The Earth’s crust is divided up into seven major tectonic plates. (Gary Hincks / Science Source / Photo Researchers Inc.)

A Major Breakup?

Scientists see a new tectonic plate being born after an enormous earthquake last spring

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The earthquake last spring has begun the process of separating the Indian and Australian subplates. (Jim McMahon)

This past April, a massive earthquake struck beneath the Indian Ocean near the Indonesian island of Sumatra. Now, scientists realize that the quake was part of Earth’s crust breaking apart.

The magnitude 8.7 earthquake was caused by four fault ruptures under the ocean. Faults are the boundaries along which rocks slide past one another. The quake lasted nearly three minutes and was felt from India to Australia. It didn’t cause much damage—but it did indicate a major change in the surface of our planet.

Earth’s outer shell is covered in enormous, slowly moving rock slabs called tectonic plates. There are seven major plates across the planet, along with dozens of smaller, or minor, plates.

When scientists analyzed the Sumatran jolts, they found the quake took place because the Indian and Australian subplates (part of the Indo-Australian plate) are breaking up beneath the Indian Ocean.

“What we’re seeing here is the Indo-Australian plate fragmenting into two separate plates,” says Thorne Lay, professor of earth sciences at the University of California, Santa Cruz. “We’ve seen local fragmentation on a small scale, but this is an unprecedented opportunity for us to witness it on the scale of a giant tectonic plate.”

The Indo-Australian plate is smashing into the continent of Asia in the northwest while subducting beneath, or diving under, Sumatra in the northeast. This movement is causing the plate to break. The breakup, which started around 50 million years ago, will likely continue for millions more until the Indian subplate and Australian subplate eventually separate.

“This was a huge earthquake, but it’s going to happen again and again to make a through-going fracture that separates the plates,” Lay says.

The good news is that because this type of quake does not displace large amounts of water—which is what generates big tsunamis—it doesn’t pose much danger of that.

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