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The story
On October 16, 2026, an earthquake early warning from the Japan Meteorological Agency (JMA) reporting a magnitude 9.9 quake set off alerts on smartphones nationwide, sparking an uproar on 5ch. The figure would have been the largest ever recorded, and the fact that Yahoo! Search was briefly unreachable around the same time fueled suspicions of a cyberattack. After the alert went out, the JMA explained that it had not suffered a cyberattack. On 5ch, discussion continued over the cause and fallout, including speculation that the system had mistakenly merged a minor tremor near Hokkaido with an earthquake near the Kamchatka Peninsula into a single event, reports that the Yamanote Line had stopped, and accounts of the alert sounding differently on iPhone versus Android.
JMA says it has not suffered a cyberattack
[Jiji Press]
October 16, 2026, 14:06
Source: jiji.com / Original article here
What people said
TL;DR why you'd think that (three lines or less)
Because Japan can't do anything about it anyway
Could it be that we're already in the afterlife?
That would mean a human was eyeballing the number before issuing the alert.
What era are we living in?
This is supposed to be judged automatically by the system.
It wouldn't be surprising if the JMA got hit by a cyberattack, so they should just come clean about it.
The 'they just misread it' theory, of all things
Maybe they just unplugged the alarm?
Do you have any idea how many times bigger the energy difference is?
Maybe the times are swinging back to anti-high-tech, lol
Make it 6am every morning, please
Even if it was just a test, M9.9 is pretty malicious, no?
That's an impossible number to pick.
598 M7.74 (Mie Prefecture [Warning] Kuril Islands M9.9/140km, intensity 7) 2026/10/16 (Fri) 12:40:12.94 ID:LBLvZpLs0
Did the Kyoshin Monitor (real-time seismic intensity map) glitch out?
Hokkaido's lit up red
My phone didn't go off, but the phones around me did.
Didn't the Yamanote Line in Tokyo stop because of it?
and the system judged it to be the same event as an M6.9 earthquake at 150km depth near the Kamchatka Peninsula,
which produced an M9.9 reading centered on Etorofu Island.
There was a similar case before, where separate earthquakes off Wakayama and near Toba were misjudged as one event, and the epicenter came out as Nara.
This kind of thing happens because the system prioritizes speed over accuracy, so false alarms are bound to occur.
The detection logic is just bad
I'm near Hakodate, and the alert hit right when there was an intensity-1 tremor, so I think this is the final answer.
That can't be it, because the Kyoshin Monitor reacted too.
It aggregates and displays shaking in real time using sensors buried underground.
If this were a false alarm,
it would mean all those sensors malfunctioned at the same time.
Could this be an AI hacker's target?
Surely they're using dedicated, closed-off lines for that, right?
Something's definitely going on. It's laughable that they're claiming they weren't attacked.
I'll go ask the giraffe
Office PCs and Wi-Fi too?
The moment you're carrying a smartphone, you're already exposed, aren't you?
Only security-hardened devices can be used there.
Same goes for the Wi-Fi.
But it did arrive on my work Android.
Same for people around me.
I think that's a problem too.
What kind of system is this?
Maybe it's your carrier?
It went off on both my iPhone and my Pixel.
The iPhone rang twice — once for the alert, once for the 'false alarm' correction.
I'm in Tokyo and both went off.
About 3-4 seconds later, the disaster-prevention PA speakers outside started blaring too.
Because once you go past 9.9, it rolls over to 0.
An M9.x quake happens somewhere in the world often enough that it actually makes me go dead serious.
Background and Key Points of This Discussion
Japan’s Earthquake Early Warning system works by having sensors automatically detect shaking, with the system judging it in real time and prioritizing speed of notification over accuracy. Because of this, there have been past cases where multiple separate earthquakes were mistakenly merged into a single massive one. Many on the thread believed that this time, an intensity-1 tremor near Hakodate was combined with a nearly simultaneous earthquake near the Kamchatka Peninsula, producing a calculated magnitude of 9.9 — surpassing the Great Chilean Earthquake (M9.5), the largest ever recorded. The JMA’s statement that it “did not suffer a cyberattack” only denies unauthorized outside access; it does not rule out a misjudgment by the system itself. Conflating the two can easily lead to the mistaken idea that “if it wasn’t an attack, then everything’s fine.” Opinion on the thread was split between those pointing out how sloppy the detection logic is and those arguing that a false alarm causes less real-world harm than an actual cyberattack would.
*This article is composed of excerpts and a summary from the 5ch (News Flash+) thread “[Breaking] JMA says it has not suffered a cyberattack.”
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