Pegasus Research Consortium

Quake split a tectonic plate in two, and geologists are shaken

Robin George Andrews  16 hrs ago
https://www.msn.com/en-us/news/technology/quake-split-a-tectonic-plate-in-two-and-geologists-are-shaken/ar-BBOP3xQ?li=BBnbfcL

QuoteOn September 7, 2017, a magnitude 8.2 earthquake struck southern Mexico, killing dozens and injuring hundreds. While earthquakes are common enough in the region, this powerful event wasn't any run-of-the-mill tremor.

That's because part of the roughly 37-mile-thick tectonic plate responsible for the quake completely split apart, as revealed by a new study in Nature Geoscience.
https://www.nature.com/articles/s41561-018-0229-y
This event took place in a matter of tens of seconds, and it coincided with a gargantuan release of energy.

"If you think of it as a huge slab of glass, this rupture made a big, gaping crack," says lead author Diego Melgar, an assistant professor of earthquake seismology at the University of Oregon. "All indications are that it has broken through the entire width of the thing."
Such colossal fragmentation events have been observed before in a handful of places around the world, and all these epic earthquakes have one thing in common: No one really knows how they happen. This information gap matters, because huge populations from the western seaboard of the Americas to the eastern shores of Japan could be threatened by these enigmatic earthquakes.

For one thing, the deep quakes can induce strong shaking over a wide area that can level plenty of multistory buildings. One that took place beneath the Chilean town of Chillán in 1939, for example, killed at least 30,000 people. And when they happen near an ocean coastline, their destructive potential could be magnified.

"My real worry over these kinds of events is the tsunami," Melgar says.

World's most elusive earthquakes
Tectonic plates, also known as lithospheric slabs, are made up of the planet's crust and the hot-but-solid upper mantle. They constantly move around Earth's surface, either grinding side by side, crumpling up into one another and forming mountains, or descending under another plate in what is referred to as a subduction zone.

Along these various plate boundaries, you get earthquakes when friction generates stress that's ultimately released. But quakes can also occur far from these plate boundaries, in the part of the slab that's been pushed through a subduction zone and into the lower mantle. (Here's what will happen when Earth's tectonic plates grind to a halt.)

"If you bend an eraser, you can see the top half being extended and stretched, whereas the bottom bit is squashed and compressed," Melgar notes. The same applies to these slabs. This bending can activate faults within the slab and trigger what are known as intraslab earthquakes.

Intraslab quakes are happening all the time at low to moderate magnitudes, often on faults involving side-to-side movement or the upward push of a block. On occasion, some incredibly energetic ones happen on so-called normal faults, where the movement of a chunk of rock follows gravity's lead as it falls downward.

Melgar points to the 1933 Sanriku earthquake in Japan, which came in at a magnitude 8.5, as a good example of one of these intraslab normal quakes. Another would be the magnitude 7.8 Tarapaca earthquake in northern Chile in 2005. Sometimes, as in southern Mexico, the rupture can cut right through a slab. The same is thought to have happened beneath Iran in 2013 during a magnitude 7.7 tremor.

Whether they feature this type of dramatic severance or not, these powerful quakes are inherently mysterious. Seismic surveys normally used to visualize tectonic movements can't penetrate to such depths. The mapping of oceanic slabs is also in its infancy, and there's not much high-resolution historical data to go on. That means geoscientists are currently scrambling for ways to best explain what's going on.

Plate tectonics pandemonium
The new study's geophysical measurements and models found that the Tehuantepec quake in Mexico was even more bizarre than any of the others. Normal faults can only rupture where the slab is being extended within the shallower segments. The Tehuantepec quake rupture, however, spread to even deeper parts of the slab that should be compressed.

This is potentially solvable. The paper suggests that the slab is being pulled down by its own weight so effectively that gravity is creating a major extensional force. This trumps the expected compressional forces, thereby allowing normal faulting to take place.

Far more problematic is the rupture's staggering reach, which extended to a depth of around 47 miles. At this point, temperatures exceed 2,012°F, hot enough to permit the rocky slab to act more like a mushier plastic. A quake like Tehauntepec requires rock to be cooler and therefore harder, so it can break in a more brittle way.

Powerful normal fault earthquakes can take place in deep-ish parts of slabs, says study coauthor Emmanuel Garcia, a tectonics expert at Kyoto University. However, this only really applies to truly ancient tectonic plates that have had many millions of years to cool down, which makes them more prone to break in a brittle fashion.

