Chance of M8-M9 Nankai Trough Earthquake Hitting Japan in 30 Yrs Raised to ‘Around 80％’; Head of Earthquake Panel Urges Public to ‘Stay Alert’

The Yomiuri Shimbun

13:10 JST, January 16, 2025

The probability of a magnitude-8 to 9 earthquake occurring in the Nankai Trough in the next 30 years has been raised from “70% to 80%” to “around 80%,” according to a report released Wednesday by the government’s Earthquake Research Committee.

For earthquakes that are expected to occur periodically, the likelihood of an earthquake increases as more time passes without an occurrence, according to the committee.

A Nankai Trough earthquake has been predicted to occur about once every 100 years, and the probability increases every year that passes since the last one.

However, there have been no unusual phenomena observed in the Nankai Trough area. As a result, the probability of an earthquake occurring there within the next 10 years was unchanged from the previous year at “around 30%,” and the probability of one occurring in the next 20 years was also unchanged at “around 60%.”

University of Tokyo Prof. Emeritus Naoshi Hirata, who heads the committee, said: “The figures [of 70% and 80%] mean that an earthquake can occur at any time, so the things that need to be prepared remain the same. I want the public to stay alert.”

The report also included the committee’s findings on the probability of earthquakes along active inland faults. Such faults have a relatively long interval between quakes, so the probability of one occurring along those faults is less than that of the Nankai Trough.

The quake that occurred along the fault that caused the 1995 Great Hanshin Earthquake was calculated to have had a 0.02% to 8% chance of occurring within 30 years before it struck.

According to the report, there are eight active faults with quake probabilities exceeding 8%, including the Itoigawa-Shizuoka-Kozosen fault zone and the Hinagu fault zone, which is thought to be related to the 2016 Kumamoto Earthquake.