  A globally driven self-organized critical model of earthquakes with
conservative dynamics has been studied. An open but moving boundary condition
has been used so that the origin (epicenter) of every avalanche (earthquake) is
at the center of the boundary. As a result, all avalanches grow in equivalent
conditions and the avalanche size distribution obeys finite size scaling
excellent. Though the recurrence time distribution of the time series of
avalanche sizes obeys well both the scaling forms recently observed in analysis
of the real data of earthquakes, it is found that the scaling function decays
only exponentially in contrast to a generalized gamma distribution observed in
the real data analysis. The non-conservative version of the model shows
periodicity even with open boundary.
