Urbanization in Coastal Chilean Cities: Spatial Monitoring and Impact Assessment Using Sentinel Satellites

We integrate Sentinel-1 P-SBAS InSAR (2019–2023), continuous GNSS and Sentinel-2 multitemporal urban-footprint data to characterize surface deformation in three Chilean coastal cities (30–38°S) on contrasting substrates: La Serena, Valparaíso and Concepción. A regional velocity field emerges, modulated by postseismic relaxation of the 2010 Maule and 2015 Illapel earthquakes. After GNSS correction, line-of-sight (LOS) velocities reach −30.5 mm/yr in Concepción, and points with |LOS| > 5 mm/yr are about eight times more frequent in Valparaíso (3.1%) and Concepción (3.3%) than in La Serena (0.4%), independently of point density. Negative velocities concentrate on Quaternary deposits at peripheral expansion fronts, including wetland margins in Concepción, with basement and urban cores stable. By 2020, built-up area on mapped wetlands reached 48, 7 and 3 ha in Concepción, Valparaíso and La Serena, respectively, rising to 60, 7 and 4 ha by 2030 (1.6%, 0.3%, 0.2%). The spatial distribution of deformation is therefore spatially associated with unconsolidated, low-lying substrates rather than with tectonic position, although groundwater extraction cannot be excluded as a contributing mechanism. Substrates of the same type failed in Concepción in 2010; continued expansion onto low-lying wetlands may increase the exposure of the built environment to both slow ground deformation and earthquake-induced ground failure, which warrants further geotechnical assessment.