The North Anatolian Fault Zone (NAFZ) in the north of Türkiye is considered one of the most active faults on earth and have caused many major earthquakes in the last century. Surface ruptures by those earthquakes indicate that this tectonic feature consists of many segments, which reveal different characteristics in terms of geometry and mechanism. NAFZ lies along between Bingöl in the eastern Turkey and Saros Gulf in the west. This study focuses on the central part of the NAFZ between Niksar and Ilgaz provinces. In addition to the main branch, the central section of the NAFZ also contains two sub-branches extending southward: Merzifon-Esençay and Sungurlu Faults. In the literature, there are several studies for the region, however a comprehensive study mainly focusing on the main branch of the NAFZ and its sub-branches along the central NAFZ has not been conducted yet, which would fully reveal the fault mechanism and seismic potential in the region. The aim of this study is to derive an up-to-date high-spa-tial-resolution Global Navigation Satellite Systems (GNSS) velocity field for the central NAFZ and to correlate with the strain accumulations along the faults. Based on this, a high-spatial-resolution GNSS network consisting of 60 sites was established enclosing the central NAFZ. The previously archived GNSS data for the same observation sites were collected from the different studies in the region and a new GNSS campaign measurement was conducted between October 2023 and February 2024. All GNSS data were processed using GAMIT/GLOBK software, and the results indicate the GNSS velocities ranging from 3-30 mm/year and their associated uncertainties of maximum ± 1.5 mm/year with respect to the Eurasian tectonic plate.

The advancements in Unmanned Aerial Vehicles (UAVs) have significantly enhanced the capability of the photogrammetric approaches, particularly with the integration of Real-Time Kinematic (RTK) sensors. That approach enables the operators to use the Global Navigation Satellite System (GNSS) more efficiently with the production of high-precision 3D Digital Terrain Models (DTMs). Traditionally, Ground Control Points (GCPs) are used to link those models to a ground coordinate system, but their establishment is time-consuming and labor-intensive, requiring static or rapid-static GNSS observations over two hours for each point. However, RTK-embedded UAVs offer a significant improvement by facilitating direct geo-referencing of DTMs, which includes the estimation of internal and external orientation parameters more efficiently and potentially eliminating the need for GCPs. In this study, UAV flights over a test area at various altitudes (30m, 45m, 60m) were conducted to evaluate the 3D positioning accuracy of photogrammetric models generated without using any GCP, and their locations were compared against the precise GNSS observations for 22 control points. Results indicated that UAVs with RTK ability could achieve centimeter-level accuracy in positioning, making this kind of evaluation a viable alternative to traditional methods. This study also discusses the implications of those results within the context of large-scale map production and their regulations in Türkiye. The elimination of GCPs should significantly reduce the time and effort associated with map production, suggesting a potential alternative in regulatory standards to incorporate these technological approaches.

UAVs (Unmanned Aerial Vehicles) are commonly used in photogrammetric observa-tions in research fields like agriculture, archaeology, industry and construction of base maps. They present several advantages like low-cost platforms, rapid results, high positioning accuracy and less labor effort in the field. In this study, we evaluate the positioning accuracy of UAV based photogrammetry with conventional observation techniques in a sample area. Our main motivation is to examine if the final model of a low altitude UAV can reach the positioning accuracy of conventional observation techniques, especially in residential regions. For this purpose, we evaluate the results of 3 separate photogrammetric f lights in a pre-observed field. Results indicate that low-altitude UAV f lights can provide high accuracy both in 2D and 3D posi-tioning in residential and densely constructed areas. Keywords: UAV, Photogrammetry, GNSS, Terrestrial observations, Sf M, Positioning accuracy. DOI: 10.17350/HJSE19030000180 Full Text:

Changes in the earth's crust or natural/artificial structures are often referred as “deformation”. Those changes can be monitored in both vertical and horizontal positions. Specifically, vertical deformation is usually detected with high-precision leveling. In that method, the area is covered with reference and object points surrounding the possible deformation region. Object points are established directly to the sectors where deformation is expected, while reference positions are selected to the position where there is no vertical or horizontal movement. The results of the observations at certain time intervals are evaluated by the least-squares method using the free-network adjustment and the vertical displacements for the object points are estimated according to the time difference. This study was carried out to determine possible vertical deformation in Obruk Dam, Çorum. A local leveling network consisting of 58 points (44 objects and 14 references) were established. For evaluation, 0.6 mm/km precision electronic levelling equipment with round trip observations is used within this ~22 km network. Observations in the field were organized considering the time intervals when the water level in the dam is at the maximum and the minimum throughout the year. With the DEFANA module in PANDA deformation analysis software, the observations of four campaigns between 2016 and 2017 were analyzed. Results indicate significant deformations at the object points ranging from ±2 – ±5 mm in comparison between campaigns 1 and 4, but there is no clear evidence of deformation that could compromise the integrity of the dam.

The North Anatolian Fault Zone (NAFZ) is one of the most destructive fault in the eastern Mediterranean region. After Izmit and Düzce earthquakes, the projects on monitoring the fault motion increase using instrumental tools like GPS, InSAR, LIDAR, creepmeter, etc. The eastern and central part of the NAFZ from Karlıova to Vezirköprü has almost strike slip mechanism. The western part of the central NAFZ from Vezirköprü to Bolu has transpressive character. The aseismic fault deformation (creep) is also important phenomena for these two sections. The InSAR and LIDAR studies showed that the Ismetpasa and Destek regions have creep motions. For this purpose, the new project has been started to proof this phenomena with GPS data and to determine quantitatively the rate of convergence and its variation along segment of the NAF between Bolu and Çorum. The main aim of this study is determination of creep rate with geodetic measurements and combination of the data obtained from seismology, geodesy and geophysics to understand fault mechanism. Therefore, in this paper we discuss tectonic phenomena on the central part of the NAFZ and present the first results of the project.