| 11 December 2002 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity in November 2002
*On November 3, there was a M6.1 earthquake at a depth of approximately 45km off-shore of Miyagi prefecture. This event had a maximum seismic intensity 5 Lower.
*On November 4, there was a M5.7 earthquake at a depth of approximately 35km in Hyuganada. This event had a maximum seismic intensity 5 Lower. to supplementary reports
*On November 17, there was a deep M7.0 earthquake at a depth of approximately 500km under the southern region of the Sea of Okhotsk. to supplementary reports
*On November 3, there was a M6.1 earthquake at a depth of approximately 45km off-shore of Miyagi 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. The seismic activity was a main shock-aftershock sequence. Activity gradually declined following the mainshock and now is at normal levels. M6 class earthquakes occurred repeatedly in this vicinity in the past (1954, 1973, 1986). In addition, this event was located approximately 80km north of the epicenter of the 1978 Offshore of Miyagi Prefecture Earthquake (M7.4) on June 12, 1978, but the recent event was located out of the immediate aftershock area of the 1978 earthquake.
*On November 16, there was a M4.2 earthquake at a depth of approximately 10km in northern Miyagi prefecture. There were M4.1 earthquakes in this vicinity on September 9 and September 19. to supplementary reports
*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.
*On November 17, there was a M4.5 earthquake at a depth of approximately 10km in the Kaga Region, Ishikawa prefecture. The focal mechanism showed a reverse fault with a nearly E-W compression axis. The seismic activity was increasing in this vicinity since November 15, but it has mostly subsided by the end of November. to supplementary reports
There was no remarkable activity. to supplementary reports
*On November 4, there was a M5.7 earthquake at a 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 subducting Philippine Sea plate. The seismic activity is a main shock-aftershock sequence, and following the mainshock, activity has been declining. to supplementary reports
*On December 1, there was a M5.4 earthquake at a depth of approximately 100km off-shore of Tokachi, Hokkaido.
*On December 5, there was a M5.2 earthquake at a depth of approximately 40km off-shore of Miyagi prefecture. This event was located approximately 30km southeast of the epicenter of the earthquake on November 3 (M6.1).
*On December 4, there was a M4.2 earthquake at a depth of approximately 10km in southern Nagano prefecture. In this vicinity, the Western Nagano Earthquake (M6.8) occurred on September 14. 1984.
| December 11, 2002 |
| Earthquake Research Committee |
49 earthquakes of M4.0 or greater occurred in Japan and the surrounding area during November (164 events occurred in October, and 100 of these events were part of the seismic activity off-shore north of Ishigakijima. An average of 46 earthquakes per month have occurred over the past thirty years through the end of 2000). 4 of these earthquakes in November were M5.0 or greater. (19 events of M5.0 or greater occurred in October.)
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 November 2002, and there has been a total of 11 M6.0 or greater events by the end of October this year.
The following regions have been noted as having significant seismic activity during the period from November 2001 to the end of October 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 | |
| -Ocean area east of Aomori prefecture | M5.9 on Oct. 14, 2002 (depth of approximately 50km) |
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 November 2002 and show no signs of acceleration.
(This evaluation is in agreement with the views presented at the procedural meeting on November 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 and its vicinity" (Japan Meteorological Agency, Department of Seismology and Volcanology, November 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 are no changes in the slowing of the subduction rate near Omaezaki ,that was reported at the previous meeting. Volumetric strainmeters around the area showed no changes either. 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.
- Seismic activity, which had started off-shore north of Ishigakijima on October 24, mostly subsided by the beginning of December.
| 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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