May 12, 2009
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity. to supplementary reports
* On April 28, there was a M5.4 earthquake at a depth of approximately 40km off-shore of Kushiro. This event occurred near the boundary between the Pacific and the continental plates. The focal mechanism had a tension axis in a NNE-SSW direction.
* On April 5, there was a M4.8 earthquake at a depth of approximately 55km 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 April 7, there was a M6.7 earthquake under the ocean area of the Chishima Islands. Also on April 19, there was a M6.5 earthquake at nearly the same place. The focal mechanisms of these events showed reverse faults with compression axes in a NW-SE direction. It is thought that these events occurred at the plate boundary. to supplementary reports
* On April 25, there was a M5.0 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 April 21, there was a M5.2 earthquake at a depth of approximately 45km, 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 April 28, there was a M5.0 earthquake at a depth of approximately 50km, 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.
* 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 April 5, there was a M5.6 earthquake at a depth of approximately 30km in Hyuganada. 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. to supplementary reports
May 12, 2009
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during April 2009.
Of the events listed above, 41 earthquakes of M4.0 or greater, 16 earthquakes of M5.0 or greater, and 2 earthquakes of M6.0 or greater, were associated with the aftershock activity of the earthquakes under the ocean area of the Chishima Islands on April 7 and 19.
(reference)
The following regions have been noted as having major seismic activity during the period from April 2008 to the end of March 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.
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 April 27 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, April 27, 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.
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."
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: