  We present a detailed statistical analysis of acoustic emission time series
from laboratory rock fracture obtained from different experiments on different
materials including acoustic emission controlled triaxial fracture and
punch-through tests. In all considered cases, the waiting time distribution can
be described by a unique scaling function indicating its universality. This
scaling function is even indistinguishable from that for earthquakes suggesting
its general validity for fracture processes independent of time, space and
magnitude scales.
