Japan’s government panel has sharply revised its megaquake risk estimate, now placing the chance of a magnitude‑8 to 9 earthquake along the Nankai Trough at 60 percent to 94.5 percent over the next 30 years. This adjustment underscores growing concerns about seismic hazards and calls for intensified preparedness across the country.
The Earthquake Research Committee issued its revised estimate in a report on Friday. Previously, the probability had been stated more simply as “around 80 percent.” The update expands the range due to doubts about past data reliability and new insights into tectonic strain accumulation.
Naoshi Hirata, an honorary professor at the University of Tokyo and chair of the panel, stressed that “an actual earthquake is an unpredictable natural phenomenon.” He added that the shock might occur within a year or might lie beyond the 30‑year window. The Nankai Trough lies off Japan’s Pacific coast and has produced major quakes historically every 90 to 150 years. The last significant event is thought to have occurred in 1946, with an estimated magnitude of 8.
In earlier risk assessments, the government also computed a lower bound probability ranging between 20 percent and 50 percent. The committee now recommends emphasizing the higher probability to alert residents and authorities. In a separate projection released in March, the government estimated that a magnitude‑9 quake in the Nankai region could cause up to 298,000 fatalities. The projected economic damage would reach as high as ¥292 trillion.
The revision reflects mounting uncertainties in earlier assumptions. For example, ground uplift data from Muroto Port in Kochi Prefecture has come under scrutiny. In addition, researchers now question the consistency of plate strain accumulation over time. The committee said it could not determine which probability estimate is definitively superior. Yet it urged communicating the higher end of risk to boost preparedness among regional governments, industries, and communities.
Leaders and agencies across Japan may need to revise disaster response plans, infrastructure standards, and emergency drills. Coastal municipalities in prefectures such as Kochi, Shizuoka, and Tokushima might feel particular urgency to act.
Economically, this updated megaquake risk could affect insurance models, real estate planning, and public investment in resilience. Companies in construction, utilities, and disaster services may see increased demand. Politically, the change may intensify pressure on national and local authorities to allocate more budget for seismic retrofitting and early warning systems. Socially, it may foster greater public demand for stronger building codes and evacuation readiness.
Looking ahead, the committee is likely to monitor new geophysical data, refine models of plate movement, and issue further updates as evidence evolves. National and local governments must use this window to strengthen preparedness. Japan now faces the challenge of translating elevated megaquake risk estimates into concrete actions before disaster strikes.
