Extended Abstract
Introduction:
The landforms created by tectonic processes are studied by morphotectonics, in other words, morphotectonics is the science of applying geomorphic principles in solving tectonic problems. Quantitative landscape measurements are usually based on the calculation of geomorphic indices, using topographic maps, satellite images aerial photographs, and field visits. Coastal deltas are part of landforms and landscapes that, due to the proximity of two environments, land, and water, leave visible effects against tectonic activities, such as changing the pattern and location of deltas due to the change in the course of coastal rivers, the formation of unbalanced coastal terraces in parts of the coast, and the emergence of cut beaches in the form of seawalls.
One of the methods of identifying and measuring land changes is using radar remote sensing. The principles of this technique were first described by Graham in 1974 (Pacheco et al., 2006). Interferometry using radar images with an artificial window or SAR is a precise method based on the use of at least two radar images of the same area, which measures the height displacement changes in wide areas and during different time intervals with a significant accuracy of millimeters (Dong et al., 2018).
The coastal areas of northern Iran are of great importance due to the high population density and the ability to grow and develop economically and agriculturally, so monitoring geomorphic changes in the direction of sustainable development of these areas is particularly important.
In this research, the eastern coast of the Caspian Sea from Gomishan to Joibar is investigated in terms of subsidence and uplift using radar remote sensing techniques to determine the active tectonic zones of the coast in terms of temporal and spatial changes.
Materials and Methods:
The Eastern Caspian Plain is the border between the Caspian Sea and West Gorgan and includes the cities of Gomishan, Bandare Turkman, Bandare Gaz, Gulugah, Khazarabad, and Joybar. The absolute height of the Caspian Plain along the coastline is determined according to the sea level, based on the hydrographic data of the Baku station, since 1850, the Caspian sea level has varied between -25.4 and -29.4 (Abdolhi Kakrodi, 2012).
The history of seismic activity in North Alborz shows that cities like Rasht, Lahijan, Amol, and Gorgan, have been destroyed many times due to destructive earthquakes (Aqhanbati, 2013). The Alborz fault is an active fault that is stretched in a clockwise direction in the southern Caspian basin.
In this research, according to the desired goals and radar remote sensing techniques, a series of Sentinel-1 radar images with a suitable time and space difference (maximum 30 days and maximum 150 meters respectively) including 61 images in time from 2014 to 2021 were prepared and processed.
Results:
The results obtained from the SBAS model indicate that the eastern part of the Caspian coast is more affected by the uplift and this trend continues up to Gorgan Bay. The Gorgan city has an uplift between 20 and 40 mm/year, which is reversed towards the coastal area, and subsidence of 10 to 52 mm/year occurs, which decreases as it approaches the coast and reaches 10 mm /year.
Discussion, Conclusion:
According to the results obtained from radar interferometry, the eastern coast of the Caspian Sea is more affected by uplifting. The Gorgan city has an uplift between 20 and 40 mm/year, which is reversed towards the coastal area, and subsidence of 10 to 52 mm/year occurs, which decreases as it approaches the coast and reaches 10 mm/year.
To verify the results obtained, the data of the Gorgan geodynamic station was used, which shows subsidence of about 90 to 100 mm in a 6-year period, which is consistent with the values obtained from radar interferometry Based on comments Shahpasandzadeh (2013) and the reports of Nazari et al (2021), active tectonics caused by the Caspian fault that indicates the horizontal geodynamic displacement diagram of Gorgan, the small area towards the north and east during this time, which is observed in the form of numerous branches with a thrust (reverse) mechanism and a right-slip component with a slope to the south in Golestan province.
Considering that the main feature of the coast of the Caspian Sea is the Surface rivers and the use of groundwater is very little and also the extraction of gas, oil, and mining resources, which is another factor in the occurrence of land subsidence, does not exist in this area, and there isn’t also huge and heavy structure in the study area that affects the subsidence of the surface; so displacement in the study area is the result of active tectonics.