February 9, 2022
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Seismic Activities for January 2022

1 Major Seismic Activities

* On January 4, there was a magnitude (M) 6.1 earthquake under the ocean near Chichijima Island. Maximum seismic intensity 5 Upper was observed in Tokyo prefecture (Ogasawara Village).

* On January 22, there was an M6.6 earthquake under the Hyuganada. Maximum seismic intensity 5 Upper was observed in Oita and Miyazaki prefectures. Long-period seismic intensity 2 was observed in Kumamoto, Oita and Miyazaki prefectures. Also was caused damage with injured persons and so on.

• Seismic Activities for All of Japan in January 2022 (Magnitude 4.0 or over)

to supplementary reports

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

There was no remarkable activity.

• Hokkaido Region

to supplementary reports

(2) Tohoku Region

There was no remarkable activity.

• Tohoku Region

to supplementary reports

(3) Kanto-Chubu Region

* In the crust of the Noto region, Ishikawa prefecture, the number of earthquakes is increasing since about 2018, and the seismic activity became high since December 2020, and it has become higher since about July 2021. The largest is an M5.1 earthquake occurring on September 16, 2021. The high seismic activity continues in January 2022 and later, such as an M4.1 earthquake on February 7. From December 1, 2020 till February 7, 2022, there occurred 78 earthquakes with seismic intensity 1 or over: 8 earthquakes from January 1, 2022 till February 7.
According to the GNSS observation, since about December 2020, the following crustal deformation has been observed in the Noto Peninsula: the cumulative displacement of 1 cm over in the south-southwest direction at the Noto observatory in Noto Town, Ishikawa prefecture, and the uplift of 3 cm over at the Suzu observatory in Suzu City.
Based on the situation of the seismic activity and the crustal deformation, the series of the seismic activity will continue for the time being.

* On January 4, there was an M6.1 earthquake at a depth of approximately 60 km (CMT solution) under the ocean near Chichijima Island. The focal mechanism showed a strike-slip fault type with a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate. Then in the vicinity of the recent event till 31^st, there occurred 13 earthquakes with seismic intensity 1 or over.
According to the result of the GNSS observation, no significant crustal deformation associated with the event was observed.

• Kanto - Chubu Region
• Seismic Activity in the Noto Region, Ishikawa Prefecture
• Observed Data at the Time of the Seismic Activity in the Noto Region, Ishikawa Prefecture (provisional)
• Observed Data at the Time of the Seismic Activity in the Noto Region, Ishikawa Prefecture (provisional)
• Earthquake Under the Ocean near Chichijima Island on January 4
• Observed Data Before and After the Earthquake Under the Ocean near Chichijima Island (January 4, M6.1) (provisional)

to supplementary reports

(4) Kinki-Chugoku-Shikoku Region

There was no remarkable activity.

• Kinki-Chugoku-Shikoku Region

to supplementary reports

(5) Kyushu-Okinawa Region

* On January 22, there was an M6.6 earthquake at a depth of approximately 45 km under the Hyuganada. The focal mechanism had a tension axis in the subducting direction of the Philippine Sea plate. This event occurred within the Philippine Sea plate. Then in the area including the recent event, extending 15 km in an NNE-SSW direction, till February 3 there occurred 42 earthquakes with seismic intensity 1 or over: 5 earthquakes with seismic intensity 3 or over.
The earthquake fault estimated from the focal mechanism, the distribution of seismic activity and the analytical result of seismic waves is an almost vertical fault striking in an NNE-SSW direction.
According to the result of the GNSS observation, crustal deformation associated with the event was observed mainly in Oita and the northern Miyazaki prefectures such as a slight horizontal displacement at Ume and Yonouzu observatories, Saiki City, Oita prefecture and subsidence of 1 cm order at Kitagawa observatory, Kitagawa Town, Miyazaki prefecture and Oita-Saiki observatory, Saiki City, Oita prefecture.

• Kyushu Region
• Earthquake Under the Hyuganada on January 22 (1)
• Earthquake Under the Hyuganada on January 22 (2)
• Earthquake Under the Hyuganada on January 22, 2022 at 01:08 (JST)
• Earthquake Under the Hyuganada on January 22 (Distribution of Hypocenters Determined by Waveform Correlation DD Method)
• Earthquake Under the Hyuganada on January 22, 2022 - Analysis of Focal Process by Near-Field Strong Motion Waveforms (provisional) - (1)
• Earthquake Under the Hyuganada on January 22, 2022 - Analysis of Focal Process by Near-Field Strong Motion Waveforms (provisional) - (2)
• Observed Data Before and After the Earthquake Under the Hyuganada (January 22, M6.6) (provisional) (1)
• Observed Data Before and After the Earthquake Under the Hyuganada (January 22, M6.6) (provisional) (2)
• 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 great earthquakes 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 - Kii Peninsula and Around Muroto Cape

to supplementary reports

(7) Other Regions

* On January 3, there was an M6.3 earthquake at a depth of approximately 25 km near Taiwan. The focal mechanism had a compression axis in an N-S direction.

