January 15, 2014
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On December 31, there was a magnitude (M) 5.4 earthquake in the northern Ibaraki prefecture. The maximum seismic intensity 5 Lower generated by this event was observed in Ibaraki prefecture.
* On December 9, there was a M6.4 earthquake offshore southeast of Etorofu Island. The focal mechanism showed a compression axis in an NNW-SSE direction.
* On December 16, there was a M4.6 earthquake at a depth of approximately 80 km under the southern middle-Kushiro region. The focal mechanism showed a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.
* On December 27, there was a M5.0 earthquake at a depth of approximately 40 km, offshore Iwate prefecture. This event occurred near the boundary between the Pacific and the continental plates. The focal mechanism showed a compression axis in a WNW-ESE direction.
* On December 3, there was a M4.5 earthquake at a depth of approximately 10 km, offshore east of Chiba prefecture. The focal mechanism showed a normal fault with a tension axis in a WNW-ESE direction. This event occurred within the crust of the continental plate
* On December 3, there was a M5.5 earthquake offshore Ibaraki prefecture. The focal mechanism had a tension axis in a WNW-ESE direction.
* On December 14, there was a M5.5 earthquake at a depth of approximately 50 km, offshore east of Chiba prefecture. Furthermore, on 21st, there was also a M5.5 earthquake at almost the same place. The focal mechanisms of these two events showed reverse faults with compression axes in an E-W direction. Both events occurred on the boundary between the Pacific and the Philippine Sea plates.
* On December 21, there was a M5.2 earthquake at a depth of approximately 60 km under southern Ibaraki 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 31, there was a M5.4 earthquake at a depth of approximately 5 km under northern Ibaraki prefecture. The focal mechanism showed a strike-slip fault with a tension axis in an NE-SW 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.
There was no remarkable activity.
* On December 18, there was a M6.6 earthquake at the very shallow depth in the Mariana Islands. The focal mechanism showed a normal fault with a tension axis in an NE-SW direction.
* From January 2, there has been slightly brisk seismicity. The largest
so far is a M5.0 earthquake which occurred on 2nd 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
at the boundary between the Philippine Sea and the continental plates.
In this region, slow slips were observed in May 1996, October 2002, August 2007 and October 2011.
* 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 in the Philippine Sea plate
* On January 9, there was a M4.6 earthquake at a depth of approximately 5 km in northern Ibaraki prefecture. The focal mechanism showed a normal fault with a tension axis in an E-W direction. This event occurred in the crust.
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 15, 2014
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during December 2013.
(reference)
The following events for the period from December 2012 to late November 2013 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities".
| – Offshore Sanriku | M7.3 on December 7, 2012 | |
| – Northern Ibaraki Prefecture | M4.8 on January 28, 2013 (Depth of approximately 75km) |
|
| – Northern Ibaraki Prefecture | M4.7 on January 31, 2013 (Depth of approximately 10km) |
|
| – 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) |
|
| – 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) |
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.
–"On December 31, there was a M5.4 earthquake at a depth of approximately 5 km in northern Ibaraki prefecture. (Excerpted)":
After this event, in northern Ibaraki prefecture, there were 20 earthquakes with seismic intensity 1 or over until January 13, 2014, and on January 9, there was a M4.6 earthquake.
Within the crust from Hamadori, Fukushima prefecture through northern Ibaraki prefecture, the seismicity increased after "the 2011 off the Pacific Coast of Tohoku Earthquake". Although it has gradually been declining on the whole with some up and down, it still keeps the higher level than that of prior to the occurrence of the 2011 off the Pacific Coast of Tohoku Earthquake.
–"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 24 of the Assessment Committee for Areas under Intensified
Measures against Earthquake Disaster (reference below).)
(Reference)
This evaluation is in agreement with the views presented at the regular meeting on December 24 of the Assessment Committee for Areas under Intensified Measures against Earthquake Disaster (reference below).
"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: