| 10 October 2001 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity in September 2001
There was no marked activity. to supplementary reports
There was no marked activity. to supplementary reports
There was no marked activity. to supplementary reports
*On September 4th, there was an M5.2 earthquake at a depth of approximately 50 km in the sea off Ibaraki Prefecture. This event occurred in conjunction with the subduction of the Pacific Plate.
*On September 13th, there was an M5.5 earthquake in the sea near Chichijima Island.
*On September 18th, there was an M4.2 earthquake at a depth of approximately 40 km in Tokyo Bay.
*On September 25th, there were two earthquakes, of M4.3 and M4.5, both at a depth of approximately 70 km in southwestern Ibaraki Prefecture.
*On September 27th, there was an M4.3 earthquake at a depth of approximately 15 km in central Aichi Prefecture.
*Low seismic activity in the area from Miyakejima to Niijima-Kodushima 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 previous 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
There has been continued microearthquake activity (maximum M3.6) near the border between Wakayama and Nara Prefectures since late May. to supplementary reports
There was no marked activity. 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.
*On October 4th, there was an M6.0 earthquake at a depth of approximately 320 km in the Chishima (Kurile) Islands.
*On October 8th, there was an M4.1 earthquake at a depth of approximately 10 km in eastern Shimane Prefecture.
| October 10, 2001 |
| Earthquake Research Committee |
There were 44 M4.0 or greater earthquakes in Japan and the surrounding area (as compared to 46 in August 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 5 in August).
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 September; there have been eight such events in the period from January 2001 to the present.
The following are evaluations of major seismic activity in the period from September 2000 to the end of August 2001.
| -from the area near Miyakejima to the area near Niijima-Kozushima | ||
| In the period from the end of June to September, there was continued seismic activity in association with magma activity in the area, and on July 1st there was an M6.4 event (at a depth of about 10 km), and another M6.5 event (at a depth of about 10 km) on July 30th. | ||
| -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 is no supplementary information for the Hokkaido region.
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 three to four months, there seems to have been a measurable increase in seismic activity within the crust. This trend seems to have continued in September.
In September, the results of GPS observations in an area centered in western Shizuoka continued to show a trend toward moderate change, 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 September 26th 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, September 26 2001)
'There has been a moderate increase in activity within the slab in the Tokai Region and surrounding areas recently, including the M5.1 earthquake that occurred in central Shizuoka Prefecture on April 3rd and related events.
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.'
There was the following additional seismic activity in the Kanto-Chubu region:
- On September 13th, there was an M4.4 earthquake at a depth of approximately 40 km in the Kumano Nada.
- On September 22nd, there was an M4.2 earthquake at a depth of approximately 40 km in the center of western Aichi Prefecture.
'There has been continued microearthquake activity (maximum M3.6) near the border between Wakayama and Nara Prefectures since late May.':
Since mid-August the microearthquake activity (maximum M3.6 to date) that has continued near the border between Wakayama and Nara Prefectures since the latter half of May, new occurrences began and have continued in a location 2 to 3 km northeast of the May zone of activity (with a maximum M3.4 to date in this new zone). Then again, in mid-September another new zone of activity appeared and continues approximately 2 km southeast of the May active zone (with a maximum M3.1 to date in this 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. However, there has been no marked crustal movement observed in this region
In addition , there was the following seismic activity in the Kinki-Chugoku-Shikoku region:
- Aftershocks to the M5.1 earthquake that occurred in southern Kyoto on August 25th are subsiding, but continue.
There was the following seismic activity in the Kyushu-Okinawa region:
- Aftershock activity to the M6.3 earthquake that occurred on August 18th in the sea near the main island of Okinawa (approximately 80 km southwest of Kumejima) have subsided since mid-September.
| 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. |