May 13, 2025
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On April 18, a magnitude (M) 5.1 earthquake occurred at a depth of approximately 15 km in northern Nagano Prefecture. The quake registered a maximum seismic intensity 5 Lower and resulted in damage and injuries in Nagano Prefecture.
* On April 5, an M4.1 earthquake occurred at a depth of approximately 10 km offshore southwest of Hokkaido. It occurred within the crust of a continental plate and involved a reverse faulting mechanism with an NW-SE pressure axis.
There was no remarkable activity.
* While seismic activity in the activity zone of the M7.6 earthquake has been decreasing, however, the ongoing activity from December 2020 persists. Notably, the occurrence of the M6.6 earthquake (maximum seismic intensity 5 Lower) offshore west of Ishikawa Prefecture on November 26, 2024. Between April 1 and April 30, 12 earthquakes with a seismic intensity 1 or greater have occurred, including 6 events in the seismic activity zone of the M6.6 earthquake offshore west of Ishikawa Prefecture. Throughout March, 12 earthquakes with a seismic intensity 1 or greater also occurred, including 4 events offshore west of Ishikawa Prefecture.
GNSS observations indicate that during the 15 months following the January 1, M7.6 earthquake, a horizontal deformation of about 7 cm in the west-northwest direction was recorded at the Suzu observatory and a horizontal deformation exceeding 1 cm across a wide area centered on the Noto Peninsula affecting Toyama, Niigata, and Nagano prefectures. At the Wajima observatory, a subsidence of about 11 cm was recorded. These crustal deformations are attributed to the effects of afterslip.
Since 2018, the number of earthquakes in the Noto region, Ishikawa Prefecture has been on the rise, with a notable increase in seismic activity starting in December 2020. This includes the M5.4 earthquake in June 2022, the M6.5 earthquake in May 2023, the M7.6 earthquake in January 2024 and, the M6.0, and M6.6 earthquakes in June and November 2024, respectively. From December 1, 2020 to April 30, 2025, a total of 2,690 earthquakes with a seismic intensity 1 or greater were recorded, along with crustal deformation observed around December 2020.
From the current status of seismic activity and crustal deformation, a series of earthquake activity from December 2020 is expected to continue for the time being. There is also a possibility of future earthquakes in the affected area and the surroundings following the M7.6 earthquake; potentially accompanied by strong shaking and tsunamis.
* On April 8, an M4.6 earthquake occurred at a depth of approximately 35 km in western Aichi Prefecture. It occurred within the Philippine Sea Plate and involved strike-slip faulting mechanism with a E-W tension axis.
* On April 18, at 20:19 an M5.1 earthquake occurred at a depth of about 15 km in northern Nagano Prefecture. It occurred within the crust and involved a strike-slip faulting mechanism with an NW-SE pressure axis. At almost the same area as this earthquake, M4.5 and M4.3 earthquakes occurred at 23:39 on March 18 and 19, respectively, at depths of about 15 km and 10 km. These two events also occurred within the crust and involved strike-slip faulting mechanisms with an NW-SE pressure axis. Between April 18 and 30, the region recorded 65 earthquakes with a seismic intensity 1 or greater.
The source area of this earthquake is near the Itoigawa-Shizuoka Tectonic Line Fault Zone and the western margin of the Nagano Basin Fault Zone.
GNSS observations showed no significant crustal deformation related to this earthquake.
There was no remarkable activity.
* On April 2, an M6.1 earthquake occurred at a depth of about 35 km offshore east of the Osumi Peninsula. It occurred at the boundary between the Philippine Sea Plate and the continental plate and involved a reverse faulting mechanism with a WNW-ESE pressure axis.
GNSS observations revealed that this earthquake resulted in approximately 1 cm of crustal deformation in the SSE direction at Kushima-2 station.
* On April 9, an M5.4 earthquake occurred at a depth of 120 km near Yonagunijima Island. It occurred within the Philippine Sea Plate and involved an NNE-SSW tension axis.
* 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.
#1: The place name of the epicenter used by the JMA's information released was "Tsugaru Strait."
Note: GNSS is a general name of a satellite positioning system such as GPS.
May 13, 2025
Earthquake Research Committee
The numbers of earthquakes by magnitude (M) in and around Japan in April 2025 are as follows.
