September 9, 2025
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
* On August 2, a magnitude (M) M5.4 earthquake occurred offshore of Kushiro at a depth of approximately 15 km. Its focal mechanism shows a pressure axis oriented in an NW-SE direction.
* On August 12, an M5.5 earthquake occurred offshore of Kushiro at a depth of approximately 20 km. This earthquake occurred within the continental plate and was associated with reverse faulting, with the pressure axis oriented in an NNW-SSE direction. Seismic activity persists near the epicenter where an M6.0 earthquake previously occurred on May 31.
* On August 19, an M5.1 earthquake occurred in the eastern Oshima region at a depth of approximately 130 km. This earthquake occurred within the Pacific Plate (at the top surface of the double seismic zone) and was associated with the pressure axis aligned with the subducting direction of the Pacific Plate.
* On August 22, an M5.6 earthquake occurred offshore of Miyagi Prefecture at a depth of approximately 45 km. It was associated with reverse faulting, with the pressure axis oriented in an NW-SE direction. On August 30, an M5.8 earthquake occurred approximately 30 km south of the epicenter, at a depth of about 40 km, also involving reverse faulting with a pressure axis oriented in an E-W direction. Both events occurred at the boundary between the Pacific and continental plates.
* On August 14, an M5.2 earthquake occurred offshore of Ibaraki Prefecture at a depth of approximately 45 km. This earthquake occurred within the Pacific plate and was associated with the pressure axis oriented in a NW-SE direction.
There was no remarkable activity.
* On August 7, an M4.8 earthquake occurred in western Oita Prefecture at a very shallow depth. This was an intraplate earthquake associated with strike-slip faulting, with the tension axis oriented in an N-S direction.
* On August 7, an M5.6 earthquake occurred in the ocean near Yonagunijima Island at a depth of approximately 110 km. This earthquake occurred within the Philippine Sea Plate and was associated with a tension axis oriented in an NE-SW direction.
* On August 17, an M5.7 earthquake occurred under the Hyuganada Sea at a depth of approximately 30 km. This earthquake occurred within the Philippine Sea Plate and was associated with a tension axis oriented in an NW-SE 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.
Note: GNSS is a general name of a satellite positioning system such as GPS.
September 9, 2025
Earthquake Research Committee
The numbers of earthquakes by magnitude (M) in and around Japan in August 2025 are as follows.
(Reference)
The following events for the period from August 2024 until the end of July 2025 have been listed as "Major Seismic Activities" in the monthly "Evaluation of Seismic Activities."
| – Under the Hyuganada Sea | M7.1 on August 8, 2024 (Depth of approximately 30 km) |
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| – In western Kanagawa Prefecture | M5.3 on August 9, 2024 (Depth of approximately 15 km) |
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| – In the northern Ibaraki Prefecture | M5.1 on August 19, 2024 (Depth of approximately 10 km) |
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| – 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.
– 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 6 earthquakes with seismic intensity 1 or greater were recorded in July, suggesting that seismic activity is still ongoing.
GNSS observations indicate that crustal deformation, including horizontal deformation exceeding 2 cm over a 19-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 indicate that since spring 2019, central Shikoku has experienced crustal deformations that deviate from previous trends. 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 surrounding central Shikoku. Recently, these crustal deformations have ceased.
– 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 were recorded in northern Yamaguchi Prefecture. This activity has been declining since June, but it saw a slight resurgence in August. Additionally, GNSS observations have detected slight crustal deformations associated with this seismic activity.
– GNSS observations indicated that afterslip from crustal deformation was recorded at the Miyazaki observation point for approximately seven months following the M6.6 earthquake under the Hyuganada Sea on January 13, 2025, including a horizontal shift of about 3 cm in the southeast direction.
– Intense seismic activity in the ocean near Tokara Islands (near Kodakarajima Island) began on June 21, 2025. By July 7, a total of 8 earthquakes with maximum seismic intensity 5 Lower or greater were recorded, including an M5.5 earthquake (maximum seismic intensity 6 Lower) on July 3. Since July 20, seismic activity has been decreasing, along with the number of large earthquakes. The largest earthquake in August was an M4.4 event (maximum seismic intensity 3) on August 9. These seismic events occurred within the continental plate.
GNSS observations recorded horizontal movements on Takarajima, Kodakarajima, and Akusekijima islands during the recent surge in seismic activity; however, these have since decreased.
Furthermore, in August alone, 66 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.
– Intense seismic activity in the ocean near Tokara Islands (near Suwanosejima Island) began in July. By the end of August, a total of 67 earthquakes with seismic intensity 1 or greater were recorded (August alone had 34 events, 3 with maximum seismic intensity 3). The largest earthquake in August was an M3.4 event (maximum seismic intensity 3) at 23:11 on August 27. These seismic events occurred within the continental plate.
– "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 September
5 (reference below).)
(Reference)
Recent Crustal Activity Around the Nankai Trough (Seismological and Volcanological Department, Japan Meteorological Agency, September 5, 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: