May 13, 2014
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On April 2, there was a moment magnitude (Mw) 8.1 earthquake along the northern coast of Chile. This event caused tsunami which was observed along the Pacific coast from Hokkaido to Kyushu, at Okinawa prefecture and Izu-Ogasawara Islands.
There was no remarkable activity.
* On April 3, there was a magnitude (M) 5.5 earthquake at a depth of approximately 65 km, under southern coast of Iwate prefecture. The focal mechanism had a compression axis in an E-W direction. This event occurred within the Pacific plate.
* On April 5, there was a M5.3 earthquake at a depth of approximately 35 km, offshore Iwate prefecture. The focal mechanism showed a normal fault type with a tension axis in an E-W direction.
* On April 13, there was a M4.9 earthquake at a depth of approximately 65 km, offshore Fukushima prefecture. The focal mechanism showed a reverse fault type with a compression axis in an NW-SE direction. This event occurred within the Pacific plate.
* On April 17, there was a M5.1 earthquake offshore Fukushima prefecture. The focal mechanism showed a normal fault type with a tension axis in an NNE-SSW direction.
* On April 8, there was a M4.4 earthquake at a depth of approximately 10 km in the Chuetsu region, Niigata prefecture. The focal mechanism showed a reverse fault type with a compression axis in an NW-SE direction. This event occurred within the crust.
* On April 18, there was a M4.7 earthquake at a depth of approximately 50 km under southern Ibaraki prefecture. The focal mechanism showed a reverse fault type with a compression axis in an NNW-SSE direction. This event occurred on the boundary between the Philippine Sea 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.
There was no remarkable activity.
* On April 2 at 08:46 (JST), there was a Mw8.1 earthquake along the northern coast of Chile. This event caused tsunami which was observed along the Pacific coast from Hokkaido to Kyushu, and at Izu-Ogasawara Islands, especially 55 cm height at Kuji Port (Iwate 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 Nazca and the South American plates.
In the vicinity of this event, seismic activity before the main shock was
observed such as a Mw6.7 earthquake on March 17. After the main shock,
aftershock activity was high, such as a Mw7.7 earthquake on April 3. but
it has decreased afterwards.
* On May 3, there was a M6.0 earthquake under the ocean area near Iwotou Island. The focal mechanism of this event had a compression axis in an NW-SE direction. This event occurred within the subducting Pacific plate.
* On May 5, there was a M6.0 earthquake at a depth of approximately 160 km under the ocean area near Izu-Oshima. The focal mechanism of this event had a tension axis in the subducting direction of the Pacific plate. This event occurred within the Pacific plate.
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.
May 13, 2014
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during April 2014.
(reference)
The following events for the period from April 2013 to late March 2014 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities".
| – 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) |
|
| – 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) |
There is no supplementary information for the Hokkaido region.
There is no supplementary information for the 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-Oki Earthquake.
In case of the earthquake (Mw 9.1) offshore west of the northern Sumatra Island in 2004, there were Mw8.6 after four months, Mw8.5 after about two and a half years, Mw7.5 after about five and a half years, and Mw8.6 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-Oki 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-Oki 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 April 8, there was a M4.4 earthquake at a depth of approximately
10 km in the Chuetsu region, Niigata prefecture. (Excerpted)":
This event occurred in the aftershock area of "the Mid Niigata Prefecture Earthquake in 2004"
–From May 3, seismic activity became active in the area from Hida region, Gifu prefecture to the middle Nagano prefecture (near the border between Gifu and Nagano prefectures). Including a M3.9 earthquake on May 3 (maximum seismic intensity 3), 44 earthquakes with seismic intensity 1 or over have occurred until May 12. After May 6, the activity has been decreasing. In the vicinity of this area, active seismicity was observed from August to October in 1998, the earthquake of maximum M5.6 (maximum seismic intensity 4) occurring on August 16. In addition, seismic activity became active in March, 2011, after the occurrence of the 2011 off the Pacific Coast of Tohoku Earthquake, and there was a M4.8 earthquake (maximum seismic intensity 4) on March 21.
–"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 April 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, April 21, 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.
–"On April 2 at 08:46 (JST), there was a Mw8.1 earthquake along the
northern coast of Chile. (Excerpted)":
In the vicinity of the recent event, a M8.5 earthquake in 1868 and a M8.3 one in 1877 occurred and tsunamis associated with these were observed along the Pacific coast of Japan.
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: