NW Peloponnesus Research Articles

Palaeoenvionmental inferences on the Pleistocene deposits of the Charadros River (Rio graben, Western Corinth Gulf, Greece)

Rio graben is a region of significant stratigraphic and palaeontological interest where several environmental changes have been recorded during the Quaternary. These changes are a result of active tectonism, related to the well-known rifting process that has been occurring in the geotectonic region of the Corinth-Patras Rift, as well as of the influence of continuous eustatic and climatic changes. Fossil assemblages from Middle to Upper Pleistocene transitional to marine and terrestrial sedimentary sequences located at Sichaena (Rio Graben) on the west side of Charadros river in NW Peloponnesus, Greece, are analyzed herein in order to distinguish tectonic and eustatic controls.The name of the studied section is Vigla 1 (50 m thickness), belonging to the NE-trending Rio graben, a structure bridging the Corinth graben to the east and the Patras graben to the west. The presence of two normal antithetic second order faults and an unconformity were identified separating the studied stratigraphic section into four distinct sedimentological sequences. The purpose of this work is to determine the palaeoenvironmental conditions of the studied section and to unravel the Middle-Late Pleistocene palaeoenvironmental changes. The micro-fauna evidences oligohaline lagoon sediments at the lower sequence (Sequence 1). Conversely, at the middle (Sequence 2) and at the upper sequence (Sequence 3), the recorded species indicate lagoonal to shallow marine depositional environments. At the top of the section, an unconformity brings into contact Sequence 3 with a sequence consisting a red conglomerate (Sequence 4) that indicates an alluvial fan environment. In order to constrain chronologically the sediments Optically Stimulated Luminescence (OSL) dating was applied. According to the OSL dating results, an Upper Middle Pleistocene age has been attributed for the studied sequences. Moreover, projecting the dating results to the marine isotope curve, a high degree of consistency can be seen between the OSL ages and MIS 7e, 7c and 6d, where the transition from lagoonal facies to shallow marine alternations in sequence 2 correlates well with the MIS 7c highstand, and sequence 3 with MIS 7e and the MIS 6d low stand. Thus, our results indicate the spatial palaeoenvironmental evolution of the studied area which during the Upper Middle Pleistocene is characterised by intense local tectonic movements in conjunction with eustatic sea level changes.

Mineralogy of siliceous concretions, cretaceous of ionian zone, western Greece: Implication for diagenesis and porosity

Siliceous (chert) concretions are a prominent component of Cretaceous limestones in the Ionian zone of western Greece. This study investigates the diagenetic evolution of such cherts from two localities: largely undeformed strata on Kastos Island and highly faulted strata at Araxos. In both areas, lower Cretaceous limestones contain abundant small chert nodules, whereas in the upper Cretaceous nodules are larger but less abundant. Seventy seven powdered samples, from 67 representative field samples, were analyzed by X-ray Powder diffraction (XRPD). The analyzed samples came from both nodular and siliceous beds and showed that quartz is the dominant mineral, with rare to common residual calcite. The presence of moganite and opal-A minerals suggests that quartz recrystallized from original amorphous silica. A few samples from Araxos contain traces of halite and anhydrite. The variability in the calcite content and the presence/absence of halite and anhydrite in the different studied areas are related with the different tectonic activity in these areas, with more intense tectonic activity in NW Peloponnesus than in Kastos Island. Size of nodules is related to variation in primary porosity of the host rocks. Finally, the presence of dolomite was related with the pre-existing underlying dolomites of Early Cretaceous age in Ionian basin, whereas the presence of maghemite is due to the presence of iron minerals in water solutions. • Zoned chert nodules and beds in Cretaceous calcturbidites and landslide deposits. • Moganite and opal-A minerals recrystallized from original amorphous silica. • Size of chert concretions related to porosity of host limestones. • Dolomite in cherts only where underlying dolostone. • Halite and anhydrite in cherts due to Paleogene deformation of Triassic evaporites .

