October 7, 2011
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On September 7, there was a M5.1 earthquake in the central Hidaka region [offshore Urakawa]. This event had a maximum seismic intensity 5 Upper in Hokkaido and caused damage.
* On September 21, there was a M5.2 earthquake in northern Ibaraki prefecture. This event had a maximum seismic intensity 5 Lower in Ibaraki prefecture.
* On September 29, there was a M5.4 earthquake in Hamadori, Fukushima prefecture [offshore Fukushima prefecture]. This event had a maximum seismic intensity 5 Upper in Fukushima prefecture.
* On September 7 at 22:29 (JST), there was a M5.1 earthquake at a depth of approximately 10 km in the central Hidaka region [offshore Urakawa]. The focal mechanism showed a reverse fault with a compression axis in an NE-SW direction. This event occurred within the crust. In addition, brisk seismicity was seen such as a M4.3 earthquake at 07:27 on the same day.
* On September 13, there was a M4.5 earthquake at a depth of approximately 100 km under the western Hidaka region. The focal mechanism had a compression axis in an NW-SE. This event occurred within the Pacific plate.
* On September 18, there was a M5.0 earthquake at a depth of approximately 65 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 September 17 at 04:26, there was a M6.6 earthquake offshore Iwate 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. There was a series of earthquake, such as a M6.1 earthquake at 06:08 on the same day and 10 earthquakes of M5.0 or over from September 17 to 18. According to the GPS data, very small crustal movements associated with this event were observed.
* On September 26, there was a M4.2 earthquake at a depth of approximately 10 km in Aizu, Fukushima prefecture. The focal mechanism showed a reverse fault with a compression axis in an N-S direction. This event occurred within the crust.
* On September 29, there was a M5.4 earthquake at a depth of approximately 10 km in Hamadori, Fukushima prefecture [offshore Fukushima prefecture]. The focal mechanism showed a normal fault with a tension axis in an NW-SE direction. This event occurred within the crust. According to the GPS data, small crustal movements associated with this event were observed in the vicinity of the epicenter.
* On September 4, there was a M4.7 earthquake at a depth of approximately 90 km under southern Saitama prefecture. This event occurred near the boundary between the Pacific and the Philippine Sea plates. The focal mechanism showed a reverse fault with a compression axis in an ENE-WSW direction.
* On September 21, there was a M5.2 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.
* There was no remarkable activity.
* There was no remarkable activity.
* On October 5 at 18:59, there was a M5.4 earthquake at a very shallow depth in eastern Toyama prefecture [northern Nagano prefecture]. The focal mechanism showed a strike-slip fault with a compression axis in an NW-SE direction. This event occurred within the crust. There was a M5.2 earthquake at 19:06 on the same day, too. According to the GPS data, small crustal movements associated with this event were observed in the vicinity of the epicenter.
* On October 5, there was a M4.5 earthquake at a depth of approximately 10 km in the Kumamoto region, Kumamoto prefecture. The focal mechanism showed a normal fault with a tension axis in an N-S direction. This event occurred within the crust.
Note:[ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.
Octobert 7, 2011
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during September 2011.
(reference)
The following events for the period from September 2010 to the end of August 2011 have been listed as "Major Seismic Activity" in monthly "Evaluation of Seismic Activity"
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– Joetsu Region, Niigata Prefecture | M4.7 on October 3, 2010 (Depth of approximately 20km) |
| – Under the Ocean near Miyakojima | M6.4 on October 4, 2010 | |
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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) |
There is no supplementary information for the Hokkaido region.
"On September 26, there was a M4.2 earthquake at a depth of approximately
10 km in Aizu, Fukushima prefecture. (Excerpted)":
A series of seismicity has been continuing in Aizu, Fukushima prefecture
since mid-March.
– 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 September 26 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, September 26, 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.
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: