Seismic Activity for December 2007

1 Major Seismic Activity

* There was no remarkable activity. to supplementary reports

• Seismic Activity for All of Japan during December 2007 (Magnitude 4.0 and greater)

2 Nationwide Seismic Activity by Region

(1) Hokkaido Region

* There was no remarkable activity. to supplementary reports

• Hokkaido Region

(2) Tohoku Region

* On December 25, there was a M5.6 earthquake at a depth of approximately 40km off-shore of Miyagi prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates. to supplementary reports

• Tohoku Region
• Earthquake Off-shore of Miyagi Prefecture on December 25

(3) Kanto-Chubu Region

* On December 24, there was a M3.6 earthquake at a depth of approximately 10km in northern Tochigi prefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred within the crust.

* On December 21, there was a M4.5 earthquake at a depth of approximately 5km in the Reihoku Region, Fukui prefecture. The focal mechanism showed a strike-slip fault with a compression axis in a NW-SE direction. This event occurred within the crust.

* On December 7, there was a M6.0 earthquake under the ocean area near Torishima. The focal mechanism had a compression axis in a NW-SE direction. It is thought that this event occurred within the Pacific plate.

* There have been no anomalous changes observed in the GPS data for the Tokai region. to supplementary reports

• Kanto-Chubu Region
• Earthquake in Northern Tochigi Prefecture on December 24
• Earthquake in the Reihoku Region, Fukui Prefecture on December 21
• Earthquake under the Ocean Area near Torishima on December 7
• Continuous GPS Monitoring in the Area from Kakegawa to Omaezaki
• Recent Crustal Movements in the Tokai Region (Horizontal Movements) [Ogata is the fixed reference point] (December 2006–December 2007)
• Crustal Movements in the Tokai Region, Time series, Ogata is the fixed reference point

(4) Kinki-Chugoku-Shikoku Region

* There was no remarkable activity. to supplementary reports

• Kinki-Chugoku-Shikoku Region

(5) Kyushu-Okinawa Region

* There was no remarkable activity. to supplementary reports

• Kyushu Region
• Okinawa Region

Supplementary Information to the Evaluation of Seismic Activity for December 2007 by the Earthquake Research Committee

January 11, 2008

1 Major Seismic Activity

The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during December 2007.

• M4.0 or greater: 72 (69 events occurred in November)
• M5.0 or greater: 14 (7 events occurred in November)
• M6.0 or greater: 1 (There has been a total of 23 events for 2007 by the end of November.)

(reference)

• M4.0 or greater: 73 / month (Median number of earthquakes over the past 10 years from 1996 through 2005)
• M5.0 or greater: 9 / month (Median number of earthquakes over the past 30 years from 1976 through 2005)
• 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 major seismic activity during the period from December 2006 to the end of November 2007.

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

"On December 25, there was a M5.6 earthquake at a depth of approximately 40km off-shore of Miyagi prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates.":

This event occurred near the northern edge of the aftershock area of the off-shore Miyagi prefecture earthquake on August 16, 2005 (M7.2).

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(3) Kanto-Chubu Region

- Light seismic activity that started in western Shizuoka prefecture in mid-November with the largest earthquake a M3.6 event (on December 2), has been gradually subsiding.

• Seismic Activity in Western Shizuoka Prefecture

"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 November 26 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, December 25, 2007)

"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. Under central Shizuoka, the seismicity remains at a level lower than normal within the plate, and higher within the crust. 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."

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(4) Kinki-Chugoku-Shikoku Region

There is no supplementary information for the Kinki-Chugoku-Shikoku region.

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(5) Kyushu-Okinawa Region

There is no supplementary information for the Kyushu-Okinawa region.

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