| 9 April 2003 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity in March 2003
There was no remarkable activity. to supplementary reports
*On March 16, there was a M4.6 earthquake at a depth of approximately 100 km in the southern Tokachi region. to supplementary reports
*On March 3, there was a M5.8 earthquake at a depth of approximately 40 km 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 plate and the continental plate. to supplementary reports
*On March 17, there was a M4.1 earthquake at a depth of approximately 10 km in northern Saitama prefecture.
*On March 13, there was a M4.8 earthquake at a depth of approximately 45 km in southwestern Ibaraki prefecture. 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 plate and the continental plate.
*On March 4, there was a M4.1 earthquake at a depth of approximately 35 km in eastern Aichi prefecture.
*On March 13, there was a M4.1 earthquake at a depth of approximately 15 km in the Reinan 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 March 27, there was a M4.2 earthquake at a depth of approximately 15 km in western Shimane prefecture. This is the first time that an earthquake over M4.0 occurred near the epicenter of this event, since the earthquake of May 15, 1971(M4.3). to supplementary reports
There was no remarkable activity. to supplementary reports
*On April 8, there was a M4.6 earthquake at a depth of approximately 45 km in southwestern Ibaraki prefecture.
*On April 1, there was a M4.1 earthquake at a depth of approximately 10 km near the boundary between Nagano and Gifu prefectures.
*On April 2, there was a M4.2 earthquake at a depth of approximately 10 km in eastern Shimane prefecture.
| April 9, 2003 |
| Earthquake Research Committee |
48 earthquakes of M4.0 or greater occurred in Japan and the surrounding area during March (42 events occurred in February, and an average of 46 earthquakes per month have occurred over the past thirty years through the end of 2000). 4 of these earthquakes in March were M5.0 or greater. (5 events of M5.0 or greater occurred in February.)
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 March 2003.
The following regions have been noted as having significant seismic activity during the period from March 2002 to the end of February 2003.
| -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 March 2003 and show no signs of acceleration.
(This evaluation is in agreement with the views presented at the procedural meeting on March 28 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, March 28, 2003)
" In central and western Shizuoka prefecture, micro-seismicity is slightly increasing. On the other hand, it is seemed that the seismic activity is declining under the Hamana Lake. On the whole, the activity is rather calm.
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."
- On March 26, there was a M4.5 earthquake at a depth of approximately 10 km under the Bungo Strait.
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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