Deformation pattern of a creeping slope revealed by continuous GNSS monitoring in northern Taiwan

Movement of a dip slope in sedimentary rock in northern Taiwan has led to the development of ground cracks and persistent deformation of local buildings and facilities on the slope surface. Geomorphological and geological investigations have been conducted to reveal its probable failure mechanism. To monitor and understand the movement patterns of sliding blocks, 12 low-cost and 2 Trimble continuous Global Navigation Satellite System (i.e., GNSS) stations were installed in 2016. The 6-year surficial surveying results, presented as a time series of displacements and velocity fields, are revealed by the GNSS data. The continuous and automatic recording results, obtained at a high sample rate, reveal distinct movement patterns of the sliding blocks in relation to rainfall duration and amount. Additionally, the velocity field shows that the surficial movement velocity varies in different parts of the slope mass, possibly reflecting the underground geometry of the sliding surface. Finally, the continuous GNSS data show an average velocity of 1.13–1.96 × 10⁻⁶ mm/s, classified as “Very slow” on the global velocity scale of landslides, which may be related to weak fluvial erosion at the toe and dilation in northern Taiwan. Additionally, surficial traces of a potential fault related to regional tectonic processes within the dip slope can be inferred from the GNSS data in this study.