April 9, 2015
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
* On March 6, there was a magnitude (M)4.9 earthquake at a depth of approximately 55 km under the central Hidaka region. The focal mechanism of this event had a compression axis in an NE-SW direction. This event occurred within the continental plate.
* On March 25, there was a M5.0 earthquake at a depth of approximately 50 km under the southern Tokachi region. The focal mechanism of this event showed a reverse fault type with a compression axis in an NW-SE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On March 12, there was a M5.0 earthquake at a depth of approximately 45 km, offshore Fukushima prefecture. The focal mechanism 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.
* On March 4, there was a M4.6 earthquake at a depth of approximately 40 km under the western Aichi prefecture [Middle Western Mino Region, Gifu Prefecture]. The focal mechanism of this event showed a strike-slip fault type with a tension axis in an NE-SW direction. This event occurred within the Philippine Sea plate.
* On March 24, there was a M3.8 earthquake at a depth of approximately 5 km in the northern Nagano 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 March 24, there was a M4.6 earthquake at a depth of approximately 70 km under the southern Ibaraki prefecture. The focal mechanism 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 Philippine Sea 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.
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.
April 9, 2015
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during March 2015.
(reference)
The following events for the period from March 2014 to late February, 2015 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities".
| – 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) |
|
| – Northern Tochigi Prefecture | M5.1 on September 3, 2014 (Depth of approximately 5 km) |
|
| – Southern Ibaraki Prefecture | M5.6 on September 16, 2014 (Depth of approximately 45 km) |
|
| – Northern Nagano Prefecture | M6.7 on November 22, 2014 (Depth of approximately 5 km) |
|
| – Southern Tokushima Prefecture | M5.1 on February 6, 2015 (Depth of approximately 10 km) |
|
| – Offshore Sanriku | M6.9 on February 17, 2015 | |
| – Offshore Iwate Prefecture | M5.7 on February 17, 2015 (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 (March 2012 ~ February 2013) became under one fifth smaller, during one year from March 2013 (March 2013 ~ February 2014) became under one tenth smaller, and during one year from March 2014 (March 2014 ~ February 2015) became under one fifteenth smaller, than the number during about one year just after the Tohoku-Oki Earthquake, and thus the aftershock activity has been decaying.
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. Although both the horizontal and the vertical deformations were almost less than 1cm during the recent one month, the deformation has not yet returned to the state before 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.
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 fear that large earthquakes will occur from now on, and there is a possibility of strong shaking and high tsunami. It is necessary to pay attention continuously for it.
– "On March 24, there was a M 3.8 earthquake at a depth of approximately
5 km in the northern Nagano prefecture. (Excerpted)":
This earthquake occurred within the aftershock area of the earthquake (M6.7
maximum seismic intensity 6 Lower) which occurred on November 22, 2014
in the northern Nagano prefecture. The aftershock activity is gradually
decaying.
– "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 March 23 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, March 23, 2015)
"No changes of activity which are likely to be associated with the Tokai earthquake have been observed until now. (Excerpted)"
– Non-stationary crustal deformation around the Bungo Channel that was observed in the summer of 2014 is stagnant now. This deformation is considered to be caused by the gradual slip (slow-slip) at the boundary between the Philippine Sea and the continental plates.
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: