the average coefficient of static friction are also shown to decrease with the normal stress applied to the faults, as a result of the increased surface wear under increased loading.