February 9, 2023
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
* On January 17, there was a magnitude (M) 4.5 earthquake at a very shallow depth in the northern Kamikawa region. This event occurred within the crust. In the vicinity of the event, from January 13 to 18, there were 5 earthquakes including the recent one with seismic intensity 1 or over observed.
* On January 3, there was an M5.1 earthquake at a depth of approximately 35 km, offshore Iwate prefecture. The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On January 20, there was an M5.0 earthquake at a depth of approximately 45 km, offshore Miyagi prefecture. The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On January 25, there was an M5.1 earthquake at a depth of approximately 55 km, offshore Fukushima prefecture. The focal mechanism showed a reverse fault type with a compression axis in an NNE-SSW direction. This event occurred within the Pacific plate.
* In the crust of the Noto region, Ishikawa prefecture, where the number of earthquakes is increasing since about 2018, the seismic activity became high since December 2020, and it has become higher since about July 2021. In January 2023, there was an M 4.5 earthquake on 6th: the serial seismic activity still continues in an active state, without any sign of decline at present.
The largest so far is the M5.4 earthquake which occurred on June 19, 2022. Beside this there occurred an M5.1 earthquake on September 16, 2021 and an M5.0 earthquake on June 20, 2022. From December 1, 2020 till February 8, 2023 at 08 o'clock (JST), there occurred 277 earthquakes with seismic intensity 1 or over observed: of these 40 earthquakes with seismic intensity 3 or over observed. From January 1, 2023 till February 8, 2023 at 08 o'clock (JST), there occurred 12 earthquakes with seismic intensity 1 or over observed: of these 2 earthquakes with seismic intensity 3 or over observed.
According to the result of the GNSS observation, since about December 2020, the following crustal deformation has continued: the cumulative displacement of 1 cm over in the south-southeast direction and the uplift of 4 cm or so at the Suzu observatory, Suzu City, Ishikawa prefecture and the cumulative displacement of 1 cm over in the south-southwest direction at the Noto observatory, Noto Town and so on are observed.
Based on the situation of the seismic activity and the crustal deformation, the series of the seismic activity will continue for the time being and we should pay attention for a strong shaking.
* On January 16, there was an M5.9 earthquake at a depth of approximately 420 km, offshore west of the Ogasawara Islands. The focal mechanism had a compression axis in the subducting direction of the Pacific plate. This event occurred within the Pacific plate.
* On January 29, there was an M4.9 earthquake at a depth of approximately 140 km under the western Kanagawa prefecture. The focal mechanism had a tension axis in the subducting direction of the Pacific plate. This event occurred within the Pacific plate.
There was no remarkable activity.
There was no remarkable activity.
* There has been observed no unusual change which indicates that the possibility of occurrence of great earthquakes along the Nankai Trough has relatively raised compared to the normal time.
Note: GNSS is a general name of satellite positioning system such as GPS.
February 9, 2023
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during January 2023.
(Reference)
The following events for the period from January 2022 to late December 2022 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – Under the Ocean near Chichijima Island | M6.1 on January 4, 2022 (Depth of approximately 60 km) |
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| – Under the Hyuganada |
M6.6 on January 22, 2022 (Depth of approximately 45 km) |
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| – Offshore Fukushima Prefecture | M7.4 on March 16, 2022 (Depth of approximately 55 km) |
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| – Offshore Iwate Prefecture | M5.6 on March 18, 2022 (Depth of approximately 20 km) |
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| – Under the Northern Ibaraki Prefecture | M5.4 on April 19, 2022 (Depth of approximately 95 km) |
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| – Offshore Ibaraki Prefecture | M6.0 on May 22, 2022 (Depth of approximately 5 km) |
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| – In the Noto Region, Ishikawa Prefecture |
M5.4 on June 19, 2022 (Depth of approximately 15 km) |
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| – In the Kumamoto Region, Kumamoto Prefecture |
M4.7 on June 26, 2022 (Depth of approximately 10 km) |
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| – In the Northern Kamikawa Region |
on August 11, 2022 M5.4 (Depth of approximately 5 km) M5.2 (very shallow) |
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| – Offshore East of the Osumi Peninsula | M5.9 on October 2, 2022 (Depth of approximately 30 km) |
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| – Offshore Fukushima Prefecture | M5.0 on October 21, 2022 (Depth of approximately 30 km) |
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| – Under the Southern Ibaraki | M4.9 on November 9, 2022 Prefecture (Depth of approximately 50 km) |
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There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
There is no supplementary information for Kanto-Chubu region.
– According to the GNSS observation, the crustal deformation different from the ordinary trend in the central Shikoku has been observed from 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 and the continental plates.
There is no supplementary information for Kyushu-Okinawa region.
– "There has been observed no unusual change which indicates that the possibility of occurrence of great earthquakes along the Nankai Trough has relatively raised compared to the normal time.":
(This evaluation is in agreement with the views presented at the regular
meeting on February 7 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, February 7, 2023)
"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 raised 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: