April 11, 2017
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Seismic Activities for March 2017

1 Major Seismic Activities

There was no remarkable activity.

• Seismic Activities for All of Japan in March 2017 (Magnitude 4.0 or over)

to supplementary reports

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

* On March 14, there was a magnitude (M) 4.7 earthquake at a depth of approximately 80 km under the western Hidaka region. The focal mechanism had a tension axis in an NE-SW direction. This event occurred within the Pacific plate.

• Hokkaido Region
• Earthquake under the Western Hidaka Region on March 14

to supplementary reports

(2) Tohoku Region

* On March 8, there was a M5.2 earthquake at a depth of approximately 65 km, offshore east of Aomori 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 continental plates.

* On March 12, there was a M5.4 earthquake at a depth of approximately 45 km, offshore Fukushima 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 continental plates.

• Tohoku Region
• Earthquake Offshore East of Aomori Prefecture on March 8
• Earthquake Offshore Fukushima Prefecture on March 12

to supplementary reports

(3) Kanto-Chubu Region

* On March 5, there was a M4.7 earthquake at a depth of approximately 50 km under the northeastern Chiba 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 Philippine Sea 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.

• Kanto - Chubu Region
• Earthquake under the Northeastern Chiba Prefecture on March 5
• Continuous GNSS Monitoring in the Area from Kakegawa to Omaezaki

to supplementary reports

(4) Kinki-Chugoku-Shikoku Region

There was no remarkable activity.

• Kinki-Chugoku-Shikoku Region

to supplementary reports

(5) Kyushu-Okinawa Region

* On March 2, there was a M5.3 earthquake at a depth of approximately 35 km under Hyuganada. The focal mechanism showed a normal fault type with a tension axis in an E-W direction. This event occurred within the Philippine Sea plate.

* On March 12, there was a M5.1 earthquake at a depth of approximately 140 km under the ocean area near Tanegashima [Offshore west of Satsuma Peninsula]. The focal mechanism had a tension axis in the subducting direction of the Philippine Sea plate. This event occurred within the Philippine Sea plate.

* On March 25, there was a M5.1 earthquake at a depth of approximately 85 km under the ocean area near Okinawa main island. The focal mechanism had a compression axis in an NNW-SSE direction. This event occurred within the Philippine Sea plate.

• Kyushu Region
• Earthquake under Hyuganada on March 2
• Earthquake under the Ocean Area near Tanegashima on March 12
• Okinawa Region
• Earthquake under the Ocean Area near Okinawa Main Island on March 25

to supplementary reports

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.

Supplementary Information to the Evaluation of Seismic Activities for March 2017

April 11, 2017
Earthquake Research Committee

1 Major Seismic Activities

The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during March 2017.

• M4.0 or greater: 63 (82 events in February)
• M5.0 or greater: 8 (7 events in February)
• M6.0 or greater: 0 (0 event in February)

(reference)

• M4.0 or greater: 73 / month (Median number of earthquakes over the past 10 years from 1998 through 2007)
• M5.0 or greater: 9 / month (Median number of earthquakes over the past 35 years from 1973 through 2007)
• M6.0 or greater: 1.4 / month, approximately 17 / year (Average number of earthquakes over the past 84 years from 1924 through 2007)

The following events for the period from March 2016 to late February 2017 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."

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2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

There is no supplementary information for Hokkaido region.

to the text

(2) Tohoku Region

There is no supplementary information for Tohoku region.

to the text

(3) Kanto-Chubu Region

–"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 March 27 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 27, 2017)
"No change of activity which is likely to be associated with the Tokai earthquake has been observed until now. (Excerpted)"

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(4) Kinki-Chugoku-Shikoku Region

There is no supplementary information for Kinki-Chugoku-Shikoku region.

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(5) Kyushu-Okinawa Region

– In March, no earthquake with maximum seismic intensity 4 or over (0 in February) and 1 earthquake with maximum seismic intensity 3 (1 in February) occurred in the Kumamoto and Aso regions, Kumamoto prefecture. 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 of 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.
A year has passed since the occurrence of the 2016 Kumamoto earthquakes. Note that in Kyushu region, there are several examples of an occurrence of an earthquake of the same order magnitude in a few years after an earthquake of M6.0 or so, such as the 1889 Kumamoto earthquake.

• "The 2016 Kumamoto Earthquakes" (1)
• "The 2016 Kumamoto Earthquakes" (2)
• "The 2016 Kumamoto Earthquakes" (3)
• Comparison of the Aftershock Activities for Major Earthquakes Occurring in the Inland and Coastal Areas (M3.5 or over)
• Distribution of epicenters of shallow, inland earthquakes in Kyushu
• Postseismic Deformation of the 2016 Kumamoto Earthquake (April 16, M7.3) (1)
• Postseismic Deformation of the 2016 Kumamoto Earthquake (April 16, M7.3) (2)

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