September 9, 2011
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On August 1, there was a M6.2 earthquake in Suruga Bay. This event had a maximum seismic intensity 5 Lower in Shizuoka prefecture and caused damage with a seriously injured person.
* On August 19, there was a M6.5 earthquake offshore Fukushima prefecture. This event had a maximum seismic intensity 5 Lower in Miyagi and Fukushima prefectures and caused damage with injured persons.
* On August 1, there was a M5.5 earthquake at a depth of approximately 35 km, offshore Urakawa. This event occurred near the boundary between the Pacific and the continental plates. The focal mechanism had a tension axis in an N-S direction.
* On August 22, there was a M4.7 earthquake at a depth of approximately 25 km in the southern Tokachi region [central Tokachi region]. The focal mechanism showed a strike-slip fault with a compression axis in an E-W direction. This event occurred within the crust.
* On August 5, there was a M4.7 earthquake at a depth of approximately 5 km in Hamadori, Fukushima prefecture. The focal mechanism showed a normal fault with a tension axis in an NNW-SSE direction. This event occurred within the crust.
* On August 19, there was a M6.5 earthquake at a depth of approximately 50 km, offshore Fukushima prefecture. This event occurred within the Pacific plate. The focal mechanism showed a reverse fault with a compression axis in an E-W direction.
* On August 1, there was a M6.2 earthquake at a depth of approximately 25 km in Suruga Bay. This event occurred within the Philippine Sea plate. The focal mechanism showed a reverse fault with a compression axis in an N-S direction.
* On August 7, there was a M4.7 earthquake at a depth of approximately 5 km in northern Ibaraki prefecture. The focal mechanism showed a normal fault with a tension axis in an E-W direction. This event occurred within the crust.
* On August 15, there was a M4.7 earthquake at a depth of approximately 65 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. In addition, on August 22, there was a M4.7 earthquake at a depth of approximately 65 km under southern Ibaraki prefecture. The focal mechanism showed a strike-slip fault with a compression axis in an E-W direction.
* On August 17, there was a M4.3 earthquake at a depth of approximately 80 km under southern Saitama prefecture [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 August 31, there was a M4.6 earthquake at a depth of approximately 70 km under Tokyo Bay [northwestern Chiba 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.
* 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 August 10, there was a M4.7 earthquake at a depth of approximately 60 km under northern Wakayama prefecture. This event occurred within the Philippine Sea plate. The focal mechanism had a tension axis in an ENE-WSW direction.
* There was no remarkable activity.
* 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 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 (preliminary result). This event occurred within the crust. In addition, there was a M4.3 earthquake at 07:27 on the same day, and brisk seismicity has been seen..
Note:[ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.
Septembert 9, 2011
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during August 2011.
(reference)
The following events for the period from August 2010 to the end of July 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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– Off-shore of 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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– Off-shore of 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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| – Off-shore 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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| – Off-shore 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) |
There is no supplementary information for the Hokkaido region.
– Brisk 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 bee seen, such as earthquakes with a maximum seismic intensity 5 Lower, except for the earthquakes which were evaluated in Nationwide Seismic Activities by Region. 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 August 31 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, August 31, 2011)
"There were a M6.2 earthquake on August 1 in Suruga Bay and a M5.2 earthquake on August 12 in Enshu-nada. They occurred within the supposed source region of the Tokai earthquake or in the area around it, but 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: