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Deadly Mexico earthquake had unusual cause
- okonomiyaki3000 9y agotl;dr - It was graboids.
- stephengillie 9y ago> 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 agoCompression 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 agoThe 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 agoContinents are basically rafts of granite. Like any raft, if you put more stuff on it, it sinks a bit.
- alan-crowe 9y agoThank 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 agoI 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 agoRight. 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 agohot spot below? magma on it's way up?
- latrasis 9y agoI'm curious, how viable would a controlled underground atomic blast be in this scenario?
- eponeponepon 9y agoYou 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 agoMy 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 agoWhich 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 agoIt'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 agoTo 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.
- njarboe 9y agoSimilar to the New Madrid earthquakes (1811-1812) in the US. These intraplate earthquakes also cause more damage than other earthquakes of the same size because they travel greater distances than the more common ones near plate boundaries. The less fractured bedrock in the middle of plates propagates the energy with less loss.
- deleted 9y ago[deleted]
- devb 9y agoSame with the 2011 Virginia earthquake! https://en.wikipedia.org/wiki/2011_Virginia_earthquake https://en.wikipedia.org/wiki/2011_Virginia_earthquake
- cbogie 9y ago> “I said ‘this is it’ and even thought about jumping out the window. I got very scared." I've never considered this as a survival option during a quake. I suppose the consideration is between getting crushed should the building collapse vs surviving a 23 story fall onto ???.
- King-Aaron 9y agoI think it's more of a 'quick and painless exit' option rather than the potential of being crushed alive over the course of hours.
- Freestyler_3 9y agoThis person seems not to have much survival instinct or knows that he can't get out. How fast can you get out from the 23rd floor? He had 84 seconds right?
- futun 9y agoI wonder if it's statistically safer to run upstairs or downstairs if one is on the 23rd floor?
- cossatot 9y agoQuick explainer about intraslab/intraplate subduction zone events (a slab is a subducting plate): There are two major classifications of crust on earth: oceanic and continental. Oceanic crust (mostly basalt/gabro) is quite a bit more dense and thin than continental crust (mostly granite). Both float on the more dense mantle like big rafts, but the much thinner and denser oceanic crust sits ~3 km lower on average, creating ocean basins. In fact, the cold oceanic crust (and its attached subcrustal lithosphere) is in some places more dense than warmer mantle at depth; this density contrast is part of the convection cells in the mantle that drive plate tectonics. When an oceanic tectonic plate converges with a continental plate, the denser oceanic plate slides underneath, at a subduction zone. (edit: I tried some ascii art to illustrate but HN deleted the spaces and ruined it; I fixed it in a comment below.) There are three types of earthquakes that happen in oceanic plates in subduction zone environments. The first, most familiar and strongest are subduction zone or 'megathrust' earthquakes, like Tohoku (Japan 2011). This is an earthquake caused by the release of stored energy due to frictional locking between the downgoing oceanic plate and the upper continental plate. The second type is an 'outer rise' event. These are almost always small (M~6 max) and not very damaging. This is caused by the flexing of the oceanic plate as it gets ready to dive down (@stephengillie, this is the stress you're asking about). These types of earthquakes are easily observed because they're shallow and relatively well understood. The third type of earthquake is what the Mexican event was; it's an earthquake that happens within the subducting (downgoing) slab/plate at depth (see diagram in comment below). It's not clear exactly why these happen but the pattern of energy release is consistent with vertical(ish) contraction and horizontal(ish) extension, i.e. normal faulting. The best explanation for why a downgoing slab would be contracting vertically and extending horizontally is that it is slowing down as it descends, probably due to a decreasing density contrast between the cold (but warming) slab and the mantle around it. So basically the downgoing slab is buckling like a train would if the front train cars slammed on the brakes but not the back train cars. Actually the best way to visualize this is to think about dropping a flexible rubber sheet (that is more dense than water) into a pool. It will continue to sink in the pool but more slowly than in the air above, and will buckle at the interface due to the buoyancy contrast. But (unlike at the surface) we can't directly test this hypothesis because we don't really have any data on the velocity field to see if there is a deceleration of the downgoing slab (plate). Many of these deep intraslab events, particularly at 100-700 km depth, are thought to be associated with density changes in the downgoing slab as it undergoes mineralogical transformations to thermodynamically restabilize in vastly different P-T conditions.
- AdamJeffe 9y agoSo earthquakes can happen anywhere now? Sounds kinda scary. Hope they will find better methode to find out about this before they happend.
- nso 9y agoThey always could. An earth quake does not need to come from a fault line.
- hyperpallium 9y agoA bit far-fetched, but: I read one theory that artic icebergs melting did not produce a rise in sea-level was because the crust may have moved slightly vertically with the change in ice-mass weighing it down. If the crust is getting slightly redistributed in one place, might there not be some pings and bongs elsewhere?
- madaxe_again 9y agoI think you may have some slightly crossed wires... Land ice, such as that which covers Greenland and Antarctica, does indeed depress the local crust. Exactly how much we're not quite sure, but ice penetrating and non-penetrating radar observations over both places has revealed that as the ice mass decreases, the crust uplifts, very slowly. This actually amplifies sea level rise, as you have both the melt water and the additional displaced volume from the uplifted land to account for. As to pings and bongs, totally. A lateral movement in one place or expansion or uplift could all increase tension elsewhere, which would then be released as an earthquake. The most readily observed example of this is aftershocks, which are often hypocentred near but not at the original hypocentre.
- hyperpallium 9y agoThanks! Yeah, icebergs didn't seem to quite make sense. But if the basic idea is sound, is it a possible explanation for this Mexico quake, despite the artic being so far away? [Though it seems more likely to me that 50 years of data isn't enough to tell whether a geological event is unusual or not...]
- madaxe_again 9y agoI wouldn't say it's an explanation, but there's certainly a causal link between all major geological activity on Earth.
- mosselman 9y agoClick baity title.