| 13 February 2002 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity in January 2002
There was no marked activity. to supplementary reports
*On January 19, there was an M5.6 earthquake in the sea east of Hokkaido, which occurred in conjunction with the subduction of the Pacific plate. to supplementary reports
*On January 27, there was an M5.3 earthquake at a depth of approximately 50 km in the sea off Iwate Prefecture. The focal mechanism was a reverse fault type with a roughly east-west pressure axis, and the event occurred in conjunction with the subduction of the Pacific plate. to supplementary reports
*Low seismic activity and crustal movements continues in the area from Miyakejima to Niijima-Kodushima.
*On January 15, there was an M4.3 earthquake at a depth of approximately 40 km in southern Ibaraki Prefecture.
*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 or somewhat higher than normal activity.
Although the slight changes of crustal movements centered in western Shizuoka Prefecture fluctuated and showed some indications of lessening, since that time the activity appears to have continued as before, which were seen in the results of GPS observation of the Tokai region. to supplementary reports
*On January 4, there was an M4.0 earthquake at a depth of approximately 10 km near the border of Wakayama and Nara Prefectures. There has been continued microearthquake activity in this area since late in May 2001, with 1 to 2 earthquakes of M3.0 or greater per month up to December. The activity increased in January, and on January 4, there were 15 events of M3.0 or greater, but the level of activity has gradually declined. The activity may continue with fluctuation for the time being.
*On January 24, there was an M4.5 earthquake at a depth of approximately 10 km in eastern Shimane Prefecture. to supplementary reports
*Aftershocks of the M5.8 earthquake that occurred on Amami Oshima on December 9 have decreased.
*Aftershocks of the M7.3 earthquake that occurred in the sea near Yonagunijima on December 18 have decreased. to supplementary reports
*On February 2, there was an M4.3 earthquake at a depth of approximately 10 km in the Chuetsu region of Niigata Prefecture.
*On February 5, there was an M4.4 earthquake at a depth of approximately 70 km in south western Ibaraki Prefecture.
*On February 11, there was an M5.0 earthquake at a depth of approximately 40 km in the sea off Ibaraki Prefecture (in the sea approximately 20 km east of Inubozaki).
*On February 12, there was an M5.0 earthquake at a depth of approximately 50 km in the sea off Ibaraki Prefecture (in the sea approximately 30 km east of the city of Hitachi), which registered a maximal seismic intensity of 5 lower. There was attendant damage. The focal mechanism was a reverse fault type, with a WNW-ESE pressure axis, similar to the focal mechanisms for past events in this area. It is believed that this earthquake occurred near the junction of the subducting Pacific and the continental plate. Aftershock activity has been low.
A review of past seismic activity shows that this neighborhood is a seismically active zone all along and there have been two approximately two events of M5.0 or greater per year within the zone of seismic activity in this area. Recently, there was an M6.4 earthquake on July 21 2000.
| February 13, 2002 |
| Earthquake Research Committee |
There were 63 M4.0 or greater earthquakes in Japan and the surrounding area (as compared to 105 in December and a monthly average incidence of 46 in the thirty-year period up to the end of 2000). Of that number, 6 events were M5.0 or greater (as compared to 8 in December).
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). No such events were recorded in January 2002; there were two in December 2001.
The following are evaluations of major seismic activity in the period from January 2001 to the end of December 2001.
| -Chuetsu region of Niigata Prefecture | January 2 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) | ||
| January 4 M5.1 (at a depth of about 10 km) | ||
| -Northern Hyogo Prefecture | January 12 2001 M5.4 (at a depth of about 10 km) | |
| -Near Niijima-Kodushima | February 13 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 3 2001 M5.1 (at a depth of about 35 km) | ||
| -Southern interior Iwate Prefecture | ||
| December 2 2001M6.4 (at a depth of 120 km) | ||
| -Western Kanagawa Prefecture | December 8 2001M4.5 (at a depth of 25 km) | |
| -Amami Oshima | December 9 2001M5.8 (at a depth of 40 km) | |
| -Sea near Yonagunijima | December 18 2001M7.3 (at a depth of 10 km) | |
"On January 19, there was an M5.6 earthquake in the sea east of Hokkaido":
This event was an aftershock to the 1994 Eastern Offshore Hokkaido Earthquake (M8.2)
There was the following seismic activity in the Tohoku Region:
-On January 29, there was an M4.6 and an M4.8 earthquake at a depth of approximately 40 km in the sea off Fukushima Prefecture.
"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 or somewhat higher than normal activity.":
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, representing a return to the activity level seen prior to October 2000.
In addition, seismic activity within the subducting Philippine Sea plate (slab) is slightly lower than normal.
"Although the slight changes of crustal movements centered in western Shizuoka Prefecture fluctuated and showed some indications of lessening, since that time the activity appears to have continued as before, which were seen in the results of GPS observation of the Tokai region.":
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 trend has continued in January 2002. However, there are no signs that the changes are accelerating.
(This evaluation is in agreement with the views (see reference below) expressed at the January 28 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, January 28 2001)
"Seismic activity within the slab had been high in the first half of this year in the Tokai region, but recent activity has been normal or slightly below average.
Seismic activity in Suruga Bay and the western coast is now occurring at a normal or slightly higher than normal level.
Additionally, 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 since last year. While there have been recent signs of weakening, at present, the activity appears to be continuing as before. There have been no indications of direct linkage between crustal movement and seismic activity in the Tokai region."
"On January 24, there was an M4.5 earthquake at a depth of approximately 10 km in eastern Shimane Prefecture.":
This event was an aftershock to the 2000 Western Tottori Earthquake (M7.3).
There was the following additional seismic activity in the Kyushu-Okinawa region
-Seismic activity including a maximal M5.2 earthquake in the East China Sea in the period from January 12 to 13
-M5.6 earthquake in the sea near Miyakojima on January 16
| 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. |