October 10, 2008
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On September 11, there was a M7.1 earthquake off-shore of Tokachi. This event had maximum seismic intensity 5 Lower and caused tsunamis observed on the Pacific coast in Hokkaido and in the Tohoku region, with a tsunami height of 0.5m at Erimo and 0.2m at Urakawa. to supplementary reports
* On September 11, at 09:20 (JST) there was a M7.1 earthquake off-shore of Tokachi. 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.
This event caused tsunamis observed on the Pacific coast in Hokkaido and in the Tohoku region, with a tsunami height of 0.5m at Erimo and 0.2m at Urakawa.
Associated with this event, small crustal movements were observed in the area centered on the southern Tokachi region and the Hidaka region, Hokkaido.
The seismic activity was a main shock-aftershock sequence. The largest aftershock, until October 9, was a M5.7 event at 09:32 on September 11. The aftershock activity has been generally declining.
The source fault model of this event, determined from GPS data, is a low-angle reverse fault striking in a NNE-SSW direction and dipping toward the WNW.
This event occurred in the aftershock region of the 2003 Off-shore Tokachi Earthquake.
* On September 12, there was a M5.2 earthquake at a depth of approximately 40km off-shore of Kushiro. to supplementary reports
* On September 22, there was a M5.6 earthquake at a depth of approximately 150km under Tsugaru Strait. The focal mechanism had a tension axis in a NW-SE direction. This event occurred within the subducting Pacific plate. to supplementary reports
* On September 21, there was a M4.8 earthquake at a depth of approximately 70km under Tokyo Bay [under northwestern Chiba prefecture]. This event occurred near the boundary between the subducting Pacific plate and the Philippine Sea plate. The focal mechanism had a compression axis in a NNE-SSW direction.
* 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
*On September 14, there was a M5.1 earthquake off-shore northeast of Amami Oshima. to supplementary reports
*On October 4, there was a M3.5 earthquake at a depth of approximately 10km in mid-northern Rumoi subprefecture.
*On October 8, there was a M4.7 earthquake at a depth of approximately 65km under northwestern Chiba prefecture. to supplementary reports
[ ] were the regional names of the epicenters used in the Japan Meteorological Agency announcement.
October 10, 2008
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during September 2008.
(reference)
The following regions have been noted as having major seismic activity during the period from September 2007 to the end of August 2008.
| - Western Kanagawa prefecture | M4.9 on October 1, 2007 (depth approximately 15km) | |
| - Noto region, Ishikawa prefecture | M4.8 on January 26, 2008 (depth approximately 10km) | |
| - 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) |
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 September 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" (Japan Meteorological Agency, Department of Seismology and Volcanology, September 29, 2008)
"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, and there is slightly strong seismicity within the crust in Aichi prefecture. In other regions, seismic activity is generally at a normal level.
In addition, there were deep low-frequency earthquakes observed near the plate boundary under the area from southern Nagano prefecture to Aichi prefecture during the periods from August 25 through September 4 and from September 7 through 8.
2. Status of crustal movements
There were no notable changes observed in general.
According to the GPS data and leveling results, the trend of subsidence at Omaezaki has been continuing as before.
In addition, there were crustal movements observed on the strainmeters in the neighboring region from August 25 through September 4, which were thought to be caused by the short-term slow slip in the area around the plate boundary under southern Nagano prefecture through Aichi prefecture. This deformation is still continuing. A similar phenomenon was seen in this vicinity in January this year."
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
- On September 10, there was a M4.5 earthquake at a depth of approximately 50km under the ocean area near Miyakojima.
- On October 1, there was a M4.4 earthquake at a depth of approximately 15km in mid-western Mino, Gifu prefecture.
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: