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This study revisits subduction processes at the Hellenic Subduction Zone (HSZ) including tearing, segmentation, and backstepping, by refining the geometry of the Nubian slab down to 150–180 km depth using well-located hypocentres from global and local seismicity catalogues. At the western termination of the HSZ, the Kefalonia Transform Fault marks the transition between oceanic and continental lithosphere subducting to the south and to the north of it, respectively. A discontinuity is suggested to exist between the two slabs at shallow depths. The Kefalonia Transform Fault is interpreted as an active Subduction-Transform-Edge-Propagator-fault formed as consequence of faster trench retreat induced by the subduction of oceanic lithosphere to the south of it. A model reconstructing the evolution of the subduction system in the area of Peloponnese since 34 Ma, involving the backstepping of the subduction to the back-side of Adria, provides seismological evidence that supports the single-slab model for the HSZ and suggests the correlation between the downdip limit of the seismicity to the amount of subducted oceanic lithosphere. In the area of Rhodes, earthquake hypocentres indicate the presence of a NW dipping subducting slab that rules out the presence of a NE-SW striking Subduction-Transform-Edge-Propagator-fault in the Pliny-Strabo trenches region. Earthquake hypocentres also allow refining the slab tear beneath southwestern Anatolia down to 150–180 km depth. Furthermore, the distribution of microseismicity shows a first-order slab segmentation in the region between Crete and Karpathos, with a less steep and laterally wider slab segment to the west and a steeper and narrower slab segment to the east. Thermal models indicate the presence of a colder slab beneath the southeastern Aegean that leads to deepening of the intermediate-depth seismicity. Slab segmentation affects the upper plate deformation that is stronger above the eastern slab segment and the seismicity along the interplate seismogenic zone.

The segmentation and differentiation of subducting slabs have considerable effects on mantle convection and tectonics. The Hellenic subduction zone is a complex convergent margin with strong curvature and fast slab rollback. The upper mantle seismic anisotropy in the region is studied focusing at its western and eastern edges in order to explore the effects of possible slab segmentation on mantle flow and fabrics. Complementary to new SKS shear-wave splitting measurements in regions not adequately sampled so far, the source-side splitting technique is applied to constrain the depth of anisotropy and to densify measurements. In the western Hellenic arc, a trench-normal subslab anisotropy is observed near the trench. In the forearc domain, source-side and SKS measurements reveal a trench-parallel pattern. This indicates subslab trench-parallel mantle flow, associated with return flow due to the fast slab rollback. The passage from continental to oceanic subduction in the western Hellenic zone is illustrated by a forearc transitional anisotropy pattern. This indicates subslab mantle flow parallel to a NE–SW smooth ramp that possibly connects the two subducted slabs. A young tear fault initiated at the Kefalonia Transform Fault is likely not entirely developed, as this trench-parallel anisotropy pattern is observed along the entire western Hellenic subduction system, even following this horizontal offset between the two slabs. At the eastern side of the Hellenic subduction zone, subslab source-side anisotropy measurements show a general trench-normal pattern. These are associated with mantle flow through a possible ongoing tearing of the oceanic lithosphere in the area. Although the exact geometry of this slab tear is relatively unknown, SKS trench-parallel measurements imply that the tear has not reached the surface yet. Further exploration of the Hellenic subduction system is necessary; denser seismic networks should be deployed at both its edges in order to achieve a more definite image of the structure and geodynamics of this area.

In this study, we report the first robust apatite (U-Th)/He thermochronology data from the syn-extensional Eybek, Solarya and Cataldag plutons from NW Turkey. The Solarya and Cataldag plutons display similar (U-Th)/He apatite ages which range from 21.5 ± 1.6 to 12 ± 1.9 and 22.4 ± 1.2 to 13.7 ± 1.3 Ma, respectively. The Eybek Pluton, on the other hand, yielded younger (U-Th)/He apatite ages between 8.4 ± 1.9 Ma and 5.6 ± 0.5 Ma. Exhumation rates of the plutons change between 214 m/Myr and 122 m/Myr. The exhumation rates and thermal modelling results show that the Solarya and Cataldag plutons experienced fast uplift and exhumation from early to middle Miocene. A low angle detachment fault(s) associated with Cataldag Metamorphic Core Complex was responsible for the exhumation of the Cataldag and Solarya plutons. In contrast, late Miocene cooling and exhumation of the Eybek Pluton was controlled by high angle normal faults. The collective evaluation of our data together with published low-temperature thermochronology data obtained from the spatially associated basement rocks and the metamorphic core complexes indicate that the region-wide exhumation of NW Anatolia was accommodated by different fault systems throughout the Miocene. We infer that the crustal exhumation in northwestern and centralwestern Anatolia occurred contemporaneously during the Miocene, and developed as a result of back-arc extension driven by slab roll-back beneath Hellenic arc and the preceding thermal weakening of the western Anatolian orogenic crust.

We examine the active stress field of the Southern Aegean Sea subduction area from fault plane solution data, focusing on the variability resulting from the application of different stress inversion methods. The study area is characterized by a high seismicity level and has been struck repeatedly by large destructive shallow and intermediate-depth earthquakes (up to M∼8.0). A larger number of previously published Fault Plane Solutions (FPS), as well as additional FPS computed in the framework of this study, provide the basis for the detailed study of the Southern Aegean active stress field. The active stress field is examined using three well-established algorithms, as well as an adapted method proposed in this study, based on the statistical processing of solutions provided by the Gephart and Forsyth (1984) method. The results obtained from all methods show a systematic consistency, with the Gephart and Forsyth method exhibiting the largest discrepancy, in comparison to other approaches. The determined active stress field reveals several domains with similar seismotectonic characteristics. Along the Southern Aegean (Hellenic) volcanic arc, the roughly North-South extension field shows an excellent correlation with the local arc geometry (arc-normal extension). The outer arc is characterized by compression, as a result of the active subduction, with an almost constant NE-SW direction. Between these two regions, a narrow zone with approximately East-West extension develops along the whole Hellenic Arc with subtle spatial differences, while in the eastern Hellenic Arc a well-developed strike-slip faulting pattern is recognized along the broader area of the Pliny and Strabo trenches. Finally, all intermediate-depth events show the same transpressional pattern, with a characteristic down-dip extension along the subduction direction and an arc-parallel compression, which follows the local arc orientation.

The tectonic setting of western Peloponnese and central Ionian Islands, Greece, is characterized by the subduction of the oceanic African plate beneath the Aegean micro-plate. The transition from subduction to continental collision in northwestern Greece is accommodated by the right-lateral Cephalonia transform fault. In this work, we exploit the recordings of a temporary seismic network composed of 15 stations operating from July 2016 until May 2017 to investigate the complex deformation of this region. Our local network fills in a major observational gap in one of the most tectonically active regions of the Hellenic arc. We detected and located more than 1200 local earthquakes and constrained five 1D optimum local velocity models. The relocated seismicity (including the aftershock sequence that followed the October 2018 Mw 6.7 earthquake offshore Zakynthos) and associated focal mechanisms constrained for the major earthquakes point out a complex crustal deformation. We propose a clockwise rotation of the Ionian Akarnania Block accommodated by major marginal strike-slip fault zones that appear segmented along their strike. Additionally, left-lateral motion is observed on the Kyllini-Cephalonia fault along a north-west direction. Finally, the seismicity recorded in north Cephalonia (offshore Myrtos and Fiskardo) suggests that the Cephalonia transform fault is a large deformation zone where secondary WNW-striking sinistral strike-slip faults occur.

This paper reviews the tectonic, magmatic, and metallogenic history of the Tethyan orogen from the Carpathians to Indochina. Focus is placed on the formation of porphyry Cu ± Mo ± Au deposits, as being the most characteristic mineral deposit type formed during both subduction and collisional processes in this region. Relatively little is known about the history of the Paleotethys ocean, which opened and closed between Gondwana and Eurasia in the Paleozoic, and few ore deposits are preserved from this period. The Neotethyan ocean opened in the Permian–Early Triassic as the Cimmerian continental fragments (the cores of Turkey, Iran, Tibet, and Indochina) rifted from the northern Gondwana margin and drifted northwards. These microcontinents docked with the Eurasian margin at various points in the Mesozoic and Cenozoic, and formed a complex archipelago involving several small back-arc basins and remnants of the Paleotethyan ocean. The main Neotethyan ocean and these smaller basins were largely eliminated by collision with India and Africa–Arabia in the early Eocene and early-mid Miocene, respectively, although Neotethyan subduction continues beneath the Hellenic arc and the Makran. The majority of porphyry-type deposits are found in association with Neotethyan subduction (mainly in the Mesozoic and Paleogene), and syn- to post-collisional events in the mid-Paleogene to Neogene. They are found throughout the orogen, but some sections are particularly well-endowed, including the Carpathians–Balkans–Rhodopes, eastern Turkey–Lesser Caucasus–NW Iran, SE Iran–SW Pakistan, southern Tibet, and SE Tibet–Indochina. Other sections that appear barren may reflect deeper levels of erosion, young sedimentary cover, or lack of exploration, although there may also be real reasons for low prospectivity in some areas, such as minimal subduction (e.g., the western Mediterranean region) or lithospheric underthrusting (as proposed in western Tibet). Over the last decade, improved geochronological constraints on the timing of ore formation and key tectonic events have revealed that many porphyry deposits that were previously assumed to be subduction-related are in fact broadly collision-related, some forming in back-arc settings in advance of collision, some during collision, and others during post-collisional processes such as orogenic collapse and/or delamination of subcontinental mantle lithosphere. While the formation of subduction-related porphyries is quite well understood, collisional metallogeny is more complex, and may involve a number of different processes or sources. These include melting of: orogenically thickened crust; previously subduction-modified lithosphere (including metasomatized mantle, underplated mafic rocks, or lower crustal arc plutons and cumulates); or upwelling asthenosphere (e.g., in response to delamination, slab breakoff, back-arc extension, or orogenic collapse). The most fertile sources for syn- and post-collisional porphyry deposits appear to be subduction-modified lithosphere, because these hydrated lithologies melt at relatively low temperatures during later tectonomagmatic events, and retain the oxidized and relatively metalliferous character of the original arc magmatism. Unusually metallically enriched lithospheric sources do not seem to be required, but the amount of residual sulfide phases in these rocks may control metal ratios (e.g., Cu:Au) in subsequent magmatic hydrothermal ore deposits. Relatively Au-rich deposits potentially form in these settings, as observed in the Carpathians (e.g., Rosia Montana), Turkey (Kisladag, Copler), and Iran (Sari Gunay, Dalli), although the majority of syn- and post-collisional porphyries are Cu–Mo-rich, and resemble normal subduction-related deposits (e.g., in the Gangdese belt of southern Tibet). This similarity extends to the associated igneous rocks, which, being derived from subduction-modified sources, largely retain the geochemical and isotopic character of those original arc magmas. While still retaining a broadly calc-alkaline character, these rocks may extend to mildly alkaline (shoshonitic) compositions, and may display adakite-like trace element signatures (high Sr/Y and La/Yb ratios) reflecting melting of deep crustal garnet amphibolitic sources. But they are otherwise hard to distinguish from normal subduction-related magmas. Small, post-collisional mafic, alkaline volcanic centers are common throughout the orogen, but for the most part appear to be barren. However, similar rocks in other post-subduction settings around the world are associated with important alkalic-type porphyry and epithermal Au ± Cu deposits, and the potential for discovery of such deposits in the Tethyan orogen should not be overlooked.

In arc lavas, elements of the extended high field strength element group (HFSE; Nb, Ta, Zr, Hf, W, and Mo) are valuable tracers to unravel magma source processes. These elements can also help to identify residual mineral assemblages in subducting slabs and in the mantle. Most high-precision studies on HFSE behaviour to date only focused on intra-oceanic arc suites and data for mafic lavas of the K-rich series (medium-K, high-K and shoshonitic) are scarce. Arguably, K-rich series are the most incompatible element-rich end-members of subduction zone magmatism, and they often record sediment recycling into the mantle. Understanding HFSE fractionation in K-rich lavas can therefore provide important insight into the global HFSE budget. Here we present a comprehensive extended HFSE dataset obtained by isotope dilution on well-characterised K-rich lavas from the Eastern Mediterranean, also including subducting sediment samples drilled during DSDP Leg 13 and ODP Leg 160 South and West of Crete. The volcanic samples include mafic calc-alkaline lavas from the active Aegean Island arc (Santorini) and post-collisional Tertiary lavas from SE Bulgaria. The Santorini lavas record a hydrous sediment melt-mediated source overprint of a depleted mantle source by components from the subducting African plate. The Bulgarian lavas tap lithospheric mantle sources that were overprinted by fluid- and melt-like subduction components during Eocene subduction of the African Plate. The sediments in this study comprise silts/sands, marl oozes, limestones and clay-rich debris flows and approximate the bulk sediment subducted beneath the Hellenic arc. The marked enrichment of all HFSE in the lavas is controlled by the composition of the subducted sediments as shown by low 176Lu/177Hf (0.008630–0.02433) and Zr/Nb (11.3–29.4), combined with variable eHf (−3 to +11) and elevated W contents (up to 2.45 ppm) in the lavas. Nevertheless, the lavas display unfractionated ratios of Nb/Ta and Zr/Hf of 12.3–16.5 and 34.4–38.6, respectively, with respect to MORB. This feature may be explained by the Nb/Ta in the sediments that are on average higher (15.2 ± 2) compared to typical upper crustal estimates (12.5 ± 1.8), indicating a strong regional control on the HFSE ratios in Eastern Mediterranean sediments. The lavas exhibit low Ta/W (

On October 12, 2013, an earthquake with Mw = 6.5 occurred in the southern Hellenic Arc, approximately 20 km off the west coast of Crete. The main shock, the focal depth of which is on the order of 40 km, was followed by aftershocks felt in the nearby cities and villages, although the aftershock sequence was poor. The epicentre was located at approximately 60 km from a radio receiver in Crete (CRE), which belongs to the European VLF/LF Radio Network. Several days before the earthquake, a clear disturbance occurred in one of the ten radio signals that the CRE receiver sampled. The disturbance, which can be considered an anomaly, appeared in the 216 kHz radio signal radiated by the Radio Monte Carlo (MCO) transmitter. The radio path MCO-CRE crossed directly over the epicentre area of the aforementioned earthquake. In this work, we present a detailed analysis of the MCO signal anomaly using spectral tools. We also investigate the behaviour of other radio signals sampled by the CRE receiver and consider other possible causes of disturbances on the MCO radio signal. We conclude that the disturbance in the MCO radio signal is a convincingly possible precursor of the earthquake in Crete. Emission of electromagnetic waves with a frequency band that includes 216 kHz from the focal zone of the earthquake can provide a satisfactory explanation of the radio anomaly.

In this paper we investigate the tidal triggering evidence on the earthquakes of the seismic area of the Hellenic Arc using the Hist(ogram)Cum(mulation) method. We analyze the series of the earthquakes occurred in the area which is confined by the longitudes 22° and 28°E and latitudes 34° and 36°N in the time period from 1964 to 2012. In this time period 16,137 shallow and of intermediate depth earthquakes with ML up to 6.0 and 1,482 deep earthquakes with ML up to 6.2 occurred. The result of the this analysis indicate that the monthly variation of the frequencies of earthquake occurrence is in accordance with the period of the tidal lunar monthly variations, and the same happens with the corresponding daily variations of the frequencies of earthquake occurrence with the diurnal luni-solar (K1) and semidiurnal solar (S2) tidal variations. These results are in favor of a tidal triggering process on earthquakes when the stress in the focal area is near the critical level.

Evolution of the east–west-trending Gokova Graben structure is related to the north–south extension of the Aegean segment of the Aegean–Anatolian Microplate. The Pliocene–Quaternary successions surrounding the onland portion of the Gokova Graben as well as coeval successions within the marine portion of the graben are cut by at least three families of faults that strike northwest–southeast, east–west and east-northeast–west-southwest. These orientations are inconsistent with a simple north–south extensional regime. Interpretation of seismic reflection profiles, multibeam bathymetry and GPS vectors indicates that the Gokova Graben developed as a lazy-S-shaped graben in the back-arc setting north of the Hellenic Arc. A counterclockwise rotation of the Aegean segment of the Aegean–Anatolian Microplate is the suggested mechanism for this geometry, as subduction zone rolled back occurred during the Pliocene–Quaternary. The Gulf of Gokova is the youngest of a series of basins that developed within this large back-arc system, including the Nisyros, Karpathos, and Kamilonisi basins, collectively named to as the Gokova–Nisyros–Karpathos Graben. It is proposed that this graben experienced a scissor-like opening initiating from the west during the Pliocene and progressing eastward during the Quaternary. Faults that are seemingly un-correlated onland and in the marine areas become remarkably aligned when the Marmaris-Rhodes Block is progressively rotated by 6° counterclockwise relative to the Mugla Block using a pole position located within the Gulf of Gokova. The scissor-like opening of the westernmost regions of the Gokova Graben likely occurred during the late Pliocene, whereas the central and eastern portions of the graben developed during the early–middle Pleistocene and late Pleistocene–Holocene, respectively. The onset of the opening of the westernmost segment of the Gokova–Nisyros–Karpathos Graben occurred at a time earlier than the late Pliocene.

Throughout its history, the northern coast of Alexandria has experienced devastating earthquakes and tsunamis impacts from tsunamigenic sources in the Eastern Mediterranean. The most hazardous tsunami events for Northern coast of Egypt were related to the earthquakes of 365 in Crete with Mw8.5, 1222 in Cyprus with Mw 7–7.5, and 1303 in Rhodes Island with Mw8.0.The 365 and 1303 earthquakes were accompanied by tsunamis that resulted in widespread destruction and subsequent fatalities along the coast of Alexandria as evidenced by the available historical reports for the Mediterranean region, geomorphologic and paleo-tsunami investigations accomplished recently. In this work, for each tsunamigenic source, i.e., West Hellenic Arc, East Hellenic Arc, and Cyprian Arc, the maximum credible earthquake (MCE) is defined then modeled with NAMI-DANCE. The comparison of the tsunami inundation maps of MCE scenarios computed for each tsunami source shows that the East Hellenic arc (EHA) is the most hazardous source for the Alexandria coast, with a tsunami wave height of 5.5–6.0 m, while the Cyprian arc (CA) is the least hazardous source. The aggregated tsunami inundation map for Alexandria defines the furthest boundary between inundated and non-inundated lands and is associated with hazard levels based on water heights. This map shows that the coasts of Al Amereya district and Borg Al Arab city are expected to be more affected than the others districts. It also indicates that the west side of Alexandria, called Al Sahel Al Shamally, is expected to have less impact than the eastern side, because it is naturally protected by a barrier of carbonate material parallel to the shoreline. The exposure analysis shows that more than 85,000 people are located in the tsunami hazard zone (representing 15.8% of Alexandria governorate's population). Regarding buildings and infrastructure, the most exposed district is Al Amereya with 65.8% of total exposed objects. Among the buildings, the residential ones are the most exposed and about 21% can be classified as highly vulnerable. In terms of risk assessment, the Al Amereya district is identified as the area with the highest tsunami risk.

Earthquakes exhibit complex correlations in space, time, and magnitude. As such, they present a unique example for a time series exhibiting complexity. To uncover hidden dynamic features of seismicity before the Mw6.4, October 12, 2013 earthquake in the South West part of the Hellenic Arc, we apply the recently introduced methods of natural time analysis along with the ideas of non-extensive statistical physics. Using non-extensive statistics, the analysis of the magnitude distribution of the 2013 seismicity in the South West part of the Hellenic Arc, struck by a strong earthquake ( M w = 6.4 ), was performed for a time period before the main event, which was the strongest one in the South West part of the Hellenic Arc in the last 40 years. The analysis of the frequency magnitude (energy) distribution reveals that the non-extensive parameter q E varies during the last period of the earthquake preparatory phase with a sharp increase a couple of days before the occurrence of the main strong event, indicating an increase in the degree of out-of-equilibrium state before the occurrence of the Mw6.4 earthquake. In addition using the natural time analysis it is shown that foreshock seismicity approaches the critical stage, where the k 1 parameter reaches the critical value of k 1 = 0.070 few days before the occurrence of the main event.

The Aegean region including western Turkey, mainland Greece, and the Hellenic Arc is the most seismological and geodynamical active domain in the Alpine Himalayan Belt. In this study, we processed 3 years of survey-mode GPS data and present the analysis of a combination of geodetic and seismological data around Izmir, which is the third most populated city in Turkey. The velocities obtained from 15 sites vary between 25 mm/yr and 28 mm/yr relative to the Eurasian plate. The power law exponent of earthquake size distribution (b-value) ranges from 0.8 to 2.8 in the Izmir region between 26.2 degrees E and 27.2 degrees E. The lowest b-value zones are found along Karaburun Fault (b = 0.8) and, between Seferihisar and Tuzla Faults (b = 0.8). A localized stress concentration is expected from numerical models of seismicity along geometrical locked fault patches. Therefore, areas with lowest b-values are considered to be the most likely location for a strong earthquake, a prediction that is confirmed by the 2005 M-w = 5.9 Seferihisar earthquake sequences, with epicentres located to the south of the Karaburun Fault. The north-south extension of the Izmir area is corroborated by extension rates up to 140 nanostrain/yr as obtained from our GPS data. We combined the 3-year GPS velocity field with the published velocity field to determine the strain rate pattern in the area. The spatial distribution of b-value reflects the normal background due to the tectonic framework and is corroborated by the geodetic data. b-Values correlate with strain pattern. This relationship suggests that decrease of b-values signifies accumulating strain. (c) 2013 Elsevier Ltd. All rights reserved.

It is well known that anelasticity has significant effects on the propagation of seismic waves, as manifested by physical dispersion and dissipation. Investigations of anelasticity provide complementary constraints on the physical properties of Earth materials, but — contrary to imaging with elastic waves — progress in mapping Earthʼs anelasticity has been relatively slow, and there is only limited agreement between different studies or methodologies. Here, within the framework of adjoint tomography, we use frequency-dependent phase and amplitude anomalies between observed and simulated seismograms to simultaneously constrain upper mantle wavespeeds and attenuation beneath the European continent and the North Atlantic Ocean. In the sea-floor spreading environment beneath the North Atlantic, we find enhanced attenuation in the asthenosphere and within the mantle transition zone (MTZ). In subduction zone settings, for example beneath the Hellenic arc, elevated attenuation is observed along the top of the subducting slab down to the MTZ. No prominent reductions in wavespeeds are correlated with these distinct attenuation features, suggesting that non-thermal effects may play an important role in these environments. A plausible explanation invokes the transport of water into the deep Earth by relatively cold subducting slabs, leading to a hydrated MTZ, as previously suggested by mineral physics and geodynamics studies.

WOS: 000318381400003, Both seismological and geodynamic studies emphasize that the Aegean region is deforming internally mainly under pure shear stress and rotating in an anti-clockwise direction relative to the Eurasia plate. The Aegean region is seismically the most active region in western Anatolia, which comprises the Hellenic Arc, Greece, and western Turkey. Izmir is the third largest city in Turkey, with a population about 2.7 million in 2010. The Tuzla fault has a particular importance in terms of its proximity to the city of Izmir and its seismic activity. The Tuzla fault has NE-SW trending lineaments and lies between the towns of Menderes and Cape Doganbey. This study intended to investigate crustal deformation and relative displacement along the Tuzla fault and Izmir Bay by two different geodetic techniques: GPS and precise leveling. Toward this aim, a geodetic network consisting of 16 points has been established. The first GPS observation campaign and precise leveling measurements were performed in 2009, and the second set of measurements was performed in 2010. The data collected by the GPS campaigns were processed with GAMIT/GLOBK software. The displacements inferred from GPS data are between 21 mm/yr and 25 mm/yr with respect to Eurasia as the fixed reference frame. In addition, the precise leveling results show that there is a vertical displacement in the region of around 7 mm along the fault, which is higher than expected during a nine-month interval. (C) 2012 Elsevier Ltd. All rights reserved., TUBITAK-CAYDAG [108Y295]; Bogazici University Scientific Research Projects (BAP) [5056]; Geodesy Department of Kandilli Observatory; Earthquake Research Institute, The authors would like to thank the Geodesy Department of Kandilli Observatory and Earthquake Research Institute and the project's members for their support. We also thank Rob Reilinger and an anonymous reviewer for their comments and suggestions. We are grateful to the district governor of Seferihisar, officials of Izmir Metropolitan and Seferihisar Municipalities, and local people in the region for their help. Maps were drawn using GMT 4.5 (Wessel and Smith, 2001). This study was mainly supported by TUBITAK-CAYDAG under grant no. 108Y295 and Bogazici University Scientific Research Projects (BAP) under grant no. 5056.

The complicated tectonics of the Mediterranean region, dominated by the subduction of the African plate under Eurasia, affects the whole of Greece. A significant extension rate across the Aegean sea is estimated from satellite geodetic observations, while intense seismicity is observed in parts of the Hellenic arc, manifested by strong earthquakes ( M s > 6) of intermediate depth that take place along it. In Western Greece, the Ionian Islands are situated in a transitional zone (from the Hellenic subduction to the Adriatic collision), characterised by a high crustal deformation rate as revealed by the high seismicity of this zone, the highest in Greece, and the GPS velocity field estimated for the region. In this part of the Aegean plate, transcurrent fault systems dominate, one of which is the Kephalonia Transform Fault (KTF), located offshore the Kephalonia and Lefkada Islands, with a right-lateral slip of the order of 3 cm/year. In the present work an attempt is made to assess the Coulomb stress change associated with well documented earthquake activity, from 1973 to 2003, in the Ionian Island of Lefkada. The results of this study suggest that the early 1973 event did not influence any subsequent moderate earthquakes in the area. On the other hand, the 1994 earthquake may have triggered the north segment of the 2003 event, while the 2003 earthquake ruptured two segments with the north one initiating rupture on the south segment.

International audience; We review the geodynamic evolution of the Aegean-Anatolia region and discuss strain localisation there over geological times. From Late Eocene to Present, crustal deformation in the Aegean backarc has localised progressively during slab retreat. Extension started with the formation of the Rhodope Metamorphic Core Complex (Eocene) and migrated to the Cyclades and the northern Menderes Massif (Oligocene and Miocene), accommodated by crustal-scale detachments and a first series of core complexes (MCCs). Extension then localised in Western Turkey, the Corinth Rift and the external Hellenic arc after Messinian times, while the North Anatolian Fault penetrated the Aegean Sea. Through time the direction and style of extension have not changed significantly except in terms of localisation. The contributions of progressive slab retreat and tearing, basal drag, extrusion tectonics and tectonic inheritance are discussed and we favour a model (1) where slab retreat is the main driving engine, (2) successive slab tearing episodes are the main causes of this stepwise strain localisation and (3) the inherited heterogeneity of the crust is a major factor for localising detachments. The continental crust has an inherited strong heterogeneity and crustal-scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation. The dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate. Successive slab ruptures from the Middle Miocene to the Late Miocene have isolated a narrow strip of lithosphere, still attached to the African lithosphere below Crete. The formation of the North Anatolian Fault is partly a consequence of this evolution. The extrusion of Anatolia and the Aegean extension are partly driven from below (asthenospheric flow) and from above (extrusion of a lid of rigid crust).

The Greek island of Nisyros is the source of tephra found in distal settings throughout the Aegean. In this contribution, we define geochemical fingerprints for the Lower and Upper Pumice eruptions of Nisyros based on micron-beam major (EMPA) and trace (LA-ICP-MS) element data. These two eruptions are compositionally distinct from each other. The high phenocryst content of proximal Lower and Upper Pumice tephra means that the differences between the two magmas are masked in whole-rock analyses. We demonstrate that all previous reports of distal marine and continental tephras correspond to the younger Upper Pumice not the older Lower Pumice. This has important implications for the marine tephrochronology of the Mediterranean and for the age of the Upper and Lower Pumice eruptions. We suggest an age of at least 47 ka for the Upper Pumice and an older, unconstrained age for the Lower Pumice.

Neither large magnitude nor tsunamigenic earthquakes occur frequently in the eastern Mediterranean, hampering comprehensive study of these events and consequential hazards whenever digital data are required. Using analog seismograms, travel-time catalogs, and hydrodynamic simulations, we reassess here four large (M ~ 7) historical earthquakes occurring in various regions of the Hellenic Arc: on 6 October 1947, in the Peloponnesus; 9 February 1948, near Karpathos; and a couplet east of Rhodos on 24 and 25 April 1957. Damaging near-field tsunamis are associated with the 1947 and 1948 earthquakes. Results include seismic moments (in units of 1027 dyn·cm) of 1.26 (1947), 0.97 (1948), 0.56 (1957a), and 1.09 (1957b); recovered focal mechanisms and hypocentral locations are consistent with the regional stress field resulting from the ongoing collision between the Nubia plate and Aegea microplate. Seismological reassessments indicate that the sources of the 1947 and 1948 tsunamis involved submarine slumping; hydrodynamic simulations assuming a submarine landslide source for the 1948 tsunami recreate run-up and inundation values consistent with eyewitness accounts presented here. Hydrodynamic simulations also show that the 25 April 1957 earthquake likely generated an unobserved tsunami with a maximum 50 cm run-up in Rhodos.

The present-day eastern Mediterranean region is characterized by two main arc systems: the western Hellenic arc and the eastern Cyprian arc, the latter having no significant trench unlike the former. Therefore, plate interactions in the western-northwestern side of the island of Cyprus is a matter of debate concentrating mainly on subduction or wrench systems. In order to understand the plate interactions within the area between the Isparta Angle and western segment of the Cyprus arc, the epicenter distribution of earthquakes, b -values and gravity anomalies for 5 depth intervals (0–35 km, 35–55 km, 55–75 km, 75–95 km, >95 km) have been analyzed on NE-SW trending regional profiles, and compared with geological structures. Although there are no earthquakes with depths greater than 50 km (i.e. crustal scale earthquakes) in the northern part of the Isparta Angle, all earthquake epicenters lie on a linear zone from southwest of Cyprus to the northwest, nearly parallel to the NW-SE trending Florence Rise. The b -value distribution shows a very good consistency with the epicentral and tectonic maps of Antalya Bay. The b -value maps, deeper than 55 km, show that low b -values depicting a NW-SE trending linear pattern correspond to seismic zones. Furthermore, this pattern shifts to the northeast and resembles the epicenters of the deep-focus earthquakes on the northeast dipping plane supporting the existence of a subduction zone. The gravity profiles show low gravity anomalies along the Florence Rise, high gravity anomalies at a certain distance interval to the NE direction which presumably resulted from subducting oceanic lithosphere, and again low gravity anomalies corresponding to the end of subducting slab and continental eastern limb of the Isparta Angle. On the other hand, the observed gravity anomalies are found to be consistent with the earthquake distribution patterns in the area. As a conclusion, for the area between the apex of the Isparta Angle and the western Cyprian arc, the distribution of earthquake epicenter locations, b -values, and gravity data suggest the presence of a subduction zone inclined to the northeast beneath the eastern limb of the Isparta Angle.

This paper provides new relative sea level data inferred from coastal archaeological sites located along the Turkish coasts of the Gulf of Fethye (8 sites), and Israel, between Akziv and Caesarea (5 sites). The structures selected are those that, for effective functioning, can be accurately related to sea level at the time of their construction. Thus their positions with respect to present sea level provide a measure of the relative sea level change since their time of construction. Useful information was obtained from the investigated sites spanning an age range of ˜2.3–˜1.6 ka BP. The inferred changes in relative sea level for the two areas are distinctly different, from a rise of 2.41 to 4.50 m in Turkey and from 0 to 0.18 m in Israel. Sea level change is the combination of several processes, including vertical tectonics, glacio–hydro-isostatic signals associated with the last glacial cycle, and changes in ocean volume. For the Israel section, the present elevations of the MIS-5.5 Tyrrhenian terraces occur at a few meters above present sea level and vertical tectonic displacements are small. Data from GPS and tide gauge measurements also indicate that any recent vertical movements are small. The MIS-5.5 shorelines are absent from the investigated section of the Turkish coast, consistent with crustal subsidence associated with the Hellenic Arc. The isostatic signals for the Israel section of the coast are also small (ranging from −0.11 mm/yr to 0.14 mm/yr, depending on site and earth model) and the observed (eustatic) average sea level change, corrected for this contribution, is a rise of 13.5 ± 2.6 cm during the past ˜2 ka. This is attributed to the time-integrated contribution to sea level from a combination of thermal expansion and other increases in ocean volume. The observed sea levels from the Turkish sites, in contrast, indicate a much greater rise of up to 2.2 mm/yr since 2.3 ka BP occurring in a wide area between Knidos and Kekova. The isostatic signal here is also one of a rising sea level (of up to ˜1 mm/yr and site and earth-model dependent) and the corrected tectonic rate of land subsidence is ˜1.48 mm/yr. This is the primary cause of dramatic relative sea level rise for this part of the coast.

The Aegean is the most seismically active and tectonically complex region in Europe. Damaging earthquakes have occurred here throughout recorded history, often resulting in considerable loss of life. The Monte Carlo method of probabilistic seismic hazard analysis (PSHA) is used to determine the level of ground motion likely to be exceeded in a given time period. Multiple random simulations of seismicity are generated to calculate, directly, the ground motion for a given site. Within the seismic hazard analysis we explore the impact of different seismic source models, incorporating both uniform zones and distributed seismicity. A new, simplified, seismic source model, derived from seismotectonic interpretation, is presented for the Aegean region. This is combined into the epistemic uncertainty analysis alongside existing source models for the region, and models derived by a K -means cluster analysis approach. Seismic source models derived using the K -means approach offer a degree of objectivity and reproducibility into the otherwise subjective approach of delineating seismic sources using expert judgment. Similar review and analysis is undertaken for the selection of peak ground acceleration (PGA) attenuation models, incorporating into the epistemic analysis Greek-specific models, European models and a Next Generation Attenuation model. Hazard maps for PGA on a “rock” site with a 10% probability of being exceeded in 50 years are produced and different source and attenuation models are compared. These indicate that Greek-specific attenuation models, with their smaller aleatory variability terms, produce lower PGA hazard, whilst recent European models and Next Generation Attenuation (NGA) model produce similar results. The Monte Carlo method is extended further to assimilate epistemic uncertainty into the hazard calculation, thus integrating across several appropriate source and PGA attenuation models. Site condition and fault-type are also integrated into the hazard mapping calculations. These hazard maps are in general agreement with previous maps for the Aegean, recognising the highest hazard in the Ionian Islands, Gulf of Corinth and Hellenic Arc. Peak Ground Accelerations for some sites in these regions reach as high as 500–600 cm s − 2 using European/NGA attenuation models, and 400–500 cm s − 2 using Greek attenuation models.

