Morphotectonic characteristics and earthquake analysis of Erzincan plain and surroundings

This doctora thesis delves into the morphotectonic characteristics of the Erzincan Plain and its surrounding areas, situated on the eastern part of the North Anatolian Fault Zone NAFZ). The study includes earthquake analyses conducted in the region. The Erzincan Plain, positioned along the NAFZ, is a tectonic plain shaped by the movement of this fault. Located in the middle towering mountainous terrain, the city of Erzincan stands as the prominent settlement within this plain. Geographically situated in the Upper Euphrates Section of the Eastern Anatolia Region, the Erzincan Plain serves as a transitional zone where the Black Sea and Eastern Anatolia Regions converge. The North Anatolian Fault (NAF) significantly contributes to the formation of the Erzincan Plain. This right-lateral strike-slip fault extends in a Northwest-Southeast direction around the plain and comprises numerous fractures. The fault system is prominently visible on the southern slopes of the Esence Mountains to the north of the plain, while the remaining portions within the plain are covered by alluvium. The northern slopes of the Erzincan Plain offer a clear observation of the NAF. As a result, distinctive features related to fault morphology have developed on these slopes. These include linear valleys, shifted streams, ridges, pressure ridges, fans, mass movements, fault lakes, hot water outlets, travertine formations, and volcanic domes. Morphometric indices were employed to ascertain the morphotectonic characteristics of the Erzincan Plain and its environs. The analysis of geomorphic indices on a basin-by-basin basis was conducted to gauge the activity level of faults bordering the Erzincan Plain. A total of 53 sub-stream basins, identified in the northern and southern regions of the plain, underwent various analyses, including Mountain Front Sinuosity (Smf), Valley Floor Width-Valley Height Ratio (Vf), Stream Length-Gradient (Sl), Asymmetry Factor (Af), Topographic Symmetry Factor (T), Hypsometric Curve (He)-Hypsometric Integral (Hi), Stream Concavity (Sci), Stream Sinuosity Ratio and Channel Pattern, Basin Shape (Bs), Drainage Density (Dd), Linearity (Rose Diagram), Minimum Basin Breach, and Relative Tectonic Activity Grading (IAT). The results of the analysis provide numerical data on the horizontal and vertical changes in drainage basins, offering a comparative assessment of the North Anatolian Fault Zone's (NAFZ) impact on the morphotectonics of these basins. The findings reveal that none of the basins fall into the category of low tectonic activity. Out of all sub-basins, 16 (30%) exhibit very high tectonic activity, 24 (45%) show high tectonic activity, and 13 (25%) demonstrate medium tectonic activity. These results indicate that the Relative Tectonic Activity Grading (IAT) of basins to the north of the Erzincan Plain surpasses that of basins to the south. Additionally, sub-basins located in the western part of the plain calculating relatively low tectonic activity. While the displacement between the rivers to the north and south of the Erzincan Plain varies, so does the displacement along fault segments. The rivers in the northern part of the plain experience a higher degree of displacement compared to those in the south. Additionally, vertical thrust components have emerged in certain sections of the Erzincan basin due to the presence of strike-slip faults. Consequently, considerable height differences have arisen between the plain floor and the mountainous areas. Distinctive features resulting from faulting include deformed erosion surfaces, parallel river drainage on fault slopes, linear valleys, displaced stream beds, fault steepness (slope fractures), pull-apart basins, fault steps, linear pressure ridges, closing ridges, triangular surfaces, hanging valleys, collapse areas (swamps), alluvial fans, volcanic formations, and hot springs—all observable within the fault zone. Erzincan city, a crucial settlement within the study area, is situated on the North Anatolian Fault Zone NAFZ) and its associated secondary faults. Simultaneously, the earthquake risk has escalated, attributed to the heightened activity of the Ovacik Fault in the northeast part of the Eastern Anatolian Fault Zone EAFZ). The fractures along the main faults have given rise to up to 15 volcanic domes in the eastern part of the plain, accompanied by the emergence of hot water and mineral water outflows. Consequently, the tectonic movements within the NAFZ have not only altered the morphological structure but also induced changes in the social and economic structure, stemming from earthquakes that resulted loss of life and property. To conduct earthquake analysis of the Erzincan Plain and its vicinity, earthquakes with a magnitude of Mw≥4 from the period 1900 to 2023 were considered. A comprehensive set of analyses was performed, including Epicenter, Magnitude Class, and Hypocenter Analyses, Buffer Analysis, Average Center, and Weighted Average Center Analysis, as well as Standard Distance and Weighted Standard Distance Analysis. These analyses utilized data from 46 earthquakes with Mw≥4. Intensity analyses were also preparation, encompassing Point Intensity Analysis, Kernel Intensity Analysis, Average Nearest Vicinity Analysis, Hot-Cold Point (Getis-Ord Gi*) Analysis, and Anselin Local Moran's I analyses. Through these methods, the intensity of earthquakes in the region was determined, facilitating the assessment of relationships between intense areas and fault lines. According to analysis result, the study area is tectonically active and corresponds to an area with high earthquake activity level. According to the earthquake analysis results, the probability of destructive earthquakes in and around Erzincan Plain is very high. Due to this risk, new settlement areas should be established in solid areas outside the fault lines. Apart from earthquake risk, meteorological-climatological and hydrographic disasters should also be taken into consideration in determining settlement areas. If these criteria are not taken into account, losses of life and property will be high, as in the recent Kahramanmaras earthquake of February 6, 2023. Keywords: Erzincan Plain, North Anatolian Fault Zone, Morphotectonic, Morphometric indice, Earthquake Analysis, Kernel Intensity Analysis