## 3 Methodology
### Extraction of the LOS and Azimuth Coseismic Deformation Field  
The previous study [22] used the conventional DInSAR method based on four images pairs of ALOS-2 and Sentinel-1A to extract the LOS deformation field. The same procedures were performed step by step. We used the Precise Orbit Ephemerides for all images acquired. A digital elevation model (DEM) derived from the Shuttle Radar Topography Mission (SRTM) with 3 arcsec resolution [31] was used to remove the topographic effects from interferograms. The DEM data of the study area is depicted as a shaded relief map in Figure 1. In order to reduce the influence of noise, the method of Goldstein [32] is used to filter interferograms. Then, for avoiding the accuracy loss caused by orbit error and correcting the orbit and phase shift, refinement and re-flattening is processed by selecting enough and high coherence reference points, which distribute uniformly and far from the deformation field in the interferograms. And phase unwrapping was processed by the minimum-cost flow (MCF) method [33]. In addition, we performed the range split-spectrum method to ALOS-2 ScanSAR interferogram to estimate the differential ionospheric phase [30]. Figure 2 shows the LOS coseismic deformation fields measured by the DInSAR method based on four interferometric pairs. It has two clear deformation lobes (here refers to lobe G and H) which divided by an NNW trending bound (see black line AB in Figure 2). As the Figure 2a,c shows, the maximum value of uplift in lobe G and subsidence in lobe H are approximately 100 cm and \(-\)30 cm, respectively; and Figure 2b,d shows the maximum value of uplift in lobe G and subsidence in lobe H are approximately 50 cm and \(-\)50 cm, respectively. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**SAR Sensor** & **Master Image** & **Slave Image** & **Observation Mode** & \(B_{\perp}\) **(m)** & \(B_{\overline{\text{\text{T}}}}\) **(days)** & **Orbit** \\ \hline \multirow{2}{*}{ALOS-2} & 20160809 & 2017114 & ScanSAR & \(-\)70 m & 462 & Ascending \\  & 20171004 & 20171115 & ScanSAR & \(+\)160 m & 42 & Descending \\ \hline \multirow{2}{*}{Sentinel-1A} & 20171111 & 20171123 & IW Tops mode & \(-\)33.6 m & 12 & Ascending \\  & 20171107 & 20171119 & IW Tops mode & 15.3 & 12 & Descending \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The parameters of selected SAR images. To extract the AT (along-track) deformation fields, we performed the conventional MAI method based on two interferometric pairs of ALOS-2 (only one burst will be used). The achieved accuracy of the AT deformation is approximately 8 cm with coherence of 0.6. Around the epicenter, the coherence is high enough. Furthermore, the coherence can be further enhanced by multilooking and filtering processes. It is suitable to use this method to measure the AT deformation of this earthquake. Four SLC images, composed of both forward- and backward-looing SLC images from master and slave SAR data of ALOS-2, were generated by controlling the Doppler Centroids and processing bandwidth (PBW) for sub-aperture images according to the MAI processor [9; 10; 11; 12]. The conventional MAI processing for the SLC data includes azimuth common-band filtering between the master and slave SLC images and beam-splitting for the purpose of dividing forward- and backward-looking spectrum. During the MAI processing, we apply thirteen-looks and two-looks in the azimuth and range directions, respectively, to reduce the phase noise in the interferograms. The band-width of common band filtering is 482.39 Hz and 731.23 Hz, two forward-looking and two backward-looking images were separated out from interferometric pairs of ALOS-2, firstly. Subsequently, both forward- and backward-looking interferograms were generated independently. Finally, MAI interferograms were obtained through dual-interferometry between forward- and backward-looking interferograms.