June 9, 2017
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Seismic Activities for May 2017

1 Major Seismic Activities

There was no remarkable activity.

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

to supplementary reports

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

* On May 22, there was a magnitude (M) 5.7 earthquake at a depth of approximately 60 km (CMT solution) offshore east of Hokkaido. The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.

• Hokkaido Region
• Earthquake Offshore East of Hokkaido on May 22

to supplementary reports

(2) Tohoku Region

There was no remarkable activity.

• Tohoku Region

to supplementary reports

(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.

• Kanto - Chubu Region
• 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 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 at a depth of approximately 20 km (CMT solution) under the ocean area near Miyakojima. The focal mechanism showed a strike-slip fault type with a tension axis in an NNW-SSE direction.

* On May 11, there was an M4.4 earthquake at a depth of approximately 15 km in the Ariake Sea [Kumamoto region, Kumamoto prefecture]. The focal mechanism showed a normal fault type with a tension axis in an N-S direction. This event occurred within the crust.

• Kyushu Region
• "The 2016 Kumamoto Earthquakes" (1)
• "The 2016 Kumamoto Earthquakes" (2)
• Okinawa Region
• Earthquake under the Ocean Area near Miyakojima on May 9

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 May 2017

June 9, 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 May 2017.

• M4.0 or greater: 58 (75 events in April)
• M5.0 or greater: 10 (11 events in April)
• M6.0 or greater: 1 (0 event in April)

(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 May 2016 to late April 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 May 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, May 29, 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

–"On May 4, there was an M4.1 earthquake at a depth of approximately 10 km in the Kumamoto region, Kumamoto prefecture. (Excerpted) " "On May 11, there was an M4.4 earthquake at a depth of approximately 15 km in the Ariake Sea [Kumamoto region, Kumamoto prefecture]. (Excerpted) ":
In May, 2 earthquakes (0 in April) with maximum seismic intensity 4 or over and 1 earthquake (1 in April) with maximum seismic intensity 3 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 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.

• "The 2016 Kumamoto Earthquakes" (1)
• "The 2016 Kumamoto Earthquakes" (2)
• 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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