Asia Air Survey, Co., Ltd. took Airborne Lidar measurement on April 15, 2016 for confirm the seismic surface fault after the earthquake occurred on April 14.

The expected mainshock struck in the early morning of April 16, and we confirmed seismic surface fault appeared in the same area where we have taken Lidar measurement on April 15. So we decided to take another Lidar measurement on April 23, along the same courses, using same airplane and same sensors of the measurement of April 15.

Based on the results from two period’s measurement, we confirmed seismic surface fault and detected very small deformation of the fault.

Fig.1 Lidar measurement area before and after the mainshock of the Kumamoto Earthquake

Fig.2 Comparison of Red Relief Image Maps created by Lidar data of April 15 and 23 (Near Tsumori Elementary School of Kamijin, Masuki Town)

A very clear right-lateral displacement can be recognized along the central part of the study area, as the upper (north) side is moving right (east) direction compared to the lower (south) side.

Fig.3 Differential map in a large area

We tried to show height differences between the two period’s data by color expression. In this map, the height differences of minus 10 m, minus 2 m and 0 m were expressed by indigo, blue and white, respectively, while plus 10 m and 2 m were expressed by red and black, respectively. The differential map was shown as Fig.3. In the case of house damages, especially the fully destroyed houses will cause minus several m, so it will be expressed as blue color in this map. The map shows tendency of the blue colored area was concentrated in specific narrow zones. Seismic surface fault was recognized in flat area in the central part of the map, also along the border of flat area and hill area. In the northern part of the Mitake area, Mashikimachi near the center of the map (rectangle in the Fig.3), we found two parallel faults and another fault crossing the former two, and checked the deformation after enlarging the map.

Fig.4, Overlapped map of RRIM and differential map (the white color is expressed by minus 0.8 m for easy to understand the relationship between differential amount and color).

According to blue color appeared in the western side and red color appeared in the eastern side of the embankment near ①, the deformation is considered to be from west to east direction. This moving tendency also can be recognized from the paddy banks near the embankment. From the width of the blue colored part caused by deformation was being smaller in the southern part of the fault line marked by ②③④, the fault was considered to be a right-lateral one. The vertical deformation is downward in the northern part near ②③, but relative difference of height was not recognized from ③ to ④. A fault can be confirmed from ⑤ to ⑥. The paddy banks in the southern side of the fault were blue colored but no blue colored part appeared in the northern side. According to this characteristics, the fault between ⑤ and ⑥ can be seen as a left-lateral one. A local uplift can be recognized near ⑤⑥. In the southern side of the fault of ⑦～⑧, according to the blue color was appeared in the eastern side of the houses while red color appeared in western side, the fault can be considered a right-lateral one. In the northern side of the fault, a downward deformation was confirmed near ⑦ and uplift confirmed near ⑧. Because no deformation was confirmed near ⑨ in the two sides of paddy banks, nearly no horizontal deformation was existed.

Fig.5 A method to interpret movement of strike-slip fault from differential map

In the case of a trapezoid north-south directed road embankment moved from west to east, minus displacement will be appeared in the western part while plus displacement will be appeared in the eastern part in the differential map. It is possible to know horizontal movement from such a vertical displacement. However, it must be notable that amount of displacement is expressed by color but not related to the depth of colors.

(a)Photo No.6695

Near the junction of two faults (near ⑥)。River Revetment structure has been destroyed by fault movement.

（b）Photo No.6691

The above (a) seen from opposite bank from river.

River Revetment structure was uplifted due to two faults.

（c）Photo No.6690

The left side looking to photo is being higher.

（d）Photo No.6687

A series of left-stepping ruptures were appeared and showing the right-lateral faulting.

(e）Photo No.6685

A series of left-stepping ruptures were appeared and showing the right-lateral faulting.

(f）Photo No.6683

The remained rice plants was displaced systematically to right along the line in the center of the photo (left-right line), while the front side was displaced to left, showing the right-lateral faulting.

(h）Photo No.6678

The fault was recognized as right-lateral one based on the deformation of road and its guard rail due to the fault crossing the paved road.

(j）Photo No.6702

Right-lateral displacement observed across road.

(k)Photo No.6700

The right side looking to photo is being higher. A series of left-stepping ruptures were appeared and showing the right-lateral faulting.

(l）Photo No.6701

A right-lateral fault was estimated according to en echelon ruptures.

(o）Photo No.6719

The waterway revetment was displaced right-laterally. The waterway revetment in the left side in the picture was destroyed seriously.

(p）Photo No.6705

Right-lateral displacement of vegetable and rice plants along the road.

(q）Photo No.6707

River revetment was seriously destroyed where the surface faulting occurred.

(r）Photo No.6708

The opposite side of photo (q), shows the damage of road in the left bank of the river.

(s）Photo No.6710

The fault clearly detected by the Lidar measurement of April 23.
A series of left-stepping ruptures were appeared and showing the right-lateral faulting.

(t）Photo No.6711

The fault clearly detected by the Lidar measurement of April 23. A series of left-stepping ruptures were appeared and showing the right-lateral faulting.