Frontal modification and lee cyclogenesis in the Alps: A case study using the ALPEX reanalysis data set

Summary The interaction of a cold front with the Alps is studied by means of real-case numerical simulations for a case occurring at the end of the Alpine Experiment (ALPEX) on 28 April–2 May, 1982. Simulations are performed with the numerical weather prediction model chain Europa-Modell (EM) and its one-way nested high-resolution model (HM) of the German and Swiss Weather Services. The outer EM simulation (56 km horizontal resolution) uses initial and lateral boundary fields taken from the ALPEX-IIIb reanalysis data set. This reanalysis data set is based on the operational EM analysis scheme, but takes into consideration a wide range of field phase data taken during the ALPEX field campaign. A comparison of simulations driven by the ALPEX and ECMWF reanalysis (ERA) data is performed. The simulation driven by the former captures the intensity and vertical depth of the developing lee cyclone substantially better than the corresponding run driven by the ERA. The transient development of the impingement of a cold front on the Alps induces a wide range of mesoscale phenomenon such as flow splitting, mistral, north foehn, cyclogenesis, anticyclonic vortex and bora. These flow evolutions are analyzed using HM simulations with a horizontal resolution of 14 km and visualized performing comprehensive trajectory calculations. Received September 9, 2000/Revised November 28, 2000     

Risk Assessment of Vertical Breakwaters -A Case Study in Turkey

In the reliability-risk assessment, the second order reliability index (βⅡ ) method and the Conditional Expectation Monte Carlo (CEMC) simulation are interrelated as a new Level Ⅲ approach for the analysis of the safety level of the Dalaman yacht harbor vertical wall breakwater in Turkey. The missing wave data of the Dalaman measurement station are hindcasted by use of multi-layer feed-forward neural networks with the steepest descent and conjugate gradient algorithms. The structural failure probabilities of sliding and overturning failure modes are forecasted by approximation of the failure sur-face with a second-degree polynomial of an equal curvature at the design point. in the new approach, for each randomly generated load and tide combination, the joint failure probability reflects both the occurrence probability of loading condition and the structural failure risk at the limit state. The approach can be applied to risk assessment of vertical breakwaters in short CPU durations of portable comput     

Late Pleistocene–Holocene history of the Golden Horn Estuary,Istanbul

The historical Golden Horn Estuary (GHE), near the confluence of the Istanbul Strait (Bosphorus) and the Sea of Marmara in the European part of Istanbul, has been used as a natural harbor since 330 a.d. The sedimentary infill of the GHE is 15–46 m thick, deposited unconformably above the turbiditic sandstones of the Carboniferous Trakya Formation. Chronostratigraphic and paleontological analyses of the infill sequence indicate that the GHE was a fluvial channel prior to 13,500 cal. a (calibrated to calendar years) B.P. It subsequently became gradually influenced by marine waters, and was a brackish-water environment until 9,500 cal. a B.P. Normal marine salinities prevailed at ca. 9,500−5,600 cal. a B.P., with suboxic/dysoxic bottom-water conditions. The increase in salinity at 9,500 cal. a B.P. was most likely caused by Mediterranean water outflow into the Black Sea through the Istanbul Strait. The estuary was influenced by large fluvial inputs between 5,600 and 1,000 cal. a B.P., possibly during a distinct pluvial period, as shown by coarse siliciclastic sediments deposited on the flanks. It has become a highly polluted environment with marked anthropogenic inputs during the last millennium. The finding that the sediment infill sequence above the Carboniferous basement is not older than about 20 ka strongly suggests that the Golden Horn Estuary acquired its present-day morphology during the late glacial–Holocene period.     

Probabilistic seismic hazard assessment for Lake Van basin,Turkey

The seismic hazard for the Lake Van basin is computed using a probabilistic approach, along with the earthquake data from 1907 to present. The spatial distribution of seismic events between the longitudes of 41–45° and the latitudes of 37.5–40°, which encompasses the region, indicates distinct seismic zones. The positions of these zones are well aligned with the known tectonic features such as the Tutak-Çald?ran fault zone, the Özalp fault zone, the Geva? fault zone, the Bitlis fault zone and Karl?ova junction where the North Anatolian fault zone and East Anatolian fault zone meet. These faults are known to have generated major earthquakes which strongly affected cities and towns such as Van, Mu?, Bitlis, Özalp, Muradiye, Çald?ran, Erci?, Adilcevaz, Ahlat, Tatvan, Geva? and Gürp?nar. The recurrence intervals of M _s ≥ 4 earthquakes were evaluated in order to obtain the parameters of the Gutenberg–Richter measurements for seismic zones. More importantly, iso-acceleration maps of the basin were produced with a grid interval of 0.05 degrees. These maps are developed for 100- and 475- year return periods, utilizing the domestic attenuation relationships. A computer program called Sistehan II was utilized to generate these maps.     

Amphibole perspective to unravel pre-eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes: a case study from Ciomadul volcano (SE Carpathians)

Ciomadul is the youngest volcano in the Carpathian–Pannonian region produced crystal-rich high-K dacites that contain abundant amphibole phenocrysts. The amphiboles in the studied dacites are characterized by large variety of zoning patterns, textures, and a wide range of compositions (e.g., 6.4–15 wt% Al₂O₃, 79–821 ppm Sr) often in thin-section scale and even in single crystals. Two amphibole populations were observed in the dacite: low-Al hornblendes represent a cold (<800 °C) silicic crystal mush, whereas the high-Al pargasites crystallized in a hot (>900 °C) mafic magma. Amphibole thermobarometry suggests that the silicic crystal mush was stored in an upper crustal storage (~8–12 km). This was also the place where the erupted dacitic magma was formed during the remobilization of upper crustal silicic crystal mush body by hot mafic magma indicated by simple-zoned and composite amphiboles. This includes reheating (by ~200 °C) and partial remelting of different parts of the crystal mush followed by intensive crystallization of the second mineral population (including pargasites). Breakdown textures of amphiboles imply that they were formed by reheating in case of hornblendes, suggesting that pre-eruptive heating and mixing could take place within days or weeks before the eruption. The decompression rim of pargasites suggests around 12 days of magma ascent in the conduit. Several arc volcanoes produce mixed intermediate magmas with similar bimodal amphibole cargo as the Ciomadul, but in our dacite the two amphibole population can be found even in a single crystal (composite amphiboles). Our study indicates that high-Al pargasites form as a second generation in these magmas after the mafic replenishment into a silicic capture zone; thus, they cannot unambiguously indicate a deeper mafic storage zone beneath these volcanoes. The simple-zoned and composite amphiboles provide direct evidence that significant compositional variations of amphiboles do not necessarily mean variation in the pressure of crystallization even if the Al-tschermak substitution can be recognized, suggesting that amphibole barometers that consider only amphibole composition may often yield unrealistic pressure variation.     

Origin of dolomite in the Late Jurassic platform carbonates,Bolkar Mountains,Central Taurides,Turkey: Petrographic and geochemical evidence

The Late Jurassic-early Senonian Cehennemdere Formation extending in an E-W direction in a wide area at the south of the Bolkar Mountains (Central Taurides, Turkey) is composed of platform carbonates. The formation was deposited in an environment that was being transformed from a shallow carbonate platform to an open shelf and a continental slope, and was buried until late Paleocene uplift. The formation, with a thickness of about 360 m, was chiefly developed as textures consisting of mudstone and wackestone and has been commonly dolomitized. Based on petrographic and geochemical properties, four types of replacement dolomites and two types of dolomite cements were distinguished. Replacement dolomite (RD), which is cut by low-amplitude stylolites developed as (1) fine crystalline planar-s dolomite (RD1); (2) medium crystalline planar-s dolomite (RD2); (3) medium-coarse crystalline planar-e dolomite (RD3) and; (4) coarse crystalline planar-s (e) dolomite (RD4). Two types of dolomite cements (CD) observed in low abundance and overlie low-amplitude stylolites: (1) coarse crystalline dolomite cement (CD1) filling dissolution voids and fractures in RD1 dolomites, and; (2) rim dolomite cement (CD2) that commonly develops on the space-facing surfaces of RD4 dolomite. Replacement dolomites are non-stoichiometric (Ca_54–59Mg_41–46), have similar geochemical properties, and are generally dull red/non luminescent in appearance. Replacement dolomite is represented by δ¹⁸O values from −4.5 to −0.5‰ VPDB, δ¹³C values of −0.7 to 2.7‰ VPDB, and ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.707178 to 0.707692. Petrographic and geochemical data indicate that replacement dolomite (particularly RD2, RD3, and RD4 dolomite) was formed at shallow-intermediate burial depths during the Late Jurassic-Early Cretaceous, from seawater and/or from slightly modified seawater. The replacement dolomite (RD) was then recrystallized at increased burial depths and temperatures. Dolomite cements are similar to replacement dolomites in that they are non-stoichiometric (Ca₅₅Mg₄₅) and have similar trace element compositions. CD1 dolomite, which cuts low-amplitude stylolites, was formed during intermediate to deep burial following stylolite development. CD2 dolomite was precipitated in intercrystal pores in association with RD4 dolomite. Remaining pore space was filled with bitumen.     

Tectonic significance of deformation patterns in granitoid rocks of the Menderes nappes, Anatolide belt, southwest Turkey

Deformation fabrics in Proterozoic/Cambrian granitic rocks of the Çine nappe, and mid-Triassic granites of the Bozdag nappe constrain aspects of the tectonometamorphic evolution of the Menderes nappes of southwest Turkey. Based on intrusive contacts and structural criteria, the Proterozoic/Cambrian granitic rocks of the Çine nappe are subdivided into older orthogneisses and younger metagranites. The deformation history of the granitic rocks documents two major deformation events. An early, pre-Alpine deformation event (D_PA) during amphibolite-facies metamorphism affected only the orthogneisses and produced predominantly top-to-NE shear-sense indicators associated with a NE-trending stretching lineation. The younger metagranites are deformed both by isolated shear zones, and by a major shear zone along the southern boundary of the Çine submassif. We refer to this Alpine deformation event as D_A3. D_A3 shear zones are associated with a N-trending stretching lineation, which formed during greenschist-facies metamorphism. Kinematic indicators associated with this stretching lineation reveal a top-to-south sense of shear. The greenschist-facies shear zones cut the amphibolite-facies structures in the orthogneisses. ²⁰⁷Pb/²⁰⁶Pb dating of magmatic zircons from a metagranite, which crosscuts orthogneiss containing amphibolite-facies top-to-NE shear-sense indicators, shows that D_PA occurred before 547.2ǃ.0 Ma. Such an age is corroborated by the observation that mid-Triassic granites of the Çine and Bozdag nappes lack D_PA structures. The younger, top-to-south fabrics formed most likely as a result of top-to-south Alpine nappe stacking during the collision of the Sakarya continent with Anatolia in the Eocene.