July 9, 2015
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On June 4, there was a magnitude (M) 5.0 earthquake in the Abashiri region [Middle southern Kushiro region]. The maximum seismic intensity 5 Lower was observed in Hokkaido.
* On June 4, there was a magnitude (M) 5.0 earthquake in the Abashiri region [Middle southern Kushiro region]. The maximum seismic intensity 5 Lower was observed in Hokkaido.
* On June 8, there was a M5.6 earthquake at a depth of approximately 65 km, offshore east of Aomori prefecture. In addition, on June 23, there was a M4.6 earthquake at almost the same place. The focal mechanisms of these events showed a reverse fault type with a compression axis in a WNW-ESE direction. These events occurred at the boundary between the Pacific and the continental plates.
* On June 11, there was a M5.9 earthquake offshore Sanriku. 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 June 9, there was a M4.4 earthquake at a depth of approximately 50 km under the southern Ibaraki prefecture. 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 Philippine Sea and the continental plates.
* On June 23, there was a M6.8 deep earthquake at a depth of approximately 480 km, offshore west of Ogasawara Islands. The focal mechanism of this event had a compression axis in a subducting direction of the Pacific plate. This event occurred within the Pacific plate.
* 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.
There was no remarkable activity.
* On July 7, there was a M6.3 earthquake offshore east of Hokkaido. The focal mechanism of this event had a compression axis in a WNW-ESE direction (preliminary).
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.
July 9, 2015
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during June 2015.
(reference)
The following events for the period from June 2014 to late May, 2015 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities".
| – 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 | |
| – 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) |
|
| – 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) |
-"On June 4, there was a M5.0 earthquake at a very shallow depth in Abashiri region [Middle southern Kushiro region]. (Excerpted)":
After that, there were 12 earthquakes with seismic intensity 1 or over, in the area near the epicenter, until June 16. The aftershock activity is gradually decaying.
-" On June 11, there was a M5.9 earthquake offshore Sanriku. (Excerpted)":
In the vicinity of the recent event, after the occurrence of a M5.8 earthquake on July 10 at 17:32 through June11, the seismic activity was observed such as 6 earthquakes with seismic intensity 1 or over.
– 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 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.
–"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 June 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, June 29, 2015)
"No change of activity which is likely to be associated with the Tokai earthquake has been observed until now. (Excerpted)"
– In Mt. Hakone, there have been clusters of small magnitude earthquakes from April 26 (the maximum is M3.3 as of June 30). Tilt-meters and volumetric-strain-meters around Mt. Hakone and GNSS observations show a crustal deformation at the same period.
There is no supplementary information for Kinki-Chugoku-Shikoku region.
There is no supplementary information for Kyushui-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: