The Earthquake Early Warning System
Japan's Earthquake Early Warning system buys you seconds between detection and destruction. When your phone screams its unmistakable tone, strong shaking is seconds away; this article explains how that is possible and what to do with the time.1
Procedures, fees, and requirements can change. Confirm current details at the Japan Meteorological Agency site.
Overview
The 緊急地震速報 (kinkyū jishin sokuhō, "Earthquake Early Warning," abbreviated EEW) is JMA's system for announcing estimated shaking before the strongest tremors arrive. JMA launched public provision through media outlets on 1 October 2007.1
The system exists for one purpose: converting detection into protected seconds. Trains slow, elevators park, and people shelter, all before the main motion arrives.2
How seconds of warning are possible
Quakes radiate two main wave types. P-waves, the initial tremors, travel around 7 km per second. S-waves, the main tremors that cause most damage, travel around 4 km per second.3 EEW is a race against the slower wave: seismographs near the focus catch the P-wave, computers estimate the focus and magnitude within seconds, and the announcement goes out before the S-wave reaches farther cities.3
The sensor net makes this possible. JMA maintains around 200 seismographs, with roughly 800 more from the national earth-science institute feeding the same analysis.3 From that data the system estimates the shaking each location should expect and its arrival time.2
Lead time is a few seconds to a few tens of seconds.4 Distance buys time: far from the focus you may get half a minute, while near the focus the warning can arrive at the same moment as the shaking.4
Which channels carry the alert
Mobile phones: Emergency Alert Mail
Most phones sold in Japan receive EEW through the carriers' cell-broadcast emergency mail, an area-specific warning pushed to every compatible handset in the target zone. Reception needs a compatible handset with emergency alerts enabled; check the setting once, today.1
Travel guides sometimes advise silencing the alert tone because it is loud. A muted phone skips the only warning that buys protected seconds. Keep the alerts on and learn the tone instead.1
TV and radio broadcasts
Television and radio interrupt programming with the emergency tone and a message naming the expected regions and intensities.1 NHK's EEW chime is the sound most residents learn first; when it cuts into a broadcast, shaking follows within seconds.
Apps and municipal systems
Disaster-prevention apps push EEW notifications, often faster or more persistently than the broadcast channels, and many offer English translations of the initially Japanese message.1 Municipal outdoor speakers and facility systems in stations and factories relay the alert locally, triggering automated countermeasures such as slowing trains and parking elevators.2
EEW is not J-Alert
Newcomers confuse two similarly named systems. EEW forecasts earthquake shaking and comes from JMA. J-Alert is the separate nationwide instant-warning system that relays non-quake emergencies, such as missile-launch information, from the national government through municipalities to local speakers and phones.1
The practical difference: an EEW means shaking is seconds away and you should shelter now. A J-Alert means something else entirely; read its message rather than assuming an earthquake.
What to do with seconds of warning
Seconds allow only pre-decided moves. Drop, cover, and hold on first. If a stove or heater is within arm's reach, switch it off. Brace a door open if you pass one, and stop any dangerous activity such as carrying hot liquid or standing on a ladder.4
| Situation | The seconds move |
|---|---|
| At home | Under the table, away from glass4 |
| Cooking | Stove off if within reach, then shelter4 |
| In a train or elevator | Grip a strap or rail, crouch low4 |
| Outdoors | Away from walls, glass, and vending machines4 |
Honest limitations
Near the focus there may be no lead time at all. Strong tremors can arrive simultaneously with the warning, which is why the during-shake response must be reflex, not something you start planning after the tone.4
An EEW is also not a tsunami warning. It forecasts shaking, not waves; near the coast, strong shaking itself remains your evacuation signal regardless of what any alert says.2
Find your municipal hazard map
Alerts tell you when; your hazard map tells you where to go. Every municipality publishes hazard maps marking tsunami zones, landslide zones, and designated shelters for its own neighborhoods.
Start at the national Hazard Map Portal run by the Ministry of Land, Infrastructure, Transport and Tourism at https://disaportal.gsi.go.jp/, which overlays national risk data on one map.5 Then follow the portal to your own municipality's published map and confirm your shelter and zone in advance, since boundaries are revised over time.5
Good to know
The alert tone is unmistakable; decide your move now
The tone is deliberately harsh so it cuts through sleep and noise. Decide today what you do on hearing it in each room you occupy: under which table, away from which shelf. Seconds leave no room for deciding.4
Japanese first, English seconds later
The initial broadcast message is Japanese. Apps with English translation catch up within seconds, but do not wait for a language you prefer. The tone plus the word for strong shaking is enough to act on.1
One alert does not mean the sequence is over
Follow-on quakes trigger fresh alerts through the same channels. Stay sheltered and keep alert settings on through the whole sequence rather than standing down after the first all-clear feeling.4