Nankai Trough Megaquake Could Damage ¥1,466 Trillion in Economic Losses, Engineers Warn
A megaquake along the Nankai Trough could lead to ¥1,466 trillion (approximately $10 trillion) in economic damages over a 22-year recovery period, according to a revised estimate by the Japan Society of Civil Engineers released on June 11, 2025. This figure reflects a 4% increase from the 2018 estimate of ¥1,410 trillion, attributed to updated economic data and expanded flood risk assessments.
The Nankai Trough, a 700-kilometer subduction zone extending from Suruga Bay off Shizuoka Prefecture to the Hyuganada Sea off Miyazaki Prefecture, has an 80% probability of producing a magnitude 8 to 9 earthquake within the next 30 years, as reported by the government’s Earthquake Research Committee. The engineers’ estimate includes ¥225 trillion in direct damage to infrastructure and buildings, with an additional ¥1,241 trillion in long-term economic losses due to disruptions in productivity, manufacturing, and transportation networks.
The Japan Society of Civil Engineers suggests that investing ¥58 trillion in disaster prevention measures, such as reinforcing roads, levees, and seawalls, could reduce economic losses by 31%. These measures also include seismic retrofitting of buildings and enhancing utility infrastructure resilience. The report emphasizes the urgency of these investments to lessen the long-term economic impact.
Separately, the engineers estimate that a magnitude-7 earthquake directly hitting the Tokyo area could cause ¥1,110 trillion in economic damage, a 10% increase from the 2024 estimate of ¥1,001 trillion, driven by rising costs and economic factors. Investments exceeding ¥21 trillion in disaster prevention could reduce Tokyo’s losses by approximately ¥410 trillion.
Historically, the Nankai Trough has triggered major earthquakes every 100 to 150 years, with significant events in 1944 (magnitude 7.9) and 1946 (magnitude 8.0). A magnitude-9 quake could generate tsunamis up to 30 meters high, impacting 764 municipalities across regions from Fukushima to Okinawa. A March 2025 government report projected up to 298,000 fatalities and ¥270.3 trillion in economic damage in a worst-case scenario, with tsunamis accounting for 215,000 deaths.
Japan’s 2014 Basic Plan for National Resilience aimed to reduce earthquake-related fatalities by 80% and building collapses by 50% within a decade, but current projections show only a 20% reduction in deaths. Discussions for a 2026–2030 national resilience plan and a dedicated disaster prevention agency are underway to address these gaps.
The Japan Society of Civil Engineers calls for immediate action to bolster disaster preparedness, highlighting the severe economic and societal risks posed by a Nankai Trough megaquake.
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