  We present a simple model of earthquakes on a pre-existing hierarchical fault
network. The system self-organizes on long time scales in a stationary state
with a power law Gutenberg-Richter distribution of earthquake sizes. The
largest fault carries irregular great earthquakes preceded by precursors
developing over long time scales and followed by aftershocks obeying an Omori's
law. The cumulative energy released by precursors follows a time-to-failure
power law with log-periodic structures, qualifying a large event as an
effective dynamical (depinning) critical point. Down the hierarchy, smaller
earthquakes exhibit the same phenomenology, albeit with increasing
irregularities.
