Earthquake Offshore East of Aomori Prefecture on December 8
On December 8, 2025, at 23:15, an M7.5 earthquake occurred offshore east of Aomori Prefecture at a depth of 54 km. It registered a seismic intensity 6 Upper in Hachinohe City, Aomori Prefecture, and seismic intensities between 6 Lower and 1 were recorded from Hokkaido to the Kinki region. Additionally, a long-period ground motion class 3 was registered in Sanpachi-Kamikita, Aomori Prefecture, whereas long-period ground motion between class 2 and 1 were recorded from Hokkaido to the Kanto region, including Niigata Prefecture. The earthquake also triggered a tsunami, primarily affecting the Pacific coast from Hokkaido to the Tohoku region. Tsunami heights of 0.7 m (Note 2) were recorded at Kuji Port in Iwate Prefecture (Note 1) and 0.5 m (Note 2) at Urakawa in Hokkaido (Note 1).
At 23:15:24.0, just 4.1 seconds after detecting the first seismic waves, the Japan Meteorological Agency issued an Earthquake Early Warning (Warnings). Later, at 23:17 on the same day, it issued a Tsunami Advisory for the central Pacific coast of Hokkaido, as well as the Pacific coasts of Aomori and Iwate Prefectures. By 23:23, this advisory was upgraded to a Tsunami Warning for those areas. The next day, December 9th, the Tsunami Warning was downgraded to an advisory at 02:45, and at 06:20, the Tsunami Advisory was lifted.
At 02:00 on December 9th, the Japan Meteorological Agency issued an "Off the Coast of Hokkaido and Sanriku Subsequent Earthquake Advisory." This decision was based on a detailed examination of the earthquake's epicenter and magnitude, which met the criteria for issuing such advisory information urging caution for subsequent earthquakes, as outlined in the national basic plan and regulations.
The focal mechanism involved reverse faulting, with the pressure axis oriented in the WNW-ESE direction (CMT solution) and occurred at the boundary between the continental and Pacific Plates.
Between December 8 and 11:00 on December 9, 14 earthquakes with seismic intensity 1 or greater were recorded near the earthquake's epicenter (1 event with seismic intensity 6 Upper, 1 event with seismic intensity 4, 2 events with seismic intensity 3, 5 events with seismic intensity 2, and 5 events with seismic intensity 1) (Note 3).
The quake caused damage, including 35 injuries (as of 12:00 PM on December 9, 2025, according to the Fire and Disaster Management Agency, Ministry of Internal Affairs and Communications).
A review of seismic activity since October 1997 reveals that earthquakes of M6.0 or greater have often occurred near the epicenter (Area c). Notably, an M6.1 quake that occurred on May 24, 2012 (maximum seismic intensity 5 Upper), which caused damage in Aomori Prefecture, partially damaged educational facilities (such as broken glass) at 10 locations (according to the Fire and Disaster Management Agency, Ministry of Internal Affairs and Communications).
(Note 1) Observation facilities of Ports and Harbours Bureau, the Ministry of Land, Infrastructure, Transport, Tourism.
(Note 2) Observation values may change after further review.
(Note 3) The number of earthquakes with a seismic intensity 1 or higher may change based on future investigations.
Japan Meteorological Agency
[Evaluation of Earthquake Offshore East of Aomori Prefecture on December 8, 2025 (December 9, 2025)]