Mapping topographic instability hazard potentials based on synthetic aperture radar (SAR) dual-orbit images at Mt. Merapi, Indonesia
Mudju Silfara Rifu Rinamu*, Asep Saepuloh

Faculty of Earth Sciences and Technology, Bandung Institute of Technology, Jl. Ganesha No. 10, Bandung, West Java, Indonesia.

*Corresponding author: Silfara.rr[at]gmail.com

Abstract

Since 2018, Mt. Merapi has consistently experienced eruptions, bringing new materials from the earth is interior to the surface, forming new volcanic product layers. This has significantly increased soil fertility, attracting people to settle in the surrounding areas, despite the area is high disaster risk. Mt. Merapi is known as the most active volcano with complex geological structures, making it susceptible to various natural disasters, including landslides. Geological lineaments, which represent fault lines and fractures, serve as weak zones that may increase the risk of ground movement triggered by slope instability. Analyzing geological lineaments aids in mapping areas prone to landslides. Lineaments are related oftenly to landslide phenomena, particularly in active volcanic regions such as Mt. Merapi, where the vulnerability to ground deformation is high. Soil along these lineaments may lose cohesion, making it more prone to movement, especially when triggered by volcanic activity, heavy rainfall, or seismic events. Thus, understanding and mapping geological lineaments is crucial for mitigating landslide risk in the Mt. Merapi region. This study aims to spatially analyze weak zones prone to landslides, particularly in areas with steep topography and unstable slopes, by integrating lineament density using the modified segment tracing algorithm (mSTA) method with the density of landslide occurrences from 2018 to 2023. The mSTA method automatically detect lineaments on dual-orbit synthetic aperture radar (SAR) images from Sentinel-1A satellite. Accordingly, we have obtained, about 1,100 and 1,148 lineaments for area about 88 km2 in the ascending and descending orbit modes, respectively. Integrating the landslide occurences, we have quantified the detected lineaments by calculating their density. We have obtained that the 63 landslide occurences from 2018 to 2023 located mainly at medium to high anomaly of the lineament frequency density (Lf). In addition, we have also obtained that the dominant lineament orientation was W-E indicating as the main control to the landslide. The W-E directions agreed to the geological structures of Mt. Merapi and direct field observations of geomorphological features. The results of this study can be used to mitigate landslide hazards in a large area.

Keywords: Mt. Merapi, mSTA, weak zone, landslides, Sentinel-1 SAR.

Topic: Interdisciplinary Earth Science and Technology