| 11 September 2002 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity in August 2002
There was no remarkable activity. to supplementary reports
*On August 25, there was a M5.8 earthquake at a depth of approximately 40km under the ocean southeast of Nemuro Peninsula. This event occurred near the boundary between the Pacific plate and the continental plate. The seismic activity is typical of a main shock-aftershock sequence, and is subsiding at the present time at the end of August. The 1973 June 17, Earthquake off the Coast of Nemuro Peninsula (M7.4) occurred in this same area. to supplementary reports
*On August 12, there was a M5.0 earthquake at a depth of approximately 25km off-shore, east of Aomori prefecture. This event occurred near the boundary between the Pacific plate and the continental plate. to supplementary reports
*On August 3, there was a deep M6.2 earthquake at a depth of approximately 450km under the ocean near Torishima. The focal mechanism had a compression axis in a downward and nearly westward direction. This event occurred within the Pacific plate.
*On August 11, there was a M4.3 earthquake at a depth of approximately 40km near the border of Shizuoka and Aichi prefectures.
* Light seismic activity has occurred at a depth of approximately 10km near Hachijojima since August 13, and the active region is extending toward the west in phases. According to the GPS data, 5-6 cm of movement to the east and several cm of uplift were seen on Hachijojima during the period from August 15 to 16. The largest event (M4.1) occurred on August 23, but the activity has been subsiding since the beginning of September.
*On August 18, there was a M4.5 earthquake at a depth of approximately 10km in the Reihoku region of Fukui prefecture.
*On August 20, there was a shallow M6.1 earthquake under the ocean east of Torishima. The focal mechanism showed a reverse fault with a nearly E-W compression axis. This event is associated with the subduction of the Pacific plate.
*Seismic activity and crustal movements in the area from Miyakejima to Nijima-Kozushima have been continuing at a low level.
*The long-term changes that have been observed since last year 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 September 2, there was a M4.0 earthquake at a depth of approximately 10km in northern Wakayama prefecture.
*On September 8, there was a M3.8 earthquake, and a M4.1 earthquake on September 9 at a depth of approximately 10km in northern Miyagi prefecture.
| September 11, 2002 |
| Earthquake Research Committee |
55 earthquakes of M4.0 or greater occurred in Japan and the surrounding area during August. (73 events occurred in July, and an average of 46 earthquakes per month have occurred over the past thirty years through the end of 2000) 7 of these earthquakes in August were M5.0 or greater. (7 events of M5.0 or greater occurred in July)
Earthquakes of M6.0 or greater occurred, on average, 16 times a year during 1998 to 2000. (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 were 2 events of magnitude equal to or over M6.0 in August 2002 and there were a total of seven M6.0 or greater events by the end of July this year.
The following regions have been noted as having significant seismic activity during the period from August 2001 to the end of July 2002.
| -Southern Iwate Prefecture | M6.4 on Dec. 2 2001 (depth of approximately 120km) | |
| -Western Kanagawa Prefecture | M4.5 on Dec. 8 2001 (depth of approximately 25km) | |
| -Amami Oshima | M5.8 on Dec. 9 2001 (depth of approximately 40km) | |
| -Ocean area near Yonagunijima | M7.3 on Dec. 18 2001 (depth of approximately 10km) | |
| -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 |
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 last year 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 August 2002 and show no signs of acceleration.
(The Assessment Meeting held at the Japan Meteorological Agency during the 'Comprehensive Disaster Drills' on September 1, presented the view that there had been no large changes in seismic activity in Tokai region since the procedural meeting of the Regional Assessment Committee for Strengthening Countermeasures against Earthquake Disaster on July 29. This evaluation is in agreement with this view.)
(reference) "Recent seismic and crustal activity in the Tokai Region" (Japan Meteorological Agency, Department of Seismology and Volcanology, July 29 2002)
"In the Tokai region, seismic activity within the Philippine Sea plate has declined since the activity in central Shizuoka prefecture that occurred from April to June last year, but there has been recent seismicity of M3.0 class earthquakes. Seismic activity within the crust is at normal levels overall, but the activity under the coast of Suruga Bay has declined since the beginning of this year. According to the observations by the Geographical Survey Institute, there have been long-term changes in crustal movements in the Tokai region and its vicinity since last year. The activity still appears to be continuing. So far, there have been no changes of activity which are likely to be associated with the so-called Tokai earthquake."
- Seismic activity at a depth of approximately 10km near the border of Wakayama and Nara prefectures, has been continuing intermittently in August. The largest event in August was M2.7.
- On August 30, there was a M3.7 earthquake in the Kumamoto region of Kumamoto prefecture. Also, on September 2, there was a M3.8 earthquake 20km to the southeast of this location. The September 2nd earthquake was located near the Futagawa-Hinagu fault zone. A M4.8 earthquake (maximum seismic intensity 5 Lower) occurred on June 8, 2000 in this same area.
| 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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