SELF-ORGANIZED CRITICALITY OF PLASTIC SHEAR BANDS IN ROCKS

We show that the shear bands that appear during the pure shear numeric al simulations of rocks with a non-associated plastic flow rule form f ractal networks. The system drives spontaneously into a state in which the length distribution of shear bands follows a power law (self-orga nized critically) with exponent 2.07. The distribution of local gradie nts in deviatoric strain rate has different scaling exponents for each moment, in particular the geometrical fractal dimension is 1.7. Sampl es of granodiorite sheared under high confining pressure from the Pyre nees are analyzed and their properties compared with the numerical res ults.