Aftershocks Can Occur Centuries After Original Earthquake, Says Study (theguardian.com) 37
Large earthquakes are always followed by aftershocks -- a series of smaller but still potentially damaging quakes produced as the ground readjusts. But how long does it take for the aftershocks to die out? A new study suggests some areas can experience aftershocks decades or even centuries after the original earthquake. From a report: In earthquake-prone areas it is hard to tell the difference between aftershocks and ordinary background seismicity. But recognising aftershocks is an important part of assessing a region's disaster risk. To understand how long aftershocks can persist, researchers turned to the stable continental interior of North America, where earthquakes are uncommon. Using statistical analysis they assessed the timing and clustering of quakes that followed three large magnitude 6.5 to 8 historical earthquakes: one near south-east Quebec in Canada in 1663; a trio of quakes around the Missouri-Kentucky border from 1811 to 1812; and an earthquake in Charleston in South Carolina in 1886. Their results, published in Journal of Geophysical Research: Solid Earth, suggest that the Quebec quake in 1663 has likely shaken itself out, but to their surprise nearly a third of modern quakes in the Missouri-Kentucky area were most likely to be aftershocks from the 1811-12 event, and about 16% of recent quakes in the Charleston region are probably aftershocks from the 1886 quake.
There's a "Your Mom" joke in here somewhere (Score:2)
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Let's get off moms, since I just got off yours.
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We don't feel the aftershocks because your mom's massive ass damps them.
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Questions and doublts (Score:4, Interesting)
Re: Questions and doublts (Score:2)
Iâ(TM)d like to know what the exact semantics are. After all, it seems like all earthquakes are tension in the ground building up until it suddenly overcomes the strength of the rocks stopping it from moving. What determines if the tension came from a previous earthquake? It seems like it all âoejustâ comes from the fault slowly moving.
My guess would be that you can see this like a very complex 2D function. A major earthquake might push your position on the function up over a large maxima
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There's a problem with your very reasonable model - the tension build up typically isn't a one-time thing. So after an earthquake releases some, it's probably building up again more or less immediately after.
So now how do you decide how much of a long-delayed 'aftershock' belongs to the original quake, and how much is due to buildup that came after it? /Not a seismologist, probably sound like a loon to anyone who is.
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Also, some stuff might go a little over on a strong quake and come back toward its original spot afterwards.
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The scale of earthquakes almost seems fractal in nature.
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It is not clear from the article how they are determining if something is an aftershock or just a minor quake on the same fault.
Just speculation here, but they're classifying them as aftershocks because it fits their model. We do know there is a link between frequency and magnitude of earthquakes. The more powerful the earthquake, the less frequently they happen. From that regard, classifying the low power earthquakes as aftershocks of the high power earthquakes makes sense.
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Turns out there's only one earthquake and the rest are just aftershocks /s
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Oh, really? Let's take a look at the 1994 Northridge Earthquake [wikipedia.org], a 6.7 tembler. I was not only in LA at the time, I was within a few miles of the epicenter. The first aftershock came about a minute of the quake, and seemed like just a continuation of the main quake. A second came 11 hours later, with both of magnitude 6.0. By the time things quieted down, there'd been several thousand aftershocks. I don't know about you, but that doe
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don't know about you, but that doesn't sound like less aftershocks for a stronger earthquake.
You are correct because I am claiming exactly the opposite. I was stating that earthquake intensity and frequency are inversely correlated (on a log scale).
I'm speculating that the authors are claiming this is a causal relationship. Frequent low intensity earthquakes are caused by the infrequent high intensity quakes, likely following some sort of decay model. Perhaps my phrasing was too ambiguous.
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Everything is just an aftershock of the Big Bang...
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It is not clear from the article how they are determining if something is an aftershock or just a minor quake on the same fault. The difference would seem to be somewhat semantic in many cases.
Also, all of the examples quoted are for quakes in areas internal to a plate rather than plate boundaries, which are likely to be atypical of the great majority of events.
Exactly, while at it; "Aftershocks from the big bang can be felt millions of years after the event" /s
What was the Earthquakes punishment? (Score:2)
It was grounded.
What is an "aftershock"? (Score:2)
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Isn't everything an aftershock then?
Yes. Unless you can reverse time.
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No, it's only an aftershock if there is no significant external build up of strain prior to the secondary slip event. An after shock is just more release of energy built up in a single strain building event.
Which this paper actually doesn't seem to be taking into account. Admittedly I only skimmed it, but I did do a quick search for rebound, tension, uplift, isostatic, and glaciation, and didn't find even partial matches. Large portions of the "stable" plate they are studying are still rebounding from being
No, no no no (Score:2)
Sorry, but an aftershock coming centuries later isn't an 'aftershock'.
I don't know what the correct term would be, but whatever it is, 'aftershock' isn't it. Yes, yes, I know it's technically "a smaller earthquake following the main shock of a large earthquake", but I call bullshit on the time scale. Maybe to a mountain it's an 'aftershock' but that's a bit of a stretch.
It's like saying your grandchildren are an 'aftershock' of meeting your spouse. Yeah sort of but no not really.
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Conceptually we don't think of it as an aftershock if there is not an immediate cause and effect relationship on human time scales. For geology, it's great science when cause and effect relationships can be established, but it's semantically problematic to call this an aftershock.
Everything is caused by everything in history (Score:3)
If we had enough computing power, we could potentially trace every single movement everywhere, to their roots 100 or 1,000,000 years ago. That does not establish a clear cause/effect relationship.
Did Mt. Vesuvius eruption cause today's activity? (Score:2)
Mt. Vesuvius erupted more than 2,000 years ago, destroying Pompeii. Today, that volcano is still active. Did that eruption long ago "cause" today's volcanic activity? In a manner of speaking, I suppose, since the location and movement of the magma have continued to be active ever since. But did that eruption actually "cause" the tremors felt today? Would a larger, or smaller, eruption have any significant impact on today's tremors? No, I don't think so. Over time, the activity averages out. If that eruption
Surprise ... really? (Score:2)
After shock is within a limited amount of time (Score:2)
Someone trying to get famous by rebranding something as a new study? Well! When the planet formed millions of years ago the initial shift of the plates caused an earthquake and they've kept moving causing aftershocks ever since!
Literally this is just saying that previous earth quakes influence future ones. Who would of thought? What's next? Previous volcanos still influence how the atmosphere of today is, and the life on the planet?
Aftershocks are used to explain the situation where a quake happened that wa
Here's the methodology for saying 'aftershock' (Score:3)
Here, we used the nearest-neighbor (NN) method to identify long-lived aftershocks. The NN method calculates the distances between pairs of earthquakes in a space-time-magnitude domain. If the distances are too close to be expected for independent background events that follow the Gutenberg-Richter law and Poisson distribution, the pairs are taken as clustered events (i.e., the later one in a pair is an aftershock of the earlier one). From the abstract of the actual scientific article, https://agupubs.onlinelibrary.... [wiley.com]
And a relevant thought from my Structural Geology course of last year:
In continents in particular, a lot of far field stress earthquakes occur along pre-existing faults. So it would make sense that the same fault that was activated by the continental earthquake also shows additional movement later on. If you look at the earthquake distribution (Figure 1) in the AGU article, you'll see a lot around the failed mid-continent rift in Missouri (the New Madrid Fault Zone.)
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So, an aftershock is an earthquake that is less likely according to some theoretical (empirical, arbitrary) statistical distribution.
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Actually, I think it's the opposite. An 'aftershock' is one that fits withIN the statistical parameters for proximity. And the distinction is relatively arbitrary for classifying individual earthquakes, the question is more about the pattern of earthquakes over time.
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Their methodology (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023JB026482 - it's "