May 11, 2012
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On April 1, there was a M5.9 earthquake offshore Fukushima prefecture. This event had a maximum seismic intensity 5 Lower in Fukushima prefecture.
* On April 29, there was a M5.8 earthquake under northeastern Chiba prefecture. This event had a maximum seismic intensity 5 Lower in Chiba prefecture.
* On April 21, there was a M4.5 earthquake at a depth of approximately 105 km under the western Hidaka region. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.
* On April 1, there was a M5.9 earthquake at a depth of approximately 55 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 April 13, there was a M6.0 earthquake at a depth of approximately 30 km, offshore Fukushima prefecture. The focal mechanism showed a normal fault with a tension axis in a WNW-ESE direction. This event occurred within the continental plate. In addition to this event, there was a M5.6 earthquake offshore Ibaraki prefecture, and there was a sequence of seismicity offshore southern Fukushima prefecture to northern Ibaraki prefecture.
* On April 27, there was a M5.0 earthquake at a depth of approximately 65 km, offshore east of Aomori 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 April 29, there was a M5.8 earthquake at a depth of approximately 50 km under northeastern 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 addition to this event, there was a sequence of seismicity such as a M5.5 earthquake on April 25.
* 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.
There was no remarkable activity.
* On May 4, there was a M4.5 earthquake at a depth of approximately 85 km under the southern Nemuro region [Near the Kunashir Island]. The focal mechanism had a tension axis in an N-S direction. 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.
May 11, 2012
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during April 2012.
(reference)
The following events for the period from April 2011 to late March 2012 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activitie"
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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) |
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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) | |
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– 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) |
There is no supplementary information for the Hokkaido region.
– Since mid-March, 2011, a series of seismicity has gradually been decaying in the vicinity of the prefectural border of Aizu, Fukushima prefecture and the Okitama region, Yamagata prefecture, but it has been continuing. There was a M4.4 earthquake in the Okitama region, Yamagata prefecture on April 24.
– 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 April 23 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, April 23, 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.
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: