| 13 December 2000 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity in November 2000
On November 14th, there was an M4.4 earthquake at a depth of about 10 km near Iriomotejima, which registered a maximum seismic intensity of 5 lower. to supplementary reports
On November 14th, there was an M5.9 earthquake at a depth of 50 km in the sea off Kushiro. An M5.2 event occurred on the same day in about the same location. The focal mechanism for both events was a reverse fault type with a northwest-southeast pressure axis. These earthquakes occurred in conjunction with the subduction of the Pacific Plate. to supplementary reports
On November 16th, there was an M5.0 event at a depth of about 50 km in the sea off Fukushima Prefecture. This earthquake occurred in conjunction with the subduction of the Pacific Plate. to supplementary reports
*The seismic activity that began on June 26th in the area from Miyakejima to Niijima-Kodushima decreased to an even lower level than in October; there was, however, an M3.5 event about 10 km east of Kodushima on November 9th. The continuing crustal movements have also near ceased.
*Although there has been a recent trend toward the resumption of seismic activity within the subducting Philippine Sea Plate in central Shizuoka Prefecture, the overall activity level has continued to be lower than average since August of last year. However, results of GPS observation and leveling surveys of Tokai region show no marked changes in the trends seen to present. to supplementary reports
Since the beginning of November, the aftershock activity following the M7.3 (tentative data) 2000 Western Tottori Earthquake that occurred on October 6 has gradually declined; there was, however, an M4.5 aftershock in the northern part of the aftershock zone on the third. Furthermore, the triggered by the M7.3 (tentative) event in the areas 25 km WSW and 30 km ENE of the aftershock zone has also gradually been declining. to supplementary reports
*On November 9th, there was an M6.2 event near the sea trench of the Nansei Shoto about 100 km south of Ishigakijima. The focal mechanism had a northwest-southeast pressure axis. This event occurred in conjunction with the subduction of the Philippine Sea Plate.
*On November 14th, there was an M4.4 event at a depth of about 10 km near Iriomotejima, which registered a maximum seismic intensity of 5 lower. The middle of the month was briefly active, with three M4.0 or greater events including this one. to supplementary reports
*On December 5th, there was an M5.3 event at a depth of about 40 km in the sea off Ibaraki Prefecture.
*On December 7th, there was an M4.2 aftershock to the 2000 Western Tottori Earthquake at a depth of about 10 km in eastern Shimane Prefecture.
| December 13, 2000 |
| Earthquake Research Committee |
There were 90 events of M4.0 or greater in Japan and the surrounding area (or 60 such events, not including the aftershock activity in western Tottori Prefecture). In September, about 40 such events were recorded (the average monthly incidence for the past thirty years has also been around 40). Of this total, there were 12 events of M5.0 or greater (compared with five such events in September). In addition, although the average yearly incidence of M6.0 or greater earthquakes in the 1997-1999 period was 11 (or eight, not including events in the Taiwan region), there have already been 21 such events as of the end of October this year (or 16, not including events in the area from Miyakejima to Niijima-Kozushima). Please note that none of the above figures includes that earthquake that occurred in central Sakhalin on August 5th.
There has been the following major seismic activity in the period from October of last year to October of this year:
Forty events of M4.0 or greater were recorded in Japan and the surrounding area (as compared to 60 in October, and a monthly average of about 40 such events over the past thirty years). Of that number, five events were of M5.0 or greater (12 such events in October). Furthermore, although the average annual incidence of M6.0 or greater events in the period from 1997 to 1999 was 11 (or eight, not including events in the Taiwan area), there have already been 22 such events (or 17, not including events in the area from Miyakejima to Niijima-Kodushima) as of the end of November this year. None of the above figures reflects the event that occurred central Sakhalin in August 5th.
There was the following major seismic activity in the period from November of last year to the end of October this year:
| -Kumamoto region of Kumamoto Prefecture (at a depth of about 10 km), off the coast of Fukui Prefecture (at a depth of about 15km) | |
| and western Aichi Prefecture (at a depth of about 50 km), in November 1999, all M4.0 or greater earthquakes | |
| -Off the eastern coast of Hokkaido | 28 January, 2000, an M6.8 event (at a depth of about 60 km) |
| -Iburi administrative district (in the vicinity of Mt. Usuzan) | |
| 30 March, 2000, an M4.3 event (at a depth of less than 10 km) and 1 April, an M4.6 event (at a depth of less than 10 km), seismic activity associated with the volcanic activity | |
| -Northeastern Chiba Prefecture | 3 June 2000, M6.0 (at a depth of about 50km) |
| -Off the west coast of Ishikawa Prefecture | 7 June 2000, M6.1 (at a depth of less than20 km) |
| -The Kumamoto region of Kumamoto Prefecture | 8 June 2000, M4.8 (at a depth of about 10km) |
| -In the area from Miyakejima to Niijima-Kozushima | There was seismic activity associated with magma activity, including events of M6.4 (at a depth of 10 km) on July 1st, and M6.4 (at a depth of 10 km) on July 30th. |
| -The sea off Ibaraki Prefecture | July 21st 2000, M6.0 (at a depth of 50 km) |
| -from the area near Miyakejima to the area near Niijima-Kozushima | |
| In August 2000, there were five M5.0 or greater events (on August 18th, maximum M6.0). | |
| -from the area near Miyakejima to the area near Niijima-Kozushima | |
| September 11th 2000, in the sea west of Toshima, an M5.3 event | |
| -Western Tottori Prefecture | On October 6th, there was an M7.3 (tentative) event (at a depth of about 10 km) |
There was also the following seismic activity:
*On November 9th, there was an M4.4 event in the sea west of Hokkaido.
There are no supplements in the Tohoku Region.
"*Although there has been a recent trend toward the resumption of seismic activity within the subducting Philippine Sea Plate in central Shizuoka Prefecture, the overall activity level has continued to be lower than average since August of last year."
Until August 1999 the average monthly incidence of M1.5 and greater events within the Philippine Sea Plate in central Shizuoka Prefecture was around six. Since that time, the overall activity level has continued to be below average, despite occasional transient periods of higher than average activity.
There was also the following seismic activity:
-November 5th, there was an M5.5 event in the sea east of the Kanto region.
-There was a low frequency seismic activity at a depth of 15 km near Mt. Fuji (There were about 30 events of M1.5 or greater. A maximal event of M2.2 occurred on November 11th.)
"... the aftershock activity following the... 2000 Western Tottori Earthquake... has gradually declined...."
The aftershock activity in the north is more active than that in the south.
There was also the following seismic activity:
- On November 2nd, there was an M3.7 event at a depth of about 30 km in southwest Hiroshima Prefecture. Based on the epicenter distribution of earthquakes over the past three years, events occurring at this depth have been concentrated in this vicinity.
"On November 9th, there was an M6.2 event near the sea trench of the Nansei Shoto about 100 km south of Ishigakijima. The focal mechanism had a pressure axis in an NW-SE direction"
In May 1998, in the sea south of Ishigakijima, there was an M7.6 earthquake whose epicenter was about 150 km southeast of this event's.
Corrections:
In the Seismic activity in September 2000 report issued by this committee on October 11th, there was an error in the "Major seismic activity" supplementary section.
Error: (4 to 6 lines from the top of the section) "... as of the end of August this year."
Correct: (4 to 6 lines from the top of the section) "... as of the end of September this year."
| 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. |