CRACK-LIKE PROCESSES GOVERNING THE ONSET
OF FRICTIONAL SLIP
Shmuel M.
Rubinstein, Meni Shay, Gil Cohen, and Jay Fineberg
The Racah
Institute of Physics, The
Author for
correspondence (E-mail: jay@vms.huji.ac.il)
Abstract. We perform real-time measurements of the net
contact area between two blocks of like material at the onset of frictional
slip. We show that the process of interface detachment, which immediately
precedes the inception of frictional sliding, is governed by three different
types of detachment fronts. These crack-like detachment fronts differ by both
their propagation velocities and by the amount of net contact surface reduction
caused by their passage. The most rapid fronts propagate at intersonic
velocities but generate a negligible reduction in contact area across the
interface. Sub-Rayleigh fronts are crack-like modes which propagate at
velocities up to the Rayleigh wave speed, V, and give rise to an approximate
10% reduction in net contact area. The most efficient contact area reduction (~20%)
is precipitated by the passage of “slow detachment fronts”. These fronts
propagate at “anomalously” slow velocities, which are over an order of
magnitude lower than V yet orders of magnitude higher than other characteristic
velocity scales such as either slip or loading velocities. Slow fronts are
generated, in conjunction with intersonic fronts, by the sudden arrest of
sub-Rayleigh fronts. No overall sliding of the interface occurs until either of
the slower two fronts traverses the entire interface, and motion at the leading
edge of the interface is initiated. Slip at the trailing edge of the interface
accompanies the motion of both the slow and sub-Rayleigh fronts. We might
expect these modes to be important in both fault nucleation and earthquake dynamics.