4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record | |
Anonymous Coward User ID: 8417061 United States 04/12/2012 03:13 AM Report Abusive Post Report Copyright Violation | Thanks, answers my question below posted in another thread: Okay so this was reportedly a strike-slip fault rupture, whereby two plates slide by one another, horizontally... It's the mega-thrust quakes that are most prone to causing large tsunamis, as one plate is thrust vertically upwards, thereby displacing a significant section of ocean. So I was wondering, this has to be on the high end of magnitude for strike-slip EQ's... I did not know they were capable of producing in the 9 range. Is this common? It was my understanding that the large monster quakes were typically always of the mega-thrust variety. Anyone know? Quoting: ANHEDONIC |
JadeDone
(OP) User ID: 2546215 United States 04/12/2012 03:22 AM Report Abusive Post Report Copyright Violation | Thanks, answers my question below posted in another thread: Quoting: ANHEDONIC Okay so this was reportedly a strike-slip fault rupture, whereby two plates slide by one another, horizontally... It's the mega-thrust quakes that are most prone to causing large tsunamis, as one plate is thrust vertically upwards, thereby displacing a significant section of ocean. So I was wondering, this has to be on the high end of magnitude for strike-slip EQ's... I did not know they were capable of producing in the 9 range. Is this common? It was my understanding that the large monster quakes were typically always of the mega-thrust variety. Anyone know? Quoting: ANHEDONIC I didn't know they were capable of producing such large quakes either. I thought strike/slip tended to top out in the upper 7's or low 8's. I've been watching a facebook forum for my local seismic network and the director was also talking about the unusual aftershock pattern. No one is sure what to make of it. |
JadeDone
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JadeDone
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Solar Guardian
User ID: 25806894 Malaysia 10/19/2012 10:21 PM Report Abusive Post Report Copyright Violation | in remembrance of this awesome historic quake! |
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Anonymous Coward User ID: 39768279 United States 05/14/2013 04:14 PM Report Abusive Post Report Copyright Violation | The 8.6 magnitude earthquake that hit off the coast of Sumatra on April 11, 2012 was one of a pair of great quakes that hit within 100 km of each other that day. The second great quake registered a magnitude 8.2. Here is some pertinent information about this set of twin strike-slip great quakes. The April 11, 2012, M8.6 and M8.2 earthquakes off the west coast of northern Sumatra, Indonesia, occurred as a result of strike-slip faulting within the oceanic lithosphere of the Indo-Australia plate. The quakes were located respectively 100 km and 200 km to the southwest of the major subduction zone that defines the plate boundary between the India/Australia and Sunda plates offshore Sumatra. At this location, the India/Australia plates move north-northeast with respect to the Sunda plate at a velocity of approximately 52 mm/yr. [link to earthquake.usgs.gov] It is my understanding that because these great quakes resulted from a strike-slip mechanism AND they occurred in tandem AND with their epicenters so close together AND at a major plate boundary REALLY SURPRISED many who spend their lives studying such phenomena. What follows is some commentary about these two great quakes with references to three scientific papers that were focused on these quakes. The magnitude 8.7 and 8.2 earthquakes that struck off the coast of Sumatra that day [April 11, 2012] herald the breakup of the Indo-Australian plate along an unclear boundary beneath the Indian Ocean southeast of India, according to two studies published online today [Sept 27, 2012?] in Nature. In one of the reports, seismologists from the University of Utah and University of California, Santa Cruz, say the main shock—the combined outcries of four separate faults rupturing in a span of 160 seconds—measured 8.7 in magnitude. That’s about 40 times larger than the previous estimate of 8.6. The 8.2-magnitude quake followed along a fifth fault two hours later. Two of the largest strike-slip earthquakes ever recorded, these earthquakes struck where the Indo-Australian plate is being torn asunder as it marches to the northeast. The trouble happens because the west of breakup region is not keeping pace with the segment to the east. The western portion of the plate is slowed by its ongoing collision with Asia, whle eastern part of the plate moves relatively unimpeded as it dives, or subducts, under the island of Sumatra. Sudden vertical motion along this subduction zone off Sumatra caused the catastrophic magnitude-9.1 Sumatra-Andaman earthquake of Dec. 26, 2004—a jolt that generated massive tsunamis that killed most of the 228,000 victims in the Indian Ocean region. By changing stress patterns in the earth’s crust, that 2004 catastrophe probably helped to trigger the 2012 quakes, which were much less upsetting from humanity’s point of view: only ten people are known to have died as a result. The difference? Among other reasons, the horizontal movements along the strike-slip faults out in the middle of the Indo-Australian plate simply cannot move as much water as the vertical motion along its subducting edges can. (The first April 11, 2012, quake did cause small tsunamis, but none more than 12 inches high, according to the U.S. Geological Survey.) That doesn’t mean last year’s twin strike-slip jolts were impotent. A third paper published online today [Sept 27, 2012?] in Nature reports a fivefold increase in the rate of remote earthquakes (those greater than 1,500 kilometers from the epicenter) with magnitudes of 5.5 or greater during the six days following the initial events. Four earthquakes of magnitude 6.0 or greater noted off western North America occurred within the first 24 hours of the Indian Ocean events. Such a brazen cluster of tremors that size is highly unusual; the global average is one every three days. “We’ve never seen an earthquake like this,” the University of Utah’s Keith Koper said in a press release. “This is part of the messy business of breaking up a plate. This is a geologic process. It will take millions of years to form a new plate boundary and, most likely, it will take thousands of similar large quakes for that to happen.” [link to news.discovery.com] Here is a link to a discussions about the 8.6 magnitude Sumatran quake that was published in the blog for the scientific journal Nature. Why the 11 April Sumatran earthquake has scientists puzzled [link to blogs.nature.com] |
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