ارزیابی وضعیت تکتونیکی قلمروهای کوهستانی با استفاده از شاخص‌های ژئومورفیک و روش سری زمانی SBAS (مطالعه موردی: حوضه آبریز سد لتیان)

Tectonic activities play a crucial role in the formation and structural changes of the Earth and can have significant impacts on the environment and human communities. In this study, the tectonic status of the Latian dam basin was evaluated using geomorphic indices and radar imagery. The main objective was to assess the level of tectonic activity and vertical displacements in the region over a specified period and to provide practical results for better management of geological hazards. Sentinel-1 radar images and the 12.5 m ALOS PALSAR digital elevation model were the primary data sources used. The main analytical tools were GMT and ArcGIS. The study examined the tectonic status using eight geomorphic indices alongside the SBAS time-series method, and the results from both approaches were compared. According to the findings, the Latian dam basn is active based on the AF, S, Br, and P indices, and relatively active according to the T and Gi indices. Furthermore, the SBAS time-series for the two years period (2020–2022) revealed significant vertical displacements ranging from -4 to 36 mm, with the northern parts of the basin experiencing the highest uplift. It should be noted that the results obtained in this study are based on radar images and the method used and represent approximate displacement values. Considering the results obtained, in order to accurately assess tectonic activities in the study basin, it is recommended to implement continuous monitoring programs using satellite observation systems and ground stations to accurately and timely identify displacement changes.
 
Extended Abstract
 
Introduction
Watersheds, as fundamental units in geomorphological and tectonic studies, reflect active tectonic processes and surface dynamics of the Earth. Evaluating the tectonic status of these basins, especially in mountainous and tectonically active regions, is crucial for understanding geological hazards, managing water resources, and developmental planning. The Latian Dam basin, located northeast of Tehran and on the southern slopes of the Alborz mountain range, due to its unique tectonic setting and proximity to active faults, is considered one of the promising areas for analyzing tectonic activities. In recent years, the use of geomorphic indices as quantitative and efficient tools for assessing tectonic activity at the basin scale has expanded. On the other hand, advances in remote sensing technologies and the use of radar imagery, particularly high-resolution satellite data such as Sentinel-1 and ALOS-PALSAR, have enabled the study of micro-scale changes in topography and surface displacements. Radar images, especially in mountainous environments with dense vegetation cover, perform better than optical images and, with the aid of radar interferometry techniques (InSAR), tectonic activities can be analyzed with higher accuracy. In this study, to evaluate the tectonic status of the Latian watershed, a combination of geomorphic indices analysis and radar image interpretation was applied. This multi-faceted approach not only facilitates the identification of tectonically active zones but also proves effective in analyzing hazards such as landslides, subsidence, and seismicity. The results of this research can contribute to a better understanding of the tectonic dynamics of the region and aid in the principled planning for sustainable development in the Latian basin.
 
Methodology
In this study, Sentinel-1 radar images and the 12.5-meter resolution ALOS PALSAR digital elevation model were used as the primary data sources. The main tools employed were GMT, for implementing the SBAS time series method, and ArcGIS, for generating the required maps. The research was conducted in two main stages: first, the tectonic status of the Latian Dam watershed was assessed using eight geomorphic indices, which were calculated digitally using the digital elevation model to minimize computational errors. After evaluating the tectonic conditions based on each index, the Relative Tectonic Activity Index (IAT) was applied for an overall assessment and comparison of the watershed’s tectonic activity. In the second stage, vertical displacement of the Latian watershed was calculated using Sentinel-1 radar images from a one-year period (January 2021 to January 2022) through the SBAS time series method. Finally, the results from both methods were compared and analyzed together.
 
Results and Discussion
The results of the evaluation of the Transverse Topographic Symmetry Factor (T) indicate a value of 0.43 for the studied watershed. Based on the elevation characteristics of the basin, the Hypsometric Integral (Hi) was calculated as 0.37. The Asymmetry Factor (AF) was found to be 30, and the Stream Sinuosity Index (S) was calculated at 1.24. According to the stream order classification, the Basin Bifurcation Ratio (Br) for the study area was determined to be 3.8. The Drainage Density Index (P), calculated based on the basin area and the total length of streams, was 1.1. Additionally, the values for the Basin Shape Index (Bs) and the Gravelius Index (Gi) were 1.51 and 1.56, respectively. Furthermore, using the SBAS time series method, a vertical displacement map of the region was generated, which showed that the study area experienced vertical displacement ranging from -5 to 41 millimeters over the one-year period from 2021 to 2022.
 
Conclusion
The evaluation of tectonic indices for the studied watershed indicates that the area is active according to most indices (AF, S, Br, and P) and relatively active based on the T and Gi indices. Overall, the geomorphic index assessment shows that the Latian Dam watershed is tectonically active, with ongoing geological processes related to structural displacement and movement. Additionally, the SBAS time series results and interferogram maps, depicting vertical displacements over a one-year period (2021–2022), reveal significant movements ranging from -5 to 41 millimeters, with the northern parts of the basin experiencing the highest uplift. This confirms the tectonic activity of the region and the influence of tectonic processes on vertical surface changes. Given these findings, it is recommended to implement continuous monitoring programs using satellite observation systems and ground stations to accurately and timely detect displacement changes. Moreover, conducting seismological studies and active fault investigations is essential for better hazard identification and pinpointing high-risk zones. Furthermore, geotechnical engineering studies are advised in areas with the greatest displacement to ensure the stability of structures and infrastructure. Finally, enhancing education and raising awareness among local communities about the consequences of tectonic activity and coping strategies plays a vital role in reducing human and financial damages.