July 9, 2009
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity. to supplementary reports
* On June 5, there was a M6.4 earthquake at a depth of approximately 30km, off-shore of Tokachi. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. This event occurred at the boundary between the Pacific and the continental plates. Associated with this event, small crustal movements were observed in the area centered in the southern Hidaka region of Hokkaido. to supplementary reports
* On June 23, there was a M5.6 earthquake at a depth of approximately 40km, off-shore of Miyagi prefecture. It is thought that this event occurred within the Pacific plate. The focal mechanism showed a reverse fault with a compression axis in a NNW-SSE direction. to supplementary reports
* On June 6, there was a M5.9 earthquake off-shore east of Chiba prefecture. The focal mechanism showed a normal fault with a tension axis in a NNE-SSW direction. It is thought that this event occurred within the Pacific 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
* On June 25, there was a M4.7 earthquake at a depth of 10km in western Oita prefecture. The focal mechanism showed a normal fault with a tension axis in a N-S direction. This event occurred within the crust. to supplementary reports
July 9, 2009
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during June 2009.
(reference)
The following regions have been noted as having major seismic activity during the period from June 2008 to the end of May 2009.
| - 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 |
"On June 5, there was a M6.4 earthquake at a depth of approximately 30km, off-shore of Tokachi. (excerpted)"
This event occurred within the aftershock area of the 2003 Off-shore Tokachi Earthquake. Also, the largest aftershock (M7.1, maximum seismic intensity 6 Lower, on September 26, 2003) occurred in this vicinity.
- Off-shore of Sanriku, there was a M5.4 earthquake on June 20 and a M5.2 earthquake on June 23. Both focal mechanisms showed reverse faults with compression axes in a WNW-ESE direction.
"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 June 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, June 29, 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 slightly strong within the crust in mid-western Shizuoka prefecture. In other regions, seismic activity is generally at a normal level.
In addition, deep low-frequency earthquakes occurred under Nara prefecture on May 4. Subsequently the events moved to the northeast from Aichi through southern Nagano prefectures, and continued until June 4. This type of seismic activity which moves northeastward from Nara to Aichi prefectures also occurred in January 2006.
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 regions from May 18 through 22 and from May 26 through June 2, which are thought to have been caused by the short-term slow slip around the plate boundary, and are consistent with the deep low-frequency seismicity mentioned above. Crustal movements related to short-term slow slip had not been observed since mid-February this year."
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
"On June 5, there was a M6.4 earthquake at a depth of approximately
30km, off-shore of Tokachi. (excerpted)"
In this vicinity, light seismic activity was seen since June 8, and increased after this earthquake. Presently the seismicity has been gradually declining.
- At a depth of approximately 10km under Omura Bay [in northern Nagasaki prefecture], seismicity was temporarily active with a M4.0 earthquake on June 28 and a M3.9 earthquake on June 30. Presently activity has been gradually subsiding.
[ ] were the regional names of the epicenters 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: