August 5, 2011
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On July 5, there was a M5.5 earthquake in northern Wakayama prefecture. This event had a maximum seismic intensity 5 Upper in Wakayama prefecture and caused damage.
* On July 10, there was a M7.3 earthquake offshore Sanriku. Tsunamis with a height of 12 cm were observed at Sendai Port (Miyagi prefecture).
* On July 15, there was a M5.4 earthquake under southern Ibaraki prefecture. This event had a maximum seismic intensity 5 Lower in Tochigi prefecture.
There was no remarkable activity.
* On July 3, there were consecutively M3.8 and M3.9 earthquakes at a depth of approximately 10 km in Aizu, Fukushima prefecture. These events occurred within the crust.
* On July 10, there was a M7.3 earthquake offshore Sanriku. This event occurred within the Pacific plate. The focal mechanism showed a strike-slip fault with a tension axis in a WNW-ESE direction. Tsunamis associated with this event were observed with a height of 10 cm at Ofunato (Iwate prefecture), with a height of 12 cm at Sendai Port (Miyagi prefecture) and with a height of 9cm at Soma (Fukushima prefecture). According to the GPS data, very small crustal movements associated with this event were observed in Miyagi prefecture and its surroundings.
* On July 11, there was a M4.4 earthquake at a depth of approximately 10 km in Hamadori, Fukushima prefecture. The focal mechanism showed a normal fault with a tension axis in a NW-SE direction. This event occurred within the crust.
* On July 15, there was a M5.4 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.
* On July 24, there was a M4.8 earthquake at a depth of approximately 40 km under southern Mie prefecture. This event occurred within the Philippine Sea plate. The focal mechanism had a compression axis in a NW-SE direction.
* 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 July 5 at 19:18 (JST), there was a M5.5 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 NW-SE direction. This event occurred within the crust. In addition, there were brisk seismic activities, such as a M4.5 earthquake at 19:34 on the same day.
* On July 21, there was a M5.2 earthquake at a depth of approximately 60 km near Okinoerabujima [under the ocean area near the Okinawa Main Island]. The focal mechanism showed a reverse fault with a compression axis in an ENE-WSW direction.
* On August 1, there was a M5.5 earthquake at a depth of approximately 35 km, offshore Urakawa. The focal mechanism had a tension axis in a NE-SW 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 a N-S direction.
Note:[ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.
August 5, 2011
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during July 2011.
(reference)
The following events for the period from July 2010 to the end of June 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) |
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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) |
There is no supplementary information for the Hokkaido region.
"On July 3, there were consecutively M3.8 and M3.9 earthquakes at
a depth of approximately 10 km in the Aizu region, Fukushima prefecture.
(Excerpted)":
Brisk seismicity has been continuing in the vicinity of the recent events
since mid-March.
"On July 11, there was a M4.4 earthquake at a depth of approximately
10 km in Hamadori, Fukushima prefecture. (Excerpted)":
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, but the frequency has been decaying.
– 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 Upper. 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.
"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 July 25 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, July 25, 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 postseismic deformation associated with the 2011 off the Pacific Coast of Tohoku Earthquake has also been seen in the Tokai region."
– Since around June 29, there has been a sequence of seismicity with the largest M5.4 in central Nagano prefecture.
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: