June 9, 2022
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On May 22, there was a magnitude (M) 6.0 earthquake offshore Ibaraki prefecture and maximum seismic intensity 5 Lower was observed in Fukushima prefecture. Long-period ground motion class 2 was observed in Fukushima prefecture. Also damage with partially damaged houses and so on was caused.
* On May 22, there was an M4.7 earthquake at a depth of approximately 45 km in the eastern Hidaka region. The focal mechanism showed a reverse fault type with a compression axis in an NE-SW direction. This event occurred within the continental plate.
* On May 23, there was an M5.6 earthquake at a depth of approximately 25 km, offshore east of Aomori 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 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 M5.1 earthquake which occurred on September 16, 2021. From December 1, 2020 till June 8, 2022 at 08 o'clock (JST) there occurred 142 earthquakes with seismic intensity 1 or over.
The high seismic activity continues in May 2022 and later: such as an M4.1 earthquakes on May 2 and 20. From May1 till June 8 at 08 o'clock (JST) there occurred 20 earthquakes with seismic intensity 1 or over: of these 4 earthquakes with seismic intensity 3 or over. Note that in the serial seismic activity area, the number of earthquakes of M3.0 or over has increased since March 2022 in the eastern region.
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. The deformation at the Suzu observatory continues at present. On the other hand, the deformation at the Noto observatory seems to have decayed since about January 2022.
Based on the situation of the seismic activity and the crustal deformation, the series of the seismic activity will continue for the time being.
* On May 3, there was an M4.6 earthquake at a depth of approximately 130 km under the eastern Tama, Tokyo prefecture. The focal mechanism had a compression axis in an NNE-SSW direction. This event occurred within the Pacific plate.
* On May 5, there was an M4.8 earthquake at a depth of approximately 50 km in the southern Ibaraki prefecture. The focal mechanism showed a reverse fault type with a compression axis in an NNW-SSE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On May 22, there was an M6.0 earthquake at a depth of approximately 5 km, offshore 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 crust of the continental plate.
According to the GNSS observation, no significant crustal deformation was observed accompanying the event.
* On May 23, there was an M6.1 earthquake at a depth of approximately 10 km (CMT solution), offshore east of Hachijojima Island. The focal mechanism showed a reverse fault type with a compression axis in an E-W direction. In the vicinity of the event, there occurred 7 earthquakes of M5.0 or over in May, such as M5.6 earthquakes on May 17 and 18.
* On May 29, there was an M5.3 earthquake at a depth of approximately 45 km, offshore Ibaraki 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 May 2, there was an M4.4 earthquake at a depth of approximately 15 km in the southern Kyoto prefecture. The focal mechanism showed a strike-slip fault type with a compression axis in an E-W direction. The event occurred within the crust. In the vicinity of the event, the seismic activity became high since March 31: on March 31 occurred an M4.4 earthquake, and on April 30 occurred an M4.3 earthquake. From March 31 till June 8 at 08 o'clock (JST), there occurred 16 earthquakes with seismic intensity 1 or over: of these, 4 earthquakes with seismic intensity 3 or over.
In the neighborhood 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.
* Within the continental plate offshore northwest of Okinawa Main Island, an active seismic activity is observed from January 30 and till June 8 at 08 o'clock (JST), and there occurred 54 earthquakes with seismic intensity 1 or over. From May 1 till June 8 at 08 o'clock (JST), there occurred 8 earthquakes. In the series of seismic activity, till June 8 at 08 o'clock (JST) there occurred 14 earthquakes of M5.0 or over, the largest being M5.9 earthquakes on March 17 and June 3.
According to the GNSS observation, crustal deformation was observed from about February 2022 such as a south-southeastward displacement of 1 cm or so 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.
* On May 2, there was an M5.0 earthquake at a depth of approximately 20 km in the Hyuganada. 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.
* On May 9, there was an M6.6 earthquake at a depth of approximately 20 km in the ocean near Yonagunijima Island. The focal mechanism had a compression axis in an NNW-SSE direction.
In the vicinity of the recent event there are several cases in which earthquakes of similar scale consecutively occurred: on April 20, 2015 there was an M6.8 earthquake and after 10 hours occurred an M6.4 earthquake.
* 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.
Note: GNSS is a general name of satellite positioning system such as GPS.
June 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 May 2022.
(Reference)
The following events for the period from May 2021 to late April 2022 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – Offshore Miyagi Prefecture | M6.8 on May 1, 2021 (Depth of approximately 50 km) |
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| – 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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There is no supplementary information for Hokkaido region.
– In the aftershock area of the M7.4 earthquake on March 16 within the Pacific plate, from May 1 till June 8 at 08 o'clock (JST), there occurred 23 earthquakes with seismic intensity 1 or over. The largest in May is an M4.7 earthquake on 27th. From March 16 till June 8 at 08 o'clock (JST), there occurred 148 earthquakes with seismic intensity 1 or over. The seismic activity continues but is decaying with time.
– In the area extending from the northern to central Kii Peninsula, from May 18 till 31, deep low-frequency earthquakes (tremors) were observed, near the boundary between the Philippine Sea and the continental plates. According to the strain and tilt data in the surrounding area, slight crustal deformation was observed, almost synchronous with the deep low-frequency earthquake (tremor) activity. 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 has been observed from about 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.
– 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. Recently this crustal deformation seems to be stagnant.
– "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 June 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, June 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: