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

Evaluation of Seismic Activities for February 2022

1 Major Seismic Activities

There was no remarkable activity.

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

to supplementary reports

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

* On February 17, there was a magnitude (M) 5.0 earthquake at a depth of approximately 55 km, offshore Urakawa. The focal mechanism had a compression axis in an ENE-WSW direction. This event occurred within the continental plate.

• Hokkaido Region
• Earthquake Offshore Urakawa on February 17

to supplementary reports

(2) Tohoku Region

* On February 18, there was an M5.3 earthquake at a depth of approximately 50 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.

• Tohoku Region
• Earthquake Offshore Miyagi Prefecture on February 18

to supplementary reports

(3) Kanto-Chubu Region

* 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. The largest is an M5.1 earthquake which occurred on September 16, 2021. The high seismic activity continues in February 2022 and later, such as an M4.1 earthquake on February 7 and an M4.8 (preliminary) on March 8. From December 1, 2020 till March 9, 2022 at 12:00 (JST) there occurred 88 earthquakes with seismic intensity 1 or over: 12 earthquakes from February 1, 2022 till March 9 at 12:00 (JST).
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.

• 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)

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 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

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

Supplementary Information to the Evaluation of Seismic Activities for February 2022

March 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 February 2022.

• M4.0 or greater: 89 (85 events in January)
• M5.0 or greater: 10 (5 events in January)
  M6.0 or greater: 0 (3 events in January)
  

(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 February 2021 to late January 2022 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."

to the text

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

– 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

to the text

(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)

to the text

(5) Kyushu-Okinawa Region

– In the continental plate offshore northwest of Okinawa Main Island, since January 30 a cluster of earthquakes is observed and till February 28 there occurred 13 earthquakes with seismic intensity 1 or over. There occurred an M5.6 earthquake on February 9 and the largest M5.8 earthquake on February 22. Near the recent seismic activity there were clusters in the past: from February to March, 1980 and in August 2007 there were clusters including earthquakes of M6.0 or over. In the cluster from February to March 1980, there occurred M6.7 and M6.3 earthquakes.

– In the continental plate in the ocean near Tokara Islands (near Kodakarajima Island), from February 13 to 22, there occurred 12 earthquakes with seismic intensity 1 or over. The largest was an M3.5 earthquake on February 22. Near the recent seismic activity, the seismic activity became high since December 4, 2021 and there was an M6.1 earthquake on December 9.

– 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.

• Seismic Activity in the Ocean near Tokara Islands (near Kodakarajima Island)
• 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)
• Seismic Activity Offshore Northwest of Okinawa Main Island

to the text

(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 March 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, March 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)"

to the text