Structure of the Nemrut caldera (Eastern Anatolia, Turkey) and associated hydrothermal fluid circulation

Plio-Quaternary volcanism played an important role in the present physical state of Eastern Anatolia. Mount Nemrut, situated to the west of Lake Van is one of the main volcanic centers in the region, with a spectacular summit caldera 8.5 × 7 km in diameter. The most recent eruptions of the volcano were in 1441, 1597 and 1692. Nemrut Lake covers the western half of the caldera; it is a deep, half-bowl-shaped lake with a maximum depth of 176 m. Numerous eruption centers are exposed within the caldera as a consequence of magma–water interaction. Current activity of Nemrut caldera is revealed as hot springs, fumaroles and a small, hot lake.Self-potential and bathymetric surveys carried out in the caldera were used to characterize the structure of the caldera and the associated hydrothermal fluid circulation. In addition, analyses based on digital elevation models and satellite imagery were used to improve our knowledge about the structure of the caldera. According to SP results, the flanks of the volcano represent “the hydrogeologic zone”, whereas the intra-caldera region is an “active hydrothermal area” where the fluid circulation is controlled by structural discontinuities. There is also a northern fissure zone which exhibits hydrothermal signatures. Nemrut caldera collapsed piecemeal, with three main blocks. Stress controlling the collapse mechanism seems to be highly affected by the regional neotectonic regime. In addition to the historical activity, current hydrothermal and hydrogeologic conditions in the caldera, in which there is a large lake and shallow water table, increase the risk of the quiescent volcano.     

Volcanic ash and tsunami record of the Minoan Late Bronze Age Eruption (Santorini) in a distal setting,southwestern Turkey

We present the volcanic ash and tsunami record of the Minoan Late Bronze Age Eruption of Santorini (LBAES) in a distal setting in southwestern Turkey. In one of the drilled cores at the Letoon Hellenic antique site on Eşençay Delta, we encountered a 4 cm thick tephra deposit underlain by 46 cm thick tsunami-deposited sand (tsunamite), and an organic-rich layer that we ¹⁴C dated to 3295 ± 30 bp or 1633 bc. The relationship between Santorini distal volcanic ash and underlying tsunamite is described and interpreted. LBAES occurred in four main phases: (1) plinian; (2) phreatomagmatic; (3) phreatomagmatic with mudflows; and (4) ignimbritic flows and co-ignimbrite tephra falls. In this study, we aim to understand which eruptive phases generate distal ash during the Minoan eruptive sequence by examining the 3D surface morphology of ash formed by different fragmentation processes. To that end, we used numerous statistical multivariates, 3D fractal dimension of roughness, and a new textural parameter of surface area-3D/plotted area-2D to characterise the eruption dynamics. Based on ash surface morphologies and the calculated statistical parameters, we propose that that distal ash is represented by a single layer composed of well-mixed (coarse to fine) magmatic and phreatomagmatic ash.     

Applying the New Extended Direct Algebraic Method to Solve the Equation of Obliquely Interacting Waves in Shallow Waters

In this study, the potential Kadomtsev-Petviashvili(pKP) equation, which describes the oblique interaction of surface waves in shallow waters, is solved by the new extended direct algebraic method. The results of the study show that by applying the new direct algebraic method to the pKP equation, the behavior of the obliquely interacting surface waves in two dimensions can be analyzed. This article fairly clarifies the behaviors of surface waves in shallow waters. In the literature, several mathematical models have been developed in attempt to study these behaviors, with nonlinear mathematics being one of the most important steps; however, the investigations are still at a level that can be called ‘baby steps'. Therefore, every study to be carried out in this context is of great importance. Thus, this study will serve as a reference to guide scientists working in this field.     

Exploring Economic Development Through Headquarters: The Spatial Distribution of Turkey's Large Industrial Enterprises and Its Implications for Urban Systems

This article examines the distribution of the headquarters of top 500 large industrial enterprises in Turkey. It contributes to the knowledge of economic geography by examining regional clusters of headquarters activity in Turkey. As a country, Turkey's corporations have not been extensively analyzed or integrated into the international economic geography literature especially given the fact that headquarters activities in general are important but understudied in the literature of geography. This study therefore extends the corporate literature further in an international dimension, a priority that has been noted as important in the headquarters literature of geography. It argues that not only does the spatial organization of corporations remain important in urban systems but also that they are linked to the dynamics of local and regional economies within developing countries. It shows that various Turkish cities have distinctive internal structures comprising agglomerations of different industries. Although some of these industries are better performing in big cities, the majority of the cities in the top 500 large enterprises list underperform on average.     

