September 9, 2022
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On August 11 at 00:53 (JST), there was a magnitude (M) 5.4 earthquake in the northern Kamikawa region (#) and maximum seismic intensity 5 Upper was observed in Hokkaido. In the vicinity of the event, at 00:35(JST) on the same day, there was an M5.2 earthquake and maximum seismic intensity 5 Lower was observed in Hokkaido.
* On August 4, there was an M4.1 earthquake at a depth of approximately 5 km in the northern Soya region. This event occurred within the crust. In the vicinity of the event, from August 4 till 31st there occurred 6 earthquakes with seismic intensity 1 or over observed.
Also, in the vicinity of this event, on June 20 there was an M4.4 earthquake.
* On August 7, there was an M6.0 earthquake offshore east of Hokkaido.
* On August 11 at 00:53 (JST), there was an M5.4 earthquake at a depth of approximately 5 km in the northern Kamikawa region (#). The focal mechanism showed a reverse fault type with a compression axis in an E-W direction. This event occurred within the crust. In the vicinity of the event, at 00:35(JST) on the same day, there was an M5.2 earthquake.
In the vicinity of these events, from August 11 till September 8 at 08 o'clock (JST) there occurred 28 earthquakes with seismic intensity 1 or over observed.
According to the GNSS observation, accompanying the recent event, very slight crustal deformation in the north direction was observed at Horonobe observatory, Horonobe Town, Hokkaido.
In the vicinity of the recent seismic activity area, from July 15 till 18th there were 4 earthquakes with M4.1~4.3. Note that the M4.1 earthquake in the northern Soya region on August 4, 2022 occurred approximately 30 km northwest of the recent seismic activity area.
* On August 4, there was an M5.6 earthquake at a depth of approximately 55 km, offshore Fukushima prefecture. The focal mechanism showed a reverse fault type with a compression axis in an NE-SW direction. Also, on August 18, there was an M5.2 earthquake at a depth of approximately 55 km. The focal mechanism showed a reverse fault type with a compression axis in an NNE-SSW direction. These events occurred within the Pacific plate.
In the vicinity of these events, on March 16, there had been an M7.4 earthquake within the Pacific plate. The seismic activity continues: from March 16 till September 8 at 08 o'clock (JST) there occurred 176 earthquakes with seismic intensity 1or over observed, and from August 1 till September 8 at 08 o'clock (JST) there occurred 8 earthquakes. The M5.6 earthquake on August 4 was the largest after the M7.4 one on March 16.
* In the crust of the Noto region, Ishikawa prefecture, where the number of earthquakes is increasing since about 2018, the seismic activity became high since December 2020, and it has become higher since about July 2021. The largest is an M5.4 earthquake which occurred on June 19, 2022. Beside this there occurred an M5.1 earthquake on September 16, 2021 and an M5.0 earthquake on June 20, 2022. From December 1, 2020 till September 8, 2022 at 08 o'clock (JST), there occurred 201 earthquakes with seismic intensity 1 or over observed: of these 31 earthquakes with seismic intensity 3 or over observed.
From August 2022 till September 8 at 08 o'clock (JST) there occurred 10 earthquakes with seismic intensity 1 or over observed: such as an M4.1 earthquake on August 14. The serial seismic activity still continues in an active state, without any sign of decline.
According to the GNSS observation, since about December 2020, the following crustal deformation has been observed: the cumulative displacement of 1 cm over in the southeast direction and the uplift of 4 cm or so at the Suzu observatory, Suzu City, Ishikawa prefecture and the cumulative displacement of 1 cm over in the south-southwest direction at the Noto observatory, Noto Town.
Based on the situation of the seismic activity and the crustal deformation, the series of the seismic activity will continue for the time being and we should pay attention for a strong shaking.
* On August 6, there was an M5.0 earthquake at a depth of approximately 30 km, offshore Ibaraki prefecture. The focal mechanism showed a normal fault type with a tension axis in a WNW-ESE direction. This event occurred within the continental plate.
* On August 18 at 13:07 (JST), there was an M5.0 earthquake at a depth of approximately 20 km, offshore east of Chiba prefecture. At 13:06 (JST) just before the recent event, at almost the same place there occurred an M4.9 earthquake. The focal mechanism of the M4.9 earthquake at 13:06 (JST) had a compression axis in an NNE-SSW direction.
There was no remarkable activity.
* On August 26, there occurred an M4.5 earthquake at a depth of approximately 10 km in the Amakusanada. The focal mechanism showed a normal fault type with a tension axis in an N-S direction. This event occurred within the crust of the continental plate.
* 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.
#: The region name [in the northern Soya region] was used in the Japan Meteorological Agency announcement.
Note: GNSS is a general name of satellite positioning system such as GPS.
September 9, 2022
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during August 2022.
(Reference)
The following events for the period from August 2021 to late July 2022 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – In the Noto Region, Ishikawa Prefecture | M5.1 on September 16, 2021 (Depth of approximately 15 km) |
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| – Offshore Iwate Prefecture | M5.9 on October 6, 2021 (Depth of approximately 55 km) |
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| – Under the Northwestern Chiba Prefecture | M5.9 on October 7, 2021 (Depth of approximately 75 km) |
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– Under the Eastern and Fujigoko Regions, |
M4.8 on December 3, 2021 Regions, Yamanashi prefecture |
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| – Under the Kii Channel | M5.4 on December 3, 2021 (Depth of approximately 20 km) |
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| – In the Ocean near Tokara Islands | M6.1 on December 9, 2021 | ||
| – Under the Ocean near Chichijima Island | M6.1 on January 4, 2022 (Depth of approximately 60 km) |
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| – Under the Hyuganada |
M6.6 on January 22, 2022 (Depth of approximately 45 km) |
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| – Offshore Fukushima Prefecture | M7.4 on March 16, 2022 (Depth of approximately 55 km) |
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| – Offshore Iwate Prefecture | M5.6 on March 18, 2022 (Depth of approximately 20 km) |
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| – Under the Northern Ibaraki Prefecture | M5.4 on April 19, 2022 (Depth of approximately 95 km) |
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| – Offshore Ibaraki Prefecture | M6.0 on May 22, 2022 (Depth of approximately 5 km) |
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| – In the Noto Region, Ishikawa Prefecture |
M5.4 on June 19, 2022 (Depth of approximately 15 km) |
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| – In the Kumamoto Region, Kumamoto Prefecture |
M4.7 on June 26, 2022 (Depth of approximately 10 km) |
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There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
– Offshore east of Hachijojima Island, within the Pacific plate in the east side of the trench, the seismic activity became high from July 29 and till September 6, there occurred 62 and 16 earthquakes, respectively with M4.0 or over and M5.0 or over. The largest is the M5.7 earthquake on August 4. The focal mechanisms of the major earthquakes of the recent seismic activity showed a normal fault type with a tension axis in the NE-SW to E-W direction.
Near the trench axis about 80 km distant in the north-northwest direction from the recent seismic activity area, during August there occurred 4 and 2 earthquakes, respectively with M4.0 or over and M5.0 or over, such as an M5.7 earthquake on August 17.
– According to the GNSS observation, the crustal deformation different from the ordinary trend in the central Shikoku has been observed from about 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, being observed from about 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. The crustal deformation seems to have decayed about spring 2022 and to be in the same state at present.
– Within the continental plate offshore northwest of Okinawa Main Island, an active seismic activity is observed from January 30, and till September 8 at 08 o'clock (JST), there occurred 67 earthquakes with seismic intensity 1 or over observed: of these from August 1 there occurred 2 earthquakes. In the series of seismic activity there occurred 19 earthquakes of M5.0 or over, the largest being M5.9 earthquakes on March 17 and June 3. Since August 1, there has occurred no earthquake of M5.0 or over. The seismic activity is decaying with time.
According to the GNSS observation, crustal deformation was observed from about February 2022 such as a south-southeastward displacement of 1 cm over of Gushikawa observatory, Kumejima Town, Okinawa prefecture.
In the neighborhood of the area of the recent seismic activity, there were several seismic clusters: from February to March 1980 and in August 2007, there were clusters including earthquakes of M6.0 or over. In the seismic activity from February to March 1980, there were M6.7 and M6.3 earthquakes.
– According to the GNSS observation, the crustal deformation different from the ordinary trend in the southern Kyushu, being observed from about 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 be stagnant since autumn 2021, but now seems to have returned to the former state.
– "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 September 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, September 7, 2022)
"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: