Carbonate weathering and connate seawater influencing karst groundwaters in the Gevas–Gurpinar–Güzelsu basins,Turkey

There are 59 springs at the Gevas–Gurp?nar–Güzelsu basins, 38 of these springs emerge from the fractured karst aquifers (recrystallized limestone and travertine) and 21 emerge from the Yuksekova ophiolites, K?rkgeçit formation and alluvium. The groundwater samples collected from 38 out of the total of 59 springs, two streams, one lake and 12 wells were analyzed physico-chemically in the year 2002. EC and TDS values of groundwater increased from the marble (high altitude) to the ophiolites and alluvium (toward Lake Van) as a result of carbonate dissolution and connate seawater. Five chemical types of groundwater are identified: Ca–Mg–HCO₃, Mg–Ca–HCO₃, Mg–Na–HCO₃, Na–Ca–HCO₃ and Mg–Ca–Na–HCO₃. The calculations and hydrochemical interpretations show that the high concentrations of Ca²⁺, Mg²⁺ and HCO₃ ^? as predominant ions in the waters are mainly attributed to carbonate rocks and high pCO₂ in soil. Most of the karst springs are oversaturated in calcite, aragonite and dolomite and undersaturated in gypsum, halite and anhydrite. The water–rock interaction processes that singly or in combination influence the chemical composition of each water type include dissolution of carbonate (calcite and dolomite), calcite precipitation, cation exchange and freshening of connate seawater. These processes contribute considerably to the concentration of major ions in the groundwater. Stable isotope contents of the groundwater suggest mainly direct integrative recharge.     

Ground water radon anomalies in Bodrum Peninsula

Bodrum Peninsula is located between Hellenic Trench in the west and Gökova Fault Zone in the east which is affected by hundreds of earthquakes every year. Because of its active environment is allowed to monitor tracers/precursors continuously to analyse natural processes. This study focused on the determination of ground water radon (²²²Rn) concentrations in the Bodrum Peninsula in terms of seismic activities. Radon levels of ten ground water wells were measured periodically throughout the peninsula and these wells were divided into two groups according to the number of earthquakes they are exposed. Radon variations in second group stations are fairly significant as a result of high number of earthquakes. In these stations, radon continuously increased before the seismic storm and then decreased step by step. The results indicated that radon variations in ground waters of Bodrum Peninsula can be a good indicator for seismic storms instead of one specific event.     

Seismic failure probability of concrete slab on CFR dams with welded and friction contacts by response surface method

In this study, failure probability of the concrete slab on concrete-faced rockfill (CFR) dams with welded and friction contact is investigated under earthquake effects by reliability analysis. For this purpose, Torul CFR dam is selected as an example and numerical solutions are performed by considering combination of reliability analysis–finite element method. 1992 Erzincan earthquake acceleration record is used in the finite element analysis considering deconvolved-base rock input model. In this model, the ground motion to be applied to the foundation base rock is obtained by deconvolution of the free-field surface record. In the materially nonlinear analysis, Drucker–Prager model is used for concrete slab and multi-linear kinematic hardening model is utilized for rockfill. Geometrically nonlinearity is also taken into account. Viscous boundary conditions are defined in the finite element model for both foundation soil and reservoir water. The hydrodynamic pressure of the reservoir water is considered using 2D fluid finite elements based on the Lagrangian approach. Both welded contact and friction contact based on the Coulomb’s friction law are defined in the structural connections. Improved Rackwitz–Fiessler method is used with response surface method in the reliability analysis. The tensile and compression strengths of the concrete slab are utilized in the implicit limit state functions considering various thicknesses. The probability of failure of the most critical points in the concrete slab is obtained. According to this study, the probabilities of failure obtained from the CFR dam including friction contact are lower. When the welded contact is considered in joints, the probability of failure of the concrete slab is 1 due to tensile stress limit state and compression stress limit state only if concrete slab is linear. The most critical probability of failure of the concrete slab appears in the case that the concrete slab is linear and rockfill is materially nonlinear. The probability of failure of the concrete slab decreases if the nonlinearity of the concrete is considered. Also, hydrodynamic pressure decreases the reliability of the concrete slab.     

Linear and nonlinear response of concrete slab on CFR dam during earthquake

The joint between concrete slab and rockfill is designed as welded contact in the classical modeling of concrete-faced rockfill (CFR) dams and earthquake response of the CFR dams is determined by this method. In this study, linear and nonlinear response of Torul CFR Dam including interface element between concrete slab and rockfill were investigated for the duration of strong seismic excitation. The finite element analyses were performed by employing both cases, empty and full reservoir, to research the effect of the reservoir water on the earthquake response of the dam. The reservoir water was modeled with fluid finite elements by the Lagrangian approach. The Drucker-Prager model was used in nonlinear analyses for concrete slab, rockfill and soil materials. According to finite element analyses, displacement and stress components were increased by hydrodynamic pressure. The nonlinear response of the concrete slab was monitored about the peak ground acceleration (pga). This study reveals that the size of sliding zone increases with increasing acceleration amplitudes.     

Evaluation of displacement coefficient method for seismically retrofitted buildings with various ductility capacities

This research study is aimed at evaluating the accuracy of the displacement coefficient method (DCM) of FEMA 440 and associated nonlinear static procedure (NLSP) for actual buildings with soft story mechanism and various ductility capacities. The DCM and associated NLSP are evaluated using two existing seismically vulnerable buildings with soft story mechanism. The buildings are first retrofitted using a ductile steel‐brace‐link system to represent those with good ductility capacity and then retrofitted with RC squat infill shear panels (SISPs) to represent those with relatively poor ductility capacity. The evaluation of the DCM of FEMA 440 and associated NLSP is then performed by comparing the roof displacements (target displacements), maximum interstory drifts, and maximum plastic hinge rotations of the original and retrofitted buildings obtained from NLSP (at the target displacement level of DCM) with those obtained from nonlinear response history (NRH) analyses for three different seismic performance levels. It is observed that the DCM, and hence, the NLSP fail to accurately predict the NRH analyses results mainly due to uncertainties in the coefficient C₁ of the DCM in the short period range, the inability of the DCM to capture the failure of structural members beyond a certain lateral displacement or plastic rotation limit and associated soft story mechanism. Copyright © 2013 John Wiley & Sons, Ltd.     

Winter mean temperature variability in Turkey associated with the North Atlantic Oscillation

Changes and variability in seasonal average mean and monthly mean winter (DJF) air temperature series at 70 stations of Turkey and the circulation types at 500-hPa geopotential height level were investigated to explain atmospheric controls of temperature variations during the extreme (weak and strong) phases and normal (negative and positive) phases of the North Atlantic Oscillation (i.e., Ponta Delgada–Reykjavik and the Gibraltar–Reykjavik) indices. During the positive phases of the North Atlantic Oscillation indices (NAOIs), northeasterly circulation increased, and thus spatially coherent and significant cold signals dominate over the majority of Turkey. This pattern is closely linked to anomalously low 500-hPa heights over the region of the Icelandic Low, and anomalously high geopotential heights over the regions of the Azores High, the western Mediterranean basin and the Europe, in general including the Balkans and northwest Turkey. Contrarily, during the negative phases of the NAOIs, prevailing westerly winds that originate from the subtropical northeast Atlantic increase, and thus spatially coherent and significant warm signals over the Anatolian peninsula appear. This pattern is closely linked to the increased cyclonic activity and associated increased westerly and southwesterly circulation causing warm maritime air advection over the Mediterranean basin toward Turkey.     

Seismic behaviour of the North Anatolian Fault beneath the Sea of Marmara (NW Turkey): implications for earthquake recurrence times and future seismic hazard

Possible long-term seismic behaviour of the Northern strand of the North Anatolian Fault Zone, between western extreme of the 1999 İzmit rupture and the Aegean Sea, after 400 AD is studied by examining the historical seismicity, the submarine fault mapping and the paleoseismological studies of the recent scientific efforts. The long-term seismic behaviour is discussed through two possible seismicity models devised from M _S ≥ 7.0 historical earthquakes. The estimated return period of years of the fault segments for M1 and M2 seismic models along with their standard deviations are as follows: F4 segment 255 ± 60 and 258 ± 12; F5 segment 258 ± 60 and 258 ± 53; F6 segment 258 ± 60 and 258 ± 53; F7 segment 286 ± 103 and 286 ± 90; F8 segment 286 ± 90 and 286 ± 36. As the latest ruptures on the submarine segments have been reported to be during the 1754–1766 earthquake sequence, and the 1912 mainshock rupture has been evidenced to extend almost all over the western part of the Sea of Marmara, our results imply imminent seismic hazard and, considering the mean recurrence time, a large earthquake to strike the eastern part of the Sea of Marmara in the next two decades.     

Iron Budget and Its Correlations with Macronutrients in the Inshore Waters of the Aegean Sea

Macronutrients and micronutrients were measured during the phytoplankton bloom period and then seasonally monitored after the bloom in the polluted Izmir Bay. Iron and the macronutrients (phosphate, ammonium, nitrate, nitrite, and silicate) were abundant in the waters of the inner and middle sections of Izmir Bay. The iron concentration decreased exponentially from the eutrophic inner bay to the oligotrophic outer bay. Suboxic–anoxic processes and the resuspension dynamics in the sediment were the most important factor in the control of iron, ammonium, and phosphate enrichment in the bay beside the anthropogenic activities. The biological removal of Fe in the inner and middle bay and nonbiological removal in the outer bay were effective in controlling iron concentration in Izmir Bay. The nitrate, nitrite, and ammonium nitrogen (N) and Si decreased to critical levels in the middle and outer bay at the end of the summer as long as the concentration of phosphate was high. The N/P ratios in the bay suggested that N might be the controlling nutrient for phytoplankton growth particularly in the middle and outer bay throughout summer. Furthermore, Si was also able to have controlling impact probably on diatom growth during autumn and winter in the inner and middle bay and in the early spring in the outer bay. The N/Si/Chelex labile Fe ratios implied that the iron could be a critical controlling nutrient for phytoplankton growth during early April in the outer bay unless the other macronutrients were low.     

Stress history controls the spatial pattern of aftershocks: case studies from strike-slip earthquakes

International Journal of Earth Sciences - Earthquake ruptures perturb stress within the surrounding crustal volume and as it is widely accepted now these stress perturbations strongly correlates...