title: Properties of the shear stress peak radiated ahead of rapidly accelerating rupture fronts that mediate frictional slip.
abstract: 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 finite-element 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.
authors.affiliation: The Racah Institute of Physics, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel;
authors.forename: Ilya
authors.initials: I
authors.lastname: Svetlizky
authors.affiliation: Civil Engineering Institute, Materials Science and Engineering Institute, Ecole Polytechnique Fédérale de Lausanne, Station 18, CH-1015 Lausanne, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Pino Muñoz
authors.affiliation: Civil Engineering Institute, Materials Science and Engineering Institute, Ecole Polytechnique Fédérale de Lausanne, Station 18, CH-1015 Lausanne, Switzerland.
authors.forename: Mathilde
authors.initials: M
authors.lastname: Radiguet
authors.affiliation: The Racah Institute of Physics, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel;
authors.forename: David S
authors.initials: DS
authors.lastname: Kammer
authors.affiliation: Civil Engineering Institute, Materials Science and Engineering Institute, Ecole Polytechnique Fédérale de Lausanne, Station 18, CH-1015 Lausanne, Switzerland.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Molinari
authors.affiliation: The Racah Institute of Physics, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 91904, Israel; jay@vms.huji.ac.il.
authors.forename: Jay
authors.initials: J
authors.lastname: Fineberg
keywords: acoustic radiation; earthquake dynamics; friction; nonsteady rupture dynamics; seismic radiation