January 11, 2012
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
* On December 10, there was a M5.7 earthquake at a depth of approximately 430 km under the southern Okhotsk Sea. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.
* On December 20, there was a M5.0 earthquake at a depth of approximately 30 km, offshore Iwate prefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred on the boundary between the Pacific and the continental plates.
* On December 1, there was a M4.6 earthquake at a very shallow depth in northern Nagano prefecture. The focal mechanism had a compression axis in an NW-SE direction. This event occurred within the crust.
* On December 3, there was a M5.2 earthquake at a depth of approximately 20 km in northeastern Chiba prefecture [southern Chiba prefecture]. The focal mechanism showed a reverse fault with a compression axis in an NNW-SSE direction. This event occurred on the boundary between the Philippine Sea and the continental plates.
* On December 14, there was a M5.1 earthquake at a depth of approximately 50 km under eastern Mino, Gifu prefecture. The focal mechanism showed a normal fault with a tension axis in an E-W direction. This event occurred within the Philippine Sea plate.
* On December 31, there was a M4.5 earthquake at a depth of approximately 10 km in northern Ibaraki prefecture. The focal mechanism showed a normal fault with a tension axis in a WNW-ESE direction. This event occurred within the crust
* In the GPS data for the Tokai region, there have been no changes of activity which are likely to be associated with the Tokai earthquake.
There was no remarkable activity.
* On December 11, there was an M5.5 earthquake in the sea near Amami Oshima. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction.
* On January 1, there was a M4.2 earthquake at a depth of approximately 5 km in the vicinity of the border of Nagano and Niigata prefectures. The focal mechanism showed a strike-slip fault with a compression axis in an NNW-SSE direction. This event occurred within the crust.
* On January 1, there was a M7.0 earthquake at a depth of approximately 400 km under the sea near Torishima. The focal mechanism had a compression axis in a direction of the subducting Pacific plate. This event occurred within the Pacific plate.
Note:[ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.
January 11, 2012
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during December 2011.
(reference)
The following events for the period from December 2010 to the end of November 2011 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities
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– Under the Ocean near Chichijima |
M7.8 on December 22, 2010 |
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– Offshore Sanriku |
M7.3 on March 9, 2011 |
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– The 2011 off the Pacific Coast of Tohoku Earthquake | M9.0 on March 11, 2011 (Depth of approximately 25 km) |
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– Izu Region, Shizuoka Prefecture | M4.6 on March 11, 2011 (Depth of approximately 5 km) |
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– Near the Border between Nagano and Niigata Prefectures | M6.7 on March 12, 2011 (Depth of approximately 10 km) |
| – Eastern Shizuoka Prefecture | M6.4 on March 15, 2011 (Depth of approximately 15 km) |
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| – Northern Ibaraki Prefecture | M6.1 on March 19, 2011 (Depth of approximately 5 km) |
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– Hamadori, Fukushima Prefecture | M6.0 on March 23, 2011 (Depth of approximately 10 km) |
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– Southern Ibaraki Prefecture | M4.8 on March 24, 2011 (Depth of approximately 50 km) |
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– Northern Inland, Akita Prefecture | M5.0 on April 1, 2011 (Depth of approximately 10 km) |
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– Southern Ibaraki Prefecture | M5.0 on April 2, 2011 (Depth of approximately 55 km) |
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– Offshore Miyagi Prefecture | M7.2 on April 7, 2011 (Depth of approximately 65 km) |
| – Hamadori, Fukushima Prefecture | M7.0 on April 11, 2011 (Depth of approximately 5 km) |
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| – Northern Nagano Prefecture | M5.6 on April 12, 2011 (Very shallow depth) |
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| – Offshore East of Chiba Prefecture | M6.4 on April 12, 2011 (Depth of approximately 25 km) |
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| – Southern Ibaraki Prefecture | M5.9 on April 16, 2011 (Depth of approximately 80 km) |
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| – Near the Border between Nagano and Niigata Prefectures | M4.9 on April 17, 2011 (Depth of approximately 10 km) |
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| – Southern Inland, Akita Prefecture | M4.9 on April 19, 2011 (Depth of approximately 5 km) |
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| – Offshore East of Chiba Prefecture | M6.0 on April 21, 2011 (Depth of approximately 45 km) |
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– Hamadori, Fukushima Prefecture | M5.2 on May 6, 2011 (Depth of approximately 5 km) |
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– Chuetsu Region, Niigata Prefecture | M4.7 on June 2, 2011 (Depth of approximately 5 km) |
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– Offshore Iwate Prefecture | M6.9 on June 23, 2011 (Depth of approximately 35 km) |
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– Central Nagano Prefecture | M5.4 on June 30, 2011 (Depth of approximately 5 km) |
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– Northern Wakayama Prefecture | M5.5 on July 5, 2011 (Depth of approximately 5 km) |
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– Offshore Sanriku | M7.3 on July 10, 2011 |
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– Southern Ibaraki Prefecture | M5.4 on July 15, 2011 (Depth of approximately 65 km) |
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– Suruga Bay | M6.2 on August 1, 2011 (Depth of approximately 25 km) |
| – Offshore Fukushima Prefecture | M6.5 on August 19, 2011 (Depth of approximately 50 km) |
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– Central Hidaka Region | M5.1 on September 7, 2011 (Depth of approximately 10 km) |
| – Northern Ibaraki Prefecture | M5.2 on September 21, 2011 (Depth of approximately 10 km) |
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| – Hamadori, Fukushima Prefecture | M5.4 on September 29, 2011 (Depth of approximately 10 km) |
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| – Kumamoto Region, Kumamoto Prefecture | M4.5 on October 5, 2011 (Depth of approximately 10 km) |
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– Northern Ibaraki Prefecture | M5.3 on November 20, 2011 (Depth of approximately 10 km) |
| – Northern Hiroshima Prefecture | M5.4 on November 21, 2011 (Depth of approximately 10 km |
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| – Offshore Urakawa | M6.2 on November 24, 2011 (Depth of approximately 45 km) |
"On December 10, there was a M5.7 earthquake at a depth of approximately
430 km under the southern Okhotsk Sea. (Excerpted)":
Due to an efficient transmission of seismic waves within the subducting Pacific plate, the area along the Pacific coast from the Hokkaido region to the northern Tohoku region had stronger shaking (Zone of abnormal seismic intensity).
– Since mid-March, a series of seismicity has been continuing in the vicinity of the border of Aizu, Fukushima prefecture and the Okitama region, Yamagata prefecture.
"On December 31, there was a M4.5 earthquake at a depth of approximately
10 km in northern Ibaraki prefecture. (Excerpted)":
In the region from Hamadori, Fukushima prefecture through northern Ibaraki
prefecture, brisk seismicity has been continuing since the 2011 off the
Pacific Coast of Tohoku Earthquake.
– In the aftershock area of the 2011 off the Pacific Coast of Tohoku Earthquake that occurred on March 11, brisk seismic activities have been seen. There is fear that large aftershocks will occur from now on, and there is a possibility that it will be hit by strong shaking and high tsunami. Crustal movements to the east which are thought to be the postseismic deformation have still been observed in a wide area from the Tohoku through the Kanto-Chubu regions, but they have gradually been decaying.
"On December 3, there was a M5.2 earthquake at a depth of approximately
20 km in northeastern Chiba prefecture [southern Chiba prefecture]. (Excerpted)"
Within the area from offshore east of Chiba prefecture to the eastern Boso
Peninsula in the vicinity of the recent event, there was a series of seismic
activities from around October 25. While these activities were decaying,
the recent event occurred.
"In the GPS data for the Tokai region, there have been no changes of activity which are likely to be associated with the Tokai earthquake":
(This evaluation is in agreement with the views presented at the regular
meeting on December 19 of the Assessment Committee for Areas under Intensified
Measures against Earthquake Disaster (reference below).)
(Reference)Recent seismic and crustal activity in the Tokai region and its vicinity (Seismological and Volcanological Department, Japan Meteorological Agency, December 19, 2011)
"No changes of activity which are likely to be associated with the Tokai earthquake have been observed until now. (Excerpted))"
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
There is no supplementary information for the Kyushu-Okinawa region.
"On January 1, there was a M7.0 earthquake at a depth of approximately
400 km under the sea near Torishima. (Excerpted)":
Due to an efficient transmission of seismic waves within the subducting Pacific plate, the area along the Pacific coast from the Tohoku region to the Kanto region had stronger shaking (Zone of abnormal seismic intensity).
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: