June 9, 2026
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On May 15, a magnitude (M) 6.4 earthquake occurred offshore of Miyagi Prefecture. The earthquake recorded maximum seismic intensity 5 Lower in Miyagi Prefecture, and a long-period ground motion of class 3 in northern Miyagi Prefecture.
* On May 20, an M5.9 earthquake occurred in the ocean near Okinawa Main Island. The quake recorded maximum seismic intensity 5 Upper in Kagoshima Prefecture. The earthquake caused damage and injuries.
There was no remarkable activity.
* On May 5, an M5.4 earthquake occurred offshore of Sanriku at a depth of approximately 15 km. Its focal mechanism showed a normal fault type with a tensile axis oriented in the E-W direction.
This seismic activity zone was observed close to the focal area of the earthquake offshore of Sanriku (M7.7) on April 20. To the southeast of this M7.7 event lies the earthquake offshore of Sanriku (M6.9) on November 9, 2025. The activity of the earthquake offshore east of Aomori Prefecture (M7.5) on December 8, 2025, was observed north of the above seismic activity zone.
Since the occurrence of an earthquake offshore of Sanriku on November 4, 2025 (M5.3), tremor activity has continued intermittently around the focal area of this seismic activity series. Following the M7.7 event, tremor activity surged to the east of the M7.7 epicenter.
GNSS observations indicate that following the M7.7 earthquake, horizontal deformations believed to result from post-seismic deformation were observed primarily in Iwate Prefecture. At the Taro-A observation point, an eastward shift of approximately 4 cm was recorded over a period of approximately 1 month. The post-seismic slip inferred from the post-seismic deformation is thought to continue on the west side of the activity zone of the M7.7 earthquake. Furthermore, an analysis of repeating earthquakes in the surrounding area suggests that aseismic slip is ongoing.
This seismic activity occurred near the southern edge of the focal area of the "1968 Tokachi-oki Earthquake" (M7.9) and in a region adjacent to the southern side of the focal area of the "1994 Sanriku-haruka-oki Earthquake" (M7.6). Furthermore, 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 in the central and northern parts of the focal area of the "1968 Tokachi-oki Earthquake," respectively.
* On May 14, an M4.8 earthquake occurred in the northern inland of Iwate Prefecture at a depth of approximately 10 km. The focal mechanism involved a reverse fault type with a pressure axis oriented in the ENE-WSW direction. It occurred in the crust.
* On May 15, an M6.4 earthquake occurred offshore of Miyagi Prefecture at a depth of approximately 45 km. The focal mechanism involved a reverse fault type with a pressure axis oriented in the WNW-ESE direction. It occurred at the boundary between the Pacific and continental plates.
GNSS observations revealed that the earthquake was accompanied by crustal deformation. At the Ofunato observation point in Iwate Prefecture, an ESE shift of approximately 2 cm was recorded. Furthermore, approximately 2 weeks after the earthquake, approximately 1 cm of eastward horizontal displacement was recorded at the Kamaishi observation point in Iwate Prefecture.
* On May 15, an M5.8 earthquake occurred in the ocean near Ioto Island. The focal mechanism involved a pressure axis oriented in the WNW-ESE direction.
* On May 2, an M5.8 earthquake occurred in southern Wakayama Prefecture at a depth of approximately 65 km (#1). The focal mechanism revealed a strike-slip fault type with a tension axis oriented in the NE-SW direction. It occurred within the Philippine Sea Plate.
* On May 20, an M5.9 earthquake occurred in the ocean near Okinawa Main Island at a depth of approximately 50 km. The focal mechanism involved a reverse fault type with a pressure axis oriented in the NW-SE direction. It occurred at the boundary between the Philippine Sea Plate and the continental plate.
GNSS observations have revealed no evidence of crustal deformation associated with this earthquake.
* No unusual changes have been recorded that would suggest that the likelihood of a great earthquake occurring along the Nankai Trough has increased compared to the normal background level.
* On June 8, an earthquake with a moment magnitude (Mw) of 7.7 occurred in Mindanao, the Philippines. The focal mechanism revealed a reverse fault type with a pressure axis oriented in the E-W direction. The earthquake triggered a tsunami that was recorded along the Pacific coast from Mie Prefecture to Okinawa Prefecture, as well as in the Izu Islands and Chichijima Island. At Futami in Chichijima Island, a 0.2 m tsunami was recorded (provisional results).
