9:45 AM - 10:00 AM
[HDS11-03] Displacement of the western flank of Mt. Iwaki by InSAR
Keywords:Mt. Iwaki, InSAR, Landslide
Mt. Iwaki is an active volcano located west of the Tsugaru Plain in western Aomori Prefecture. Lava flows, which erupted in the second stage about 200,000 to 30,000 years ago, are distributed on the flank of the west of Mt. Iwaki (e.g., Sasaki, 2015). Moreover, a displacement away from the satellite (about 1 cm/yr) was reported on the western flank of Mt. Iwaki in a nationwide interferometric SAR time series analysis of ALOS-2/PALSAR-2 data by the GSI. Mt. Iwaki has collapsed in the past, and the behavior of such mountain slopes needs to be well monitored. In this study, interferometric SAR analysis using ALOS-2/PALSAR-2 data was performed to clarify the behavior on the western flank of Mt. Iwaki to clarify the causes and mechanisms of this behavior. This presentation discusses the timing of significant displacement and its causes and relationship with topography, as revealed by the analysis.
The analysis results show that significant surface displacement on the western flank of Mt. Iwaki was observed in pairs across the summer of 2022 and was hardly observed during the other periods. The displacement was in the away-from-satellite direction for the Descending right-looking pair and the toward-satellite direction for the Ascending right-looking pair. It was only a few centimeters for both. Therefore, the direction of this displacement is westward (slope), suggesting a landslide displacement. Furthermore, a 2.5D analysis was performed for the 2020-2023 3-year pair, and the estimated displacement was approximately 5 to 7 cm to the west and 1 to 2 cm of subsidence. In August of 2022, heavy rainfall caused nearby rivers to overflow, recording the most significant precipitation since 2014, the observation period of ALOS-2. The fact that the displacement was observed in pairs across the summer of 2022 suggests that extreme rainfall triggered the landslide displacement.
The Active Fault Research Group (1991) indicated the existence of an east-west striking south-falling fault on the western flank of Mt. Iwaki, the Okkomori Fault. The northern end of the displacement detected by this study corresponds well to the lineament of the possible Okkomori fault, suggesting that the fault is a gravity fault formed due to the slope displacement. Based on the geomorphological features, some crack-like landforms were observed on the displaced blocks, suggesting that the progress of the landslide displacement caused the deformations.
We are currently attempting to detect the deformation concentration zone (where the rigidity is lower than the surrounding area) below the landslide displacement area by applying the method used by Doke et al. (2024) for the Hakone volcano. We will also report the results of the analysis in the presentation.
The analysis results show that significant surface displacement on the western flank of Mt. Iwaki was observed in pairs across the summer of 2022 and was hardly observed during the other periods. The displacement was in the away-from-satellite direction for the Descending right-looking pair and the toward-satellite direction for the Ascending right-looking pair. It was only a few centimeters for both. Therefore, the direction of this displacement is westward (slope), suggesting a landslide displacement. Furthermore, a 2.5D analysis was performed for the 2020-2023 3-year pair, and the estimated displacement was approximately 5 to 7 cm to the west and 1 to 2 cm of subsidence. In August of 2022, heavy rainfall caused nearby rivers to overflow, recording the most significant precipitation since 2014, the observation period of ALOS-2. The fact that the displacement was observed in pairs across the summer of 2022 suggests that extreme rainfall triggered the landslide displacement.
The Active Fault Research Group (1991) indicated the existence of an east-west striking south-falling fault on the western flank of Mt. Iwaki, the Okkomori Fault. The northern end of the displacement detected by this study corresponds well to the lineament of the possible Okkomori fault, suggesting that the fault is a gravity fault formed due to the slope displacement. Based on the geomorphological features, some crack-like landforms were observed on the displaced blocks, suggesting that the progress of the landslide displacement caused the deformations.
We are currently attempting to detect the deformation concentration zone (where the rigidity is lower than the surrounding area) below the landslide displacement area by applying the method used by Doke et al. (2024) for the Hakone volcano. We will also report the results of the analysis in the presentation.