Crackling noise and universality in fracture systems

We have analysed the temporal properties of crackling noise arising from two fracture systems at very different scales: the sequence of Italian earthquakes for the years 1984–2002 and the AE time series from a laboratory fracture experiment on a concrete specimen. In both cases the rescaled waiting-time distributions, obtained for several threshold event sizes, exhibit scaling collapse, thus reinforcing the idea that fracture of heterogeneous materials has similar scaling properties than earthquakes. The obtained results essentially agree with recent findings for fracture phenomena in rocks at the laboratory and at the geological scale. However, the existence of a unique scaling function valid for all fracture processes, irrespective of time, length and magnitude scales, remains a problem not completely solved.