July 9, 2019
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Seismic Activities for June 2019

1 Major Seismic Activities

* On June 18, there was a magnitude (M) 6.7 earthquake offshore Yamagata prefecture. Maximum seismic intensity 6 Upper was observed in Niigata prefecture and damage was caused with injured persons and so on.

• Seismic Activities for All of Japan in June 2019 (Magnitude 4.0 or over)

to supplementary reports

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

There was no remarkable activity.

• Hokkaido Region

to supplementary reports

(2) Tohoku Region

With regard to the earthquake offshore Yamagata prefecture on June 18, refer to another report (Evaluation of Earthquake Offshore Yamagata Prefecture on June 18, 2019).

• Tohoku Region

to supplementary reports

(3) Kanto-Chubu Region

* On June 1, there was an M4.7 earthquake at a depth of approximately 35 km under the northeastern Chiba prefecture. The focal mechanism showed a normal fault type with a tension axis in a WNW-ESE direction. This event occurred within the Philippine Sea plate. In the vicinity of this event, there was an M5.1 earthquake on May 25.

* On June 4, there was an M6.2 earthquake at a depth of approximately 450 km under the ocean area near Torishima Island. The focal mechanism had a compression axis in the subducting direction of the Pacific plate. This event occurred within the Pacific plate.

* On June 17, there was an M5.1 earthquake at a depth of approximately 75 km under the northern Ibaraki prefecture. The focal mechanism showed a normal fault type with a tension axis in an ENE-WSW direction. This event occurred within the Pacific plate.

* On June 24, there was an M5.2 earthquake at a depth of approximately 60 km, offshore southeast of Chiba prefecture. The focal mechanism showed a reverse fault type with a compression axis in an NNW-SSE direction. This event occurred within the Philippine Sea plate.

* On June 24, there was an M4.1 earthquake at a depth of approximately 10 km, offshore east of the Izu Peninsula. The focal mechanism showed a strike-slip fault type with a compression axis in an NNW-SSE direction. This event occurred within the crust of the Philippine Sea plate.

• Kanto - Chubu Region
• Earthquake Under the Northeastern Chiba Prefecture on June 1
• Earthquake Under the Ocean Area near Torishima Island on June 4
• Earthquake in the Northern Ibaraki Prefecture on June 17
• Earthquake Offshore Southeast of Chiba Prefecture on June 24
• Earthquake Offshore East of the Izu Peninsula on June 24

to supplementary reports

(4) Kinki-Chugoku-Shikoku Region

There was no remarkable activity.

• Kinki-Chugoku-Shikoku Region

to supplementary reports

(5) Kyushu-Okinawa Region

There was no remarkable activity.

• Kyushu Region
• Okinawa Region

to supplementary reports

(6) Around the Nankai Trough

* There has been observed no unusual change which indicates that the possibility of occurrence of great earthquakes along the Nankai Trough has relatively raised compared to the normal time.

• Vertical Movement of GNSS-Based Control Stations - Omaezaki
• Vertical Movements of GNSS-Based Control Stations - Kii Peninsula and Around Muroto Cape

to supplementary reports

Supplementary Information to the Evaluation of Seismic Activities for June 2019

July 9, 2019
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 2019.

• M4.0 or greater: 76 (78 events in May)
• M5.0 or greater: 9 (8 events in May)
• M6.0 or greater: 2 (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 2018 to late May 2019 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."

to the text

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

There is no supplementary information for Kanto-Chubu region.

to the text

(4) Kinki-Chugoku-Shikoku Region

– According to the GNSS observation in the northern Kyushu from 2018 spring, and according to the GNSS and strain observations in the western Shikoku from 2018 autumn, crustal deformations different from the ordinary trend have been observed. These phenomena are considered to be caused by a slow slip at the deeper part of the boundary between the Philippine Sea and the continental plates, which continues at the northern Hyuganada and around the Bungo Channel.

• Non-Stationary Horizontal Crustal Deformation of Northern Kyushu and Western Shikoku (Linear trend, annual component, semi-annual component removed)
• Time Series of GNSS Continuous Observation: Northern Kyushu and Western Shikoku
• Long-Term Slow Slip in the Hyuganada and Bungo Channel Estimated from GNSS Data (provisional) (1) - Distribution of Estimated Slip -
• Long-Term Slow Slip in the Hyuganada and Bungo Channel Estimated from GNSS Data (provisional) (2) - Comparison Between Observed Values (black) and Calculated Values (white)-

to the text

(5) Kyushu-Okinawa Region

There is no supplementary information for Kyushu-Okinawa region.

to the text

(6) Around the Nankai Trough

–"There has been observed no unusual change which indicates that the possibility of occurrence of great earthquakes along the Nankai Trough has relatively raised compared to the normal time.":
(This evaluation is in agreement with the views presented at the regular meeting on July 5 of the Assessment Committee for Earthquakes along the Nankai Trough (reference below).)

(Reference)

Recent Crustal Activity Around the Nankai Trough (Seismological and Volcanological Department, Japan Meteorological Agency, July 5, 2019)
"In the present, there has been observed no unusual change which indicates that the possibility of occurrence of great earthquakes along the Nankai Trough has relatively raised compared to the normal time. (Excerpted)"

to the text