The Tehauntepec quake involved the Cocos plate, which is a relatively young 25 million years old and is somewhat warmer than plenty of other tectonic plates. That, according to Melgar, makes the 2017 slab-splitting tremor "unheard of."

"Something funny is going on with the slab in Mexico," says Eric Fielding, a geophysicist at NASA's Jet Propulsion Laboratory who coauthored a paper on the 2013 Iran quake.

Making a break for it
Part of the solution, according to Melgar's team, may involve deep water. As the Cocos slab heads into the subduction zone under the North American plate, it bends and cracks. This creates normal faults, which take in seawater. As the slab passes into and through the subduction zone into the lower mantle, it warms up and dehydrates. This dehydration creates mechanical weaknesses and can cause brittle fracturing, creating small quakes or, perhaps, a huge one. The same theory was applied to the 2013 Iran and 2005 Chilean quakes.

The fact that the Cocos plate is younger and warmer could have created a "perfect storm" of events, suggests Stephen Hicks, a seismologist at the University of Southampton who was not involved in the new research. The plate's relative warmth might mean that the vital dehydration process took place quicker, creating brittle conditions and faults early on that could eventually slip in a violent manner.

Melgar adds that when the oceanic Cocos plate first formed at a fiery mid-ocean trench, its cooling pattern created little hills and valleys in its rock. These imperfections may have eventually formed zones of weaknesses that could have generated the Tehuantepec earthquake, making this a story of destruction tens of millions of years in the making.
However, he notes, it still seems curious that brittle fracturing could take place so spectacularly at such hellishly hot depths. The slab could be oddly cold or made up of some strange rocks, he suggests, but both ideas go against what scientists expect conditions down there to be like.

Either way, figuring out the root cause of intraslab normal quakes is more than just an intellectual endeavour. Whether they are shallow or deep, these tremors can be powerful enough to suddenly shift any seafloor nearby, pushing vast quantities of water forward and creating tsunamis.

The Tehauntepec tremor took place on the landward side of the subduction zone, so the seafloor wasn't deformed enough to create more than a 10-foot tsunami. By contrast, the 1933 Sanriku quake took place on the oceanward side of the subduction zone and created a devastating 66-foot tsunami.

When it comes to these strange, destructive earthquakes, "we don't truly know what's happening, to be honest," says Hicks. But it's clear that solving this titanic mystery could one day be a life-saver.

https://www.nature.com/articles/s41561-018-0229-y

Article | Published: 01 October 2018

Deep embrittlement and complete rupture of the lithosphere during the Mw 8.2 Tehuantepec earthquake
Diego Melgar, Angel Ruiz-Angulo, Emmanuel Soliman Garcia, Marina Manea, Vlad. C. Manea, Xiaohua Xu, M. Teresa Ramirez-Herrera, Jorge Zavala-Hidalgo, Jianghui Geng, Nestor Corona, Xyoli Pérez-Campos, Enrique Cabral-Cano & Leonardo Ramirez-Guzmán
Nature Geoscience (2018) | Download Citation

Abstract

QuoteSubduction zones, where two tectonic plates converge, are generally dominated by large thrust earthquakes. Nonetheless, normal faulting from extensional stresses can occur as well. Rare large events of this kind in the instrumental record have typically nucleated in and ruptured the top half of old and cold lithosphere that is in a state of extension driven by flexure from plate bending. Such earthquakes are limited to regions of the subducting slab cooler than 650 °C and can be highly tsunamigenic, producing tsunamis similar in amplitude to those observed during large megathrust events. Here, we show from analyses of regional geophysical observations that normal faulting during the moment magnitude Mw 8.2 Tehuantepec earthquake ruptured the entire Cocos slab beneath the megathrust region. We find that the faulting reactivated a bend-fault fabric and ruptured to a depth well below the predicted brittle–ductile transition for the Cocos slab, including regions where temperature is expected to exceed 1,000 °C. Our findings suggest that young oceanic lithosphere is brittle to greater depths than previously assumed and that rupture is facilitated by wholesale deviatoric tension in the subducted slab, possibly due to fluid infiltration. We conclude that lithosphere can sustain brittle behaviour and fail in an earthquake at greater temperatures and ages than previously considered.

a squashed orange of tectonic plates doesnt like being uplifted.
ive been calling for mexico to sink as the final outcome.
irans quake involved drought just as washington dc quake was mississippi river drought.
odds are drought in mexico was involved but i dont know their weather.
drilling by russians and americans through tectonic plate found gravel and water.so im in doubt of high temps.
except at the fracture zone.its a broad and relative term,imho.

thankyou for the detailed explanation s.o.
very informative.

Quote from: robomont on October 27, 2018, 03:14:56 AM
irans quake involved drought just as washington dc quake was mississippi river drought.

Different seismic zones, Iran has all types of geologic activity, including a subduction zone, Washington DC is mostly inactive.

Quotedrilling by russians and americans through tectonic plate found gravel and water.

Different locations have different characteristics, we can only compare between locations with similar condition.

@ArMaP, Hi buddy, I am surprised that the Great Lisbon EQ of 1755 wasn't included by the scientists, I understand that the magnitude was somewhere between 8.0 and a 9! [depending which sources you can read on the web] and the death toll was huge also, but I don't know a definitive value [in the many thousands] - I was wondering if this quake was part of Portugal's mainstream history or if you might have data that you can share that we cannot see on the web please ?


Specifically I am interested in how prone Lisbon/Portugal is to EQ's if you have any information that you can share with us I would be super grateful.

https://en.wikipedia.org/wiki/1755_Lisbon_earthquake

Cheers,

Fans'


PS- The Bam EQ in Iran in 2003 - see link for all the details - At Cisco we were going to send equipment & engineers to help the region get back on their feet after the clear up operation had begun [for free, Corporate Responsibility Program 2000] we got as far as getting all the equipment together, and I worked out a implementation plan but at the 11th hour the US State Dept blocked us from going in, we had a multinational team made up from engineers from the ME, Europe and Asia who had all volunteered to support the project.

As you can imagine we were all very angry and upset that we were denied the chance to help, when we offered to go volunteer out there we where informed that we could go but don't expect a job when you come back  >:(  - anyhow  many thousends died in that Earthquake, and mainstream media soon forgot about it.

https://en.wikipedia.org/wiki/2003_Bam_earthquake

I think they focused only on the most recent earthquakes, so they didn't include the 1755 earthquake (we don't call it "the Lisbon earthquake" in Portugal, only "the 1755 earthquake").

Although we don't have many earthquakes we have had some big ones, the most famous being the 1755 Lisbon earthquake, caused, apparently, by the Azores–Gibraltar Transform Fault (https://en.wikipedia.org/wiki/Azores%E2%80%93Gibraltar_Transform_Fault), who was also responsible for the biggest earthquake I felt, in 1969, and the more recent ones, in 2007 and 2009 (the strongest since 1969).

Besides that, we also have some local geological faults that, sometimes, create earthquakes, like the Tagus fault that originated the 1909 earthquake, with a magnitude of 6.1, that killed 42 people.

Between smaller and bigger earthquakes I think I have witnessed around 6 events, starting with the 1969 earthquake.

PS: although I was born in Lisbon I now live on the other side of the Tagus river, in Almada, that was also largely affected by the 1755 earthquake, but not that much by the tsunami, as the lower part of this area, the parish of Cacilhas, is in the beginning of a slight bend of the river, and, apparently, the tsunami went straight on and didn't destroy much of Cacilhas, located on the inside of that bend. Every year there's a procession on November 1st to celebrate the event.

Thank you ArMap for coming back on this topic bud.

Quote from: ArMaP on October 27, 2018, 01:45:14 PM
Different seismic zones, Iran has all types of geologic activity, including a subduction zone, Washington DC is mostly inactive.
Different locations have different characteristics, we can only compare between locations with similar condition.

nobody has drilled a well as deep as the two partners,so until somebody does and gets different results,its reasonable to believe the entire planet has a sea of gravel under the techtonic plates.

as for quakes.when the west was droughted a few years back,a canyon formed basically in the middle of the western united states plate in bighorn mountain range.it immediately started raining three day later in cali and oregon.my suspicion is the airforce and nexrad created the conditions for rain.
due to panic of the canyon formation possibly splitting the entire techtonic plate.
as for now we have had tremendous amounts of rain thats filling the mississippi.almost a month of rain from houston to the north east.with droughting in california.this creates an uneven techtonic plate load and i suspect uplift on the cali plate zone.thus movement of san andreas but mild quakes.
the reason i suspect the canyon didnt form across the usa southward is because of a lava tube from yellowstone to las vegas acting as a hinge of sorts.the combination of load and hinge is mellowing quake activity in cali.

Quote from: robomont on November 14, 2018, 11:28:10 PM
nobody has drilled a well as deep as the two partners,so until somebody does and gets different results,its reasonable to believe the entire planet has a sea of gravel under the techtonic plates.

What two partners? And why is it reasonable?

