| 14 November 2002 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity in October 2002
On October 14, there was a M5.9 earthquake at a depth of approximately 50km off-shore east of Aomori prefecture. This event had a maximum seismic intensity 5 Lower. to supplementary reports
*On October 19, there was a M6.4 earthquake near Etorofu Island. to supplementary reports
*On October 14, there was a M5.9 earthquake at a depth of approximately 50km off-shore east of Aomori prefecture. This event had a maximum seismic intensity 5 Lower. The focal mechanism showed a reverse fault with a WNW-ESE compression axis. This event occurred near the boundary between the Pacific plate and the continental plate.
*On October 12, there was a M5.6 earthquake at a depth of approximately 30km off-shore Fukushima prefecture. There also was a M5.2 earthquake in almost the same point on October 11. to supplementary reports
*On October 21, there was a M5.2 earthquake at a depth of approximately 50km off-shore Ibaraki prefecture.
*Systematic crustal movement of 1-2cm to the SE direcition in southeastern Bousou Peninsula was observed in the GPS data in the beginning of October. It is thought that slow slip at the plate boundary caused it. Around the same time, since October 2, the seismic activity occurred off-shore east of Bousou Peninsula. And, since October 6, the seismisity was seen in southern Chiba prefecture, too. Since the middle of October, the activity in southern Chiba prefecture has been continuing at a low level, and the seismic activity and the crustal movement off-shore east of Bousou Peninsula has almost subsided. In addition, the similar phenomenon was observed in this vicinity in May, 1996.
*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
*On October 23, there was a M4.4 earthquake at a depth of approximately 10km in eastern Shimane prefecture. to supplementary reports
There was no remarkable activity. to supplementary reports
*On November 3, there was a M6.1 earthquake at a depth of approximately 45km off-shore Miyagi prefecture. This event had a maximum seismic intensity 5 Lower. The focal mechanism showed a reverse fault with a nearly WNW-ESE compression axis. This event occurred near the boundary between the Pacific plate and the continental plate. The seismic activity is a main shock-aftershock sequence, and it has been declining. M6 class earthquakes occurred several times in this vicinity in the past (1954, 1973, 1986). In addition, this event was located approximately 80km north of the epicenter of the 1978 Earthquake off the Coast of Miyagi Prefecture (M7.4) on June 12, 1978, but the event was located out of the immediate aftershock area of the 1978 earthquake.
*On November 4, there was a M5.7 earthquake at the depth of approximately 35km in Hyuganada. This event had a maximum seismic intensity 5 Lower. The focal mechanism had a tension axis in the direction of the subducting plate, and this event is associated with the subduction of the Philippine Sea plate. The seismic activity is a main shock-aftershock sequence, and it has been declining.
| November 14, 2002 |
| Earthquake Research Committee |
164 earthquakes of M4.0 or greater occurred in Japan and the surrounding area during October. (56 events occurred in September, and an average of 46 earthquakes per month have occurred over the past thirty years through the end of 2000) 100 of the events were part of the seismic activity off-shore north of Ishigakijima. 19 of these earthquakes in October were M5.0 or greater. (11 events of M5.0 or greater occurred in September)
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 was 1 event of magnitude equal to or over M6.0 in October 2002 and there has been a total of 10 M6.0 or greater events by the end of September this year.
The following regions have been noted as having significant seismic activity during the period from October 2001 to the end of September 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.
- On October 25 there was a M4.5 earthquake at a depth of approximately 20km off-shore Akita prefecture (near Akita city).
"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 October 2002 and show no signs of acceleration.
(This evaluation is in agreement with the views presented at the procedural meeting on October 25 of the Regional Assessment Committee for Strengthening Countermeasures against Earthquake Disaster. (see reference below))
(reference) "Recent seismic and crustal activity in the Tokai Region" (Japan Meteorological Agency, Department of Seismology and Volcanology, October 25, 2002)
"In the Tokai region, seismic activity within both the crust and Philippine Sea plate is at normal levels. There have been long-term changes in crustal movements in the Tokai region and its vicinity since last year. There are no large changes in the slow slip on the plate boundary which is the cause of those long-term changes. According to the leveling and the GPS observations by the Geographical Survey Institute, there have been small changes which seem to indicate a slowing of the subduction rate near Omaezaki, but volumetric strainmeters around the area show no corresponding changes. So far, there have been no changes of activity which are likely to be associated with the so-called Tokai earthquake."
- On October 13, there was a M4.7 earthquake at a depth of approximately 40km under the Bungo Strait.
- Since October 24, shallow seismic activity has started off-shore north of Ishigakijima. Activity was quite active with M5 or greater earthquake occurring 10 times during the period from October 24 to 25, but it has declined since the beginning of November.
| 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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