In 2007 , southern Sumatra,Indonesia,was hit with M 8.4 and M 7.8 quakes, near the same plate boundary where four other quakes greater than M 7.9 had occurred since 1998. At this boundary, sub ducting beneath the Sunda plate on which Sumatra rides, at a relative speed of 6.6 cm/year (2.6 in./year). This is where the M 9.1 Sumatra-Andaman earthquake struck December 26,2004, triggering the devastating Indian Ocean tsunami (more on this in Chapter 16); the quake and seismic wave took 228000 lives. For complete listings of these and other earthquakes, go to