CLAY MINERAL VARIATIONS IN AN ACTIVE FAULT ZONE AND THEIR IMPACT ON LANDSLIDES
Keywords:Cianjur-Garut region, Cilaki river, Clay mineral, Fault zone, Landslide
Clay minerals are a common material of the earth, which are formed in soil and rock. This research aims to investigate variations in the characteristics and physical properties of clay minerals in an active fault zone and assess their impact on landslide occurrence in the southern part of the Cianjur-Garut region. The morphotectonic approach is applied as an indicator of the location of the active fault zone. The Cilaki river valley has a unique wine glass-like shape, indicating active fault control on its formation. Tertiary sedimentary rocks and Quaternary volcanic deposits compose the strata in this area. Rock samples were collected from the active fault zone. Petrographic analysis was carried out on these samples, including optical microscopic (OM), Scanning Electron Microscopy (SEM), and X-Ray Diffraction (XRD). Six rock samples have clay mineral of about 32% to 60% and are characterized by the presence of saponite a mineral of the Smectite group. Illite and kaolin were not indicated in XRD analysis but were recognize by SEM analysis. The clay assemblages in fault zone are the result of gradual mineral alteration processes under low temperature and pressure. Smectite is the group of clay minerals with the highest swelling index. High swelling clays tend to have low strength which is very relevant in areas vulnerable to landslide occurrence. The analysis of variability and physical properties of clay minerals can be used to know characteristics of soils and their impact on landslides.