August 9, 2013
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
* On July 16, there was a magnitude (M) 5.1 earthquake at a depth of approximately 45 km, offshore Kushiro [offshore southeast of Nemuro Peninsula]. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the continental plates.
* On July 10, there was a M4.9 earthquake at a depth of approximately 80 km under the northern coast of Iwate prefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred within the Pacific plate (in the upper plane of the double seismic zone).
* On July 16, there was a M5.1 earthquake at a depth of approximately 70 km, offshore Iwate prefecture. The focal mechanism showed a tension axis in a direction of the subducting Pacific plate. This event occurred within the Pacific plate (in the lower plane of the double seismic zone).
* On July 20, there was a M5.4 earthquake at a depth of approximately 45 km, offshore Fukushima prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the continental plates.
* On July 23, there was a M5.2 earthquake at a depth of approximately 10 km in Hamadori, Fukushima prefecture. The focal mechanism showed a normal fault with a tension axis in a WNW-ESE direction. This event occurred within the crust.
* On July 31, there was a M5.0 earthquake at a depth of approximately 20 km, offshore Miyagi prefecture. The focal mechanism showed a normal fault with a tension axis in an NE-SW direction. This event occurred within the crust of the continental plate.
* On July 10, there was a M3.9 earthquake at a depth of approximately 10 km in Sagami Bay. The focal mechanism had a compression axis in an NNW-SSE direction. This event occurred within the Philippine Sea plate.
* On July 20, there was a M5.4 earthquake at a depth of approximately 35 km, offshore Ibaraki prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the continental plates.
* On July 21, there was a M4.5 earthquake at a depth of approximately 50 km under northeastern Chiba prefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred on 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.
* On August 3, there was a M4.9 earthquake at a depth of approximately 35 km in Enshu-Nada. The focal mechanism showed a normal fault with a tension axis in a WNW-ESE direction. This event occurred within the Philippine Sea plate.
* On August 4, there was a M6.0 earthquake at a depth of approximately 60 km, offshore Miyagi prefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred within the Pacific plate. In the vicinity of this event, there was a M7.2 earthquake (maximum seismic intensity 6 Upper) on April 7, 2011.
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.
August 9, 2013
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during July 2013.
(reference)
The following events for the period from July 2012 to late June 2013 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities"
| – Northern Nagano Prefecture | M5.2 on July 10, 2012 (Depth of approximately 10 km) |
|
| – Southern Tokachi Region | M6.1 on August 25, 2012 (Depth of approximately 50 km) |
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| – Offshore Miyagi Prefecture | M5.6 on August 30, 2012 (Depth of approximately 60 km) |
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| – Offshore Miyagi Prefecture | M5.6 on October 25, 2012 (Depth of approximately 50 km) |
|
| – Offshore Sanriku | M7.3 on December 7, 2012 | |
| – Northern Ibaraki Prefecture | M4.8 on January 28, 2013 (Depth of approximately 75km) |
|
| – Northern Ibaraki Prefecture | M4.7 on January 31, 2013 (Depth of approximately 10km) |
|
| – Southern Tokachi Region | M6.5 on February 2, 2013 (Depth of approximately 100 km) |
|
| – Northern Tochigi Prefecture | M6.3 on February 25, 2013 (Depth of approximately 5 km) |
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| – Near Awajishima | M6.3 on April 13, 2013 (Depth of approximately 15 km) |
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| – Under the Ocean Near Miyakejima | M6.2 on April 17, 2013 (Depth of approximately 10 km) |
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| – Offshore Miyagi Prefecture | M5.9 on April 17, 2013 (Depth of approximately 60 km) |
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| – Offshore Fukushima Prefecture | M6.0 on May 18, 2013 (Depth of approximately 45 km) |
There is no supplementary information for the Hokkaido region.
–"On July 23, there was a M5.2 earthquake at a depth of approximately
10 km in Hamadori, Fukushima prefecture. (Excerpted)":
Within the crust extending from Hamadori, Fukushima prefecture to northern Ibaraki prefecture, seismic activity has become high after the occurrence of the 2011 off the Pacific Coast of Tohoku Earthquake, and there have been mostly earthquakes with normal fault type. There were a M7.0 earthquake on April 11, 2011, and a M6.4 one on the next day. After these earthquakes seismic activity higher than that of pre-the 2011 off the Pacific Coast of Tohoku Earthquake days still continues.
– During about one year (March 2012 - February, 2013), the number
of earthquakes of M4.0 or over in the aftershock area of the 2011 off the
Pacific Coast of Tohoku Earthquake became under one fifth smaller than
the one during about one year (March 11, 2011 - February, 2012) just after
the Earthquake, and thus the aftershock activity has been decaying. However,
in comparison with the mean activity before the 2011 off the Pacific Coast
of Tohoku Earthquake, the number of earthquakes of M4.0 or over in the
aftershock area was more than four times, and the aftershock activity still
remains in brisk state.
According to the GNSS data during about one month just after the 2011 off the Pacific Coast of 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 movement was gradually decaying. Although the horizontal movement was slightly larger than 1 cm, and the vertical movement was less than 1cm during the recent one month, crustal movements which are thought to be the postseismic deformation have still been observed in a wide area from the Tohoku through the Kanto-Chubu regions.
In case of the earthquake (moment magnitude (Mw) 9.1) offshore west of the northern Sumatra Island in December 2004, within the source area and its surroundings, there have been large earthquakes for long period. As to the 2011 off the Pacific Coast of Tohoku Earthquake, within the aftershock area and its surroundings, there is 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 July 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, July 29)
"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 August 4, there was a M6.0 earthquake at a depth of approximately
60 km, offshore Miyagi prefecture. (Excerpted).":
This earthquake occurred in the aftershock area of the earthquake occurring on April 7, 2011 (itself an aftershock of the 2011 off the Pacific Coast of Tohoku Earthquake: M7.2, maximum seismic intensity 6 Upper). In this area high seismic activity has continued, and there were a M5.6 on August 30 and a M5.2 on November 24 in 2012.
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: