January 14, 2015
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
* On December 19, there was a magnitude (M) 5.3 earthquake at a depth of approximately 45 km, offshore Kushiro. The focal mechanisms of this event showed a reverse fault type with a compression axis in an NW-SE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On December 18, there was a M4.6 earthquake at a depth of approximately 45 km, offshore Miyagi prefecture.
* On December 20, there was a M6.0 earthquake at a depth of approximately 45 km, offshore Fukushima prefecture. The focal mechanism of this event showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On December 25, there was a M5.6 earthquake at a depth of approximately 35 km, offshore Fukushima prefecture. The focal mechanism of this event showed a normal fault type with a tension axis in a WNW-ESE direction. This event occurred within the continental plate.
* On December 11, there was a M4.3 earthquake at a depth of approximately 25 km, in eastern Yamanashi prefecture - Fujigoko. The focal mechanism showed a reverse fault type with a compression axis in an NW-SE direction.
* 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 26, there was a M4.2 earthquake at a depth of approximately 15 km in the northern Shiga prefecture. The focal mechanism showed a strike-slip fault type with a compression axis in a WNW-ESE direction. This event occurred within the crust.
* On December 11, there was a M6.1 earthquake at a depth of approximately 250 km, offshore northwest of Ishigakijima. The focal mechanism had a compression axis in the subducting direction of the Philippine Sea plate. This event occurred within the Philippine Sea plate.
* On January 1, there was a M4.5 earthquake at a depth of approximately 30 km, offshore Tomakomai. The focal mechanism had a compression axis in an NE-SW direction. This event occurred within the crust of the continental plate.
* On January 9, there was a M5.5 earthquake at a depth of approximately 125 km under northern Nemuro region [Central Nemuro Region]. The focal mechanism had a tension axis in an NNE-SSW direction. This event occurred within the Pacific plate.
Note: [ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.
GNSS (Global Navigation Satellite System) is a general name of satellite
positioning system such as GPS.
January 14, 2015
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during December 2014.
(reference)
The following events for the period from November 2013 to late October 2014 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities".
| – Northern Ibaraki Prefecture | M5.4 on December 31, 2013 (Depth of approximately 5 km) |
|
| – Iyonada | M6.2 on March 14, 2014 (Depth of approximately 80 km) |
|
| – Along the Northern Coast of Chile | Mw8.1 on April 2, 2014 | |
| – Ocean Area Near the Izu-Oshima | M6.0 on May 5, 2014 (Depth of approximately 160 km) |
|
| – Rat Islands, Aleutian Islands | Mw7.9 on June 24, 2014 | |
| – Offshore IwatePrefecture | M5.9 on July 5, 2014 (Depth of approximately 50 km) |
|
| – Middle Eastern Iburi Region | M5.6 on July 8, 2014 (Depth of approximately 5 km) |
|
| – Offshore Fukushima Prefecture | M7.0 on July 12, 2014 | |
| – Offshore East of Aomori Prefecture | M6.1 on August 10, 2014 (Depth of approximately 50 km) |
|
| – Northern Tochigi Prefecture | M 5.1 on September 3, 2014 (Depth of approximately 5 km) |
|
| – Southern Ibaraki Prefecture | M 5.6 on September 16, 2014 (Depth of approximately 45 km) |
|
| – Northern Nagano Prefecture | M 6.7 on November 22, 2014 (Depth of approximately 5 km) |
There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
– Within the aftershock area, the number of earthquakes of M4.0 or
over, during one year from March 2012 (from March 2012 to February 2013)
became under one fifth smaller, and during one year from March 2013 (from
March 2013 to February 2014) became under one tenth smaller, than the number
during about one year just after the Tohoku Earthquake.
In case of the earthquake (Mw 9.1) offshore west of the northern Sumatra Island in 2004, there were Mw8.6 event after four months, Mw8.5 event after about two and a half years, Mw7.5 event after about five and a half years, and Mw8.6 event after about seven and a half years in the region of outer rise. Thus, there have been large earthquakes for long period within the source area and its surroundings.
According to the GNSS data, crustal deformation which is thought to be postseismic deformation has still been observed in a wide area from the Tohoku through the Kanto-Chubu regions. During about one month just after the Tohoku Earthquake, at the maximum value, the horizontal movement was 30 cm, and the vertical subsidence and upheaval were 6 cm and 5 cm, respectively. The deformation is decaying: the horizontal deformation was up to around 1 cm, and the vertical deformation was 1 cm or so during the recent one month.
Although the aftershock activity is gradually decaying as a whole, the activity is still in higher state than the one before the Tohoku Earthquake. In addition, there are overseas examples for gigantic earthquakes. Synthetically judging from these facts, within the aftershock area and its surroundings, there is a fear that large earthquakes will occur from now on, and there is a possibility that it will be hit by strong shaking and high tsunami. It is necessary to do care continuously for it.
– For the aftershock activity of the earthquake (M6.7) in the northern Nagano prefecture on November 22, there was a M4.4 aftershock on December 22 at almost the same place of the main shock. It is decaying as a whole.
– "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 22 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 22, 2014)
"No changes of activity which are likely to be associated with the Tokai earthquake have been observed until now.(Excerpted)"
– Non-stationary crustal deformation around the Bungo Channel that was observed in the summer of 2014 is now decaying. This deformation is considered to be caused by the gradual slip (slow-slip) at the boundary between the Philippine Sea and the continental plates.
There is no supplementary information for 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: