Seismicity patterns vary substantially from place to
place, showing various clustering features, though some of
the fundamental physical processes leading to earthquakes
may be common to all events. Kanamori (1981) postulates
that fault zone heterogeneity and complexity are responsible
for the observed variations. Such complex features have
been tackled in terms of stochastic point-process models for
earthquake occurrence. The stochastic models have to be
accurate enough in the sense that they are spatio-temporally
well adapted to and predict various local patterns of normal
activity. The epidemic type aftershock sequence (ETAS)
model and its space-time extension have been introduced
for such a purpose (Ogata, 1985, 1988, 1993, 1998).