• Earthquake near Taiwan on January 3

to supplementary reports

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

Supplementary Information to the Evaluation of Seismic Activities for January 2022

February 9, 2022
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 2022.

• M4.0 or greater: 85 (149 events in December)
  M5.0 or greater: 5 (14 events in December)
  M6.0 or greater: 3 (2 events in December)
  

(Reference)

• M4.0 or greater: 81 / month (69-104)
• (Median monthly number from 1998 to 2017, half of data 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 data 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 data 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 data are included in the interval shown in parentheses)

The following events for the period from January 2021 to late December 2021 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.

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(2) Tohoku Region

There is no supplementary information for Tohoku region.

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(3) Kanto-Chubu Region

– In the Tokai Region during the period from January 14 till February 2, deep low-frequency earthquakes (tremors) were observed near the boundary between the Philippine Sea and the continental plates. According to the observation of strain and tilt, almost synchronous with the deep low-frequency earthquake (tremor) activity, slight crustal deformations were observed in the surrounding area. These phenomena are considered to be caused by the short-term slow slip along the deep part of the boundary between the Philippine Sea and the continental plates.

• Deep Low-Frequency Earthquake (Tremor) Activity and Short-Term Slow Slip in the Tokai Region
• Fig.2 Time Variation of Strain and Tilt (1) (2022/01/07 00:00 - 2022/01/28 00:00 (JST))
• Fig.2 Time Variation of Strain and Tilt (2) (2022/01/07 00:00 - 2022/01/28 00:00 (JST))
• Fig.2 Time Variation of Strain and Tilt (3) (2022/01/07 00:00 - 2022/01/28 00:00 (JST))
• Fig.3 Fault Model Explaining the Variation of Strain and Tilt (Fig.2[A]) 2022/01/15 - 19
• Fig.4 Fault Model Explaining the Variation of Strain and Tilt (Fig.2[B]) 2022/01/20 - 23

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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.

– According to the GNSS observation, the crustal deformation different from the ordinary trend in the western Kii Peninsula and the eastern Shikoku has been observed from about summer 2020. This phenomenon is considered to be caused by a long-term slow-slip around the Kii Channel at the deeper part of the boundary between the Philippine Sea and the continental plates.

• Non-Stationary Horizontal Crustal Deformation of the Central Shikoku (After Linear Trend, Annual Component, and Semi-Annual Component Removed)
• Time Series of GNSS Continuous Observation: the Central Shikoku (1) Graphs After Linear Trend, Annual Component, and Semi-Annual Component Removed
• Time Series of GNSS Continuous Observation: the Central Shikoku (2) Graphs After Linear Trend, Annual Component, and Semi-Annual Component Removed
• Long-Term Slow Slip in the Central Shikoku Estimated from GNSS Data (provisional)
• Non-Stationary Horizontal Crustal Deformation of the Western Kii Peninsula and the Eastern Shikoku (After Linear Trend, Annual Component, and Semi-Annual Component Removed)
• Time Series of GNSS Continuous Observation: the Western Kii Peninsula and the Eastern Shikoku (1) Graphs After Linear Trend, Annual Component, and Semi-Annual Component Removed
• Time Series of GNSS Continuous Observation: the Western Kii Peninsula and the Eastern Shikoku (2) Graphs After Linear Trend, Annual Component, and Semi-Annual Component Removed
• Long-Term Slow Slip in the Kii Channel Estimated from GNSS Data (provisional)

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(5) Kyushu-Okinawa Region

– According to the GNSS observation, the crustal deformation different from the ordinary trend in the southern Kyushu, being observed from about summer 2020, is considered to be caused by a long-term slow-slip around the southern Hyuganada at the deeper part of the boundary between the Philippine Sea and the continental plates. Recently this crustal deformation seems to be stagnant.

• Non-Stationary Horizontal Crustal Deformation of the Kyushu Region (After Removal of Linear Trend)
• Time Series of GNSS Continuous Observation: the Kyushu Region
• Long-Term Slow Slip Around the Southern Hyuganada Estimated from GNSS Data (provisional)

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(6) Around the Nankai Trough

–"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, 2022)
"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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(7) Other Regions

There is no supplementary information for other regions.

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