July 9, 2021
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
* On June 20, there was a magnitude (M) 5.4 earthquake at a depth of approximately 160 km under the central Kamikawa region. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate
* On June 9, there was an M5.0 earthquake at a depth of approximately 40 km, offshore Iwate 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 June 7, there was an M5.1 earthquake at a depth of approximately 95 km, offshore southeast of Chiba prefecture. The focal mechanism showed a normal fault type with a tension axis in an E-W direction. This event occurred within the Pacific plate.
* On June 19, there was an M4.7 earthquake at a depth of approximately 40 km, in the Nanyo region, Ehime prefecture. The focal mechanism showed a normal fault type with a tension axis in an E-W direction. This event occurred within the Philippine Sea plate.
* On June 8, there was an M3.9 earthquake at a depth of approximately 10 km in the Kumamoto region, Kumamoto prefecture. The focal mechanism showed a strike-slip fault type with a tension axis in an N-S direction. This event occurred within the crust.
* 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.
July 9, 2021
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during June 2021.
(Reference)
The following events for the period from June 2020 to late May 2021 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – 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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| – Offshore Fukushima Prefecture | M7.3 on February 13, 2021 (Depth of approximately 55 km) |
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| – In Kermadec Islands | Mw8.1 on March 5, 2021 | ||
| – In the Northern Wakayama M4.6 on March 15, 2021 Prefecture | M4.6 on March 15, 2021 (Depth of approximately 5 km) |
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| – Offshore Miyagi Prefecture | M6.9 on March 20, 2021 (Depth of approximately 60 km) |
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| – Offshore Miyagi Prefecture | M6.8 on May 1, 2021 (Depth of approximately 50 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 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, observed from summer 2020, 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 southern Kyushu, observed from summer 2020, 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. This crustal deformation seems to have slowed down recently.
–"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 July 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, July 7, 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: