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Comment by cedws | Hacker News Reader

People were freaking about the July megaquake prophecy and nothing happened. Trying to time it is silly, just chill and enjoy your stay, you'll probably be fine.

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Megaquake is following a major earthquake is well documented. This is not silly prophercy stuff. Parent was talking about that case.

True, but when it not known. Worse, this may be the "megaquake". There are earthquakes all the time. There often isn't a megaquake following a big one. They do often enough to be documented, but not every time.

This is different than the July megaquake prophecy, which was indeed dumb. With a strong quake like this there will be aftershocks. Most will be small, but there is a risk (about 5% according to the USGS) of an even stronger quake than the first within the next week or so [1].

I agree the parent will likely be fine, but it can be stressful in the aftermath of a large quake. And if they want to leave the area and have the opportunity to do so calmly and safely, I think that’s justified.

[1] https://www.usgs.gov/faqs/what-probability-earthquake-a-fore...

Why was the July megaquake, an 8.8 magnitude, a dumb prophecy, but this "strong quake" at a magnitude of 7.6 is a smart prophecy?

This isn’t something that I personally wish to debate, but I’ll leave link to the wikipedia page for the July 2025 prophecy [1] for anyone who may not know what we are talking about.

And also point out that last night’s earthquake in Northern Japan was not a “prophecy”. Just a regular, large earthquake - which do occur pretty frequently in Japan. And I say "large" not just because of the magnitude, but because parts of Aomori experienced 6+ shaking on the shindo scale [2] which is categorized as "brutal" [3].

[1] https://en.wikipedia.org/wiki/July_2025_Japan_megaquake_prop...

[2] https://www.data.jma.go.jp/multi/quake/quake_detail.html?eve...

[3] https://en.wikipedia.org/wiki/Japan_Meteorological_Agency_se...

Source: it came to me in a manga.

Strange question.

The July megaquake prophecy scare was dumb because it originated in a work of fiction, not intended to be taken seriously by its author and not based on any scientific evidence. If the "prophecy" had come true, it'd be by luck alone. fwiw, I'd say it didn't come true; the 8.8 magnitude earthquake was near Kamchatka and didn't actually damage Japan, though a tsunami seemed plausible enough that there was a precautionary evacuation.

This "strong quake" is a thing that happened, not a "smart prophecy" [1]. Talk of aftershocks is not a prophecy either; it's a common-sense prediction consistent with observations from many previous earthquakes.

[1] smart prophecy is an oxymoron. A prediction is either based on scientific evidence (not a prophecy) or a (dumb) prophecy.

You are certainly reading something into my question that isn't there. I'm genuinely ignorant. I thought you were saying that predictions of a strong aftershock following an M8.8 were dumb, but the same thing following an M7.6 were smart. Is that not the case?

Again, sorry if this seemed antagonistic or something, I really am just unsure of what you were saying.

A manga book published in 1999 randomly predicted a disaster in March 2011, which seemed to come true with Fukushima. The manga was re-published in 2021 predicting a M8.8 in July 2025, but nothing happened. This is the dumb prophecy part, it was not based on seismology studies, just a shot in the dark to try to seem prophetic again. Countless works of fiction are published every year which predict some future disaster at an arbitrary date. Every once in a while, one of those thousands of random predictions can be interpreted as coming true when something bad happens on that day, which retroactively drives interest in that work of fiction, and less scientific minds believing the author has actual future predicting power beyond the abilities of science.

A relatively major (but not M8.8) quake has now hit in December 2025. It is intelligent to expect there may be aftershocks in the days after a significant earthquake actually happens, which can sometimes be larger than the initial quake. This is a well-accepted scientific fact born out of large amounts of data and statistical patterns, not whimsical doomsdayism.

Fukushima's M9.0-9.1 was around a 1-in-1000-year scale event. The last time Japan saw such a powerful earthquake was in the 869 AD. It would be reasonable to expect one of that scale to not happen again for another 1000 years.

Math nazi in me really wants to point out that an event with a 1:1000 probability would be expected to be seen (> 50% probability) in about 700 years, not 1000.

Heh, hence why I said 1-in-1000-year, rather than just 1-in-1000. Indeed 1:1000 would happen within 693 years with 50% probability, 1:1443 would happen within 1000 years with 50% probability.

Roughly how many Paul Erdős's to every Oswald Teichmüller though?

https://www.youtube.com/watch?v=RqlQYBcsq54

Great response and very informative - no clue how I totally missed the references and stories about this manga. That’s pretty cool - I’ll have to look it up!

You asked what I would have asked, in a sentence, my understanding is: it was LITERALLY a prophecy, I.e. an unscientific statement out of thin air, that in July, there would be an earthquake followed by a larger one. Here, we have reality, an earthquake, ergo the first prong of a mega quake was satisfied, as opposed to prophesied.

Ah, that's probably it. Thank you.

That's a bit like comparing apples to oranges. One was published by social media, one was published by the Government of Japan.

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