Friday 5 October 2012

Break-up of a plate?

An April 2012 earthquake in Indonesian may signal the breakup of the Indo-Australian tectonic plate and gave the earth's crust such a shaking that earthquakes happened all over the globe. That's the thrust of new articles in Nature, one of which analyses the quake and says the 11 April 2012 event had an extraordinarily complex four-fault rupture. The event was also noteworthy for being a slip-strike, an unusual type of earthquake that sees the crust split. Subduction, which happens when one plate slides beneath another, is a more common source of earthquakes. The article notes that “Occurrence of great intraplate strike-slip faulting located seaward of a subduction zone is unusual” and goes on to explain that the event started with one shock that "initially expanded bilaterally with large slip (20–30 metres)” before a “bilateral rupture was triggered on an orthogonal left-lateral strike-slip fault … that crosses the first fault.” Next came “westward rupture on a second … strike-slip fault” and the event finished when “rupture was triggered on another ... fault about 330 kilometres west of the epicentre crossing the Ninetyeast ridge.”

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