AVO signatures of actual and synthetic reflections from different petrophysical targets1

We use a marine seismic dataset to examine the reflections from two gas sands, a lignitic sand and a cineritic bed, by means of their amplitude versus offset (AVO) responses. This offset-dependent signature is related to specific petrophysical and thus elastic situations or to peculiar interference patterns and may help to distinguish the nature of the amplitude anomalies on the stack sections. The prestack analysis is carried out on seismic data which have undergone an accurate true-amplitude processing. It is found that the lignitic-sand reflections exhibit a decreasing AVO while the two-gas sands show markedly increasing AVO trends. Also the reflections from the cineritic layer show increasing amplitudes with offset that may be due either to the petrophysical nature of the cinerites or to thin-layer interference or to both. In order to verify the reliability of the actual AVO responses we develop a detailed model from well data and compute a synthetic CMP seismogram. In order to account for mode conversions and thin-layer effects, the synthetic seismograms are computed using the reflectivity method. The wavelets used in the synthetics are retrieved from actual seismic and borehole data by means of wavelet processing. When finely layered structures are present, the estimation of a reliable wavelet is extremely important to get the correct synthetic AVO response. In particular, the AVO responses of the cineritic layer differ substantially if we make use in the computation of the synthetics of a Ricker wavelet or of a wavelet estimated through wavelet processing. The good match between the observed and modelled data confirms the reliability of the processing sequence and of the final AVO signatures.     

Hydrology,hydrogeology and hydrochemistry of wetlands: a case study in Izmir Bird Paradise,Turkey

Izmir Bird Paradise is one of the most valuable wetlands in Turkey, but this area is now being threatened by the drying out of marshes and water pollution. This wetland consists of two ecosystems: fresh- and saltwater. The recharge of marshes is from rainfall, the Gediz River and groundwater from Can Suyu Pond. The water type of the river is Ca-Mg-Na-HCO₃-SO₄, whereas the groundwater is a Na-Cl water type. The reasons for the drying are long-term drought (evapotranspiration at 894 mm is >> rainfall at 546 mm), and excessive pumping of groundwater and seawater intrusion into Menemen Plain. Therefore, an additional freshwater resource is necessary. This water can be supplied from the limestone levels of Neogene sedimentary rocks in and around Izmir Bird Paradise that have a Ca-HCO₃ water type. Water pollution levels were also analysed. In the freshwater ecosystem Cd, Cr, Fe, Mn, Ni, Pb, Sb and Zn values, in the open channel in Izmir Bird Paradise Sb, Fe, Ni and Cd values, and in the river Fe, Pb and Sb values exceed the TSE 266 and EPA 2000 standards probably due to agricultural and industrial sources.     

Thermal behaviour of β-anhydrite CaSO<Subscript>4</Subscript> to 1,263 K

The thermal behaviour of β-anhydrite CaSO₄ has been investigated to 1,263 K in-situ real-time using laboratory parallel-beam X-ray powder diffraction data. The cell parameters expanded anisotropically, the c axis being the “softest”. This behaviour is due to the deformation of the CaO₈ polyhedron. In fact the two longest, independent, Ca–O bond distances show a significant component along the z direction.     

Thermal behaviour and kinetics of dehydration of gypsum in air from in situ real-time laboratory parallel-beam X-ray powder diffraction

Thermal behaviour and kinetics of dehydration of gypsum in air have been investigated using in situ real-time laboratory parallel-beam X-ray powder diffraction data evaluated by the Rietveld method. Thermal expansion has been analysed from 298 to 373 K. The high-temperature limits for the cell edges and for the cell volume, calculated using the Einstein equation, are 4.29 × 10⁻⁶, 4.94 × 10⁻⁵, 2.97 × 10⁻⁵, and 8.21 × 10⁻⁵. Thermal expansion of gypsum is strongly anisotropic being larger along the b axis mainly due to the weakening of hydrogen bond. Dehydration of gypsum has been investigated in isothermal conditions within the 348–403 K range with a temperature increase of 5 K. Dehydration proceeds through the CaSO₄·2H₂O → CaSO₄·0.5H₂O → γ-CaSO₄ steps. Experimental data have been fitted with the Avrami equation to calculate the empirical activation energy of the process. No change in transformation mechanism has been observed within the analysed temperature range and the corresponding E _a is 109(12) kJ/mol.     

The thermal behaviour of γ-CaSO<Subscript>4</Subscript>

Thermal behaviour of γ-anhydrite (γ-CaSO₄, soluble anhydrite) has been investigated in situ real-time using laboratory parallel-beam X-ray powder diffraction data. Thermal expansion has been analysed from 303 to 569 K with temperature steps of 4 K. Lattice parameters and volume were fitted with a second-order polynomial to calculate thermal expansion coefficients. Thermal expansion of γ-anhydrite is anisotropic being larger along the c axis. Within the 343–383 K thermal range, γ-anhydrite has been found to partially re-hydrate to bassanite CaSO₄·0.5H₂O. At 455 K the transformation γ-CaSO₄ → β-CaSO₄, insoluble anhydrite, starts reaching completion at 653 K.     

3-D Crustal Velocity Structure in Northwestern Greece

— The three-dimensional crustal velocity structure in the area of the northwestern Greek mainland was determined by P-wave travel time inversion, applying a two-step tomography procedure. The data set consists of the travel-time residuals of 584 well located earthquakes. In order to improve the initial (reference) velocity model, before the inversion of travel times, the minimum 1-D model was determined. Several tests were conducted to estimate model stability and hypocenter uncertainties. The velocity distribution in the shallow layers (4 and 7 km) is strongly affected by the crustal thickness variation and the complex tectonics. A first, well-defined velocity discontinuity appears at a depth of 3–6 km, along the Hellenides Mountain chain. A second low velocity anomaly is detected at a depth of 9–12 km and may be connected with the Alpidic orogenesis. Another interesting feature appears beneath the Amvrakikos Gulf (horstgraben structure), where relatively low velocities (<6.0 km^-1) appear to a depth of 20 km. Finally, a well-pronounced velocity boundary is found at a depth of 16 km. In general, low velocities are predominant along the Dinarides-Hellenides Mountain chain, rather typical for the upper crust.Acknowledgement. The authors thank the referees for their useful comments. Moreover, we would like to thank the General Secretariat for Research and Technology of Greece, for the partial support of this study.     

Hydrogeochemical investigation of Küçük Menderes River coastal wetland,Selçuk–Izmir,Turkey

Küçük Menderes River forms a rich coastal wetland inside in the Selçuk plain. Three saline/brackish lakes, one swamp and Küçük Menderes River are these wetlands’ components. Alkaline-slightly alkaline type lakes are recharged from precipitation and karstic springs that discharge from marble-schist and marble-alluvium contacts in the northern and southern parts of the study area. Water types of the wetland are Na–Cl and Na–Ca–Mg–HCO₃–Cl in both rainy and dry seasons. Both seawater intrusion and evaporation, as being the sources of the ions, justify the presence of Na–Cl, Na–SO₄ and Cl–SO₄, in the wetland water. Environmental isotopes were used to identify the relationship between wetland and groundwater in the Selçuk plain. The δ¹⁸O and δD composition of wetland area samples have changed between ?6.42 to ?4.56‰, and ?36.40 to ?23.80‰, respectively. The lakes and rivers are plotted on the mixing line by slope of 5.2 and these data indicate that wetland is affected from seawater intrusion. The recharge area that was sampled in order to compare the wetland has Ca–HCO₃ water type with a neutral-slightly alkaline pH values and the main hydrogeochemical process is weathering the different types of silicates. Iron, manganese and selenium are the dominant minor ions due to the high biological activities and organic matters in the lakes. There are two contamination risks for this wetland: (1) waste disposal site and (2) water treatment plant where the purified waters are released into the river. EC, Al, As, Cd, Cu, Fe and Zn values exceed those of aquatic life standards. In the near future these sites will pose a danger for wetland wild life and surrounding irrigation water suppliers.     

Determination of Selected Endocrine Disrupter Compounds at Trace Levels in Sewage Sludge Samples

Simultaneous determination of endocrine disrupter compounds (EDCs), namely diltiazem, progesterone, benzylbutylphthalate (BBP), estrone, and carbamazepine (Cbz) were performed by using high performance LC–electrospray tandem MS. The ultrasound‐aided sequential extraction of sludge samples was optimized to increase extraction efficiencies of the analytes; ranging between 93.0–98.3% recovery. The limit of detection values for diltiazem, progesterone, BBP, estrone, and Cbz were found as 0.78, 0.72, 0.24, 0.75, and 0.72 µg/kg, respectively. Sludge samples taken from Ankara Tatlar; Hurma, Lara and Kemer of Antalya, and Middle East Technical University‐vacuum rotating membrane wastewater treatment plant (WWTP) aeration tanks were analyzed for their EDCs contents under optimized conditions. Diltiazem was found in all the samples in the range between 116.4–180.8 ng/g while progesterone and estrone were not detected in any of the samples analyzed with the exception of Tatlar WWTP. The BBP concentration was between beyond detection and 9195.5 ng/g. In addition, Cbz was found in all the samples ranging from 25.6 to 118.8 ng/g.     

An extension of Szebehely's problem to holonomic systems

We study the problem of the determination of the potential function of forces generating a given family of orbits in the n-dimensional configuration space of the representative point of a holonomic system. We obtain first-order partial differential equations to solve the problem and we discuss some particular examples.

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Sunto Si studia il problema della determinazione del potenziale delle forze atte a far descrivere al punto rappresentativo di un sistema olonomo ad n gradi di libertà una traiettoria appartenente ad una assegnata famiglia di curve. Si scrivono le equazioni differenziali alle derivate parziali del primo ordine che reggono il problema e si considerano alcuni esempi particolari.