## 5 Discussion  
### Interpretation of Deformations and Geophysical Modelling  
In order to quantitatively interpret the deformation at Ulsan, we defined a total of 14 units over the major InSAR observations considering geological contexts and the deformation characteristics represented in Figure 6 and Table 4. The first possible assumption on the categorized deformation patterns was that the main deformation in the Ulsan area was induced by the Ulsan fault and its interactions with the surrounding geological units. Together with the analyses of ongoing deformations, we investigated the influences of the two recent major earthquakes using the observations of horizontal and vertical deformation time series shown in Figures 8 and 9. It is clear that none of the units showed a noticeable footprint from the two earthquakes. Thus, we concluded that the 2016 and 2017 earthquakes were not coupled with the deformation sources in the Ulsan local area. Note that a significant deformation change occurred around February to March 2017, which we surmise to be a PS time series processing blunder because we did not identify any seismic activity or significant water vapor distribution as an error source. The interpretation is as follows. The southern Korean peninsula in the 2017 spring season had one of the worst droughts. The record in our WOLS, ULSN GPS Precipitation Water Vapor (PWV) also showed 1-2 mm values in high contrast to the mean spring PWV 10-12 mm in 2016 and 2017 as well as 70-80 mm for the summer season PWV. As the master image of the ascending time series was assigned to February 2017, the tropospheric phase delays around the InSAR image pairs of winter to spring 2017 are considerable low compared to the other pairs. Therefore, InSAR APS in the winter to spring 2017 term behaved like the nonsteady component proposed by [PERSON] et al. [53]; thus, it is difficult to address, especially with the linear APS modelling that is normally implemented [54] in PS routines, considering that the tropospheric error by such extreme change on the temporal weather condition might cause different APS patterns from topography correlated components which is better studied [55]. Fortunately, it did not impair the overall quality of the DInSAR analysis deformation because the blunder only constituted a small portion of the time series observation. The solution is to introduce presuppression of APS via an atmospheric model combined with time series analyses as shown in [PERSON] et al. [56] and [PERSON] et al. [57], if high-resolution weather modelling is feasible. The other issue to be addressed is whether the observed defamation originated by genuine fault migrations or the remnants of InSAR processing errors. It should be noted that the Ulsan fault has been proven to be active by multiple geological surveys [30; 32], compared to the Yangsan fault represented in Unit 6. Thus, the only problem is confirmation of the Ulsan fault line's activeness up to 20 mm/year as identified by InSAR time series analysis. The possibility that the InSAR phase difference around fault lines (P1 and P3) originated from error elements was refuted as follows. First, the error elements by base DEM and/or atmospheric effects should be removed by PS time series algorithms. Although there is a minor effect of the unresolved error components, it can't produce the deformation patterns in both ascending and descending modes that fit exactly with our active Ulsan fault scenario. Although PS time series algorithms cannot effectively address orbital components, a candidate of the false surface deformation source, as stated in some studies [58; 59], the orbital error is usually represented by a tilt shape [60; 61] in InSAR time series output. Therefore, it does not fit with the observed deformation pattern around the Ulsan fault line.