The Every Earthquake a Precursor According to Scale (EEPAS) model has performed well
in retrospective studies of long-range forecasting of major earthquakes in a number of real
earthquake catalogues. It is based on the precursory scale increase phenomenon and associated
predictive scaling relations, the detailed physical basis of which is not well understood.
Synthetic earthquake catalogues generated deterministically from known fault physics and
long- and short-range stress interactions on fault networks have been analysed using the
EEPAS model, to better understand the physical process responsible for the precursory scale
increase phenomenon. In a generic fault network with one major fault and a number of parallel
minor faults, the performance of the EEPAS model is poor. But in a more elaborate network
involving major faults at a variety of orientations and a large number of small, randomly oriented
faults, individual examples of the precursory scale increase phenomenon can be readily
identified and the performance of the EEPAS model is similar to that in real catalogues, such
as those of California and central Japan, albeit with some differences in the scaling parameters
for precursor time and area. The fault geometry therefore affects conformity to the EEPAS
model. Tracking the stress evolution on a set of individual cells in the synthetic seismicity
model may give new insights into the origin of the precursory scale increase phenomenon.