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

Evaluation of Seismic Activities for June 2017

1 Major Seismic Activities

* On June 20, there was a magnitude (M) 5.0 earthquake under the Bungo Strait. The maximum seismic intensity 5 Upper was observed in Oita prefecture.

* On June 25, there was an M5.6 earthquake in the southern Nagano prefecture. The maximum seismic intensity 5 Upper was observed in Nagano prefecture, and damage was caused with some injured persons and so on.

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

to supplementary reports

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

* On June 28, there was an M5.7 earthquake at a depth of approximately 70 km (CMT solution), offshore east of Hokkaido. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.

• Hokkaido Region
• Earthquake Offshore East of Hokkaido on June 28

to supplementary reports

(2) Tohoku Region

* On June 19, there was an M4.5 earthquake at a depth of approximately 5 km in the Nakadori, Fukushima prefecture. The focal mechanism showed a normal fault type with a tension axis in an NE-SW direction. This event occurred within the crust.

• Tohoku Region
• Earthquake in Nakadori, Fukushima Prefecture on June 19

to supplementary reports

(3) Kanto-Chubu Region

* On June 25, there was an M5.6 earthquake at a depth of approximately 5 km in the southern Nagano prefecture. The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred within the crust. According to the GNSS observation, the crustal deformation of about 1 cm (provisional) north-north-eastward displacement was observed at Mitake observatory, Nagano prefecture. In the vicinity of this event, aftershock activity continues and including an M4.5 and an M4.7 on June 25, 69 earthquakes with seismic intensity 1 or over occurred until July 3.

* 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 in the Southern Nagano Prefecture on June 25 (1)
• Earthquake in the Southern Nagano Prefecture on June 25 (2)
• Observed data before and after the Earthquake in the Southern Nagano Prefecture (June 25, M5.6)
• Continuous GNSS Monitoring in the Area from Kakegawa to Omaezaki

to supplementary reports

(4) Kinki-Chugoku-Shikoku Region

* On June 14, there was an M4.5 earthquake at a depth of approximately 40 km in the central Kochi prefecture. The focal mechanism showed a strike-slip fault type with a tension axis in an E-W direction. This event occurred within the Philippine Sea plate.

• Kinki-Chugoku-Shikoku Region
• Earthquake under the Central Kochi Prefecture on June 14

to supplementary reports

(5) Kyushu-Okinawa Region

* On June 9, there was an M4.3 earthquake at a depth of approximately 15 km in the Tachibana Bay, Nagasaki prefecture. The focal mechanism showed a normal fault type with a tension axis in an N-S direction. This event occurred within the crust.

* On June 20, there was an M5.0 earthquake at a depth of approximately 40 km under the Bungo strait. The focal mechanism had a compression axis in the subducting direction of the Philippine Sea plate. This event occurred within the Philippine Sea plate.

* On June 30, there was an M5.2 earthquake at a depth of approximately 100 km offshore northwest of Miyakojima. The focal mechanism had a compression axis in the subducting direction of the Philippine Sea plate. This event occurred within the Philippine Sea plate.

• Kyushu Region
• Earthquake in the Tachibana Bay on June 9
• Earthquake under the Bungo Channel on June 20
• Okinawa Region
• Earthquake Offshore Northwest of Miyakojima on June 30

to supplementary reports

Supplement

* On July 1, there was an M5.1 earthquake at a depth of approximately 25 km under the central and eastern Iburi region, Hokkaido. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred within the crust.

* On July 2, there was an M4.5 earthquake at a depth of approximately 10 km in the Aso region, Kumamoto prefecture. The focal mechanism showed a strike-slip fault type with a tension axis in an NW-SE direction. This event occurred within the crust.

* On July 11, there was an M5.3 earthquake at a depth of approximately 10 km in the Kagoshima Bay. The focal mechanism showed a strike-slip fault type with a tension axis in a WNW-ESE direction (preliminary). This event occurred within the crust.

• Earthquake under the Central and Eastern Iburi Region on July 1
• "The 2016 Kumamoto Earthquakes" (1)
• "The 2016 Kumamoto Earthquakes" (2)
• Earthquake in the Kagoshima Bay on July 11, 2017 (Details about the generating place)

Note: 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 June 2017

July 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 June 2017.

• M4.0 or greater: 74 (58 events in May)
• M5.0 or greater: 10 (10 events in May)
• M6.0 or greater: 0 (1 event in May)

(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 June 2016 to late May 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.

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(2) Tohoku Region

There is no supplementary information for Tohoku region.

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(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 June 26 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 26, 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 June, no earthquake (2 in May) with maximum seismic intensity 4 or over and 1 earthquake (1 in May) with maximum seismic intensity 3 occurred in the Kumamoto and Aso regions, Kumamoto prefecture. Note that 1 earthquake with maximum seismic intensity 5 Lower occurred in July. 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 subsiding 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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