| 12 March 2003 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity in February 2003
There was no remarkable activity. to supplementary reports
*On February 19, there was a M6.1 earthquake at a depth of approximately 220km in the southern Rumoi region. to supplementary reports
*On February 16, there was a M5.0 earthquake at a depth of approximately 60km off-shore of Fukushima prefecture. to supplementary reports
*On February 11, there was a M4.0 earthquake at a depth of approximately 5km in the Reihoku region of Fukui 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
*On February 6, there was a M4.5 earthquake at a depth of approximately 15km in southern Kyoto prefecture. to supplementary reports
There was no remarkable activity. to supplementary reports
*On March 3, there was a M5.8 earthquake at a depth of approximately 40km off-shore of Fukushima prefecture (70km northeast of the epicenter of the event on February 16). 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 plate and the continental plate.
*On March 4, there was a M4.1 earthquake at a depth of approximately 30km in eastern Aichi prefecture.
| March 12, 2003 |
| Earthquake Research Committee |
42 earthquakes of M4.0 or greater occurred in Japan and the surrounding area during February (41 events occurred in January, 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 February were M5.0 or greater. (5 events of M5.0 or greater occurred in January.)
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 1 event of magnitude equal to or over M6.0 in February 2003.
The following regions have been noted as having significant seismic activity during the period from March 2002 to the end of February 2003.
| -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.
There is no supplementary information for the Tohoku region.
"The long-term changes that have been observed since 2001 in the continuous GPS data of 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 February 2003 and show no signs of acceleration.
(This evaluation is in agreement with the views presented at the procedural meeting on February 24 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, February 24, 2003)
"In the Tokai region, seismic activity within the crust is at normal levels. The activity within the Philippine Sea plate has been increasing slightly. 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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