Potential for 'Superquakes' Underestimated

Potential for 'Superquakes' Underestimated : Discovery News: "The earthquakes that rocked Tohoku, Japan in 2011, Sumatra in 2004 and Chile in 1960 — all of magnitude 9.0 or greater — should not have happened, according to seismologist's theories of earthquake cycles. And that might mean earthquake prediction needs an overhaul, some researchers say."