April 9, 2010
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On March 14, there was a M6.7 earthquake off-shore of Fukushima prefecture. This event had a maximum seismic intensity 5 Lower in Fukushima prefecture, and caused some damage.
* On March 6, there was a M5.5 earthquake off-shore east of Hokkaido.
* On March 30, there was a M5.8 earthquake off-shore southwest of Hokkaido. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction.
* On March 1, there was a M4.9 earthquake at a depth of approximately 120km under the southern inland area of Akita prefecture [the southern inland area of Iwate prefecture]. The focal mechanism had a compression axis in the direction of the subducting Pacific plate. This event occurred within the Pacific plate.
* On March 13, there was a M5.5 earthquake at a depth of approximately 80km, off-shore of Fukushima prefecture. The focal mechanism had a tension axis in the direction of the subducting Pacific plate. This event occurred within the Pacific plate.
* On March 14, there was a M6.7 earthquake at a depth of approximately 40km, 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. According to the continuous GPS monitoring, small crustal movements associated with this earthquake were observed in the area centered on the Pacific coastal region of Miyagi and Fukushima prefectures.
* On March 16, there was a M4.5 earthquake at a depth of approximately 70km under northwestern Chiba prefecture.
* On March 31, there was a M4.6 earthquake at a depth of approximately 55km off-shore of Ibaraki 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.
* There have been no anomalous changes observed in the GPS data for the Tokai region.
There was no remarkable activity.
There was no remarkable activity.
* On March 4, there was a M6.4 earthquake in Taiwan. The focal mechanism had a compression axis in an E-W direction.
[ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.
April 9, 2010
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during March 2010.
(reference)
The following events for the period from March 2009 to the end of February 2010 have been listed as "Major Seismic Activity" in monthly "Evaluation of Seismic Activity"
| – Under Suruga Bay | M6.5 on August 11, 2009 (depth of approximately 25km) | |
| – Off-shore East of Hachijojima | M6.6 on August 13, 2009 | |
| – Under the Ocean Area near Ishigakijima | M6.7, M6.6 on August 17, 2009 | |
| – Off-shore East of the Izu Peninsula | Seismic activity with M5.0 on December 17, M5.1 on December 18, 2009 |
|
| – 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 |
There is no supplementary information for the Hokkaido region.
There is no supplementary information for the Tohoku region.
"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 procedural meeting on March 29 of the Assessment Committee for Areas under Intensified Measures against Earthquake Disaster. (see reference below))
(reference) Recent seismic and crustal activity in the Tokai region and its vicinity (Seismological and Volcanological Department, Japan Meteorological Agency, March 29, 2010)
"So far, there have been no changes of activity which are likely to be associated with the so-called 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 Hamana lake.
In other regions, seismic activity is generally at a normal level.
In addition, deep low-frequency earthquakes were observed near the plate boundary under western Aichi prefecture from around March 10 through 18. In this vicinity, deep low-frequency earthquakes were observed from late September through early October last year.
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 as before.
In addition, crustal movements were observed on the strainmeters in the neighboring regions from March 10 to11 and from March 16 to 18, which are thought to have been caused by short-time slow slip around the plate boundary, and were concurrent with the deep low-frequency seismicity mentioned above. Crustal movements related to short-term slow slip had not been observed since early October last year."
– Non-stationary crustal movements are still observed near Bungo Strait, which have been seen since around autumn 2009. It is thought that they have been caused by slow slip at the boundary between the Philippine Sea and the continental plates. In addition, in nearly the same region deep low-frequency tremors have been active since February 2010. A long-term slow slip was also seen in this vicinity during the period from 2003 through 2004, and at that time deep low-frequency tremor activity was also active.
There is no supplementary information for the Kyushu-Okinawa region.
There is no supplementary information for the other regions.
The magnitude of the earthquake that occurred under the ocean area near Okinawa Main Island on February 27 was 6.9 (preliminary) in the "Evaluation of Seismic Activity for February 2010". It is now 7.2 as a result of detailed inspection.
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: