Effects of asperities and roughness on frictional slip of laboratory faults

Abstract

<p>Natural faults are heterogeneous features, with complex geometries and material properties. Understanding how the geometrical complexities of a fault affects the dynamics and preparatory phase of earthquakes is of crucial importance for seismic hazard assessment. In laboratory samples, frictional sliding along prefabricated faults may produce so called stick-slips comparable to dynamic ruptures observed during earthquakes. While the effect of roughness has been shown to influence significantly the frictional behavior of laboratory faults, there are only a few studies investigating more complex types of fault heterogeneities. In this study, we conduct friction experiments on granite with inclined sawcut faults, under a constant confining pressure of 35MPa. Samples are loaded using an axial displacement rate of 0.5 µm/s.  At  similar boundary conditions we compare the slip behavior of (1) a smooth fault, (2) a smooth fault with a single asperity, a 7 mm diameter vertical pin traversing the contact interface, and (3) a rough fault prepared by sandblasting the surface with silicon carbide. A key result of this study is that slip behavior depends on fault roughness and is influenced in a non-trivial way by asperities. The smooth fault displays unstable stick-slip as opposed to the rough fault showing predominantly creep. The smooth fault with the pin exhibits a slip behavior in-between, with very regular stress oscillations that seem to be attenuated by the presence of the pin (asperity). Only after failure of the pin, we observe the stress drop during instabilities to increase regularly with cumulative slip. We also show that in the case of a fault with a single asperity, the slip velocity is less than an order of magnitude lower compared to a similar smooth fault without this asperity.</p>

A Synthesis of Fracture, Friction and Damage Processes in Earthquake Rupture Zones

“…Laboratory fracture and friction experiments culminating in a sample-size stick-slip motion and rapid stress drop represent lab analogues for crustal earthquakes (Brace & Byerlee, 1966). Here we briefly summarize some results from a series of lab tests with different geological materials (claystone, sandstone, quartzite, granite) performed at varying loading conditions and confining pressures up to 150 MPa (Goebel et al, 2012(Goebel et al, , 2017Guerin-Marthe et al, 2022). Depending on material and loading conditions, the samples mostly failed in episodic stick slip events accompanied by rapidly evolving bursts of acoustic emission (AE) activity (Fig.…”

“…On rough fractured faults, the AE activity spreads across the surface forming a single or a few expanding clusters (Fig. 5), while on smooth faults the AE activity is generally low or in some cases non-existent (Dresen et al, 2020;Guerin-Marthe et al, 2022). The AE clusters highlight larger asperities that persist over several stick-slip cycles.…”

Fracture, friction and damage processes in earthquake rupture zones

“…5, 6) attest to loading and dynamic failure of grain-scale and larger asperities across different length scales (Ohnaka and Shen, 1999;Goebel et al, 2017;Dresen et al, 2020). As AE activity relates to roughness, preparatory fault slip on smooth faults is often dominantly aseismic and small, involving a few and generally large AEs close to failure at peak stress that initiate a macroscopic slip event (Guerin-Marthe et al 2022).…”

“…On rough fractured faults, the AE activity spreads across the surface forming a single or a few expanding clusters (Fig. 5), while on smooth faults the AE activity is generally low or in some cases non-existent (Simon Guerin-Marthe et al, 2022;Dresen et al, 2020). The AE clusters highlight larger asperities that persist over several stick-slip cycles.…”

“…Laboratory fracture and friction experiments culminating in a sample-size stick-slip motion and rapid stress drop represent lab analogues for crustal earthquakes (Brace and Byerlee, 1966). Here we brie y summarize some results from a series of lab tests with different geological materials (claystone, sandstone, quartzite, granite) performed at varying loading conditions and con ning pressures up to 150 MPa (Goebel et al, 2012;Guerin-Marthe et al, 2022). Depending on material and loading conditions, the samples mostly failed in episodic stick slip events accompanied by rapidly evolving bursts of AE activity (Fig.…”