This study focuses on the extraction of structural lineaments in the South Caspian Basin using satellite gravity data. Lineaments, as linear features in the Earth's crust, provide critical insights into the region's geological structure and tectonic history. The research employs Bouguer anomaly data and satellite gravity gradient data, combined with advanced edge detection techniques, including the Logistic Function of the Total Horizontal Gradient (LTHG) filter, to identify and analyze these features. The study area spans latitudes 36° to 39° N and longitudes 48° to 51° E, encompassing parts of the western and central Alborz Mountains and the southern Caspian Basin.

The South Caspian Basin is a distinct tectonic unit, characterized by a complex interplay of oceanic and continental crusts. The region's geological framework includes thick sedimentary deposits (15–25 km) ranging from the Cretaceous to the present. Evidence suggests the presence of an ancient oceanic crust beneath the Caspian Sea, remnants of the Paleo-Tethys Ocean, which has been subducted beneath the Alborz Mountains. The basin is surrounded by major fault systems, including the Astara, Lahijan, and North Alborz faults, which exhibit diverse kinematic behaviors, primarily strike-slip and normal mechanisms, reflecting the area's intense tectonic activity.

The methodology involved applying various edge detection filters to satellite gravity data, with the LTHG filter proving particularly effective for identifying structural discontinuities. The LTHG filter balances the detection of shallow and deep structures by leveraging logistic function-based enhancements to the total horizontal gradient. This approach minimizes noise interference and improves resolution, making it suitable for mapping fault systems and crustal boundaries. Additionally, the vertical gradient component G_yz of the satellite gravity tensor was analyzed to further delineate lineaments and separate regional from residual anomalies.

The study successfully revealed three parallel lineaments adjacent to the Lahijan Fault, which are likely to represent lineaments or subsidiary faults aligned with its general trend. Furthermore, the analysis of the regional anomaly of the G_yz gravity‑gradient component indicates the presence of a deep-seated structure along the Lahijan Fault that extends toward the Apsheron–Balkan zone within the semi‑oceanic lithosphere, potentially marking an important tectonic boundary. In addition, portions of a transitional boundary between the possible oceanic crust and continental crust in the western and southern parts of the South Caspian Basin were identified. These findings collectively point to a complex and active tectonic regime in the region. Nevertheless, due to the limited availability of surface geological evidence, the precise nature of these features requires further investigation.

The results were validated through comparison with existing geological maps and studies, confirming the accuracy of the LTHG filter in detecting lineaments. The integration of geophysical and geological data highlighted the method's robustness in identifying both surface and subsurface structures. For instance, the Astara fault, with its NW-SE trend, and the Lahijan fault, with a NE-SW orientation, were clearly delineated, along with their intersections and associated secondary structures. The North Alborz fault, marking the boundary between the sedimentary basin and the Alborz orogenic belt, was also accurately traced.

The study underscores the importance of combining multiple edge detection techniques to overcome limitations inherent in individual methods. This multi-method approach enhances the reliability of lineament extraction and supports a more comprehensive interpretation of the region's tectonic framework.

In conclusion, this research demonstrates the efficacy of satellite gravity data and advanced edge detection filters in unraveling the structural complexity of the South Caspian Basin. The identification of key lineaments and crustal boundaries contributes to a deeper understanding of the basin's tectonic history and its implications for hydrocarbon exploration and seismic hazard assessment. The findings also highlight the potential for further applications of these techniques in other tectonically active regions.