| ▲ | markus_zhang 20 hours ago |
| I heard that smaller (relative) earthquakes actually lower the prob of larger ones, so maybe it is a good thing? A bunch of 7.X earthquakes in the ocean are not going to be hugely destructive. |
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| ▲ | Someone 18 hours ago | parent | next [-] |
| On the one hand earthquakes remove tension from the earth’s crust and release energy that can’t be used in future shocks. On the other hand, if a shock doesn’t release all energy it may come to rest in a relatively weak spot that will soon give away again (https://en.wikipedia.org/wiki/Earthquake_swarm: “The Matsushiro swarm lasted from 1965 to 1967 and generated about 1 million earthquakes. This swarm had the peculiarity of being sited just under a seismological observatory installed in 1947 in a decommissioned military tunnel. It began in August 1965 with three earthquakes too weak to be felt, but three months later, a hundred earthquakes could be felt daily. On 17 April 1966, the observatory counted 6,780 earthquakes, with 585 of them having a magnitude great enough to be felt, which means that an earthquake could be felt, on average, every two and a half minutes.”) Because of that, I think an earthquake will increase the probability of one occurring again soon, but decrease its strength. |
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| ▲ | lostlogin 19 hours ago | parent | prev | next [-] |
| > A bunch of 7.X earthquakes in the ocean are not going to be hugely destructive. New Zealand’s 5th most deadly disaster was Christchurch’s 6.2 which killed 185 people. It was a shallow aftershock from a larger, less destructive quake. The damage was huge. https://en.wikipedia.org/wiki/2011_Christchurch_earthquake |
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| ▲ | xvedejas 16 hours ago | parent | prev | next [-] |
| Almost all energy released in earthquakes is released in the biggest ones. No realistic number of smaller quakes is ever going to add up to even the single biggest earthquake ever recorded. |
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| ▲ | ed 12 hours ago | parent [-] | | To dissipate the energy of a M9 (which happens about once per decade) you'd need about 32,000 quakes of M6 (still big enough to collapse buildings). Energy scales as 10^(1.5 × ΔM) ΔM = 9.0 − 6.0 = 3.0 10^(1.5 × 3) = 10^4.5 ≈ 31,600 |
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| ▲ | jacquesm 20 hours ago | parent | prev | next [-] |
| That's correct, if relatively small earthquakes would stop that could be the precursor to a much bigger one. It's like releasing tension gradually rather than all at once. |
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| ▲ | tonmoy 20 hours ago | parent [-] | | Isn’t that a myth? Do you have any sources to back up your claim? | | |
| ▲ | __s 20 hours ago | parent | next [-] | | Seems like it, & each rank is 30x more energy than the last[1] https://www.usgs.gov/faqs/what-probability-earthquake-a-fore... Suggests 5% for larger quake to follow within week. But overall most sources I could find suggested it's hard to know, needs more research 1: https://www.reddit.com/r/askscience/comments/10wecl8/do_litt... | |
| ▲ | jacquesm 19 hours ago | parent | prev | next [-] | | https://www.geo.ruhr-uni-bochum.de/en/new-study-connects-ear... | | |
| ▲ | mturmon 16 hours ago | parent | next [-] | | I think you intended this to be a validation of the idea that small quakes relieve stress and therefore lower the chance of a large quake. The above link does not answer that question. It is relating stress release to "fault strength", or the maximum shear stress that can be withstood by the fault. There is an incidental relationship with depth that plays a role. The video linked nearby (on criticality) also does not address the question at issue. I'm only replying because I work adjacent to this area, and my understanding is that the idea that small EQ's release stress is a myth. Here [1] is another link, listed as #1 in the "Myths" category. And you can dig up quotes from none other than Lucy Jones [2] saying that this is a myth. I don't work directly in this area, so I'm not willing to say absolutely no. But I'd really like to see a head-on reference supporting the claim that it's not a myth. [1] https://earthquakes.berkeley.edu/outreach/faq.html [2] https://en.wikipedia.org/wiki/Lucy_Jones | | |
| ▲ | fc417fc802 14 hours ago | parent [-] | | EQs are a release of energy. That energy is stored as stress prior to release. There is a finite amount of stored energy at any given time. So the statement "EQs release stress" is true and it follows that adding the modifier "small" to the front doesn't change this. It should also be immediately apparent that it would be very surprising if there were not statistical implications as a result of this. So surprising in fact that I would suggest that the burden of evidence should fall on those claiming that any such statistical effects are unexpected. | | |
| ▲ | mitthrowaway2 9 hours ago | parent [-] | | This part is unquestionably true. But since we don't have a direct measurement of the stored energy at a given time, the occurrence of an earthquake acts as both an indicator of release of stored energy but also, potentially, evidence of increasing stored energy. Like how buying a Porsche costs money, and leaves you poorer than before you bought it, but when you see stranger buy a Porsche, you update towards believing that they're wealthy rather than poor. Disclaimer: I am not a geoscientist. | | |
| ▲ | fc417fc802 6 hours ago | parent [-] | | Fair enough. I'm also not a geoscientist, and to clarify I didn't mean to imply any specific statistical effect there. It seems entirely reasonable to me that a series of EQs might tend to increase in intensity. In reality I think (layman's impression) that there's rough (post hoc) evidence for both things. Foreshocks followed by noticably larger EQs as well as trains of progressively smaller EQs. |
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| ▲ | criddell 18 hours ago | parent | prev [-] | | https://news.caloes.ca.gov/earthquake-myths-separating-fact-... Myth 5 is "Small Earthquakes Relieve Pressure and Prevent Larger Ones" | | |
| ▲ | fc417fc802 17 hours ago | parent | next [-] | | GP is correct; I'm not sure why CA gov is calling that a myth (it's not). However keep in mind that it's not necessarily true 100% of the time. Or at least the things it might seem to imply at first glance aren't true - the presence or absence of small quakes in a given period doesn't necessarily tell you anything useful about the future. | | |
| ▲ | jacquesm 16 hours ago | parent [-] | | Indeed. But I get why people are confused because it is a subtle difference between 'stress relieved through small earthquakes is stress expended' vs 'stress relieved through small earth quakes is not indicative of the magnitude of future events'. The long term absence of stress relief small quakes on a known fault line might be bad news, or no news at all, statistics are where the difference is here, not in particular events. See also, 'the big one' and various theories around it. |
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| ▲ | jacquesm 18 hours ago | parent | prev [-] | | Myth: new knowledge never trumps old knowledge. Check the dates on those two publications. |
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| ▲ | numpad0 16 hours ago | parent | prev | next [-] | | This type of argument is kind of logical but not so immediately useful. Earthquakes just happen and no one is involved in that process. There could still be the big one coming, or that one might have been defused by this one. No one knows. | |
| ▲ | indigodaddy 20 hours ago | parent | prev [-] | | Various scientists in this video. The video is a great watch btw. https://youtu.be/HBluLfX2F_k (stresses build up and are often released through many small, unfelt earthquakes (25:54). If these small movements don't dissipate the stress, it can accumulate and lead to a powerful chain reaction (26:25) * disclaimer I used YouTube's built-in AI to find/summarize the timestamps, as I couldn't remember offhand where it was when I previously watched this. | | |
| ▲ | mturmon 15 hours ago | parent [-] | | I don't believe the video quite says this (I watched the relevant section). It's worth noting that they are mostly interested in critical phenomena in general, and earthquakes are kind of a drive-by application, treated along with fires and sand piles. They do hint around the edges, but they don't head-on make the claim for earthquakes that small EQs materially lessen stress buildup and thereby make larger EQ's less likely. I was looking for a credential of one of the people they interview, to see if they are really a solid earth person or more of a critical phenomena person -- their names aren't easy to find. This particular myth ("small earthquakes relieve stress") is a bit of a stinker in the solid earth community, and I think a solid earth person would be quite careful about their words as they discuss this. | | |
| ▲ | indigodaddy 15 hours ago | parent [-] | | I think you've summed it up correctly. It's not proof and some scientists claiming some things isn't the same as studies/evidence. However, is there evidence that it's not true? The fact is we do have these smaller movements and earthquakes quite regularly, so we don't really know what would happen after a long absence of them (do we? I suppose there are simulations perhaps that could be run? But I don't know that that's proof either way). To me though it makes a lot of sense that it would/could spur a huge event. |
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| ▲ | jansan 19 hours ago | parent | prev | next [-] |
| That is correct, but OTOH there was a 7.3 foreshock two days before the 2011 Tōhoku earthquake. So the only thing we can say for sure is that it is still extremely difficult to predict earthquakes. |
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| ▲ | 19 hours ago | parent | prev [-] |
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