| 8 August 2002 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity in July 2002
There was no remarkable activity. to supplementary reports
*On July 25, there was a M5.6 earthquake in the ocean area east of Hokkaido. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. This event is related to the subduction of the Pacific plate and located within the aftershock area of the 1994 earthquake off the East Coast of Hokkaido (M8.2).
*On July 28, there was a M4.8 earthquake at a depth of approximately 50km under the southern Tokachi region. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. This event occurred near the boundary between the Pacific plate and the continental plate. to supplementary reports
*On July 1, there was a M4.3 earthquake at a depth of approximately 80km under eastern Aomori prefecture. This event occurred within the Pacific plate.
*On July 24, there was a M5.7 earthquake at a depth of approximately 30km off-shore of Fukushima prefecture. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. This event occurred near the boundary between the Pacific plate and the continental plate.
*On July 30, there was a M4.1 earthquake at a depth of approximately 100km under eastern Aomori prefecture. This event occurred within the Pacific plate. to supplementary reports
*On July 13, there was a M4.8 earthquake at a depth of approximately 65km under southwestern Ibaraki prefecture. The focal mechanism showed a reverse fault with a compression axis in a nearly E-W direction. This event occurred near the boundary between the Pacific plate and the Philippine Sea plate.
*On July 27, there was a M4.5 earthquake at a depth of approximately 60km under northern Ibaraki prefecture. The focal mechanism showed a reverse fault with a compression axis in a nearly E-W direction. This event occurred near the boundary between the Pacific plate and the continental 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
*On July 16, there was a M4.2 earthquake at a depth of approximately 15km in southern Kyoto prefecture. to supplementary reports
*On July 15, there was a M5.1 earthquake at a depth of approximately 50km under the ocean near Amami Oshima. This event is associated with the subduction of the Philippine Sea 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.
| August 8, 2002 |
| Earthquake Research Committee |
73 earthquakes of M4.0 or greater occurred in Japan and the surrounding area during July. (57 events occurred in June, and an average of 46 earthquake per month have occurred over the past thirty years through the end of 2000) 7 of these earthquakes were M5.0 or greater. (4 events of M5.0 or greater occurred in June)
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 no events of magnitude equal to or over M6.0 in July 2002 and there has been a total of seven M6.0 or greater events so far this year.
The following regions have been noted as having significant seismic activity during the period from July 2001 to the end of June 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 around April 2001. The trends have continued through July 2002 and show no signs of acceleration.
(This evaluation is in agreement with the views presented at the procedural meeting on July 29 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, 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."
"On July 16, there was a M4.2 earthquake at a depth of approximately 15km in southern Kyoto prefecture.":
A M5.1 earthquake occurred on August 25, 2001 in this same area.
There was additional activity in the Kinki-Chugoku-Shikoku region, as follows.
- Seismic activity, at a depth of approximately 10km near the border of Wakayama and Nara prefectures that had increased temporarily in June, increased temporarily again in July. The seismicity has been continuing at a low level. The activity occurred mainly on the southwestern edge of the area that was previously active.
There is no supplementary information for the Kyushu-Okinawa region.
| 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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