ScienceDaily (May 22, 2011) — Earthquake scientists trying to unravel the mysteries of an unfelt, weeks-long seismic phenomenon called episodic tremor and slip have discovered a strange twist. The tremor can suddenly reverse direction and travel back through areas of the fault that it had ruptured in preceding days, and do so 20 to 40 times faster than the original fault rupture.

to read more go to:   http://www.sciencedaily.com/releases/2011/05/110522141545.htm