February 9, 2018
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Seismic Activities for January 2018

1 Major Seismic Activities

There was no remarkable activity.

• Seismic Activities for All of Japan in January 2018 (Magnitude 4.0 or over)

to supplementary reports

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

* On January 14, there was a magnitude (M) 4.7 earthquake at a depth of approximately 40 km, offshore Urakawa. The focal mechanism had a compression axis in an ENE-WSW direction.

• Hokkaido Region
• Earthquake Offshore Urakawa on January 14

to supplementary reports

(2) Tohoku Region

* On January 24, there was an M6.3 earthquake at a depth of approximately 35 km, offshore east of Aomori 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 continental plates.

• Tohoku Region
• Earthquake Offshore East of Aomori Prefecture on January 24

to supplementary reports

(3) Kanto-Chubu Region

* On January 6, there was an M4.7 earthquake at a depth of approximately 70 km under the Tokyo Bay [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 January 6, there was an M4.5 earthquake at a depth of approximately 10 km, offshore east of Izu peninsula [the ocean area near Izu Oshima]. The focal mechanism showed a strike-slip fault type with a compression axis in an NW-SE direction. This event occurred within the crust of the Philippine Sea plate.

• Kanto - Chubu Region
• Earthquake under the Tokyo Bay on January 6
• Earthquake Offshore East of Izu Peninsula on January 6

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

Supplement

* On February 7, there was an M6.7 earthquake at a depth of approximately 10 km near Taiwan. The focal mechanism had a compression axis in an N-S direction. In the vicinity of the recent event, on February 4, there was an M6.5 earthquake and there were 3 earthquakes of M6.0 or over until February 7.

• Seismic activity near Taiwan since February 4
• Past seismic activity and damage situation near Taiwan

Note: [ ] is the regional name of the epicenter used in the Japan Meteorological Agency announcement.

Supplementary Information to the Evaluation of Seismic Activities for January 2018

February 9, 2018
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 2018.

• M4.0 or greater: 90 (90 events in December 2017)
• M5.0 or greater: 10 (11 events in December 2017)
• M6.0 or greater: 1 (1 event in December 2017)

(reference)

• M4.0 or greater: 73 / month (Median number of earthquakes over the past 10 years from 1998 through 2007)
• M5.0 or greater: 9 / month (Median number of earthquakes over the past 35 years from 1973 through 2007)
• M6.0 or greater: 1.4 / month, approximately 17 / year (Average number of earthquakes over the past 84 years from 1924 through 2007)

The following events for the period from January 2017 to late December 2017 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

There is no supplementary information for Kanto-Chubu region.

to the text

(4) Kinki-Chugoku-Shikoku Region

There is no supplementary information for Kinki-Chugoku-Shikoku region.

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(5) Kyushu-Okinawa Region

There is no supplementary information for Kyushu-Okinawa region.

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 January 29 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, January 29, 2018)
"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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