## 5 Discussion  
In this section, we discuss the combined SBAS-DInSAR results, taking into account the characteristics of the deformation signals retrieved from the ocean-reclaimed platforms of Shanghai. First, we focus on the detected deformation signals, and we discuss the assumption of negligibility of the east-west component of the surface displacements with respect to the vertical (subsidence/uplift) one. We note that such an assumption is valid in ocean-reclaimed platforms, but it is not true of the overall Shanghai megacity area. Indeed, the southwestern sector of the Shanghai area has recently been claimed to be crossed by a geological fault, the so-called Dachang-Zhoupu fault (see black line in Figure 1). The fault is responsible for appreciable east-west deformation movements in that sector of the city (with a magnitude, however, less than 1 cm/year, with respect to a reference point located in correspondence with the GPS station labeled as SHAO in Figure 1). Such displacements were measured in the 2002-2005 period, through a network of 17 GPS stations (see [68] for the locations of the GPS stations, and their relative movements), and were related to the neotectonic activity of an existing geological fault [68; 69]. Nevertheless, there is no direct evidence that these east-west deformations also extend to the reclaimed areas, located southeast of Shanghai, where it is known that the deformations are dominated by soil compaction mechanisms, which are primarily responsible for vertical movements. For this reason, the additional contributions to settlement, due to fault mechanisms, have been assumed to be negligible in our study. We note that, despite the fact that ASAR/ENVISAT and CSK data have been acquired through ascending and descending passes, they cannot be combined to extrapolate the east-west and vertical (up-down) components of deformations, as they do not span the same period of observation. Furthermore, it is worth highlighting that, for Lingang New City, the deformation is mostly non-linear in time, thus, the simple option to extrapolate a linear rate from ASAR/ENVISAT time series, and to use that value for linking ASAR/ENVISAT and CSK vertical deformation time-series, appears to be unreliable. With respect to the used model in Equation (5), we note that it is derived from laboratory tests aimed at assessing, for instance, the stability and capacity of building foundations. Its fundamental principle is to recreate the conditions that would exist in a full-scale construction by using a model on a reduced scale. Centrifuge model testing provides researchers with simulated data that can improve the understanding of the underlying mechanisms of deformation, allowing the retrieval of experimental data for the verification of numerical models. Of particular interest, due to the peculiar alluvial soil characteristics of Shanghai, is the settlement model found in [40], which permits to analyze ground settlements caused primarily by self-weight consolidation mechanisms. The simplified model in [40] can be derived from the general model described in [46], and those presented in [14], which relate kinematic parameters to soil physical characteristics. At this stage, we discuss the achieved results, by specifically focusing on the ocean-reclaimed area of Lingang New City. As mentioned earlier, the multi-platform time-series combination was performed by searching for the model parameters, as well as the (unknown) bias between the ASAR/ENVISAT and the CSK time-series that best fit the data. Subsequently, we also checked the quality of the nonlinear curve fitting, by calculating the root mean square error (RMSE) of the difference between the (reconstructed) DInSAR-based (vertical) deformation time-series and the obtained best-fit model. The map of the RMSE values is shown in Figure 5b. Looking at Figure 5b, it is evident that the obtained RMSE is, on average, on the order of a few millimeters.