October 9, 2020
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
On September 4, there was a magnitude (M) 5.0 earthquake in Reihoku, Fukui prefecture. The maximum seismic intensity 5 Lower was observed in Fukui prefecture, and was caused damage with injured persons and so on.
There was no remarkable activity.
* On September 12, there was an M6.2 earthquake at a depth of approximately 45 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.
* On September 2, there was an M4.6 earthquake at a depth of approximately 10 km in the Kaga region, Ishikawa 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 September 3, there was an M4.8 earthquake in the ocean area near Chichijima Island.
* On September 4, there was an M5.0 earthquake at a depth of approximately 5 km in Reihoku, Fukui prefecture. The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred within the crust. According to the GNSS observation, any significant crustal deformation accompanying this event was not observed.
* On September 7, there was an M5.2 earthquake at a depth of approximately 40 km, offshore Ibaraki prefecture. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On September 27, there was an M5.1 earthquake at a depth of approximately 45 km in the western Shizuoka prefecture. The focal mechanism showed a strike-slip fault type with a tension axis in an E-W direction. This event occurred within the Philippine Sea plate.
There was no remarkable activity.
There was no remarkable activity.
* 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.
* On October 3, there was an M5.8 earthquake offshore east of Hachijolima Island. The focal mechanism showed a reverse fault type with a compression axis in an E-W direction.
# "The western Toyama prefecture" is the region name used in the announcement of Japan Meteorological Agency.
Note: GNSS is a general name of satellite positioning system such as GPS.
October 9, 2020
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during September 2020.
(reference)
The following events for the period from September 2019 to late August 2020 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – Offshore East of Aomori Prefecture | M5.5 on December 19, 2019 (Depth of approximately 50 km) |
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| – Noto Region, Ishikawa Prefecture | M5.5 on March 13, 2020 (Depth of approximately 10 km) |
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| – Offshore East of Chiba Prefecture | M6.1 on June 25, 2020 (Depth of approximately 35 km) |
There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
– Near the border between Nagano and Gifu prefectures (the central Nagano prefecture and the Hida region, Gifu prefecture) within the crust, there was an active seismic activity such as the increase of earthquakes of M3.0 over beginning on April 22 and the occurrence of an M5.5 earthquake on April 23, an M5.4 earthquake on May 19 and an M5.3 on 29th. This activity still continues in September, but there occurred no earthquake of M3.0 over.
In the neighborhood, also in 1998, the seismic activity became high: there occurred an M5.0 earthquake on August 12, and an M5.6 on 16th, and earthquakes of M3.0 over in December.
– According to the GNSS observation, the crustal deformation different from the ordinary trend observed in the Shima Peninsula from mid-2019 seems to be decaying recently. This phenomenon is considered to be caused by a long-term slow slip around the Shima Peninsula 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 central Shikoku has been observed from 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.
There is no supplementary information for Kyushu-Okinawa region.
–"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 October 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, October 7, 2020)
"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.
Reference 2
Information that is described in the "Supplementary Information to the Evaluation" includes: