The two massive earthquakes that hit off the coast of Sumatra in April caused only a fraction of the deaths and damage of 2004's killer quake, but scientists now realize they were part of a momentous change in the planet's surface, the BBC reports. Researchers believe the quakes, the strongest of which was a magnitude 8.7, were part of the break-up of the vast Indo-Australian tectonic plate, which will eventually split into two pieces. The main quake broke four faults and triggered more large aftershocks further away than any other quake ever recorded.
"It was jaw-dropping," a professor of planetary sciences tells the Los Angeles Times. "It was like nothing we'd ever seen." The main quake did not cause a devastating tsunami because the rock moved horizontally along the breakage instead of vertically. This is the first time scientists have observed the splitting of a tectonic plate, but they're not going to redraw the maps just yet: The process began around 50 million years ago and will not be complete until after tens of millions more years and thousands more large quakes.