Multifractal scaling in the Bak-Tang-Wiesenfeld sandpile and edge events

A widely applicable analysis of numerical data shows that, while the distri bution of avalanche areas obeys finite size scaling, that of toppling numbe rs is universally characterized by a full, nonlinear multifractal spectrum. Boundary effects determine an unusual dependence on system size of the mom ent scaling exponents of the conditional toppling distribution at a given a rea. This distribution is also multifractal in the bulk regime. The resulti ng picture brings to light unsuspected physics of this long-studied prototy pe model.