January 15, 2025
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
There was no remarkable activity.
* On December 28, an earthquake of magnitude (M) 5.3 occurred at a depth of about 40 km offshore of Fukushima Prefecture. The focal mechanism of the earthquake was of a reverse fault type with a compression axis in the WNW-ESE direction, and the earthquake occurred at the boundary between the Pacific Plate and the continental plate.
* In the seismically active area of the M7.6 earthquake on January 1, 2024,
seismic activity, which has been active since December 2020, is still ongoing,
although overall seismic activity has been declining outside of the active
area of the earthquake offshore west of Ishikawa Prefecture on November
26, 2024. There were 37 earthquakes of seismic intensity 1 or over from
December 1 to 31 (29 events offshore west of Ishikawa Prefecture, including
one with seismic intensity 3). The largest earthquake in December was an
M4.4 earthquake (maximum seismic intensity 3) at 7:11 on December 24. Note
that the number of earthquakes of seismic intensity 1 or over in November
was 136 (123 events offshore west of Ishikawa Prefecture).
According to the GNSS observation, crustal deformations, which were considered to be post-seismic deformation, were observed in 12 months after the M7.6 earthquake on January 1: the horizontal displacements larger than 1 cm were observed in wide areas; in Toyama, Niigata, and Nagano Prefectures centering on the Noto Peninsula such as the displacement of about 6 cm in an WNW direction at the Suzu observatory and subsidence of about 9 cm at the Wajima observatory.
The number of earthquakes in the crust of the Noto region, Ishikawa Prefecture, has been increasing since around 2018. The seismic activity became high from December 2020: there was an M5.4 earthquake in June 2022, an M6.5 in May 2023, an M7.6 in January 2024, an M6.0 in June, and an M6.6 in November. In the series of seismic activities, 2,629 earthquakes with seismic intensity 1 or over occurred from December 1, 2020 to December 31, 2024. Crustal deformation has also been observed since December 2020.
Based on the seismic activity and crustal deformation to date, the series of seismic activity from December 2020 is considered to continue for the time being, and there is a possibility of future earthquakes with strong shaking and tsunamis in and around the active area after the M7.6 earthquake.
* On December 17, an M4.2 earthquake occurred at a depth of about 55 km under southern Ibaraki Prefecture. The focal mechanism of this earthquake was of a reverse fault type with an NW-SE compression axis. The earthquake occurred at the boundary between the Philippine Sea Plate and the continental plate.
* On December 27, an M6.2 earthquake occurred at a depth of about 10 km (according to the CMT solution) in the ocean area near Torishima Island. The focal mechanism of this earthquake was of a reverse fault type with an E-W compression axis.
There was no remarkable activity.
* On December 17, an M5.2 earthquake occurred at a depth of about 160 km offshore west of Satsuma Peninsula. The earthquake occurred within the Philippine Sea 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.
* On December 8 and 27, earthquakes of M6.1 and M6.8 occurred under the Kuril Islands at depths of about 210 km and 150 km, respectively. The focal mechanisms of these earthquakes had ENE-WSW and NW-SE compression axes, respectively, both of which occurred inside the Pacific Plate.
* On January 13, 2025, an M6.6 earthquake occurred at a depth of about 35 km under the Hyuganada Sea. The focal mechanism of this earthquake was of a reverse fault type with an WNW-ESE compression axis, and the earthquake occurred at the boundary between the Philippine Sea Plate and the continental plate. This earthquake caused tsunamis to be observed from Miyazaki Prefecture to Kochi Prefecture, including 0.2 m tsunamis at Miyazaki Port in Miyazaki Prefecture and Aburatsu in Nichinan City.
The earthquake occurred within the active area after the M7.1 earthquake on August 8, 2024. Immediately after the M7.1 earthquake, activity remained high and the number of earthquakes had been decreasing over time. The M6.6 earthquake occurred in this situation. The seismic activity since the M6.6 earthquake has remained active, including an M5.4 (preliminary value) earthquake on the 15th. In past cases, the percentage of earthquakes of the same magnitude occurring after a major earthquake was 10 to 20%. Therefore, in areas of strong shaking, attention should be paid to earthquakes with a maximum seismic intensity 5 Lower for about one week after the earthquake.
According to GNSS observations, crustal deformation associated with the earthquake was observed mainly in Miyazaki Prefecture. The largest crustal deformation detected by GNSS so far is about 5 cm to the southeast at the Sadowara observatory. In the five months after the M7.1 earthquake on August 8, 2024, crustal deformations were observed mainly in the southern part of Miyazaki Prefecture, including a deformation of about 5 cm in the southeast direction at the Miyazaki observatory.
The earthquake occurred in the area of "smaller inter plate earthquakes of the Hyuganada Sea," which the Earthquake Research Committee had evaluated in its “Long-Term Evaluation of Seismic Activity of Hyuganada Sea and Nansei Islands Trench (Second Edition) (released on March 25, 2022). There were an M6.9 and an M6.7 earthquake on October 19 and December 3, 1996, respectively, in the surrounding area. Both earthquakes caused damage. According to the long-term evaluation, the probability of an earthquake of M7.0 to M7.5 occurring within 30 years in this area is ranked III (#), which is classified as a group with a high probability of occurrence among subduction zone earthquakes. It is noted that the 1662 earthquake around the Hyuganada Sea was likely an M8-class giant earthquake.
#: Rank of the probability of occurrence of a subduction zone earthquake within 30 years is expressed as follows; rank: probability, III: greater than 26%, II: 3% ~ 26%, I: smaller than 3%, X: unknown (an immediate occurrence of an earthquake cannot be denied).
Note: GNSS is a general name of a satellite positioning system such as GPS.
January 15, 2025
Earthquake Research Committee
The numbers of earthquakes by magnitude (M) in and around Japan in December 2024 are as follows.
(Reference)
The following events for the period from December 2023 until the end of November 2024 have been listed as "Major Seismic Activities" in the monthly "Evaluation of Seismic Activities."
| – in Mindanao, the Philippine Islands | Mw7.5 on December 2, 2023 | ||
| – In the Noto Region, Ishikawa Prefecture# | M7.6 on January 1, 2024 (Depth of approximately 15 km) |
||
| – Offshore of Fukushima Prefecture | M5.8 on March 15, 2024 (Depth of approximately 50 km) |
||
| – Under Southern Ibaraki Prefecture | M5.3 on March 21, 2024 (Depth of approximately 45 km) |
||
| – 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) |
||
# 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 appears to be continuing 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.
– Slight crustal deformations were observed from December 15 to December 31, almost synchronously with deep low-frequency earthquakes (tremors) with epicenters near the plate boundary from central to western Shikoku. These are presumed to be due to a short-term slow slip at the deep boundary between the Philippine Sea plate and the continental plate.
There is no supplementary information for Kyushu-Okinawa region.
– "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 on January 10 and the extraordinary meeting on January 13 of the Nankai Trough Earthquake Assessment Committee (reference below).)
(Reference)
Recent Crustal Activity Around the Nankai Trough (Seismological and Volcanological Department, Japan Meteorological Agency, January 10, 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: