This map of the Indian Ocean region shows boundaries of Earth’s tectonic plates in the area, and the epicenters (red stars) of two great earthquakes that happened April 11, 2012. A new study from the University of Utah and University of California, Santa Cruz, says the main shock measured 8.7 in magnitude, about 40 times larger than the previous estimate of 8.6. An 8.2-magnitude quake followed two hours later.The scientists explain how at least four faults ruptured during the 8.7 main shock, and how both great quakes are likely part of the breakup of the Indo-Australian Plate into separate subplates. The northeastward-moving plate is breaking up over scores of millions of years because the western part of the plate is bumping into Asia and slowing down, while the eastern part is sliding more easily beneath Sumatra and the Sunda plate.