## 4 Results
### Main Subsidence Areas Combined with Land Reclamation and Land Use Planning information  
According to the previous studies, ground subsidence is induced by primary consolidation and secondary compression of the clay beneath the reclamation [9; 44], and the ground subsidence on Dadeng Island is closely correlated to the completion time of land reclamation [8]. Therefore, we combined historical land reclamation with land use planning to analyze the main subsiding areas on Dadeng Island. The InSAR measurements of regions A, B, and C in Figure 6a are shown in Figures 7-9, respectively. The base map is based on the land use planning of Dadeng Island (see Figure 2). And the dashed lines present boundaries of historical land reclamation (see Figure 3). Figure 8: Mean subsidence velocity profiles of A-A\({}^{\prime}\) and B-B\({}^{\prime}\) in the runways of Xiamen New Airport. Figure 7: Annual subsidence in Xiamen New Airport (Region A in Figure 6a). Figure 7 presents different spatial subsidence patterns for the region A (will be built as XXNA), which was reclaimed between 2014 to 2017. The significant spatial subsidence patterns were observed in reclaimed land of this region are non-uniform. The maximum subsidence occurred close to the Apron and Runway B in the east of this region with a maximum subsidence rate of 192 mm/year. Combined with historical land reclamation, we found two boundaries of reclaimed land (see the red dashed line and the yellow dashed line in Figure 7) in the region. It indicates that there is a correlation between subsidence and historical land reclamation, i.e., the remarkable subsidence occurred inside the red dashed line and the yellow dashed line, which means that the most significant subsidence was reclaimed in 2014 to 2017. Except for these regions, clear subsidence can also be observed in the west of Runway A, Terminal, Airport Repair Area, and Airport North Road. As the runways in the airport are the infrastructures that require an extremely stable surface [28], two profiles along the runways were selected to reveal the spatial characteristics of subsidence at XXNA. Profile locations are shown in Figure 7 (i.e., A-A' and B-B'), and the mean subsidence rate along the runways are shown in Figure 8. We can clearly see that there has been obvious significant non-uniform subsidence along profiles A-A' and B-B'. The maximum mean subsidence rate in Runway B can reach 84 mm/year, which is more severe than Runway A (with subsidence of 30 mm/year). It means that the subsidence is uneven along runways and poses a great threat to the safety of aircrafts. To understand the non-uniform subsidence at XXNA, we combined the subsidence with land reclamation history. We marked different land reclamation periods with blue, yellow, and red colors, which indicate the reclamation before 2013, 2013 to 2015, and after 2015. We can see that the subsidence profile curve changes rapidly in the boundary of different reclamation periods. Different reclamation periods mean the land has different physical properties, resulting in different level of subsidence. Figures 9 and 10 present detailed spatial subsidence patterns in region B (Qiaotou) and region C (Dengqi), respectively. For Qiaotou area, the most remarkable subsidence reaches 169 mm/year occurred in the northeast of this region, where the land was reclaimed in 2019 and will be used as retail commercial land and residential land. And for Dengqi, the subsidence reaches 156 mm/year in the center region, which was reclaimed in 2017 and will be used as retail commercial land, commercial and financial land. It should be noted that there will be a metro built in Qiaotou and Dengqi. Slight subsidence was observed near Dadeng Station in Qiaotou (see Figure 9), while the Shuanghu Station in Dengqi (see Figure 10) has significant subsidence. In addition, the observed subsidence in Qiaotou will affect the Xi East Road and Yang Tang Road (see solid white lines in Figure 9) and in Dengqi, the subsidence will affect Yingbing Road and Airport Hightway (see Figure 10).