PALAEOXYLOTOMICAL STUDIES IN THE CENOZOIC PETRIFIED FORESTS OF GREECE. PART TWO – CONIFERS

This paper reports the palaeoxylotomical study of petrified conifer remains from Velitzelos collection, orig-inating from some fossiliferous sites of Greece, especially from the Aegean area (Evros, Limnos, Lesbos), aged of late Oligocene to early Miocene. Ten species were identified: Cupressinoxylon akdikii, Juniperoxylon acarcae, Tetraclinoxylon velitzelosii, Taxodioxylon gypsaceum, Taxodioxylon taxodii, Glyptostroboxylon rudolphii, Glyptostroboxylon tenerum, Pinuxylon pineoides, Pinuxylon halepensoides and Pinuxylon sp. aff. Pinus canariensis. These new identifications add new elements to the forest assemblages of the Oligocene - Miocene Greek flora, useful for understanding the evolution of the Cenozoic palaeovegetation and palaeoclimate in the Aegean area.

Joint interpretation of macroseismic and strong motion data for recent large shallow mainshocks of the Aegean area using a Monte Carlo optimization of finite-fault stochastic simulations

<p>The study of strong historical and early instrumental earthquakes is based almost exclusively on the use of their macroseismic data, which usually constrain the area that has suffered the heaviest damage. In the recent decades, strong-motion data have been also employed for the same purpose. We present a stochastic simulation approach to jointly model macroseismic and strong motion data for selected shallow strong (<strong>M</strong>≥6.0) earthquakes that occurred in the broader Aegean region between 1978 and 1995. For the simulations we employed the finite-fault stochastic simulation method, as realized by the EXSIM algorithm. We calibrated several parameters for the stochastic simulation modeling using a priori published information (e.g., moment magnitude, stress parameter). Other rupture zone information were collected from published works, such as fault plane solutions, relocated seismicity, etc. A Monte Carlo approach was adopted to perform a parametric search for the stress parameter and the modelling both independently and jointly the available macroseismic data and the strong motion instrumental recordings. The validity and the reliability of this semi-automated simulation approach was examined, to test if this method could be applied either in a fully automated manner, or for the study of the source properties of historical earthquakes. The results suggest that a joint-misfit minimization from the simultaneous simulation of macroseismic and strong motion data is a feasible target, that can be potentially employed for the simulation of older events, for which a limited number of instrumental data is often available. In general, a good agreement of the spatial distribution of the original and modeled macroseismic intensities is observed, showing that can reliably reconstruct the main features of the damage distribution for strong shallow mainshocks in the Aegean area using the proposed joint interpretation approach.</p>

Identifying the main factors that control Probabilistic Seismic Hazard Assessment (PSHA) in the Aegean area: Results from OFAT (One Factor at A Time) analysis

<p>The broader Aegean area is one of the highest seismicity regions in Europe, with almost half of the European seismicity released in this region, often with damaging mainshocks, such as the recent <strong>M</strong>7.0 Samos event. While several Probabilistic Seismic Hazard Assessment (PSHA) studies have been performed for this area, an attempt to quantify the main factors controlling PSHA has not been performed. To study the effect that each input factor (seismic source model, GMPE, seismicity parameters, etc.) has on the seismic hazard calculations, an <strong>OFAT</strong> (One Factor at A Time) analysis has been conducted. For this analysis we considered two standard peak ground motion parameters, PGA and PGV, for a typical PSHA scenario, namely 10% probability of exceedance for a mean return period of 50 years (equivalent to a 476 yr return period). For the analysis the following factors were considered: a) Four (4) seismicity area-type source models for the broader Aegean area (Papazachos, 1990; Papaioannou and Papazachos, 2000; Woessner et al., 2015; Vamvakaris et al., 2016), as well as various uncertainties for the associated G-R seismicity parameters and active fault geometries of each seismic source, b) ten (10) Ground Motion Prediction Equations (GMPEs), which contain four NGA-West2 (Abrahamson et al., 2014; Boore et al., 2014; Campbell and Bozorgnia, 2014; Chiou and Youngs, 2014), two European (Bindi et al., 2011; Cauzzi and Faccioli, 2008) and four “Greek” (Theodulidis and Papazachos, 1992; Skarlatoudis et al., 2003; Danciu and Tselentis, 2007; Chousianitis et al., 2018) equations, as well as a variable number of sigma for each equation and, c) the minimum (Mmin) and maximum (Mmax) source magnitude of each seismic source. Tornado diagrams (Howard, 1988) were generated for 42 selected sites of seismological interest that span the study area, allowing to explore the extent of each factor’s effect on the PSHA results. The sensitivity analysis results suggest that the GMPE selection, as well as uncertainties in the G-R parameters <strong>a</strong> and <strong>b</strong> are the most critical factors, significantly affecting the PGA/PGV levels for all sites. They also reveal a strong correlation of PSHA sensitivity with other seismicity parameters. For example, the employed source model and Mmax play a more critical role for regions of low seismicity, while the least important factor is the selected Mmin. The spatial distribution of the PSHA sensitivity on the various factors considered was also examined through the generation of several maps, exposing regions of high and of low PSHA uncertainty. The results can be efficiently employed by scientists and engineers in order to focus research and application efforts for a targeted uncertainty minimization of the most critical factors (which may not be the same for all sub-regions of the examined Aegean area), as well as to evaluate the reliability and uncertainty of the current PSHA estimates that are employed in seismic design.</p>

Lower Ionospheric turbulence variations during the intense tectonic activity in Eastern Aegean area

This paper may be considered as an additional approval of the way the tectonic activity affects the lower Ionosphere. The results of our investigation, on the occasion of the recent East Aegean tectonic activity, indicate that the High - Frequency limit, fo, of the ionospheric turbulence content, increases as the site and the time of the earthquake occurrence is approaching, pointing to the earthquake location.We conclude that the Lithosphere Atmosphere Ionosphere Coupling (LAIC) mechanism through acoustic or gravity wave could explain this phenomenology, as a result of a the frequency differential damping of the propagating turbulent in the ionosphere. Proper use of this result may lead to a method of earthquake hazard mitigation using the byproducts of the Global Positioning Network (actually Total Electron Contain, TEC, estimations) which are available freely.

Evolution of Poecilimon jonicus group (Orthoptera: Tettigoniidae): a history linked to the Aegean Neogene paleogeography

The Aegean archipelago is among the largest on Earth with astonishing biodiversity within Europe. Its territory underwent a massive geotectonic transformation in Neogene that resulted in multitude of changes in land-sea configuration and disintegrated the formerly united Aegean land to a complicated mainland-archipelago system. Therefore, it represents an excellent laboratory for studying evolution of terrestrial fauna. In the present study, we use a model group of flightless bush crickets with annual reproduction cycle—Poecilimon jonicus species group—to trace correlation of lineage diversification with the known paleogeographic events in the Aegean area. The group belongs to the hyperdiverse genus Poecilimon and has a disjunct distribution along the Hellenic arc from southwestern Anatolia through Crete to the western Balkans and the Apennines. To test our hypothesis, we inferred phylogenetic relationships of the P. jonicus group sensu lato using a nuclear fragment covering two spacers of the ribosomal cistron (ITS1 + ITS2). To study intra-group phylogeny, we compared mitochondrial phylogenies based on two matrices—(1) a concatenated ND2 and COI dataset of 1656 bp and (2) a 16S rRNA + 12S rRNA dataset of 1835 bp. As a second step, we estimated divergence times applying Bayesian approach with BEAST and a relative rate framework with RelTime on the mitochondrial matrices. We compare trees calibrated based on evolutionary rates and tectonic events and discuss radiation scenarios in concordance with known paleogeographic events in the Aegean area. Our results revealed robust phylogeny of the Poecilimon jonicus group and confirmed a strong link between its evolution and the Aegean paleogeography. The phylogenetic relationships of the group supported reconsideration of its systematics.

Dispersal versus vicariance in the Aegean: combining molecular and morphological phylogenies of eastern Mediterranean Dendarus (Coleoptera: Tenebrionidae) sheds new light on the phylogeography of the Aegean area

The Aegean archipelago, as an ‘evolutionary laboratory of nature’, is an ideal model for research in phylogeography. In this area, the darkling beetles of the genus Dendarus (distributed from Morocco to the Caucasus) exhibit a high level of diversity with 36 species, 27 of which are island endemics. However, their taxonomy is complex and unstable, having undergone continuous revision to address extensive morphological and ecological plasticity. Here, we examine the phylogenetic relationships of 23 species from Greece and Turkey, using mitochondrial and nuclear DNA sequences and 61 morphological characters, to unveil their phylogeny in the Aegean. This helps to clarify phylogeographic scenarios and historical processes that shaped the observed patterns. The analyses reveal 13 distinct lineages with several para- and polyphyletic cases that correspond to three major phylogroups [south/south-east Aegean (D. foraminosus complex, D. rhodius, D. sporadicus, D. wettsteini); central to north Aegean, Turkey and mainland Greece (D. crenulatus, D. moesiacus group, D. sinuatus complex, D. stygius) and mainland Greece (D. messenius, D. paganettii)], indicating the need for further taxonomic re-evaluation. Lineage topology and phylogeography suggest a spatial and temporal sequence of geographic isolation, following either a vicariant or a dispersal model coincident with major palaeogeographic separations in the Aegean.

Lake Lerna: investigating Hercules' ancient myth

<p>Greece and the Aegean area are among the first areas in Europe to have been occupied by humans. The record of human interventions in natural environments is thus particularly rich. Some of the interventions of the people inhabiting various localities of the country have been recorded in local mythology. Through the interdisciplinary field of geomythology it is possible to attempt to uncover the relationships between the geological history of early civilizations and ancient myths.</p><p>In the present work, we focused on the history of Lake Lerni in the Eastern Peloponnese, an area that is better known through the myth of Hercules and the Lernaean Hydra. The area of the lake – now dried and cultivated – was part of a karstic system and constituted a marshland that was a source of diseases and needed to be dried.</p><p>A new core is studied from the area of modern-day Lerni using palaeontological methods in order to reconstruct environmental changes that occurred during the last 6.000 years approximately. The area is known to have gone from marsh-lacustrine environments to dryer environments after human intervention or the intervention of Hercules according to mythology. Levels of peat considered to represent humid intervals were dated using the radiocarbon method so as to have an age model of the core. Samples of sediment were taken every 10 cm; the grain size was analysed for each sample as well as the fossil content for the environmental reconstruction.</p><p>The presence of numerous freshwater gastropods reflects the intervals of lacustrine environment accompanied with extremely fine dark sediment. Sedimentology is stable throughout the core with few levels of coarse sand/fine gravel, only changes in colour hint to multiple levels richer in organic material.</p>

Geochemical and geological evidence for a Triassic transition from subduction- to rift-related volcanic activity in the Cycladic Blueschist Unit in Attica (Greece)

<p>Triassic geodynamic phenomena in the Aegean area are largely controlled by subduction of the Paleotethys ocean and opening of the Neotethys oceans. Triassic volcanosedimentary sequences have a complex composition in many cases, reflecting both subduction and rifting setting.</p><p>Detailed mapping of NE Attica (Penteli Mt., Marathonas, Varnavas) revealed the existence of a structurally lower meta-volcanosedimentary sequence, which, comprises quartzofeldspathic rocks, schists, quartzite, metabasite and acid meta-volcanics This sequence is isoclinally folded in the macro-scale with marble layers and the axial plane foliation displays greenschist facies assemblages, whereas earlier HP minerals are mostly preserved as inclusions in albite porphyroblasts. The sequence of rocks has been investigated for their geochemical composition and their field relationships. Two assemblages of volcanic rocks are distinguished based on geochemical criteria: (a) a predominant subalkaline andesite-rhyolite series with a significant proportion of meta-tuffs in the stratigraphic sequence and (b) minor alkali basalts. Lenses of felsic meta-volcanic rocks alternate with siliciclastic layers showing sedimentary banding and allow for an interpretation of a volcano-sedimentary succession.</p><p>The geochemical characteristics of the alkali basalts are typical of rift settings (positive anomalies in Nb, Ta, Ti and P) and plot in the field of within plate basalts in the tectonic discrimination diagrams.  The trace element and Rare Earth Element characteristics of the andesites and rhyolites in the subalkaline group show many characteristics of subduction zone melts e.g. negative Nb and Ta anomalies, positive Pb anomaly and LREE-enriched suggesting that a metasomatized mantle wedge source played an important role in the formation of the calcalkaline magmas. A geodynamic model of rift formation in the active continental margin of Pelagonia is proposed to explain the transition from a subduction- to an extension-related magmatic activity in the Late Permian/Triassic time in the broader NE Attica-central Evvia region.</p>

