Analysis on Surface Deformation and Cracks in Paddy Fields by 2016 Kumamoto Earthquake using GNSS and Photogrammetry

抄録

Paddy fields in Kumamoto Prefecture were struck seriously by the 2016 Kumamoto Earthquake. The surface deformation and cracks damaged water distribution system for paddy fields. In order to clarify damages with rapidity, the surveying combining the aerial-based surveying and ground-based surveying was necessary. The aerial photogrammetry was conducted for the surface deformation and crack area, to clarify them quantitatively. The aerial photos were taken by an airplanes after the earthquakes. The aerial photogrammetry by airplane is suited to compare the topographic model after earthquakes to the topographic model before earthquakes, because the topographic model before earthquakes was surveyed by airplane. The Global Navigation Satellite System (GNSS) surveying was also conducted at the ground points in the area of aerial photos. The orthophoto mosaic and the Digital Elevation Model (DEM) after the earthquakes were made from these surveying. Further, the orthophoto mosaic and the DEM after the earthquakes were input into the Geographic Information System (GIS), to analyze the surface deformation and cracks in paddy fields. The accurate positions for cracks were found by overlaying the translucent orthophoto mosaic on the existing map. The differences between the DEMs before and after the earthquakes were analyzed by overlaying the DEM after the earthquakes on the DEM before the earthquakes. As the results, it was found that the overall upheaval and the local cave-in arose in the focused paddy field. The overall upheaval was 0.0 m - 0.4 m. The local cave-in was about 2.0 m. In order to check the differences between the DEMs before and after the earthquakes, the DEM after the earthquakes was compared to the elevation value by the GNSS surveying at the verification points. As the result, it was verified that the difference was 0.118 m as standard deviation.