Investigating the impact of earthquakes on man-made structures in the vicinity of coastlines (Case study, earthquake on 2nd of July 2022, Sayekhosh)

Coastal zones are one of the most sensitive areas with the constant changes due to their dynamic nature. They are also precious zones in terms of fisheries, transportation, recreational activities, and other rich resources. Thus, any changes in such areas can influence all such activities. Natural disasters are one of the main concerns in sensitive areas such as coastal zones. Due to its sensitivities, these areas may be affected significantly by such disasters. Coastal zone management (CZM) mechanism is a proper choice, which is applied and implemented with the aim of ensuring the sustainability of resources and these environment. In the operational and research framework of CZM, natural phenomenon and disasters are considered and their affects are surveyed for best managements of the area. Large-scale natural phenomena such as earthquakes or groundwater depletion due to climate change in coastal low-lying areas cause various types of instability. On the 2nd of July 2022, three strong and consecutive earthquakes occurred in the coastal area of Sayekhosh, Located 123 km from Bandar Abbas city and 70 km from Bandar Lengeh city (South of Iran). As a result of these earthquakes, the Sayekhosh Shrimp farm center was seriously damaged. In this study, using RS and GIS techniques, the impact of these earthquakes on the coastal area has been investigated. Using the data of the SAR images from Sentinel-1 satellite and applying the DInSAR technique, a coherence map, differential interferograms and vertical changes map of the region have been produced, which are used to determine the uplift or subsidence of the land's surface. By using the data of Sentinel-2, Landsat-5, and Landsat-8 satellites and using the band ratio technique, the conditions of the farm ponds and the shoreline of the region were determined. Using the Normalized Difference Water Index (NDWI) (with Green and NIR bands) and applying unsupervised K-means classification, two water and land features have been separated. These were done using ENVI, SNAP and ArcMap software. The surface of the area in the northwestern part of the farm has changed in the form of uplift (up to 0.2 m) and in the eastern part of the farm along the coast in the form of subsidence (up to -0.1 m). Band ratio results showed that after five days of the earthquakes, 189 ponds were discharged. Besides; we detected about -30 m shoreline transformation in the areas close to the farm canals and river mouths due to the earthquakes. The results showed that the location and/or the establishment of traditional shrimp farming system should be reconsider, to avoid such damages in upcoming disasters. Since natural disasters strongly affects man-made structures especially in the coastal area, the use of satellite data and RS and GIS techniques can be useful to precisely monitor and manage the changes in the coastal area.