| 13 September 2000 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity in Japan August 2000
In August, the seismic activity in the area from Miyakejima to Niijima-Kozushima, which began at the end of June, included a total of five events of magnitude 5 or greater. The August activity also included two events of maximum seismic intensity 6 lower, two of 5 upper, and eight of 5 lower. to supplementary reports
On August 16th, there was an M5.7 event at a depth of about 60 km in the sea east of Hokkaido. There was an M6.8 earthquake in this area on January 28th of this year, and it is believed that the August 16th event was an aftershock to that event. Also, on August 20th, 70 km north-northeast of the August 16th event, there was an M5.7 event at a depth of about 60 km. to supplementary reports
There was no marked activity. to supplementary reports
*On August 6th, there was an M7.3 event at a depth of about 430 km in the sea near Torishima. The focal mechanism had a pressure axis in the direction of the subduction of the Pacific Plate. On August 20th 1998, there was an M7.1 event in this area.
*On August 19th, there was an M5.4 event at a depth of about 40 km in the sea off Ibaraki Prefecture. On July 21st, there was an M6.0 event at a depth of about 50 km, about 50 km northwest of this event.
*For the seismic activity in the area from Miyakejima to Niijima-Kozushima, which started on June 26th, the zone of activity continued to shift in August, and activity levels continued to rise and fall, but activity declined in mid-month. Crustal movement also slowed (see separate document).
*The seismic activity within the subducting Philippine Sea Plate (in central Shizuoka) has continued at a reduced level since August of last year. However, the results of GPS observation and leveling in the Tokai region from Kakegawa to Omaezaki showed no deviations from the trends to present. to supplementary reports
On August 27th, there was an M4.1 event at a depth of about 10 km near the border of Osaka and Nara Prefecture. Aftershock activity has been decreasing since that time. On February 21st 1936, there was an M6.4 event (the Kawachi Yamato Earthquake) 10 km southeast of the epicenter of this event. to supplementary reports
*On August 3rd, there was an M5.1 event at a depth of about 40 km in the sea near Tanegashima (in the sea southeast of the Osumi Peninsula). On June 25th, there was an M5.9 event in this area, and the August 3rd event occurred at the northwest tip of the aftershock region for that event.
*On August 10th, there was an M4.0 event at a depth of about 15 km in the Kumamoto region of Kumamoto Prefecture. On June 8th, there was an M4.8 event about 10 km southwest of this event. to supplementary reports
On August 5th, there was an M7.3 3event (Meteorological Agency magnitude) at a depth of about 10 km in central Sakhalin.
On September 9th, there was an M4.2 event at a depth of about 70 km in eastern Saitama Prefecture.
Corrections
1. The following are corrections to the July 12th report of the Earthquake Survey Committee, Department for the Promotion of Earthquake Survey and Research, which was an attachment to the June 2000 seismic activity report.
Incorrect: c) In the sea near Amami Oshima, on June 6th.... And furthermore, in the sea to the west on June 15th....
Corrected: c) In the sea near Amami Oshima, on June 6th.... And furthermore, in the sea to the east on June 15th....
Inorrect: c) Also, for events of M6.0 and greater... there have been 13....
Corrected: c) Also, for events of M6.0 and greater... there have been 15.... to supplementary reports
| September 13, 2000 |
| Earthquake Research Committee |
There were 182 events of M4.0 and greater (compared with 431 in July) in Japan and the surrounding area, or 44 such events if those occurring in the area from Miyakejima to Niijima-Kozushima are not included. (The monthly average over the past 30 years is 43.) Of that total, 14 events were M5.0 or greater (compared with 139 in July), or nine such events if those occurring in the area from Miyakejima to Niijima-Kozushima are not included. In August, there were many seismic events in the area from Miyakejima to Niijima-Kozushima, but with the exception of those events, the month saw about average activity. Additionally, there were an average of 11 M6.0 and greater events per year (or an average of eight if the Taiwan area is not included) in the period from 1997 to 1999. But there have already been 18 such events by the end of August this year (of that number, there were five events of M6.0 or greater in the area from Miyakejima to Niijima-Kozushima). The above statistics do not include the event which occurred on August 5th in central Sakhalin. There was the following major seismic activity from March of last year to this July.
| -The sea near Niijima-Kozushima | 14 March, 1999, an M4.7 event (at a depth of less than 10 km) |
| 28 March, 1999, an M5.0 event (at a depth of less than 20 km) | |
| -Southern central Kushiro administrative district | 13 May, 1999, a relatively deep M6.4 event(at a depth of about 100 km) |
| -Northern Wakayama Prefecture | 21 August, 1999, an M5.4 event (at a depth of about 70 km) |
| -Taiwan | 21 September, 1999, an M7.7 event (source:US Geological Survey) |
| -Central Inland Sea | 30 October, 1999, an M4.5 event (at a depth of about 15 km) |
| -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) |
There was the following seismic activity in the Hokkaido region:
*On August 27th, in the sea off Urakawa, an M4.7 event
*Since May of this year, the incidence of seismic events in northwestern Hokkaido has been four times that recorded up to that time.
There was the following seismic activity in the Tohoku region:
*On August 27th, in the sea off Akita Prefecture, an M4.3 event
*On August 28th, in the sea off Fukushima Prefecture, an M4.8 event
"The seismic activity within the subducting Philippine Sea Plate (in central Shizuoka) has continued at a reduced level since August of last year."
The average monthly incidence of earthquakes (M1.5 or greater) in the Philippine Sea Plate in central Shizuoka is about six, but the activity level has been lower than average since August of 1999.
There are no supplements in the Kinki-Chugoku-Shikoku Region.
*Activity has been declining since the M4.8 event in the Kumamoto region of Kumamoto Prefecture on June 8th.
*On August 8th, in the sea near Amami Oshima, an M5.2 event
| 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. |