M6.6 quake hits southwest Japan, small tsunami observed

TOKYO – An earthquake with a preliminary magnitude of 6.6 struck southwestern Japan on Monday, with no immediate reports of injuries or damage and a small tsunami observed in parts of Miyazaki and Kochi prefectures, the weather agency said.

Japan’s meteorological agency issued its second-ever Nankai Trough Extra Information, after doing so last August, and also opened an investigation into whether there was an increased risk of a megaquake. The agency later concluded that the earthquake was not considered to have increased the risk.

The earthquake at At 9:19 p.m., a lower 5 on the Japanese seismic scale measured 7 in Miyazaki, Shintomi and Takanabe in Miyazaki prefecture, the agency said. The earthquake occurred in the Hyuga Nada Sea off the coast of the prefecture at a depth of approximately 36 kilometers.

The size was revised twice, initially estimated at 6.4, then updated to 6.9 and later adjusted to 6.6.

Tsunamis with heights of about 20 centimeters were observed in part of Miyazaki Prefecture and 10 cm in some areas of Kochi Prefecture. The agency has since lifted all tsunami advisories.

Some sections of the Kyushu Shinkansen bullet train line were temporarily suspended due to the storm, the train operator said.

No abnormalities were detected at the Ikata nuclear power plant in Ehime Prefecture and the Sendai nuclear power plant in Kagoshima Prefecture, according to the operators.

The quake was also felt in large areas of western Japan.

The agency said the storm occurred at the western edge of the hypothesized epicenter of an earthquake in the Nankai Trough.

Megaquakes in the Nankai Trough, which runs along the Pacific coast, occur every 100 to 150 years, the most recent being the 1944 Tonankai and 1946 Nankai earthquakes, which together affected a wide area from central to southwestern Japan.

A weather bureau official speaks at a news conference in Tokyo on Jan. 13, 2025. (Kyodo)

A magnitude 8 to 9 earthquake has a 70 to 80 percent chance of occurring within 30 years, according to a government estimate.

The central government issued a Nankai Trough mega-quake advisory on August 8 following a M7.1 quake that occurred in the Hyuga Nada Sea, the first since the system’s implementation in 2017, urging caution regarding the increased risk of strong shaking over a large area.

While the government called for increased disaster preparedness as opposed to evacuation in anticipation of a megaquake, some municipalities in the region set up evacuation centers and advised elderly residents in particular to be safe.

Related Coverage:

Japan braces for heavy snow, possible traffic disruption

M6.8 quake shakes China’s Tibet region with nearly 130 dead