Türkiye Jeoloji Bülteni

Abstract: This study provides a detailed mapping of active fault segments in Bursa and its surrounding regions, along with a comprehensive analysis of seismic behavior derived from paleoseismological data. As one of Türkiye`s strategic economic centers with a dense population and industrial infrastructure, Bursa requires a holistic seismicrisk assessment for effective disaster preparedness and mitigation. Paleoseismological analyses of the eastern segment of the Ulubat Fault indicate that it has been in a seismic quiescence period for approximately 1855 years. This prolonged period of inactivity highlights the potential for a large earthquake in the future around the Nilüfer Region of Bursa. Trench investigations conducted in Bursa citycentre reveal that the Bursa Fault has produced at least six surface ruptures over the past 12000 years, recurring approximately every 2000 years. Additionally, trench studies on the İnegöl Fault indicate that the İnegöl Fault hasproduced at least five surface ruptures over the last 12000 years, with the most recent major earthquake occurring more than 2500 years ago. Obtained results emphasize the potential for the Bursa and İnegöl faults to rupture simultaneously either in close succession, possibly triggering one another. Thus, the surface rupture caused by the1855 Bursa earthquake is evaluated to have potentially triggered stress accumulation along the İnegöl Fault. Thissituation reveals a high probability of a surface-rupturing earthquake (M=6.2-6.9) occurring at any time on the İnegöl Fault, after 2500 years of seismic silence. Overall, these findings underscore the critical role of the faults in Bursa and its surroundings within the regionalseismicity. In particular, the potential for sequential ruptures along the Bursa and İnegöl faults presents a significant earthquake hazard. This comprehensive analysis contributes to a deeper understanding of the seismotectonic dynamics of the region, providing valuable insights for seismic hazard assessment and risk mitigation efforts.

Abstract: The purpose of this study is to analyse the structural evolution of the region where the Eastern Pontidesand the Eastern Taurides are closest to each other. The main tectonic units in the area, from north to south, are theKelkit Paraautochthonous Unit, Çimendağ Nappe, Erzincan Nappe and Munzurdağ Limestone Unit.The pre-Jurassic basement of the tectonic units consists of heterogeneous rock units in different areas. Since the relationships between these units cannot be established in the study area, it is not possible to create a model for thepre-Jurassic period with the evidence from this locality. Therefore, the tectonics, tectono-stratigraphic and structural evolution of the study region were evaluated only for the Jurassic-Quaternary interval. The Jurassic-Early Cretaceous Kelkit Paraautochthonous Unit and Çimendağ Nappe represent the genesis of rifting and then deposition of platform-type carbonates in the Eastern Pontides. The Jurassic-Early Cretaceous Munzurdağ Limestone Unit represents the northern most part of the Eastern Taurides and also has features ofplatform-type carbonates. During this period, a mid-oceanic ridge and ensimatic arc were active together along the North Anatolian Ophiolitic Belt. Therefore, it is possible to suggest a model representing passive continental margins to the north and south, with the mid-oceanic ridge in the north and the ensimatic arc in the south along the intervening oceanic environment in the Jurassic-Early Cretaceous periods.In the Late Cretaceous-Palaeocene, all evidence shows that the extensional regime completely converted toa compressional regime. In this time interval, an ensialic arc-forearc occurred along the Eastern Pontides and an ensimatic arc with subduction complex occurred along the North Anatolian Ophiolitic Belt. In the south, pelagiccarbonates were deposited along the Munzur Mountains. It seems inevitable that the existence of two different northdipping subduction zones should be accepted in this time interval.The Eocene and Oligo-Miocene units overlie older structural units with a polygenic conglomerate and angular unconformity. These units underwent intense deformation and the entire study area first became a shallow marine and then a terrestrial environment. Eocene volcanism indicates a post-collisional phase in the Eastern Pontides.The Pliocene-Quaternary rocks, reflecting continental deposits, unconformably overlie the older units, withan approximately horizontal layered structure. Considering this unconformity and the intense deformation before the Pliocene, it is possible that the North Anatolian Fault (NAF) developed during the Pliocene and had dextralmovement with at least 25 km offset. In this context, the annual slip value for the fault may be 4.7 cm/year. 

Abstract: Gürlevik tufa, located in the southeast of the Erzincan (East Anatolia) pull-apart basin, represents atypical cascade/waterfall deposit developed in a fluvial environment. Calcareous tufa formed at three different levels. However, the facies properties and depositional system of the Gürlevik tufa formation remain unknown. This study aims to investigate the evolution of the tufa deposits and to clarify their facies changes in this tectonically active basin. For this purpose, seven measured sedimentary logs were obtained from field studies, and the lithofacies were described and interpreted based on their morphological properties, microscopic and biological contents. According tofacies analysis, six lithofacies were identified and two depositional systems (perched springline/cascade and barragedammed) were determined. The monumental cascade/waterfall tufa accumulation is a consequence active tectonicand climatic factors in the region. Gürlevik tufa deposits are located in a protected natural site. This preliminary study draws attention to the geological importance of these sedimentary rocks, which record climate changes with high precision, as well as their geological heritage potential, that should be preserved and transferred to future generations.

Abstract: The Iğdır Fault Zone (IFZ) is located at the easternmost edge of Turkey, approximately 13 km northwest of Mount Ağrı. The fault extends from Küllük village in the northwest to Kavaktepe village in the southeast. Theright-lateral strike-slip Iğdır Fault Zone, which exhibits strike variations between N20°E and N60°E, consists of 19 sub-geometric segments. Fault-controlled drainage networks, offset streams, alluvial and colluvial fans,and truncated valleys are key morphological indicators of the fault`s activity. This study aims to determine the tectonic influence of the Iğdır Fault Zone, which is situated within the Small Caucasus Tectonic Block. To achieve this objective, both historical and instrumental earthquake catalogs were compiled for the IFZ and its vicinity. Additionally, morphometric analyses were conducted on the fault zone, including surface roughness, hypsometricintegral, basin asymmetry factor, mountain front sinuosity, and the ratio of valley floor width to valley height. The identified morphotectonic markers and index results indicate that the IFZ also possesses a normal fault component.The fault zone consists of five parallel sub-branches and exhibits a releasing bend structure, merging with the Mount Ağrı extensional crack in the southeastern section. The historical seismicity and morphometric index results suggest that the study area is morphologically young, with an uplift rate exceeding 0.5 mm per year in the NW and SE sections. When the fault length and index results are evaluated, it is observed that the southeastern segments ofthe Iğdır Fault Zone, particularly those closer to Mount Ağrı, have accumulated relatively higher deformation andexhibit a greater uplift rate.  

Abstract: Karst plateaus are generally characterized by a dense distribution of solution dolines, and the morphometric properties of these dolines can be utilized to determine the morphotectonic characteristics of karst plateaus. This study investigated the interrelation between the spatial distribution and morphometric features of karstic depressions onMount Engizek and the broader morphotectonic evolution of the region. Using topographic maps, Digital ElevationModel (DEM) data, and satellite imagery, a total of 872 karstic depressions (dolines and uvalas) were identified within the mountainous terrain. These depressions were digitized to numerical data by delineating polygons, and their associations with morphotectonic processes were analyzed. In this context, rose diagrams were generated to determine the correspondence between the long-axis orientations of the karstic depressions and structural elements. Morphometric analyses revealed that the average length of the karstic depressions on Mount Engizek is 62 m,while their average width is 41 m, and their approximate surface area is 2,884 m². The average elevation of the depressions was calculated as 2,106 m, with an average slope of 12°. Additionally, the mean depth of the depressionswas determined to be 8.3 m, and it was found that the area contains an average of five karstic depressions per km².The orientation of the mountain follows a NE-SW trend, consistent with NW-SE compression. The morphotectonic evolution of the massif, which shares the same structural trends as the thrust and fold systems within the region,exhibits a structural framework that governs karst processes, as observed throughout the Taurus Mountains. The karstic depressions distributed parallel to the long axis of the summit plateau largely developed under the control oftectono-structural factors. The observed relationship between discontinuity surfaces – such as longitudinal fracture soriented perpendicular to the compression axis and transverse fractures aligned with it – and the development of karstic depressions further substantiates this interpretation.