July 9, 2024
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On June 3 (JST, hereinafter the same time), a magnitude (M) 6.0 earthquake occurred at a depth of about 15 km in the Noto region, Ishikawa Prefecture. The earthquake caused a maximum seismic intensity 5 Upper in Ishikawa Prefecture, resulting in injuries and other damage. A long-period ground motion class 2 was observed in Ishikawa Prefecture for this earthquake.
There was no remarkable activity.
* On June 23, an M4.9 earthquake occurred at a depth of about 50 km, offshore of Fukushima Prefecture. The focal mechanism of this earthquake was a reverse fault type with a compression axis in a WNW-ESE direction. The earthquake occurred at the boundary between the Pacific Plate and the continental plate.
* Although seismic activity around the focal region of the M7.6 earthquake on January 1 in the Noto region, Ishikawa Prefecture has been decreasing, seismic activity, which has been high since December 2020, is still ongoing, including an M6.0 (maximum seismic intensity 5 Upper) and an M5.0 (maximum seismic intensity 4) earthquakes occurring on June 3. The M6.0 earthquake on June 3 had a focal mechanism of a reverse fault type with a compression axis in an NW-SE direction and occurred deep within the southeast-dipping focal region of the M7.6 earthquake. There were 35 earthquakes with seismic intensity 1 or over (maximum seismic intensity: number of earthquakes, 5 Upper: 1, 4: 1, 3: 1) from June 1 to June 30. The largest earthquake in June was the M6.0 event (maximum seismic intensity 5 Upper) at 06:31 on June 3. Note that there were 28 earthquakes with seismic intensity 1 or over in May.
Although the overall trend in the hypocenter distribution after the M7.6 earthquake is on southwest-dipping fault planes, detailed hypocenter distribution obtained from temporal ocean bottom seismic observations indicates that the earthquakes also occur on northwest-dipping planes in the northeastern part of the focal region.
In the case of major earthquakes in the continental plate, large earthquakes occurred more than several months after the largest earthquake, while the number of earthquakes was gently decreasing such as the 2004 Mid Niigata prefecture Earthquake (M6.8), the 2016 Kumamoto Earthquakes (M7.3), and the 2018 Hokkaido Eastern Iburi Earthquake (M6.7).
According to the GNSS observation, following crustal deformations considered to be post-seismic deformation were observed in the six months after the M7.6 earthquake on January 1: the horizontal displacements larger than 1 cm observed in wide areas, in Toyama, Niigata, and Nagano Prefectures centering on the Noto Peninsula such as the displacement of about 4 cm in an NW direction at the Noto observatory and subsidence in the northern Noto Peninsula such as about 7 cm at the Wajima observatory. In addition, crustal deformation was observed following the M6.0 earthquake on June 3, including horizontal displacements of about 1 cm in a WSW direction and uplift of about 2 cm at the Suzu observatory, and horizontal displacements and uplifts of up to 2 cm around the epicenter of this earthquake.
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 earthquake in May 2023, and an M7.6 earthquake in January 2024. In the series of seismic activity, 2,386 earthquakes with seismic intensity 1 or over occurred from December 1, 2020, to June 30, 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.
* Since the M6.6 earthquake on April 17 in the Bungosuido Strait, seismic activity has continued, with an M4.5 earthquake on June 1, although it has been decreasing. There were 82 earthquakes of seismic intensity 1 or over (maximum seismic intensity: number of earthquakes, 6 Lower: 1, 4: 2) between 23:00 on April 17 and 24:00 on June 30.
There was no remarkable activity.
* 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.
July 9, 2024
Earthquake Research Committee
The numbers of earthquakes by magnitude (M) in and around Japan in June 2024 are as follows.
(Reference)
The following events for the period from June 2023 until the end of May 2024 have been listed as "Major Seismic Activities" in the monthly "Evaluation of Seismic Activities."
| – Offshore of Tomakomai | M6.2 on June 11, 2023 (Depth of approximately 140 km) |
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| – In the Ocean Area near Torishima Island | Maximum M6.5 October 2 ~ 9, 2023 | ||
| – 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) |
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| – Offshore of Fukushima Prefecture | M5.8 on March 15, 2024 (Depth of approximately 50 km) |
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| – Under Southern Ibaraki Prefecture | M5.3 on March 21, 2024 (Depth of approximately 45 km) |
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| – Under the Northern Coast of Iwate Prefecture | M6.0 on April 2, 2024 (Depth of approximately 70 km) |
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| – 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) |
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| – Under the Bungosuido Strait | M6.6 on April 17, 2024 (Depth of approximately 40 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 from 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.
– Deep low-frequency earthquakes (tremors) were observed in the Tokai region from June 17 to 24 near the boundary between the Philippine Sea plate and the continental plate. According to strain and tilt data, slight crustal deformations were observed in the surrounding area almost synchronously with the deep low-frequency earthquakes (tremors). 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.
– 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, but appears to have continued recently.
– Deep low-frequency earthquakes (tremors) were observed in central Shikoku from June 20 to 29 near the boundary between the Philippine Sea plate and the continental plate. According to strain and tilt data, slight crustal deformations were observed in the surrounding area almost synchronously with the deep low-frequency earthquakes (tremors). 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.
– Under the ocean area near Tokara Islands (near Kodakarajima Island), a rather high seismic activity was observed from around 15:00 on June 18 to June 20, and from 15:00 on June 18 to June 30, there were 16 earthquakes with a seismic intensity 1 or over and three with a seismic intensity 3 or over. The largest of these earthquakes was an M3.7 earthquake (maximum seismic intensity 3) at 16:16 on June 19. These seismic events occurred within the continental plate.
In the vicinity of this seismic activity area, an M6.1 earthquake occurred in December 2021 with a maximum seismic intensity 5 Upper. High seismic activity had also continued in the past, with 346 earthquakes with seismic intensity 1 or over occurring as recently as September 2023.
– "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 July 5 of the Assessment Committee for Earthquakes Along the Nankai Trough (reference below).)
(Reference)
Recent Crustal Activity Around the Nankai Trough (Seismological and Volcanological Department, Japan Meteorological Agency, July 5, 2024)
"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: