Coastal areas concentrate a large portion of the country’s population around urban areas, which in subduction zones commonly are affected by drastic tectonic processes, such as the damage earthquakes have registered in recent decades. The seismic cycle of large earthquakes primarily controls changes in the coastal surface level in these zones. Therefore, quantifying temporal and spatial variations in land level after recent earthquakes is essential to understand shoreline variations better, and to assess their impacts on coastal urban areas. Here, we measure the coastal subsidence in central Chile using a multi-temporal differential interferometric synthetic aperture radar (MT-InSAR). This geographic zone corresponds to the northern limit of the 2010 Maule earthquake (Mw 8.8) rupture, an area affected by an aftershock of magnitude Mw 6.8 in 2019. The study is based on the exploitation of big data from SAR images of Sentinel-1 for comparison with data from continuous GNSS stations. We analyzed a coastline of ~300 km by SAR interferometry that provided high-resolution ground motion rates from between 2018 and 2021. Our results showed a wide range of subsidence rates at different scales, of analyses on a regional scale, and identified the area of subsidence on an urban scale. We identified an anomalous zone of subsidence of ~50 km, with a displacement <−20 mm/year. We discuss these results in the context of the impact of recent earthquakes and analyze the consequences of coastal subsidence. Our results allow us to identify stability in urban areas and quantify the vertical movement of the coast along the entire seismic cycle, in addition to the vertical movement of coast lands. Our results have implications for the planning of coastal infrastructure along subduction coasts in Chile.

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.