Detection of Ground Deformation after the Xinmo Rock Avalanche in Sichuan, China, using 2.5-D Analysis Based on PALSAR-2 InSAR image

The Xinmo rock avalanche in Maoxian, Sichuan Province, China, occurred in June 2017. Three InSAR images were produced from six ALOS-2/PALSAR-2 data observed after the rock avalanche. The PALSAR-2 data, which were observed using the L-band (the wavelength of the microwave is ca. 23 cm), are not significantly affected by vegetation cover, mak-ing them suitable for detecting the deformation of a slope covered with vegetation, especially in humid climates such as the Asian region. 2.5-D analysis, which uses both ascending and descending data, revealed the east–west (EW) and up–down components of deformation in the rock avalanche area. These results indicated that the eastern edge on the west-ern flank (3,060–3,080 m in elevation) of the rock avalanche was deformed up to 5.7 cm (3.2 cm eastward and 4.7 cm downward) for 28 days at the end of 2017. It was estimated that the edge at the 135 m EW width was moved from the land-slide body. However, by focusing on the rock avalanche area for 17 and 28 days, it was found that neither the slope under the bedrock exposure of the main scarp nor the central valley floor of the main scarp was deformed. Furthermore, defor-mation was neither observed in the transportation area (including the east and west scarp areas) nor in the upper depos-its. In the lower deposit area (2,340–2,360 m in elevation), up to 2.0 cm deformation downward was observed for 28 days at the end of 2017. If the bedrock of the rock avalanche is deformed not only in the lower deposits area but also in the main scarp, the transportation area and upper deposits would also be deformed. It is thought that the deformation in the lower deposits was attributed to the compaction of debris deposits, and this inference was supported by downward defor-mation up to 2.8 cm observed for 17 days in the flat deposit area (2,280–2,300 m in elevation) on the right bank of the Songping River.