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

Evaluation of Seismic Activities for November 2022

1 Major Seismic Activities

* On November 9, there was a magnitude (M) 4.9 earthquake under the southern Ibaraki prefecture. Maximum seismic intensity 5 Upper was observed and damage with injured persons was caused in Ibaraki prefecture.

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

to supplementary reports

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

* On November 6, there was an M5.4 earthquake at a depth of approximately 50 km, offshore east of Hokkaido. The focal mechanism showed a reverse fault type with a compression axis in an NW-SE direction.

• Hokkaido Region
• Earthquake Offshore East of Hokkaido on November 6

to supplementary reports

(2) Tohoku Region

* On November 17, there was an M5.0 earthquake at a depth of approximately 65 km, offshore east of Aomori prefecture. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.

* On November 30, there was an M5.1 earthquake at a depth of approximately 40 km, offshore Fukushima 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 East of Aomori Prefecture on November 17
• Earthquakes Offshore Fukushima Prefecture on November 30

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. In November 2022, there was a shallow seismic activity in the southeastern side of the hitherto active area, and there was an M4.4 earthquake near the western end of the activity area: the serial seismic activity still continues in an active state, without any sign of decline at present.
The largest so far was an 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 December 9, 2022 at 08 o'clock (JST), there occurred 255 earthquakes with seismic intensity 1 or over observed: of these 37 earthquakes with seismic intensity 3 or over observed. From November 1, 2022 till December 9 at 08 o'clock (JST), there occurred 28 earthquakes with seismic intensity 1 or over observed: of these 5 earthquakes with seismic intensity 3 or over observed, including an earthquake (M4.2) with seismic intensity 4 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 November 3, there was an M4.9 earthquake at a depth of approximately 70 km under the northwestern Chiba prefecture. 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.

* On November 9, there was an M4.9 earthquake at a depth of approximately 50 km under the southern Ibaraki prefecture. The focal mechanism showed a reverse fault type with a compression axis in an NNW-SSE direction. This event occurred at the boundary between the Philippine Sea and the continental plates.
According to the result of the GNSS observation, no significant crustal deformation accompanying this event has been observed.

* On November 14, there was an M6.4 earthquake at a depth of approximately 360 km offshore southeast of Mie prefecture. The focal mechanism had a compression axis in the subducting direction of the Pacific plate. This event occurred within the Pacific plate. Seismic intensity ranging from 4 to 1 was observed in the area extending from Hokkaido to Chugoku regions. Due to seismic waves propagated within the subducting Pacific plate, ground motions in Tohoku and Kanto regions, remote from the epicenter, were large (the abnormal seismic intensity).

• Kanto - Chubu Region
• Seismic Activity in the Noto Region, Ishikawa Prefecture
• Crustal Deformation of the Noto Region, Ishikawa Prefecture (provisional) – Vector Diagram –
• Crustal Deformation of the Noto Region, Ishikawa Prefecture (provisional) – Graphs After Removal of the Linear Trend, Year-Periodic Component, and Half-Year Periodic Component –
• Crustal Deformation of the Noto Region, Ishikawa Prefecture (provisional) – Portable GNSS Continuous Observing Device (REGMOS) –
• Earthquake Under the Northwestern Chiba Prefecture on November 3
• Earthquake Under the Southern Ibaraki Prefecture on November 9
• Earthquake Under the Southern Ibaraki Prefecture on November 9 (Seismic Intensity of [Ogachi, Shirosato Town])
• Earthquake Under the Southern Ibaraki Prefecture on November 9 (Acceleration Waveforms, Spectra of Seismic Intensity Observing Stations)
• Observed Data Before and After the Earthquake Under the Southern Ibaraki Prefecture (November 9, M4.9)
• Earthquake Offshore Southeast of Mie Prefecture on November 14
• [Reference] On the Earthquake of Which Seismic Intensity at the Far Place from the Epicenter Is Observed to Be Larger Than That in the Vicinity of the Epicenter
• Examples of Distribution Map of Seismic Intensity of the Past Earthquakes Accompanied with the Abnormal Seismic Intensity

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 November 2022

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

1 Major Seismic Activities

The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during November 2022.

• M4.0 or greater: 99 (86 events in October)
  M5.0 or greater: 13 (12 events in October)
  M6.0 or greater: 1 (0 event in October)
  

(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 November 2021 to late October 2022 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

There is no supplementary information for Kanto-Chubu region.

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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.

– From November 16 till 30 in the western Shikoku, deep low-frequency earthquakes (tremors) were observed near the boundary between the Philippine Sea and the continental plates. According to strain, tilt and GNSS data, slight crustal deformations synchronous with deep low-frequency earthquakes (tremors) were observed in the surrounding area. These phenomena are considered to be generated by the short-term slow-slip at the deep boundary between the Philippine Sea and the continental plates.

• Time Series Representing Non-Stationary Crustal Deformation of the Observatories in the Central Shikoku and Calculated Values
• Long-Term Slow Slip in the Central Shikoku Estimated from GNSS Data (provisional)
• Deep Low-Frequency Earthquake (Tremor) Activity and Short-Term Slow Slip in the Western Shikoku
• Fig.8 Time Variation of Strain and Tilt in Shikoku (1) (2022/11/10 00:00 - 2022/11/30 00:00 (JST))
• Fig.8 Time Variation of Strain and Tilt in Shikoku (2) (2022/11/10 00:00 - 2022/11/30 00:00 (JST))
• Fig.9 Fault Model Explaining the Variation of Strain and Tilt (Fig.8[A]) during 2022/11/17 - 18AM
• Fig.10 Fault Model Explaining the Variation of Strain and Tilt (Fig.8[B]) during 2022/11/18PM - 20
• Fig.11 Fault Model Explaining the Variation of Strain and Tilt (Fig.8[C]) during 2022/11/21 - 24AM
• Fig.12 Fault Model Explaining the Variation of Strain and Tilt (Fig.8[D]) during 2022/11/24PM - 26
• Slow Slip Synchronized with Deep Low-Frequency Earthquakes (Tremors) in the Western Shikoku Estimated from GNSS Data (provisional)

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(5) Kyushu-Okinawa Region

– Within the continental plate offshore northwest of Okinawa Main Island, an active seismic activity has been observed from January 30, but after October the activity became low. In the series of seismic activity, the largest was an M6.0 earthquake on September 18.
According to the result of the GNSS observation, the crustal deformation has been observed from about February 2022 such as a south-southeastward displacement of 2 cm or so of Gushikawa observatory, Kumejima Town, Okinawa prefecture, but it has become stagnant since about November.

• Seismic Activity Offshore Northwest of Okinawa Main Island
• Crustal Deformation Around Kumejima Island (provisional)

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(6) Around the Nankai Trough

– "here 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 December 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, December 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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