  The Drossel-Schwabl model of forest fires can be interpreted in a coarse
grained sense as a model for the stress distribution in a single planar fault.
Fires in the model are then translated to earthquakes. I show that when a
second class of trees that propagate fire only after some finite time is
introduced in the model, secondary fires (analogous to aftershocks) are
generated, and the statistics of events becomes quantitatively compatible with
the Gutenberg Richter law for earthquakes, with a realistic value of the $b$
exponent. The change in exponent is analytically demonstrated in a simplified
percolation scenario. Experimental consequences of the proposed mechanism are
indicated.
