February 9, 2024
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Seismic Activities for January 2024

1 Major Seismic Activities

* On January 1, there was a magnitude (M) 7.6 earthquake (#1) in the Noto region, Ishikawa Prefecture, and maximum seismic intensity 7 was observed in Ishikawa Prefecture. Long-period ground motion class 4 was observed in Ishikawa Prefecture. This event caused tsunami observed at the Sea of Japan side of the area extending from Hokkaido to Kyushu, such that of height 80 cm observed at Kanazawa observatory (Ports and Harbours Bureau) and 0.8 m at Sakata observatory (JMA) and damage with fatalities.

• Seismic Activities for All of Japan in January 2024 (Magnitude 4.0 or over)

to supplementary reports

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

* On January 13, there was an M4.0 earthquake at a very shallow depth in the northern Kushiro region. The event occurred within the crust.

• Hokkaido Region
• Earthquake in the Northern Kushiro Region on January 13

to supplementary reports

(2) Tohoku Region

There was no remarkable activity.

• Tohoku Region

to supplementary reports

(3) Kanto-Chubu Region

* With regard to the 2024 Noto Peninsula Earthquakes, refer to another report "Evaluation of the 2024 Noto Peninsula Earthquakes."

* On January 28, there was an M4.7 earthquake at a depth of approximately 75 km under Tokyo Bay. The focal mechanism showed a reverse fault type with a compression axis in an E-W direction. This event occurred at the boundary between the Pacific and the Philippine Sea plates.

• Kanto - Chubu Region
• Earthquake Under Tokyo Bay on January 28

to supplementary reports

(4) Kinki-Chugoku-Shikoku Region

There was no remarkable activity.

• Kinki-Chugoku-Shikoku Region

to supplementary reports

(5) Kyushu-Okinawa Region

There was no remarkable activity.

• Kyushu Region
• Okinawa Region

to supplementary reports

(6) Around the Nankai Trough

* There has been observed no unusual change which indicates that the possibility of occurrence of a great earthquake along the Nankai Trough has relatively raised compared to the normal time.

• Vertical Movement of GNSS-Based Control Stations - Omaezaki
• Vertical Movements of GNSS-Based Control Stations – the Kii Peninsula and Around Cape Muroto

to supplementary reports

  #1: "The 2024 Noto Peninsula Earthquakes" (named by JMA) denotes the series of earthquakes after January 1, 2024 and the series of seismic activity in the Noto region since December 2020.

Note: GNSS is a general name of satellite positioning system such as GPS.

Supplementary Information to the Evaluation of Seismic Activities for January 2024

February 9, 2024
Earthquake Research Committee

1 Major Seismic Activities

The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during January 2024.

• M4.0 or greater: 282 (90 events in December)
• M5.0 or greater: 24 (6 events in December)
• M6.0 or greater: 3 (1 event in December)

Note that in the above monthly numbers, are included the numbers of earthquakes in the Noto region, Ishikawa Prefecture, offshore of the Noto Peninsula, and near Sadoshima Island associated with the 2024 Noto Peninsula Earthquakes, i.e. 207, 20, 3 for M4.0 or greater, M5.0 or greater, M6.0 or greater earthquakes, respectively.

(Reference)

• M4.0 or greater: 81 / month (69-104)
• (Median monthly number from 1998 to 2017, half of numbers are included in the interval shown in parentheses)
• M5.0 or greater: 10 / month (7-14)
• (Median monthly number from 1973 to 2017, half of numbers are included in the interval shown in parentheses)
• M6.0 or greater: 1 / month (0-2)
• (Median monthly number from 1919 to 2017, half of numbers are included in the interval shown in parentheses)
• M6.0 or greater: 16 / year (12-21)
• (Median annual number from 1919 to 2017, half of numbers are included in the interval shown in parentheses)

The following events for the period from January 2023 to late December 2023 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."

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2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

There is no supplementary information for Hokkaido region.

to the text

(2) Tohoku Region

There is no supplementary information for Tohoku region.

to the text

(3) Kanto-Chubu 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.

– In the period from December 22 till January 6, in the area extending from Tokai to the central Kii Peninsula, deep low-frequency earthquakes (tremors) were observed near the boundary between the Philippine Sea and the continental plates. According to the strain and tilt data, almost synchronized with the deep low-frequency seismic (tremor) activity, slight crustal deformations were observed in the surrounding area. These phenomena are considered to be caused by the short-term slow slip at the boundary between the Philippine Sea and the continental plates.

• Coordinate Time Series (Black Circles) and Calculated Values (Red Lines) of Observing Stations in Tokai Region
• Long-Term Slow Slip in the Tokai Region Estimated from GNSS Data (provisional)
• Deep Low-Frequency Seismic (Tremor) Activity and Short-Term Slow-Slip in the Area Extending from Tokai to the Central Kii Peninsula
• Fig.2 Time Variation of Strain and Tilt (1) (2023/12/16 00:00 – 2024/01/10 00:00 (JST))
• Fig.2 Time Variation of Strain and Tilt (2) (2023/12/16 00:00 – 2024/01/10 00:00 (JST))
• Fig.2 Time Variation of Strain and Tilt (3) (2023/12/16 00:00 – 2024/01/10 00:00 (JST))
• Fig.2 Time Variation of Strain and Tilt (4) (2023/12/16 00:00 – 2024/01/10 00:00 (JST))
• Fig.2 Time Variation of Strain and Tilt (5) (2023/12/16 00:00 – 2024/01/10 00:00 (JST))
• Fig.3 Fault Model Explaining the Variation of Strain and Tilt (Fig.2[A]) During 2023/12/23 – 24
• Fig.4 Fault Model Explaining the Variation of Strain and Tilt (Fig.2[B]) During 2023/12/25 – 30
• Fig.5 Fault Model Explaining the Variation of Strain and Tilt (Fig.2[C]) on 2023/12/31
• Fig.6 Fault Model Explaining the Variation of Strain and Tilt (Fig.2[D1]) During 2024/01/02PM – 03AM
• Fig.7 Fault Model Explaining the Variation of Strain and Tilt (Fig.2[D2]) During 2024/01/02PM – 03AM
• Fig.8 Fault Model Explaining the Variation of Strain and Tilt (Fig.2[E]) During 2024/01/03PM – 04AM
• Fig.9 Fault Model Explaining the Variation of Strain and Tilt (Fig.2[F]) During 2024/01/04PM – 06AM

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(4) Kinki-Chugoku-Shikoku 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. Recently this crustal deformation seems to be decaying.

– In the central Shikoku, in the period from December 23 till January 2, deep low-frequency earthquakes (tremors) were observed near the boundary between the Philippine Sea and the continental plates. According to the strain and tilt data, almost synchronized with the deep low-frequency seismic (tremor) activity, slight crustal deformations were observed in the surrounding area. These phenomena are considered to be caused by the short-term slow slip at the boundary between the Philippine Sea and the continental plates.

• Time Series (Black Points) Representing the Coordinates of the Observatories in the Central Shikoku and Calculated Values (Red Lines) – Time-Dependent Inversion –
• Long-Term Slow Slip in the Central Shikoku Estimated from GNSS Data (Provisional)
• Deep Low-Frequency Seismic (Tremor) Activity and Short-Term Slow-Slip in the Central Shikoku
• Fig.13 Time Variation of Strain and Tilt (1) (2023/12/17 00:00 – 2024/01/06 00:00 (JST))
• Fig.13 Time Variation of Strain and Tilt (2) (2023/12/17 00:00 – 2024/01/06 00:00 (JST))
• Fig.14 Fault Model Explaining the Variation of Strain and Tilt (Fig.13[A]) During 2023/12/24 – 31AM

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(5) Kyushu-Okinawa Region

There is no supplementary information for Kyushu-Okinawa region.

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(6) Around the Nankai Trough

– "There has been observed no unusual change which indicates that the possibility of occurrence of a great earthquake 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, 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 raised compared to the normal time. (Excerpted)"

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