New Analytical Solutions for Time Fractional Benjamin–Ono Equation Arising Internal Waves in Deep Water

In this article, the author sets up the abundant traveling wave solutions for time fractional Benjamin–Ono equation which was introduced to describe internal waves in stratified fluids by using Jacobi elliptic function expansion method. The traveling wave solutions are expressed in terms of the hyperbolic functions, the trigonometric functions and the rational functions. It can be seen that the obtained results are found to be important for the statement of some physical demonstrations of problems in mathematical physics and ocean engineering. In ocean engineering Benjamin–Ono equations are generally used in computer simulation for the water waves in deep water and open seas.     

Earthquake response analysis of the olive view hospital psychiatric day clinic

The collapse of the Olive View Hospital Psychiatric Day Clinic is studied using three biaxial force-deflection models to represent the columns of the building. These models are: shear collapse, elastic and inelastic. The biaxial models for shear and inelastic behaviour are new developments and are useful for non-linear structural dynamic studies. In the present study, the shear collapse model is intended to represent the actual prototype behaviour. The inelastic model, which is based on a hardening rule of plasticity, is used to study the performance of a hypothetical structure with the same storey shear capacity as the prototype but which exhibits ductile behaviour. The prototype structure had a base storey shear capacity of 25 per cent, and actually failed by shearing of all of the first floor columns. In the present study, the shear collapse model predicted this behaviour even with the El Centro accelerogram as input. This result may have far-reaching significance because many low-rise reinforced concrete buildings which were designed according to recent codes have similar storey shear capacity coefficients and column properties. According to this study, such buildings may collapse even in a moderate earthquake. In the inelastic representation, the structure was found to have a base storey shear capacity of 80 per cent when moment hinging was assumed to occur at the top and bottom of the columns. Even with this high strength capacity, the permanent offset computed from the inelastic model corresponded to a ductility factor of 5 when the Pacoima Dam accelerogram was used as input. On the basis of damage to other structures observed on the site, it seems likely that ground motion of about the Pacoima Dam intensity occurred at Olive View. From this it is concluded that a low-rise ductile frame concrete building, even with this high shear force capacity, may not prove satisfactory for hospital use when subjected to strong ground motion.     

Geochemistry of I-type granitoids in the Karaburun Peninsula, West Turkey: Evidence for Triassic continental arc magmatism following closure of the Palaeotethys

Abstract Triassic granitoids related to Palaeo- and Neo-Tethyan events occur widely in the metamorphic terranes largely affected by the Alpine orogeny. A first recorded unmetamorphosed plutonic body intruded into the Palaeotethyan mélange in western Turkey, called the Karaburun granodiorite, is composed of two small intrusive stocks that were emplaced between 240 and 220 Ma. It is compositionally diverse, ranging from granodiorite and tonalite to diorite. These rocks show heterogeneous compositions with 54 to 65 wt % SiO₂ and are calc-alkaline in character. They are also subalkaline with molar ratios of Al₂O₃/(Na₂O + K₂O) from 0.74 to 1.00 and are metaluminous. Most samples are diopside-normative (0.36–8.64), with Na₂O > K₂O. Chondrite normalized rare earth element (REE) patterns show various degrees of light REE (LREE) enrichment, with La _N = 57.79 to 99.59 and (La/Yb) _N = 5.98–7.85 and Eu negative anomalies (Eu/Eu* = 0.62–0.86). These rocks have coherent patterns in ocean ridge granite (ORG) normalized trace-element plots, marked by variable enrichment in K, Rb, Ba, Th, Ce and depletion in Ta and Nb, similar to I-type granites from subduction zones. In primitive mantle-normalized multi element variation diagrams, the granodiorites show pronounced depletions in the high-field-strength elements (HFSE; Nb, Ta, Zr), Sr, P, and Ti. Trace-element modeling of the Karaburun granodiorite suggests an origin through partial melting of the subduction-modified mantle wedge with minor contribution of crustal components through a process of strong fractional crystallization (FC) combined with slight assimilation-fractional crystallization (AFC). Exposures of typical continental-arc granodiorites in the Karaburun Mélange support the validity of the subduction-accretion model that implies the presence of an active continental margin following closure of the Palaeotethyan Ocean during the Triassic.     

Geochemistry and Ar/Ar geochronology of Miocene volcanic rocks from the Karaburun Peninsula: Implications for amphibole-bearing lithospheric mantle source,Western Anatolia

New geochemical and ⁴⁰Ar/³⁹Ar age data are presented from the Neogene volcanic units of the Karaburun Peninsula, the westernmost part of Western Anatolia. The volcanic rocks in the region are associated with Neogene lacustrine deposition and are characterized by (1) olivine-bearing basaltic-andesites to shoshonites (Karaburun volcanics), high-K calc-alkaline andesites, dacites and latites (Yaylaköy, Arma?anda? and Kocada? volcanics) of ~ 16–18 Ma, and (2) mildly-alkaline basalts (Ovac?k basalt) and rhyolites (Urla volcanics) of ~ 11–12 Ma. The first group of rocks is enriched in LILE and LREE with respect to the HREE and HFSE on N-MORB-normalised REE and multi-element spider diagrams. They are comparable geochemically with volcanic rocks in the surrounding regions such as Chios Island and other localities in Western Anatolia. The Ovac?k basalt is geochemically similar to the first stage early–middle Miocene volcanic rocks but differs from NW Anatolian late Miocene alkali basalts.     

Tsunamis Observed on and Near the Turkish Coast

For centuries, inhabitants of coastal areas have suffered from the effects of tsunamis. Turkey, with a coastline of 8333 km, has experienced many tsunamis.Historical records reveal that, during the observation period over 3000 years, the coastal and surrounding areas of Turkey have been affected by more than ninety tsunamis. These tended to cluster around the Marmara Sea, the city of Istanbul and the gulfs of Izmit, Izmir, Fethiye and Iskenderun. Each of the tsunami occurrences surveyed in this paper deserves further individual study. The most extensive available information concerns the tsunamis associated with the Istanbul Earthquakes of 1509 and 1894, the Eastern Marmara Earthquake in 1963 and that of Izmit in 1999,which disturbed the Marmara Sea; the Earthquake of 1939 in Erzincan ineastern Anatolia; and the 1968 Bartn Earthquake, which affected Fatsa and Amasra on the Black Sea. In addition to these, it is known that a tsunami occurred in 1598 on the shores of the Black Sea in connection with an earthquake at Amasya in northern Anatolia.     

Coexistence of abyssal and ultra-depleted SSZ type mantle peridotites in a Neo-Tethyan Ophiolite in SW Turkey: Constraints from mineral composition,whole-rock geochemistry (major–trace–REE–PGE), and Re–Os isotope systematics

We present new, whole-rock major and trace element chemistry, including rare earth elements (REE), platinum-group elements (PGE), and Re–Os isotope data from the upper mantle peridotites of a Cretaceous Neo-Tethyan ophiolite in the Mu?la area in SW Turkey. We also report extensive mineral chemistry data for these peridotites in order to better constrain their petrogenesis and tectonic environment of formation. The Mu?la peridotites consist mainly of cpx-harzburgite, depleted harzburgite, and dunite. Cpx-harzburgites are characterized by their higher average CaO (2.27 wt.%), Al₂O₃ (2.07 wt.%), REE (53 ppb), and ¹⁸⁷Os/¹⁸⁸Os_(i) ratios varying between 0.12497 and 0.12858. They contain Al-rich pyroxene with lower Cr content of coexisting spinel (Cr# = 13–22). In contrast, the depleted harzburgites and dunites are characterized by their lower average CaO (0.58 wt.%), Al₂O₃ (0.42 wt.%), and REE (1.24 ppb) values. Their clinopyroxenes are Al-poor and coexist with high-Cr spinel (Cr# = 33–83). The ¹⁸⁷Os/¹⁸⁸Os_(i) ratios are in the range of 0.12078–0.12588 and are more unradiogenic compared to those of the cpx-harzburgites.Mineral chemistry and whole rock trace and PGE data indicate that formation of the Mu?la peridotites cannot be explained by a single stage melting event; at least two-stages of melting and refertilization processes are needed to explain their geochemical characteristics. Trace element compositions of the cpx-harzburgites can be modeled by up to ~ 10–16% closed-system dynamic melting of a primitive mantle source, whereas those of the depleted harzburgites and dunites can be reproduced by ~ 10–16% open-system melting of an already depleted (~ 16%) mantle. These models indicate that the cpx-harzburgites are the products of first-stage melting and low-degrees of melt–rock interaction that occurred in a mid-ocean ridge (MOR) environment. However, the depleted harzburgites and dunites are the product of second-stage melting and related refertilization which took place in a supra subduction zone (SSZ) environment. The Re–Os isotope systematics of the Mu?la peridotites gives model age clusters of ~ 250 Ma, ~ 400 Ma and ~ 750 Ma that may record major tectonic events associated with the geodynamic evolution of the Neo-Tethyan, Rheic, and Proto-Tethyan oceans, respectively. Furthermore, > 1000 Ma model ages can be interpreted as a result of an ancient melting event before the Proto-Tethys evolution.