5:15 PM - 7:15 PM
[HDS07-P06] Movement of landslide bodies (hillslope slump) associated with the 2024 Noto Peninsula Earthquake using SAR image analysis
Keywords:Landslide, 2024 Noto Peninsula Earthquake, SAR image, Pixel offset analysis
Strong motions of large earthquakes trigger landslides on mountain and hill slopes. Over 2,000 slope failures were triggered by the 2024 Noto Peninsula Earthquake (GSI, 2024). Fukushima et al. (2024) performed a pixel offset analysis of the SAR images and reported that the landslide bodies with over ~ 5 km width along the Wakayama River was displaced up to 2 m by this earthquake, and that similar landslide movements (hillslope slumps) simultaneously occurred widely in the mountain area of the peninsula. But the details of such hillslope slumps are yet to be known. We carried out a detailed SAR pixel offset analysis and mapped hillslope slumps which seem to have been triggered by the 2024 Noto Peninsula Earthquake. In this presentation, we will report the spatial distribution of hillslope slumps and discuss how they could have affected the development of the landforms and landscape of the Noto Peninsula.
The pixel offset analysis was performed using eleven pairs of SAR images taken before and after the earthquake. We then mapped areas showing different trends from the surroundings on the displacement maps obtained by the pixel offset analysis. The mapping criteria of displacement were as follows: (1) the width of displacement area was over ~300 m, (2) displacement signals were almost uniform, (3) displacements were observed in the results of multiple pairs, and (4) the direction of displacement is consistent with that of mountain slope.
As a result, we found 246 hillslope slumps. The largest slump had an area of 1.3×106 m2. Because the areas and directions of the hillslope slumps largely overlap with the landslide map published by NIED, we infer that most of them are remobilization of known landslide bodies. Hillslope slumps were densely distributed in the mountains of northeastern and western parts of the peninsula that experienced a large coseismic uplift and that have undulating reliefs (Figure). In the field survey performed in the areas of the identified hillslope slumps, we found large cracks consistent with the direction of displacements many of which ignored micro-ridges and valleys. This observation allowed us to confirm that these signals reflect the actual displacements of hillslope slumps. Although the number of slope failures reported by GSI (2024) was the largest in the outcrop areas of dacite and rhyolite (Abe et al., 2024), that of hillslope slumps found by this study was the largest in the siliceous mudstones (31.4%). This implies that the slope failure and hillslope slump are different processes and that the basement lithology controls the processes of slope development and erosion.
Although the same kind of hillslope slumps could have happened during previous large earthquakes, their identification in aerial photographs should have been difficult because they are movement of large bodies (widths of hundreds of meters to kilometers) of up to a few meters without any sediment collapse. The effectiveness of the SAR pixel offset analysis for identification of these phenomena was demonstrated in this study. We infer that the hillslope slumping is an unignorable process in the mountain and hills of the Noto Peninsula, and that it could be one of the significant processes on the landform development of other uplifting mountains and hills dominated by landslides.
The pixel offset analysis was performed using eleven pairs of SAR images taken before and after the earthquake. We then mapped areas showing different trends from the surroundings on the displacement maps obtained by the pixel offset analysis. The mapping criteria of displacement were as follows: (1) the width of displacement area was over ~300 m, (2) displacement signals were almost uniform, (3) displacements were observed in the results of multiple pairs, and (4) the direction of displacement is consistent with that of mountain slope.
As a result, we found 246 hillslope slumps. The largest slump had an area of 1.3×106 m2. Because the areas and directions of the hillslope slumps largely overlap with the landslide map published by NIED, we infer that most of them are remobilization of known landslide bodies. Hillslope slumps were densely distributed in the mountains of northeastern and western parts of the peninsula that experienced a large coseismic uplift and that have undulating reliefs (Figure). In the field survey performed in the areas of the identified hillslope slumps, we found large cracks consistent with the direction of displacements many of which ignored micro-ridges and valleys. This observation allowed us to confirm that these signals reflect the actual displacements of hillslope slumps. Although the number of slope failures reported by GSI (2024) was the largest in the outcrop areas of dacite and rhyolite (Abe et al., 2024), that of hillslope slumps found by this study was the largest in the siliceous mudstones (31.4%). This implies that the slope failure and hillslope slump are different processes and that the basement lithology controls the processes of slope development and erosion.
Although the same kind of hillslope slumps could have happened during previous large earthquakes, their identification in aerial photographs should have been difficult because they are movement of large bodies (widths of hundreds of meters to kilometers) of up to a few meters without any sediment collapse. The effectiveness of the SAR pixel offset analysis for identification of these phenomena was demonstrated in this study. We infer that the hillslope slumping is an unignorable process in the mountain and hills of the Noto Peninsula, and that it could be one of the significant processes on the landform development of other uplifting mountains and hills dominated by landslides.