Rupture zones of the 26 December 2004 (seismic moment magnitude Mw = 9.2) and 28 March 2005 (Mw = 8.7) great Sumatra earthquakes. The 2004 event generated a tsunami that claimed over 225,000 lives around the Indian Ocean. International teams of seismologists and geodesists have studied how the rupture spread over the fault, how slip varied along the subduction zone, and how aseismic after-slip occurred for several months after the events. Efforts to establish new tsunami-warning systems for the Indian Ocean and Caribbean are now underway. (Image courtesy of C.J. Ammon.)