January 12, 2010
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was strong seismic activity off-shore east of the Izu Peninsula from December 17 to 20. A M5.0 earthquake occurred at 23:45 on December 17, and a M5.1 occurred at 08:45 on December 18. Both events had maximum seismic intensity 5 Lower in Shizuoka prefecture, and caused some damage.
* On December 28, there was a M5.0 earthquake at a depth of approximately 85km under mid-southern Kushiro subprefecture. This event occurred within the Pacific plate. The focal mechanism had a compression axis in an E-W direction.
There was no remarkable activity.
* (Seismic activity that started off-shore east of the Izu Peninsula on December 17 is described in a separate section.)
* On December 18, there was a M5.1 earthquake at a depth of approximately 80km under southern Tochigi prefecture. It is thought that this event occurred within the Philippine Sea plate. The focal mechanism had a compression axis in a NNW-SSE direction.
* There have been no anomalous changes observed in the GPS data for the Tokai region.
* On December 16, there was a M4.6 earthquake at a depth of approximately 30km under Tosa Bay. The focal mechanism showed a strike-slip fault with a compression axis in a N-S direction. This event occurred within the Philippine Sea plate.
* On December 19, there was a M6.7 earthquake near Taiwan. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction.
* On December 24, there was a M6.1 earthquake at a depth of approximately 380km under the northern Japan Sea. The focal mechanism showed a compression axis in the direction of the subducting Pacific plate. This event occurred within the Pacific plate.
* On January 7, there was a M4.8 earthquake under the ocean area near Amami Oshima.
January 12, 2010
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during December 2009.
(reference)
The following regions have been noted as having major seismic activity during the period from December 2008 to the end of November 2009.
| – 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 December 21 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, December 21, 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
Within the crust under mid-western Shizuoka prefecture, general seismicity has been slightly strong since mid-2005. On December 10, there were three earthquakes that had seismic intensity 1 or greater within the crust of western Shizuoka prefecture (a M3.0 event at 00:35 with maximum seismic intensity 1, a M3.7 at 05:55 with maximum seismic intensity 3, and a M3.3 at 06:00 with maximum seismic intensity 2). No changes were observed on strainmeters before or after those earthquakes. In the vicinity of the recent events, there was strong seismicity from mid-November 2007 to early February 2008, where 30 earthquakes that had seismic intensity 1 to 3 occurred. (The largest was a M4.2 event on January 27, 2008, maximum seismic intensity 3.)
There continue to be fewer events within the Philippine Sea plate under the region around Hamana lake.
In other regions, seismic activity is generally at a normal level.
In addition, off-shore east of the Izu Peninsula, seismic activity started to increase on December 17. There was a M5.0 earthquake on December 17, and a M5.1 earthquake on December 18. The seismicity has declined since December 20.
2. Status of crustal movements
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, associated with the seismic activity off-shore east of the Izu Peninsula, some changes were observed on the GPS data, strainmeters, tiltmeters and groundwater levels."
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: