No Tsunami as Strong Earthquake Strikes Western Japan; Blocked Roads, Burst Water Pipes Reported (Update 1)

The Yomiuri Shimbun

6:50 JST, April 18, 2024 (updated at 17:15 JST)

A powerful earthquake with an estimated magnitude of 6.6 struck western Japan late Wednesday night, primarily in the Shikoku region. No tsunami were reported.

The quake occurred at 11:14 p.m. Wednesday, registering a lower 6 on the Japanese seismic intensity scale of 7 in Ainancho, Ehime Prefecture, and in Sukumo, Kochi Prefecture, both in western Shikoku.

The quake’s epicenter was at the Bungo Suido channel between Ehime Prefecture in the Shikoku region and Oita Prefecture in the Kyushu region. It was located at a depth of 39 kilometers.

This is the first time that an earthquake registering lower 6 or stronger has occurred in the Shikoku region since the current seismic intensity scale was introduced in 1996.

“This earthquake occurred within the predicted epicenter area for a Nankai Trough earthquake, but it seems unlikely that the possibility of a Nankai Trough earthquake has suddenly increased,” a Japan Meteorological Agency official said at a press conference early Thursday morning.

Agency officials said Wednesday’s earthquake occurred inside a plate and the mechanism was different from that of a Nankai Trough earthquake, which is expected to occur at the boundary between plates.

They also said the earthquake did not reach magnitude 6.8, the level required for launching research into the possible occurrence of a large-scale earthquake. The energy level of Wednesday’s earthquake is believed to be about half that of the anticipated Nankai Trough quake, they said.

Ten people were injured – seven in Ehime Prefecture, one in Kochi Prefecture, and two in Oita Prefecture, as a result of such incidents as falling down. The injuries were not life-threating.

In Ozu, Ehime Prefecture, where the quake measured lower 5, rocks fell on National Route 197 in the Hijikawacho district, causing the road to be closed.

In Yusuharacho, Kochi Prefecture, 10 people in five households in the Matsudani area were temporarily isolated as a town road was blocked by fallen rocks and trees. The earthquake measured 4 on the seismic scale in Yusuharacho.

Water was cut off in the Hijikawa district of Ozu. In Ehime Prefecture, there were numerous reports of burst water pipes and water leaks at residences in Ainancho and Uwajima.

According to Shikoku Railway Co. (JR Shikoku), services on some sections in Ehime and Kochi prefectures were suspended or canceled Thursday.

At Shikoku Electric Power Co.’s Ikata Nuclear Power Plant in Ikatacho, Ehime Prefecture, where a seismic intensity of 4 was recorded, monitoring stations measuring the radiation levels in surrounding areas showed no abnormalities, the Nuclear Regulation Authority said.

According to Shikoku Electric Power Co., the generator output of the No. 3 reactor decreased by about 2 percent, but this did not affect the operation of the reactor.

The Nuclear Regulation Authority also said no abnormalities had been confirmed at other facilities, including Kyushu Electric Power Co.’s Genkai Nuclear Power Plant in Saga Prefecture and the company’s Sendai Nuclear Power Plant in Kagoshima Prefecture.

The Japan Meteorological Agency called on the public to be alert for earthquakes with a maximum seismic intensity of around lower 6 for about a week. It also urged caution as it is expected to rain in Ehime and Kochi prefectures from Saturday to Sunday.

“In areas where the tremors were strong, there is an increased risk of collapsed houses and landslides. Please pay close attention to rainfall,” the agency said.

The government set up a taskforce under the crisis management center of the Prime Minister’s Office late Wednesday night to take necessary measures. Prime Minister Fumio Kishida issued instructions to assess the damage caused by the earthquake as soon as possible; make thorough efforts to save lives and rescue disaster victims in close coordination with local governments; and provide timely and accurate information to the public regarding evacuation, damage and other matters.