June 9, 2020
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
* On May 31, there was a magnitude (M) 5.6 earthquake at a depth of approximately 95 km, offshore Tokachi. The focal mechanism had a tension axis in an N-S direction. This event occurred within the Pacific plate.
* On May 18, there was an M5.2 earthquake at a depth of approximately 50 km, offshore Miyagi 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 19, there was an M5.4 earthquake at a depth of approximately 50 km, offshore Fukushima 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 4, there was an M5.6 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 May 6, there was an M5.0 earthquake at a depth of approximately 70 km under the northwestern Chiba prefecture. The focal mechanism showed a reverse fault type with a compression axis in an ENE-WSW direction.
* On May 11, there was an M5.8 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.
* Near the border between Nagano and Gifu prefectures (the central Nagano prefecture and the Hida region, Gifu prefecture) there was an active seismic activity such as the increase of earthquakes with M3.0 over beginning on April 22 and an M5.5 earthquake occurring on April 23. In May there were an M5.4 earthquake on 19th and an M5.3 on 29th. The focal mechanisms of these 3 earthquakes showed a strike-slip fault type with a compression axis in an NW-SE direction. These events occurred within the crust. There occurred 173 earthquakes with the maximum seismic intensity 1 or over in the period from April 22 till June 9 at 9 o'clock.
Also, in 1998, the seismic activity became high: there occurred an M5.0 earthquake on August 12, and an M5.6 on August 16, and earthquakes with M3.0 over in December.
* On May 17, there was an M4.6 earthquake at a depth of approximately 35 km under the Kii Channel. The focal mechanism showed a strike-slip fault type with a tension axis in an E-W direction. This event occurred within the Philippine Sea plate.
* On May 3, there was an M6.2 earthquake at a depth of approximately 10 km (CMT solution), offshore west of the Satsuma Peninsula. 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.
* On May 23, there was an M4.9 earthquake at a depth of approximately 50 km under the ocean area near Okinawa Main Island (near Okinoerabujima). 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 27, there was an M5.2 earthquake at a depth of approximately 50 km, under the ocean area near Miyakojima. The focal mechanism showed a reverse fault with a compression axis in an NW-SE direction. This event occurred at the boundary between the Philippine Sea and the continental plates.
* 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 June 1, there was an M5.2 earthquake at a depth of approximately 95 km under the northern Ibaraki prefecture. The focal mechanism had a tension axis in an NW-SE direction. This event occurred within the Pacific plate.
* On June 1, there was an M4.3 earthquake at a depth of approximately 10 km, offshore west of the Satsuma Peninsula. The focal mechanism showed a strike-slip fault type with a tension axis in an NW-SE direction. This event occurred within the crust.
* On June 4, there was an M4.8 earthquake at a depth of approximately 50 km, offshore Ibaraki 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.
June 9, 2020
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during May 2020.
(reference)
The following events for the period from May 2019 to late April 2020 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – Northern Hyuganada | M6.3 on May 10, 2019 (Depth of approximately 25 km) |
|
| – Northeastern Chiba Prefecture | M5.1 on May 25, 2019 (Depth of approximately 40 km) |
|
| – Offshore Yamagata Prefecture | M6.7 on June 18, 2019 (Depth of approximately 15 km) |
|
| – Offshore Fukushima Prefecture | M6.4 on August 4, 2019 (Depth of approximately 45 km) |
|
| – Offshore East of Aomori Prefecture | M5.5 on December 19, 2019 (Depth of approximately 50 km) |
|
| – Noto Region, Ishikawa Prefecture | M5.5 on March 13, 2020 (Depth of approximately 10 km) |
There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
– According to the GNSS observation, a slight crustal deformation different from the ordinary trend has been observed in the Shima Peninsula from mid-2019. This phenomenon is considered to be caused by a long-term slow slip around the Shima Peninsula 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 spring 2019 seems to be stagnant recently. 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 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.
There is no supplementary information for Kyushu-Okinawa region.
–"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 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, June 5, 2020)
"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: