1:45 PM - 2:00 PM
[HDS10-01] Distribution of deep-seated gravitational slope deformation features in Saigawa Hills and Chikuma Mountains, Nagano Prefecture based on high-resolution DEMs
Keywords:High-resolution DEMs, Deep-seated gravitational slope deformation feature, Landslide, Active fault, Saigawa Hills, Chikuma Mountains
Small scarps parallel to ridge in mountainous areas have been considered to be deep-seated gravitational slope deformation (DGSD) features since the late 1970s (e.g., Shimizu et al., 1980). These previous studies have progressed mainly by using aerial photographs. However, small geomorphic features distributed under vegetation can’t be detected by using aerial photographs (Lin et al., 2013). Therefore, the actual distribution of such DGSD features is still unknown in most areas of Japan. On the other hand, digital elevation models (DEMs) acquired from airborne lidar surveys have been developed, and in particular, small geomorphic features distributed under vegetation can be identified by using high-resolution DEMs since the 2000s (Lin et al., 2013; Kaneda and Chiba, 2019). Kaneda and Kono (2017) used high-resolution DEMs and identified a total of 10487 DGSD features in the Etsumi Mountains, Gifu Prefecture. DGSD may develop into large-scale landslides or may be triggered by nearby fault activity (e.g., Chigira, 1998; Lin et al., 2013; Komura et al., 2020). Understanding the distribution of DGSD features will contribute to clarify and generalize the processes and factors of mountain growth and breaking. It is also an important topography from the aspect of disaster prevention in predicting the location of landslides, especially when residential and agricultural areas are located nearby. In this study, we identified the distribution of DGSD features in Saigawa Hills and Chikuma Mountains in Nagano prefecture, where landslide topography is densely distributed and high-activity active faults are located nearby. Moreover, the characteristics of the distribution of DGSD features are clarified, and the relationship between DGSD features and landslides or active faults is discussed.
In this study, 1 m mesh DEMs based on airborne lidar surveys published by Nagano Prefecture were used to create a morphometric protection index red relief image map (MPI-RRIM) devised by Kaneda and Chiba (2019). Stereopaired MPI-RRIMs were used to interpret scarplets, including DGSD features and small active faults. Scarplet was classified into uphill-facing scarp and downhill-facing scarp. GIS analysis was conducted based on the results of geomorphic interpretation.
A total of 3841 scarplets, including 3593 uphill-facing scarps and 248 downhill-facing scarps were identified as a result of geomorphic interpretation. Numerous uphill-facing scarps parallel to ridge were identified, and most of them are considered to be DGSD features. GIS analysis indicates that the distribution of scarplets is more related to geomorphological features such as elevation and slope than to geology. In particular, the index of ridgeness, which indicates whether the topography is a ridge or valley, indicates that many DGSD features are located on ridge. This index is the best indication of where DGSD features developed.
The distribution areas of scarplets were mostly consistent with that of landslides. For example, in Omachi City, Nagano Prefecture, east-falling uphill-facing scarps were identified south of the Karagemi and Aigawa landslides (Ueki, 2001), extending about 5 km from north to south. The geology of this area is called the Omine Belt (Kosaka, 1980), and its geological structure is east dipping. The geological map shows that the location of the bedding plane and the uphill-facing scarps are mostly consistent, suggesting that the uphill-facing scarps were formed by flexural slip, and some of them have already developed into large-scale landslides. These uphill-facing scarps are also considered important for predicting landslide occurrence.
In addition, the distribution, slip style, and subsurface geometry of active faults may be related to the formation of scarplets. The strike of scarplets was random in areas where active faults are not distributed, but tended to mostly consistent with the strike of active faults near reverse faults. The areas of surface deformation inferred from the subsurface geometry of active faults also tended to consistent with the areas where scarplets are frequently distributed.
In conclusion, the distribution of DGSD features was identified in Saigawa Hills and Chikuma Mountains. The distribution of scarplets showed a high correlation with geomorphological features and may also be related to landslides and active faults. However, since there are still few data for generalization, it is hoped that the distribution of DGSD features in other regions will be identified in more detail.
In this study, 1 m mesh DEMs based on airborne lidar surveys published by Nagano Prefecture were used to create a morphometric protection index red relief image map (MPI-RRIM) devised by Kaneda and Chiba (2019). Stereopaired MPI-RRIMs were used to interpret scarplets, including DGSD features and small active faults. Scarplet was classified into uphill-facing scarp and downhill-facing scarp. GIS analysis was conducted based on the results of geomorphic interpretation.
A total of 3841 scarplets, including 3593 uphill-facing scarps and 248 downhill-facing scarps were identified as a result of geomorphic interpretation. Numerous uphill-facing scarps parallel to ridge were identified, and most of them are considered to be DGSD features. GIS analysis indicates that the distribution of scarplets is more related to geomorphological features such as elevation and slope than to geology. In particular, the index of ridgeness, which indicates whether the topography is a ridge or valley, indicates that many DGSD features are located on ridge. This index is the best indication of where DGSD features developed.
The distribution areas of scarplets were mostly consistent with that of landslides. For example, in Omachi City, Nagano Prefecture, east-falling uphill-facing scarps were identified south of the Karagemi and Aigawa landslides (Ueki, 2001), extending about 5 km from north to south. The geology of this area is called the Omine Belt (Kosaka, 1980), and its geological structure is east dipping. The geological map shows that the location of the bedding plane and the uphill-facing scarps are mostly consistent, suggesting that the uphill-facing scarps were formed by flexural slip, and some of them have already developed into large-scale landslides. These uphill-facing scarps are also considered important for predicting landslide occurrence.
In addition, the distribution, slip style, and subsurface geometry of active faults may be related to the formation of scarplets. The strike of scarplets was random in areas where active faults are not distributed, but tended to mostly consistent with the strike of active faults near reverse faults. The areas of surface deformation inferred from the subsurface geometry of active faults also tended to consistent with the areas where scarplets are frequently distributed.
In conclusion, the distribution of DGSD features was identified in Saigawa Hills and Chikuma Mountains. The distribution of scarplets showed a high correlation with geomorphological features and may also be related to landslides and active faults. However, since there are still few data for generalization, it is hoped that the distribution of DGSD features in other regions will be identified in more detail.