Sumatra quake was part of crustal plate breakup: Study shows huge jolt measured 8.7, ri... - 0 views
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Seismologists have known for years that the Indo-Australian plate of Earth's crust is slowly breaking apart
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quake was caused by at least four undersea fault ruptures
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within a 2-minute, 40-second period
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This is part of the messy business of breaking up a plate. … This is a geologic process
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will take millions of years to form a new plate boundary
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likely, it will take thousands of similar large quakes for that to happen."
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All four faults
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were strike-slip faults, meaning ground on one side of the fault moves horizontally past ground on the other side
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great quake of last April 11 "is possibly the largest strike-slip earthquake ever seismically recorded
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although a similar size quake in Tibet in 1950 was of an unknown type
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2012 quakes likely were triggered, at least in part, by changes in crustal stresses caused by the magnitude-9.1 Sumatra-Andaman earthquake of Dec. 26, 2004
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the 8.7 and 8.2 quakes were generated by horizontal movements
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not by vertical motion
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explains why they didn't generate major tsunamis
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8.7 quake caused small tsunamis, the largest of which measured about 12 inches in height at Meulaboh, Indonesia
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Indo-Australian plate is breaking into two or perhaps three pieces
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happening because it is colliding with Asia in the northwest, which slows down the western part of the plate, while the eastern part of the plate continues moving more easily by diving or "subducting" under the island of Sumatra to the northeast
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subduction zone off Sumatra caused the catastrophic 2004 magnitude-9.1 quake and tsunami
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ruptured along a roughly 90-mile length
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seafloor on one side of the fault slipped about 100 feet past the seafloor on the fault's other side
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second fault, which slipped about 25 feet, began to rupture 40 seconds after
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extended an estimated 60 miles to 120 miles north-northeast to south-southwest – perpendicular to the first fault and crossing it.
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third fault was parallel to the first fault and about 90 to the miles southwest
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started breaking 70 seconds after the quake began
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along a length of about 90 miles
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slipped about 70 feet
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The fourth fault paralleled the first and third faults
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began to rupture 145 seconds after the quake began
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fault rupture was roughly 30 miles to 60 miles long.
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fault slipped about 20 feet past ground on the other side