January 11, 2013
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On December 7, there was a M7.3 earthquake offshore Sanriku. This event had a maximum seismic intensity 5 Lower. This event caused tsunamis with a height of 98 cm at Ayukawa, Ishinomaki City (Miyagi prefecture) and they were observed along the Pacific coast of the Tohoku region. In addition, this shock caused damage with causalities.
There was no remarkable activity.
* On December 4, there was a M4.1 earthquake at a depth of approximately 10 km in the southern inland, Akita prefecture. The focal mechanism showed a strike-slip fault with a tension axis in an NW-SE direction. This event occurred within the crust.
* On December 7 at 17:18, there was a M7.3 earthquake offshore Sanriku.
The focal mechanism showed a normal fault with a tension axis in a WNW-ESE
direction. This event occurred within the Pacific plate near the Japan
Trench. This event is an aftershock of "the 2011 off the Pacific Coast
of Tohoku Earthquake". In addition, just before this event, in the
vicinity of this event, there was an estimated M7 class earthquake with
a different mechanism.
These events caused tsunamis with a height of 98 cm at Ayukawa, Ishinomaki City (Miyagi prefecture) and they were observed along the Pacific coast of the Tohoku region.
In the vicinity of these events, there was a M6.6 earthquake at 17:31 on the same day. There was a sequence of earthquakes such as 8 earthquakes of M5.0 or over by December 10.
* On December 15, there was a M5.3 earthquake at a depth of approximately 60 km, offshore Fukushima prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.
* On December 29, there was a M5.5 earthquake at a depth of approximately 40 km, offshore Miyagi prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the continental plates.
* On December 7, there was a M4.6 earthquake at a depth of approximately 65 km under northwestern Chiba prefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred on the boundary between the Pacific and the Philippine Sea plates.
* On December 15, there was a M5.0 earthquake offshore Ibaraki prefecture. The focal mechanism showed a normal fault with a tension axis in an E-W direction. This event occurred within the crust of the continental plate.
* In the GNSS data for the Tokai region, there have been no changes of activity which are likely to be associated with the Tokai earthquake.
* On December 22, there was a M4.5 earthquake at a depth of approximately 45 km under Iyonada. The focal mechanism showed a normal fault with a tension axis in an E-W direction. This event occurred within the Philippine Sea plate.
There was no remarkable activity.
* On January 3, there was a M4.8 earthquake at a depth of approximately 25 km in the central northern Rumoi region. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred within the crust.
* On January 7, there was a M5.4 earthquake at a depth of approximately 70 km under the ocean near Yonagunijima. This event occurred within the Philippine Sea plate.
* On January 8, there was a M5.4 earthquake at a depth of approximately 35 km, offshore Iwate prefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred on the boundary between the Pacific and the continental plates.
Note: GNSS (Global Navigation Satellite System) is a general name of satellite positioning system such as GPS.
January 11, 2013
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during December 2012.
(reference)
The following events for the period from December 2011 to late November 2012 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities"
| |
– Offshore Fukushima Prefecture | M5.1 on January 23, 2012 (Depth of approximately 50 km) |
| – Eastern Yamanashi Prefecture-Fujigoko | M5.4 on January 28, 2012 (Depth of approximately 20 km) | |
| |
– Near Sado | M5.7 on February 8, 2012 (Depth of approximately 15 km) |
| – Northern Ibaraki Prefecture | M5.2 on February 19, 2012 (Depth of approximately 5 km) |
|
| – Offshore Ibaraki Prefecture | M5.3 on March 1, 2012 (Depth of approximately 55 km) |
|
| – Northern Ibaraki Prefecture | M5.4 on March 10, 2012 (Depth of approximately 5 km) |
|
| – Offshore Sanriku | M6.9 on March 14, 2012 | |
| – Offshore East of Chiba Prefecture | M6.1 on March 14, 2012 (Depth of approximately 15 km) |
|
| – Offshore Iwate Prefecture | M6.6 on March 27, 2012 (Depth of approximately 20 km) |
|
| – Offshore Fukushima Prefecture | M5.9 on April 1, 2012 (Depth of approximately 55 km) |
|
| – Northeastern Chiba Prefecture | M5.8 on April 29, 2012 (Depth of approximately 50 km) |
|
| – Offshore East of Aomori Prefecture | M6.1 on May 24, 2012 (Depth of approximately 60 km) |
|
| – Northern Nagano Prefecture | M5.2 on July 10, 2012 (Depth of approximately 10 km) |
|
| – Southern Tokachi Region | M6.1 on August 25, 2012 (Depth of approximately 50 km) |
|
| – Offshore Miyagi Prefecture | M5.6 on August 30, 2012 (Depth of approximately 60 km) |
|
| – Offshore Miyagi Prefecture | M5.6 on October 25, 2012 (Depth of approximately 50 km) |
There is no supplementary information for the Hokkaido region.
There is no supplementary information for the Tohoku region.
– In the aftershock area of the 2011 off the Pacific Coast of Tohoku Earthquake, brisk seismicity has been seen. There is fear that large aftershocks will occur from now on, and there is a possibility that it will be hit by strong shaking and high tsunami. Crustal movements to the east which are thought to be the postseismic deformation have still been observed in a wide area from the Tohoku through the Kanto-Chubu regions, but they have gradually been decaying.
"In the GNSS data for the Tokai region, there have been no changes
of activity which are likely to be associated with the Tokai earthquake":
(This evaluation is in agreement with the views presented at the regular meeting on December 17 of the Assessment Committee for Areas under Intensified Measures against Earthquake Disaster (reference below).)
(Reference)
Recent seismic and crustal activity in the Tokai region and its vicinity (Seismological and Volcanological Department, Japan Meteorological Agency, December 17, 2012)
"No changes of activity which are likely to be associated with the Tokai earthquake have been observed until now. (Excerpted)"
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
There is no supplementary information for the Kyushu-Okinawa region.
Reference 1
Earthquakes that are described in the "Evaluation of Seismic Activity" (Monthly Report of Seismic Activity in Japan) have the following features.
Reference 2
Information that is described in the "Supplementary Information to the Evaluation" includes: