5 ms·

> But this quake was different: it occurred within the Cocos plate as it warped or bent, not at the boundary with the North American plate, according to the US

> But this quake was different: it occurred within the Cocos plate as it warped or bent, not at the boundary with the North American plate, according to the US Geological Survey. “The type of faulting that occurred here does not usually produce earthquakes of this magnitude,” says Polet. “There have been others in the past 50 years of similar type and location, but none that was even close to this size.” It is still too early to say why the earthquake was so massive, she adds, but “it is sure to inspire much future research”. Cause isn't too clear but the scenario sure appears unusual. What vector of pressure would cause a tectonic plate to flex or bend like a drum?

diggernet 9y ago
Compression stress due to insufficient slipping at the boundary with the North American plate? This also suggests that the sea floor may now be shallower (or deeper?) in that area.
maxerickson 9y ago
The flooding in Houston did that, albeit 2 centimeters. https://www.theatlantic.com/technology/archive/2017/09/hurricane-harvey-deformed-the-earths-crust-around-houston/538866/ https://www.theatlantic.com/technology/archive/2017/09/hurri... (I'm not suggesting a link between the flooding and the quake. It would be fascinating if there were a link though)
- cossatot 9y ago
  Continents are basically rafts of granite. Like any raft, if you put more stuff on it, it sinks a bit.
  - alan-crowe 9y ago
    Thank you for that comment. I've been taught that Northern Europe was depressed by the weight of the ice sheets during the Ice Age and is still rebounding now that the ice sheets have gone and the weight is off. I was imagining this as like compressing a sponge and never quite believed that re-expanding would take thousands of years. But an enormous raft of granite, floating on an extremely viscous sea of even denser hot rock? At least I can see clearly that I have no useful intuitions about this. Does the raft bob up and down on a ten thousand year time scale? (Probably too heavily damped to oscillate) But the raft metaphor implies some lateral flow of the "sea" as the raft rises, so that is something to think about.
- AnimalMuppet 9y ago
  I don't see it. It's not even the same plate. You'd need the North American Plate to distort from Houston (definitely happened, but as you said, 2 cm). You'd need that to make the edges of the North American Plate move (maybe, but how much?). You'd need that to shove on the edge of the Cocos Plate in a way that adds to the stress in the center of the plate rather than on the edge. I'm not a geologist, but as I said, I don't see it.
  - maxerickson 9y ago
    Right. I don't see it either, I wrote that stuff to try to clarify that I was responding to the question about what might bend a plate, that I wasn't trying to tie the events together.
cbogie 9y ago
hot spot below? magma on it's way up?
latrasis 9y ago
I'm curious, how viable would a controlled underground atomic blast be in this scenario?
- eponeponepon 9y ago
  You might be underestimating the size of even a small tectonic plate. Large explosions will cause seismic waves, of course, but to actually move anything, I believe you'd need a spectacularly big one - bigger by far than anything we've detonated before.
- sandworm101 9y ago
  My understanding is that the thousands of tiny detectable tremors each day worldwide involve as much energy as several atomic bombs exploding every day. The energy to move hundreds of cubic miles of rock even a nanometer is difficult to imagine.
  - EwanG 9y ago
    Which suggests finding a place with constant tremors might be worthwhile to try to harvest energy from? Possibly just by having a material that generates a current when flexed?
    - dmix 9y ago
      It's nearly impossible to predict earthquakes so I don't see how this could be feasible at all. Scientists have been trying hard for decades with no luck. It's been one of the most impenetrable natural phenomenons. At most you get decade+ long likelihoods of the number of earthquakes of x strength, across a very large geographic area. Even in places with a high number of them it's very challenging to give probabilities of when, where, or how often they'll hit. There's a good reason the predictions for the upcoming US Westcoast major earthquake is always given within the span of centuries.
    - sandworm101 9y ago
      To harvest energy you need a device on either side of an energy differential. To pull substantial energy from shifting plates you would need something as long, and deep, as those plates. Point devices, ropes being pulled across a slowly separating plate, wouldn't generate much of anything. You would need millions of ropes attached to billions of anchors, all several KM deep within the earth before you could hope to pull any fraction of the energy.

diggernet 9y ago

Compression stress due to insufficient slipping at the boundary with the North American plate? This also suggests that the sea floor may now be shallower (or deeper?) in that area.

maxerickson 9y ago

The flooding in Houston did that, albeit 2 centimeters. https://www.theatlantic.com/technology/archive/2017/09/hurricane-harvey-deformed-the-earths-crust-around-houston/538866/ https://www.theatlantic.com/technology/archive/2017/09/hurri... (I'm not suggesting a link between the flooding and the quake. It would be fascinating if there were a link though)

cossatot 9y ago
Continents are basically rafts of granite. Like any raft, if you put more stuff on it, it sinks a bit.
- alan-crowe 9y ago
  Thank you for that comment. I've been taught that Northern Europe was depressed by the weight of the ice sheets during the Ice Age and is still rebounding now that the ice sheets have gone and the weight is off. I was imagining this as like compressing a sponge and never quite believed that re-expanding would take thousands of years. But an enormous raft of granite, floating on an extremely viscous sea of even denser hot rock? At least I can see clearly that I have no useful intuitions about this. Does the raft bob up and down on a ten thousand year time scale? (Probably too heavily damped to oscillate) But the raft metaphor implies some lateral flow of the "sea" as the raft rises, so that is something to think about.
AnimalMuppet 9y ago
I don't see it. It's not even the same plate. You'd need the North American Plate to distort from Houston (definitely happened, but as you said, 2 cm). You'd need that to make the edges of the North American Plate move (maybe, but how much?). You'd need that to shove on the edge of the Cocos Plate in a way that adds to the stress in the center of the plate rather than on the edge. I'm not a geologist, but as I said, I don't see it.
- maxerickson 9y ago
  Right. I don't see it either, I wrote that stuff to try to clarify that I was responding to the question about what might bend a plate, that I wasn't trying to tie the events together.

cbogie 9y ago

hot spot below? magma on it's way up?

latrasis 9y ago

I'm curious, how viable would a controlled underground atomic blast be in this scenario?

eponeponepon 9y ago
You might be underestimating the size of even a small tectonic plate. Large explosions will cause seismic waves, of course, but to actually move anything, I believe you'd need a spectacularly big one - bigger by far than anything we've detonated before.
sandworm101 9y ago
My understanding is that the thousands of tiny detectable tremors each day worldwide involve as much energy as several atomic bombs exploding every day. The energy to move hundreds of cubic miles of rock even a nanometer is difficult to imagine.
- EwanG 9y ago
  Which suggests finding a place with constant tremors might be worthwhile to try to harvest energy from? Possibly just by having a material that generates a current when flexed?
  - dmix 9y ago
    It's nearly impossible to predict earthquakes so I don't see how this could be feasible at all. Scientists have been trying hard for decades with no luck. It's been one of the most impenetrable natural phenomenons. At most you get decade+ long likelihoods of the number of earthquakes of x strength, across a very large geographic area. Even in places with a high number of them it's very challenging to give probabilities of when, where, or how often they'll hit. There's a good reason the predictions for the upcoming US Westcoast major earthquake is always given within the span of centuries.
  - sandworm101 9y ago
    To harvest energy you need a device on either side of an energy differential. To pull substantial energy from shifting plates you would need something as long, and deep, as those plates. Point devices, ropes being pulled across a slowly separating plate, wouldn't generate much of anything. You would need millions of ropes attached to billions of anchors, all several KM deep within the earth before you could hope to pull any fraction of the energy.