Sidescan survey results from a multibeam sonar system—sea beam 2000     

Kushal Talukdar  William Capell  Christos Zabounidis 《Marine Geodesy》2013,36(2-3):63-79

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Loading protocols for European regions of low to moderate seismicity     

Panagiotis E. Mergos  Katrin Beyer 《Bulletin of Earthquake Engineering》2014,12(6):2507-2530

Existing loading protocols for quasi-static cyclic testing of structures are based on recordings from regions of high seismicity. For regions of low to moderate seismicity they overestimate imposed cumulative damage demands. Since structural capacities are a function of demand, existing loading protocols applied to specimens representative of structures in low to moderate seismicity regions might underestimate structural strength and deformation capacity. To overcome this problem, this paper deals with the development of cyclic loading protocols for European regions of low to moderate seismicity. Cumulative damage demands imposed by a set of 60 ground motion records are evaluated for a wide variety of SDOF systems that reflect the fundamental properties of a large portion of the existing building stock. The ground motions are representative of the seismic hazard level corresponding to a 2 % probability of exceedance in 50 years in a European moderate seismicity region. To meet the calculated cumulative damage demands, loading protocols for different structural types and vibration periods are developed. For comparison, cumulative seismic demands are also calculated for existing protocols and a set of records that was used in a previous study on loading protocols for regions of high seismicity. The median cumulative demands for regions of low to moderate seismicity are significantly less than those of existing protocols and records of high seismicity regions. For regions of low to moderate seismicity the new protocols might therefore result in larger strength and deformation capacities and hence in more cost-effective structural configurations or less expensive retrofit measures.  相似文献   

The Role of GNSS Vertical Velocities to Correct Estimates of Sea Level Rise from Tide Gauge Measurements in Greece     

Stylianos Bitharis  Christos Pikridas  Aristeidis Fotiou  Dimitrios Rossikopoulos  Harald Schuh 《Marine Geodesy》2017,40(5):297-314

In this study, we show how the Global Navigation Satellite System (GNSS)-derived vertical velocities contribute to the correction of tide gauge (TG) measurements used for the sea level rise estimation in Greece. Twelve sites with records of local sea level heights are processed in order to estimate their trend. Certain error sources related to TGs, e.g. equipment changes, data noise, may lead to biased or erroneous estimations of the sea level height. Therefore, it would be preferred to follow a robust estimation technique in order to detect and reduce outlier effects. The geocentric sea level rise is estimated by taking into account the land vertical motion of co-located GNSS permanent stations at the Hellenic area. TGs measure the height of the water relative to a monitored geodetic benchmark on land. On the other hand, using GNSS-based methods the vertical land motion can be derived. By means of extended models fitted to the GNSS time-series position, obtained from seven years of continuous data analysis, periodic signals are well described. The synergy of the two co-located techniques results in the correction of TG relative sea level heights taking into account the GNSS vertical velocities and consequently obtaining the conversion to absolute (geocentric) sea level trend.  相似文献   

On the accuracy of the ground force estimated in vibroseis acquisition   总被引：1，自引：0，他引：1  

Christos Saragiotis  Péter Scholtz  Claudio Bagaini 《Geophysical Prospecting》2010,58(1):69-80

For a linear elastic Earth the time derivative of the ground force is considered proportional to the far-field wavelet. Under the assumption that the baseplate is stiff and the bending forces of the baseplate are negligible, the ground force is also approximated by the sum of the accelerations of the baseplate and the reaction mass weighted by the respective masses. Combining these two assumptions, the time derivative of the weighted sum is considered proportional to the far-field wavelet. This result, often referred to as the far-field wavelet assumption, although convenient and most often employed is not always valid. We explore its validity using the spectral harmonic ratios of recorded data, which are used extensively in data filtering and analysis of vibratory data. We show that the far-field wavelet assumption fails particularly for harmonic components of even order. More compact soil after repeated shots further invalidates this assumption. Non-linear modelling of the ground under the vibrator point may provide a direction towards solving this discrepancy. Finally, we describe a method for the estimation of the harmonic spectral ratios.  相似文献   

Lowermost Mantle Velocity Estimations Beneath the Central North Atlantic Area from Pdif Observed at Balkan,East Mediterranean,and American Stations     

Marian Ivan  Daniela Veronica Ghica  Andrej Gosar  Panagiotis Hatzidimitriou  Rami Hofstetter  Gulten Polat  Rongjiang Wang 《Pure and Applied Geophysics》2015,172(2):283-293

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Turbulence in vegetated flows: Volume-average analysis and modelling aspects     

Dimitris Souliotis  Panagiotis Prinos 《Acta Geophysica》2008,56(3):894-917

Two approaches for the modelling of turbulence in vegetated flows have been developed in the past. The “microscopic” approach which is straightforward but limited to simple cases and the “macroscopic” approach which is based on Volume Average Theory (VAT). In this study, aspects of Volume-Average (VA) analysis and modelling are investigated for turbulent vegetated flow using computed three-dimensional results from the solution of the Reynolds-Averaged Navier-Stokes (RANS) equations around a representative vegetal element. In particular (a) the VA transport equations for k and ε, based on VAT, are properly derived, (b) the Boussinesq hypothesis for the VA quantities, employed in 〈k〉-〈ε〉 turbulence models is tested, and (c) the values of the coefficients used in such turbulence models are assessed in comparison with those used in the classical turbulence models.  相似文献   

Addendum     

Christos Katagas 《Contributions to Mineralogy and Petrology》1974,48(2):148-148

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About applying linear structural method on ocean data: Adjustment of satellite wave data     

Takvor Soukissian  Christos Kechris 《Ocean Engineering》2007,34(3-4):371-389

Linear structural relations express the linear relationship between random variables when each of the variables under consideration is subjected to inherent variability and measurement error. The linear structural method is more general than the classical regression, which is often used incorrectly in calibration of altimeter data or validation of wave model results. In this work the linear structural method is elaborated and applied for the adjustment of TOPEX/Poseidon (T/P) data by means of in situ measured wave data in the Aegean Sea. In addition, a comparison of the buoy and T/P data with the WAM wave model predictions is performed revealing an underestimation trend of the model.  相似文献   

Study of the N, P and Si fluxes between fish farm sediment and seawater. Results of simulation experiments employing a benthic chamber under various redox conditions   总被引：2，自引：0，他引：2  

Christos Belias  Manos Dassenakis  Michael Scoullos   《Marine Chemistry》2007,103(3-4):266-275

The rapidly expanding industry of marine cage fish farming of sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) in the Mediterranean Sea over the last decade has often had damaging effects on the benthic aquatic environment near the fish farm installations. It has been observed that the food-remains, together with the pellets and metabolic products from fish, frequently form a “nepheloid” sediment layer covering large areas of the seabed. Under these conditions anoxia and/or hypoxia develop and affect benthic communities while the quality of the marine environment deteriorates for long periods, extending even beyond the life span of the fish farm itself. In most cases the affected areas act initially as sediment traps and in a second phase as secondary sources of organic carbon, nutrients and other substances.The aim of this paper is to explore the behaviour of such an affected area under different redox regimes by measuring the fluxes of ammonium, nitrite, nitrate, TDN, phosphate, TDP and silicate between the surface sediment and the overlying waters. To achieve this goal we constructed a prototype benthic chamber capable of sampling considerable quantities of affected undisturbed sediment along with its overlying water. The chamber was transported to the laboratory where simulation experiments reproducing the conditions occurring in nature, including the extreme ones, were carried out and studied carefully. The chamber allows the full and fine control of the dissolved oxygen concentration – and thus of the redox potential – as well as water temperature while subsamples of both water and sediment could be obtained and analysed for a series of chemical substances. The controlled laboratory chamber experiments reproduced four successional phases: 1) deoxygenation, 2) hypoxia, 3) reoxygenation and 4) anoxia.The results showed that even minor changes in the redox conditions at a relatively narrow zone near the water sediment interface have significant impacts on the concentrations of dissolved nitrogen, phosphorus and silicate compounds.With decreasing oxygen supply (phases 1, 2 and 4), the concentrations of ammonium, nitrite, TDN, phosphate, TDP and silicate rapidly increase, those of nitrate decrease. DON and DOP exhibit remarkable fluctuations.During reoxygenation (phase 3) the concentrations of ammonium stabilise, the nitrate concentration decreases while nitrite shows an increasing trend. Decreases in phosphate and silicate concentrations were also observed paralleled by TDP stabilization and DOP increasing trend. TDN shows a relatively small increase while the DON concentration fluctuates significantly.  相似文献   

Mineralogical and fluid inclusion constraints on the evolution of the Plaka intrusion-related ore system, Lavrion, Greece     

P. Voudouris  V. Melfos  P. G. Spry  T. Bonsall  M. Tarkian  M. Economou-Eliopoulos 《Mineralogy and Petrology》2008,93(1-2):79-110

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