October 9, 2014
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On September 3, there was a Magnitude (M) 5.1 earthquake in the northern Tochigi prefecture. Maximum seismic intensity 5 Lower was observed in Tochigi prefecture.
* On September 16, there was a M5.6 earthquake under the southern Ibaraki prefecture. Maximum seismic intensity 5 Lower was observed in Ibaraki, Gunma, and Saitama prefectures and it caused damage with injured persons.
* On September 4, there was a M4.7 earthquake at a depth of approximately 30 km, under the western Hidaka region. The focal mechanism showed a reverse fault type with a compression axis in an E-W direction. This event occurred within the crust.
* On September 10, there was a M4.9 earthquake at a depth of approximately 65 km, offshore Iwate prefecture. The focal mechanism showed a reverse fault type with a compression axis in an E-W direction. This event occurred within the Pacific plate.
* On September 24 at 21:45, there was a M5.1 earthquake at a depth of approximately 50 km, offshore Fukushima prefecture. In addition, on the same day at 22:30, there was a M5.1 earthquake at almost the same place. The focal mechanisms of these events showed reverse fault types with a compression axis in a WNW-ESE and E-W direction, respectively. These events occurred at the boundary between the Pacific and the continental plates.
* On September 3, there was a M5.1 earthquake at a depth of approximately 5 km in the northern Tochigi prefecture. In the vicinity of this event, there was a M4.5 one on September 4. The focal mechanisms showed a strike-slip fault type with a compression axis in a WNW-ESE direction. These events occurred within the crust.
* On September 3, there was a M5.1 earthquake at a depth of approximately 5 km in the northern Tochigi prefecture. In the vicinity of this event, there was a M4.5 one on September 4. The focal mechanisms showed a strike-slip fault type with a compression axis in a WNW-ESE direction. These events 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 September 18, there was a M5.2 earthquake at a depth of approximately 50 km under the ocean near Miyakojima. The focal mechanism of this event showed a reverse fault type with a compression axis in an NNW-SSE direction. This event occurred at the boundary between the Philippine Sea and the continental plates.
* On October 3, there was a M5.7 earthquake at a depth of approximately 30 km, offshore Iwate prefecture. The focal mechanisms 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.
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.
October 9, 2014
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during September 2014.
(reference)
The following events for the period from September 2013 to late August 2014 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities".
| – 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) |
|
| – 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) |
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 1cm, and the vertical deformation was 1cm 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.
– "On September 3, there was a M5.1 earthquake at a depth of
approximately 5 km in the northern Tochigi prefecture. (Excerpted)":
Afterwards, in the vicinity of this event, aftershock activity was rather high. There were 30 earthquakes with seismic intensity 1 or over. But the activity is decreasing now.
In the border area between Gunma and Tochigi prefectures, where the recent activity was observed, the seismic activity became high after the 2011 off the Pacific Coast of Tohoku Earthquake. On February 25, 2013, there was a M6.3 earthquake (maximum seismic activity 5 Upper).
– "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 September 29 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, September 29, 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: