Microseismicity and focal mechanisms at the western termination of the North Anatolian Fault and their implications for continental tectonics

For seven weeks, a temporary network of 68 seismological stations was operated in Central Greece, in the region of Thessaly and Evia, located at the western termination of the North Anatolian Fault system. We recorded 510 earthquakes and computed 80 focal mechanisms. Seismic activity is associated with the NE–SW dextral North Aegean Fault, or with very young E–W-striking normal faults that are located around the Gulf of Volos and the Gulf of Lamia. The important NW–SE-striking faults bounding the Pilion, or the basins of Larissa and Karditsa, are not seismically active, suggesting that it is easier to break continental crust, creating new faults perpendicular to the principal stresses, than to reactivate faults that strike obliquely to the principal stress axes     

First archaeomagnetic results and dating of Neolithic structures in northern Greece

Archaeomagnetism in Greece has continuously developed during the last decades. Numerous studies have provided high quality data and accurate secular variation curves for the direction and intensity of the geomagnetic field have been constructed. The Greek Secular Variation Curves (SVCs) cover the last 8 millennia for intensity and 6 millennia for direction. The coverage of the archaeological periods remains uneven, with several gaps, mostly in the directional dataset, with only two results for periods older than 2500 B.C. In the present contribution, the first archaeomagnetic results from Neolithic settlements in northern Greece are presented. For the present study, samples were collected from three different archaeological sites: burnt structures in Avgi (Kastoria) and Vasili (Farsala) and one oven from Sosandra (Aridaia). The natural remanent magnetization (NRM) grouping of all specimens indicated that the majority of the samples were burnt in situ, providing thus a reliable direction of the ancient field. Magnetic cleaning (both alternating-field and thermal) revealed the presence of one stable component of magnetisation. Rock magnetic experiments (acquisition of isothermal remanent magnetization (IRM), thermal demagnetisation of the IRM, thermomagnetic curves) have been performed on pilot samples indicating that low coercivity magnetic minerals such as magnetite or Timagnetite are prevailing. The mean directions (declination D, inclination I and parameters of the Fisherian statistics), which arose from the three sites are as follows: Sosandra: D = 343°, I = 55.6°, ??₉₅ = 4.8°; Avgi: D = 10.1°, I = 53.4°, ??₉₅ = 4.2° and Vasili: D = 357.5°, I = 43.1°, ??₉₅ = 4.1°. The obtained data are in a very good agreement with results from Neolithic Bulgaria. This study represents the beginning of an effort to fill the gaps of the Greek secular variation curves and their extension to the Neolithic period.     

An updated catalogue of Greek archaeomagnetic data for the last 4500 years and a directional secular variation curve

We present an updated compilation of Greek directional archaeomagnetic data for the last 4.5 millennia. The data set comprises 89 directions from archaeological artefacts and volcanic rocks. Most of the data come from the Late Bronze Age (1700-1400 BC) that is the flourishing period of the Minoan civilization in Crete, while parts of the classical (480-323 BC), Hellenistic (323-31 BC) and Roman (146 BC-330 AD) periods are also well covered. The dataset has been analysed using the Bayesian approach for curve building and a directional secular variation (SV) curve for Greece is proposed. Comparisons with regional and global model predictions show a general agreement even though some discrepancies are observed for some time intervals. The new curves together with the previously published intensity SV curve for Greece, also using the Bayesian approach, form a homogeneous set and enrich our knowledge of the full geomagnetic field vector variation in Greece during the last millennia.     

Simulation of polychlorinated biphenyls transport in the vadose zone

Polychlorinated biphenyls (PCBs) are the main constituents of clophen (the liquid of the electric transformers and capacitors) and have been characterized as potential human carcinogens. PCBs can be a hazardous contaminant of soil and groundwater. We used the mathematical model variably saturated 2D flow and transport (VS2DT model) to simulate the transport of PCBs from the soil surface to groundwater for a time period of 30 years. We also used a mathematical model to simulate the colloid-facilitated PCB transport, under saturated flow conditions. The results showed that PCBs dissolved in water cannot be transported to large depths in unsaturated soils, because of their strong sorption onto soil and low solubility in water. For soils with very low or no organic matter content, PCB transport is much faster and the probability of groundwater contamination is much higher. PCBs can partition to colloids originating from dissolved organic matter in groundwater. Colloid-facilitated PCB transport is faster compared to PCB transport in aqueous solution with no colloids present.     

Winter atmospheric circulation patterns and their relationship with the meteorological conditions in Greece

This study presents an analysis of the relationship between winter large-scale circulation and surface meteorological conditions over Greece for the period 1979–2009. The adopted methodology involves the application of an automated atmospheric circulation classification scheme based on the self-organizing map approach. The impact of each of the identified relevant 19 winter atmospheric circulation patterns on local meteorological condition is examined at seven sites by calculating the corresponding differences from the mean meteorological conditions. The conditional transition probabilities of circulation patterns indicate the existence of increased 1-day persistence, especially for the anticyclonic and the pattern related to Genoa depressions. Positive temperature anomalies are observed for the cyclonic patterns, while negative anomalies are attributed to the effect of anticyclonic circulation.     

New magnetic mineralogy and archaeointensity results from greek kilns and baked clays

Seven archaeological sites in Northern Greece and a pottery assemblage from Ithaki Island (Ionian Sea) have provided material from kilns and a collection of baked clays. The whole dataset consists of 69 samples and covers a period of almost 4000 years. Although the majority of the samples was oriented, only few directions could be obtained, mostly due to small sample size and fragility. Detailed rock magnetic experiments identified magnetite/titano-magnetite and substituted magnetite as the main magnetic minerals. Variable amounts of haematite were detected in some cases. In three out of eight sites, multi-domain grains prevail, whereas single-, pseudo-single domain or mixtures are detected in the remaining five. The classical Thellier-Thellier palaeointensity method was applied to 94 specimens. Following stringent acceptance criteria, 66 results from the 8 sites were considered successful and retained. These new results show a convergence with regional and global compilations and improve the knowledge of the past geomagnetic field behaviour in Greece.     

Palaeotemperature estimation of the pyroclastic deposit covering the pre-Minoan palaeosol at Megalochori Quarry, Santorini (Greece): Evidence from magnetic measurements

Thermal remanent magnetization analyses were carried out on ceramic fragments and lithic clasts embedded in the first pumice fall deposits of the Minoan eruption. The aim of this study is to estimate the equilibrium temperature after deposition of these pyroclastic fall deposits and their thermal effect on the pre-Minoan surface. A total of 30 samples from 22 independent ceramic fragments and 20 samples from 14 lithic clasts have been studied. Samples were collected from the Megalochori Quarry, located at the southern part of Santorini island. Stepwise thermal demagnetization reveals that the ceramics were mostly re-heated at temperatures around 140–180°C; in few ceramics a higher temperature component is also present, probably related to the original heating or the use of the ceramics before the eruption. Thermal demagnetization of the lithic clasts shows similar results with slightly higher re-heating temperatures, around 180–240°C. The estimated temperatures represent the equilibrium temperatures obtained after the deposition of the pumice fall and show that the pyroclastic fall deposits at a distance of around 6 km from the eruption vent maintained a temperature high enough to re-heat the buried ceramics at temperatures around 140–180°C.     

A one year water monitoring study of Klisova lagoon (Mesolonghi, W. Greece)

During a one year study in Klisova lagoon of Mesolonghi, it was found that between West Klisova and East Klisova there exist great differences in the degree of pollution owing to eutrophication, as expressed mainly by BOD and primary productivity measurements. East Klisova showed higher values for both these parameters all year round. In West Klisova there exist also some places with bad water circulation conditions, exhibiting extreme variations in temperature-salinity, anoxic conditions and high BOD. In East Klisova salinity is much lower than West Klisova because of a constant inflow of fresh water from the insufficiently functioning sewage water treatment plant of Mesolonghi town and from irrigation water pumping stations. In the sea around Klisova lagoon, there were also occasionally measured high values for BOD, ammonia and nutrient ions indicating a rather polluted environment. Considering temperature it became possible to create regression equations between water and air temperature. This was the result of a very frequent sampling, showing high regression coefficients (> 0.8) having thus a predictive value for use in lagoonal fisheries management.     

The gutenberg-richter law for earthquakes in air pollution episodes: A case study for Athens, Greece

The main aim of this study is to investigate whether the main components of the photochemical smog episodes over megacities obey the Gaussian distribution or do they follow the distribution of the Gutenberg-Richter law. To this end, a case study has been implemented for Athens, Greece, which is among the most densely populated capitals in the middle latitudes of the Northern Hemisphere. The data employed are hourly mean values of surface ozone and nitrogen dioxide concentrations collected by the National Air Pollution Monitoring Network during the period 1988–2008. The results obtained show that the surface ozone and nitrogen dioxide concentrations obey the Gutenberg-Richter law, while their extreme values follow the Generalized Pareto distribution. This finding is important for current efforts to reliably forecast the air pollutants concentrations and to quantify their contribution to climate change. Finally, the plausible mechanisms involved in air pollution dynamics leading to the above-mentioned behaviour are also discussed, assuming the air pollution system governed by non-linear processes.