October 12, 2022
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
There was no remarkable activity.
* On September 13, there was a magnitude (M) 5.1 earthquake at a depth of approximately 55 km, offshore east of Aomori 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 20, there was an M4.4 earthquake at a depth of approximately 50 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.
* 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 October 11, 2022 at 08 o'clock (JST), there occurred 219 earthquakes with seismic intensity 1 or over observed: of these 32 earthquakes with seismic intensity 3 or over observed.
From September 2022 till October 11 at 08 o'clock (JST), there occurred 18 earthquakes with seismic intensity 1 or over observed. The serial seismic activity still continues in an active state, without any sign of decline at present.
According to the GNSS observation, since about December 2020, the following crustal deformation has continued: the cumulative displacement of 1 cm over in the south-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 and so on are observed.
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 September 9, there was an M4.5 earthquake at a depth of approximately 5 km in the northern Ibaraki prefecture. The focal mechanism showed a normal fault type with a tension axis in a WNW-ESE direction. This event occurred within the crust.
* On September 18, there was an M4.7 earthquake at a depth of approximately 50 km under the northeastern Chiba prefecture. The focal mechanism showed a reverse fault type with a compression axis in an E-W direction. This event occurred at the boundary between the Pacific and the Philippine Sea plates.
* On September 23, there was an M4.7 earthquake at a depth of approximately 85 km, under the southern Ibaraki prefecture. The focal mechanism showed a strike-slip fault type with a tension axis in an E-W direction. This event occurred within the Pacific plate.
* On September 30, there was an M4.4 earthquake at a depth of approximately 45 km under the southern Ibaraki prefecture. The focal mechanism showed a reverse fault type with a compression axis in an NW-SE direction. This event occurred at the boundary between the Philippine Sea and the continental plates.
There was no remarkable activity.
* On September 18, there occurred an M6.0 earthquake offshore northwest of Okinawa Main Island. The focal mechanism showed a strike-slip fault type with a tension axis in an NW-SE direction. This event occurred within the crust of the continental plate. In the vicinity of this event, from September 14 till October11 at 08 o'clock (JST) there occurred 8 earthquakes with seismic intensity 1 or over observed, such as an M5.7 earthquake which occurred about 2 hours later than the recent event.
Near the recent seismic activity area, there are example cases of the successive occurrences of earthquakes with similar scales. On December 24, 2003, an M6.0 earthquake occurred, preceded by an M5.6 one immediately before, and followed by an M5.5 one immediately after.
Note that within the continental plate about 60 km apart from the recent seismic activity area in the northwest direction, there was a high seismic activity from January 30, 2022.
* 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 September 18, there was an M7.3 earthquake at a depth of approximately 5 km near Taiwan. The focal mechanism had a compression axis in an NNW-SSE direction. This event occurred within the crust. On the previous day, 17th, there were M6.6 and M6.0 earthquakes. In the vicinity of these earthquakes, the seismic activity became high since 17th. According to the image of Interferometry analysis of Synthetic Aperture Radar data by Advanced Land Observing Satellite "Daichi-2", a crustal deformation with 1m over was observed in the area around the epicenter.
* On October 2, there was an M5.9 earthquake at a depth of approximately 30 km, offshore east of the Osumi peninsula, and maximum seismic intensity 5 Lower was observed in Miyazaki prefecture. Long-period ground motion class 2 was observed in Miyazaki 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 Philippine Sea and the continental plates. According to the GNSS observation, no significant crustal deformation accompanying this event was observed.
#: The region name [offshore Urakawa] was used in the Japan Meteorological Agency announcement.
Note: GNSS is a general name of satellite positioning system such as GPS.
October 12, 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 September 2022.
(Reference)
The following events for the period from September 2021 to late August 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) |
||
| – 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) |
||
| – In the Northern Kamikawa Region |
on August 11, 2022 M5.4 (Depth of approximately 5 km) M5.2 (very shallow) |
||
There is no supplementary information for Hokkaido region.
– In the seismic activity area of the M7.4 earthquake on March 16 within the Pacific plate, the seismic activity continues: from September 1 till October 11 at 08 o'clock (JST), there were 9 earthquakes with seismic intensity 1 or over observed. The largest in September is an M4.8 earthquake on 4th. From March 16 till October 11 at 08 o'clock (JST), there were 183 earthquakes with seismic intensity 1 or over observed.
There is no supplementary information for Kanto-Chubu Region.
– In the area extending from the central to the western Shikoku, from September 1 till September 13, deep low-frequency earthquakes (tremors) were observed. According to the strain and tilt data in the surrounding area, almost synchronized with the deep low-frequency earthquake (tremor) activity, slight crustal deformations were observed. These phenomena are considered to be caused by the short-term slow slip 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 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, seems to have completely converged. The deformation was 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 long-term slow-slip seems to have already decayed.
– Within the continental plate offshore northwest of Okinawa Main Island, an active seismic activity is observed from January 30, and till October 11 at 08 o'clock (JST), there occurred 69 earthquakes with seismic intensity 1 or over observed: of these from September 1 there occurred 3 earthquakes. In the series of seismic activity, the largest are 2 M5.9 earthquakes on March 17 and June 3. The seismic activity is decaying with time.
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 ocean near Tokara Islands, a seismic activity began on September 9, and till 30th there occurred 16 earthquakes with seismic intensity 1 or over observed. The largest is an M3.9 earthquake on 10th. In the recent seismic activity area, there were several seismic clusters: from September to October 2020, there was a cluster. Note that in Suwanosejima Island, the volcanic activity became high on September 26, 2022.
– 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 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, 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)"
There is no supplementary information for other regions.
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: