| 12 December 2001 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity in November 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 November 17th, there was an M4.4 earthquake at a depth of approximately 75 km in northwestern Chiba Prefecture.
*Low seismic activity in the area from Miyakejima to Niijima-Kozushima continues. The results of GPS observation of the area also show that recent crustal movements have not yet entirely ceased.
*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 of crustal movements centered in western Shizuoka Prefecture, which were seen in the results of GPS observation of the Tokai region, continues, but the rate of changes might be lower than before. to supplementary reports
*There has been continuing microearthquake activity (maximum M3.6) near the border between Wakayama and Nara Prefectures since late May. to supplementary reports
*On November 24th, there was an M5.1 earthquake at a depth of approximately 70 km in the sea near Miyakojima. This event occurred in conjunction with the subduction of the Philippine Sea Plate. to supplementary reports
Supplement
*On December 2nd, there was a moderately deep M6.4 earthquake at a depth of approximately 130 km in southern interior Iwate Prefecture. The event had a maximum seismic intensity of 5 lower, and there was attendant damage. This event occurred in conjunction with the subduction of the Philippine Sea Plate, on the lower plane of a double-planed seismic zone. The focal mechanism had a tension axis in the direction of the subduction. Aftershock activity is diminishing. There have been three moderately deep earthquakes of M6 or greater in the northern Tohoku region since 1926. Results of GPS observations of the area do not show any marked crustal movement.
*On December 8th, there was an M4.5 earthquake at a depth of approximately 25 km in western Kanagawa Prefecture, with a maximum seismic intensity of 5 lower. Aftershock activity is diminishing.
*On December 8th, there was an M4.5 earthquake at a depth of approximately 5 km near the border of Fukushima and Tochigi Prefectures (Nakadori region of Fukushima Prefecture).
*On December 9th, there was an M5.8 earthquake at a depth of approximately 40 km in Amami Oshima (the sea near Amami Oshima) . The event had a maximum seismic intensity of 5 upper, and there was attendant damage. From the location of the hypocenter, it is believed that the event occurred within the continental plate. The focal mechanism had a east-west pressure axis. Subsequent to this event, there were 16 M1 or greater earthquake on December 9th, 1 such event on December 10th, and 2 such events on December 11th. A foreshock of M4.0 occured approximately 20 minites before the M5.8 event. This seismic activity followed a foreshock - main shock - aftershock pattern. Aftershock activity subsequent to the event has experienced some fluctuations, but is decreasing in a pattern similar to the historical average aftershock declination pattern for Japan and the surrounding area. The results of GPS observation of the area before and after the M5.8 event do not show any marked crustal movement.
*On December 9th, there was an M4.5 earthquake at a depth of approximately 10 km in the sea west of Niijima (the sea near Niijima-Kozushima). to supplementary reports
| December 12, 2001 |
| Earthquake Research Committee |
There were 47 M4.0 or greater earthquakes in Japan and the surrounding area (as compared to 45 in October and a monthly average incidence of 46 in the thirty-year period up to the end of 2000). Of that number, 10 events were M5.0 or greater (as compared to 6 in October).
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 November; 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 November 2000 to the end of October 2001.
| -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 November 4th, there was a moderately deep M5.4 earthquake at a depth of approximately 220 km in the sea west of Hokkaido.
- On November 18th, there was an M5.1 earthquake near the island of Etorofu.
- On November 22dn, there was an M4.9 earthquake in the sea off Tokachi (the sea off Kushiro), which was the site of M4.6 and M4.7 events on October 27th, and since that time there has been continuing microearthquake activity in the area. The M8.2 Offshore Tokachi Earthquake occurred in this area in 1952.
- On November 27th, there was an M3.9 earthquake (the highest magnitude since April) near Yoichidake, which area has experienced microearthquake activity since April of this year. Microearthquake activity, including this event, continues in the area.
There was the following seismic activity in the Tohoku 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 other events of similar scale in this area approximately every five years.
- On November 26th, there was an M5.1 earthquake in the sea off Sanriku, and there has been subsequent seismic activity including 6 events of M4 or greater.
"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 of crustal movements centered in western Shizuoka Prefecture, which were seen in the results of GPS observation of the Tokai region, continues, but the rate of changes might be lower than before.":
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 half year, there seems to have been a measurable increase in seismic activity within the crust. This trend has continued in November.
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. However, recently there has been some weakening of these changes.
(This evaluation is in agreement with the views (see reference below) expressed at the November 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, November 26 2001)
"Crustal seismic activity had been high this year in the Tokai region, but has settled somewhat 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 there have been recent signs of weakening. There have been indications of direct linkage between crustal movement and seismic activity in the Tokai region."
There was the following additional seismic activity in the Kanto-Chubu region:
- On November 12th, there was a deep M5.7 earthquake at a depth of approximately 380 km in the sea off Tokaido.
"There has been continuing 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 (maximum magnitude to date, M3.6) that has continued in the area of the border between Wakayama and Nara Prefectures since late May, continued in November (maximum M3.1 in November), within the same zone of activity. Since early November, activity has been focused in the southern 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
There was the following additional seismic activity in the Kinki-Chugoku-Shikoku region:
- Aftershocks to the earthquake (M5.1) that occurred on August 25th in southern Kyoto Prefecture are subsiding, but continue.
There was the following seismic activity in the Kyushu-Okinawa region:
- On November 24th, there was a moderately deep M5.2 eartquake near Taiwan.
- On November 25th, there was an M5.6 earthquake in the sea south of Ishigakijima.
- On November 29th, there was an M5.0 earthquake near Taiwan.
| 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. |