February 12, 2014
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
There was no remarkable activity.
* On January 16, there was a magnitude (M) 5.1 earthquake at a depth of approximately 30 km, offshore Iwate 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.
* From about January 2, there has been slightly brisk seismicity offshore
east of Chiba prefecture. On January 2, a M5.0 earthquake occurred at a
depth of approximately 25 km. The focal mechanism showed a reverse fault
with a compression axis in an NW-SE direction. This event occurred on the
boundary between the Philippine Sea and the continental plates. According
to the GNSS and tiltmeters, non-stationary crustal deformation has been
observed in Boso Peninsula for the same period with the seismic activity
from January 2.
This deformation seems to be due to a slow slip on the boundary between the Philippine Sea and the continental plates.
The seismicity decreased after that and non-stationary crustal deformation almost subsided. The magnitude of the recent slow-slip event is estimated to be Mw (moment magnitude) 6.5 or so.
In this region, recently, slow slips occurred in May 1996, October 2002, August 2007 and October 2011, and associated slightly brisk seismicity and non-stationary crustal deformation were observed.
* On January 9, there was a M4.6 earthquake at a depth of approximately 5 km in the northern Ibaraki prefecture. The focal mechanism showed a normal fault with a tension axis in an E-W direction. This event occurred within the crust.
* 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.
There was no remarkable activity.
* On January 9, there was a M5.5 earthquake at a depth of approximately 70 km near Iriomotejima [under the ocean near Ishigakijima]. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred within the Philippine Sea plate.
* On February 2, there was a M4.5 earthquake under the ocean near Amami Oshima. The focal mechanism showed a reverse fault with a compression axis in an NNW-SSE direction. This event occurred on the boundary between the Philippine Sea and the continental plates.
* On February 6, there was a M5.3 earthquake at a depth of approximately 40 km offshore Miyagi prefecture. The focal mechanism showed a reverse fault with a compression axis in an NW-SE direction. This event occurred within the Pacific plate.
* On February 6, there was a M5.0 earthquake at a depth of approximately 50 km under the ocean near Miyakojima. The focal mechanism had a tension axis in an NNE-SSW direction.
* On February 8, at 02:18 (JST), there was a M5.0 earthquake at a depth of approximately 50 km offshore Fukushima prefecture. In addition, on the same day at 11:34, there was a M4.8 earthquake at a depth of approximately 50 km.
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.
February 12, 2014
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during January 2014.
(reference)
The following events for the period from January 2013 to late December 2013 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities".
| – Northern Ibaraki Prefecture | M4.8 on January 28, 2013 (Depth of approximately 75 km) |
|
| – Northern Ibaraki Prefecture | M4.7 on January 31, 2013 (Depth of approximately 10 km) |
|
| – Southern Tokachi Region | M6.5 on February 2, 2013 (Depth of approximately 100 km) |
|
| – Northern Tochigi Prefecture | M6.3 on February 25, 2013 (Depth of approximately 5 km) |
|
| – Near Awajishima | M6.3 on April 13, 2013 (Depth of approximately 15 km) |
|
| – Under the Ocean Near Miyakejima | M6.2 on April 17, 2013 (Depth of approximately 10 km) |
|
| – Offshore Miyagi Prefecture | M5.9 on April 17, 2013 (Depth of approximately 60 km) |
|
| – Offshore Fukushima Prefecture | M6.0 on May 18, 2013 (Depth of approximately 45 km) |
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| – Offshore Miyagi Prefecture | M6.0 on August 4, 2013 (Depth of approximately 60 km) |
|
| – Hamadori, Fukushima Prefecture | M5.9 on September 20, 2013 (Depth of approximately 15 km) |
|
| – Offshore Fukushima Prefecture | M7.1 on October 26, 2013 | |
| – Southern Ibaraki Prefecture | M5.5 on November 10, 2013 (Depth of approximately 65 km) |
|
| – Northern Ibaraki Prefecture | M5.4 on December 31, 2013 (Depth of approximately 5 km) |
There is no supplementary information for the Hokkaido region.
There is no supplementary information for the Tohoku region.
– During about one year (March 2012 - February, 2013), the number
of earthquakes of M4.0 or over in the aftershock area of the 2011 off the
Pacific Coast of Tohoku Earthquake became under one fifth smaller than
the one during about one year (March 11, 2011 - February, 2012) just after
the Earthquake, and after that the aftershock activity has gradually been
decaying. However, in comparison with the mean activity before the 2011
off the Pacific Coast of Tohoku Earthquake, the number of earthquakes of
M4.0 or over in the aftershock area was more than four times, and the aftershock
activity still remains in brisk state.
According to the GNSS data during about one month just after the 2011 off the Pacific Coast of 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 movement was gradually decaying. Although the horizontal movement was up to around 1cm, and the vertical movement was up to around 1cm during the recent one month, crustal movements which are thought to be the postseismic deformation have still been observed in a wide area from the Tohoku through the Kanto-Chubu regions.
In case of the earthquake (moment magnitude (Mw) 9.1) offshore west of the northern Sumatra Island in December 2004, within the source area and its surroundings, there have been large earthquakes for long period. As to the 2011 off the Pacific Coast of Tohoku Earthquake, within the aftershock area and its surroundings, there is 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.
–"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 January 20 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, January 20, 2014)
"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 Kinki-Chugoku-Shikoku region.
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: