June 25, 2026
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On June 25, at 7:30, a magnitude (M) 7.2 earthquake (provisional) occurred offshore of Iwate Prefecture at a depth of approximately 45 km. The earthquake recorded a maximum seismic intensity 6 Upper in Aomori Prefecture. It caused damage and injuries. Furthermore, a long-period ground motion of class 2 was recorded from Hokkaido to the Tohoku region.
The event caused slight fluctuations in sea level. These were recorded at the Kuji Port observation station (Port and Harbor Bureau) in Iwate Prefecture.
* The focal mechanism involved reverse faulting, with the pressure axis oriented in the WNW-ESE direction. The focal mechanism and hypocenter depth suggest that the earthquake occurred at the boundary between the continental and Pacific Plates.
* GNSS observations revealed that the earthquake was accompanied by crustal deformation from northern Iwate Prefecture to Aomori Prefecture. For instance, a east-south-east shift of approximately 2cm was recorded at the Hachinohe observation point in Aomori Prefecture.
* As of 13:00 on June 25, 9 earthquakes with maximum seismic intensity 1 or greater had been recorded, and the seismic activity continues. The M7.2 source fault, estimated from GNSS observations and seismic wave analysis, is extending around the rupture initiation point.
* To the southeast of the seismic activity zone lies the seismic activity of the earthquake offshore of Sanriku on November 9, 2025 (M6.9), and on April 20, 2026 (M7.7). To the east of these series of seismic activity zones, tremor activity has continued intermittently since the earthquake offshore of Sanriku on November 4, 2025 (M5.3).
GNSS observations indicate that approximately 2 months following the earthquake offshore of Sanriku on April 20 (M7.7), horizontal displacements, attributed to post-seismic deformations, were primarily recorded in Iwate Prefecture. At the Taro-A observation point in Iwate Prefecture, an eastward deformation of approximately 5 cm was recorded. The afterslip, inferred from these post-seismic deformations, is believed to continue west of the seismic activity zone of the earthquake offshore of Sanriku on April 20 (M7.7) and east of the seismic activity zone of this earthquake. Furthermore, the analysis of repeating earthquakes indicates the ongoing occurrence of aseismic slip events in these regions.
* This seismic activity is occurring near the epicenter of the largest aftershock (M7.2 on January 7, 1995) on the western edge of the source region of the "1994 Sanriku-haruka-oki Earthquake" (M7.6). Furthermore, this seismic activity zone and the series of seismic activity zones from offshore of Sanriku to offshore of Iwate Prefecture since November 2025, the focal area of the "1994 Sanriku-haruka-oki Earthquake," and the seismic activity zone of the earthquake offshore east of Aomori Prefecture (M7.5 on December 8, 2025), are located respectively in the southern, central, and northern parts of the focal area of the "1968 Tokachi-oki Earthquake" (M7.9).
* This earthquake occurred in the area anticipated by the Earthquake Research Committee as likely to experience "slightly smaller interplate earthquakes" (approximately M7.0 to M7.5) in its "Long-Term Evaluation of Seismic Activity Along the Japan Trench" (published February 26, 2019) for "offshore east of Aomori Prefecture and offshore north of Iwate Prefecture regions" and "offshore south of Iwate Prefecture." The probability of such an earthquake occurring within 30 years is classified as Rank III (high probability)(#), this represents the highest probability among subduction-zone earthquakes. Note that the "1994 Sanriku-haruka-oki Earthquake," which occurred in the same area, is categorized as a "slightly smaller interplate earthquake", whereas the 1968 Tokachi-oki Earthquake, also in the same area, is considered as a "large interplate earthquake" (approximately M7.9). Both have a 30-year occurrence probability classified as Rank III (high).
* Based on past general trends, there is a 10-20 percent chance of an earthquake of a similar magnitude occurring following a major earthquake. Therefore, in areas that experienced strong shaking, caution is required for about one week due to the possibility of an earthquake with maximum seismic intensity of approximately 6 Upper. Mainly, earthquakes that cause strong shaking often occur within about 2 to 3 days of the initial shock.
#: The probability of a subduction-zone earthquake occurring within the next 30 years is ranked as follows: Rank III: greater than 26%, Rank II: 3% ~ 26%, Rank I: less than 3%, Rank X: unknown (an immediate earthquake cannot be ruled out).
Note: GNSS refers to a generic term for satellite positioning systems, including GPS.