Japan's Nankai Trough Megaquake: 298,000 Deaths in the Worst Case, Mapped | New Disaster Agency

Japan's official worst-case estimate for a Nankai Trough megaquake and tsunami is up to about 298,000 deaths (Cabinet Office, March 2025). And on 2 November 2026, Japan opened a new Disaster Management Agency (防災庁, Bosai-cho), with a staff quota of 352. What the record shows: Probability (Earthquake Research Committee, reference date 1 Jan 2026): for an M8–9 quake within 30 years, "60–90% or more" with the slip-based model and "20–50%" with the interval model. The committee says neither ranks above the other, asks people to keep 60–90% in mind for preparedness, and says not to merge them into "20–90%". The 298,000 is a designed worst case: land-side shaking, winter late night, wind 8 m/s, low early evacuation. Later deaths (separate): 26,000–52,000. Up to 2.35 million buildings lost; 12.3 million evacuees after a week; assets ¥224.9 trillion. By prefecture (same case, Cabinet Office table p.123, "read with a margin"): Shizuoka ~101,000 (about one third — our calculation), Miyazaki ~33,000, Mie ~29,000, Kochi ~25,000, Ehime ~21,000, Aichi and Wakayama ~19,000, Tokyo ~1,400. Each prefecture's own worst case is a different scenario (e.g. Wakayama ~65,000) and can't be added up. About 215,000 of the 298,000 are tsunami deaths (72% — our calculation). Intensity 7 in 149 municipalities, mainly the coast from Shizuoka to Miyazaki; tsunami up to about 34 m in Kochi; a 1 m+ wave in as little as 2 minutes in some places. Behavior moves the number: worst-case tsunami deaths of ~215,000 fall to ~94,000 with early evacuation and effective warnings, and ~73,000 if everyone starts to evacuate right away. Across cases: 2.3–9.8× fewer tsunami deaths. 2014 goal: −80% deaths in 10 years; old-model progress 332,000 → 264,000 (about −20%). The new 298,000 uses an updated method. The new agency: Establishment Act promulgated 17 July 2026, in force 2 November 2026; headed by the Prime Minister, run by a Minister for Disaster Management with the power to issue recommendations ministries must respect; staff quota 352 (1.6× the Cabinet Office unit); FY2026 budget ~¥20.2 billion (including the old unit and setup office); FY2027 request ~¥65.2 billion (House of Councillors research paper). Households: 46.1% keep food, water and supplies ready (Cabinet Office survey, Aug 2025; 40.8% in 2022; 10.8% in 1991). Official advice: at least 3 days, ideally 1 week. Limits: a modeled worst case, not a prediction; prefecture figures carry a margin; two models, two probabilities; FY2027 is a request. ■ Sources (checked 2 Nov 2026) ・Earthquake Research Committee (地震調査研究推進本部), probability update, 14 Jan 2026, p.3: https://www.static.jishin.go.jp/resou... ・Earthquake Research Committee, Nankai Trough evaluation revision (26 Sep 2025) Q&A: https://www.jishin.go.jp/evaluation/l... ・Cabinet Office (内閣府), Nankai Trough working group report, summary (Mar 2025): https://www.bousai.go.jp/jishin/nanka... ・Cabinet Office, working group report (Mar 2025), pp.15, 41: https://www.bousai.go.jp/jishin/nanka... ・Cabinet Office, damage estimate, explanatory material (Mar 2025): https://www.bousai.go.jp/jishin/nanka... ・Cabinet Office, damage estimate (quantitative), Mar 2025: https://www.bousai.go.jp/jishin/nanka... and https://www.bousai.go.jp/jishin/nanka... (p.123 prefecture table) ・Disaster Management Agency (防災庁), laws: https://www.bousai.go.jp/about/hourei... ・House of Councillors, 『立法と調査』 No.487 (29 Sep 2026), pp.63–64: https://www.sangiin.go.jp/jpn/shiryo/... ・Cabinet Office (Disaster Management), FY2026 budget: https://www.bousai.go.jp/taisaku/yosa... ・White Paper on Disaster Management 2026, fig. 4-2-2: https://www.bousai.go.jp/kaigirep/hak... How we calculated: map from the Cabinet Office table (p.123; "－" shown as 0); shares are our division of its rounded figures. 被害想定 = damage estimate; 防災庁 = Disaster Management Agency. ■ Credits Voice: Kokoro TTS (hexgrad/Kokoro-82M, Apache 2.0). This video uses a synthetic voice. Photos, Wikimedia Commons: くろふね (CC BY 4.0); DimiTalen, Araiyasushige (CC0); Batholith, Yones (public domain). Document pages: Cabinet Office (内閣府) under the Cabinet Office terms of use; Headquarters for Earthquake Research Promotion (地震調査研究推進本部) under the MEXT website terms. ■ Credits Music track: Jay by Lukrembo Music track: Daily by Lukrembo Music track: Sunflower by Lukrembo Music track: Cloud by Lukrembo Source: https://freetouse.com/music