Modeling the dynamical profile of a BL Lacertae object

A simple dynamical model for a BL Lacertae active galaxy is presented. The model consists of a logarithmic potential with an additional term representing internal perturbations. The time independent and the evolving model are investigated. In both cases we search for regular and chaotic motion and study the velocity distribution near the centre of the system. Numerical calculations suggest that responsible for the chaotic phenomena is the internal perturbation, the flattening parameter and the dense nucleus. The radius of the nucleus also affects the maximum velocity in the central regions of the galaxy. Our numerical outcomes are supported by theoretical arguments and analytical calculations. A linking of our numerical outcomes to observational data is also presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Operational Monitoring and Forecasting in the Aegean Sea: System Limitations and Forecasting Skill Evaluation

The POSEIDON system, based on a network of 11 oceanographic buoys and a system of atmospheric/oceanic models, provides real-time observations and forecasts of the marine environmental conditions in the Aegean Sea. The buoy network collects meteorological, sea state and upper-ocean physical and biochemical data. The efficiency and functionality of the various system components are being evaluated during the present pre-operational phase and discussed in this paper. The problem of bio-fouling on optical and chemical sensors is found to be a main limitation factor on the quality of data. Possible solutions to this problem as well as quality control methods that are being developed are also described. Finally, an evaluation of the numerical models is presented through the estimation of their forecasting skill for selected periods.     

Conventional and modern seismic investigations for rock quality determination at a dam site—a case history1

Refraction seismics and modern tomographic surveys were employed at the Platanovrissi dam site on the Nestos river in northern Greece in an effort to investigate the dynamic elastic properties and rockmass condition of gneiss-schist outcropping in the area under investigation. Six seismic refraction traverses were run on the ground surface, inside the exploratory tunnels and between tunnels and the ground surface. The results provided information about the low-velocity surface layer parameters and the stress relief zones on the walls of all the tunnels in which seismic tomography tests were performed. Ultrasonic tests, conducted both in situ and in the laboratory, enabled the determination of the ratio Vp/Vs and the Poisson's ratio calculation. From the tomography data analysis and the geological interpretation of the results, three main velocity zones, ranging between 3500 and 4000, 3000 and 3500 and less than 3000m/s, were detected in each tunnel. High-velocity zones were found to be compatible with the hard rockmass of gneiss-schist material, while moderate velocities are closely related to jointed and fractured zones. Finally, low-velocity zones were well correlated with weathered gneiss-schist material.     

Geotechnical properties of the Ptolemais lignite

Summary The paper describes an investigation of the geotechnical properties of the Ptolemais lignite (brown coal) and shows that the soil mechanics principles used in the study of natural and cemented soils are applicable. The material has a high and variable void ratio incompatible with its preconsolidation pressure, which may be attributed to the existence of structure (chemical bonding). Bond strength and degradation have been studied and are found to be isotropic, while the stress-strain response in the prevield domain is intensely cross-anisotropic. The shear strength determined from triaxial CU and CD tests is variable but strongly dependent on the in situ moisture content. Tests on high quality intact specimens having a wide range of moisture contents (100–150%) verify a hypothesis that the magnitude of bond strength (expressed by the peak shear strength) is inversely proportional to the moisture content. A Hvorslev-type normalization process shows that the peak shear strength of the material can be estimated from the in situ moisture content with reasonable accuracy, thus facilitating preliminary stability calculations of production cuts in lignite mines. The properties of the Ptolemais lignite are compared with the properties of a lignite from another location in Greece (Megalopolis) and an Australian lignite (Morwell). It is shown that the shear strength characteristics of the lignite types studied are similar and strongly dependent on the in situ moisture content, which seems to be a measure of the magnitude of inter-particle bonding.     

Seismic properties in the eastern part of the South Aegean volcanic arc

The South Aegean active volcanic arc lies along the 150-km seismic isodepth of a Benioffzone and consists in andesitic, dacitic and rhyolitic volcanoes of an orogenic calc-alkaline type. In the eastern part of the arc there are two main volcanic sites in the Nisyros and Kos islands. High shallow and intermediate depth seismic activity occurs in this volcanic area. Seismological data concerning the 1911–1980 period have been used to investigate seismic properties in that area. Two, distinct regions with different seismotectonic features have been defined. The internal region (Nisyros active volcano and its proximity) is characterized by a shallow, thin seismogenetic layer with abnormally highb-value, locally concentrated stresses, low seismicity and highly heterogeneous structure. These features are probably due to a magmatic body intruded in shallow depths within the crust. The possibility of magma formation in the upper surface of the descending slab or within the upper mantle wedge overlying this slab in the Nisyros-Kos area is herein discussed. On the contrary, the remaining (external) region, including the non-active volcanic island of Kos, is characterized by normal for tectonic shocksb-value, thick seismogenetic layer and high seismicity. It seems that in this region there is not a magmatic intrusion at least in shallow depths within the crust.     

Archaeo- and palaeoseismological investigations in Northern Thessaly (Greece): Insights for the seismic potential of the region

Northern Thessaly may represent an important seismic gap within the broader Aegean Region, with major faults bordering the ESE–WNW trending Late Pleistocene–Holocene Tyrnavos Basin. In order to obtain information about the characteristics of past earthquakes and improve our knowledge on the seismic potential of the investigated area, historical and archaeological observations are analysed and compared with the results of palaeoseismological trenches excavated across one of the major bordering structures, the Tyrnavos Fault. The former data clearly document (i) a strong seismic activity affecting the area during the last 2–3 ka and (ii) the occurrence of recent earthquakes not included in the seismic catalogues. Also, the sedimentological, structural and chronological data (TL, OSL and AMS) obtained from the palaeoseismological trenches indicate Late Pleistocene to Holocene morphogenic activity of the Tyrnavos Fault, characterised by vertical co-seismic displacements of 20–40 cm and possible return periods of a few thousands of years. Advantages and limitations in using historical and archaeoseismological data are discussed, as well as the problems arising from analysing low slip-rate faults.