[intunderflow]

Was in a hotel in Sapporo, almost got thrown out of bed. Lot of people in the hotel lobby now.

Considering leaving Hokkaido by air if a Hokkaido and Sanriku Subsequent Earthquake Advisory is issued, don't really want to be in a potential megaquake.

[cedws]

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.

[fogj094j0923j4]

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

[bluGill]

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.

[freetime2]

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...

[kulahan]

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?

[freetime2]

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...

[sph]

Source: it came to me in a manga.

[scottlamb]

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.

[kulahan]

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.

[hnuser123456]

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.

[refulgentis]

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.

[intunderflow]

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

[jmward01]

I'm not a geologist, but this was pretty deep (44.1k) so not likely a foreshock right? Any actual geologists have a thought here? I know we have seen some indications that foreshocks can happen before megathrust earthquakes but it would need to be at the interface right? This looks like it is just the subducted slab deep down which in the 'intermediate zone' so not impacting the interface that 'slips' in a megathrust earthquake. (again, not a geologist) Now there have been, by that I mean just now, a 6.6 aftershock that was only 10km deep so that is potentially more concerning?

[akg_67]

Good luck, the Sapporo Chitose airport is closed for inspection of both runways.

BTW, you are safer in hotel than outside. No need to stay in lobby, go to bed, just protect your head. I experienced much bigger one in Sapporo in 2018.

[pcl]

When I moved to SF, someone told me that the three most important things you can do for earthquake safety are:

- make sure nothing can fall on you when you're in bed (no mounted artwork above the headboard; no lamps etc on side tables that are high enough to fall on you)

- make sure you have footwear in your bedroom, so you can be mobile if there's broken glass everywhere

- store extra drinking water somewhere (I used a 6-gallon carboy that I periodically refilled)

Probably there are other good things to do, but all those made a lot of sense to me. Most of us spend more time in bed than in any other fixed location, so making sure the bed is a safe place rings true. And water is life.

[parl_match]

Keep in mind that this is a major metropolitan area in a state that has a history of earthquakes. You can expect state level response (and federal as well) within the same day. Their main priority will be water, and elements exposure.

Guidance varies. California list here https://earthquake.ca.gov/wp-content/uploads/sites/8/2025/02...

You should have water, food, medical supplies, and cash.

btw you might find this interesting https://www.amusingplanet.com/2021/01/san-franciscos-hidden-...

[komali2]

Sf fire department has also a pdf with what you should have in an at home emergency kit. It's some simple things you can get in one trip to a camping store and Walgreens. https://sf-fire.org/media/794/download?inline

I also recommend SF people consider joining NERT: neighborhood emergency response team. Disaster after disaster should teach us the opposite of what you argue in terms of response: in fact it's more likely that the scale of people affected will quickly overwhelm resources, and the existence of choke points will severely limit movement of people and resources, especially if infrastructure is damaged and people are flooding out of the city. That can be mitigated by having locals trained to help facilitate emergency response efforts. It's less "pulling people out from under bookshelves" and more "help managing the bureaucracy of the fire department," forms on forms on forms! Though the training does involve pulling someone out from under a bookshelf. It's a week long and quite fun!

[rishikeshs]

I’m curious, how is it more safer inside a building than being outside?

[jasonvorhe]

Modern buildings like hotels are built to withstand earthquakes of some magnitudes. Wouldn't count on that at a local construction site or a worn down house you might pass on the street.

[buildbot]

Especially somewhere like Japan. A newer hotel is probably one of the safest places to be.

[traceroute66]

> worn down house you might pass on the street.

That "worn down house" might be good until "upper 6". Beyond that it all depends on when it was built and the associated construction standards at the time.

Source: https://isec-society.org/ISEC_PRESS/ASEA_SEC_03/pdf/St-5_v5_...

[nerbert]

Buildings are built to resist earthquakes. Outside, anything (electric poles, roof tiles...) can fall on you.

[decae]

Shards of glass falling from ten stories up would be one of the main things to try to avoid.

[traceroute66]

Japan has had earthquakes forever. Their building regulations mandate things like isolation and dampers.

It all stems from an earthquake in 1923 in Yokohama which killed 140,000. Since then Japan's has over time developed some of the strictest seismic standards.

[klempner]

Sure, in the middle of a magnitude 9 earthquake I'd rather be in the middle of a suburban golf course (as long as it is far from any coastal tsunami) than any building, but I don't spend the majority of my time outside.

Two issues: 1. If you're making this choice during an earthquake, "outside" is often not a grassy field but rather the fall zone for debris from whatever building you're exiting. 2. If the earthquake is big/strong enough that you're in any real danger of building level issues, the shaking will be strong enough that if you try to run for the outside you're very likely to just fall and injure yourself.

[lmm]

The main two ways people get injured in earthquakes (at least in Japan) are a) gas fires b) things falling on them. And being outside but near buildings is a good way for things to fall off those buildings onto you.

[linenmerchant]

Best of luck!