Conceptual model of the Gülbahçe geothermal system, Western Anatolia, Turkey: Based on structural and hydrogeochemical data

The Gülbahçe Geothermal Field is located on the eastern margin of the Karaburun Peninsula, about 45 km from the city of İzmir, western Anatolia, Turkey. The stratigraphy of the study area is represented by a Miocene volcano-sedimentary succession, including several sedimentary and volcanic units. These units overlie the basement rocks of the Karaburun Platform and Bornova Flysch Zone which consist of sandstones, shales and carbonate blocks. These rock units are cut and deformed by a series of NW-SE- to NE-SW-trending faults, extending from Sığacık Bay to Gülbahçe Bay. Structural studies suggest that while most of the geothermal systems in western Anatolia are controlled by normal faults, the geothermal system at Gülbahçe is controlled by a strike-slip dominated shear zone, previously named the İzmir-Balıkesir Transfer Zone. Along the fault zone, associations of active fault segments accommodate deep circulation of hydrothermally modified sea water, and thus the resulting negative flower structure is the primary control mechanism for the geothermal system. Hydrogeochemical properties of the field show that surface temperature of fluid ranges from 30 to 34 °C. Geothermal fluids in Gülbahçe have high salinity (EC > 34 mS/cm) and low enthalpy. Piper and Schoeller diagrams indicate that geothermal fluid is in the NaCl facies. Chemical geothermometers suggest that the reservoir temperature is around 53–136 °C. The isotopic data (oxygen-18, deuterium and tritium) suggest that geothermal fluids are formed by local recharge and deep circulation of sea water

Reconstructing the Sedimentary Evolution of the Miocene Aksu Basin Based on Fan Delta Development (Eastern Mediterranean-Turkey)

The Aksu Basin in southern Turkey is dominantly represented by an alluvial fan and five fan deltas (FDs) developed along the tectonically controlled margins of the basin during the Miocene. Four alternating compressional and tensional tectonic phases have influenced the basin since its formation. Strong tectonic movements caused high sedimentation rates and progradation of large debris-flow and mass-flow dominated FDs. Here we describe two FDs (the Karadag and Kargi FDs) in detail. The Karadag FD began to develop under the control of a compressional regime and continued the evolution under a tensional regime. The same tensional regime caused the separation of the Karadag FD from its source and the deposition of the Kargi FD into the newly formed accommodation area. The alternating tectonic regimes and sea-level oscillations in the Aksu Basin gave rise to the development of coral colonies on the shallow delta fronts, forming patch reefs despite the large amounts of conglomerates supplied by fan deltaic processes

Age and Geochemical Constraints on Formation of Fault-related Late Quaternary Carbonate Veins from Southern Turkey

Combined U-series dating and high-resolution geochemical analyses of co-seismic carbonate veins offer an invaluable opportunity to document young (<1 Ma) earthquake activity and for tracing origins of associated fluids. In this study, we analysed a total of 23 samples of fault-related carbonate veins and slickenfibered calcites collected from two separate SW– S-trending fault zones developed near Anamur and Gazipaşa areas in Southern Turkey. Microtexturally the carbonate veins mainly comprise medium- to coarse-grained, columnar calcite crystals elongated along growth direction. U-series dating indicated episodic fault-related carbonate mineralization between 132 ± 2 and 5.6 ± 0.4 ka and between 530 ± 63 and 30.0 ± 2.1 ka in Anamur and Gazipaşa areas, respectively. Carbon and oxygen isotope compositions of carbonates from both Anamur (δ13C = -12 to -6‰, δ18O = -7 to -4‰; relative to V-PDB) and Gazipaşa (δ13C = -12 to -7‰, δ18O = -7 to -3‰) areas are almost identical, whereas Anamur samples (0.7074–0.7080) have slightly lower 87Sr/86Sr ratios compared to Gazipaşa samples (0.7081–0.7096). The 87Sr/86Sr values correlate well with that of modern and Cenozoic seawater (~0.709) and Permian limestone host rocks (~0.707). PAAS-normalized rare earth element-Yttrium patterns of most samples are characterized by negative Ce and positive Y anomalies, confirming a predominantly seawater source for calcite precipitating fluids. Our acquired age and geochemical data not only has revealed young (<500 ka) seismic activity for these previously undocumented fault systems, but it also has implications for upper crustal fluid flow and palaeoclimatological conditions in the region

Influences of human activities and agriculture on groundwater quality of Kayseri-Incesu-Dokuzpinar springs, central Anatolian part of Turkey

Human activities and agriculture have had direct and indirect effects on the rates of contamination of groundwater in the Incesu-Dokuzpinar spring area. Direct effects include dissolution and transport of excess quantities of fertilizers with associated materials and hydrological alterations related to irrigation and drainage. Indirect effects may include changes in water-rock reactions in soils and aquifers caused by increased concentrations of dissolved oxidants, protons, and major ions. Agricultural activities have directly or indirectly affected the concentrations of a large number of inorganic chemicals in groundwater, for example NO3, N2, Cl, SO42, H+, K, Mg, Ca, Fe, Cu, B, Pb, and Zn, as well as a wide variety of pesticides and other organic compounds. For reactive contaminants like NO3, it is recommended that a combination of hydrochemical and environmental-tracer analytical approaches might be required to resolve changing inputs from subsequent alterations as causes of concentration gradients in groundwater. The water type of Dokuzpinar springs is mainly Na-Mg-Ca-Cl-HCO3. Note that the water types of the springs were directly related to the hydrogeochemical properties of outcrops at the study area. Thus, the high concentration of Ca2+ and HCO3 is mainly related to the high CO2 contents in the marbles, whereas the high Na concentration arises from the existing syenite, volcanic ash, basalt, and clay units, although the İncesu-Dokuzpinar springs cover most of the drinking and irrigation water demands of this area. The high concentrations of NO3 and NaCl show that the area around the springs is continuously being contaminated by untreated sewage and agricultural wastes, especially during dry periods. Therefore, this approach is based on the vulnerability studies of the catchment area, determination of the transfer time of the pollutant, and the water-bearing formations of İncesu-Dokuzpinar springs. Vulnerability in this study is defined as the intrinsic hydrogeochemical characteristics of an aquifer, which may show the sensitivity of groundwater to be contaminated by different human activities

Structural controls and hydrogeochemical properties of geothermal fields in the Varto region, East Anatolia

Varto and the surrounding region have important geothermal fields, developing in strike-slip tectonic setting in East Anatolia, which resulted from the collision of the Arabian and Eurasian plates. The main structural elements in the area are the NE-trending sinistral and NW-trending dextral strike-slip fault segments and N-S trending extension zones. In order to determine fault-controlled geothermal circulation, it is very important to fully characterize the structural elements in these complex environments. The widely distributed volcanic rocks have fracture and crack systems that play an important role in surface infiltration, geothermal fluid, and groundwater circulation. Especially in areas where the fault segments intersect, hot springs outlets and natural resources easily come to the surface. In order to understand the flow paths of geothermal fluid along the faults in these geothermal systems, it is necessary to determine the stress state of the faults and to map the distribution of the structural elements. For this reason, we conducted a detailed study on the Varto Fault Zone, which has important geothermal fields in Eastern Anatolia. We present conceptual models of the geothermal fields in the Varto region that show favorable geothermal activity on the intersecting fault segments, fault bends, step-overs, and accompanying fracture-crack sets. As a result, we emphasize that the planes of strike-slip faults in transtensional areas are more favorable for secondary permeability and enhances the geothermal fluid circulation, and this can be supported by hydrogeochemical data

Seismic Geomorphology of October 23, 2011 tabanlı-Van Earthquake and Its relation to active tectonics of East Anatolia

