December 11, 2017
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Seismic Activities for November 2017

1 Major Seismic Activities

There was no remarkable activity.

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

* On November 3, there was a magnitude (M) 5.0 earthquake at a depth of approximately 65 km, offshore Tokachi. The focal mechanism had a tension axis in an NE-SW direction. This event occurred within the Pacific plate.

(2) Tohoku Region

* On November 11, there was an M4.7 earthquake at a depth of approximately 60 km, offshore Miyagi prefecture. The focal mechanism showed a reverse fault type with a compression axis in an E-W direction. This event occurred within the Pacific plate.

* On November 13, there was an M6.0 earthquake at a depth of approximately 10 km (CMT solution), offshore Sanriku. The focal mechanism showed a normal fault type with a tension axis in an NW-SE direction. This event occurred within the Pacific plate east of the Japan Trench.

* On November 17, there was an M4.8 earthquake at a depth of approximately 50 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.

(3) Kanto-Chubu Region

* On November 3, there was an M4.8 earthquake at a depth of approximately 10 km in the northern Ibaraki prefecture. The focal mechanism showed a normal fault type with a tension axis in an NE-SW direction. This event occurred within the crust.

* On November 16, there was an M6.0 earthquake offshore east of Hachijojima. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.

(4) Kinki-Chugoku-Shikoku Region

There was no remarkable activity.

(5) Kyushu-Okinawa Region

* On November 1, there was an M3.8 earthquake at a depth of approximately 10 km in the Kagoshima bay. The focal mechanism had a tension axis in a WNW-ESE direction. This event occurred within the crust.

(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.

Supplement

* On December 2, there was an M4.4 earthquake at a depth of approximately 45 km under the southern Ibaraki prefecture. The focal mechanism showed a reverse fault type with a compression axis in an NW-SE direction. This event occurred at the boundary between the Philippine Sea and the continental plates.

* On December 6, there was an M5.3 earthquake at a depth of approximately 10 km in the central Nagano prefecture. The focal mechanism showed a strike-slip fault type with a compression axis in a WNW-ESE direction. This event occurred within the crust.

* On December 6, there was an M4.5 earthquake at a depth of approximately 10 km in the northern Ibaraki prefecture. The focal mechanism showed a normal fault type with a tension axis in an NE-SW direction. This event occurred within the crust.



Supplementary Information to the Evaluation of Seismic Activities for November 2017

December 11, 2017
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 November 2017.

(reference)

The following events for the period from November 2016 to late October 2017 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."

  – Offshore Fukushima Prefecture  M7.4 on November 22, 2016
(Depth of approximately 10 km)
  – Northern Ibaraki Prefecture  M6.3 on December 28, 2016
(Depth of approximately 10 km)
  – Offshore Fukushima Prefecture  M5.7 on February 28, 2017
(Depth of approximately 50 km)
  – Bungo Channel  M5.0 on June 20, 2017
(Depth of approximately 40 km)
  – Southern Nagano Prefecture  M5.6 on June 25, 2017
(Depth of approximately 5 km)
  – Central and Eastern Iburi Region  M5.1 on July 1, 2017
(Depth of approximately 25 km)
  – Aso Region, Kumamoto Prefecture  M4.5 on July 2, 2017
(Depth of approximately 10 km)
  – Kagoshima Bay  M5.3 on July 11, 2017
(Depth of approximately 10 km)
  – Southern Inland, Akita Prefecture  M5.2 on September 8, 2017
(Depth of approximately 10 km)
  – Offshore Fukushima Prefecture  M5.9 on October 6, 2017
(Depth of approximately 55 km)

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

There is no supplementary information for Hokkaido region.

(2) Tohoku Region

There is no supplementary information for Tohoku region.

(3) Kanto-Chubu Region

There is no supplementary information for Kanto-Chubu region.

(4) Kinki-Chugoku-Shikoku Region

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

(5) Kyushu-Okinawa Region

"On November 1, there was an M3.8 earthquake at a depth of approximately 10 km in the Kagoshima bay.":
The seismic activity in the Kagoshima bay after an M5.3 earthquake on July 11 continues, decaying as a whole.

(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 27 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 27, 2017)
"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)"

Reference 1
Earthquakes that are described in the "Evaluation of Seismic Activity" (Monthly Report of Seismic Activity in Japan) have the following features.

  1. Events of M6.0 and greater, or events that have maximum seismic intensity 4 or greater
  2. Onshore events of M4.5 and greater that have maximum seismic intensity 3 or greater
  3. Events under the ocean areas of M5.0 or greater that have maximum seismic intensity 3 or greater

Reference 2
Information that is described in the "Supplementary Information to the Evaluation" includes:

  1. Reference information related to seismic activity described in the "Evaluation of Seismic Activity"
  2. Recent earthquake activity over the past year related to the events described in "Major Seismic Activity" in the "Evaluation of Seismic Activity"
  3. Seismic activity that has been evaluated, but not included in the "Evaluation of Seismic Activity" because it is within normal bounds and not prominent