The size of the 2011 Tohoku earthquake need not have been a surprise

The devastating 11 March 2011 magnitude 9.1 earthquake along the Tohoku coast of northeastern Japan reminded seismologists again of the adage, “It ain't what you don't know that gets you into trouble—it's what you know for sure that just ain't so.” Many seismologists—and hence disaster planners—thought that such huge earthquakes could not occur on this subduction zone [ Chang , 2011; Geller , 2011]. Great earthquakes—magnitude 8—were expected and planned for. However, a giant magnitude 9 earthquake, which would release 30 times more energy, was not considered.