This study aims to explore the origin and location of the October 23, 2011 Tabanlı-Van earthquake within active tectonic framework of Van city and its surroundings. Field-based studies have been done just after the Tabanlı-Van earthquake, and then geometry and type of observed deformational structures were evaluated and integrated with the results of previous active tectonic studies in the region. The observed structures can, based on seismic geomorphological indicators, be grouped into two main categories: (1) seismotectonic landforms related to tectonic stress, and (2) seismogravitational landforms related to seismic shaking and earth’s gravity. Seismotectonic landforms are common within a 10-km-long deformation zone located between Van Lake and Erçek Lake. These occurs as N50–70°E trending synclines and anticlines, most commonly in the area between Bardakçı and Topaktaş villages. Seismogravitational landforms are common in water-saturated sediments of Lake Van, particularly along its eastern margin; they are mostly liquefaction-induced features and are expressed in the form of lateral spreading, ground subsidence, and mass movement. Reverse fault planes deforming and displacing Upper Pliocene-Pleistocene sediments form the other group of common structures in the region. They trend in N50–70°E direction direction and dip at 45-50° to the north; they are oblique structures with sinistral strike-slip components. Similar active faults were mapped by Özkaymak (2003) at three locations to the north of Van city center: north of Beyüzümü village, near the main gate of the Yüzüncü Yıl University Zeve Campus and southern part of the Aşıt village. Evaluation of previously mapped fault segments and recent observations in the deformation zone are consistent with an approximately 10 km wide active thrust fault zone that comprises, at least, five N50–70°E striking and north-diping (ca. 47°) fault segments. Kinematics of these faults is consistent with fault plane solutions of 23 October, 2011 Tabanlı-Van earthquake. We suggest that newly formed and/or reactived fault segments in this fault zone were the source of the 23 October, 2011 Tabanlı-Van earthquake. The absence of surface rupture(s) is attributed to the geometry of a blind thrust. According to geological mapping and kinematic analyses, the active tectonics of the region is the manifestation of, in addition to ENE-WSW-striking thrust faulting, NNW-SSE-directed compression as expressed by NE-SW-trending sinistral strike-slip faulting, NW-SE-trending dextral strike-slip faulting and N-S-trending normal faulting.Bu çalışma, 23 Ekim 2011 tarihinde meydana gelen Tabanlı-Van (M = 7.2) depreminin bölgenin aktif tektoniği içerisindeki konumunu açıklamayı amaçlamaktadır. Bu bağlamda Tabanlı-Van depreminden sonra arazi çalışmaları yapılmış, depremle ilişkili deformasyon yapıları incelenmiş ve arazi gözlemlerinden elde edilen veriler ile Van ili ve çevresiyle ilgili olarak daha önce yapılmış aktif tektonik çalışmaları karşılaştırılarak değerlendirmeye gidilmiştir. Deprem sırasında veya hemen sonrasında yeryüzünde/yeryüzüne yakın kesimlerde meydana gelen deformasyonlar (sismik jeomorfolojik belirteçler) iki ana sınıfta toplanmıştır: (1) tektonik gerilmelere bağlı sismotektonik yüzey deformasyonları ve (2) sismik sarsılma ve yerçekimiyle ilgili sismogravitasyonal yüzey deformasyonları. Sismotektonik yüzey deformasyonları, Van Gölü ile Erçek Gölü arasında 10 km genişliğindeki kuşak boyunca gözlenir. Bu yapılar, genel uzanımları K50-70ºD olan senklinal ve antiklinal geometrili çöküntü ve sırtlar şeklindedir ve genellikle Bardakçı ile Topaktaş köyleri arasındaki asfalt yollarda gelişmiştir. Sismogavitasyonal yüzey deformasyonları yanal yayılma, oturma ve kütle hareketleri şeklinde gelişmiştir. Bu yapılar, Van Gölü doğu kenarı boyunca yüzlek veren eski Van Gölü çökelleri ve güncel alüvyonlarda yaygın olarak gelişmiştir. Tabanlı-Van depremi nedeniyle gelişen sismotektonik yüzey deformasyonlarının yanısıra, deformasyon kuşağı içerisinde ters faylanmalar da gözlenmiştir. Bu lokasyonlarda Üst PliyosenPleyistosen birimleri K50–70°D doğrultulu ve 45-50° kuzeybatıya eğimli sol yanal bileşenli ters faylarla kesilip ötelenmektedir. Benzer aktif fay hatları önceki çalışmalarda (Özkaymak, 2003), Van il merkezinin kuzeyinde yer alan Beyüzümü köyü kuzeyinde, Yüzüncü Yıl Üniversitesi Zeve Kampüsü girişinde ve Aşıt köyü güneyinde haritalanmıştır. Birbirinden bağımsız olarak haritalanan bu fay segmentleri birlikte değerlendirildiğinde, Çitören ile Beyüzümü köyleri arasında, yaklaşık 10 km genişliğinde, ortalama K50- 70°D doğrultulu ve 47° kuzeybatıya eğimli, birbirine paralel en az beş fay segmenti içeren aktif bir bindirme zonunun varlığı ortaya çıkar. Söz konusu fayların kinematik verileri 23 Ekim 2011 Tabanlı-Van depremini oluşturan ters fayın odak mekanizma çözümüyle uyumludur. Dolayısıyla, Pleyistosen-Holosen birimlerini kesen fay zonunun, 23 ekim Tabanlı-Van depreminde yeniden aktif hale geçerek yeni fay kolları oluşturduğu anlaşılmaktadır. Deprem sırasında oluşan fay koluna ait sıkışma kökenli yüzey deformasyonlarının belirgin bir yüzey kırığı oluşturacak şekilde gelişmemiş olması, yeni oluşan fayın geometrisi nedeniyle henüz yüzeye ulaşmadığı ve dolayısıyla gömülü fay niteliği taşıdığını göstermektedir. Jeolojik haritalama ve kinematik analiz verilerine göre, KKB-GGD eksenli sıkışma kuvvetleri etkisinde şekil değiştiren bölge; Tabanlı-Van depremini oluşturan DKD-BGB doğrultulu bindirme fay zonunun yanı sıra, KD-GB uzanımlı sol yönlü doğrultu atımlı faylar, KB-GD uzanımlı sağ yönlü doğrultu atımlı faylar ve yaklaşık K-G doğrultulu normal faylarla simgelenen aktif tektonik bir yapıya sahiptir. Van ilinin depremselliği söz konusu aktif fay mekanizması içinde değerlendirilmelidir

Seismic geomorphology of October 23 2011 Tabanlı Van earthquake and its relation to active tectonics of East Anatolia

This study aims to explore the origin and location of the October 23, 2011 Tabanlı-Van earthquake within active tectonic framework of Van city and its surroundings. Field-based studies have been done just after the Tabanlı-Van earthquake, and then geometry and type of observed deformational structures were evaluated and integrated with the results of previous active tectonic studies in the region. The observed structures can, based on seismic geomorphological indicators, be grouped into two main categories: (1) seismotectonic landforms related to tectonic stress, and (2) seismogravitational landforms related to seismic shaking and earth’s gravity. Seismotectonic landforms are common within a 10-km-long deformation zone located between Van Lake and Erçek Lake. These occurs as N50–70°E trending synclines and anticlines, most commonly in the area between Bardakçı and Topaktaş villages. Seismogravitational landforms are common in water-saturated sediments of Lake Van, particularly along its eastern margin; they are mostly liquefaction-induced features and are expressed in the form of lateral spreading, ground subsidence, and mass movement. Reverse fault planes deforming and displacing Upper Pliocene-Pleistocene sediments form the other group of common structures in the region. They trend in N50–70°E direction direction and dip at 45-50° to the north; they are oblique structures with sinistral strike-slip components. Similar active faults were mapped by Özkaymak (2003) at three locations to the north of Van city center: north of Beyüzümü village, near the main gate of the Yüzüncü Yıl University Zeve Campus and southern part of the Aşıt village. Evaluation of previously mapped fault segments and recent observations in the deformation zone are consistent with an approximately 10 km wide active thrust fault zone that comprises, at least, five N50–70°E striking and north-diping (ca. 47°) fault segments. Kinematics of these faults is consistent with fault plane solutions of 23 October, 2011 Tabanlı-Van earthquake. We suggest that newly formed and/or reactived fault segments in this fault zone were the source of the 23 October, 2011 Tabanlı-Van earthquake. The absence of surface rupture(s) is attributed to the geometry of a blind thrust. According to geological mapping and kinematic analyses, the active tectonics of the region is the manifestation of, in addition to ENE-WSW-striking thrust faulting, NNW-SSE-directed compression as expressed by NE-SW-trending sinistral strike-slip faulting, NW-SE-trending dextral strike-slip faulting and N-S-trending normal faulting.Bu çalışma, 23 Ekim 2011 tarihinde meydana gelen Tabanlı-Van (M = 7.2) depreminin bölgenin aktif tektoniği içerisindeki konumunu açıklamayı amaçlamaktadır. Bu bağlamda Tabanlı-Van depreminden sonra arazi çalışmaları yapılmış, depremle ilişkili deformasyon yapıları incelenmiş ve arazi gözlemlerinden elde edilen veriler ile Van ili ve çevresiyle ilgili olarak daha önce yapılmış aktif tektonik çalışmaları karşılaştırılarak değerlendirmeye gidilmiştir. Deprem sırasında veya hemen sonrasında yeryüzünde/yeryüzüne yakın kesimlerde meydana gelen deformasyonlar (sismik jeomorfolojik belirteçler) iki ana sınıfta toplanmıştır: (1) tektonik gerilmelere bağlı sismotektonik yüzey deformasyonları ve (2) sismik sarsılma ve yerçekimiyle ilgili sismogravitasyonal yüzey deformasyonları. Sismotektonik yüzey deformasyonları, Van Gölü ile Erçek Gölü arasında 10 km genişliğindeki kuşak boyunca gözlenir. Bu yapılar, genel uzanımları K50-70ºD olan senklinal ve antiklinal geometrili çöküntü ve sırtlar şeklindedir ve genellikle Bardakçı ile Topaktaş köyleri arasındaki asfalt yollarda gelişmiştir. Sismogavitasyonal yüzey deformasyonları yanal yayılma, oturma ve kütle hareketleri şeklinde gelişmiştir. Bu yapılar, Van Gölü doğu kenarı boyunca yüzlek veren eski Van Gölü çökelleri ve güncel alüvyonlarda yaygın olarak gelişmiştir. Tabanlı-Van depremi nedeniyle gelişen sismotektonik yüzey deformasyonlarının yanısıra, deformasyon kuşağı içerisinde ters faylanmalar da gözlenmiştir. Bu lokasyonlarda Üst PliyosenPleyistosen birimleri K50–70°D doğrultulu ve 45-50° kuzeybatıya eğimli sol yanal bileşenli ters faylarla kesilip ötelenmektedir. Benzer aktif fay hatları önceki çalışmalarda (Özkaymak, 2003), Van il merkezinin kuzeyinde yer alan Beyüzümü köyü kuzeyinde, Yüzüncü Yıl Üniversitesi Zeve Kampüsü girişinde ve Aşıt köyü güneyinde haritalanmıştır. Birbirinden bağımsız olarak haritalanan bu fay segmentleri birlikte değerlendirildiğinde, Çitören ile Beyüzümü köyleri arasında, yaklaşık 10 km genişliğinde, ortalama K50- 70°D doğrultulu ve 47° kuzeybatıya eğimli, birbirine paralel en az beş fay segmenti içeren aktif bir bindirme zonunun varlığı ortaya çıkar. Söz konusu fayların kinematik verileri 23 Ekim 2011 Tabanlı-Van depremini oluşturan ters fayın odak mekanizma çözümüyle uyumludur. Dolayısıyla, Pleyistosen-Holosen birimlerini kesen fay zonunun, 23 ekim Tabanlı-Van depreminde yeniden aktif hale geçerek yeni fay kolları oluşturduğu anlaşılmaktadır. Deprem sırasında oluşan fay koluna ait sıkışma kökenli yüzey deformasyonlarının belirgin bir yüzey kırığı oluşturacak şekilde gelişmemiş olması, yeni oluşan fayın geometrisi nedeniyle henüz yüzeye ulaşmadığı ve dolayısıyla gömülü fay niteliği taşıdığını göstermektedir. Jeolojik haritalama ve kinematik analiz verilerine göre, KKB-GGD eksenli sıkışma kuvvetleri etkisinde şekil değiştiren bölge; Tabanlı-Van depremini oluşturan DKD-BGB doğrultulu bindirme fay zonunun yanı sıra, KD-GB uzanımlı sol yönlü doğrultu atımlı faylar, KB-GD uzanımlı sağ yönlü doğrultu atımlı faylar ve yaklaşık K-G doğrultulu normal faylarla simgelenen aktif tektonik bir yapıya sahiptir. Van ilinin depremselliği söz konusu aktif fay mekanizması içinde değerlendirilmelidir