Properties of the shear stress peak radiated ahead of

rapidly accelerating rupture fronts that mediate

frictional slip

Ilya Svetlizkya, Daniel Pino Muñozb, Mathilde Radiguetb, David S. Kammera, Jean-François Molinarib,

and Jay Fineberga,1

aThe Racah Institute of Physics, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel; and bCivil Engineering Institute, Materials Science

and Engineering Institute, Ecole Polytechnique Fédérale de Lausanne, Station 18, CH-1015 Lausanne, Switzerland


Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved November 30, 2015 (received for review September 2, 2015)


We study rapidly accelerating rupture fronts at the onset of frictional

motion by performing high-temporal-resolution measurements of

both the real contact area and the strain fields surrounding the

propagating rupture tip. We observe large-amplitude and localized

shear stress peaks that precede rupture fronts and propagate

at the shear-wave speed. These localized stress waves, which

retain a well-defined form, are initiated during the rapid rupture

acceleration phase. They transport considerable energy and are

capable of nucleating a secondary supershear rupture. The amplitude

of these localized waves roughly scales with the dynamic

stress drop and does not decrease as long as the rupture front

driving it continues to propagate. Only upon rupture arrest does

decay initiate, although the stress wave both continues to propagate

and retains its characteristic form. These experimental results

are qualitatively described by a self-similar model: a simplified

analytical solution of a suddenly expanding shear crack. Quantitative

agreement with experiment is provided by realistic finiteelement

simulations that demonstrate that the radiated stress

waves are strongly focused in the direction of the rupture front

propagation and describe both their amplitude growth and spatial

scaling. Our results demonstrate the extensive applicability of brittle

fracture theory to fundamental understanding of friction. Implications

for earthquake dynamics are discussed.