June 9, 2011
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On May 6, there was a M5.2 earthquake in Hamadori, Fukushima prefecture. This event had a maximum seismic intensity 5 Lower in Fukushima prefecture.
* On May 15, there was a M5.0 earthquake at a depth of approximately 50 km, off-shore southeast of Nemuro Peninsula. The focal mechanism showed a strike-slip fault with a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.
* On May 4, there was a M4.6 earthquake at a depth of approximately 90 km under the Sanpachi-Kamikita region, Aomori prefecture. This event occurred within the Pacific plate. The focal mechanism had a compression axis in a WNW-ESE direction.
* On May 5, there was a M6.1 earthquake off-shore of Sanriku. The focal mechanism showed a normal fault with a tension axis in a WNW-ESE direction. This event occurred within the Pacific plate.
* On May 6, there was a M5.2 earthquake at a depth of approximately 5 km in Hamadori, Fukushima prefecture. The focal mechanism showed a normal fault with a tension axis in a NNW-SSE direction. This event occurred within the crust.
* On May 7, there was a M4.6 earthquake at a depth of approximately 10 km in the Aizu region, Fukushima prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred within the crust.
* On May 27, there was a M4.6 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 NW-SE direction. This event occurred within the crust.
* On May 20, there was a M4.6 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 the vicinity of this event, there was a M4.5 earthquake on May 25.
* On May 22, there was a M5.5 earthquake at a depth of approximately 50 km under northeastern Chiba 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 GPS data for the Tokai region, there have been no changes of activity which are likely to be associated with the Tokai earthquake.
* On May 10, there was a M4.2 earthquake at a depth of approximately 5 km in northern Wakayama prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred within the crust.
* There was no remarkable activity.
* On June 2, there was a M4.7 earthquake at a depth of approximately 5 km in the Chuetsu region, Niigata prefecture. The focal mechanism had a compression axis in a NW-SE direction. This event occurred within the crust.
* On June 3, there was a M6.1 earthquake off-shore of Fukushima prefecture. The focal mechanism showed a normal fault with a tension axis in a NW-SE direction. This event occurred within the Pacific plate.
* On June 3, there was a M4.5 earthquake at a depth of approximately 60 km under southern Ibaraki prefecture.
* On June 4, there was a M5.2 earthquake at a depth of approximately 10 km in eastern Shimane prefecture. The focal mechanism showed a strike-slip fault with a compression axis in a NW-SE direction. This event occurred within the crust.
June 9, 2011
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during May 2011.
(reference)
The following events for the period from May 2010 to the end of April 2011 have been listed as "Major Seismic Activity" in monthly "Evaluation of Seismic Activity"
| – Off-shore of Fukushima Prefecture | M6.2 on June 13, 2010 (Depth of approximately 40km) |
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| – Northeastern Chiba Prefecture | M5.0 on July 23, 2010 (Depth of approximately 35km) |
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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 |
M7.4 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) |
There is no supplementary information for the Hokkaido region.
"On May 6, there was a M5.2 earthquake at a depth of approximately
5 km in Hamadori, Fukushima prefecture. (Excerpted))":
After this earthquake, on May 25, there was a M5.0 earthquake with a maximum
seismic intensity 5 Lower, and brisk seismicity has been seen since the
2011 off the Pacific Coast of Tohoku Earthquake.
"On May 7, there was a M4.6 earthquake at a depth of approximately 10 km in the Aizu region, Fukushima prefecture. (Excerpted)":
In the vicinity, brisk seismicity has been seen since mid-March.
– 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. 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 post seismic deformation have still been observed in a wide area from the Tohoku through the Kanto-Chubu regions.
"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 May 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, May 31, 2011)
"So far, there have been no changes of activity which are likely to be associated with the Tokai earthquake.
1. Status of seismicity
General seismicity has been slightly brisk since mid-2005 within the crust under mid-western Shizuoka prefecture.
There continue to be fewer events within the Philippine Sea plate under the region around Hamanako.
In other regions, seismic activity is generally at a normal level.
2. Status of crustal movements
There have been no remarkable changes observed over the entire region.
According to the GPS measurement results, the trend of long-term subsidence at Omaezaki has been continuing. In view of the observation data of tilt, strain meters and others as a whole, the data showing remarkable changes associated with coupling state of the Philippine Sea and the continental plates in the expected focal region of the Tokai earthquake and its surrounding area have not been obtained.
According to the GPS data, the post seismic deformations associated with the 2011 off the Pacific Coast of Tohoku Earthquake have also been seen in the Tokai region."
– Since the 2011 off the Pacific Coast of Tohoku Earthquake, in inland from Tohoku through Kanto-Chubu regions, there are some places where brisk activities have still been seen.
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
– In the Kumamoto region, Kumamoto prefecture, there were 4 earthquakes of M3.0 or over. In the vicinity, brisk seismicity has been seen since mid-April.
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: