| 8 May 2002 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity in April 2002
There was no marked activity. to supplementary reports
There was no marked activity. to supplementary reports
*On April 4, there was an M5.3 earthquake at a depth of approximately 60 km in the sea east of Aomori Prefecture. This event occurred near the juncture of the Pacific and continental plates. to supplementary reports
*The seismic activity in the Chuetsu region of Niigata Prefecture that began around March 25 continued into April, and included an M4.0 earthquake on April 11, but the activity had for the most part subsided by the end of the month.
*On April 11, there was an M4.2 earthquake at a depth of approximately 40 km in western Aichi Prefecture. This event occurred within the subducting Philippine Sea plate.
*Low levels of seismic activity and crustal movement continue in the area from Miyakejima to Niijima-Kozushima.
*The long-term changes seen in the results of GPS observations of the Tokai region since last year, appear to be continuing at present. to supplementary reports
*On April 6, there was an M4.5 earthquake at a depth of approximately 40 km in the Nan'yo region of Ehime Prefecture. This event occurred within the subducting Philippine Sea plate.
*After a transient increase in activity at the end of March, the seismic activity that had been occurring at a depth of approximately 10 km near the border of Wakayama and Nara Prefectures, has decreased since mid-April. to supplementary reports
There was no marked activity. to supplementary reports
*On May 4, there was an M4.6 earthquake at a depth of approximately 30 km in northeastern Chiba Prefecture.
*On May 6, there was an M5.0 earthquake at a depth of approximately 40 km in the sea off Miyagi Prefecture.
| May 8, 2002 |
| Earthquake Research Committee |
There were 52 M4.0 or greater earthquakes in Japan and the surrounding area (as compared to 69 in March and a monthly average incidence of 46 in the thirty-year period up to the end of 2000). Of that number, 5 events were M5.0 or greater (as compared to 9 in March).
The average number of M6.0 or greater earthquakes in the period from 1998 to 2000 was 16 per year. (The 30-year average up to 2000 was also approximately 16 per year.) There were no such events in April 2002, and a total of 4 for the year up to the end of April.
The following are evaluations of major seismic activity in the period from April 2001 to the end of March 2002.
| -Central Shizuoka Prefecture | ||
| April 3 2001 M5.1 (at a depth of about 35 km) | ||
| -Southern interior Iwate Prefecture | ||
| December 2 2001M6.4 (at a depth of about 120 km) | ||
| -Western Kanagawa Prefecture | December 8 2001M4.5 (at a depth of about 25 km) | |
| -Amami Oshima | December 9 2001M5.8 (at a depth of about 40 km) | |
| -Sea near Yonagunijima | December 18 2001M7.3 (at a depth of about 10 km) | |
| -In the sea off Ibaraki Prefecture | February 12 2002 M5.5 (at a depth of about 50 km) | |
| -in the sea south of Ishigakijima | March 26 2002 M6.6 (at a depth of about 10 km) | |
| -near Taiwan | March 31 2002 M7.2 | |
There is no supplementary information for the Hokkaido region.
"On April 4, there was an M5.3 earthquake at a depth of approximately 60 km in the sea east of Aomori Prefecture.":
There was an M4.7 earthquake in the vicinity of this event on April 21.
"The long-term changes seen in the results of GPS observations of the Tokai region since last year, appear to be continuing at present.":
The results of GPS observations in an area centered in western Shizuoka continued to show a trend of moderate change in the movement to the WNW of the Pacific side of the Tokai-Chubu region at a nearly steady rate in conjunction with the subduction of the Philippine Sea Plate to the northwest. This trend, which began in April 2001, continued through April 2002. However, there are no signs that the changes are accelerating.
(This evaluation is in agreement with the views (see reference below) expressed at the April 30 procedural meeting of the Regional Assessment Committee for Strengthening Countermeasures against Earthquake Disaster.)
(reference) "Recent seismic and crustal activity in the Tokai Region" (Japan Meteorological Agency, Department of Seismology and Volcanology, April 30 2002)
"Seismic activity within the Philippine Sea plate in the Tokai region has been low since the cessation of the activity that occurred from April to June last year.
Seismic activity within the crust, which had been at normal or slightly higher than normal levels last year, has returned to a normal level since the start of this year.
Additionally, regarding crustal movement in the Tokai and surrounding regions, the results of observations by the Geographical Survey Institute indicate some change over the long term since last year.
At present, the activity appears to be continuing as before. There have been no observations of changes directly linked with earthquakes in Tokai."
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
There was the following additional activity in the Kyushu-Okinawa region:
-Aftershock activity following the earthquake (M6.6) that occurred on March 26 in the sea south of Ishigakijima gradually decreased, and had ceased by the end of April.
- Aftershock activity following the earthquake (M7.2) that occurred on March 31 near Taiwan is gradually decreasing.
| Reference Material 1 Standards to select earthquakes which are to be described in "Evaluation of Seismic Activity" (Monthly Report of Seismic Activity in Japan) Events of M6.0 or greater. Or, M4.0 or greater (M5.0 or greater at sea) and having a maximum intensity of 3 or greater. Reference Material 2 Standards to describe additional explanation in "Supplementary repot of the evaluation." 1 Reference items relating to seismic activity described in "Evaluation of Seismic Activity". 2 Activity related to seismic activity (of the past 12 months or so) described in "Major Seismic Activity in Evaluation of Seismic Activity." 3 Activity that have been evaluated but not described in "Evaluation of Seismic Activity" because of being within the bounds of normal activity or because the activity is not prominent. |