| 8 January 2003 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity in December 2002
There was no remarkable activity. to supplementary reports
*On December 1, there was a M5.4 earthquake at a depth of approximately 100km off-shore of Tokachi. The focal mechanism showed a tension axis in the direction of the subducting Pacific plate (downward toward the NNW). This event occurred within the Pacific plate. On January 15, 1993, the Off-shore Kushiro Earthquake (M7.8) occurred in this vicinity. to supplementary reports
*On December 5, there was a M5.2 earthquake at a depth of approximately 40km off-shore of Miyagi prefecture. Immediately following this event, a M4.9 earthquake occurred at the same location. These events were located approximately 30km southeast of the epicenter of the earthquake on November 3 (M6.1). Also, in the vicinity of these events, on February 20, 1978, there was a M6.7 earthquake. It is thought that this event occurred, within the Pacific plate before the Off-shore of Miyagi Prefecture Earthquake (M7.4) on June 12, 1978 However, the current events are thought to have occurred on the boundary between the Pacific plate and the continental plate. to supplementary reports
*On December 23, there was a M4.1 earthquake at a depth of approximately 55km under southern Ibaraki Prefecture.
*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.
*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
There was no remarkable activity. to supplementary reports
There was no remarkable activity. to supplementary reports
*On January 7, there was a M4.6 earthquake at a depth of approximately 50km in the eastern Hidaka region.
| January 8, 2003 |
| Earthquake Research Committee |
58 earthquakes of M4.0 or greater occurred in Japan and the surrounding area during December (49 events occurred in November, and an average of 46 earthquakes per month have occurred over the past thirty years through the end of 2000). 3 of these earthquakes in December were M5.0 or greater. (4 events of M5.0 or greater occurred in November.)
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 no event of magnitude equal to or over M6.0 in December 2002, and there has been a total of 13 M6.0 or greater events by the end of November in 2002.
The following regions have been noted as having significant seismic activity during the period from December 2001 to the end of November 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) | |
| -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 December 2002 and show no signs of acceleration.
(This evaluation is in agreement with the views presented at the procedural meeting on December 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, December 24, 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, it is thought that the slowing of the subduction rate near Omaezaki during the period from June to October was a temporary fluctuation. So far, there have been no changes of activity which are likely to be associated with the so-called Tokai earthquake."
- On December 17, there was a M4.3 earthquake at a depth of approximately 10km in the southern Wakayama prefecture. The focal mechanism showed a normal fault with a tension axis in a NE-SW direction.
- On December 7, there was a M4.7 earthquake at a depth of approximately 30km under the ocean near Amami Oshima.
Supplement
- On January 6, 2003, there was a M4.9 earthquake at a depth of approximately 50km off-shore east of Aomori prefecture. In this vicinity, there was a M5.9 earthquake on October 14, 2002. This event had a maximum seismic intensity 5 Lower.
- On January 5, 2003, there was a M4.4 earthquake at a depth of approximately 100km off-shore of Miyagi prefecture.
Correction
Here is the correction for the contents of "Supplementary Information to the Evaluation of Seismic Activity for November 2002" (The Earthquake Research Committee on December 11)
(before correction)
- Systematic crustal movements which are presumably being caused by slow slip at the plate boundary, were observed in the southeastern Bousou Peninsula at the beginning of October, but these movements had mostly subsided by the middle of October. Since around the same time, seismic activity was continuing in southern Chiba prefecture, and the seismic activity also subsided by the middle of November.
(after correction)
- Systematic crustal movements which are presumably being caused by slow slip at the plate boundary, were observed in the southeastern Bousou Peninsula at the beginning of October, but these movements had mostly subsided by the middle of October. From around the same time, seismic activity was observed off-shore east of the Bousou Peninsula and in southern Chiba prefecture. The activity off-shore east of the Bousou Peninsula subsided by the middle of October. The activity in southern Chiba prefecture was continuing, but it had mostly subsided by the middle 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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