Asia has been a major testing ground for various competing models of continental deformation due to its relatively well-understood plate boundary conditions in the Cenozoic, exceptional exposure of active structures, and strain distribution, and widespread syn-collisional igneous activity as a proxy for the thermal state of the mantle and crust. Two Cenozoic orogens dominate the continent: the Himalayan–Tibetan orogen in the east induced by the India–Asia collision and the Turkish–Iranian–Caucasus orogen in the west induced by the Arabia–Asia collision. The development of the two orogens was accomplished by shortening in the early stage followed by strike-slip faulting and extension in the late stage. In the Himalayan–Tibetan orogen, shortening across two discrete thrust belts at 55–30 Ma in southern and northern Tibet created a large intracontinental basin (the Paleo-Qaidam basin) in between. Subsequent crustal thickening and a possible thermal event in the mantle (e.g., convective removal of central Tibetan mantle lithosphere) may have raised the elevation of this early intra-plateau basin up to ~ 2–3 km to its current height. Collision between India and Asia also caused lateral extrusion of southeast Asia between 32 Ma and 17 Ma. The latest stage of the India–Asia collision was expressed by north-trending rifting and the development of trench-facing V-shaped conjugate strike-slip faults in central Mongolia, central Tibet, eastern Afghanistan and southeast Asia. In the Turkish–Iranian–Caucasus orogen, early crustal thickening in the orogenic interior began at or prior to 30–20 Ma. This style of deformation was replaced by strike-slip faulting at ~ 15–5 Ma associated with further northward penetration of Arabia into Asia, westward extrusion of the Anatolia/Turkey block, and rapid extension across the Sea of Crete and Sea of Aegean. The late stage extension in both orogens was locally related to extensional core-complex development. The continental-margin extension of east Asia was developed in two stages: initially in a widely distributed zone that has an east-west width of 500–800 km during 65–35 Ma, which was followed by localized extension and opening of back-arc basins associated with the development of spreading centers at 32–17 Ma (e.g., Japan Sea or East Korea Sea, Bohai Bay, and South China Sea). Opening of the back-arc basins could be induced by (1) rapid eastward migration of the western Pacific trench system or (2) oblique subduction of Pacific plate beneath Asia that had produced a series of en echelon right-slip primary shear zones linking with back-arc spreading centers oriented obliquely to the strike of the nearby trench. Since ~ 15 Ma, the eastern margin of Asia became contractional in the east–west direction, as indicated by the collapse of back-arc basins in the western Pacific and the development of fold-thrust belts along the eastern continental margin. Coeval with the contraction is widespread east–west extension in Siberia, North China, and the Tibetan plateau. The above observations can be explained by a change in boundary condition along the eastern margin of Asia that allowed the thickened Asian continent to spread eastward, causing east-west extension in its trailing edge and east-west compression in its leading edge. In west Asia, continental-margin extension started at about 25–20 Ma in the Aegean and Cretan regions, which was associated with a rapid southward retreat of the Hellenic arc. The complex evolution of Cenozoic deformation in Asia may be explained by a combined effect of temporal changes in plate boundary conditions, thermal evolution of the upper mantle perturbed by collisional tectonics, and the built-up of gravitational energy through crustal thickening and thermal heating. Although the past research in Asia has treated the India–Asia and Arabia–Asia convergence as separate collisional processes, their interaction may have controlled the far-field Cenozoic deformation in Asia. The most pronounced result of this interaction is the creation of a northeast-trending 300–400-km wide and > 1500-km long zone of northwest-striking right-slip faults, which extends from the Zagros thrust belt in the south to western Mongolia in the north and links with the active Tian Shan and Altai Shan intracontinental orogens. Cenozoic deformation and coeval igneous activity spatially overlap with one another in the Himalayan–Tibetan and Turkish–Iranian–Caucasus orogens. A large Cenozoic magmatic gap exists between Tibet in the south and Mongolia in the north where Cenozoic deformation has not been associated with any coeval igneous activity. Finally, Cenozoic igneous activity is always associated with Jurassic–Cretaceous magmatic arcs, suggesting a causal relationship between the early arc magmatism and later syn-collisional magmatism.

Subduction plays a fundamental role in plate tectonics and when interrupted it may trigger a series of geodynamic and sedimentary responses. Synchronous structural modifications recorded across the entire eastern Mediterranean region are dated to a relatively short period — early-to-mid Pleistocene. These deformations are documented within plates (e.g., Arabian, Sinai and African plates), along plate boundaries (e.g., Dead Sea and North Anatolian faults and Cyprus Arc), and in the Mediterranean basin. During the same period the northward subduction of the Sinai plate was interrupted when the Eratosthenes Seamount–Cyprus Arc collision initiated. Subduction–collision processes of the eastern Mediterranean serve as a unique modern analogue for similar settings worldwide. Understanding their association with accompanying neo-tectonic processes is therefore predominantly important. By fostering a detailed and comprehensive approach this research provides a coherent tectonic picture for the eastern Mediterranean early-to-mid Pleistocene tectonic transition in order to explore its triggering mechanisms. Since the Neogene convergence across the eastern Mediterranean was accompanied by Eurasian indentation by Arabia northward motion, westwards Anatolia escape and southwards Aegean propagation. This semi counterclockwise plate motion was temporarily interrupted by the incipient Seamount–Arc collision which is suggested here as a trigger of the early-to-mid Pleistocene tectonic transition.

Interpretation of ~ 1500 km of multi-channel seismic reflection profiles shows that the Rhodes Basin evolved in two distinct tectonic stages. A protracted Miocene convergence (episode P1) resulted in the development of a mainly SSE-verging fold–thrust belt. This period corresponds with the emplacement of the Lycian Nappes to the northeast and fold/thrust complexes on the Island of Rhodes to the west. This phase of deformation ceased in the late Miocene. The absence of evaporites in the Rhodes Basin suggests that this region must have remained above the depositional base of marine evaporite environment during the Messinian. The morphology of the M-reflector, and the architecture of the lowermost Pliocene growth strata in the central portion of the Rhodes Basin demonstrate the existence of rugged paleo-relief over the pre-existing Miocene fold–thrust belt in early Pliocene. The middle Pliocene–Quaternary phase of deformation is characterised by NE–SW sinistral transpression (P2), and rapid regional subsidence. The P2 deformation occurred in response to an actively curving Hellenic Arc and the increasing obliquity of its eastern limb, the Pliny–Strabo Trenches (or fault zones) to the convergence vector of the African Plate. During this time, the P1 structures became re-activated as transpressional faults, further facilitating the rapid subsidence. We envisage the evolution of the Rhodes Basin as the result of subsidence associated with loading of the large imbricate thrust panels that carry the western Tauride Mountains in the north. At present, the Pliny–Strabo fault zones are delineated as a NE–SW trending 30–50 km-wide zone that continue into the western segment of the Rhodes Basin. This fault zone is further correlated with the similar trending ~ 50 km-wide Burdur–Fethiye Fault zone in southwestern Turkey.

The Aegean Sea is one of the more seismically active areas in the Euro-Mediterranean region. The seismic activity in the Aegean Sea is monitored by a number of local agencies that contribute their data to the International Seismological Centre (ISC). Consequently, the ISC Bulletin may serve as a reliable reference for assessing the capabilities of local agencies to monitor moderate and low magnitude earthquakes. We have compared bulletins of the Kandilli Observatory and Earthquake Research Institute (KOERI) and the ISC, for the period 1976–2003 that comprises the most complete data sets for both KOERI and ISC. The selected study area is the East Aegean Sea and West Turkey, bounded by latitude 35–41°N and by longitude 24–29°E. The total number of events known to occur in this area, during 1976–2003 is about 41,638. Seventy-two percent of those earthquakes were located by ISC and 75% were located by KOERI. As expected, epicentre location discrepancy between ISC and KOERI solutions are larger as we move away from the KOERI seismic network. Out of the 22,066 earthquakes located by both ISC and KOERI, only 4% show a difference of 50 km or more. About 140 earthquakes show a discrepancy of more than 100 km. Focal Depth determinations differ mainly in the subduction zone along the Hellenic arc. Less than 2% of the events differ in their focal depth by more than 25 km. Yet, the location solutions of about 30 events differ by more than 100 km. Almost a quarter of the events listed in the ISC Bulletin are missed by KOERI, most of them occurring off the coast of Turkey, in the East Aegean. Based on the frequency-magnitude distributions, the KOERI Bulletin is complete for earthquakes with duration magnitudes Md > 2.7 (both located and assigned magnitudes) where as the threshold magnitude for events with location and magnitude determinations by ISC is mb > 4.0. KOERI magnitudes seem to be poorly correlated with ISC magnitudes suggesting relatively high uncertainty in the magnitude determinations. It is apparent that KOERI, like other agencies in the region, will greatly benefit from a much improved regional cooperation.

A composite 40.2 m sediment sequence from Megali Limni, Lesvos Island, Greece, spanning the interval from 22 to 62 ka BP, contains six Pleistocene tephra layers, which can be identified on the basis of their major and trace elemental compositions. The youngest tephra deposit correlates with the 22 ka Y-2 marker, erupted during the Cape Riva eruption of Santorini. The second tephra originates from the Campanian area in Italy and corresponds to the Campanian Ignimbrite eruption (the 39 ka Y-5 marker). The next two layers are compositionally identical, and originate from Eastern islands of the Hellenic Arc; they could potentially correspond to the Upper and Lower Pumice eruptions of Nisyros or some other previously unidentified eruption from Yali. The fifth stratum corresponds to the Y-6 marker, which erupted during the Green Tuff eruption of the Pantelleria Island. The source of the last tephra layer is either the Yali-Nisyros complex or Central Anatolia; no specific corresponding eruption has yet been found. Long distal tephra sequences within terrestrial settings are rare in the eastern Mediterranean and the Megali Limni record contains the most complete sequence to date. Moreover, its age model, based on independent chronologies such as AMS and conventional radiocarbon dates and high-resolution pollen stratigraphy, provides new ages for these eruptions and places them within the context of the millennial-scale palaeoenvironmental variability of the last glacial period. Finally, the recognition of the Pantelleria tephra in this locality considerably extends the confirmed Northerly and Easterly distribution of this widespread and distinctive unit, while the existence of the Nisyros-Yali tephras on Lesvos refutes the current belief of limited tephra dispersal and small magnitude of these eruptions. © 2007 Elsevier B.V. All rights reserved.

Hurst's rescaled range analysis is a useful tool in the examination of a time series and is designed to measure memory content and determine its fractal texture. This study applies the Hurst method to a new earthquake catalogue for Greece. The study also adopts Monte Carlo simulations to provide a statistical test underpinning the Hurst analyses. Together these reveal basic temporal fractal characteristics in the earthquake occurrence time-histories' memory. Three regions are considered, approximately: all of Greece and some surrounding areas, and the sub-zones of the Hellenic Arc and the Gulf of Corinth. Three temporal textures are considered: elapsed time between earthquakes, strain energy release, and earthquake frequency. The elapsed temporal textures for the zone whole Greece indicate distinct characteristics in chronological order and possess long memory. These belong to the class non-random pattern. However, these characteristics generally disappear when the sub-zones are considered and become random patterns. The Monte Carlo simulations support this. Therefore, memoryless statistical seismic hazard estimates may not be suitable for whole Greece but could be useful for the sub-zones. The strain energy release temporal textures for whole Greece and for the sub-zones, no matter that these seem to possess long memory at first analysis, are all random patterns. In other words, the Monte Carlo simulations demonstrate that these patterns are much more likely to happen by chance. The seismic frequency textures for whole Greece and for the sub-zones suggest long memory, however, only the texture for the Hellenic Arc zone (MS ≥ 5.0) and that for whole Greece (MS ≥ 4.0) approach demonstrable non-random patterns. Except for these, other patterns happen by chance.

A 3-D density model for the Cretan and Libyan Seas and Crete was developed by gravity modelling constrained by five 2-D seismic lines. Velocity values of these cross-sections were used to obtain the initial densities using the Nafe–Drake and Birch empirical functions for the sediments, the crust and the upper mantle. The crust outside the Cretan Arc is 18 to 24 km thick, including 10 to 14 km thick sediments. The crust below central Crete at its thickest section, has values between 32 and 34 km, consisting of continental crust of the Aegean microplate, which is thickened by the subducted oceanic plate below the Cretan Arc. The oceanic lithosphere is decoupled from the continental along a NW–SE striking front between eastern Crete and the Island of Kythera south of Peloponnese. It plunges steeply below the southern Aegean Sea and is probably associated with the present volcanic activity of the southern Aegean Sea in agreement with published seismological observations of intermediate seismicity. Low density and velocity upper mantle below the Cretan Sea with ρ ≅ 3.25 × 103 kg/m3 and Vp velocity of compressional waves around 7.7 km/s, which are also in agreement with observed high heat flow density values, point out at the mobilization of the upper mantle material here. Outside the Hellenic Arc the upper mantle density and velocity are ρ ≥ 3.32 × 103 kg/m3 and Vp = 8.0 km/s, respectively. The crust below the Cretan Sea is thin continental of 15 to 20 km thickness, including 3 to 4 km of sediments. Thick accumulations of sediments, located to the SSW and SSE of Crete, are separated by a block of continental crust extended for more than 100 km south of Central Crete. These deep sedimentary basins are located on the oceanic crust backstopped by the continental crust of the Aegean microplate. The stretched continental margin of Africa, north of Cyrenaica, and the abruptly terminated continental Aegean microplate south of Crete are separated by oceanic lithosphere of only 60 to 80 km width at their closest proximity. To the east and west, the areas are floored by oceanic lithosphere, which rapidly widens towards the Herodotus Abyssal plain and the deep Ionian Basin of the central Mediterranean Sea. Crustal shortening between the continental margins of the Aegean microplate and Cyrenaica of North Africa influence the deformation of the sediments of the Mediterranean Ridge that has been divided in an internal and external zone. The continental margin of Cyrenaica extends for more than 80 km to the north of the African coast in form of a huge ramp, while that of the Aegean microplate is abruptly truncated by very steep fractures towards the Mediterranean Ridge. Changes in the deformation style of the sediments express differences of the tectonic processes that control them. That is, subduction to the northeast and crustal subsidence to the south of Crete. Strike-slip movement between Crete and Libya is required by seismological observations.

Investigating the period 1983–1994 for western Greece, a possible correlation between the selectivity characteristics of the SES (seismic electric signals of the VAN method) and earthquake parameters has been reported by Uyeda et al. [Uyeda, S., Al-Damegh, K.S., Dologlou, E., Nagao, T., 1999. Some relationship between VAN seismic electric signals (SES) and earthquake parameters, Tectonophysics, 304, 41–55.]. They found that the earthquake source mechanism changed from largely strike-slip type to thrust type at the end of 1987, and this coincided with a shift in the SES sensitive site from Pirgos (PIR) to Ioannina (IOA) VAN station. Here, we report the results for the period January 1, 2002–July 25, 2004, during which the SES sensitive site of PIR became again active, after a 10-year period of “quiescence”. This activation was followed by strike slip earthquakes (on August 14, 2003 and March 17, 2004 with magnitude 6.4 and 6.5, respectively) in the Hellenic arc, which provides additional evidence on the correlation reported by Uyeda et al. The SES activities recorded at PIR have been discriminated from “artificial” noise by employing the natural time-domain analysis introduced recently.

The western Hellenic subduction zone is characterized by a trenchward velocity of the upper plate. In the Ionian islands segment, complete seismic coupling is achieved, as is predicted by standard plate-tectonic models in which there is no slab pull force because the slab has broken off. The moderate local seismic moment rate relates to a shallow downdip limit for the seismogenic interface. This characteristic may be attributed to the ductility of the lower crust of the upper plate, which allows a decollement between the upper crust of the overriding plate and the subducting plate. Farther south, a deeper downdip limit of the seismogenic interface is indicated by thrust-faulting earthquakes, which persist much deeper in western Crete. A correspondingly larger downdip width of this seismogenic zone is consistent with the suggested larger maximum magnitude of earthquakes here. However, since the seismic moment release rate seems to be moderate in the Peloponnese and western Crete, like in in the Ionian islands, this seismically active interface cannot maintain complete seismic coupling across its larger downdip width. A cause may be the lateral addition of overweight to the part of the slab still attached in Crete, by the free fall of its part that has broken off from the surface further north. This increased slab pull reduces the compressive normal stress across the seismogenic interface and thus causes partial seismic coupling in its shallower part. However, the width of this part may provide an additional area contributing to slip in large earthquakes, which may nucleate deeper on stick-slip parts of the interface. Hints at anomalies in structure and seismicity, which need to be resolved, may relate to the present location of the edge of the tear in the slab.

