If you live in Japan, you may one day see news of a "Nankai Trough advisory" (南海トラフ臨時情報). It sounds serious, and it is worth understanding, but it is not a reason to panic. This page explains what the advisory is, what it means, and the small, sensible steps a resident can take.
What the Nankai Trough is
The Nankai Trough is a large undersea depression running roughly from off the coast of Shizuoka to the seas around Kyushu, where one tectonic plate is slowly sliding beneath another. Historically, this zone has produced very large earthquakes at irregular intervals over many centuries. Because of that history, the Japanese government monitors the area closely and has a system for communicating when the situation appears to change.
What the advisory actually is
The 南海トラフ臨時情報 (Nankai Trough Earthquake Extra Information) is issued by the Japan Meteorological Agency (気象庁, JMA) when scientific monitoring suggests the risk in the zone has been temporarily raised. A common trigger is a large earthquake occurring within or near the zone, which experts then evaluate to see whether it changes the short-term likelihood of a further large quake.
The key point to hold onto is this: the advisory is not a prediction of a specific earthquake. No one can say a quake of a certain size will strike a certain place at a certain time. The advisory simply tells the public that, based on current observations, it is a good moment to double-check your preparations. It is a prompt to prepare, not an alarm to flee.
"警戒" versus "注意"
When the advisory is issued, it usually carries one of two wordings that indicate how the situation is being assessed:
- 巨大地震警戒 (keikai, "alert") is used in the assessed scenario judged more significant, for example after a very large quake in part of the zone. In some coastal areas, authorities may ask certain residents to take precautionary evacuation steps in advance.
- 巨大地震注意 (chui, "advisory / caution") is used for a scenario judged less significant but still worth heightened attention. Here the guidance is generally to review your readiness and stay alert while continuing daily life.
In both cases the message is about preparedness and attention, not certainty. Local governments will share specific instructions for their area, so follow official announcements where you live.
What a resident should actually do
The practical response is calm and simple. Use the advisory as a checkpoint:
- Review your emergency kit and plan. Confirm that water, food, medicine, and batteries are stocked and in date. Our 7-day food plan for a family is a useful checklist.
- Confirm evacuation routes and meeting points. Know where your nearest shelter is and how your household will contact each other if phones are patchy.
- Check your power backup. If you rely on a portable power station, make sure it is charged; you can size your needs with our power station calculator.
- Keep living normally. Go to work, take your children to school, sleep in your own bed. Heightened readiness does not mean stopping daily life.
It also helps to understand how Japan's broader warning system works. Our guide to warning levels 1 to 5 explains the everyday alerts you are more likely to encounter.
Where to get official information
When an advisory is active, rely on official sources rather than rumor. The Japan Meteorological Agency (気象庁) publishes the advisory itself and the scientific basis behind it, and the Cabinet Office (内閣府) publishes guidance on how residents and communities should respond. Both provide information in clear, plain terms and update it as the situation is reassessed.
The bottom line
The Nankai Trough advisory is a well-designed way for authorities to say "now is a sensible time to be ready." It does not forecast a specific event, and it is not a signal to be afraid. Treat it as a helpful reminder to check the things you have hopefully already prepared, then carry on with your day. Preparation done calmly, in advance, is exactly what makes any future event easier to face.