(Reference)
The following events for the period from April 2024 until the end of March 2025 have been listed as "Major Seismic Activities" in the monthly "Evaluation of Seismic Activities."
| – Under the Northern Coast of Iwate Prefecture | M6.0 on April 2, 2024 (Depth of approximately 70 km) |
||
| – Near Taiwan | M7.7 on April 3, 2024 | ||
| – Offshore East of the Osumi Peninsula | M5.1 on April 8, 2024 (Depth of approximately 40 km) |
||
| – Under the Bungosuido Strait | M6.6 on April 17, 2024 (Depth of approximately 40 km) |
||
| – In the Noto Region, Ishikawa Prefecture# | M6.0 on June 3, 2024 (Depth of approximately 15 km) |
||
| – Under the Hyuganada Sea | M7.1 on August 8, 2024 (Depth of approximately 30 km) |
||
| – In western Kanagawa Prefecture | M5.3 on August 9, 2024 (Depth of approximately 15 km) |
||
| – In the northern Ibaraki Prefecture | M5.1 on August 19, 2024 (Depth of approximately 10 km) |
||
| – In the Ocean Area near Torishima Island | M5.8 on September 24 (Depth of approximately 10 km) |
||
| – Offshore west of Ishikawa Prefecture# | M6.6 on November 26, 2024 (Depth of approximately 10 km) |
||
| – Under the Hyuganada Sea | M6.6 on January 13, 2025 (Depth of approximately 35 km) |
||
| – In Aizu, Fukushima Prefecture | M5.2 on January 23, 2025 (Depth of approximately 5 km) |
||
# Seismic activity of the 2024 Noto Peninsula Earthquakes
There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
– 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 phenomenon is considered to be caused by a long-term slow slip around the Atsumi Peninsula at the deeper part of the boundary between the Philippine Sea and the continental plates.
– According to the GNSS observation, the crustal deformation different from the ordinary trend in the central Shikoku has been observed since about spring 2019. This phenomenon is considered to be caused by a long-term slow slip around the central Shikoku at the deeper part of the boundary between the Philippine Sea plate and the continental plate. This crustal deformation was temporally decaying since the fall of 2023 and appeared to continue from the spring of 2024 but slowed again in the fall of 2024.
– 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.
– Since February 2025, tremor activity has been recorded in northern Yamaguchi Prefecture, occurring in the lower crust at depths between 25 to 30 km. No events with a seismic intensity 1 or higher have been observed; the largest recorded earthquake so far is an M1.8. GNSS observations and tilt data indicate that slight crustal deformation may have occurred since the onset of this seismic activity.
– Deep low-frequency earthquakes (tremors) have been observed near the boundary between the Philippine Sea Plate and the continental plate from April 27 to May 1 in the central Kii Peninsula. Strain and tilt data indicate that slight crustal deformation occurred, this was nearly synchronized with these tremors. This activity is thought to be linked to short-term slow slip in the deep part of the boundary between the Philippine Sea Plate and the continental plate.
– According to GNSS observations, crustal deformation, considered to be post-seismic deformation, was observed mainly in the southern part of Miyazaki Prefecture for about five months (until the M6.6 earthquake on January 13, 2024) following the M7.1 earthquake under the Hyuganada Sea on August 8, 2024, including a horizontal displacement of about 5 cm to the southeast at the Miyazaki observatory. In addition, after the M6.6 earthquake, crustal deformations, considered post-seismic deformation, were also observed, including horizontal displacement of about 1 cm in the southeast direction at the Miyazaki and Sadowara stations for about a month.
– On April 18th, seismic activity significantly increased in central Oita Prefecture, particularly between 7:00 a.m. and 1:00 p.m. During the period from April 18 to 30, a total of 13 earthquakes with a seismic intensity 1 or higher were recorded (1 with a maximum seismic intensity 3 and 4 with a maximum intensity 2). The largest earthquake, an M3.7, occurred at 8:57 a.m. on April 18th. All these events occurred within the earth's crust.
– "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 May 9 (reference
below).)
(Reference)
Recent Crustal Activity Around the Nankai Trough (Seismological and Volcanological Department, Japan Meteorological Agency, May 9, 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: