http://news.yahoo.com/why-recent-sumatra-quake-strange-180805264.html
Why the Recent Sumatra Quake Was So Strange
Odd earthquake
Unusually, this quake apparently occurred in the middle of an oceanic plate. All the other top 10 quakes happened at subduction zones, where one of the tectonic plates making up the Earth's surface is diving beneath another. [13 Crazy Earthquake Facts]
Also oddly, the Sumatra temblor was a strike-slip earthquake, where two parts of Earth's crust slide past each other. Strike-slip quakes are not typically so powerful — the Sumatra event was "far and away the largest strike-slip earthquake ever recorded," said researcher Gregory Beroza, a seismologist at Stanford University. Its magnitude 8.2 aftershock was also among the largest recorded strike-slip earthquakes.
The reason why this quake was surprisingly powerful might lie in how deep the faults that triggered it ran, scientists now suggest.
Seismology readings suggest the Sumatra quake and its aftershock originated at depths between 25 to 33 miles (40 to 54 kilometers). At those depths, rock is blazingly hot, about 1,110 to 1,470 degrees Fahrenheit (600 to 800 degrees Celsius). At such temperatures, rock can become viscous at certain points, and in extreme cases, fault zones may even melt, enabling large amounts of energy to be released as parts of the Earth slide past each other.
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