Oscillatory loading can alter the velocity rate dependence of
ice-on-rock friction
Abstract
Rate and state frictional parameters are typically determined using two
types of experimental protocols: velocity steps and slide-hold-slide
events. Here we take a new approach by examining the frictional response
to controlled, harmonic oscillations in load point velocity. We present
a Matlab graphical user interface software package, called RSFitOSC,
that allows users to easily determine frictional parameters by fitting
oscillation events using the rate and state friction equations. We apply
our new methods to a set of ice-rock friction experiments conducted over
a temperature range of -16.4°C to -2°C, and described in a companion
paper: McCarthy et al. (In Review). Values of the frictional stability
parameter (a-b) determined from oscillations reveal dominantly
velocity-weakening behavior across the entire range of experimental
conditions. However, values of (a-b) determined from velocity steps in
the same experiments yield velocity-strengthening behavior. We also show
that the elastic stiffness of the ice-rock system depends on the
temperature, and is unlikely to be explained by changes in the elastic
properties of ice. Load point velocity oscillations induce oscillations
in applied shear stress. Many natural fault systems exhibit slip
behaviors that depend on harmonic oscillations in applied tidal
stresses. Our new method provides a way to study how frictional
properties directly depend on parameters relevant to tidal forcing, and
how oscillatory loading must be considered when extracting friction
parameters.