August 9, 2022
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
* On July 2, there was a magnitude (M) 5.9 earthquake at a depth of approximately 320 km under the Soya Strait. The focal mechanism had a compression axis in the subducting direction of the Pacific plate. This event occurred within the Pacific plate. Seismic intensity 3~1 was observed in the area extending from Hokkaido to Tohoku regions: in addition to epicentral area, the ground quake was large also along the Pacific side of the area from Hokkaido to Tohoku regions due to the seismic waves which propagated through the subducting Pacific plate (abnormal seismic intensity).
* On July 5, there was an M4.9 earthquake at a depth of approximately 55 km under the eastern Hidaka region. 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 July 6, there was an M5.4 earthquake at a depth of approximately 65 km, offshore Miyagi prefecture. The focal mechanism showed a reverse fault type with a compression axis in an NW-SE direction. This event occurred within the Pacific plate.
* On July 22, there was an M5.3 earthquake at a depth of approximately 85 km under the Sanpachi Kamikita region, Aomori prefecture. The focal mechanism had a tension axis in an N-S direction. This event occurred within the Pacific plate.
* 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 August 8, 2022 at 08 o'clock (JST), there occurred 192 earthquakes with seismic intensity 1 or over: of these 30 earthquakes with seismic intensity 3 or over.
The serial seismic activity has an active state, without any sign of decline, and continues in July 2022 and later: till August 8 at 08 o'clock (JST) there occurred 10 earthquakes with seismic intensity 1 or over.
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 south-southeast direction and the uplift of 4 cm or so at the Suzu observatory in Suzu City, Ishikawa prefecture and the cumulative displacement of 1 cm over in the south-southwest direction at the Noto observatory in 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.
There was no remarkable activity.
* Within the continental plate offshore northwest of Okinawa Main Island, an active seismic activity is observed from January 30, and till August 8 at 08 o'clock (JST), there occurred 65 earthquakes with seismic intensity 1 or over: of these from July 1 till August 8 at 08 o'clock (JST), there occurred 5 earthquakes. In the series of seismic activity, till August 8 at 08 o'clock (JST) there occurred 19 earthquakes of M5.0 or over, the largest being M5.9 earthquakes on March 17 and June 3. The largest between July 1 and August 8 at 08 o'clock (JST) are 3 M5.1 earthquakes on July 6, 8, and 25.
According to the GNSS observation, crustal deformation was observed from about February 2022 such as a 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.
* 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 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, on June 20 there was an M4.4 earthquake.
* 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. This event occurred within the Pacific plate.
In the vicinity of the event, on March 16 there was an M7.4 earthquake within the Pacific plate. The seismic activity continues: from March 16 till August 8 at 08 o'clock (JST) there were 170 earthquakes with seismic intensity 1 or over: of these from July 1 till August 8 at 08 o'clock (JST) 9 earthquakes. The recent event is the largest after the M7.4 earthquake on March 16.
Note: GNSS is a general name of satellite positioning system such as GPS.
August 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 July 2022.
(Reference)
The following events for the period from July 2021 to late June 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) |
||
| – Offshore Iwate Prefecture | M5.9 on October 6, 2021 (Depth of approximately 55 km) |
||
| – Under the Northwestern Chiba Prefecture | M5.9 on October 7, 2021 (Depth of approximately 75 km) |
||
– Under the Eastern and Fujigoko Regions, |
M4.8 on December 3, 2021 Regions, Yamanashi prefecture |
||
| – Under the Kii Channel | M5.4 on December 3, 2021 (Depth of approximately 20 km) |
||
| – 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) |
||
| – Under the Hyuganada |
M6.6 on January 22, 2022 (Depth of approximately 45 km) |
||
| – Offshore Fukushima Prefecture | M7.4 on March 16, 2022 (Depth of approximately 55 km) |
||
| – 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) |
||
| – Offshore Ibaraki Prefecture | M6.0 on May 22, 2022 (Depth of approximately 5 km) |
||
| – in the Noto Region, Ishikawa Prefecture |
M5.4 on June 19, 2022 (Depth of approximately 15 km) |
||
| – in the Kumamoto Region, Kumamoto Prefecture |
M4.7 on June 26, 2022 (Depth of approximately 10 km) |
||
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.
– In the crust of the southern Kyoto prefecture, the seismic activity became high since March 31, and till June 30 there occurred 16 earthquakes with seismic intensity 1 or over: of these 4 earthquakes with seismic intensity 3 or over. In July there was no earthquake with seismic intensity 1 or over. The largest are 2 M4.4 earthquakes which occurred on March 31 and May 2. Though the seismic activity still continues, it is decaying with time.
In the vicinity of the recent seismic activity, there was a cluster from February to March, 1999: an M4.2 earthquake on February 12 and an M4.0 on March 12.
– 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.
* Revision of the analytic method was performed and the representation was altered on the observed crustal deformation different from the ordinary trend in the western Kii Peninsula and the eastern Shikoku, which caused estimated long-term slow-slip around the Kii Channel at the deeper part of the plate boundary.
– 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.
* Revision of the analytic method was performed and the representation was altered on the observed crustal deformation different from the ordinary trend in the southern Kyushu, which caused estimated long-term slow-slip around the southern Hyuganada at the deeper part of the plate boundary.
– "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 August 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, August 5, 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: