June 11, 2018
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On May 12, there was a magnitude (M) 5.2 earthquake in the northern Nagano prefecture. Maximum seismic intensity 5 Lower was observed in Nagano prefecture.
* On May 25, there was an M5.2 earthquake in the northern Nagano prefecture (near the boundary between Nagano and Niigata prefectures). Maximum seismic intensity 5 Upper was observed in Nagano prefecture.
* On May 18, there was an M5.8 earthquake at a depth of approximately 45 km, offshore Kushiro. 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 Pacific and the continental plates.
* On May 7, there was an M5.1 earthquake at a depth of approximately 100 km under the northern inland, Iwate prefecture. The focal mechanism had a compression axis in an NNE-SSW direction. This event occurred within the Pacific plate.
* On May 13, there was an M4.8 earthquake at a depth of approximately 50 km, offshore Miyagi prefecture. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On May 14, there was an M5.1 earthquake at a depth of approximately 30 km offshore Iwate prefecture. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On May 6, there was an M5.7 earthquake in the ocean area near Torishima [offshore east of Hachijojima]. This event occurred within the crust of the Philippine Sea plate. In addition to tsunami with height of 0.3 m at Hachijojima, Tokyo Metropolis, weak tsunami was observed in Izu Ilands and Shizuoka prefecture.
* On May 12, there was an M5.2 earthquake in the northern Nagano prefecture. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred within the crust.
* On May 17, there was an M5.3 earthquake at a depth of approximately 50 km under the northeastern Chiba prefecture [Offshore east of Chiba 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 Philippine Sea plates.
* On May 25, there was an M5.2 earthquake at a depth of approximately 5 km in the northern Nagano prefecture (near the boundary between Nagano and Niigata prefectures). The focal mechanism showed a reverse fault type with a compression axis in an NNW-SSE direction. This event occurred within the crust.
There was no remarkable activity.
* On May 6, there was an M3.9 earthquake at a depth of approximately 10 km in the Kumamoto region, Kumamoto prefecture. The focal mechanism had a tension axis in an N-S direction. This event occurred within the crust.
* 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:[ ] is the regional name of the epicenter used in the Japan Meteorological Agency announcement.
June 11, 2018
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during May 2018.
(reference)
The following events for the period from May 2017 to late April 2018 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – Bungo Channel | M5.0 on June 20, 2017 (Depth of approximately 40 km) |
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| – Southern Nagano Prefecture | M5.6 on June 25, 2017 (Depth of approximately 5 km) |
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| – Central and Eastern Iburi Region | M5.1 on July 1, 2017 (Depth of approximately 25 km) |
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| – Aso Region, Kumamoto Prefecture | M4.5 on July 2, 2017 (Depth of approximately 10 km) |
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| – Kagoshima Bay | M5.3 on July 11, 2017 (Depth of approximately 10 km) |
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| – Southern Inland, Akita Prefecture | M5.2 on September 8, 2017 (Depth of approximately 10 km) |
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| – Offshore Fukushima Prefecture | M5.9 on October 6, 2017 (Depth of approximately 55 km) |
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| – Near Iriomotejima | M5.6 on March 1, 2018 (Depth of approximately 15 km) |
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| – Western Shimane Prefecture | M6.1 on April 9, 2018 (Depth of approximately 10 km) |
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| – Offshore southeast of Nemuro Prninsula | M5.4 on April 14, 2018 (Depth of approximately 55 km) |
There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
–" On May 12, there was an M5.2 earthquake at a depth of approximately
10 km in the northern Nagano prefecture. (Excerpted)":
In the vicinity of the event at the Kamishiro fault zone, which is a part of Itoigawa-Shizuoka Tectonic Line, there was an M6.7 earthquake in 2014. This event occurred in the area where the seismic activity became high after the M6.7 earthquake, and occurred perhaps at the deep part of the Kamishiro fault zone.
– "On May 6, there was an M5.7 earthquake in the ocean area
near Torishima [offshore east of Hachijojima]. (Excerpted)":
In the vicinity of this event, there occurred an M5.9 earthquake on June 13, 1984, an M6.2 on September 5, 1996, an M5.9 on January 1, 2006, and an M5.9 on May 3, 2015 which all caused tsunami observed, in spite of the magnitude of M6.0 or so.
There is no supplementary information for Kinki-Chugoku-Shikoku region.
–" On May 6, there was an M3.9 earthquake at a depth of approximately
10 km in the Kumamoto region, Kumamoto prefecture. (Excerpted)"
The seismic activity series in the Kumamoto and Aso regions of the 2016 Kumamoto Earthquakes, decaying as a whole, still continues and the activity at the present level is expected for the time being. According to the GNSS observation result, a slight postseismic deformation is continuing.
–"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, 2018)
"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)"
– From early June a seismic activity is observed offshore east of Chiba prefecture. In addition according to the tilt-GNSS data, slight crustal deformation is observed in Boso peninsula. These phenomena are considered to be caused by the short-term slow-slip at the boundary between the Philippine Sea and the continental plates.
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: