Three decades of coastal subsidence in the slow-moving Nice C?te d'Azur Airport area (France) revealed by InSAR (interferometric synthetic-aperture radar): insights into the deformation mechanism

Coastal areas can be tremendously biodiverse and host a substantial part of the world's population and critical infrastructure. However, there are often fragile environments that face various hazards such as flooding, coastal erosion, land salinization or pollution, earthquake-induced land motion, or anthropogenic processes. In this article, we investigate the stability of the Nice Cote d'Azur Airport, which has been built on reclaimed land in the Var River delta (French Riviera, France). This infrastructure, as well as the ongoing subsidence of the airport runways, has been a permanent concern since the partial collapse of the platform in 1979. Here, we used the full archive of ESA SAR (synthetic-aperture radar) images from 1992 to 2020 to comprehensively monitor the dynamics of the airport subsidence. We found that the maximum downward motion rate has been slowing down from 16 mm yr - 1 in the 1990s to 8 mm yr - 1 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 of the platform to better understand the motion of coastal land, which will ultimately help evaluate and reduce associated hazards.