March 9, 2009
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity. to supplementary reports
* On February 28, there was a M5.3 earthquake at a depth of approximately 110km under western Hidaka subprefecture. The focal mechanism had a tension axis in a NNE-SSW direction. This event occurred within the Pacific plate. to supplementary reports
* On February 15, there was a M5.9 earthquake at a depth of approximately 35km off-shore of Iwate 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 17, there was a M4.9 earthquake at a depth of approximately 50km 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. to supplementary reports
* On February 1, there was a M5.8 earthquake at a depth of approximately 45km 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.
* On February 17, there was a M4.6 earthquake at a depth of approximately 30km under southern Chiba prefecture. The focal mechanism showed a normal fault with a tension axis in a WNW-ESE direction. It is thought that this event occurred within the Philippine Sea plate.
* On February 18, there was a M5.2 earthquake at a depth of approximately 10km in mid-western Mino, Gifu prefecture [Reihoku, Fukui prefecture]. The focal mechanism showed a strike-slip fault with a compression axis in a WNW-ESE direction. This event occurred within the crust.
* On February 24, there was a M3.4 earthquake at a depth of approximately 10km in the Chuetsu region, Niigata prefecture.
* There have been no anomalous changes observed in the GPS data for the Tokai region. to supplementary reports
There was no remarkable activity. to supplementary reports
There was no remarkable activity. to supplementary reports
[ ] were the regional names of the epicenters used in the Japan Meteorological Agency announcement.
March 9, 2009
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during February 2009.
(reference)
The following regions have been noted as having major seismic activity during the period from February 2008 to the end of January 2009.
| - Off-shore of Ibaraki prefecture | M7.0 on May 8, 2008 | |
| - Iwate-Miyagi Nairiku Earthquake in 2008 | M7.2 on June 14, 2008 (depth approximately 10km) | |
| - Off-shore of Ibaraki prefecture | M5.2 on July 5, 2008 (depth approximately 50km) | |
| - Near Okinoerabujima | M6.1 on July 8, 2008 (depth approximately 45km) | |
| - Off-shore of Fukushima prefecture | M6.9 on July 19, 2008 | |
| - Central Iwate prefecture | M6.8 on July 24, 2008 (depth approximately 110km) |
|
| - Off-shore of Tokachi | M7.1 on September 11, 2008 |
There is no supplementary information for the Hokkaido region.
"On February 15, there was a M5.9 earthquake at a depth of approximately 35km off-shore of Iwate prefecture. (excerpted) ":
This event occurred within the aftershock area of the 1994 Far-offshore Sanriku Earthquake (M7.6). In addition, its largest aftershock (M7.2, maximum seismic intensity 5, January 7 in 1995) occurred in this vicinity.
"On February 18, there was a M5.2 earthquake at a depth of approximately 10km in mid-western Mino, Gifu prefecture [Reihoku, Fukui prefecture]. (excerpted)":
Judging from the aftershock distribution and the focal mechanism, this seismic activity is thought to have occurred on a right-lateral strike-slip fault.
"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 February 23 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, February 23, 2009)
"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
There was no remarkable seismic activity in general.
There are continued less frequent occurrences of events equal to or larger than M3.5 within the Philippine Sea plate under mid-western Shizuoka prefecture. Also, there continue to be fewer events within the Philippine Sea plate under the region around Hamana lake. On the other hand, seismicity has been continuing to be strong within the crust in mid-western Shizuoka prefecture. In other regions, seismic activity is generally at a normal level.
Also, in mid-western Yamanashi prefecture, which is the area near the expected source region of the so-called Tokai Earthquake, there was seismic activity with a M3.8 event on February 16 and a M3.5 event on February 18. There were no remarkable changes on strainmeters before and after the activity, therefore, it is not expected that this activity will have a direct impact on the so-called Tokai Earthquake. Also, from February 5 through 14, there have been deep low-frequency earthquakes observed near the plate boundary under Aichi prefecture.
2. Status of crustal movements
There were no notable changes observed in general.
According to the GPS data and leveling results, the trend of long-term subsidence at Omaezaki has been continuing as before.
In addition, there were crustal movements observed on the strainmeters in the neighboring region from February 6 through 16, which is thought to have been caused by the short-term slow slip around the plate boundary under Aichi prefecture. A similar phenomenon was seen in this vicinity from late August through early September last year."
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: