This study proposes a workflow that enables the accurate identification of earthquake-induced damage zones by using coherence image pairs of the Sentinel-1 satellite before and after an earthquake event. The workflow uses interferometric synthetic aperture radar (InSAR) processing to account for coherence variations between coseismic and preseismic image pairs. The coherence difference between two image pairs is useful information to detect specific disasters in a regional-scale area after an earthquake event. To remove background effects such as the atmospheric effect and ordinal surface changes, this study employs the two-step threshold method to develop the coseismic coherence difference (CCD) map for our analyses. Thirty-four Sentinel-1 images between January 2015 and February 2016 were collected to process 30 preseismic image pairs and two coseismic image pairs for assessing multiple types of disasters in Tainan City of southwestern Taiwan, where severe damages were observed after the Meinong earthquake event. The coseismic unwrapping phases were further calculated to estimate the surface displacement in east-west and vertical directions. Results in the CCD map agree well with the observations from post-earthquake field surveys. The workflow can accurately identify earthquake-induced land subsidence and surface displacements, even for areas with insufficient geological data or for areas that had been excluded from the liquefaction potential map. In addition, the CCD details the distribution of building damages and structure failures, which might be useful information for emergency actions applied to regional-scale problems. The conversion of 2D surface displacement reveals the complex behavior of geological activities during the earthquake. In the foothill area of Tainan City, the opposite surface displacements in local areas might be influenced by the axis activities of the Kuanmiao syncline.

The Richard’s equation was used to numerically model 1D flow within unsaturated topsoil and solved using a two-step Crank-Nicolson scheme. Under constant water supply, the Darcy velocity obtained at the upper boundary, the ground surface, is regarded as the correct infiltration rate. Based on this, three infiltration-capacity formulas by Horton, Philip, and Green-Ampt were evaluated for three types of soil. Results demonstrated that all three formulas provide similar fits to the numerical results, but the Horton formula differs most as compared to the other two formulas in terms of infiltration rate. The cumulative infiltration curves were not distinguishable from each other. By perturbing the rainfall intensity, duration, and initial soil moisture content, regression results demonstrated that only the saturated hydraulic conductivity Ks can be used as a good estimator for parameter k (or fc) in all formulas. The other two parameters, however, will deviate from their original values. Only the late-time in...