Hazel Deniz Toktay

The Bolu region, situated along the western–central segment of the North Anatolian Fault Zone (NAFZ), is characterized by a complex fault architecture in which multiple overlapping strike-slip segments and associated subsurface structures accommodate active crustal deformation. Although the principal fault strands of the NAFZ have been well mapped, several clusters of seismicity are observed in areas without clear surface fault expression, indicating the presence of subsurface or poorly expressed fault zones. In this study, we integrated edge detection methods with a seismicity approach to delineate active and buried structural features across the Bolu region. Bouguer gravity anomalies derived from the WGM2012 model were analyzed using four gradient-based filters: the total horizontal derivative, tilt derivative, tilt angle of the horizontal gradient, and modified horizontal gradient amplitude filters. Among these, the MHGA technique produced the most coherent and noise-resistant results, allowing sharper identification of lateral density contrasts associated with fault-related discontinuities. Integration of MHGA results with seismic data revealed several previously unmapped, seismically active subsurface lineaments (numbered as 1–49), indicating a distributed deformation pattern extending beyond the main NAFZ strand. These findings provide new geophysical evidence for potential faults in the Bolu region and underscore the utility of potential field methods for refining active fault maps and improving seismic hazard assessments in northwestern Anatolia.

Gravity anomaly maps often contain spatially overlapping signatures from numerous sources, each with varying shapes, depths, and density contrasts. Locating these signatures using edge detection techniques is crucial for geological structural interpretation and imaging of horizontal boundaries. This paper proposes two effective edge detection tools: one combining the balanced total horizontal gradient (BHG), and the hyperbolic tangent function, abbreviated as “MTBHG”; and the other combining the tilt angle of the total horizontal gradient (TAHG) and the hyperbolic tangent function, abbreviated as “MTAHG.” Additionally, the Modified Non‐Local Means (MNLM) filter was applied to suppress possible noise effects amplified by the gradient calculation process. Synthetic tests validated that the MTAHG and MTBHG detectors outperform other representative detectors. Two high‐resolution gravity data sets from the Western Carpathians in Slovakia and the Witwatersrand Basin in South Africa were used to test the applicability of the modified methods. Results show that the modified detectors achieve superior edge delineation and avoid creating spurious anomalies or artifacts even in the presence of unwanted noise interference. Furthermore, by eliminating false tilt‐depth (TD) solutions via the edge detection results, we enhance the accuracy of depth estimates and facilitate the credible identification of both horizontal and vertical structure distributions.

Identifying and determining buried archaeological structure limits are crucial for archaeological prospection surveys. The archaeological prospection surveys can shed light on protecting cultural heritage. Magnetic is one of the most applied methods in archaeological surveys to plan the excavation process. It aims to identify buried temples, graves, city walls, and other structures by interpreting the data obtained from magnetic measurements, which is one of the non-destructive geophysical exploration methods. In the process of interpretation of magnetic data, many methods have been developed, such as Horizontal Gradient Magnitude, Analytical Signal, Theta Map, and Tilt Angle methods, which can generate information about the boundaries of potential subsurface features. By analyzing the gradients of the magnetic field data, inferences can be made to determine the edges of subsurface potential archeological structure distributions.The Olympos is an important ancient city in Antalya (the south of Turkey) and contains many structures from the Byzantine period. This research aims to detect the pipe drain as a water system of the Episkopeion region in the Olympos ancient city. To this end, Tilt Angle (TA) and Edge detection field (ED) methods were tested on the magnetic map of the synthetic model. The horizontal boundaries of the potential pipe drain elements of the region were analyzed by applying the same procedures on the magnetic map obtained from the magnetic measurements on the area that has not been excavated in the Episkopeion archaeological excavation area. Magnetic measurements were carried out in 4 different regions within the Episkopeion area, and each area was numbered and analyzed separately. Combining the results obtained, an integrated visualization of the water system in the area was achieved.Keywords: Archaeological Prospection, Edge Detection, Olympos, Tilt, Angle, Pipe drains.

The faults and the fault zones are essential to determine the seismotectonic features and the regime of a region and to produce seismic hazard and risk maps. Many geophysical methods, such as seismic, magnetic and gravity are used to determine the location and direction of faults. This study aims to detect potential fault edges located in the south-southwest of Nisyros Island and west of Tilos Island in the southeastern Aegean Sea and to interpret the seismic activity and faulting characterization. To this end, the potential fault edges were initially detected using the total horizontal derivative method on the gravity dataset collected from the WGM2008 database. The obtained spatial locations were combined with the seismicity and the focal mechanisms of the earthquakes. The detected fault has a northeast-southwest orientation with normal faulting. It was proved that this obtained fault is not included in the active faults of the Eurasia database (AFEAD), European Fault - Source Model 2020 (EFSM20) database and the Mineral Research and Exploration General Directorate (MTA) active fault map. Moreover, this observed fault was detected as longer than the fault shown on the National Observatory of Athens (NOAFAULTs) in terms of length. Consequently, it is highly recommended that this potential fault, which produces earthquakes with a moment magnitude greater than 4.0 (on instrumental period) must be added to such fault databases to increase and spread the knowledge of seismological and seismotectonic research.

Enhancing the detection accuracy of the edges of the geological features within the subsurface remains a significant objective in geophysical data interpretation. Despite numerous advancements, approaches stemming from the directional gradients of gravity and magnetic fields still grapple with challenges such as low-resolution outcomes and susceptibility to noise contamination. In this study, we introduce a novel filtering framework based on the total horizontal gradient and its derivatives, designed to yield more precise and coherent edges free from false boundaries or disruptive artifacts. Validation using synthetic Bishop complex magnetic and gravity datasets, alongside Tuangiao aeromagnetic data from Vietnam, substantiates the robustness and applicability of our modified approach. Furthermore, recognizing the inherent susceptibility of edge detection filters to noise contamination resulting from directional derivatives, we employ the recently developed modified non-local means (MNLM) algorithm to alleviate noise effects prior to the analysis of noisy synthetic and real datasets. Our findings confirm the efficacy of the proposed method in reducing false artifacts and identifying edges with heightened precision, positioning MHGA as a valuable alternative for processing potential field data.

Potential field data play a critical role in interpreting various geologic structural features through edge detection filters that aid in mapping subsurface structural features. For this purpose, various filters have been introduced in recent years to determine lateral boundaries. However, each of these filters has its limitations and advantages. This study presents a new edge enhancement filter named “Enhanced Gradient (EG)” based on the Richards function and applies it to potential field data for structural mapping. The EG is tested on two dimensional (2D) and three dimensional (3D) synthetic magnetic models with sources buried at different depths and variable properties. The results from the EG filter provide more accurate and higher resolution horizontal boundaries and can avoid creating the false edges in the output results. In addition, the proposed filter was examined using aeromagnetic data from the Indiana region in the USA. The primary and secondary faults and geological formations are recognizable in the EG image. The results of the EG map will allow us to improve the qualitative interpretation of potential field anomalies in studying the structural and tectonic geology of the Indiana region in the USA.