For a Distant Tsunami That Brings No Shaking, Only Trust in the Warning Drives Evacuation — the Dilemma of False Alarms and Misses

In June 2026, an earthquake near the Philippines put a tsunami advisory on Japan's Pacific coast, by way of the Meteorological Agency's advisory[1]. Some municipalities then issued wide-area evacuation orders, and the government notified them that a wide-area evacuation order on a mere advisory could, on the contrary, undermine trust in the warning. Urging evacuation too strongly can backfire.

People do not readily flee even when a tsunami comes. Evacuation rates vary but are never high. In the 2024 Noto Peninsula earthquake, the rate within Ishikawa was about 60% (59.3%)[2] (the structural limits of that recovery are treated in a separate piece（このサイトの記事）). In the 2011 Great East Japan Earthquake, only 57%[3] fled right after. And for a distant tsunami with no felt shaking, it is lower still: on the Pacific coast in the 2006 Kuril Islands earthquake it was 19.9%[4].

Why the wide variation? Whether the source is near or far matters a great deal. A near-field tsunami with strong shaking is triggered by the shaking itself; in the 2003 Tokachi-oki earthquake the rate reached up to 92.9%[4] by locality. If it shakes, people flee. But a distant tsunami arrives with only the wave, no strong shaking. For a far-off earthquake off the Philippines or Tonga, the natural trigger is absent. What remains is trust in the warning.

Here the problem of "false-alarm fatigue" enters. When evacuation is urged but no tsunami comes, or only a tiny one, and this repeats, people stop believing the warning — the tale of the boy who cried wolf. Research by Toshitaka Katada and colleagues shows that after the 2006 Kuril Islands earthquake, a single false alarm markedly lowered the evacuation rate. Trust is shaved away by false alarms.

So should warnings be issued freely, unafraid of false alarms? It is not that simple. Both misses and false alarms are unavoidable, from the technical limits of disaster information. The government has set a policy of "issue early, unafraid of a false alarm," yet there is experimental evidence that the value of this strategy of issuing frequently, unafraid of false alarms, is granted in the short term but hard to grant beyond it[5]. Oikawa and Katada note prior work that finds the boy-who-cried-wolf effect empirically weak, and there is no academic consensus. Cutting false alarms, or issuing freely, is not on its own decisive.

What lies here is a trade-off between accuracy and trust. Issue too many warnings, and more false alarms make people stop believing them. But keep issuing for fear of a miss, and the value is limited. Both misses and false alarms are a technical dilemma inherent to disaster information; either way there is a cost. And for a distant tsunami, this trust is the sole trigger for evacuation. With no natural signal from shaking, the design of information decides, directly, who lives and who dies.

So the question is not only "how to cut false alarms." Within the dilemma, it is "how to keep trust." After the 2011 disaster, the Meteorological Agency rebuilt its tsunami warnings in 2013, cutting the categories from eight to five[6] and, for a giant earthquake, conveying not a number for the height but a word like "massive." A turn from competing on numerical accuracy toward a design that gets people to flee first. The government's notice to curb excessive wide-area evacuation orders on advisories can be read as part of the same trial and error in designing trust.

Distant tsunamis of the Philippine or Tongan type will draw more attention. When only the wave comes, with no felt shaking, what can move people is trust in the warning alone. That trust wavers with a false alarm, and it cannot be held by issuing warnings freely for fear of a miss either. Beyond the question of predicting the height to the centimeter lies the design of how a warning is believed. It decides the number of people who flee.

Further Reading

• 人が死なない防災 (Disaster Prevention Where No One Dies)（外部サイト、新しいタブで開きます） (Toshitaka Katada, Shueisha Shinsho, March 2012) — a tsunami-evacuation researcher rethinks disaster prevention not from warnings and information alone but from the side of how people actually flee. (In Japanese.)

References

Tsunami Evacuation in the 2024 Noto Peninsula Earthquake: A Survey of Residents — Maho Ishibashi, Shinya Yasumoto, Sayaka Irie, Yoshikazu Kagi, Naoya Sekiya. Journal of Japan Society for Natural Disaster Science 43-3

Present Conditions and Issues of Correspondence of Administrations and Inhabitants for Distant Tsunami — Toshitaka Katada, Naoki Murasawa. Journal of Disaster Information Studies, No.7

Effects of Repetitive False Evacuation Advisory on Residents' Behavior — Yasushi Oikawa, Toshitaka Katada. Journal of Disaster Information Studies, No.14

Committee on Earthquake and Tsunami Measures Learning from the 2011 Tohoku Earthquake (7th Meeting), Document 2 — Cabinet Office, Central Disaster Management Council. Cabinet Office