Systematic Analysis of Initial Settlement of new Constructions in the Mekong Delta by Coherence Change Detection of Temporary Persistent Scatterers

The Vietnamese Mekong Delta (VMD) has been affected by land subsidence for more than one decade, which is the result of different drivers, including groundwater over-exploitation and natural compaction of holocene layers. The exact share of the contributions is so far unknown. In this work, we systematically study the initial settlement of newly built constructions and built-up areas in two cities in the VMD by incorporating Temporary Persistent Scatterers (TPS) into an existing PS-InSAR approach. We find that the portion of appearing TPS with high initial subsidence rates is larger than the portion of PS and fading TPS with high subsidence rates. We furthermore cluster appearing TPS by their location and appearing date to identify and analyse new constructions and built-up areas and find that they can have really high initial settlement rates which statistically decrease over time. We attribute this signal to the loading-induced initial settlement of constructions which lack a proper foundation. We assume settlement of this kind to contribute noticeably to the measured total subsidence all across the VMD, especially due to the recent high building activity.