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November 8, 2006
Headquarters for Earthquake Research Promotion
Earthquake Research Committee
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Seismic Activity for October 2006
2 Nationwide seismic activity by region
(1) Hokkaido Region
(2) Tohoku Region
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On October 2, there was a M5.2 earthquake off-shore of Sanriku [off-shore
of Miyagi prefecture]. |
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On October 11, there was a M6.0 earthquake off-shore of Fukushima prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event is related to the subduction of the Pacific plate. to supplementary reports
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(3) Kanto-Chubu Region
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On October 14, there was a M5.1 earthquake at a depth of approximately 65km off-shore southeast of Chiba prefecture. |
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On October 24, there was a M6.8 earthquake at a shallow location under
the ocean near Torishima. Small tsunamis were observed on the Izu Islands.
The focal mechanism showed a normal fault with a tension axis in an ENE-WSW
direction. |
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There have been no anomalous changes observed in the GPS data for the Tokai region. to supplementary reports |
(4) Kinki-Chugoku-Shikoku Region
(5) Kyushu-Okinawa Region
Supplement
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On November 1, there was a M4.8 earthquake at a depth of approximately 50km under southern Tokachi subprefecture. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. This event occurred at the boundary between the Pacific and the continental plates. Also, there was a M4.3 earthquake at nearly the same location on the same day. to supplementary reports |
[ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.
Supplementary Information to the Evaluation of Seismic Activity for October
2006 by the Earthquake Research Committee
November 8, 2006
1 Major Seismic Activity
The following are the numbers of earthquakes by magnitude that occurred
in Japan and the surrounding area during October 2006.
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M4.0 or greater: 101 (73 events occurred in September) |
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M5.0 or greater: 26 (11 events occurred in September) |
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M6.0 or greater: 7 (There have been a total of 16 events for 2006 by the
end of October.) |
(reference)
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M4.0 or greater: 73 / month |
(Median number of earthquakes over the past 10 years from 1996 through
2005) |
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M5.0 or greater: 9 / month |
(Median number of earthquakes over the past 30 years from 1976 through 2005) |
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M6.0 or greater: 1.4 / month, approximately 17 / year |
(Average number of earthquakes over the past 80 years from 1926 through
2005) |
The following regions have been noted as having significant seismic activity during the period from October 2005 to the end of September 2006.
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- Off-shore of Ibaraki prefecture
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M6.3 on October 19, 2005(depth approximately 50km) |
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- Off-shore of Sanriku |
M7.2 on November 15, 2005
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- Hyuganada |
M5.5 on March 27, 2006(depth approximately 35km) |
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- Off-shore east of the Izu Peninsula |
seismic activity with M5.8 on April 21 and M4.5 on April 30, 2006
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- Central Oita prefecture |
M6.2 on June 12, 2006(depth approximately 150km)
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to the text
2 Nationwide Seismic Activity by Region
(1) Hokkaido Region
There is no supplementary information for the Hokkaido region.
to the text
(2) Tohoku Region
There is no supplementary information for the Tohoku region.
to the text
(3) Kanto-Chubu Region
"There have been no anomalous changes observed in the GPS data for the
Tokai region.":
(This evaluation is in agreement with the views presented at the procedural meeting on October 30 of the Assessment Committee for Areas under Intensified Measures against Earthquake Disaster. (see reference below))
(reference) "Recent seismic and crustal activity in the Tokai region
and its vicinity" (Japan Meteorological Agency, Department of Seismology
and Volcanology, October 30, 2006)
"So far, there have been no changes of activity which are likely to be associated with the so-called Tokai earthquake.
There was no remarkable seismic activity in general. The seismicity remains at a level lower than normal directly under the area from eastern Hamana Lake through central Shizuoka prefecture. In other regions, seismic activity is generally at a normal level.
There were no notable changes observed in crustal movements in the Tokai region and its neighboring areas."
to the text
(4) Kinki-Chugoku-Shikoku Region
There is no supplementary information for the Kinki - Chugoku - Shikoku
region.
to the text
(5) Kyushu-Okinawa Region
- Seismic activity that had started off-shore southeast of Miyakojima [under the ocean near Miyakojima] on September 18, was at a low level in early October. It, however, increased temporarily in late October.
- On October 26, there was a M4.5 earthquake at a depth of approximately 50km off-shore northeast of Miyakojima [under the ocean near Miyakojima].
to the text
(6) Other Regions
- On October 1, there were M6.8 and M6.6 earthquakes off-shore east of the Chishima Islands. Also on October 13, there was a M6.3 earthquake in the same area.
- On October 9, there was a M6.1 earthquake off-shore south of Taiwan.
Supplement
- On November 3, there was a M3.7 earthquake at a depth of approximately
10km under northern Osaka prefecture (maximum seismic intensity 4). The
aftershock activity has mostly subsided.
- Since November 5, there has been a light seismic activity with the largest event,
a M4.8 earthquake off-shore northwest of the Okinawa Main Island.
to the text
Reference 1
Earthquakes that are described in the "Evaluation of Seismic Activity"(Monthly Report of Seismic Activity in Japan) are events of M6.0 and greater, or events of M4.0 and greater (M5.0 or greater off-shore) that have maximum intensity of 3 or greater.
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Reference 2
Information that is described in the "Supplementary Information to the Evaluation" includes:
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Reference information related to seismic activity described in the "Evaluation of Seismic Activity" |
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Recent earthquake activity over the past year related to the events described in "Major Seismic Activity" in the "Evaluation of Seismic Activity" |
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Seismic activity that has been evaluated, but not included in the "Evaluation of Seismic Activity" because it is within normal bounds and not prominent. |