October 9, 2025
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On September 17, an earthquake with magnitude M4.7 occurred in the Tokara Islands (in the ocean near Suwanosejima Island) and recorded maximum seismic intensity 5 Lower in Toshima Village, Kagoshima Prefecture.
There was no remarkable activity.
There was no remarkable activity.
* On September 5, an M4.4 earthquake occurred in the southern Ibaraki Prefecture at a depth of approximately 45 km. The earthquake occurred at the boundary between the Philippine Sea Plate and the continental plate. It was associated with reverse faulting, with a pressure axis oriented in an NW-SE direction.
* On September 8, an M4.5 earthquake occurred in the Noto region, Ishikawa Prefecture, at a depth of approximately 15 km. This earthquake occurred within the activity zone of the M7.6 Noto Peninsula earthquakes that occurred in the same region on January 1, 2024.
There was no remarkable activity.
* On September 1, an M4.0 earthquake occurred in the ocean near Tokara Islands (near Kodakarajima Island). Seismicity near its epicenter became active since June 21, culminating in a magnitude 5.5 earthquake on July 3. By July 7, a total of 8 earthquakes with maximum seismic intensity 5 Lower or greater were recorded. However, since July 20, both seismic activity and the number of large earthquakes has been decreasing. These events have occurred within the continental plate.
GNSS observations recorded horizontal movements in Takarajima, Kodakarajima, and Akusekijima Islands during the recent surge in seismic activity; however, these have since decreased.
Furthermore, in September alone, 42 earthquakes of an M1 or higher were recorded. This seismic activity level (several daily earthquakes of an M1 or greater) suggests that this trend may continue for the time being.
Additionally, the area around this seismic activity zone has previously experienced extended periods of seismicity lasting several months. For example, during the 2021 activity, seismicity began in April and continued for several months before declining. After a few more months, it became active again in December.
* On September 13, an M4.5 earthquake occurred in the ocean near Tokara Islands (near Kuchinoshima and Nakanoshima Islands). This event occurred within the continental plate.
* On September 17 at 21:55, an M4.7 earthquake occurred in the ocean near Tokara Islands (near Suwanosejima Island). Shortly after, at 22:00 on the same day, an M4.8 earthquake occurred near the epicenter of the first quake. The focal mechanisms of these earthquakes indicate a tension axis oriented in an NNW-SSE direction, suggesting that they occurred within the continental plate.
Seismic activity has increased near the epicenters of these earthquakes in July. By the end of September, a total of 185 earthquakes with maximum seismic intensity 1 or greater had been recorded (September alone recorded 118 events, 1 with seismic intensity 5, and 3 with seismic intensity 4).
GNSS observations have detected slight crustal deformations in Suwanosejima Island following the M4.7 and M4.8 earthquakes that occurred on September 17.
This seismic activity may be related to volcanic activity on Suwanosejima Island.
* There has been observed no unusual change which indicates that the possibility of occurrence of a great earthquake along the Nankai Trough has relatively risen compared to the normal time.
Note: GNSS is a general name of a satellite positioning system such as GPS.
October 9, 2025
Earthquake Research Committee
The numbers of earthquakes by magnitude (M) in and around Japan in September 2025 are as follows.
(Reference)
The following events for the period from September 2024 until the end of August 2025 have been listed as "Major Seismic Activities" in the monthly "Evaluation of Seismic Activities."
| – In the Ocean Area near Torishima Island | M5.8 on September 24 (Depth of approximately 10 km) |
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| – Offshore west of Ishikawa Prefecture# | M6.6 on November 26, 2024 (Depth of approximately 10 km) |
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| – Under the Hyuganada Sea | M6.6 on January 13, 2025 (Depth of approximately 35 km) |
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| – In Aizu, Fukushima Prefecture | M5.2 on January 23, 2025 (Depth of approximately 5 km) |
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| – In northern Nagano Prefecture | M5.1 on April 18, 2025 (Depth of approximately 15 km) |
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| – 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) |
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| – 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 | ||
# Seismic activity of the 2024 Noto Peninsula Earthquakes
There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
– "On September 8, an M4.5 earthquake occurred in the Noto region, Ishikawa Prefecture, at a depth of approximately 15 km. This earthquake occurred within the activity zone of the M7.6 Noto Peninsula earthquakes that occurred in the same region on January 1, 2024.":
Seismic activity in the Noto region of Ishikawa Prefecture has been on the rise since December 2020. Initially, only relatively small earthquakes were recorded; however, this changed with the occurrence of several large events, including an M6.5 earthquake in May 2023, an M7.6 earthquake in January 2024, and an M6.6 earthquake in November 2024. In the activity area of the M7.6 earthquake, seismic activity has been decreasing, yet 8 earthquakes with seismic intensity 1 or greater were recorded in September, suggesting that seismic activity is still ongoing.
GNSS observations indicate that crustal deformation, including horizontal deformation exceeding 2 cm over a 21-month period, was still detected in a broad area centered on the Noto Peninsula and extending into Toyama, Niigata, and Nagano prefectures following the M7.6 earthquake. This deformation is believed to be an after-slip effect.
Along the Sea of Japan, earthquakes with an M6.0 or greater have been recorded several years after major seismic events, such as the 1983 Sea of Japan earthquake (M7.7). Moreover, the Noto Peninsula has experienced large, damaging earthquakes of magnitude M6.0 or greater, including the Noto Hanto Earthquake in 2007 (M6.9), which occurred prior to the current series of seismic activities that began in December 2020.
– According to the GNSS observation, the crustal deformation different from the ordinary trend in the area extending from the western Shizuoka to the eastern Aichi Prefectures has been observed since early 2022. This change is believed to result from long-term slow slip occurring deep within the boundary between the Philippine Sea Plate and the continental plate extending from the Atsumi Peninsula to Lake Hamana. The slip center is gradually shifting from the Atsumi Peninsula toward Lake Hamana.
– GNSS observations have detected crustal deformation around central Shikoku, attributed to long-term slow slip occurring deep within the boundary between the Philippine Sea Plate and the continental plate since approximately spring 2019. This deformation differs from previous trends and appears to have converged.
– According to GNSS observations, crustal deformation different from the previous trend has been observed in the southern Kii Peninsula since the beginning of 2020. This seems to be caused by long-term slow slip at the deep boundary between the Philippine Sea Plate and the continental plate around the southern Kii Peninsula. This deformation has been stagnant since the fall of 2024, but has been observed again since early 2025.
– Starting in February 2025, a series of tremors was recorded in northern Yamaguchi Prefecture, but it has currently decreased. Additionally, GNSS observations detected slight crustal movements associated with these seismic activities; however, these deformations seem to have declined.
– GNSS observations indicated that afterslip from crustal deformation was recorded at the Miyazaki observation point for approximately eight months following the M6.6 earthquake under the Hyuganada Sea on January 13, 2025, including a horizontal shift of about 4 cm in the southeast direction.
– "There has been observed no unusual change which indicates
that the possibility of occurrence of a great earthquake along the Nankai
Trough has relatively risen compared to the normal time.":
(This evaluation is in agreement with the views presented at the regular
meeting of the Nankai Trough Earthquake Assessment Committee on October
7 (reference below).)
(Reference)
Recent Crustal Activity Around the Nankai Trough (Seismological and Volcanological Department, Japan Meteorological Agency, October 7, 2025)
"In the present, there has been observed no unusual change which indicates that the possibility of occurrence of great earthquakes along the Nankai Trough has relatively risen compared to the normal time. (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: