Simulation study of spatio-temporal correlations of earthquakes as a   stick-slip frictional instability
  Spatio-temporal correlations of earthquakes are studied numerically on the basis of the one-dimensional spring-block (Burridge-Knopoff) model. As large events approach, the frequency of smaller events gradually increases, while, just before the mainshock, it is dramatically suppressed in a close vicinity of the epicenter of the upcoming mainshock, a phenomenon closely resembling the ``Mogi doughnut'' 
Takahiro Mori and Hikaru Kawamura