September 9, 2014
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On August 10, there was a Magnitude (M) 6.1 earthquake offshore east of Aomori prefecture. Maximum seismic intensity 5 Lower was observed in Aomori prefecture.
* On August 19, there was a M4.9 earthquake at a depth of approximately 45 km, offshore southeast of Nemuro Peninsula. The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the continental plates.
* On August 10, there was a M6.1 earthquake at a depth of approximately 50 km, offshore east of Aomori prefecture. The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the continental plates.
* On August 29, there was a M5.0 earthquake offshore Fukushima prefecture. The focal mechanism showed a normal fault type with a tension axis in a WNW-ESE direction. This event occurred within the continental plate.
* On August 24, there was a M4.3 earthquake at a depth of approximately 75 km under the southern Saitama prefecture [the southern Ibaraki prefecture]. The focal mechanism showed a reverse fault type with a compression axis in an E-W direction. This event occurred on the boundary between the Pacific and the Philippine Sea plates.
* On August 29, there was a M4.2 earthquake at a depth of approximately 10 km in the northern Ibaraki prefecture. The focal mechanism had 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.
* On August 6, there was a M4.3 earthquake at a depth of approximately 15 km in the southern Kyoto prefecture. The focal mechanism showed a strike-slip fault type with a compression axis in an E-W direction. This event occurred within the crust.
* On August 3, there was a M5.6 earthquake offshore northwest of Amami Oshima (about 100 km west of Amami Oshima). In the vicinity of this event, there occurred a M5.5 one on August 15. The focal mechanisms of these two events both showed a strike-slip fault type with a tension axis in an NNW-SSE direction. These events occurred within the continental plate.
* On August 29, there was a M6.0 earthquake at a depth of approximately 20 km in Hyuganada. The focal mechanism showed a reverse fault type with a compression axis in an NW-SE direction. This event occurred at the boundary between the Philippine Sea 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 occurred a M4.5 one on September 4. The focal mechanisms of these two events both showed a strike-slip fault type with a compression axis in a WNW-ESE direction. These events occurred within the crust. The aftershock activity is gradually decreasing.
* 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.
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.
September 9, 2014
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during August 2014.
(reference)
The following events for the period from August 2013 to late July 2014 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities".
| – 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) |
|
| – 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 Iwate Prefecture | 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 |
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.
– "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 August 25 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, August 25, 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.
– "On August 3, there was a M5.6 earthquake offshore northwest
of Amami Oshima (about 100 km west of Amami Oshima). (Excerpted)":
The seismic activity which began on July 26 is gradually decreasing. In the area mentioned above, there have been similar seismic activities once in several years.
– "On August 29, there was a M6.0 earthquake at a depth of approximately
20km in Hyuganada. (Excerpted)":
In the vicinity of this event, there has been an aftershock activity such as 7 earthquakes with observed seismic intensity 1 or over, but now the activity is gradually decreasing.
– "On September 3, there was a M5.1 earthquake at a depth of approximately 5 km in the northern Tochigi prefecture. (Excerpted)":
There have been 21 aftershocks with seismic intensity 1 or over until September 5. In the border area between Gunma and Tochigi prefectures, where this time activity is observed, the seismic activity became high after the off the Pacific Coast of Tohoku Earthquake. On February 25, 2013, there was a M6.3 earthquake (maximum seismic activity 5 Upper).
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: