September 11, 2012
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On August 25, there was a 6.1 earthquake under the southern Tokachi region. This event had a maximum seismic intensity 5 Lower in the Tokachi and Hidaka regions, Hokkaido.
* On August 30, there was a M5.6 earthquake offshore Miyagi prefecture. This event had a maximum seismic intensity 5 Upper in Miyagi prefecture and caused damage with seriously injured persons
* On August 25, there was a 6.1 earthquake at a depth of approximately 50 km under the southern Tokachi region. The focal mechanism showed a reverse fault with a compression axis in an N-S direction. This event occurred near the boundary between the Pacific and the continental plates. In addition, in the vicinity of this event, there was a 5.2 earthquake on August 22.
* On August 12, there was a M3.8 earthquake at a depth of approximately 5 km in Nakadori, Fukushima prefecture. The focal mechanism showed a normal fault with a tension axis in an NE-SW direction. This event occurred within the crust.
* On August 30, there was a M5.6 earthquake at a depth of approximately 60 km, offshore Miyagi prefecture. The focal mechanism showed a reverse fault with a compression axis in an NW-SE direction. This event occurred within the Pacific plate.
* On August 3, there was a M4.6 earthquake at a depth of approximately 45 km under southern Ibaraki prefecture. The focal mechanism showed a reverse fault with a compression axis in an NW-SE direction. This event occurred on the boundary between the Philippine Sea and the continental plates.
* On August 20, there was a M5.2 earthquake at a depth of approximately 55 km under southern Ibaraki 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 Philippine Sea plates.
* In the GNSS 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 August 17, there was a M4.9 earthquake at a depth of approximately 10 km in Amakusanada. The focal mechanism showed a normal fault with a tension axis in an N-S direction. This event occurred within the crust.
* On August 14, there was a M7.3 earthquake at a depth of approximately 650 km under the southern Okhotsk Sea. The focal mechanism had a compression axis in an inclined 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.
GNSS (Global Navigation Satellite System) is a general name of satellite
positioning system such as GPS.
September 11, 2012
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during July 2012.
(reference)
The following events for the period from August 2011 to late July 2012 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activitie"
| |
– 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) |
|
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– Offshore Fukushima Prefecture | M5.1 on January 23, 2012 (Depth of approximately 50 km) |
| – Eastern Yamanashi Prefecture-Fujigoko | M5.4 on January 28, 2012 (Depth of approximately 20 km) | |
| |
– Near Sado | M5.7 on February 8, 2012 (Depth of approximately 15 km) |
| – Northern Ibaraki Prefecture | M5.2 on February 19, 2012 (Depth of approximately 5 km) |
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| – Offshore Ibaraki Prefecture | M5.3 on March 1, 2012 (Depth of approximately 55 km) |
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| – Northern Ibaraki Prefecture | M5.4 on March 10, 2012 (Depth of approximately 5 km) |
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| – Offshore Sanriku | M6.9 on March 14, 2012 | |
| – Offshore East of Chiba Prefecture | M6.1 on March 14, 2012 (Depth of approximately 15 km) |
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| – Offshore Iwate Prefecture | M6.6 on March 27, 2012 (Depth of approximately 20 km) |
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| – Offshore Fukushima Prefecture | M5.9 on April 1, 2012 (Depth of approximately 55 km) |
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| – Northeastern Chiba Prefecture | M5.8 on April 29, 2012 (Depth of approximately 50 km) |
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| – Offshore East of Aomori Prefecture | M6.1 on May 24, 2012 (Depth of approximately 60 km) |
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| – Northern Nagano Prefecture | M5.2 on July 10, 2012 (Depth of approximately 10 km) |
There is no supplementary information for the Hokkaido region.
"On August 12, there was a M3.8 earthquake at a depth of approximately
5 km in Nakadori, Fukushima prefecture":
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, brisk seismicity has 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.
"In the GNSS 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 30 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 30, 2012)
"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.
– Under the sea near Tokara Islands, after August 16, there was a sequence of seismicity with the largest M3.9, and there were 15 earthquakes with a maximum seismic intensity 1.
"On August 14, there was a M7.3 earthquake at a depth of approximately
650 km under the southern Okhotsk Sea":
This event gave stronger shaking in the Pacific coast side from the Hokkaido to the northern Tohoku regions, due to a transmission of seismic waves within the subducting Pacific plate (anomalous 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: