Appraisal of active tectonics in Karangsambung Amphitheater: Insights from DEM-derived geomorphic indices and geological data

Abstract

The morphology of the Karangsambung area shows a unique form, namely the morphology of the amphitheater. This area results from the complexity of tectonic, erosion, and depositional processes. The active tectonics in this region greatly influence the drainage system and geomorphic expression. The study area provides evidence of subduction in Java. It is an ideal natural laboratory for studying evidence of tectonic activity due to the subduction of the Indo-Australian plate with the Eurasian plate during the Cretaceous period. We evaluated active tectonics using the DEM to assess the characteristics of the geomorphic index. The results obtained from these indices were combined to produce an index of relative active tectonics (IRAT) using GIS. The average of the seven geomorphic indices measured was used to evaluate the distribution of relative tectonic activity in the study area. We defined four classes to determine the relative level of tectonic activity: class 1: very high (1.0 ≤ IRAT < 1.5); class 2: high (1.5 ≥ IRAT < 2); grade 3: moderate (2 ≥ IRAT < 2.5); and grade 4: low (2.5 ≥ IRAT). The results show that the study area was strongly deformed and was influenced by tectonic activity. Landsat imagery, DEM, and field observations also proved the presence of active tectonics in the form of uplift accompanied by high vertical erosion forming pointed hills with narrow valleys, the exposure of Cretaceous-aged rocks, amphitheater morphology, and the uplift of river terraces. The indicative IRAT values were consistent with the relative uplift levels, landforms, and geology.