Looks like scientists have uncovered the source of two huge earthquakes—a fracture in a tectonic plate that's slowly breaking apart, LiveScience reports. A new study says two massive undersea quakes near Indonesia, magnitude-8.6 and 8.2, were likely caused by a breakup in the India-Australia-Capricorn plate in the Indian Ocean. The fracture is widening at about 0.06 inches per year and will be a mile wide in a fairly short time, geologically speaking—about a million years from now. "It's not a structure that is moving fast, but it's still significant compared to other planet boundaries," says co-author Aurélie Coudurier-Curveur of the Institute of Earth Physics of Paris. Both quakes struck on April 11, 2012, and had two important effects.
One, they triggered tsunami warnings that never came true. Two, they rekindled debate about a possible fracture in the India-Australia-Capricorn plate, per Eos. So scientists mapped part of the Indian Ocean by firing sound waves at the sediment and measuring them as they bounced back. They found signs of a strike-slip fault (like the San Andreas Fault) near the epicenters of both quakes. The upshot? Another major quake seems far off—say 20,000 years—but scientists know a little more about Earth's patchwork of tectonic plates. "Plates are constantly formed and destroyed on Earth," says a geoscientist. "It is detailed studies like these that will allow us to better understand how the jigsaw puzzle of plates that constitute the outermost solid layer of Earth formed and evolved." (Read more earthquake stories.)