Experimental and theoretical results of stress relaxations in a model of earthquake dynamics

We report on experimental and theoretical results on the dynamical behavior of propagating: solitary relaxations in a model system for earthquake-like dynamics. In the experiments, a continuous elastic medium is sheared at ve ry slow rate in between two coaxial cylinders. Solitary propagating relaxat ions travel at speeds that are proportional to the driving speed, though si milar to 10(3) times faster, and inversely proportional to the number of so litary relaxations in the system. We show that this behavior appears clue t o the existence of a characteristic length scale which is the typical displ acement, of a surface element in a relaxation.