## 3 Results
### Earthquake-Induced Ground Deformation Mapping over Site B--Pohang City  
Pre- and co-seismic interferometric pairs were processed to detect the surface changes related to the 15 November 2017 earthquake. Figure 11 presents the pre- and co-seismic coherence maps. It is observed that the overall co-seismic coherence is less than the pre-seismic coherence in most urban areas located in the west, southeast, and southern regions of the epicenter. This coherence degradation indicates the damaged buildings and the inherent differential settlement caused by seismic ground motion and associated liquefaction. Meanwhile, liquefaction phenomena have been reported in the northern and western parts of the epicenter, which is consistent with the observed coherence reduction.  
Figure 11: Interferometric coherence map for **(a)** pre-seismic pair and **(b)** co-seismic pair.  
Figure 10: Comparison of elevation profile between InSAR-DEM and SRTM-DEM. **(a)** Section A-A\({}^{\prime}\) and **(b)** section B-B\({}^{\prime}\).  
Figure 9: The maps shown were resampled to the pixel resolution of the InSAR-derived result. **(a)** SRTM DEM and **(b)** elevation difference.  
Figure 12 displays the coherence difference map overlaid with the reported liquefaction features, building damages, and ground cracks [41; 52; 53]. The scale of coherence difference is between \(-1\) and \(1\). The negative coherence difference (warm color) shows areas that were modified (i.e., by natural processes) before the event but were not modified during the co-seismic interval. The positive coherence difference (cold color) represents areas that had surface changes during the co-seismic interval but little to no change before the event. In the map, positive coherence difference is found mostly in the southeastern part of the AOI, which is associated with damaged buildings in urban areas. Whereas, negative coherence difference is placed dominantly in the northern region. Most areas in this northern part from the epicenter are arable land where little to no liquefaction features were reported [54].  
Figure 13 shows the co-seismic differential interferogram and the corresponding ground deformation, which were obtained by using the descending track SAR data. The interferometric fringe delineates the surface displacement in the direction of the radar's line-of-sight (LOS) in a unit of the radar half-wavelength (i.e., one fringe cycle equals 2.8 cm for Sentinel-1). The interferogram clearly reveals visible co-seismic deformation along the radar LOS. In the displacement map, uplift and subsidence areas were distinguished which caused damage to neighboring buildings. Since Sentinel-1B acquires images in a right-looking mode, positive values indicate uplift and easting, and the negative values suggest subsidence and westing. The reference area, which was assumed not to be affected by the seismic ground motion, is marked on the map and has a coherence value close to 1. The areas (or pixels) with the coherence value less than 0.30 were masked out from the map. Displacement values of more than 5 cm (uplift) from the vicinity of the epicenter were reported.  
Figure 12: Coherence difference map. The insets of the figure show a smaller area encircled in black to highlight the detected damaged buildings using the coherence difference analysis method.