28 years of coastal subsidence evolution on the slow-moving Nice-Côte d’Azur airport area (France) revealed by InSAR: Insights into the deformation mechanism

Abstract. Coastal areas can be tremendously biodiverse and host as well a substantial part of the world population and many critical infrastructures. However, there are often fragile environments and face various hazards as flooding, coast erosion, land salinization or pollution, earthquake-induced land motions, or anthropogenic processes. In this article, we investigate the stability of the Nice-Côte d’Azur airport that has been built on reclaimed land in the Var river delta (French Riviera, France). This infrastructure is 5 a permanent concern since the partial collapse of the platform in 1979 and the on-going subsidence of the airport runways. Here, we used the full archive of ESA SAR images from 1992 to 2020 to comprehensively monitor the dynamics of the airport subsidence.We find that maximum downward motion rate is slowing down from 16 mm/yr in the 1990s to 8 mm/yr today. However, sediment compaction is still active and an acceleration phase of the continuous creep leading to a potential failure of a part of the platform cannot be excluded. Our study demonstrates the importance of remotely monitoring 10 of the platform to better understand coastal land motions, which will ultimately help evaluate and reduce associated hazards.