March 9, 2011
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
There was no remarkable activity.
* On February 10, there was a M5.4 earthquake at a depth of approximately 50 km, off-shore of Fukushima prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On February 27, there was a M5.2 earthquake at a depth of approximately 45 km, off-shore of Fukushima prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On February 5, there was a M5.2 earthquake at a depth of approximately 65 km, off-shore southeast of Chiba prefecture. The focal mechanism showed a strike-slip fault with a compression axis in an ENE-WSW direction.
* On February 26, there was a M5.0 earthquake at a depth of approximately 55 km, off-shore south of Boso Peninsula. The focal mechanism had a tension axis in a WNW-ESE direction.
* On February 27 at 5:38 (JST), there was a M5.5 earthquake at a depth of approximately 5 km in the Hida region, Gifu prefecture. The focal mechanism showed a reverse fault with a compression axis in a NNW-SSE direction. This event occurred in the crust. The seismic activity was so brisk that there was a M5.0 earthquake at 2:18 on the same day, and the activity has gradually been subsiding.
* There have been no anomalous changes observed in the GPS data for the Tokai region.
* On February 21, there was a M4.8 earthquake at a depth of approximately 55 km, under northern Wakayama prefecture [southern Wakayama prefecture]. This event occurred within the Philippine Sea plate. The focal mechanism had a tension axis in a NE-SW direction.
* On February 4, there was a M5.0 earthquake off-shore northeast of Amami-Oshima. The focal mechanism had a tension axis in an E-W direction.
* On March 7, there was a M5.1 earthquake under the ocean near Tokara Islands.
* On March 9, there was a M7.3 earthquake off-shore of Sanriku.
Note: [ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.
March 9, 2011
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during February 2011.
(reference)
The following events for the period from February 2010 to the end of January 2011 have been listed as "Major Seismic Activity" in monthly "Evaluation of Seismic Activity"
| – Under the Ocean Area near Ishigakijima | M6.5 on February 7, 2010 | |
| – Under the Ocean Area near the Okinawa Main Island | M7.2 on February 27, 2010 | |
| – Along the Central Coast of Chile | Mw8.8 on February 27, 2010 | |
| – Off-shore of Fukushima Prefecture | M6.7 on March 14, 2010 (Depth of approximately 40km) |
|
| – Off-shore of Fukushima Prefecture | M6.2 on June 13, 2010 (Depth of approximately 40km) |
|
| – Northeastern Chiba Prefecture | M5.0 on July 23, 2010 (Depth of approximately 35km) |
|
| |
– 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 | |
| |
– Under the Ocean near Chichijima | M7.4 on December 22, 2010 |
There is no supplementary information for the Hokkaido region.
Since February 13, there was a series of earthquakes such as four earthquakes of M5.0 or over off-shore of Sanriku. The largest event was a M5.5 earthquake on February 16. Every focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. These events occurred at the boundary between the Pacific and the continental plates.
"There have been no anomalous changes observed in the GPS data for the Tokai region.":
(This evaluation is in agreement with the views presented at the regular
meeting on February 28 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, February 28, 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 strong 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 data and leveling results, the trend of long-term subsidence at Omaezaki has been continuing."
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
Since February 3, there was a series of earthquakes and the largest event was a M3.7 earthquake under the ocean near Suwanose-jima [under the ocean near Tokara Islands]. There were 18 earthquakes with seismic intensity of 1 or over.
Note: [ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.
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: