However, their postulate is that the parameter values are
assumed to be the same throughout the whole region and
time span considered. We learn by experience that the difference
of parameter values of the model at different subregions
becomes more significant as the catalog size increases
by lowering the magnitude threshold or as the area of the investigation
becomes larger. For example, the p-value of the
aftershock decay varies from place to place (Utsu, 1969),
besides the background seismicity that obviously depends
on the location. If the space-time ETAS model is fitted to
such a dataset, the parameter estimates on average are obtained
for the seismicity on the whole area, but they lead
to biased seismicity prediction in the subregions where the
seismicity pattern is significantly different from the one estimated
for the whole area (see Ogata, 1988, for example).