  Statistical properties of earthquakes are studied both by the analysis of
real earthquake catalog of Japan and by numerical computer simulations of the
spring-block model in both one and two dimensions. Particular attention is paid
to the spatiotemporal correlations of earthquakes, e.g., the recurrence-time
distribution or the time evolution before and after the mainshock of seismic
distribution functions, including the magnitude distribution and the spatial
seismic distribution. Certain eminent features of the spatiotemporal
correlations, e.g., foreshocks, aftershocks, swarms and doughnut-like seismic
pattern, are discussed.
