December 10, 2013
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On November 10, there was a magnitude (M) 5.5 earthquake in the southern Ibaraki prefecture. The maximum seismic intensity 5 Lower generated by this event was observed in Ibaraki prefecture.
* On November 25, there was a M5.2 earthquake under the Soya Strait [offshore west of Sakhalin]. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred in the crust.
* On November 28, there was a M5.0 earthquake at a depth of approximately 90 km offshore Tomakomai. The focal mechanism showed a normal fault with a tension axis in an N-S direction. This event occurred in the Pacific plate.
* On November 1, there was a M5.2 earthquake offshore Sanriku [offshore Miyagi prefecture]. On 3rd, there was a M5.3 earthquake at almost the same place. The focal mechanism of the former event showed a tension axis in an ENE-WSW direction, and that of the latter event showed a tension axis in an E-W direction.
* On November 15, there was a M5.3 earthquake at a depth of approximately 65 km, offshore east of Aomori 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.
* On November 26, there was a M4.9 earthquake at a depth of approximately 50 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 November 3, there was a M5.1 earthquake at a depth of approximately 65 km in southern Ibaraki prefecture. On 10th there was 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 continental plates.
* On November 16, there was a M5.3 earthquake at a depth of approximately 70 km under northwestern Chiba prefecture. The focal mechanism showed a reverse fault with a compression axes in an E-W direction. On 29th there was a M4.8 earthquake at a depth of approximately 70 km in the vicinity of the recent event. The focal mechanism of the latter event showed a compression axis in a WNW-ESE 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.
There was no remarkable activity.
* On November 16, there was a M5.0 earthquake under the ocean near Amami Oshima. The focal mechanism showed a reverse fault with a compression axis in an E-W direction.
* On November 25, there was a M6.0 earthquake in Kuril Islands (offshore southeast Urup Island). The focal mechanism showed a reverse fault with a compression axis in an NW-SE 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 in the crust of the continental plate.
* On December 3, there was a M5.5 earthquake at a depth of approximately 45 km offshore Ibaraki prefecture. The focal mechanism showed a tension axis in a WNW-ESE direction.
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.
December 10, 2013
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during November 2013.
(reference)
The following events for the period from November 2012 to late October 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 |
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 November 19 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, November 19)
"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: