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Sumatran strike-slip earthquakes challenge seismologists

Events may shed light on regional tectonics, alter stress on nearby megathrust

After the magnitude-8.6 earthquake and magnitude-8.2 aftershock that struck off the coast of Sumatra, Indonesia on April 11, scientists quickly identified why no tsunami followed either one: The earthquakes had occurred on strike-slip faults more than 400 kilometers offshore rather than on the Sunda megathrust fault that has been responsible for a series of large earthquakes since 2004. For all that can be explained, however, the earthquakes took most scientists by surprise. The combination of their size — they're the largest strike-slip earthquake ever recorded by most accounts — and their location is challenging the paradigm of strike-slip earthquakes and is raising new questions about the region’s tectonics.

11 May 2012