Huge Sumatran Quakes in April a Step in Tectonic Plate Breakup
Planet Earth may be 4.5 billion years old, but that doesn’t mean she can’t serve up a shattering surprise now and again.
Such was the case on April 11 of this year when two massive earthquakes erupted beneath the Indian Ocean, far from the usual danger zones. Now scientists say the seafloor ruptures are part of a long suspected, yet never before observed, event: the slow-motion splitting of a vast tectonic plate.
The first of the quakes, a magnitude 8.7, was 20 times more powerful than California’s long anticipated “big one” and tore a complex network of faults deep in the ocean floor. The violence also triggered unusually large aftershocks thousands of miles away, including four off North America’s western coast.
“It was jaw-dropping,” said Thorn Lay, a professor of Earth and planetary sciences at UC Santa Cruz. “It was like nothing we’d ever seen.”
At first, Lay wondered whether the computer code he used to analyze earthquakes was wrong. Eventually, he and other scientists realized that they had documented the break-up of the Indo-Australian plate into two pieces, an epic process that began roughly 50 million years ago and will continue for tens of millions more. Lay and other scientists reported their findings online Wednesday in the journal Nature.