November 12, 2019
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Seismic Activities for October 2019

1 Major Seismic Activities

There was no remarkable activity.

• Seismic Activities for All of Japan in October (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

* On October 12, there was a magnitude (M) 5.4 earthquake at a depth of approximately 75 km, offshore southeast of Chiba prefecture. 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.

• Kanto - Chubu Region
• Earthquake offshore Southeast of Chiba Prefecture on October 12

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 November 3, there was an M5.0 earthquake at a depth of approximately 40 km, offshore Fukushima prefecture.

* On November 8, there was an M4.4 earthquake at a depth of approximately 50 km, offshore Ibaraki prefecture. The focal mechanism showed a strike-slip fault type with a compression axis in an NE-SW direction.

• Earthquake Offshore Fukushima Prefecture on November 3
• Earthquake Offshore Ibaraki Prefecture on November 8

Supplementary Information to the Evaluation of Seismic Activities for October 2019

November 12, 2019
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 October 2019.

• M4.0 or greater: 79 (64 events in September)
• M5.0 or greater: 7 (7 events in September)
• M6.0 or greater: 0 (0 event in September)

(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 October 2018 to late September 2019 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

There is no supplementary information for Kanto-Chubu region.

to the text

(4) Kinki-Chugoku-Shikoku Region

– According to the GNSS observation in the northern Kyushu from spring 2018, and according to the GNSS and strain observations in the western Shikoku from autumn 2018, crustal deformations different from the ordinary trend have been observed. These phenomena are considered to be caused by a slow slip at the deeper part of the boundary between the Philippine Sea and the continental plates, which continues at the northern Hyuganada and around the Bungo Channel. These crustal deformations and the long-term slow slip seem to be stagnant since June 2019.

• Non-Stationary Horizontal Crustal Deformation of Northern Kyushu and Western Shikoku (Linear trend, annual component, semi-annual component removed)
• Time Series of GNSS Continuous Observation: Northern Kyushu and Western Shikoku
• Long-Term Slow Slip in the Hyuganada and Bungo Channel Estimated from GNSS Data (provisional) (1) - Distribution of Estimated Slip -
• Long-Term Slow Slip in the Hyuganada and Bungo Channel Estimated from GNSS Data (provisional) (2) - Comparison Between Observed Values (black) and Calculated Values (white) -

to the text

(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 November 8 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, November 8, 2019)
"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