Study of geothermal manifestations based on land surface temperature and fault fracture density analysis in the Mount Slamet Area, Central Java

Remote sensing has been increasingly applied to geothermal reconnaissance due to its cost-effectiveness and regional coverage; however, its effectiveness in detecting surface geothermal manifestations in densely vegetated volcanic environments remains uncertain. This study addresses this gap by evaluating the capabilities and limitations of Landsat-8–derived Land Surface Temperature (LST) and Fault Fracture Density (FFD) analyses for identifying geothermal manifestations in the Mount Slamet geothermal system in Central Java. LST was derived from Landsat-8 thermal infrared data, while permeable zones were delineated using FFD analysis based on Digital Terrain Model (DTM)–derived lineaments. The LST analysis identified 33 surface hot spots with temperatures ranging from 30.6–34.0 °C, primarily associated with open land, urban areas, and the summit crater, but none coincided with known geothermal manifestations. In contrast, FFD analysis delineated five very high-permeability zones with FFD values ranging from 1.413 to 2.309 km/km2, predominantly on the western flank of Mount Slamet. Of the eight mapped geothermal manifestations, seven occur within very high FFD zones and one within a medium-permeability zone, indicating a strong structural control on manifestation occurrence. The absence of geothermal anomalies in the LST results highlights the limitations of medium-resolution thermal data in vegetated and high-relief volcanic terrains, where pixel mixing, vegetation cover, and elevation effects obscure geothermal thermal signals. Nevertheless, the combined LST–FFD approach remains a meaningful screening tool, distinguishing non-geothermal thermal anomalies and emphasizing structural permeability as a more reliable indicator of the distribution of geothermal manifestations. This study demonstrates that FFD analysis provides more robust insights than LST alone for preliminary geothermal assessment in tropical volcanic settings.