March 9, 2021
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On February 13, there was a magnitude (M) 7.3 earthquake offshore Fukushima prefecture. Maximum seismic intensity 6 Upper was observed in Miyagi and Fukushima prefectures and damage with a fatality and so on was caused.
* On February 20, there was an M5.0 earthquake at a depth of approximately 70 km, offshore east of Hokkaido. The focal mechanism had a compression axis in an NNW-SSE direction. This event occurred within the Pacific plate.
* With regard to the earthquake offshore Fukushima prefecture on February 13, refer to another report (Evaluation of Earthquake Offshore Fukushima Prefecture on February 13, 2021).
* On February 14, there was an M5.1 earthquake at a depth of approximately 45 km, offshore Iwate prefecture. The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.
* On February 19, there was an M4.2 earthquake at a depth of approximately 5 km in the northern inland of Iwate prefecture. The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred within the crust.
* On February 2, there was an M4.0 earthquake at a depth of approximately 5 km in the northern Tochigi 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 February 15, there was an M4.0 earthquake at a depth of approximately 5 km in the northern Wakayama prefecture. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred within the crust.
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 March 3, there was an M5.9 earthquake, offshore west of Hokkaido. The focal mechanism showed a reverse fault type with a compression axis in an NW-SE direction.
March 9, 2021
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during February 2021.
(Reference)
The following events for the period from February 2020 to late January 2021 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – 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) |
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| – Reihoku, Fukui Prefecture | M5.0 on September 4, 2020 (Depth of approximately 5 km) |
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| – Offshore Ibaraki prefecture | M5.7 on November 22, 2020 (Depth of approximately 45 km) |
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| – Offshore Iwate Prefecture | M5.6 on December 12, 2020 (Depth of approximately 50 km) |
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| – Ocean Area Near Niijima and Kozushima Islands | M5.0 on December 18, 2020 (Depth of approximately 5 km) |
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| – Offshore East of Aomori Prefecture | M6.5 on December 21, 2020 (Depth of approximately 45 km) |
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There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
There is no supplementary information for Kanto-Chubu region.
– 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.
– According to the GNSS observation, the crustal deformation different from the ordinary trend in the western Kii Peninsula and the eastern Shikoku, has been observed from summer 2020. This phenomenon is considered to be caused by a long-term slow slip around the Kii Channel at the deeper part of the boundary between the Philippine Sea and the continental plates. This crustal deformation seems to have slowed down recently.
– According to the GNSS observation, the crustal deformation different from the ordinary trend in the northern Kyushu has been observed from summer 2020. This phenomenon is considered to be caused by a long-term slow slip around the northern Hyuganada at the deeper part of the boundary between the Philippine Sea and the continental plates. This crustal deformation seems to have slowed down recently.
– According to the GNSS observation, the crustal deformation different from the ordinary trend in southern Kyushu, has been observed from summer 2020. This phenomenon is considered to be caused by a long-term slow slip around the southern Hyuganada at the deeper part of the boundary between the Philippine Sea and the continental plates.
–"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 March 5 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, March 5, 2021)
"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: