| 12 June 2002 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity in May 2002
There was no remarkable activity. to supplementary reports
*On May 22, there was a M5.8 earthquake at a depth of approximately 150km in the area of Kunashiri Island. The focal mechanism had a tension axis parallel to the direction of the Pacific Plate motion. This event occurred in the lower surface of the double seismic zone of the subducting Pacific plate. to supplementary reports
*On May 6, there was a M5.0 earthquake at a depth of approximately 40km off-shore of Miyagi prefecture. The focal mechanism was a reverse fault type with an east-west compression axis. This event occurred near the boundary between the subducting Pacific plate and the continental plate.
*On May 12, there was a M5.1 earthquake at a depth of approximately 95km in southern Iwate prefecture. The focal mechanism showed a compression axis in the direction of the subducting Pacific plate. This event occurred in the upper surface of the double seismic zone of the subducting Pacific plate. to supplementary reports
*On May 4, there was a M4.6 earthquake at a depth of approximately 30km in northeastern Chiba prefecture. This event occurred near the boundary between the subducting Philippine Sea plate and the continental plate.
*On May 19, there was a M4.6 earthquake at a depth of approximately 70km in northwestern Chiba prefecture. This event occurred near the boundary between the Philippine Sea plate and the Pacific plate.
*On May 28, there was a M4.4 earthquake in the area from Miyakejima to Nijima-Kozushima. The level of seismic activity increased temporarily, but subsided within a matter of several hours. Since then, the low levels of seismic activity and crustal movement have been continuing at levels similar to the last few months.
*The long-term changes that have been observed since last year in the continuous GPS data in the Tokai region, appear to be still continuing. to supplementary reports
There was no remarkable activity. to supplementary reports
*On May 20, there was a M4.2 earthquake at a depth of approximately 15km in the Kumamoto region of Kumamoto prefecture. to supplementary reports
*On May 15, there was a M6.8 earthquake near Taiwan. A M7.2 earthquake occurred on March 31 in this same area.
*On June 3, there was a deep M6.2 earthquake at a depth of approximately 520km under the ocean near Torishima.
| June 12, 2002 |
| Earthquake Research Committee |
57 earthquakes of M4.0 or greater occurred in Japan and the surrounding area. (52 events occurred in April, and an average of 46 earthquake per month have occurred over the past thirty years through the end of 2000) 6 of these earthquakes were M5.0 or greater. (5 events of M5.0 or greater occurred in April)
Earthquakes of M6.0 or greater occurred, on average, 16 times a year during 1998 to 2000. (Over the past 30 years, on average, M6.0 or greater events have occurred approximately 16 times a year) There was an event of over M6.0 in May 2002 and a total of five M6.0 or greater events so far this year.
The following regions have been noted as having significant seismic activity during the period from May 2001 to the end of April 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 | M7.2 on Mar. 31 2002 |
There is no supplementary information for the Hokkaido region.
There was additional activity in the Tohoku region, as follows.
- On May 30, there was a M4.6 earthquake at a depth of approximately 60km off-shore east of Aomori prefecture. There was a M5.3 earthquake in the same vicinity on April 4.
"The long-term changes that have been observed since last year in the continuous GPS data of the Tokai region, appear to be still 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 to 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 May 2002 and show no sign of acceleration.
(This evaluation is in agreement with the views presented at the procedural meeting on May 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" (Japan Meteorological Agency, Department of Seismology and Volcanology, May 24 2002)
"Seismic activity within the Philippine Sea plate has declined since the cessation of the activity in central Shizuoka prefecture from April to June last year. Seismic activity within the crust, which was at normal or slightly higher levels last year, has returned to normal at present. 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 appears to be continuing similar to the last few months. So far, there has been no changes of activity which are likely to be associated with the so-called Tokai earthquake.
There was additional activity in the Kanto-Chubu region as follows.
- Seismic activity in the Chuetsu region of Niigata prefecture that had continued since around March 25 has declined since the beginning of May.
- There was light non-felt seismic activity under the ocean east of Izu Peninsula from May 8. Along with the seismic activity, crustal movement was also observed on GPS, tiltmeters, and strainmeters. The activity has declined since May 13.
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 has declined since the beginning of May.
"On May 20, there was a M4.2 earthquake at a depth of approximately 15km in the Kumamoto region of Kumamoto prefecture.":
There was a M4.8 earthquake in the Kumamoto region of Kumamoto prefecture on June 8 2000.
There was additional activity in the Kyushu-Okinawa region as follows.
- A M4.3 earthquake occurred on May 6 at a depth of approximately 60km under Bungo Strait .
Supplement
- Seismic activity occurred at Izu-Oshima Island during June 5 and 6, with the largest event having a magnitude of M3.6.
Erratum
a) There was an error in the caption of figure 2 in the "Evaluation of the Yamagata basin fault zone" (May 8 2002, Headquarters for Earthquake Research Promotion Earthquake Research Committee) issued last month.
P3, figure 2: publication date "2000" for all three references shoud be "2001".
b) There were 3 errors in the reading of the name of a fault in the "Evaluation of Ise Bay fault zone" (May 8 2002, Headquarters for Earthquake Research Promotion Earthquake Research Committee) issued last month.
P1, P5 and P11: "Uchiumi fault" should be "Utsumi fault".
| 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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