Quakes highlight tearing of Indo-Australian plate

The same forces that caused the Boxing Day earthquake and tsunami are breaking up Australia’s tectonic plate, according to an international team of scientists.

Earthquakes are caused by sudden and violent movement along faults and most occur at the edges of the huge tectonic plates that cover the earth’s surface. However new research by Dr Wouter Schellart of ANU and colleagues suggests the forces causing these earthquakes are also felt across the surface of each plate.

“What this means is that countries like Australia may not be as quiet, geologically-speaking, as we thought,” said Dr Schellart.

“You are still much more likely to get an earthquake along a plate boundary, but due to the transfer of stresses they can happen elsewhere on the plate — even somewhere thousands of kilometres from the boundary.”

In the case of the Indo-Australian plate, on which Australia rests, the combination of stresses are being felt in the ground beneath our feet. The Indo-Australian plate is colliding with other plates in the north (in the Himalayas and New Guinea), sinking beneath Indonesia and moving away from the Antarctic and African plates to the south and west.
 
“These forces are causing the Indo-Australian plate to buckle and deform and it will eventually break up in two,” Dr Schellart said.

Dr Schellart created a scale model of the tectonic activity where our plate is being ‘subducted’ or pulled under Indonesia, to prove the results created through numerical modelling by Professor Mike Sandiford of the University of Melbourne and Dr David Coblentz of the Los Alamos National Laboratory in the US. The team found that as much as 10 per cent of the force created during subduction is transferred back across the plate.

Scientists have long understood why earthquakes happen where tectonic plates meet and are forced against each other by movements in the mantle beneath the Earth’s surface, but the causes of earthquakes (including the one that hit Newcastle in 1989) in apparently ‘safe’ areas in the middle of the plate had remained a mystery.

Seismic activity under the Indian Ocean caused by this transfer of forces suggests that the Indo-Australian plate is breaking up to form two new plates, however there’s no need to start panicking just yet, Dr Schellart said.

“It’s a very slow process, we’re talking in terms of millions of years,” he said.

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