December 9, 2011
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On November 20, there was a M5.3 earthquake in northern Ibaraki prefecture. This event had a maximum seismic intensity 5 Upper in Ibaraki prefecture and caused damage with an injured person.
* On November 21, there was a M5.4 earthquake in northern Hiroshima prefecture. This event had a maximum seismic intensity 5 Lower in Hiroshima prefecture and caused damage with seriously injured persons.
* On November 24, there was a M6.2 earthquake offshore Urakawa. This event had a maximum seismic intensity 5 Lower in the Hidaka region, Hokkaido.
* On November 24, there was a M6.2 earthquake at a depth of approximately 45 km, offshore Urakawa. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the continental plates.
* On November 10, there was a M4.1 earthquake at a depth of approximately 5 km in the southern inland, Akita prefecture. The focal mechanism showed a strike-slip fault with a tension axis in a WNW-ESE direction. This event occurred within the crust
* On November 24, there was a M6.1 earthquake at a depth of approximately 45 km, offshore Fukushima prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the continental plates.
* On November 3, there was a M4.9 earthquake at a depth of approximately 60 km under southern Ibaraki 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 Philippine Sea plates.
* On November 7, there was a M4.5 earthquake at a depth of approximately 5 km in the vicinity of borders of Fukushima, Gunma and Tochigi prefectures. The focal mechanism showed a strike-slip fault with a compression axis in a WNW-ESE direction. This event occurred within the crust.
* On November 18, there was a M4.8 earthquake at a depth of approximately 5 km in Reihoku, Fukui prefecture. The focal mechanism showed a strike-slip fault with a compression axis in a WNW-ESE direction. This event occurred within the crust
* On November 20, there was a M5.3 earthquake at a depth of approximately 10 km in northern Ibaraki prefecture. The focal mechanism showed a normal fault with a tension axis in an ENE-WSW 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.
* On November 21, there was a M5.4 earthquake at a depth of approximately 10 km in northern Hiroshima prefecture. The focal mechanism showed a strike-slip fault with a compression axis in a WNW-ESE direction. This event occurred within the crust. After this event, there was a series of seismicity such as a M4.7 earthquake on November 25
* On November 8, there was a M7.0 earthquake at a depth of approximately 220 km, offshore northwest of the Okinawa Main Island. The focal mechanism had a tension axis in an E-W direction. This event occurred within the Philippine Sea plate.
* 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.
Note:[ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.
December 9, 2011
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during November 2011.
(reference)
The following events for the period from November 2010 to the end of October 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 | M7.1 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) |
There is no supplementary information for the Hokkaido region.
– 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 November 20, there was a M5.3 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 been decaying.
"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 November 21 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, November 21, 2011)
"No changes of activity which are likely to be associated with the Tokai earthquake have been observed until now. (Excerpted))"
– It seems that non-stationary crustal movements observed since around October 26 on the Boso Peninsula have more or less subsided by around November 8. It is thought that they have been caused by slow slip at the boundary between the Philippine Sea and the continental plates. It is estimated that the slow slip was equivalent to approximately a Mw6.6 (moment magnitude) event.
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
There is no supplementary information for the Kyushu-Okinawa region.
"On December 3, there was a M5.2 earthquake at a depth of approximately
20 km in northeastern Chiba prefecture [southern Chiba prefecture]. (Excerpted)":
Since around October 25, there has been a series of seismic activities
from offshore east of Chiba prefecture through southeastern Boso Peninsula
in the vicinity of the recent event. The present even occurred as the activities
had been decaying.
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: