October 8, 2009
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
* On September 8, there was a M4.8 earthquake at a depth of approximately 50km under eastern Hidaka subprefecture. 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 September 29, there was a M4.5 earthquake at a depth of approximately 5km in northern Nemuro subprefecture.
There was no remarkable activity.
* On September 4, there was a M4.5 earthquake at a depth of approximately 65km under northwestern Chiba 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 Philippine Sea plates.
* There have been no anomalous changes observed in the GPS data for the Tokai region.
There was no remarkable activity.
* On September 3, there was a M6.0 earthquake at a depth of approximately 170km, off-shore west of the Satsuma Peninsula. The focal mechanism had a tension axis in the direction of the subducting Philippine Sea plate. This event occurred within the Philippine Sea plate.
* On September 29, there was a M6.1 earthquake off-shore northwest of the Okinawa Main Island. The focal mechanism showed a normal fault with a tension axis in a NW-SE direction. It is thought that this event was associated with extension of the Okinawa Trough.
* On September 30, at 02:48 (JST), there was a M8.0 (USGS) earthquake in the Samoa Islands region. Tsunamis were observed all along the Pacific coast in Japan.
* On October 4, there was a M6.3 earthquake near Taiwan.
October 8, 2009
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during September 2009.
(reference)
The following regions have been noted as having major seismic activity during the period from September 2008 to the end of August 2009.
| – Off-shore of Tokachi | M7.1 on September 11, 2008 | |
| – 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 |
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 28 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, September 28, 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
On August 11, there was a M6.5 earthquake under Suruga Bay. The aftershock activity has been declining.
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 slightly strong within the crust and the Philippine Sea plate under mid-western Shizuoka prefecture, and within the Philippine Sea plate under Aichi prefecture. In other regions, seismic activity is generally at a normal level.
In addition, deep low-frequency earthquakes occurred under Mie prefecture from August 30 through September 2, and under western Aichi prefecture from August 31 through September 2. In the same vicinity, there were deep low-frequency earthquakes during the period from May through June this year.
2. Status of crustal movements
After the crustal movements associated with the earthquake (M6.5) under Suruga Bay on August 11, 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, there were crustal movements observed on the strainmeters in the neighboring regions from August 30 through 31, and from September 1 through 2, which are thought to have been caused by the short-term slow slip around the plate boundary, and are concurrent with the deep low-frequency seismicity mentioned above. Crustal movements related to short-term slow slip had not been observed since early June this year."
– The aftershock activity of the earthquake that occurred under Suruga Bay on August 11 (M6.5) has been declining.
There is no supplementary information for the Kinki - Chugoku - Shikoku region.
"On September 29, there was a M6.1 earthquake off-shore northwest
of the Okinawa Main Island. (excerpted)":
In this vicinity, there had been light seismicity since August 18.
– There has been seismic activity with the largest event a M3.9 earthquake (August 31) at a depth of approximately 10km in western Oita prefecture. At nearly the same place, there had been seismic activity from June through July, with the largest event a M4.7 earthquake.
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: