| 12 February 2004 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity for January 2004
There was no remarkable activity. to supplementary reports
*On January 15, there was a M5.1 earthquake at a depth of approximately 110km near Kunashiri Island. to supplementary reports
*On January 23, there was a M5.3 earthquake at a depth of approximately 65km off-shore of Fukushima prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate. to supplementary reports
*On January 27, there was a M5.0 earthquake at a depth of approximately 70km under the ocean near Hachijojima.
*On January 6, there was a M5.4 earthquake at a depth of approximately 35km in Kumanonada. The focal mechanism showed a strike-slip fault with a tension axis in an ENE-WSE direction. This event occurred within the Philippine Sea plate. This event occurred singly, and essentially no aftershock activity was observed.
*On January 11, there was a M4.0 earthquake at a depth of approximately 10km in central Nagano prefecture.
*On January 9, there was a M4.0 earthquake at a depth of approximately 15km in the Chuetsu region, Niigata prefecture.
*The long-term changes that have been observed since 2001 in the continuous GPS data in the Tokai region, still appear to be continuing. to supplementary reports
There was no remarkable activity. to supplementary reports
There was no remarkable activity. to supplementary reports
*On February 4, there was a M5.3 earthquake at a depth of approximately 65km off-shore of Iwate prefecture.
*On February 4, there was a M4.2 earthquake at a depth of approximately 65km in southern Ibaraki prefecture.
| February 12, 2004 |
| Earthquake Research Committee |
Following are the numbers of the earthquakes by magnitude that occurred in Japan and the surrounding area during January 2004.
M4.0 or greater: 93 (114 events occurred in December.)
M5.0 or greater: 13 (20 events occurred in December.)
M6.0 or greater: 0
(reference) Average numbers of earthquake occurrences over the past thirty years (1971 - 2000)
| M4.0 or greater: 46 / month | |
| M5.0 or greater: 8 / month | |
| M6.0 or greater: 1.3 / month, 16 / year |
The following regions have been noted as having significant seismic activity during the period from January 2003 to the end of December 2003..
| -Off-shore of Miyagi prefecture | M7.1 on May. 26, 2003 (depth of approximately 70km) | |
| -Northern Miyagi prefecture | M6.4 on July 26, 2003 (depth of approximately 10km) | |
| -Off-shore of Tokachi (2003 Off-shore Tokachi Earthquake) | M8.0 on Sep. 26, 2003 (depth of approximately 40km) | |
| -Off-shore of Fukushima prefecture | M6.8 on Oct. 31, 2003 (depth of approximately 30km) |
The aftershock activity of the off-shore Tokachi earthquake on September 26, 2003 (2003 Off-shore Tokachi Earthquake) has been declining normally. According to the GPS data, postseismic movements that were seen following the main shock have been continuing at a low level.
There is no supplementary information for the Tohoku region.
"The long-term changes that have been observed since 2001 in the continuous GPS data in the Tokai region, still appear to be continuing.":
The Pacific side of the Tokai-Chubu region maintains a steady rate with movement to the WNW, consistent with the subduction of the Philippine Sea plate toward the northwest. The results from GPS observations in the area centered on western Shizuoka prefecture, have been showing a trend of moderate change since about April 2001. The trends have continued through January 2004 and show no signs of acceleration.
(This evaluation is in agreement with the views presented at the procedural meeting on January 26 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, January 26, 2004)
"So far, there have been no changes of activity which are likely to be associated with the so-called Tokai earthquake.
There is no remarkable seismic activity in general. The seismicity continues at a level lower than normal directly under Hamana lake, however, in the other regions, seismic activity is generally at a normal level.
The long-term changes in crustal movements in the Tokai region and its vicinity caused by the slow slip on the plate boundary, have been continuing."
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) are events of M6.0 and greater, or events of M4.0 and greater (M5.0 or greater off-shore) that have maximum intensity of 3 or greater. Reference 2 Information that is described in the "Supplementary Information to the Evaluation" includes:
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