活断層地形調査における数値地形データの取得と活用 : 高縄山地東縁の川根断層を事例として

This study presents a practical methodology for acquiring digital topographical data and examines its practicality in active fault studies. We measured the fault scarps of the Kawane fault, which is distributed along the eastern margin of the Takanawa Mountain Range, northwest of Shikoku Island, Southwest Japan. The Kawane fault is newly identified by interpreting the anaglyph image produced from the 5 m-mesh digital elevation model of the Geospatial Information Authority of Japan.
The topographical profile measured by the total station, the conventional method is almost identical to PPK-GNSS on the open sky environment. The detailed digital elevation model based on the point cloud data processed from the photographs taken by a drone, UAV-SfM, effectively reveals the topographical feature of the vast area. Conversely, the terrestrial LiDAR is an accurate and appropriate method to survey areas where dense trees are harvested or where drones are restricted due to the urban area. Although the use of SLAM-LiDAR with a tablet device is not practical for measuring the extended topographical profile but it is suitable for acquiring the 3D model in a limited area, such as the fault outcrop.
The topographical survey revealed that the Kawane fault is a reverse fault with the downthrown east side inferred from the feature of fault scarps. This fault may extend to the boundary between the Geiyo-Shoto islands and the Hiuchi-Nada sea, which would play a vital role in topographical development in the Seto inland Sea.