The Sankei Shimbun 
Disaster response training conducted by the Osaka Prefectural Police in preparation for a Nankai Trough mega earthquake on January 17, 2023, Sakai City. (©Sankei by Shohei Fujiki)
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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.
Worst-Case Scenario
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.
Better Data
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.
Expanded Areas of Impact
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.
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Author: The Sankei Shimbun
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