  An analysis of moments and spectra shows that, while the distribution of
avalanche areas obeys finite size scaling, that of toppling numbers is
universally characterized by a full, nonlinear multifractal spectrum. Rare,
large avalanches dissipating at the border influence the statistics very
sensibly. Only once they are excluded from the sample, the conditional toppling
distribution for given area simplifies enough to show also a well defined,
multifractal scaling. The resulting picture brings to light unsuspected, novel
physics in the model.
