Report 3 (April 22, 2015): Emergency Survey Report

  2016 Kumamoto Earthquake Main Page

Updated on April 22, 2016

The contents of this website are English translation of the Japanese website of “Report 3: Emergency Survey by Y. Shirahama, H. Mori, T Maruyama, and M. Yoshimi“,

An emergency survey was conducted near the epicenter of the 2016 Kumamoto earthquake to survey surface deformations, starting on April 16 after the M7.3 earthquake (Figure 1). Surface ruptures are identified along the northern Hinagu fault zone (Takano-Shirahata segment), and Futagawa segment and a part of Uto segment of the Futagawa fault zone (Figure 1). Surface deformation suggesting an earthquake fault is also observed in Uto area of the Futagawa fault zone. Photos of some earthquake faults and surface deformation are shown below (Photos 1 to 16).

Valuable and helpful information about the location of the earthquake faults on the ground was provided by Dr. Takashi Nakata, Emeritus Professor at Hiroshima University, Professor Hiroyuki Goto, Kyoto University, and Dr. Masashi Omata of Pasco Corporation.

 

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Figure 1. Distribution of surface rupture and deformations identified in the current survey. The base map is the Active Fault Map in Urban Area (Ikeda et al., 2001) by the Geospatial Information Authority of Japan (modified from GSJ, 2016).

 

Photos of identified surface earthquake faults

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Photo 1. Northeastward view of right lateral displacement producing mole-track structure in a field at Douzon, Mashiki Town. The fault line extends into a hill in the back of the photo, passing by a blue vinyl greenhouse. White arrows indicate the location of the fault line and red arrows show the sense of displacement (April 16, 2016; taken from GSJ, 2016).

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Photo 2. Right lateral displacement in a field of Douzon, Mashiki Town (northwestward view). Right lateral offset of the footpath in the field is about 200 cm (April 16, 2016; taken from GSJ, 2016)

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Photo 3. Shortening deformation on the paved road in Kamijin, Mashiki Town (southeastward view). The fault runs N70E with vertical displacement of about 40 cm (April 16, 2016; taken from GSJ, 2016).

 

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Photo 4. Right lateral displacement with mole-track structure in the west of Shimojin, Mashiki Town (northeastward view). Lateral displacement is about 100 cm and vertical displacement is about 20 cm (April 16, 2016; taken from GSJ, 2016).

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Photo 5. Vertical displacement of about 35 cm is observed to continue to the crossing in the back of the photo, in a field of Mitake, Mashiki Town (northeastward view; April 16, 2016; taken from GSJ, 2016).

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Photo 6. The flexural deformation in a drained paddy field with N70W left lateral component, west of Shimojin, Mashiki Town (west-northwestward view). Vertical displacement is about 15-20 cm and left lateral displacement is about 20 cm (April 16, 2016; taken from GSJ, 2016).

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Photo 7. Right lateral displacement in a drained paddy field, southwest of Mitake, Mashiki Town (northeastward view). The fault can be traced to the place shown in Photo 5, through a deformed guardrail, crossing the road and passing the right side of a house in the far back of the photo (April 16, 2016; taken from GSJ, 2016).

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Photo 8. Right lateral displacement of about 40-50 cm in a parking lot of a community center in Akai, Mashiki Town (northwestward view; April 16, 2016; taken from GSJ, 2016).

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Photo 9. Northeastward view of right lateral displacement in a drained paddy field and mole-track structure, west of Togawa, Mashiki Town. (April 16, 2016; taken from GSJ, 2016).

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Photo 10. Right lateral displacement of about 50 cm in a drained paddy field, west of Togawa, Mashiki Town (south-southeastward view; April 16, 2016; taken from GSJ, 2016).

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Photo 11. Vertical displacement of about 15 cm, cutting the national route 443 at the south of the Iino Elementary School (west-southwestward view; April 16, 2016; taken from GSJ, 2016).

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Photo 12 Right lateral displacement on the road pavement, west of Tsuchiyama, Mashiki Town (westward view; April 16, 2016; taken from GSJ, 2016).

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Photo 13. Right lateral displacement of about 50 cm in a drained paddy field at Takaki, Mifune Town (southward view; April 17, 2016; taken from GSJ, 2016).

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Photo 14. Right lateral displacement shown by the offset of gutter in the southern border road of Kamitakano, Mifune Town (eastward view). The right lateral displacement indicated by the offset of the gutter is about 50 cm (April 17, 2016; taken from GSJ, 2016).

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Photo 15. Open cracks with vertical offset of the road pavement along the southern border of Kushijima, Mashiki Town (east-northeastward view). The vertical offset of the road surface is about 10 cm. The sporadic distribution of open cracks from northeast to southwest in the paddy field is shown by white arrows (April 16, 2016; taken from GSJ, 2016).

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Photo 16. Open cracks along the boundary between topographic high and drained paddy field, south of Kushijima, Mashiki Town. The open cracks were created on the ramp of south-side-up flexure. The fence beyond the person was deformed by the flexure (west-southwestward view). The vertical displacement of the ground along the flexure is about 20 cm or more. The south-side-up flexure and open cracks continuously distributed along the topographic boundary. Curved white arrow shows flexure ramp shape (April 17, 2016; taken from GSJ, 2016).

Reference:

Yasutaka Ikeda, Noboru Chida, Takashi Nakata, Heitaro Kaneda, Masayoshi Tajikara, Shinji Takazawa (2001) Active Faults in Urban Area Map [Kumamoto], GSI Tech. Rep. D.1-No.368.

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