Application of LTFGF and PLAAF for Topographic Characteristics and Activity Assessment: Case Studies of Wuhe and Tsaoling

Abstract

Taiwan’s convergence of active tectonic plates, heavy rainfall, and fragile geology leads to frequent landslides and persistent slope instability, further aggravated by extreme climate events. To enhance landslide susceptibility assessment and support risk management, this study systematically evaluates 2,500 potential large-scale landslides identified by the Central Geological Survey and Mineral Management Center. The Landslide Topographic Feature Grading Form (LTFGF) was developed to score topographic indicators such as scarps, sliding mass, lateral boundaries, toe morphology, and erosion conditions, classifying 1,566 sites into Grades A–D. Thirty-five representative sites, including Wuhe and Tsaoling, were further assessed using the Potential Large-scale Landslide Activity Assessment Form (PLAAF), which integrates failure mechanism interpretation, adverse stability features, historical bare area ratios, and displacement ratios (d/L). Statistical analysis shows Grades A + B represent 7.7% of sites, with LTFGF and PLAAF scores exhibiting a strong positive correlation (r = 0.706). Wuhe exhibits RS+TC composite failure mechanisms with localized toe cutting and secondary scarps, scoring 80 (Grade B) in LTFGF and 68 in PLAAF (high activity). Tsaoling shows PS+TC mechanisms, extensive scarp exposure, and significant historical landslide activity (126 records), achieving the highest PLAAF score of 80. Results confirm that the combined LTFGF–PLAAF framework effectively identifies high-risk landslides, prioritizes monitoring targets, and supports decision-making for resource allocation and long-term disaster prevention planning.