| 9 October 2002 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity in September 2002
There was no remarkable activity. to supplementary reports
There was no remarkable activity. to supplementary reports
*On September 9, there was a M4.1 earthquake at a depth of approximately 10km in northern Miyagi prefecture. Seismic activity has been seen in this area since August 29. The activity increased temporarily during the period from September 8 to 9, but mostly subsided by the end of September. There was a M4.1 earthquake 20km north of this active region on September 19. to supplementary reports
*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
*On September 2, there was a M4.0 earthquake at a depth of approximately 10km in northern Wakayama prefecture.
*On September 16, there was a M5.3 earthquake at a depth of approximately 10km in midwestern Tottori prefecture. The focal mechanism showed a strike-slip fault with a compression axis in a NW-SE direction. The seismic activity is a main shock-aftershock sequence, and at the end of September, the aftershocks were subsiding at normal rates. This event was located approximately 40km east of the Western Tottori earthquake on October 2000 (M7.3), and occurred near the western part of the aftershock area of the 1943 Tottori earthquake (M7.2). to supplementary reports
There was no remarkable activity. to supplementary reports
*On September 15, there was a deep M6.5 earthquake at a depth of approximately 640km near Vladivostok. A M7.2 earthquake at a depth of approximately 590km occurred on June 29 in this same area.
| October 9, 2002 |
| Earthquake Research Committee |
56 earthquakes of M4.0 or greater occurred in Japan and the surrounding area during September. (55 events occurred in August, and an average of 46 earthquakes per month have occurred over the past thirty years through the end of 2000) 11 of these earthquakes in September were M5.0 or greater. (7 events of M5.0 or greater occurred in August)
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 September 2002 and there has been a total of 9 M6.0 or greater events by the end of August this year.
The following regions have been noted as having significant seismic activity during the period from September 2001 to the end of August 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 September 2002 and show no signs of acceleration.
(This evaluation is in agreement with the views presented at the procedural meeting on September 30 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, September 30 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. There has been recent seismicity of M3.0 class earthquakes, but the activity is at normal levels. Seismic activity within the crust is also at normal levels overall. The activity under the coast of Suruga Bay has declined since the beginning of this year, although there has been recent seismicity of M2.0 class earthquakes. 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.
The crustal changes are caused by the movement of the continental plate sliding over the Philippine Sea plate in a SE direction at a slow speed of 2-3cm per year, or less. At first, the main part of the slip was directly under the area of Hamana Lake, but later it diffused toward the NE direction. This slip is considered to be aseismic slip occurring outside of the expected focal region of the so-called Tokai earthquake. The total amount of this slip is thought to be equivalent to a Mw6.8 event. At the present time, the changes are at a slow pace. Other observation items such as volumetric strainmeter in the Tokai area show 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 at a low level in September.
- On September 2, there was a M3.8 earthquake in the Kumamoto region of Kumamoto prefecture. This event 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.
Supplement
- Since October 2, light seismic activity has been occurring at a depth of approximately 5km in the middle region of Nagano prefecture (near the Gofukuji fault). There was a M3.1 earthquake on October 4. The activity is continuing intermittently at present.
| 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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