## 5 Discussion
### Interpretation of Deformations and Geophysical Modelling
The concurrent InSAR observation by ascending and descending modes is very useful in inferring orbital error components because the orbital error component cannot produce proper deformation patterns that fit with the modeled deformation source in two observation modes, simultaneously. Thus, our results in ascending and descending observations fully eradicated the possibility of error terms around the Ulsan fault. \begin{table}
\begin{tabular}{l l l l} \hline \hline  & **Unit** & **Description** & **Major Characteristics** \\ \hline Unit 1 & P1 and P3 & Units involving the Ulsan fault & Strong W–E deformation. Subsidence in directly connected units such as P1 and P3. \\ \hline Unit 2 & P7 and P8 & Translation areas between class 1 and class 4 & String E–W deformations and some uplift. Deformations in P8 is more obvious. \\ \hline Unit 3 & P4 and P5 & Translation areas between class 1 and class 6 & Weak W–E deformation and uplift. \\ \hline Unit 4 & P11, P14 and P9 & Sedimentary plains or reclaimed land & Weak E–W deformation and uplift. \\ \hline Unit 5 & P2 and P12 & Units around costal lines & Independent from tectonic faults but some deformation in coastal cutting area. \\ \hline Unit 6 & P6 & Unit involving the Yangsan fault & Very stable and weak deformation. \\ \hline Unit 7 & P13 and P10 & Units mainly under the influence of local deformation sources & Irregular but strong deformation patterns according to the characteristics of local deformation sources. For instance, P10 and P13 were activated by ground condensation from heavy construction, which caused strong subsidence. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Categorized deformation units and their characteristics. Figure 8: Time series observations of horizontal displacements in unit (**a**) P1, (**b**) P3, (**c**) P11, (**d**) P9, (**e**) P10, and (**f**) P6. Two vertical dotted lines represent the 2016 Gyeounju (12 September) and 2017 Pohang (15 November) earthquakes. No units show a significant change during the coseismic period. The sudden change February to March 2017 might originate from the coinciding of the master image section and extreme APS value. The task to identify the deformation source from the InSAR observations can be accomplished through modelling of fault perpendicular deformation on certain constraints such as full strike slip fault geometry [62; 63; 64]. However, in the case of the Ulsan fault, any specific constraint on fault migrations is highly unlikely as observed in precedent studies on ground surveys [29; 30; 31; 52]. In these circumstances, we performed a geophysical inversion, employing the Geodetic Bayesian Inversion Software (GBIS) [65] to define more clearly the deformation source and its contributions. This software is capable of deformation source parameter inversion using Markov-chain Monte Carlo methods [66] and the Metropolis-Hastings algorithm [67] even with InSAR observations in a complicated scenario [68]. We assigned the initial parameters of the fault line sets (Table 5) based on the known geometry of the Ulsan fault, and considered two plausible scenarios: (1) the Ulsan fault and its interaction with the surrounding soft ground units is responsible for the deformation pattern in the target area (i.e., the single fault model); and (2) full deformation is induced by the interaction between multiple faults, and thus the fault system could produce a localized deformation in the Ulsan central city area (i.e., the multifault model). The multifault line model, consisting of the Ulsan fault and the fault lines directly crossing Ulsan city area, is less feasible because it unlikely that there are unknown fault lines in the Ulsan central city area, where highly intensive survey works have been constantly conducted for several decades. However, since the multifault model based on Ulsan fault line segmentation has been proposed by recent studies [69] is remains feasible; therefore, we established fault segments along the Ulsan fault line for the multifault model scenario.