|MadSci Network: Earth Sciences|
Earthquakes are generated by an instantaneous energy release in the deep that originates elastic waves that propagate through all the planet. The energy released may be accumulated by several processes, but the usual is that this is due the continuous movement and interaction of the litospheric plates, but it can be by a volcanic eruption, a nuclear explosion, and so on. Before the main event (the earthquake itself), numerous small quakes can occur, showing that the Earth has too many energy accumulated and the rocks can't support it. After the main shock, some energy still remains, and it is usual to have some smaller events to dissipate this residual energy. Best regards Eder C. Molina Dept. of Geophysics Institute of Astronomy, Geophysics and Atmospheric Sciences University of Sao Paulo - Brasil
Try the links in the MadSci Library for more information on Earth Sciences.