Contemporary Kinematics of the South Aegean Area (Greece) Detected with Continuous GNSS Measurements

<p>We examine the kinematic characteristics of the crustal deformation in the broader southern Aegean region using 47 permanent GNNS stations distributed across the eastern Peloponnesus, Attica, Cyclades, Dodecanese, Crete and the coast of western Anatolia. Our analysis is based on the study of velocity vectors relative to local reference points at the western and eastern halves of the study area, as well as on the strain field calculated from absolute velocity vectors across the study area. We demonstrate that the South Aegean region undergoes complex distributed block deformation.</p><p>At the eastern end of the study area this varies from N210°-N220° extension and with crustal thinning across NE Peloponnesus – Attica, to N210°-N220° compression between the central-eastern Peloponnesus and western Crete, both consistent with the geodynamic setting of the Hellenic Subduction System.</p><p>A principal feature of the S. Aegean crust appears to be a broad shear zone extending between the islands of Samos/Ikaria and Kalymnos, Paros/Naxos and Amorgos and Milos – Santorini; It exhibits left-lateral kinematics and its southern boundary appears to coincide with the Amorgos – Santorini ridge and comprise the Anhydros basin and associated volcanic field (including Columbo and Santorini). Significant WNW-ESE crustal thinning is observed within the zone.</p><p>The area of the Dodecanese, to the south of Kalymnos and east of Astypalaea and north of Rhodes appears to undergo severe crustal thinning in the NW-SE direction while the SE  rim of the Aegean Plate appears to undergo thinning in the NE-SW direction. Finally, the abrupt increase in velocity between eastern Crete and Karpathos island indicates the presence of a very significant N-S tectonic boundary of unknown as yet nature, extending between 35°N and 36°N at least.</p><p>In order to assign some values to the above qualitative description, we note that with respect to a reference point at Anavyssos, Attica, the distribution of velocities allows identification of four and possibly five major tectonic blocks with different kinematics, whose location, direction of motion and average velocities respectively are:</p><ul><li>Samos – Ikaria and Naxos-Paros-Amorgos group of islands, N220° and 1.5mm/yr respectively.</li> <li>The south-western Cyclades (Anafi, Ios, Antiparos, Milos, Folegandros, Sikinos and Santorini group of islands, N210° and 3.3 mm/yr.</li> <li>The northern Dodecanese (Kalymnos, Kos, Astypalaea group), N150° and 3.0 mm/yr.</li> <li>The southern Dodecanese (Nisyros, Telos, Rhodes, Karpathos group), N120° and 7.4 mm/yr respectively.</li> <li>The Cretan Sea and Crete, N160° and 2.0 mm/yr respectively.</li> </ul><p>An interpretation of the nature and kinematics of the boundaries between these blocks will be presented and discussed. Overall, the south Aegean appears to undergo distributed block deformation associated with a rather complex kinematic pattern, the nature of which remains to be confirmed, validated and explained with future research.</p><p><em>Acknowledgements.</em> This presentation was financially supported by the Special Account for Research Grants of the National & Kapodistrian University of Athens.</p>

Palaeoxylotomical studies in the Cenozoic petrified forests of Greece. Part one – palms

The paper reports a palaeoxylotomical study of petrified palm remains (stem, root, rachis) collected from some fossil sites of Greece (Evros, Lemnos, Lesbos and Kastoria) aged to the late Oligocene to early Miocene. Five species of Palmoxylon were identified: P. daemonoropsoides (Unger) Kirchheimer, corr., P. chamaeropsoides Iamandei et Iamandei, sp. nov., P. coryphoides Ambwani et Mehrotra, P. sabaloides Greguss, P. trachycarpoides Iamandei et Iamandei, sp. nov. and P. phoenicoides Hofmann. Also found were two species of Rhizopalmoxylon (R. daemonoropsoides Iamandei et Iamandei, sp. nov., R. phoenicoides Iamandei et Iamandei, sp. nov.) and Palmocaulon sp. aff. Phoenix L. These new identifications add new elements to the forest assemblages of the Oligocene–Miocene Greek flora, useful for understanding the evolution of the Cenozoic palaeoclimate in the Aegean area.