April 11 quake a ‘record breaker’
PHUKET: The Indonesian earthquake on April 11 that caused widespread panic in Phuket broke two records, researchers reported in the American Science journal.
Friday 20 July 2012, 09:00AM
The magnitude-8.6 undersea earthquake that occurred far west of Sumatra caused no damage and triggered no tsunami, but researchers announced yesterday (July 19) it was the largest quake ever measured that far from the boundary of a tectonic plate.
In addition, the so-called ‘intraplate’ quake is the largest ever measured for a fault zone for which the two sides of the fault slide horizontally past each other, rather than having one side of the fault shoved beneath its neighbour.
The epicentre of the quake was located about 400 kilometres southwest of the magnitude-9.1, Boxing Day tsunami that occurred off the northwestern coast of Sumatra in 2004.
Over the course of about a minute and a half, the shake ruptured 500km of three separate but related faults, all of which were highly stressed, the researchers said.
A lot of that stress was shifted to the area by the December 2004 quake, the researchers suggest.
The faults unzipped at a relatively slow but steady 2.5km per second, the researchers say, with much of the slippage along the faults taking place more than 25km below the seafloor – a depth that helped contribute to the quake’s great magnitude.
– Source: Science Now