| 14 November 2001 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity in October 2001
There was no marked activity. to supplementary reports
*On October 4th, there was an M6.0 deep earthquake at a depth of approximately 320 km near the Chishima (Kurile) islands. The focal mechanism had a pressure axis in the direction of the subduction of the Pacific Plate. to supplementary reports
*On October 2nd, there was an M5.4 earthquake at a depth of approximately 40 km in the sea off Fukushima Prefecture. The focal mechanism had a WNW-ESE pressure axis, and the event occurred in conjunction with the subduction of the Pacific Plate. to supplementary reports
*On October 18th, there was an M4.3 earthquake at a depth of approximately 50 km in southwestern Ibaraki Prefecture. This event occurred near the upper face of the Philippine Sea Plate.
*Low seismic activity in the area from Miyakejima to Niijima-Kozushima continues. The results of GPS observation of the area also show that the recent crustal movements have not yet entirely stopped.
*Crustal seismic activity in Suruga Bay and the surrounding area had been at a slightly low level, but now appears to be returning to normal activity.
The slight changes in activity centered in western Shizuoka Prefecture, which were seen in the results of GPS observation of the Tokai region, have continued since that time. to supplementary reports
*On October 8th, there was an M4.1 earthquake at a depth of approximately 10 km in western Tottori Prefecture. This event occurred within the aftershock zone of the 2000 Western Tottori earthquake.
*On October 15th, there was an M4.3 earthquake at a depth of approximately 25 km in southern Wakayama Prefecture. This event occurred in the lower crust.
* There has been continued microearthquake activity (maximum M3.6) near the border between Wakayama and Nara Prefectures since late May. to supplementary reports
*On October 31st, there was a moderately deep M5.2 earthquake at a depth of approximately 120 km in the sea near Amami Oshima. to supplementary reports
| November 14, 2001 |
| Earthquake Research Committee |
There were 45 M4.0 or greater earthquakes in Japan and the surrounding area (as compared to 44 in September and a monthly average incidence of 46 in the thirty-year period up to the end of 2000). Of that number, 6 events were M5.0 or greater (as compared to 5 in September).
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 was one such event in October, no such event in September; there have been nine such events in the period from January 2001 to the present.
The following are evaluations of major seismic activity in the period from October 2000 to the end of September 2001.
| -Western Tottori Prefecture(The 2000 Western Tottori Earthquake in western Tottori Prefecture) | ||
| On October 6th, there was an M7.3event (at a depth of about 10 km) | ||
| -Near Toshimamura, Akusekijima in Kagoshima Prefecture (the sea near Amami Oshima) | ||
| M5.7 on October 2nd 2000 (at a depth of approximately 10 km) | ||
| -Central Mie Prefecture | ||
| M5.5 on October 31st 2000 (at a depth of approximately 40 km) | ||
| -Near Iriomotejima | On November 14th 2000, there was an M4.4 earthquake (at a depth of about 10 km) | |
| -Chuetsu region of Niigata Prefecture | 2 January 2001 M4.4 (at a depth of about 10 km) | |
| -Chuetsu region of Niigata Prefecture(about 40 km SSE of the 1/2/2001 event) | ||
| 4 January M5.1 (at a depth of about 10 km) | ||
| -Northern Hyogo Prefecture | 12 January 2001 M5.4 (at a depth of about 10 km) | |
| -Near Niijima-Kodushima | On February 13th 2001, an M3.9 earthquake (at a depth of about 10 km) | |
| -Akinada "2001 Geiyo earthquake" | ||
| March 24 2001, M6.7 (at a depth of about 50 km) | ||
| -Central Shizuoka Prefecture | ||
| April 3rd 2001 M5.1 (at a depth of about 35 km) | ||
There was the following seismic activity in the Hokkaido region:
- On October 1st, there was an M5.0 earthquake in the sea east of Hokkaido.
- On October 27th, there was an M4.6 and an M4.7 earthquake in the sea off Tokachi. Microearthquake activity, which included these two events, continued in this area for approximately five days.
There is no supplementary information for the Tohoku region.
"Crustal seismic activity in Suruga Bay and the surrounding area had been at a slightly low level, but now appears to be returning to normal activity.
The slight changes in activity centered in western Shizuoka Prefecture, which were seen in the results of GPS observation of the Tokai region, have continued since that time.":
A long-term review of activity shows a somewhat reduced incidence of activity since around 1996 with an even greater reduction beginning around October 2000. But in the past five months, there seems to have been a measurable increase in seismic activity within the crust. This trend has continued in October.
The results of GPS observations in an area centered in western Shizuoka continued to show a trend toward moderate change in October, which began in April 2001, involving movement at a fixed rate to the WNW in conjunction with the subduction of the Philippine Sea Plate to the northwest, on the Pacific side of the Tokai-Chubu region.
(This evaluation is in agreement with the views (see reference below) expressed at the October 29th procedural meeting of the Regional Assessment Committee for Strengthening Countermeasures against Earthquake Disasters.)
(reference) "Recent seismic and crustal activity in the Tokai Region" (Meteorological Agency, Department of Seismology and Volcanology, October 29 2001)
"There had been a moderate increase in activity within the slab in the Tokai Region and surrounding areas this year, but activity seems to have subsided recently.
Seismic activity in Suruga Bay and the western coast had been at a moderately low level, but we recognize signs of a resumption of activity.
Regarding crustal movement in the Tokai and surrounding regions, the results of observations by the National Geological Institute indicate some change over the long term, but nothing that can immediately be linked to earthquakes in the Tokai Region."
- On October 2nd, there was an M5.1 earthquake in Southeast Offshore of Boso Peninsula. And on October 5th, an M5.0 earthquake occurred approximately 50 km from the site of the October 2nd event (in the sea East of Kanto).
"There has been continued microearthquake activity (maximum M3.6) near the border between Wakayama and Nara Prefectures since late May.":
The microearthquake activity at a depth of approximately 10 km near the border between Wakayama and Nara Prefectures that began in late May (maximum M3.6 to date) continued in October (maximum M3.2 in October), within the same zone of activity. Since early October, activity has been focused in the eastern end of the zone. The cluster of zones of activity thus far extends 5 km to the north and south and 4 km to the east and west, with a gentle tilt to the west. Some activities are significant, some not. However, there has been no marked crustal movement observed in this region
"On October 15th, there was an M4.3 earthquake at the depth of approximately 25 km in south of Wakayama Prefectures. This earthquake occurred in the lower part of crust.":
Activity in the lower crust in southern Wakayama has been occurring for some time. This most recent event occurred near the northern extremity of the active zone.
There was the following additional activity in the Kinki-Chugoku-Shikoku region:
- Aftershocks to the M5.1 earthquake that occurred on August 25th in southern Kyoto are diminishing, but continue. There was an M3.0 aftershock on October 12th.
There is no supplementary information for the Kyushu-Okinawa Region
On November 13th, there was an M4.7 earthquake at a depth of approximately 50 km in the sea off Iwate Prefecture. There have been earthquakes of similar scale within this area in the past five years.
| 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. |