ANISOTROPY STUDY OF THE FEBRUARY 4TH 2008 SWARM IN NW PELOPONNESUS (GREECE)

The Gulf of Corinth, located in central Greece, is characterized by normal faulting and by high seismicity since the antiquity. On 4 February 2008 a seismic swarm burst in NW Peloponnesus characterized by the occurrence of two moderate-size earthquakes of moment magnitudes 4.7 and 4.5, respectively. Analysis of the data revealed the existence of shear-wave splitting. The events that were chosen for the anisotropy study fit the selection criteria, having clear and impulsive S wave arrival phases on the horizontal components. In addition, the amplitude of the S wave phase on the vertical component was smaller than on the horizontal ones. The representations that were used to determine the polarization direction of the fast split shear wave, the time delay between the two split shear waves and the polarization direction of the source were the polarigram and the hodogram. The uniform fast shear wave polarizations, irrespective of the azimuth of each event, are consistent with the general NNE-SSW direction of extension in the Gulf and, therefore, in agreement with the extensive dilatancy anisotropy (EDA) model. Finally, a decrease of the time delay values was observed after the occurrence of the first moderate earthquake, implying changes of the medium’s properties.

Cloud-to-ground lightning activity over Greece: Spatio-temporal analysis and impacts

Cloud-to-ground (CG) lightning activity recorded by the Hellenic National Meteorological Service (HNMS) Precision Lightning Network (PLN) is analysed over the wider area of Greece. In addition, the spatial and temporal relationships between TRMM 3B42 (Tropical Rainfall Measuring Mission) datasets and lightning are presented. The analyses concern the period from January 14, 2008 to December 31, 2012. The Laboratory of Climatology and Atmospheric Environment, University of Athens, has established a detailed dataset of lightning impacts over Greece from 1895 to 2013, based on digitized archive editions of newspapers. The mean seasonal variability of CG lightning activity revealed autumn as the most dominant season with 303 LD, while the mean monthly variability of CG indicated October as the most lightning active month and May as the month with a mean of 27 LD. The mean annual spatial distribution of CG lightning per km2, depicted the maximum frequency over Pindus mountain range (>7CG/km2). During the autumn season, the northern Ionian Sea experienced a mean frequency of more than 5CG/km2, compared to the southern Ionian Sea and NW Peloponnesus, where values of more than 7CG/km2 are depicted. During the summer season, the maximum frequency appeared along Pindus mountain range, around Attica, Thessaly and central Macedonia highlands. The spatial distribution of seasonal correlations between the number of CG flashes/day and gridded (TRMM 3B42) daily rainfall totals for the period 2008–2012 over Greece, indicated that correlations were mainly positive all over the under study area, within all seasons, and especially during summer and autumn. Regarding the lightning impacts in Greece, based on the 1895–2013 study period, more than 343 fatalities and at least 224 injured people have been recorded. The spatial analysis of lightning impacts, showed that the majority of events has been recorded over Greek mainland and only few scattered events have been reported over Ionian and Aegean Seas. The results of the performed research for Greece, during 1895–2013 (2000–2013), indicated that fatalities/injuries caused by lightning, were estimated at 2.9 (2) deaths/1.9 (1.6) injuries per year, respectively.

Rock-falls and liquefaction related phenomena triggered by the June 8, 2008, Mw=6.4 earthquake in NW Peloponnesus, Greece

<p>A strong earthquake (M<sub>w</sub>=6.4) occurred in NW Peloponnesus, Greece, on June 8, 2008. The focal mechanism shows a transcurrent kinematics, and based on aftershocks distribution the causative fault is a dextral strike-slip NNE-SSW trending structure. The shock generated severe secondary environmental effects like rock-falls and liquefaction phenomena inducing structural damages and ground failures mainly along the fault strike. Evidence of liquefaction was observed in the area of Kato Achaia and Roupakia villages, while rock-falls were triggered mainly close to the epicentre at the foothills of the Skolis Mountain. Based on a quantitative methodological approach, the ground deformation and failures generated by the event have been investigated. In particular, based on an immediate post-event survey, we mapped in detail the distribution of the earthquake-induced ground failures, defining the areas prone to liquefaction and their associated potential. Moreover, a rock-fall hazard zonation in the area of Skolis Mountain has been developed based on the shadow angle approach, confirming the validity of the safety run-out distance models.</p>

A climatology of tornadic activity over Greece based on historical records

In this study, the climatology of tornadoes, waterspouts and funnel clouds over Greece is presented for the period 1709–2012. The climatology consists of two datasets. An historical dataset (1709–1999) is based on newspaper archives, historical archives, published tornado literature, administrative records and reports of Hellenic National Meteorological Service (HNMS). A recent dataset (2000–2012) is based on newspaper articles, eyewitness reports to the media, HNMS's reports and an open-ended online tornado report database which has been developed and maintained by the Laboratory of Climatology & Atmospheric Environment of the University of Athens. Altogether, 612 Greek tornadic events compose the climatology: 171 tornadoes, 374 waterspouts and 67 funnel clouds. Tornadic events during the past 13 years (2000–2012) have occurred all over the Greek territory and there is frequent tornadic occurrence over north Crete and Corfu Island. Tornadoes are more frequent to occur over NW Peloponnesus followed by south parts of Corfu Island. However, waterspouts are more frequent over north Crete followed by Corfu Island. Tornadic monthly variability depicts a maximum during October, followed by September and November. October is the month with the highest tornado frequency, followed by November and July. The highest waterspout frequency month is September followed by October and December. Tornadoes most commonly develop during the warm time of the day, as more than 75% of all cases occur during 08:00–15:00 hours UTC with a maximum at 12:00 hours UTC. Waterspout frequency of occurrence has two maxima during the day, the first early in the morning (07:00–09:00 hours UTC) and the second after the noon time period (14:00–15:00 hours UTC). The dominant (27.7% of total cases) intensity of tornadoes in Greece is T4 based on the T-scale during the 300-year period (1709–2012); there have been at least 114 injured and 29 deaths.

Mediterranean Quaternary interglacial molluscan assemblages: Palaeobiogeographical and palaeoceanographical responses to climate change

The analysis of several central to eastern Mediterranean shallow-water deposits, mostly related to Posidonia oceanica palaeocommunities, sheds light on the presence of thermophilic molluscan assemblages throughout the Mediterranean Pleistocene. The taxonomic composition of these assemblages is totally different from that of the well-known Senegalese molluscan fauna and they play an important role in understanding some of the hydroclimatic conditions during Quaternary interglacial episodes in the central-eastern Mediterranean basin. Two of these assemblages from the Kyllini–Trypiti sequence (NW Peloponnesus) can be referred to the Upper Pleistocene interglacial marine isotope (sub)stage (MIS) 5e and 5a, on the basis of U/Th dating of corals (Cladocora coespitosa). Other assemblages belong to Lower Pleistocene (mainly Emilian substage, possible MIS 37), late Lower (Sicilian substages)–early Middle Pleistocene and late Middle–Upper Pleistocene (MIS 7 and MIS 5e). As a whole, these assemblages consist of 15 species of palaeoclimatic and stratigraphic value. Among these, Craspedochiton altavillensis (Polyplacophora), Jujubinus? bullula, Ersilia aliceae, Haedropleura bucciniformis, Strioterebrum basteroti (Gastropoda), and Plicatula mytilina (Bivalvia) are (Euro)Mediterranean strictly endemic extinct species, whereas Rissoina decussata, Niso terebellum, Kyllinia parentalis, Strioterebrum grayi, Terebra corrugata, Terebra reticularis (Gastropoda), Anadara sp., Chama placentina, and Corbula revoluta (Bivalvia) can be regarded as closely related to recent tropical West African taxa or as species living in tropical waters. The latter stock is useful for reconstructing palaeoclimatic conditions, suggesting winter sea surface temperatures 4–6°C and 2–4°C warmer than today in western Sicily and the easternmost part of the Mediterranean Sea, respectively. In contrast with Pleistocene glacial settings, detected warm episodes are characterized by a lower degree of seasonality, with a difference between summer and winter sea surface temperatures of 6–7°C vs. 10–11°C recorded at present in the Mediterranean. The molluscan assemblages also indicate that central to eastern Mediterranean salinity was lower than today, suggesting that a different hydrological regime, triggered by increase in rainfall/runoff, was manifested during warmer Pleistocene periods in that area. The distribution of some of the most meaningful taxa studied here indicates that the Mediterranean Sea was divided into two palaeobioprovinces, a cooler western and a warmer eastern one, with a boundary zone possibly located near the present Sicilian–Tunisian Strait.The Anadara sp.–Jujubinus? bullula association is a meaningful ecobiostratigraphical marker for recognizing warm Lower Pleistocene–Upper Pleistocene events. The youngest occurrence of this association has been detected in MIS 5a, in the uppermost part of the Kyllini–Trypiti sequence. Craspedochiton altavillensis, J.? bullula, Ersilia aliceae, Anadara sp., Chama placentina and Plicatula mytilina became extinct during the MIS 5a. Kyllinia parentalis and Terebra corrugata became extinct during MIS 5e. The disappearance of Niso terebellum took place during the Emilian substage (Lower Pleistocene). The gastropod Nassarius musivus musivus, previously considered as becoming extinct at the top of the Gelasian stage, has been recorded in the eastern Mediterranean deposits younger than MIS 5a and older than MIS 3.

Estimating slope failure potential in an earthquake prone area: a case study at Skolis Mountain, NW Peloponnesus, Greece

One of the most important issues in the evaluation of geological hazards is the delineation of landslide prone areas and the estimation of the slope failure potential. In this study, the GIS-based Newmark’s displacement method was applied for the first time in Greece, in order to compute the permanent displacement values and evaluate the slope failure potential in the area of the Skolis mountain in NW Peloponnesus, Greece. The resulting maps were validated using the distribution of secondary effects triggered by the 8 June 2008 earthquake. The study indicated that as the source areas of the rock falls were delineated by the Newmark displacement method, this may be a useful approach to predict earthquake-induced slope failures when the seismic potential of an area has been previously evaluated.

First reports of XXY aneuploidy in natural populations of Thomas’ pine vole Microtus thomasi (Rodentia: Arvicolidae) from Greece

As part of an extensive cytological study in natural populations of Thomas’ pine vole Microtus thomasi, two cases of XXY aneuploidy (2 n=45, FN=47) from different localities of NW Peloponnesus, Greece were recently recorded. These constitute the first report of sex chromosome aneuploidy for this species, in a sample of 366 individuals from 89 localities of Greece. Both individuals appeared with a male phenotype and normal morphology; however, measurements and histological examination in the testes of one of the two individuals imply a severely impaired fertility. The above findings translate to a relatively high rate of sex chromosome aneuploidy (0.55%) (upper 95% CI 1.96%) for the natural populations of Microtus thomasi and possible reasons for this are discussed.

Groundwater recharge via deep boreholes in the Patras Industrial Area aquifer system (NW Peloponnesus, Greece)

The economic development of the Patras Industrial Area is influenced by both the availability and the seasonal variability of water resources. Groundwater from the deep confined aquifer is the major source of water for the industries located in this area. During the 1980s, over-pumping combined with prolonged dry periods has lowered the groundwater level. The paper presents the results of groundwater recharge testing in the confined aquifer using three deep boreholes and injection rates ranging from 30.5 to 63.5 m3/h. The groundwater level rose by more than 3.5 m in the recharge boreholes and 1 m in those 0.5 km away. The field experiments provided useful guidance on the proper planning of pilot tests, data monitoring and analysis, which can also be applied to other regions with similar conditions. Based on the hydrogeological conditions a groundwater flow model was successfully used to predict the aquifer system response. The work confirms that aquifer recharge is an environmentally acceptable solution, as part of an integral water resources management plan.

Terrain Pattern Recognition and Spatial Decision Making for Regional Slope Stability Studies

A terrain partition scheme is presented that allows the identification of regions with high landslide risk in natural terrain zones on the basis of geomorphometric criteria from moderate resolution DEMs. The key factor being the terrain segmentation to aspect regions (regions formed by points preserving the same aspect direction) instead of using an artificial regular-grid terrain partition scheme. The study area is in western Greece (NW Peloponnesus) whereas a moderate resolution digital elevation model with spacing 75 m is used. Landslide inventory analysis and knowledge conceptualization identified that the landslide susceptibility of a particular aspect region is high, if the mean elevation is low and the mean gradient is high. Each aspect region was parametrically represented on the basis of its mean gradient and elevation. The domain of each parameter was divided to seven slices (classes) on the basis of the observed density. Subsequent knowledge based mapping identified aspect regions with high landslide susceptibility for the following spatial rule: (a) “mean slope in class 6 or 7” and (b) “mean elevation in class 1 to 5”. Alternatively the rule is expressed as mean slope to be equal or greater than 15∘ whereas mean elevation to be in the range 0 to 750 m. These identified zones correspond to regions where historical landslides occurred (populated coastal areas in the North) as well as to south regions (natural terrain zone) where no landslide record is available, because of the limitations posed by the natural terrain landslide mapping program in Greece. The presented terrain segmentation technique combined to the spatial decision-making process, provided both an object framework for integrating geomorphometric parameters and a method for landslide risk analysis in natural terrain zones.

Gas Hazard Induced by Methane and Hydrogen Sulfide Seepage in the NW Peloponnesus Petroliferous Basin (Greece)

Gas seeps along the Ionian coast of the northwestern Peloponnesus (Greece) constitute a severe hazard for humans and buildings. Methane, migrating from deep carbonatic hydrocarbon reservoirs, is seeping in amounts potentially explosive and hydrogen sulfide is beyond the levels that induce toxicological diseases and lethal effects. The seeps are related to intense methane microseepage in the surrounding areas (orders of 10^1 to10^5 mg m^(-2)d^(-1) over 10^4 m^2 areas, at least) and produce significant CH4-H2S enrichments in the atmosphere. Gas-charged sediments in the seafloor and bubbling plumes present a high risk for offshore constructions and facilities.

An application of factor analysis for the study of the hydrogeological conditions in Plio-Pleistocene aquifers of NW Achaia (NW peloponnesus, Greece)

R- andQ-mode factor analysis is applied to 51 groundwater samples collected from wells drilled in the Plio-Pleistocene aquifers of NW Achaia, Greece. The purpose ofR- andQ-mode factor analysis application is to identify (i) the regional groundwater flow pattern, and (ii) the deterioration of groundwater quality. Sixteen hydrogeological parameters are used in order to examine their importance and to provide significant insight into their correlations. In theR-mode factor analysis, a six-factor model is suggested which can explain more than 77.5% of the total variance. The contribution of each factor at every site (factor scores) also is computed. Maps are constructed showing the geographical distribution of the factor scores. From these maps, the high salinity areas are delineated (seawater intrusion, possible appearance of halite layers) and the areas with elevated contribution of karastic-water are defined. Using theQ-mode correspondence analysis the meaning of the electrical conductivity as the most important variable in groundwater quality characterization is demonstrated.

Geometry and kinematics of active faults and their seismotectonic significance in the western Corinth-Patras rift (Greece)

The western part of the Corinth-Patras rift is formed in an area which is being uplifted. Rifted domains have subsided relative to the adjacent areas in NW Peloponnesus and Sterea Hellas, but subsidence rates rarely exceed uplift rates. Extension is mainly accomplished by WNW-trending active faults with lengths up to 25 km. Most of these faults show an along-strike segmentation and often terminate against transfer faults. Displacement analysis, along 170 mesoscopic faults and 36 mappable faults, has been carried out to assess slip rates and to estimate the magnitudes and recurrence time intervals of earthquakes occurring along them. Earthquake magnitude ranges between 5 and 6.7. Only eight faults appear to be capable of producing earthquake magnitudes larger than 6. Recurrence times of these large earthquakes vary between 80 and 1690 years. Upper crustal deformation in the western Corinth graben can be described by six large asymmetric grabens which are inferred to bottom out to a N-dipping curved ramp. The asymmetric shape of most WNW-trending rifts in the Hellenic peninsula, including the Corinth-Patras rift promotes the simple shear model of extension against the pure shear model in the upper crustal layer.

Geotechnical properties of the neogene sediments in the NW peloponnesus, Greece : Koukis, G, Rozos, D Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990V1, P405–412. Publ Rotterdam: A A Balkema, 1990

Geotechnical properties of the neogene sediments in the NW peloponnesus, Greece : Koukis, G, Rozos, D Proc 6th International Congress International Association of Engineering Geology, Amsterdam, 6–10 August 1990V1, P405–412. Publ Rotterdam: A A Balkema, 1990

Macroseismic observations related with the strong shock of October 16th, 1988, in NW Peloponnesus, Greece: The important role of the microzonation conditions

Macroseismic observations made in the region of Elia, NW Peloponnesus, Greece, after the strong ( M s = 5.9), shallow shock of 16 October 1988, revealed that several types of ground damage (typical liquefaction in soil, cracks in incoherent alluvium) and heavy damage to structures were caused. A maximum intensity of VIII MM has been observed at the villages of Kastro, Vartholomio and Neochori, indicating a peak groud acceleration of the order of 0.30 g. This intensity is anomalously high, a feature commonly occurring in that region, as shown by its past macroseismic history independently examined on the basis of (a) an intensity attenuation model, and (b) the intensities felt at other observation sites bounded by the same with the region of Elia isoseismal lines. We suggest that local ground effects and soil conditions, such as the loosely compacted alluvium and the shallow water table, resulted in the amplification of the seismic ground motion. Great differences in the damage to structures from place to place within the residential zones of Kastro and Vartholomio indicate the important role of several microzonation factors.