Evidence and implications of massive erosion along the Strait of İstanbul (Bosphorus)

The Strait of İstanbul (SoI) (Bosphorus) is a narrow valley, which has evolved tectonically from a stream, and in which thick sediment deposits have accumulated in the course of its evolution. Detailed seismic and multi-beam bathymetric data have revealed that the upper parts of the deeper channel deposits consist of parallel strata, which have mostly been eroded subsequently to their deposition. The resulting erosion surface is represented by the present channel floor in the strait, the estimated volume of the eroded material being approximately 2×10⁸ m³ . Erosion rate and seafloor morphology indicate that the flow direction was from the south to the north. This inner channel may have been formed by an abrupt flooding of the Black Sea by Mediterranean waters at the beginning of the latest connection between the Marmara and the Black seas. Subsequently, the Mediterranean bottom current of the modern two-way flow system, which was established at about 5–4 ka b.p., has given the latest shape to the strait floor.     

Constructing a 3D structural block diagram of the Central Basin in Marmara Sea by means of bathymetric and seismic data

In this study we made a comparative interpretation of multibeam bathymetric and seismic reflection data with different resolutions and penetration properties collected in the Central Basin of the Marmara Sea. Our main objectives were (i) to investigate and compare the active tectonic deformation observed on the sea bottom and within the uppermost sedimentary layers to that of the deep-seated deformation within the limits of resolution and penetration of the available geophysical data and (ii) to build a three-dimensional (3D) block diagram of the active tectonic and buried features by means of a sliced mapping technique. In this approach, we produced slice maps of the active and buried structural features at selected depths and then combined them to form a 3D structural block diagram. Motivation for our work was to produce a 3D structural diagram to derive a more detailed image of the structural features in the Central Basin where there is no available 3D seismic data. The observations from the bathymetry and seismic data and developed 3D diagram support the presence of a through-going strike-slip fault that forms a rotational depression zone against a right-stepping strike-slip faulting causing a pull-apart basin in the Central Depression zone.     

Eiszeitliche Formen und gegenwärtige Vergletscherung im nordostanatolischen Randgebirge

Ohne Zusammenfassung     

An investigation of seismicity for western Anatolia

In order to investigate the seismicity of western Anatolia limited with the coordinates of 36°–40° N, 26°–32° E, Gutenberg–Richter magnitude–frequency relation, seismic risk and recurrence period have been computed. The data belonging to both the historical period before 1900 (I₀ ≥ 5.0 corresponding to M_S ≥ 4.4) and the instrumental period until the end of 2006 (M_S ≥ 4.0) has been used in the analysis. The study area has been divided into 13 sub-regions due to certain seismotectonic characteristics, plate tectonic models and geology of the region. All the computations have been performed for these sub-regions, separately. According to the results, a and b values in the computed magnitude–frequency relations are in the intervals 3.19±0.17 – 5.15±0.52 and 0.42±0.05 – 0.66±0.07, respectively. The highest b values have been determined for sub-regions 3 and 12 (Demirci-Gediz and Gökova Gulf-Mu?la-Gölhisar). The lowest b values have also been determined for sub-regions 1 and 9 (Bal?kesir and Bodrum-?stanköy). Finally, seismic risk and recurrence period computations from a and b values have shown as expected that sub-regions 1 and 9 which have the lowest b values and the highest risks and the shortest-recurrence periods.     

Social vulnerability and seismic risk perception. Case study: the historic center of the Bucharest Municipality/Romania

Social vulnerability is as much a part of risk as building damage, hazard magnitude, and economic loss. Social vulnerability refers to the capacity of a human community exposed during the impact of a natural hazard event (in this case, an earthquake) to resist, cope with, and recover from that impact. In the perspective of the 3rd millennium, we come to understand that the most efficient and accessible way to reduce the pressure of natural risks is to reduce the vulnerability level of the human communities exposed to that certain hazard. This study aims to test, in an exposed and vulnerable area, the relationship between social vulnerability and the perception of the seismic risk. The research focuses only on the first level of social vulnerability, defined as the ability of an individual within a household to recover from a natural hazard impact (Dwyer et al. 2004). A prevailing assumption was that social vulnerability influences the level of perception of the seismic risk, in an exposed, vulnerable area. To this end, two samples were used, different under the aspect of social vulnerability, in the context of the same residential area. Social vulnerability was computed as a normalized composed index that includes the poverty ratio and the demographic vulnerability ratio (depending on the age, gender, and education level indicators). The statistical processing has indicated a significant difference in the high perception level for the two samples that were compared, in the sense that in the context of an increased level of social vulnerability, people generally better acknowledge the seismic risk.

Ultraviolet studies of the interstellar gas in the direction of the stars AE Aur (09.5V) andθ 2 Ori A (09.0V)

We have studied high-resolution SWP spectra of AE Aur and ² Ori A, obtained from the International Ultraviolet Explorer Satellite; and derived curve of growth and column densities ofCii,Cii ^*, Alii, Siii, Siii ^*,Sii, Crii, Feii, Niii, and Znii. It has been possible to fit these ions on one empirical curve of growth with a velocity parameterb=13 km s^–1 for both stars.Based on the observations made by the International Ultraviolet Explorer (IUE), and collected at the Villafranca Satellite Tracking Station of the European Space Agency.     

Postglacial floodings of the Marmara Sea: molluscs and sediments tell the story

The early Holocene marine flooding of the Black Sea has been the subject of intense scientific debate since the “Noah’s Flood” hypothesis was proposed in the late 1990s. The chronology of the flooding is not straightforward because the connection between the Black Sea and the Mediterranean Sea involves the intermediate Marmara Sea Basin via two sills (Dardanelles and Bosphorus). This study explores the chronology of late Pleistocene–Holocene flooding by examining sedimentary facies and molluscs from 24 gravity cores spanning shelf to slope settings in the southern Marmara Sea Basin. A late Pleistocene Ponto-Caspian (Neoeuxinian) mollusc association is found in 12 of the cores, comprising 14 mollusc species and dominated by brackish (oligohaline–lower mesohaline) endemic taxa (dreissenids, hydrobiids). The Neoeuxinian association is replaced by a Turritella–Corbula association at the onset of the Holocene. The latter is dominated by marine species, several of which are known to thrive under dysoxic conditions in muddy bottoms. This association is common in early Holocene intervals as well as sapropel intervals in younger Holocene strata. It is an indicator of low-salinity outflows from the Black Sea into the Marmara Sea that drive stratification. A marine Mediterranean association (87 species) represents both soft bottom and hard substrate faunas that lived in well-ventilated conditions and upper mesohaline–polyhaline salinities (ca. 25 psu). Shallower areas were occupied by hard substrate taxa and phytopdetritic communities, whereas deeper areas had soft bottom faunas. The middle shelf part of the northern Gemlik Gulf has intervals with irregular and discontinuous sedimentary structures admixed with worn Neoeuxinian and euryhaline Mediterranean faunas. These intervals represent reworking events (slumping) likely related to seismic activity rooted in the North Anatolian Fault system. The core data and faunas indicate an oscillating postglacial sea-level rise and phases of increased/decreased ventilation in the Marmara Sea during the Holocene, as well as palaeobiogeographic reorganisations of Ponto-Caspian and Mediterranean water bodies since the latest Pleistocene (<30 ka). The findings contribute to arguments against a single catastrophic flooding of the Black Sea at about 7.5 ka (Noah’s Flood).     

Hydrochemical and isotopic properties of Heybeli geothermal area (Afyon,Turkey)

The thermal waters at the Heybeli (K?z?lkirse) low-temperature geothermal field located in the Afyonkarahisar Province (western Turkey) are discharged from Paleozoic recrystallized limestone. The temperature, specific electrical conductivity, and pH values of the thermal waters are within the range of 28.9 to 54.7 °C, 587 to 3580 μS/cm, and 6.32 to 7.37, respectively. The Heybeli geothermal system is fed by meteoric waters. The waters are heated at depth by high geothermal gradient caused by the neotectonic activity in the deep and ascend to the surface through fractures and faults by convection. The thermal waters are of Na-Ca-HCO₃-SO₄ type and their chemical composition of the waters is mainly controlled by water-rock interaction and mixing processes. The δ¹⁸O, δ²H and tritium compositions show that the thermal waters are of meteoric origin and the residence time at the reservoir is longer than 50 years. Isotope data (δ³⁴S and δ¹³C) indicate recrystallized limestones as origin of CO₂ and structural substitution of sulfate into marine carbonates (CAS) as origin of sulfur. Chemical, \( {\updelta}^{18}{\mathrm{O}}_{\left({\mathrm{SO}}_4-{\mathrm{H}}_2\mathrm{O}\right)} \) isotope geothermometers and mineral equilibrium diagrams applied to thermal waters gave reservoir temperatures between 62 and 115 °C. Saturation index calculations show that the most expected minerals causing scaling at outflow conditions during the production and utilization of Heybeli geothermal waters are calcite, aragonite, dolomite, quartz, and chalcedony.