#1: The place name of the epicenter used by the Japan Meteorological Agency in its information release was "Nara Prefecture."
Note: GNSS refers to a generic term for satellite positioning systems, including GPS.
June 9, 2026
Earthquake Research Committee
The numbers of earthquakes by magnitude (M) in and around Japan in May 2026 are as follows.
(Reference)
The following events for the period from May 2025 until the end of April 2026 have been listed as "Major Seismic Activities" in the monthly "Evaluation of Seismic Activities."
| – In the ocean near Tokara Islands | M5.3 on June 30, 2025 | ||
| – In the ocean near Tokara Islands | M5.1 on July 2, 2025 | ||
| – In the ocean near Tokara Islands | M5.6 on July 2, 2025 | ||
| – In the ocean near Tokara Islands | M5.5 on July 3, 2025 (Depth of approximately 10 km) |
||
| – In the ocean near Tokara Islands | M5.4 on July 5, 2025 | ||
| – In the ocean near Tokara Islands | M4.9 on July 6, 2025 | ||
| – In the ocean near Tokara Islands | M5.5 on July 6, 2025 | ||
| – In the ocean near Tokara Islands | M5.1 on July 7, 2025 | ||
| – Offshore east of the Kamchatka Peninsula, Russia | M8.8 on July30, 2025 | ||
| – In the ocean near Tokara Islands | M4.7 on September 17, 2025 | ||
| – Offshore southeast of the Nemuro Peninsula | M5.8 on October 25, 2025 (Depth of approximately 40 km) |
||
| – Offshore of Sanriku | M6.9 on November 9, 2025 (Depth of approximately 15 km) | ||
| – In Aso region, Kumamoto Prefecture | M5.8 on November 25, 2025 (Depth of approximately 10 km) | ||
| – Offshore east of Aomori Prefecture | M7.5 on December 8, 2025 (Depth of approximately 55 km) | ||
| – In eastern Shimane Prefecture | M6.4 on January 6, 2026 (Depth of approximately 10 km) | ||
| – In southern Ibaraki Prefecture | M5.0 on April 1, 2026 (Depth of approximately 50 km) | ||
| – In northern Nagano Prefecture | M5.0 on April 18, 2026 (Depth of approximately 10 km) | ||
| – In northern Nagano Prefecture | M5.1 on April 18, 2026 (Depth of approximately 10 km) | ||
| – Offshore of Sanriku | M7.7 on April 20, 2026 (Depth of approximately 20 km) | ||
| – In the southern Tokachi region | M6.2 on April 27, 2026 (Depth of approximately 85 km) | ||
There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
– GNSS observations suggest that the crustal deformation differs from the normal trend in the area stretching from the western Shizuoka to the eastern Aichi Prefectures, a phenomenon observed since early 2022. This change is believed to be the result of a long-term slow slip occurring deep within the boundary between the Philippine Sea Plate and the continental plate, which extends from the Atsumi Peninsula to Lake Hamana. The slip center is gradually shifting from the Atsumi Peninsula towards Lake Hamana.
– From May 2 to May 23, deep low-frequency earthquakes (tremor activity) were recorded near the boundary between the Philippine Sea Plate and the continental plate in western Shikoku. Strain and tilt data suggest that the slight crustal deformations recorded in the area were almost synchronized with the deep low-frequency earthquakes (tremors). It is believed that this phenomenon resulted from a short-term slow slip event occurring deep within the boundary between the two plates.
– Seismic activity surged in the ocean near Iriomotejima Island from mid-April. In May, 17 earthquakes with seismic intensity 1 or greater were recorded. These earthquakes occurred within the crust of the continental plate's crust.
– "No unusual changes have been recorded that would suggest
that the likelihood of a great earthquake occurring along the Nankai Trough
has increased compared to the normal background level.":
(This evaluation corroborates the views presented at the regular meeting
of the Nankai Trough Earthquake Assessment Committee on June 5 (reference
below).)
(Reference)
Recent Crustal Activity Around the Nankai Trough (Seismological and Volcanological Department, Japan Meteorological Agency, June 5, 2026)
"Currently, no unusual change has been observed there, which indicates that the possibility of occurrence of great earthquakes along the Nankai Trough has relatively risen compared to the normal background level (Excerpted)."
Reference 1
Earthquakes that are described in the "Evaluation of Seismic Activity" (Monthly Report of Seismic Activity in Japan) have the following features.
Reference 2
Information that is described in the "Supplementary Information to the Evaluation" includes: