| 12 February 2003 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity for January 2003
There was no remarkable activity. to supplementary reports
*On January 7, there was a M4.6 earthquake at a depth of approximately 50km in the southern Tokachi region. to supplementary reports
There was no remarkable activity. to supplementary reports
*On January 21, there was a M5.0 earthquake at a depth of approximately 45km off-shore of Ibaraki prefecture.
*On January 31, there was a M4.4 earthquake at a depth of approximately 65km under southern Ibaraki prefecture.
*The long-term changes that have been observed since 2001 in the continuous GPS data for 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 6, there was a M4.5 earthquake at a depth of approximately 15km in southern Kyoto prefecture.
*On February 11, there was a M4.0 earthquake at a depth of approximately 5km in the Reihoku region of Fukui prefecture.
| February 12, 2003 |
| Earthquake Research Committee |
41 earthquakes of M4.0 or greater occurred in Japan and the surrounding area during January 2003 (58 events occurred in December 2002, and an average of 46 earthquakes per month have occurred over the past thirty years through the end of 2000). 5 of these earthquakes in January 2003 were M5.0 or greater. (3 events of M5.0 or greater occurred in December 2002.)
Earthquakes of M6.0 or greater occurred, on average, 15 times a year during 1998 to 2002. (Over the past 30 years through the end of 2000, on average, M6.0 or greater events have occurred approximately 16 times a year) There was no event of magnitude equal to or over M6.0 in January 2003.
The following regions have been noted as having significant seismic activity during the period from January 2002 to the end of December 2002.
| -Off-shore of Ibaraki prefecture | M5.5 on Feb. 12, 2002 (depth of approximately 50km) | |
| -Ocean area south of Ishigakijima | M6.6 on Mar. 26, 2002 (depth of approximately 10km) | |
| -Near Taiwan | M7.0 on Mar. 31, 2002 | |
| -Ocean area east of Aomori prefecture | M5.9 on Oct. 14, 2002 (depth of approximately 50km) | |
| -Off-shore of Miyagi prefecture | M6.1 on Nov. 3, 2002 (depth of approximately 45km) | |
| -Hyuganada | M5.7 on Nov. 4, 2002 (depth of approximately 35km) |
There is no supplementary information for the Hokkaido region.
- On January 6, there was a M4.9 earthquake at a depth of approximately 45km off-shore east of Aomori prefecture. There was a M5.9 earthquake in this vicinity on October 14, 2002, and this event had a maximum seismic intensity 5 Lower.
- According to the continuous GPS data, there have been systematic crustal movements since the M6.1 earthquake on November 3, 2002 which have continued through January 2003. The maximum amplitudes are about 1 cm in a nearly eastern direction and are in the area from southern Iwate prefecture to northern Miyagi prefecture. It is thought that the movement was caused by continual slow slip at the plate boundary around the focal region after the M6.1 event. There were 4 M4 class earthquakes around the epicenter of this earthquake in January, but there have been no large changes in the seismic activity.
"The long-term changes that have been observed since 2001 in the continuous GPS data for 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 2003 and show no signs of acceleration.
(This evaluation is in agreement with the views presented at the procedural meeting on January 27 of the Regional Assessment Committee for Strengthening Countermeasures 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 27, 2003)
"In the Tokai region, seismic activity within both the crust and Philippine Sea plate is at normal levels. There was a M5.3 earthquake off-shore of Tokaido on January 19, which is slightly farther to the southwest from the expected focal region of the so-called Tokai earthquake. This event had a reverse fault mechanism near the plate boundary, with a compression axis in the WNW-ESE direction, which largely corresponds to the direction of the subducting Philippine Sea plate. The activity increased temporarily, including 3 aftershocks of M4.0 or greater caused by this event, however, activity has subsequently been declining slowly. Before and after this seismicity, there were no unusual changes of seismic activity nor crustal movements in the expected focal region. There have been long-term changes in crustal movements in the Tokai region and its vicinity since about two years ago. There are no large changes in the slow slip on the plate boundary, which is the cause of those long-term changes. So far, there have been no changes of activity which are likely to be associated with the so-called Tokai earthquake."
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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