| 10 April 2002 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity in March 2002
On March 26, there was an M6.6 earthquake at a depth of approximately 10 km in the sea south of Ishigakijima, and tsunamis were observed in parts of Okinawa Prefecture including Yonagunijima. On March 31, there was an M7.2 earthquake (as reported by Japan Meteorological Agency) near Taiwan, which registered a maximal seismic intensity of 3 and tsunamis were observed in parts of Okinawa Prefecture including Yonagunijima. to supplementary reports
*On March 7, there was a deep M6.0 earthquake at a depth of approximately 480 km in the southern Sea of Okhotsk. to supplementary reports
There was no marked activity. to supplementary reports
*On March 17, there was an M4.1 earthquake at a depth of approximately 50 km in southern Ibaraki Prefecture.
*From around March 25, there was microearthquake activity at a depth of approximately 15 km in the Chuetsu Region of Niigata Prefecture, and on March 28 an M4.1 earthquake occurred. The seismic activity has continued thereafter.
*On March 28, there was an M4.0 earthquake at a depth of approximately 15 km in western Kanagawa Prefecture.
*Low levels of seismic activity and crustal movement continue in the area from Miyakejima to Niijima-Kozushima.
* The slight changes in the crustal movements centered in western Shizuoka Prefecture, which were seen in the results of GPS observation of the Tokai region, still appear to be continuing. to supplementary reports
*On March 6, there was an M4.5 earthquake at a depth of approximately 15 km in eastern Shimane Prefecture. This event was an aftershock to the 2000 Western Tottori Earthquake (M7.3).
*On March 11, there was an M4.1 earthquake at a depth of approximately 10 km in northern Tokushima Prefecture.
*There has been continued microearthquake activity at a depth of approximately 10 km near the border of Wakayama and Nara Prefectures since end of May 2001, and although activity had declined following the increased activity in January, there was a transient increase in activity at the end of March including an M3.7 earthquake on March 28. The activity in March occurred in roughly the same area as the January active zone.
*On March 25, there was an M4.7 earthquake at a depth of approximately 50 km in the Iyo Nada. This event is believed to have occurred within the Philippine Sea Plate. to supplementary reports
*On March 26, there was an M6.6 earthquake at a depth of approximately 10 km in the sea south of Ishigakijima. Tsunamis of up to 10 cm were observed in Okinawa Prefecture following this event. The focal mechanism was a reverse fault type with a NNW-SSE pressure axis. The seismic activity has followed a main shock-aftershock pattern, and is gradually declining. A review of past seismic activity in the area shows that, in recent years, there was an M7.6 earthquake that occurred approximately 150 km ESE of the epicenter of this event on May 4 1998. to supplementary reports
(6) Other Regions
*On March 31, there was an M7.2 earthquake near Taiwan, which registered a maximal seismic intensity of 3 in parts of Okinawa Prefecture including Yonagunijima. Tsunamis of up to 20 cm were observed in Okinawa Prefecture following this event. The focal mechanism was a reverse fault type with a NNW-SSE pressure axis. This event occurred near the juncture of the subducting Philippine Sea Plate and the Eurasian Plate. The seismic activity has followed a main shock-aftershock pattern, and is gradually declining. 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.
*On April 6, there was an M4.5 earthquake at a depth of approximately 40 km in the Nan'yo region of Ehime Prefecture.
| April 10, 2002 |
| Earthquake Research Committee |
There were 69 M4.0 or greater earthquakes in Japan and the surrounding area (as compared to 34 in February and a monthly average incidence of 46 in the thirty-year period up to the end of 2000). Of that number, 9 events were M5.0 or greater (as compared to 6 in February).
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 3 such events in March 2002, and a total of 4 for the year up to the end of March.
The following are evaluations of major seismic activity in the period from March 2001 to the end of February 2002.
| -Akinada "2001 Geiyo earthquake" | ||
| March 24 2001 M6.7 (at a depth of about 50 km) | ||
| -Central Shizuoka Prefecture | ||
| April 3 2001 M5.1 (at a depth of about 35 km) | ||
| -Southern interior Iwate Prefecture | ||
| December 2 2001 M6.4 (at a depth of about 120 km) | ||
| -Western Kanagawa Prefecture | December 8 2001 M4.5 (at a depth of about 25 km) | |
| -Amami Oshima | December 9 2001 M5.8 (at a depth of about 40 km) | |
| -Sea near Yonagunijima | December 18 2001 M7.3 (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) | |
There is no supplementary information for the Hokkaido region.
There is no supplementary information for the Tohoku region.
"The slight changes in the crustal movements centered in western Shizuoka Prefecture, which were seen in the results of GPS observation of the Tokai region, still appear to be continuing."
The results of GPS observations in an area centered in western Shizuoka continued to show a trend toward moderate change, involving the movement to the WNW of the Pacific side of the Tokai-Chubu region at a fixed rate in conjunction with the subduction of the Philippine Sea Plate to the northwest. This trend, which began in April 2001, continued through March 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 March 25 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, March 25 2002)
"Seismic activity within the slab in the Tokai region has been low recently.
Last year, seismic activity in Suruga Bay and the western coast had been normal or slightly above normal, but since the beginning of this year, in the surrounding areas as well, activity has been reduced.
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 indications of direct linkage with Tokai earthquake."
There was the following additional activity:
*Microseismic activity in northern Tochigi Prefecture from the end of February to mid-March. The maximal event was an M3.5 event on March 10.
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
There is no supplementary information for the Kyushu-Okinawa Region.
| 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. |