October 9, 2024
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On September 24, a magnitude (M) 5.8 earthquake occurred at a depth of about 10 km (according to the CMT solution) in the ocean area near Torishima Island (near Sumisujima (Smith Rocks) about 100 km north of Torishima Island). The earthquake caused tsunamis in the Izu Islands and along the Pacific coast from Chiba to Kagoshima Prefectures, including a 0.7 m observed at Yaene, Hachijojima Island.
* On September 24, an M3.7 earthquake occurred at a depth of about 15 km in the central and northern Rumoi Region. This earthquake occurred within the crust.
* On September 26, an M5.7 earthquake occurred offshore of Kushiro at a depth of about 60 km. This earthquake has a focal mechanism with a WNW-ESE compression axis and occurred inside the Pacific Plate.
There was no remarkable activity.
* Although seismic activity in 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. There were 18 earthquakes with seismic intensity 1 or over (maximum seismic intensity: number of earthquakes, 2: 4) from September 1 to September 30. The largest earthquake in September was the M3.7 event (maximum seismic intensity 1) at 00:53 on September 29. Note that there were 18 earthquakes with seismic intensity 1 or over in August.
According to the GNSS observation, following crustal deformations, which were considered to be post-seismic deformation, were observed in 9 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 5 cm in an NW direction at the Suzu observatory and subsidence in the northern Noto Peninsula such as 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, and an M6.0 in June 2024. In the series of seismic activities, 2,442 earthquakes with seismic intensity 1 or over occurred from December 1, 2020 to September 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.
* On September 24, an M5.8 earthquake occurred at a depth of about 10 km (according to the CMT solution) in the ocean area near Torishima Island (near Sumisujima (Smith Rocks) about 100 km north of Torishima Island). The earthquake caused tsunamis in the Izu Islands and along the Pacific coast from Chiba to Kagoshima Prefectures, including a 0.7 m tsunami observed at Yaene, Hachijojima Island.
Similar to the present event, there have been other earthquakes in the vicinity, including an M5.9 on June 13, 1984, an M6.2 on September 5, 1996, an M5.9 on January 1, 2006, and an M5.9 on May 3, 2015, all of which have generated tsunamis despite being around M6.0 in size.
* On September 20, an M4.7 earthquake occurred at a depth of about 40 km under the Bungosuido Strait. This earthquake has a normal fault-type focal mechanism with an E-W tension axis, and occurred inside the Philippine Sea Plate.
* On September 14, an M5.7 earthquake occurred offshore southeast of Tanegashima Island. The focal mechanism of this earthquake has an east-west compression axis.
* On September 16, an M5.3 earthquake occurred at a depth of about 20 km under the Hyuganada Sea. The focal mechanism of this 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 Philippine Sea and the continental plates. An M7.1 earthquake occurred near the hypocenter of this earthquake on August 8, 2024, and 32 earthquakes of seismic intensity 1 or over were observed from August 8 to September 30 (maximum seismic intensity: number of earthquakes, 6 Lower: 1, 3: 4, 2: 6, 1: 21). Although seismic activity continues, the number of earthquakes has been decreasing over time.
According to GNSS observations, crustal deformation, which is considered to be post-seismic deformation, was observed mainly in the southern Miyazaki Prefecture, including a 3 cm displacement in the southeast direction at the Miyazaki observatory during the two months after the M7.1 earthquake.
* 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, 2024
Earthquake Research Committee
The numbers of earthquakes by magnitude (M) in and around Japan in September 2024 are as follows.
(Reference)
The following events for the period from September 2023 until the end of August 2024 have been listed as "Major Seismic Activities" in the monthly "Evaluation of Seismic Activities."
| – 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) |
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| – In the Noto Region, Ishikawa Prefecture# | M6.0 on June 3, 2024 (Depth of approximately 15 km) |
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| – 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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# 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 fall 2023, but appears to have continued recently.
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 October 7 of the Nankai Trough Earthquake Assessment Committee (reference below).)
(Reference)
Recent Crustal Activity Around the Nankai Trough (Seismological and Volcanological Department, Japan Meteorological Agency, October 7, 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: