Sumatran Earthquakes May Signal New Tectonic Plate

Two earthquakes that struck off the coast of Sumatra in April could mean the formation of a new tectonic plate boundary under the Earth, according to a new study.

The two recent quakes could mean a literal seismic shift in scientists’ understanding of tectonic plate movements, reports CBS News.

The massive earthquakes were centered under the Indian Ocean; the first quake was recorded at 8.7 magnitude and had an aftershock of 8.2 magnitude.

While these quakes were not the largest ever recorded (Japan’s 2011 earthquake was a 9.0), they were in an unusual location. Most earthquakes take place near thrust faults (massive sheets of rock that slide over or under another sheet along a fault line), but these two took place near strike-slip faults, which is where one block of rock slides alongside another.

Not only were they along a rare fault, but they are also the largest slip-strike faults ever observed. The two earthquakes also took place in the middle of a plate, not along the edge (where most quakes take place).

The BBC notes that the scientists, who published their assessment in the Nature journal this week, believe that the analysis shows the Indio-Australian tectonic plate may be splitting in two. Matthias Delescluse from the Ecole Normale Superieure in Paris assured:

“This is a process that probably started eight to 10 million years ago, so you can imagine how much longer it will take until we get a classic boundary.”

One signal the scientists had about the plate change was the lack of tsunami following the massive April earthquakes. On Devember 26, 2004, a 9.1 magnitude earthquake struck off the coast of Sumatra, triggering a tsunami that killed hundreds of thousands of people.

But the tremors on April 11, 2012, while also immense, did not produce the same devastation. This is because of the strike-slip fault line, which moves horizontally instead of vertically. Plates that move vertically have a thrust tendency, making them more likely to produce a devastating wave.

Delescluse added during his assessment that the Indio-Australian plate is being moved on both ends, causing stress in the middle. He stated:

“Australia already moves with respect to India, and India already moves with respect to Australia. They are separated by a lot of faults. And if you look on Earth today, between plates you have only one fault. So, the process we are talking about is how we go from several faults to only one fault. That’s the question – we don’t know how long it takes to weaken one so that it localises all the deformation and the others stop being active. At the moment, a lot of faults in the Indian Ocean are active.”

Scientists believe that the tectonic plate break is an event that takes thousands, if not millions of years. So, while a new fault line may be forming under the Indian Ocean, it may not be complete for many years.