May 12, 2017
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
* On April 30, there was a magnitude (M) 5.4 earthquake at a depth of approximately 55 km under the southern Tokachi region. 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 continental plates.
* On April 9, there was an M5.0 earthquake at a depth of approximately 45 km, offshore Fukushima prefecture. The focal mechanism showed a reverse fault type with a compression axis in an E-W direction. This event occurred at the boundary between the Pacific and the continental plates.
* On April 12, there was an M4.6 earthquake at a depth of approximately 55 km under the southern Ibaraki prefecture. The focal mechanism had a compression axis in an N-S direction. This event occurred within the Philippine Sea plate.
* On April 20, there was an M4.5 earthquake at a depth of approximately 5 km in the northern Ibaraki prefecture. The focal mechanism showed a strike-slip fault type with a tension axis in an ENE-WSW direction. On the same day there was also an M4.2 earthquake in the vicinity of this event. These events occurred within the crust.
* 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 April 29, there was an M5.6 earthquake offshore east of Osumi peninsula. The focal mechanism showed a normal fault type with a tension axis in a WNW-ESE direction.
* On May 4, there was an M4.1 earthquake at a depth of approximately 10 km in the Kumamoto region, Kumamoto prefecture. The focal mechanism showed a normal fault type with a tension axis in an NNW-SSE direction. This event occurred within the crust.
* On May 9, there was an M6.4 earthquake under the ocean area near Miyakojima. The focal mechanism showed a strike-slip fault type with a tension axis in an NW-SE direction (preliminary).
Note: GNSS (Global Navigation Satellite System) is a general name of satellite positioning system such as GPS.
May 12, 2017
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during April 2017.
(reference)
The following events for the period from April 2016 to late March 2017 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – Kumamoto Earthquakes | M6.5 on April 14, 2016 and M7.3 on April 16, 2016 (Depth of approximately 10 km) |
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| – Southern Ibaraki Prefecture | M5.5 on May 16, 2016 (Depth of approximately 40 km) |
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| – Uchiura Bay | M5.3 on June 16, 2016 (Depth of approximately 10 km) |
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| – Northern Ibaraki Prefecture | M5.4 on July 27, 2016 (Depth of approximately 55 km) |
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| – Kumamoto Region, Kumamoto Prefecture | M5.2 on August 31, 2016 (Depth of approximately 15 km) |
|
| – Ocean Area near Okinawa Main Island | M5.6 on September 26 (Depth of approximately 45 km) |
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| – Central Tottori Prefecture | M6.6 on October 21, 2016 (Depth of approximately 10 km) |
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| – Offshore Fukushima Prefecture | M7.4 on November 22, 2016 (Depth of approximately 10 km) |
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| – Northern Ibaraki Prefecture | M6.3 on December 28, 2016 (Depth of approximately 10 km) |
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| – Offshore Fukushima Prefecture | M5.7 on February 28, 2017 (Depth of approximately 50 km) |
There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
– Since April 6, the seismic activity in Chuetsu region, Niigata prefecture has been rather high, and there were 11 earthquakes with seismic intensity 1 or over until May 8. The largest was an M3.9 earthquake on April 14.
–"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 April 24 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 24, 2017)
"No change of activity which is likely to be associated with the Tokai earthquake has been observed until now. (Excerpted)"
There is no supplementary information for Kinki-Chugoku-Shikoku region.
– In April, no earthquake with maximum seismic intensity 4 or over (0 in March) and 1 earthquake with maximum seismic intensity 3 (1 in March) occurred in the Kumamoto and Aso regions, Kumamoto prefecture. Note that 2 earthquakes with maximum seismic intensity 4 already occurred until 11th in May. A series of seismic activity of the 2016 Kumamoto Earthquakes in the Kumamoto and Aso regions still continues, decaying as a whole, and the seismic activity at present will continue for a while. According to the GNSS observation, postseismic deformation in the area centered on the series of the seismic activity is converging as a whole.
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: