September 12, 2008
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity. to supplementary reports
* On August 14, there was a M5.4 earthquake at a depth of approximately 65km off-shore east of Hokkaido. The focal mechanism had a tension axis in a N-S direction. This event occurred within the Pacific plate. to supplementary reports
* On August 9, there was a M5.4 earthquake at a depth of approximately 50km off-shore east of Aomori 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 August 22, there was a M5.2 earthquake at a depth of approximately 55km under northern Ibaraki prefecture [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 August 20, there was a M4.6 earthquake at a depth of approximately 45km under southern Ibaraki prefecture. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. This event occurred at the boundary between the Philippine Sea and the continental plates.
* On August 8, there was a M4.6 earthquake at a depth of approximately 30km under eastern Kanagawa prefecture [eastern Tama, Tokyo]. The focal mechanism showed a reverse fault with a compression axis in a N-S direction. This event is related to the subduction of the Philippine Sea plate.
* 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.
* On September 11, at 09:20 (JST) there was a M7.1 (provisional) 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 0.2m in Urakawa.
Associated with this event, small crustal movements were observed in the area centered on the Hidaka region and the southern Tokachi region, Hokkaido.
The seismic activity was a main shock-aftershock sequence. The largest aftershock until 15:00 on September 12 was a M5.3 (preliminary) event at 09:33 on September 11.
This event occurred in the aftershock region of the 2003 Off-shore Tokachi Earthquake.
September 12, 2008
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during August 2008.
(reference)
The following regions have been noted as having major seismic activity during the period from August 2007 to the end of July 2008.
| - Off-shore west of Sakhalin | M6.4 on August 2, 2007 | |
| - Near the coastal area of Kujukurihama | seismic activity with M5.3 on August 16, and M4.8 on August 18, 2007 | |
| - Coast of Peru | M8.0 on August 16, 2007 | |
| - 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 1 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 1, 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 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 under Aichi prefecture. In other regions, seismic activity is generally at a normal level.
In the area around the expected source region of the so-called Tokai Earthquake, there were deep low-frequency events observed near the plate boundary under western Aichi prefecture on August 13. Also, since August 25, there have been deep low-frequency earthquakes observed near the plate boundary under the area from southern Nagano prefecture to Aichi prefecture, and that activity has been still continuing.
2. Status of crustal movements
There were no notable changes observed in general.
According to the GPS data and leveling results, the tendency of subsidence in Omaezaki has been continuing as before.
In addition, there have been crustal movements observed on the strainmeters in the neighboring region since August 25, which is 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. Similar phenomenon was seen in this vicinity in January this year."
- On August 8 and 30, there were M4.2 earthquakes at a depth of approximately 15km near the border between Fukui and Shiga prefectures [in northern Shiga prefecture].
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
There is no supplementary information for the Kyushu-Okinawa region.
- On September 10, there was a M4.5 earthquake at a depth of approximately 50km under the ocean area near Miyakojima.
[ ] 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: