| 11 October 2000 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity in Japan September 2000
In the seismic activity that began at the end of June from the area near Miyakejima to the area near Niijima-Kozushima, there was an M5.3 event in the sea west of Toshima on September 11th, which registered a maximum seismic intensity of 5 lower. to supplementary reports
There was no marked activity. to supplementary reports
There was no marked activity. to supplementary reports
*On September 9th, there was an M4.2 event at a depth of about 70 km in eastern Saitama Prefecture (southern Saitama Prefecture). The event occurred within the Philippine Sea Plate.
*On September 29th, there was a moderately deep M4.5 event at a depth of about 90 km in eastern Kanagawa, with a number of aftershocks, which is unusual for a deep event. The focal mechanism had a northeast-southwest pressure axis. This earthquake occurred in conjunction with the subduction o f the Pacific Plate.
*In the seismic activity that began on June 26th from the area near Miyakejima to the area near Niijima-Kozushima, since the beginning of September, there was an M5.3 event at a depth of about 10 km, which occurred about 5 km west of Toshima on September 11th. But activity on the whole has decreased. Crustal movement has also generally stopped (see separate document).
*Seismic activity within the subducting Philippine Sea Plate in central Shizuoka Prefecture has continued at a low level since August of last year. However, the results of GPS observation of the area between Kakegawa and Omaezaki in the Tokai region show no changes from the trends observed to present. to supplementary reports
There was no marked activity. to supplementary reports
*On September 25th, there was an M4.0 event at a depth of about 10 km in the Kumamoto region of Kumamoto Prefecture. There was an M4.8 event in this same area on June 8th, and the present event occurred within that event's zone of activity. On August 10th, there was an M4.0 event 15 km to the northeast of the present event. to supplementary reports
*On October 2nd, there was an M5.7 event near Akusekijima (the sea near Amami Oshima), which registered a maximum seismic intensity of 5 upper on Akuseskijima (see separate document). Since then, seismic activity has continued, and there have been two events registering maximum seismic activity of 5 lower.
*On October 3rd, there was an M5.9 event in the sea off Sanriku.
*On October 6th, there was an M7.3 event (tentative data) at a depth of about 10 km in western Tottori Prefecture, which registered a maximum seismic intensity of 6 upper in western Tottori Prefecture. There has been continued aftershock activity since that time (see separate document). to supplementary reports
| October 11, 2000 |
| Earthquake Research Committee |
In Japan and the surrounding area, there were 43 M4.0 or greater events (in August there were 182 (44, not including events in the area from Miyakejima to Niijima-Kozushima); the average monthly incidence in the thirty-year period ending last year was 3.) Of that number, there were five events of M5.0 or greater (14 such events in August). September saw an average level of seismic activity. Additionally, in the period from 1997 to 1999, there was an average of 11 M6.0 or greater events per year (or eight, not including events in the Taiwan region), but there have already been 19 such events as of the end of August this year. (Five of the M6.0 or greater events occurred in the area from Miyakejima to Niijima-Kozushima.) None of the above statistics include the August 5th event that occurred 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) |
| -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). Also within this seismic activity, there were two events with maximum seismic intensity 6 lower, two events with maximum seismic intensity 5 upper, and eight events with maximum seismic intensity 5 lower. | |
There was the following seismic activity in the Hokkaido region:
-On September 3rd, in the sea east of Hokkaido,, an M5.2 event. This event occurred in approximately the same location as the M6.8 event that occurred on January 28th, and the M5.7 event that occurred on August 16th.
There are no supplements in the Tohoku Region.
"Seismic activity within the subducting Philippine Sea Plate in central Shizuoka Prefecture has continued at a low level since August of last year.":
The average monthly incidence for M1.5 and greater events within the Philippine Sea Plate in central Shizuoka was six, but since August of 1999 the frequency of occurrence has been lower than average.
There was the following major seismic activity in the Kanto-Chubu region:
-On September 1st, in northeastern Chiba Prefecture, at a depth of about 50 km, there was an M4.1 event. This event occurred within the aftershock zone of the M6.0 event that occurred on June 3rd. Since about the end of June, aftershocks have continued at a fairly regular rate.
-On September 22nd, in Kashima Nada, at a depth of about 40 km, there was an M4.3 event.
There was the following major seismic activity in the Kinki-Chugoku-Shikoku region:
-On September 9th, in northern Kyoto, at a depth of about 10 km, there was an M3.8 event.
-On September 11th, in southern Kyoto, at a depth of about 15 km, there was an M3.8 event.
"On September 25th, there was an M4.0 event at a depth of about 10 km in the Kumamoto region of Kumamoto Prefecture. There was an M4.8 event in this same area on June 8th, and the present event occurred within that event's zone of activity. On August 10th, there was an M4.0 event 10 km to the northeast of the present event.":
Prior to June of this year, there were the following M4.0 or greater events in the area of the epicenter of this earthquake: an M4.0 event on October 31st, 1999 and an M4.1 event on November 10th. Both of those events occurred 5 km northeast of the present (September 25th) event. Since 1926, there have been the following M4.5 and greater events within a 10 km radius of the current event's epicenter: only an M5.0 event in 1928, and an M5.1 event in 1937. Also, in comparison with the June 8th seismic activity, the August 10th activity near the south-west end of Nunotagawa fault was at a lower level, with fewer seismic events and a smaller active zone.
There was the following additional seismic activity in the Kyushu-Okinawa region:
-On September 17th, about 80 km southwest of Yonagunijima, there was an M5.1 event.
There was the following seismic activity in other regions:
-On September 10th, near Taiwan, there was an M6.0 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. |