Quoteas for quakes.when the west was droughted a few years back,a canyon formed basically in the middle of the western united states plate in bighorn mountain range.it immediately started raining three day later in cali and oregon.

Sources, please.

Quotedue to panic of the canyon formation possibly splitting the entire techtonic plate.

Canyons do not split tectonic plates, they are superficial.

Quoteas for now we have had tremendous amounts of rain thats filling the mississippi.almost a month of rain from houston to the north east.with droughting in california.this creates an uneven techtonic plate load and i suspect uplift on the cali plate zone.thus movement of san andreas but mild quakes.

What are you calling "Cali plate"? Uplift of a plate would not create any special movement on San Andreas fault, which is a (more or less) North-South fault, with the land on one side moving North and the other side moving South.

https://newsline.com/2018/11/14/seismic-study-reveals-huge-amount-of-water-dragged-into-earths-interior/

canyons are not superficial when they form basically overnight.imho.

the two partners were usa and russia.the deepest well ever drilled.

i know present day theory is mantle recycles after being molten and traveling hundreds or thousands of miles to volcanoes.i dont believe this.

my belief is mantle gets ground into rock thats added to the sea of gravel under the techtonic plates.
volcanoes are nothing more than hydrated limestone thats at the edges of subducted tectonic plates.this hydrated limestone activates with fresh water to become acetyline which gets oxides for oxygen and piezo electric effect to ignite it.it boils up through a weak spot under the tectonic plate that it subsides under.but not so deep that it gets ground up into gravel.a midway point.which is why lava has such a high co2 level.limestone is calcium carbonate.

this limestone theory was proven by coincidence when a bottling plant drilled exploratory wells  near a volcano in hawaii.not long after,the volcano erupted.

then just last month nasa made the suggestion to drill wells at yellowstone with the claim it was for hydrothermal electric power.

as i have claimed in the past ́on here,i suspect the usa gov of intending to set off yellowstone.if my theory holds true,the drilling at yellowstone will activate the limestone via fissures.allowing snow melt water deep into the limestone .this limestone is coming from the cascadia subduction zone of ancient seabed and is under yellowstone,the same general area as the canyon formation.

this subduction zones final edge is just east of yellowstone.otherwise yellowstone would be further west instead of moving east over millenia.

all of this can easily be referenced with a simple search.the drilling in hawaii,the canyon formation,the date the drought was over in california and oregon.the russia american joint drilling operation.

plus the article i ran across today.which isnt much but leads to some credibility on my theory.

https://www.newsweek.com/campi-flegrei-magma-building-beneath-dangerous-supervolcano-could-signal-huge-1213424
then this just now on drudge.

Quote from: robomont on November 15, 2018, 12:01:57 PM
canyons are not superficial when they form basically overnight.imho.

A canyon is the result of erosion, so if one appeared overnight it could not be that deep. A source of that information would help.

Quotei know present day theory is mantle recycles after being molten and traveling hundreds or thousands of miles to volcanoes.

Are you sure? I don't remember reading that anywhere.

Quotemy belief is mantle gets ground into rock thats added to the sea of gravel under the techtonic plates.

What sea of gravel? Is there any real reference to that "sea of gravel"?

Quotevolcanoes are nothing more than hydrated limestone thats at the edges of subducted tectonic plates.this hydrated limestone activates with fresh water to become acetyline which gets oxides for oxygen and piezo electric effect to ignite it.it boils up through a weak spot under the tectonic plate that it subsides under.but not so deep that it gets ground up into gravel.a midway point.which is why lava has such a high co2 level.limestone is calcium carbonate.

How much limestone, water and oxygen would be needed to keep a volcano active for a year?

Quotethis limestone theory was proven by coincidence when a bottling plant drilled exploratory wells  near a volcano in hawaii.not long after,the volcano erupted.

References, please.

Quoteall of this can easily be referenced with a simple search.the drilling in hawaii,the canyon formation,the date the drought was over in california and oregon.the russia american joint drilling operation.

I'm too lazy to look for unsubstantiated claims, you presented them you should provide the source for your information.

https://en.m.wikipedia.org/wiki/Kola_Superdeep_Borehole

https://www.google.com/amp/s/www.mnn.com/earth-matters/wilderness-resources/stories/amp/massive-crack-earth-opens-suddenly-wyomings-bighorn-mountains

https://www.google.com/amp/s/www.cnbc.com/amp/2018/05/23/geothermal-plants-wells-are-plugged-as-hawaiis-volcano-sends-lava-nearby.html

Thanks for the links, robomont. :)