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

Evaluation of Seismic Activities for July 2019

1 Major Seismic Activities

There was no remarkable activity.

• Seismic Activities for All of Japan in July 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

* On July 17, there was a magnitude (M) 4.7 earthquake at a depth of approximately 80 km under the northern Miyagi prefecture＊. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.

• Tohoku Region
• Earthquake under the Northern Miyagi Prefecture on July 17

to supplementary reports

(3) Kanto-Chubu Region

* On July 25, there was an M5.1 earthquake at a depth of approximately 60 km, offshore east of Chiba prefecture. The focal mechanism showed a strike-slip fault type with a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.

* On July 28, there was an M6.6 earthquake at a depth of approximately 390 km, offshore southeast of Mie prefecture. The focal mechanism had a compression axis in the subducting direction of the Pacific plate. This event occurred within the Pacific plate. Seismic intensity 1 or over was observed in the area extending from Hokkaido to Kinki regions, especially the maximum seismic intensity 4 was observed in Miyagi prefecture, due to the seismic wave propagating through the subducting Pacific plate (abnormal seismic intensity).

* On July 30, there was an M5.9 earthquake offshore east of Hachijojima Island. The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.

• Kanto - Chubu Region
• Earthquake Offshore East of Chiba Prefecture on July 25
• Earthquake Offshore Southeast of Mie Prefecture on July 28
• [Reference] On the earthquake of which seismic intensity at the far place from the epicenter is observed to be larger than that in the vicinity of the epicenter
• Examples of Distribution Map of Seismic Intensity of the Past Earthquakes Accompanied with the Abnormal Seismic Intensity Area
• Earthquake Offshore East of Hachijojima Island on July 30

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 July 13, there was an M6.0 earthquake at a depth of approximately 260 km, offshore northwest of Amami Oshima. 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 Offshore Northwest of Amami Oshima on July 13
• 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.

• Secular variation of benchmark 2595 (Omaezaki City)
• Vertical Movement of GNSS-Based Control Stations - Omaezaki
• Vertical Movements of GNSS-Based Control Stations - Kii Peninsula and Around Muroto Cape

to supplementary reports

(7) Other Regions

* On July 27, there was an M6.0 earthquake near Philippine. The focal mechanism showed a strike-slip fault type with a compression axis in a WNW-ESE direction.

• Earthquake near Philippine on July 27

to supplementary reports

Supplement

* On August 4, there was an M6.4 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.

* On August 8, there was an M6.4 earthquake at a depth of approximately 40 km near Taiwan (depth and M: preliminary). The focal mechanism showed a strike-slip fault type with a compression axis in an NE-SW direction (preliminary).

• Earthquake Offshore Fukushima Prefecture on August 4
• Earthquake near Taiwan on August 8

# : [the southern coast of Iwate prefecture] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.

Supplementary Information to the Evaluation of Seismic Activities for July 2019

August 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 July 2019.

• M4.0 or greater: 97 (76 events in June)
• M5.0 or greater: 15 (9 events in June)
• M6.0 or greater: 3 (2 events in June)

(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 July 2018 to late June 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. These crustal deformations and the long-term slow slip seem to be stagnant since June 2019.

• 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 August 7 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, August 7, 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