  The statistical properties of avalanches in a dissipative particulate system
under slow shear are investigated using molecular dynamics simulations. It is
found that the magnitude-frequency distribution obeys the Gutenberg-Richter law
only in the proximity of a critical density and that the exponent is sensitive
to the minute changes in density. It is also found that aftershocks occur in
this system with a decay rate that follows the Modified Omori law. We show that
the exponent of the magnitude-frequency distribution and the time constant of
the Modified Omori law are decreasing functions of the shear stress. The
dependences of these two parameters on shear stress coincide with recent
seismological observations [D. Schorlemmer et al. Nature 437, 539 (2005); C.
Narteau et al. Nature 462, 642 (2009)].
