## 5 Discussion
### Land Subsidence Caused by Land Reclamation  
Laizhou Bay and southeast coastal of Shandong peninsula is suitable for land reclamation for its sandy and bedrock composition. According to the InSAR measurements in Figures 2, 10 and 11, several remarkable subsidence regions associated with land reclamation are successfully detected in Longkou Port, Jiaozhou Bay and several south coastal areas such as Regions G, J, K and the subsidence zones marked by white rectangles in Figure 10c. To reveal the deformation patterns and temporal evolution, some typical deformation regions (Regions G, J and K) of land reclamation are chosen and shown enlarged as Figures 11-13. Longkou Port (i.e., Region G), located in the south of Longkou Bay with an area of 50.41 km\({}^{2}\), is mainly composed of seven small islands, which will be the first large artificial islands in China. Figure 11a shows the deformation rate map in the LOS direction in Longkou city from October 2016 to July 2019. To study the temporal deformation evolution, four feature points over this area are extracted and given in Figure 11b. Land subsidence in Regions G-1 and G-2 is mainly associated with land reclamation and Region G-3 is associated with farm irrigation. Two groups of Google Earth images over Regions G-1 and G-2 (Figure 11c-f), acquired in January 2016 and September 2019, respectively, show the detailed changes in the reclamation process. Compared with Figure 11a,c,f, deformation coverage in Regions G-1 and G-2 is highly consistent with the surface reclamation. The cumulative deformation in p1 and p2 reached around 50 mm, and slowed down in July 2018, finally turning into a relatively mild subsidence pattern. Maximum cumulative deformations were observed at  
Figure 10: Deformation rate and time series at the selected feature points. The black solid lines mark the aquaculture fields. The white polygons in (**c**) indicate the subsidence regions caused by land reclamation. (**b,d**) The time series deformation measurements at two locations are shown in (**a–c**). p3 and p4, with a magnitude of about 100 mm, while the time series of p3 also turned into a mild subsidence trend from September 2018, which suggested that the reclaimed land entered a long-term slow compression stage. Land subsidence at p4 presents a linear land subsidence tendency with the cumulative deformation in the LOS direction larger than 100 mm. Figure 11: Deformation analyses at Longkou Port. (**a**) the deformation rate at Longkou Port (area G), (**b**) the time series at feature points p1, p2, p3 and p4, marked in (**a**), (**c**,**d**) and (**e**,**f**) are the optical images for Regions G-1 and G-2, respectively, acquired in January 2016 and September 2019. Figure 12: Deformation analysis at Region J. (**a**) the deformation rate map; (**b**,**c**) the Google Earth images acquired in January 2015 and September 2019, respectively; (**d**–**f**) the deformation time series at feature points p1, p2 and p3, marked in (**a**). Additionally, regions J and K (Figure 2) are also detected as showing land subsidence caused by soil compaction over reclaimed land. The enlarged land subsidence maps are shown in Figures 12 and 13, respectively. Compared with the Google Earth images, acquired in January 2015 and September 2019, respectively (Figure 12b,c and Figure 13b,c), the land subsidence areas in Figures 12a and 13a highly correspond to the regions with reclamation activities. In order to further investigate the temporal evolution of land subsidence after reclamation, three typical points for Region J and two for Region K (Figures 12a and 13a), are selected and shown in Figures 12d-f and 13d,e. Time series deformation measurements at three feature points in Region J present nonlinear deformation characteristics. We used cubic polynomial function (\(y=a0+a1*x+a2*x^{2}+a3*x^{3}\)) to fit the time series at feature points. The subsidence at p2 slowed down in April 2018 and then turned into a relatively mild subsidence pattern with an average deformation rate varying from 17.2 mm/a to 2.8 mm/a.