December 9, 2015
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On November 14, there was a magnitude (M) 7.1 earthquake offshore west of Satsuma peninsula. The tsunami with height of 30 cm was observed at Nakanoshima (Kagoshima prefecture).
* On November 28, there was a M5.6 earthquake at a depth of approximately 70 km, offshore southeast of Nemuro peninsula. 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.
* On November 1, there was a M5.2 earthquake at a depth of approximately 65 km, offshore east of Aomori prefecture [offshore Urakawa]. 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 November 19, there was a M4.9 earthquake at a depth of approximately 50 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 November 7, there was a M4.9 earthquake at a depth of approximately 100 km under the southern Ibaraki prefecture. The focal mechanism of this event had a tension axis in a WNW-ESE direction. This event occurred within the Pacific plate.
* On November 20, there was a M6.3 earthquake in the ocean area near Chichijima [the ocean area near Iwotou Island]. The focal mechanism of this event showed a reverse fault type with a compression axis in a WNW-ESE direction.
* On November 22, there was a M4.8 earthquake at a depth of approximately 50 km, offshore Ibaraki 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.
* In the GNSS data for the Tokai region, there has been no change of activity which is likely to be associated with the Tokai earthquake.
There was no remarkable activity.
* On November 12, there was a M5.0 earthquake at a depth of approximately 95 km in the ocean area near Yonagunijima. This event occurred within the Philippine Sea plate.
* On November 14, there was a M7.1 earthquake offshore west of the Satsuma peninsula. The focal mechanism of this event showed a strike-slip fault type with a tension axis in an NW-SE direction. This event occurred within the crust of the continental plate. The tsunami with height of 30 cm was observed at Nakanoshima (Kagoshima prefecture). According to the GNSS data, a very slight crustal deformation associated with this event was observed.
Note: [ ] is 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.
December 9, 2015
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during November 2015.
(reference)
The following events for the period from November 2014 to late October, 2015 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – 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) |
|
| – Ocean Area near Yonagunijima | M6.8 on April 20 | |
| – Ocean Area near Torishima | M5.9 on May 3, 2015 | |
| – Offshore Miyagi Prefecture | M6.8 on May 13, 2015 (Depth of approximately 45 km) |
|
| – Ocean Area near Amami Oshima | M5.1 on May 22 (Depth of approximately 20 km) |
|
| – Northern Saitama Prefecture | M5.5 on May 25, 2015 (Depth of approximately 55 km) |
|
| – Offshore West of Ogasawara Islands | M8.1 on May 30 (Depth of approximately 680 km) |
|
| – Abashiri Region | M5.0 on June 4, 2015 (At a very shallow depth) |
|
| – Northern Inland of Iwate Prefecture | M5.7 on July 10, 2015 (Depth of approximately 90 km) |
|
| – Southern Oita Prefecture | M5.7 on July 13, 2015 (Depth of approximately 60 km) |
|
| – Tokyo Bay | M5.2 on September 12, 2015 (Depth of approximately 55 km) |
|
| – Central Coast of Chile | Mw8.3 on September 17, 2015 |
There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
– Within the aftershock area of the Tohoku-Oki Earthquake, the number of earthquakes of M4.0 or over, during one year from March 2012 (March 2012 - February 2013) became less than one fifth, during one year from March 2013 (March 2013 - February 2014) became less than one tenth, and during one year from March 2014 (March 2014 - February 2015) became less than one fifteenth, of 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 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.
–"In the GNSS data for the Tokai region, there has been no change
of activity which is likely to be associated with the Tokai earthquake.":
(This evaluation is in agreement with the views presented at the regular meeting on November 17 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, November 17, 2015)
"No change of activity which is likely to be associated with the Tokai earthquake has been observed until now. (Excerpted))"
–"According to the GNSS data, non-stationary crustal deformation is observed surrounding the Kii Channel. This deformation is thought to be due to a slow movement (slow-slip) at the boundary between the Philippine Sea and the continental plates. It began in the mid-2014. Note that in this vicinity, a long-term slow movement was observed from 1996 to 1997.
–"On November 14, there was a M7.1 earthquake offshore west of Satsuma peninsula. (Excerpted)":
An aftershock activity such as 17 earthquakes with seismic intensity 1 or over occurring until December 3 in the vicinity of the event was observed, and then it is gradually decaying. The maximum aftershock is the M5.9 one which occurred on November 15. Judging from the aftershock distribution and the focal mechanism of the main shock, the seismic fault of the main shock is considered to be a right-lateral strike-slip fault extending in an N-S direction.
A seismic activity is observed in the crust of Kumamoto region, Kumamoto
prefecture since the mid-November: 15 earthquakes with seismic intensity
1 or over occurred until December 8, 16 o'clock (JST). The maximum is the
M3.2 one which occurred on December 4 at a depth of approximately 5 km.
The focal mechanism of the M3.1 earthquake on December 7 at 06:25 showed
a normal fault type with a tension axis in an NNE-SSW direction.
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: