Use of surface sediments in Pagassitikos Gulf, Greece, to detect anthropogenic influence     

A. P. Karageorgis  A. I. Sioulas  C. L. Anagnostou 《Geo-Marine Letters》2001,21(4):200-211

Volos city and its port are situated in the northern part of Pagassitikos Gulf, a shallow, semi-enclosed marine area in central Greece. A wastewater treatment plant (WWTP) and pipeline operate in the same area. Muddy sediments with low carbonate contents cover most of the seabed, except for the Volos embayment and the western part of the gulf where sandy carbonates prevail. Bulk organic carbon contents and the organic carbon contents of the clay fractions are high in the vicinity of Volos embayment. High element (Pb, Cu, and Zn) contents and Igeo (geoaccumulation index) values were found for the clay fractions in the northern part of Pagassitikos Gulf. This enrichment is attributed to the discharge of raw domestic and industrial effluents of Volos city and port before the WWTP was installed. The dispersal of pollutants is essentially controlled by diffusion from point sources (city, port and WWTP) and is limited to Volos Bay. Relatively high Mn levels are ascribed to diagenetic formation of manganese carbonates (authigenic phase), whereas Cr and Ni are elevated due to weathering of ultrabasic formations on land.  相似文献   

The Effect of Consolidation on TBM Shield Loading in Water-Bearing Squeezing Ground     

M. Ramoni  G. Anagnostou 《Rock Mechanics and Rock Engineering》2011,44(1):63-83

When planning a TBM drive in squeezing ground, the tunnelling engineer faces a complex problem involving a number of conflicting factors. In this respect, numerical analyses represent a helpful decision aid as they provide a quantitative assessment of the effects of key parameters. The present paper investigates the interaction between the shield, ground and tunnel support by means of computational analysis. Emphasis is placed on the boundary condition, which is applied to model the interface between the ground and the shield or tunnel support. The paper also discusses two cases, which illustrate different methodical approaches applied to the assessment of a TBM drive in squeezing ground. The first case history—the Uluabat Tunnel (Turkey)—mainly involves the investigation of TBM design measures aimed at reducing the risk of shield jamming. The second case history—the Faido Section of the Gotthard Base Tunnel (Switzerland)—deals with different types of tunnel support installed behind a gripper TBM.  相似文献   

An analysis of the linear fixed altimetry-gravimetry boundary-value problem     

Georgios Panou  Nikos Yannakakis  Demitris Delikaraoglou 《Studia Geophysica et Geodaetica》2013,57(2):203-216

In this paper the linear fixed altimetry-gravimetry boundary-value problem is analyzed with respect to the existence and uniqueness of the solution. Nowadays, it is possible to determine very precisely points on the physical surface of the Earth by 3D satellite positioning and the problem is to determine the disturbing potential in an unbounded domain representing the exterior of the Earth. In order to establish realistic boundary conditions, a Dirichlet condition is imposed at seas and an oblique derivative condition on land. Then, mathematical methods are used within the frame of functional analysis for attacking the problem under consideration. Specifically, the Stampacchia theorem is used to decide upon the existence and uniqueness of the weak solution of the problem in a weighted Sobolev space. Finally, we confirm that the condition of validity for such a theorem has a geometrical interpretation.  相似文献   

Dynamic Multifractality in Earthquake Time Series: Insights from the Corinth Rift,Greece     

Georgios Michas  Peter Sammonds  Filippos Vallianatos 《Pure and Applied Geophysics》2015,172(7):1909-1921

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Comparison of particulate matter distribution, in relation to hydrography, in the mesotrophic Skagerrak and the oligotrophic northeastern Aegean Sea   总被引：1，自引：0，他引：1  

A. P. Karageorgis  H. G. Kaberi  A. Tengberg  V. Zervakis  P. O. J. Hall  Ch. L. Anagnostou 《Continental Shelf Research》2003,23(17-19):1787

The seasonal vertical distribution of particulate matter (PM) was studied in two contrasting areas: (a) the mesotrophic Skagerrak (in the North Sea); and (b) the oligotrophic northeastern Aegean Sea (eastern Mediterranean). Similarities and differences of the PM distribution in the two areas are assessed with respect to the prevailing hydrographic conditions and the PM composition. Hydrographic conditions in both of the areas are characterised by strong density gradients, resulting from the inflow of low-salinity water, i.e. Baltic Sea water and Black Sea water for the Skagerrak and the northeastern Aegean Sea, respectively.Enhanced primary production and particles mainly of biogenic origin characterise the mesotrophic Skagerrak, whereas five-fold lower particle concentrations appeared in the oligotrophic Aegean Sea. The input of riverine particulates was limited in both of the areas. In the Skagerrak, the strong stratification resulted in particle accumulation on/above the pycnocline and the development of pronounced intermediate nepheloid layers (INLs). The pycnocline-related INLs were formed entirely by dinoflagellates. The pycnocline hindered the vertical movement and sinking rates of particles, thus favouring primary production. Particle horizontal advection along the density discontinuities was probably enhanced. This pattern was not observed in the stratified waters of the northeastern Aegean Sea, probably due to the very low particle concentrations and/or the fact that phytoplankton maxima appeared in deeper waters. Pronounced INLs were identified in the Skagerrak below the pycnocline; these are attributed to accumulated or advected dinoflagellate skeletal remains mixed with clay mineral particles. This was revealed only by means of SEM observations. X-ray diffraction analysis could not provide information on the type of phytoplankton present, because dinoflagellates form their skeletons from organic material. Frontal stations in the northeastern Aegean Sea exhibited pronounced vertical movement of particles towards the deeper waters. Benthic nepheloid layers (BNL) were observed in the Skagerrak; these were related to the resuspended fine-grained surface sediments. In the northeastern Aegean Sea, although near-bottom current velocities were sufficient to resuspend surface sediments, resuspension occurred only episodically. The BNLs here are related mostly to near-bottom phytoplankton growth.  相似文献   

Numerical investigation of the impact of uncertainties in satellite rainfall estimation and land surface model parameters on simulation of soil moisture     

Faisal Hossain  Emmanouil N. Anagnostou   《Advances in water resources》2005,28(12):83-1350

This study aims at evaluating the uncertainty in the prediction of soil moisture (1D, vertical column) from an offline land surface model (LSM) forced by hydro-meteorological and radiation data. We focus on two types of uncertainty: an input error due to satellite rainfall retrieval uncertainty, and, LSM soil-parametric error. The study is facilitated by in situ and remotely sensed data-driven (precipitation, radiation, soil moisture) simulation experiments comprising a LSM and stochastic models for error characterization. The parametric uncertainty is represented by the generalized likelihood uncertainty estimation (GLUE) technique, which models the parameter non-uniqueness against direct observations. Half-hourly infra-red (IR) sensor retrievals were used as satellite rainfall estimates. The IR rain retrieval uncertainty is characterized on the basis of a satellite rainfall error model (SREM). The combined uncertainty (i.e., SREM + GLUE) is compared with the partial assessment of uncertainty. It is found that precipitation (IR) error alone may explain moderate to low proportion of the soil moisture simulation uncertainty, depending on the level of model accuracy—50–60% for high model accuracy, and 20–30% for low model accuracy. Comparisons on the basis of two different sites also yielded an increase (50–100%) in soil moisture prediction uncertainty for the more vegetated site. This study exemplified the need for detailed investigations of the rainfall retrieval-modeling parameter error interaction within a comprehensive space-time stochastic framework for achieving optimal integration of satellite rain retrievals in land data assimilation systems.  相似文献   

Earthquake magnitude or seismic moment in seismic hazard evaluation?     

Georgios N. Stavrakakis 《Pure and Applied Geophysics》1988,127(1):21-31

Seismic hazard analysis requires the estimation of the probabilities that earthquakes will take place within a region of interest, and the expected level of ground motion which will be received at a site during the nextt years. The earthquake magnitude has been used as a basic parameter, because it is available, under the assumption that the earthquake occurrence is a compound Poisson process with exponential or multinomial distribution of magnitude.For improving the hazard prediction, we used the seismic moment as a basic parameter to estimate the mean rate, , of occurrence of earthquakes in a function of seismic moment rate and slip rate released in a seismogenic region.As an illustration of the model, the seismic hazard analysis at different sites in and around the Gulf of Corinth, central Greece, is presented on the basis of the earthquake magnitude and the seismic moment. Comparison of the results shows that determination of the mean rate of earthquake occurrence, using the conventional Gutenberg-Richter recurrence model, underestimates the seismic hazard at a site.  相似文献   

Iterative deconvolution of teleseismic P waves from the Thessaloniki (N. Greece) earthquake of June 20, 1978     

Georgios N. Stavrakakis  Akis-G. Tselentis  John Drakopoulos 《Pure and Applied Geophysics》1986,124(6):1039-1050

Teleseismic long-period P waves from the June 20, 1978, Thessaloniki (N. Greece) earthquake (M _s=6.4) were modeled in an attempt to extract information about asperities or barriers on the fault plane. The analysis is based on the inversion method of complex P waves developed by Kikuchi and Kanamori (1982). A far-field source time function with a rise time of 2 sec and a process time of 5 sec is inferred, corresponding to a source dimension of about 10 km when a rupture velocity of 2 km/sec is assumed.The source depth of this shock, estimated by matching synthetic seismograms to observations, is found to be 8 km. The sum of the seismic moments of the individual subevents amounts to 3.3×10²⁵ dyn-cm.  相似文献   

Aftershock patterns of the 2021 Mw 6.3 Northern Thessaly (Greece) earthquake     

Michas  Georgios  Pavlou  Kyriaki  Avgerinou  Sophia-Ekaterini  Anyfadi  Eleni-Apostolia  Vallianatos  Filippos 《Journal of Seismology》2022,26(2):201-225

Journal of Seismology - On March 3, 2021, a strong shallow earthquake of magnitude Mw 6.3 struck Northern Thessaly, an area that lies in one of the most active fault zones of mainland Greece. The...  相似文献   

On the Occurrence of Anhydrite in the Sulphatic Claystones of the Gypsum Keuper   总被引：2，自引：0，他引：2  

G. Anagnostou  K. Serafeimidis  A. Vrakas 《Rock Mechanics and Rock Engineering》2015,48(1):1-13

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