November 12, 2013
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On October 26, there was a magnitude (M) 7.1 earthquake offshore Fukushima prefecture, which caused damage. The tsunami generated by this event was observed along the Pacific coast of the Tohoku Region, for example with height of 36 cm at Ayukawa, Ishinomaki City (Miyagi prefecture).
* On October 21, there was a M4.6 earthquake at a depth of approximately 50 km under the eastern Hidaka region [southern Tokachi region]. The focal mechanism showed a reverse fault with a compression axis in an NW-SE direction. This event occurred on the boundary between the Pacific and the continental plates.
* On October 10, there was a M4.4 earthquake at a depth of approximately 50 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.
* On October 20, there was a M5.1 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 October 22, there was a M5.3 earthquake at a depth of approximately 25 km, offshore Fukushima prefecture. The focal mechanism showed a normal fault with a tension axis in an ENE-WSW direction. This event occurred within the crust of the continental plate.
* On October 26, there was a M7.1 earthquake offshore Fukushima prefecture. The focal mechanism showed a normal fault with a tension axis in an E-W direction. This event occurred within the Pacific plate, eastward of the Japan trench (in the outer-rise region).
The tsunami generated by this event was observed along the Pacific coast of the Tohoku Region, for example with height of 36 cm at Ayukawa, Ishinomaki City (Miyagi prefecture).
After this event there was a rather high activity as 5 earthquakes with M 5.0 over occurred on the same day.
* On October 12, there was a M4.8 earthquake at a depth of approximately 50 km offshore Ibaraki prefecture. On 20th, there was a M4.3 earthquake at almost the same place. The focal mechanisms of these two events showed reverse faults with a compression axes in a WNW-ESE direction. Both events occurred on the boundary between the Pacific and the continental plates.
* 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 October 3, there was a M5.1 earthquake under the ocean near Amami Oshima. The focal mechanism showed a reverse fault with a compression axis with a WNW-ESE direction.
* On October 31, there was a M6.5 earthquake near Taiwan. The focal mechanism showed a strike-slip fault with a compression axis in an NW-SE direction.
* On November 1, there was a M5.2 earthquake offshore Sanriku [offshore Miyagi prefecture]. The focal mechanism showed a tension axis in an ENE-WSW direction.
* On November 10, there was a M5.5 earthquake at a depth of approximately 65 km under southern Ibaraki prefecture. On 3rd, there was a M5.1 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.
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.
November 12, 2013
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during October 2013.
(reference)
The following events for the period from October 2012 to late September 2013 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities".
| – Offshore Miyagi Prefecture | M5.6 on October 25, 2012 (Depth of approximately 50 km) |
|
| – 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) |
There is no supplementary information for the Hokkaido region.
–"On October 26, there was a M7.1 earthquake offshore Fukushima prefecture. (Excerpted)":
This event is an aftershock of "the 2011 off the Pacific Coast of
Tohoku Earthquake".
– 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 October 21 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, October 21)
"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: