  Surface waves play important roles in many fundamental and applied areas from
seismic detection to material characterizations. Supershear surface waves with
propagation speeds greater than bulk shear waves have recently been reported,
but their properties are not well understood. In this Letter, we describe
theoretical and experimental results on supershear surface waves in rubbery
materials. We find that supershear surface waves can be supported in
viscoelastic materials with no restriction on the shear quality factor.
Interestingly, the effect of prestress on the speed of the supershear surface
wave is opposite to that of the Rayleigh surface wave. Furthermore, anisotropy
of material affects the supershear wave much more strongly than the Rayleigh
surface wave. We offer heuristic interpretation as well as theoretical
verification of our experimental observations. Our work points to the potential
applications of supershear waves for characterizing the bulk mechanical
properties of soft solid from the free surface.
