Frictional melting of gabbro under extreme experimental conditions of normal stress, acceleration, and sliding velocity

Abstract

[1] With the advent of high-velocity shear apparatus, several experimental studies have been performed in recent years, improving our understanding of the evolution of fault strength during seismic slip. However, these experiments were conducted under relatively low normal stress (<20 MPa) and using small cylindrical samples where a large gradient in slip velocity exists across the sliding surface. Given the above limitations, the extrapolation of these experimental results to natural conditions is not trivial. Here we present results from an experimental study on gabbroic rocks using a newly developed rotary shear apparatus capable of reaching higher normal stress (up to 50 MPa) on ring-shaped samples (30/50 mm internal/external diameter) and allowing precise control of the imposed slip velocity function. The results confirm that steady state shear stress during the melt-lubricated phase of the experiment depends on normal stress in the form of a power law equation as predicted by theoretical models. However, the exponent appears closer to 0.5, contrary to the theoretical prediction of 0.25. We observe no systematic dependence of shear stress on acceleration, but increasing deceleration drastically decreases the recovery of friction during final slip. We find that the slip-weakening distance decreases inversely with increasing normal stress, in agreement with theoretical considerations, and decreases with increasing slip rate. Extrapolation of the slip-weakening distance to natural conditions predicts a slip velocity for ancient seismic events of 0.3-1 m/s when compared with field estimates. These values compare well with seismological estimates.

Laboratory observations of transient frictional slip in rock–analog materials at co-seismic slip rates and rapid changes in normal stress

“…Moreover, from these experiments, we find that the slip-weakening distance is of the order of only a few tens of microns. These relatively small slip distances are in agreement with theoretical considerations presented by (Niemeijer et al, 2011) where normal stress and slip velocity together control the critical slip weakening distance. In further support of this, Brantut et al (2008) have studied the frictional properties of natural kaolinite-bearing gouge samples from the Median Tectonic Line (SW Japan) using a high-velocity rotary shear apparatus.…”

“…For sufficiently large combinations of slip speeds and effective normal stress, thermal power generated during solid-on-solid slip overwhelms the ability of thermal conduction to carry the frictional heat away from the slip interface and macroscopic melting may occur (Di Toro et al, 2006Hirose and Shimamoto, 2005;Liou et al, 2004;Nielsen et al, 2010;Niemeijer et al, 2011;Okada et al, 2001;Okada et al, 2002;Spray, 2005;Tsutsumi and Shimamoto, 1997). Since molten layers have a low viscosity, they may lead to hydrodynamic lubrication of faults reducing dynamic friction.…”

Frictional Instabilities and Carbonation of Basalts Triggered by Injection of Pressurized H2O‐ and CO2‐ Rich Fluids

“…To investigate the effect of short‐term fluid‐rock interaction on the mechanical behavior of basalt‐built faults, 20 friction experiments were performed with the rotary shear apparatus SHIVA (Slow to High Velocity Apparatus; Table S2) installed at the Istituto Nazionale di Geofisica e Vulcanologia in Rome (Italy; Di Toro et al, 2010; Niemeijer et al, 2011). The experiments were performed on hollow cylinders 30/50 mm internal/external diameter of the continental flood basalts described in section 2.1.…”

From slow to fast faulting: recent challenges in earthquake fault mechanics

“…Such knowledge has been established only recently, because the technical implementation of high-velocity, seismic-like conditions in laboratory experiments was achieved no earlier than the 1980s with the pioneering work of Shimamoto & Tsutsumi [55] and became widespread in the last decade (see [8,33,[56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72] among others). It is notable that such high-velocity weakening has been documented even on rocks which show rate-strengthening in traditional, slow frictional tests.…”