News Discussion

Nankai Trough Megaquake Could Kill 298,000 People, Latest Estimate Shows

An expert meeting of the Japanese government's Central Disaster Management Council released the latest damage estimates for the Nankai Trough Mega Earthquake on March 31. The meeting was chaired by Professor Emeritus Nobuo Fukuwa of Nagoya University.

A Nankai Trough earthquake refers to a potentially massive earthquake that occurs along the Nankai Trough, a submarine trench off Japan's southern coast that has historically triggered catastrophic earthquakes.

According to the council's estimates, in the worst-case scenario, the death toll is expected to reach around 298,000. Approximately 2.35 million buildings are projected to be destroyed.

In the Japanese government's 2014 Nankai Trough earthquake response plan, the death toll was estimated at around 332,000, with 2.5 million buildings destroyed. The government will update this basic plan based on the expert panel's latest report.

The updated worst-case death toll includes about 73,000 deaths from building collapses, 9,000 from fires, and 215,000 from tsunamis, assuming a 20% evacuation rate. If 70% of people evacuate, the death toll would drop to around 94,000. The number of completely destroyed buildings is estimated to include 1.28 million from the earthquake, 188,000 from the ensuing tsunami, and 767,000 from fires.

With improved accuracy in ground condition and topography data, the estimates show a larger area affected by seismic intensity and tsunami inundation. The region impacted by tsunami inundation of 30 cm or more has increased by 30%. A total of 764 municipalities in 31 prefectures are now expected to experience a seismic intensity of 6 or higher or tsunami heights of 3 meters or more. The estimated economic damage has also risen from ¥214 trillion JPY (about $1.43 trillion USD) to a maximum of ¥270 trillion ($1.81 trillion).

On a positive note, the report also indicates that disaster preparedness measures have improved in Japan. The seismic retrofitting rate of residential buildings is now about 90%. This is an 11-point increase since 2008. The coastal levee construction rate has also risen to approximately 65%, a 26-point increase since 2014.

Taking these improvements into account, if an earthquake and tsunami similar to the 2014 scenario occur, the experts' report estimates that the death toll would be reduced by about 20%, to around 264,000. The number of destroyed buildings would drop by 17%, to about 2.08 million. However, these reductions still fall short of the 10-year plan set in 2014. It had aimed for an 80% reduction in deaths and a 50% reduction in destroyed buildings.

The latest report also anticipates greater infrastructure damage, as more accurate data suggests a larger tsunami inundation area. The number of households without power is now expected to reach a maximum of 29.5 million, about a 10% increase from the 2024 estimate. The number of evacuees is projected to rise to about 12.3 million, an increase of approximately 30%.

For the first time, the report estimates disaster-related deaths during evacuation, with a maximum of 52,000 deaths. Additionally, a "half-split" scenario — where a large-scale earthquake strikes one half of the Nankai Trough region first, followed by a delayed earthquake in the other half — has been considered for the first time.

1. 1. estimate　見積もり、予測
   Some estimates show a global temperature increase of up to four degrees Celsius.
2. 2. collapse　（建物・組織などの）崩壊、倒壊
   The old hotel is at risk of collapse in the next storm that passes through.
3. 3. evacuate　避難する、（人を安全な場所へ）避難させる
   All of the passengers were evacuated from the ferry before the boat went down.
4. 4. retrofit　（既存の建物・装置などを）改修する、新しい装置を後付けする
   The museum needs to be retrofitted if it is going to survive the next earthquake.
5. 5. infrastructure　インフラ（橋、道路・電力・上下水道など）
   The government should spend more on repairing key infrastructure, such as bridges.

1. 1. How have estimates of damage and loss of life changed since the last report in 2014?
2. 2. How has better accuracy of the data affected the estimates?
3. 3. What is the “half-split scenario?”
4. 4. The article states that building retrofits are at 90%, yet 2.35 million buildings are still predicted to be destroyed. What do you think should be done?
5. 5. What have you done to prepare for the next earthquake? What do you need to do?

南海トラフ巨大地震への対策を検討する政府中央防災会議の有識者会議（主査・福和伸夫名古屋大名誉教授）は3月31日、被害が最大となるケースで死者約29万8000人、全壊建物約235万棟とする最新の被害想定を公表した。平成26年に策定した対策推進基本計画では死者約33万2000人、全壊建物約250万4000棟としていた。政府は有識者会議の報告を受け、基本計画を改定する。

報告書は最大級の被害が起きるケースを想定。原因別の死者は建物倒壊が約7万3000人、建物火災が約9000人。津波ではすぐ避難する人を20％と仮定した場合で約21万5000人とした。70％になれば約9万4000人に抑えられるとした。原因別の全壊建物は、地震約127万9000棟▽津波約18万8000棟▽火災約76万7000棟－としている。

見直しでは以前より地盤や地形のデータが高精度化され、震度分布や津波浸水範囲が拡大。津波浸水深30センチ以上の面積が3割増えた。震度6弱以上または津波高3メートル以上となる市町村は31都府県764市町村に及ぶ。経済被害額は214兆円から増え、最大270兆円と試算した。

一方、住宅耐震化率が約90％（平成20年比11ポイント増）、海岸堤防の整備率が約65％（26年度比26ポイント増）となるなど対策も進んだ。

これらを踏まえ、26年の基本計画と比較可能な地震津波を想定した場合、死者は約26万4000人で約20％、全壊建物は208万4000棟で約17％それぞれ削減。10年間に死者8割減、全壊建物5割減とする基本計画での目標には及ばなかった。

インフラ被害は津波浸水域の拡大などで増加。24年の被害想定と比べ、停電軒数は最大約2950万軒で約1割増、避難者数も最大約1230万人で約3割増だった。

避難生活中に死亡する災害関連死者数を初めて試算し、最大5万2000人とした。また、南海トラフ想定震源域の東半分と西半分のどちらかで先に大規模地震が起き、もう片側で時間差を空けて地震が起きた場合の「半割れ」被害も初めて想定した。