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4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record

 
JadeDone
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04/12/2012 03:06 AM
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4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
[link to www.lasvegassun.com]

`Odd duck’ Indonesia quake surprises scientists
...
The massive earthquake off Indonesia surprised scientists: Usually this type of jolt isn't this powerful.
...
Wednesday's magnitude-8.6 occurred along a strike-slip fault line similar to California's San Andreas Fault. Scientists say it's rare for strike-slip quakes, in which blocks of rocks slide horizontally past each other, to be this large.
...
"A week ago, we wouldn't have thought we could have a strike-slip earthquake of this size. This is very, very large," said Kevin Furlong, a professor of geosciences at Penn State University.
...
It's probably the largest strike-slip event though there's debate about whether a similar-sized Tibet quake in 1950 was the same kind.


Complete article at link
[link to www.lasvegassun.com]
Anonymous Coward
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04/12/2012 03:13 AM
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Re: 4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
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)

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04/12/2012 03:22 AM
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Re: 4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
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

 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  (OP)

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04/12/2012 03:47 AM
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Re: 4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
I love you too, 1 star bandit. Thanks for visiting my thread. hf
Anonymous Coward
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04/12/2012 03:51 AM
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Re: 4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
the plates are breaking apart.

cya on the other side.
JadeDone  (OP)

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04/12/2012 03:56 AM
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Re: 4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
I'm going to hold out hope that we are just making up for last week's low level of seismicity, but that's not much DOOM Fun so

DOOM ON! ;)
Solar Guardian

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10/18/2012 11:32 PM
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Re: 4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
That Indo-Aussie plate is breaking up!! Pole Shift and Crustal Displacement happening by late March 2013. Earth becomes high-dimensional planet or "Star Planet" by November 2013. banana2abductabduct
Solar Guardian

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10/19/2012 10:21 PM
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Re: 4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
bump in remembrance of this awesome historic quake! banana2
Anonymous Coward
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05/04/2013 06:12 PM
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Re: 4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
[link to earthquake.usgs.gov]

this is still rumbling away
Anonymous Coward
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05/14/2013 03:34 PM
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Re: 4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
[link to earthquake.usgs.gov]

this is still rumbling away
 Quoting: Anonymous Coward 38964246


another one, 5.6

[link to earthquake.usgs.gov]
Anonymous Coward
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05/14/2013 04:14 PM
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Re: 4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
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]
Anonymous Coward
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05/14/2013 05:00 PM
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Re: 4-11-2012 Sumatra 8.6 EQ possibly largest strike / slip EQ on record
bump





GLP