# Spatio-Temporal Distribution of Ground Deformation Due to 2018 Lombok Earthquake Series
## 2 Materials and Methods  
This study was carried out on Lombok Island, Indonesia using Sentinel 1 satellite imageries. Indeed, the application of Sentinel 1 has been used worldwide for deformation analysis mainly due to subsidence in metropolitan areas [29; 30; 31; 32; 33; 34], volcanic activity [35; 36; 37; 38; 39], landslides [29; 40; 41; 42; 43; 44], and single-event earthquakes [17; 18; 19; 20; 21; 22]. In order to study the earthquake series in Lombok, the methodology of this research focused on a DInSAR creation in SNAP using Two Pass Interferometry method based on 2 radar images with different recording times (Figure 3). One image acted as the master image and another image as the slave image (Table 1). These two images were paired to form an interferogram to produce a deformation map with uplift or subsidence values. Data selection depended on the mode and intensity of the images which was related to image polarization [2; 5]. The first stage of radar processing was TOPSAR Split, selecting bursts from Sentinel 1 radar imagery in the study area. There are three types of modes in each image obtained from the TOPSAR technique, i.e., IW1, IW2, and IW3. The choice of mode type depended on the research area. All modes in each image generally had different observation areas. In this study, we chose three bursts in IW3 to observe the research area. Perpendicular baseline affects the signal  
Figure 2: Geology map of Lombok Island (adapted from [27]). Back Arc Thrust is located next to the northern shore [1]. Photos of building structural damage were taken at alluvial area of Mataram City. phase for deformation detection. Too short of a baseline reduced the sensitivity of signal phase, while too long of a baseline produced noise resulting in phase errors [45]. The intensity of the signal was checked on one type of twin vertical polarization (VV). VV polarization was chosen because it proposed the most ideal observation of the deformation of the earth's surface since the angle of signal transmission and reception focused on vertical observations. Thus, the intensity of VV polarization was greater than that of VH and HV polarization. We also applied Orbit File in order to conduct corrections to each image. Sentinel Precise Orbits contained information about satellite positions during SAR acquisition. Precise Orbit Ephemerides (POE) covered approximately 28 h and contained orbit state vectors at fixed time steps with 10 s intervals. This orbit file was generated per day and sent within 20 days of data acquisition. It was important to unveil the information on the data type, acquisition date, position, and orbit of the images during data acquisition. These two images were selected to be combined in the image coregistration process to unify two unrelated data into a pair of data, i.e., master and slave images. The match \begin{table}
\begin{tabular}{l l l c} \hline \hline \multicolumn{1}{c}{**Earthquake**} & \multicolumn{1}{c}{**Images**} & \multicolumn{1}{c}{**Role**} & \multicolumn{1}{c}{**Perpendicular**} \\  & & & **Baseline (m)** \\ \hline
29 July 2018 & Sentinel 1A (27 July 2018) & Master & \(-4\) \\  & Sentinel 1B (2 August 2018) & Slave & \\ \hline
5 August 2018 & Sentinel 1B (2 August 2018) & Master & \(-22\) \\  & Sentinel 1A (8 August 2018) & Slave & \\ \hline
9 August 2018 & Sentinel 1A (8 August 2018) & Master & \(27\) \\  & Sentinel 1B (14 August 2018) & Slave & \\ \hline
19 August 2018 & Sentinel 1B (14 August 2018) & Master & \(-14\) \\  & Sentinel 1A (20 August 2018) & Slave & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: List of Sentinel 1 Satellite imageries corresponding to earthquakes on 29 July 2018, 5 August 2018, 9 August 2018, and 19 August 2018. Figure 3: Methodology for this study. between the two images could be observed from coherence value once the interferogram is formed. The entire pixel size of the slave image would be matched the pixel size of the master image. The image coregistration process would read two data.