We verify the existence of self-sustaining wrinkle-like Weertman velocity pulses along a prestressed interface between two dissimilar (ΔV=60%) blocks of foam rubber. Properties of the observed velocity pulses are similar to the theoretical prediction of Weertman (1980), and the numerical calculations of Andrews and Ben-Zion (1997). Particle displacement, in the direction perpendicular to the fault, is much larger in the slower medium than in the faster medium, resulting in a separation of the interface during the passage of the slip pulse. The rupture velocity is near the shear wave velocity in the slower material, and the direction of propagation is nearly always in the direction of the shear particle motion in the slower block. The pulse is self-maintaining, that is, it does not die out from radiation damping, obtaining the necessary energy by releasing locally stored shear potential energy. ¿ 1999 American Geophysical Union