Investigation the impact of active fault-induced vertical displacement on land subsidence rates using GNSS CORS data in northern coastal cities of Central Java, Indonesia

Land subsidence is commonly observed along the coastal regions of Java Island, particularly in the northern part of Central Java. This phenomenon often contributes to the intensification of coastal flooding. Subsidence rates are influenced by multiple factors, which might also relate to tectonic movements associated with active fault structures. In this study, we investigate the contribution of active fault-induced deformation to land subsidence in northern coastal cities of Central Java. We modeled the surface displacements resulting from active faults using the elastic half-space approach. We analyzed geodetic data from Continuously Operating Reference Stations (CORS) situated along the northern coast, covering the period from 2015 to 2019. The analysis revealed notable land subsidence at Pekalongan and Tegal, with annual rates of −122.54 mm/year and −11.04 mm/year, respectively. Statistical testing of annual displacement rates indicated that fault-induced surface movement was significant only at Semarang City. Conversely, the displacement observed at CORS with pronounced subsidence was not statistically significant. These findings suggest that active fault-related displacements do not play a dominant role in driving land subsidence in the study area. Instead, the magnitude of their influence appears to depend on the proximity of the faults to observation sites and the relative level of earthquake potential of the fault.