The Anaximander Mountains, occupying an outer-arc position at the junction of the Hellenic and Cyprus arcs, have been studied using a suite of geophysical data including multibeam swath bathymetry, backscatter images, seismic reflection profiles and gravity and magnetic data, which support an improved description of its deformation history. Lithologically, the western mountains can be correlated with the neritic limestones of the Bey Daǧlari unit of SW Turkey. The eastern mountains relate to the ophiolitic Antalya Nappe Complex. In addition to this lithological contrast, a deep-seated crustal difference, which is best reflected in gravimetry, relates to the mid-Tortonian Aksu thrust phase. After the Early-Middle Miocene eastward emplacement of the Lycian Nappes, the Serravallian-Tortonian stage was characterized by the development of an array of grabens with N120°E strikes, which occupied a vast continental area that extended from southern Aegean to southwestern Turkey. During the mid-Tortonian, the last phase of thrusting marked the onset of a different kinematic regime related to the westward rotation of the Anatolian platelet. This Late Miocene change marked the start of differential subsidence that resulted in the formation of the Anaximander Mountains and which is reflected by an unconformity surface between the Lower-Middle Miocene and Plio-Quaternary units. The Messinian-Quaternary period in the western part of the Anaximander Mountains was characterized by distributed sinistral shear parallel to N70°E, which was marked by the onset of an extension on N20°E-striking normal faults that formed long graben-like depressions. During the Pliocene, these basins were transected by N70°E-striking sinistral strike-slip fault zones, although continued crustal extension suggests deformation in transtension. The eastern part of the Anaximander Mountains is instead characterized by N150°E-striking normal and/or oblique normal fault zones, which lack significant evidence of strike-slip deformation. Close examination of newly calculated predicted relative plate motions between Africa (from NUVEL-1A) and Anatolia (from GPS measurements) indicates that plate motion vectors change rapidly at the junction between the Hellenic and Cyprus arcs because of the close proximity to the pole of Anatolian rotation. These calculations indicate that along both the eastern Hellenic Arc and the western Cyprus arcs (the Florence Rise), the relative motion between the Anatolian and African plates is sinistral. On the southern Florence Rise, deformation is characterized by pure left-lateral faulting, whereas farther northwest, in the eastern Anaximander Mountains, the component of strike-slip decreases. Although arc-normal convergence predicts the occurrence of thrust faulting, southwestward trench retreat also causes an extension internal to this outer-arc domain, such that the preexisting N120° E-striking thrust faults of the Aksu phase have been reactivated as normal to oblique normal faults during the Pliocene and Quaternary. The observed sinistral faulting on faults striking N70°E in the western mountains is consistent with the relative plate motion along the eastern Hellenic Arc and merges with the extensional domain in the eastern mountains. © 2004 Elsevier B.V. All rights reserved.

The Island of Crete is situated in the subaerially exposed part of the Hellenic fore-arc and was uplifted up to 1000–2000 m during Middle Pliocene to recent time. The onset of the overall emergence and northward tilting of central Crete was accompanied by the deposition of the continental Agia Galini Formation ( AGF ) during early Late Pliocene to Early Pleistocene time. The basin evolution during that time was probably related to sinistral wrench tectonics along ENE–WSW faults, which might have been active during an early stage of the incipient collision of the Hellenic fore-arc with the edge of the African continental plate at the longitude of western Crete. The development of the pronounced relief of south-central Crete strongly profits from a second stage of accelerated uplift and differential block movement starting not earlier than Early Pleistocene time or even later (post-AGF). Synchronously, the modern Timbaki basin and the extensive Messara basin (Messara plain) became striking elements in the study area. Across the study area, differences in both the morphostructural features and the amount of extension are obvious from the west to the east. Most likely, they reflect regional differences in the Pleistocene subduction process, due to the incipient continental collision at the longitude of western Crete. In the western part of the study area, arc-normal extension is driven primarily by the accumulation of high gravitational potential energy that results from the rapid uplift of the region. In the eastern part, the NW–SE to NNW–SSE regional extensional stress field is induced by the ongoing subduction of the oceanic African plate and the roll-back resulting in an arc-normal extensional component, and the extrusion of the Anatolian plate. The latter and the lengthening of the Hellenic arc, which is caused by the southward migration of the central part of the arc, support an arc-parallel extensional component. The Psiloritis Southern Escarpment Fault ( PSEF ) is one of the most prominent faults in the study area and represents the near-surface expression of a major normal detachment fault. Based on the footwall uplift mechanism vertical displacement along the PSEF intensifies the considerable asymmetric uplift of the Psiloritis massif that was induced by the regional rise of the outer-arc. In the study area a large number of faults have been identified that give clear evidence of recent activity.

We summarize seismogenic structures in four regions of active convergence, each at a different stage of the collision process, with particular emphases on unusual, deep-seated seismogenic zones that were recently discovered. Along the eastern Hellenic arc near Crete, an additional seismogenic zone seems to occur below the seismogenic portion of the interplate thrust zone—a configuration found in several other oblique subduction zones that terminate laterally against collision belts. The unusual earthquakes show lateral compression, probably reflecting convergence between the subducting lithosphere's flank and the collision zone nearby. Along oblique zones of recent collision, the equivalence between space and time reveals the transition from subduction to full collision. In particular, intense seismicity beneath western Taiwan indicates that along the incipient zone of arc–continent collision, major earthquakes occur along high-angle reverse faults that reach deep into the crust or even the uppermost mantle. The seismogenic structures are likely to be reactivated normal faults on the passive continental margin of southeastern China. Since high-angle faults are ineffective in accommodating horizontal motion, it is not surprising that in the developed portion of the central Taiwan orogen (

Summarization: Temporary local seismic networks were installed in western Crete, in central Crete, and on the island Gavdos south of western Crete, respectively, in order to image shallow seismically active zones of the Hellenic subduction zone. More than 4000 events in the magnitude range between −0.5 and 4.8 were detected and localized. The resulting three-dimensional hypocenter distribution allows the localization of seismically active zones in the area of western and central Crete from the Mediterranean Ridge to the Cretan Sea. Furthermore, a three-dimensional structural model of the studied region was compiled based on results of wide-angle seismics, surface wave analysis and receiver function studies. The comparison of the hypocenter distribution and the structure has allowed intraplate and interplate seismicity to be distinguished. High interplate seismicity along the interface between the subducting African lithosphere and the Aegean lithosphere was found south of western Crete where the interface is located at about 20 to 40 km depth. An offset between the southern border of the Aegean lithosphere and the southern border of active interplate seismicity is observed. In the area of Crete, the offset varies laterally along the Hellenic arc between about 50 and 70 km. A southwards dipping zone of high seismicity within the Aegean lithosphere is found south of central Crete in the region of the Ptolemy trench. It reaches from the interface between the plates at about 30 km depth towards the surface. In comparison, the Aegean lithosphere south of western Crete is seismically much less active including the region of the Ionian trench. Intraplate seismicity within the Aegean plate beneath Crete and north of Crete is confined to the upper about 20 km. Between 20 and 40 km depth beneath Crete, the Aegean lithosphere appears to be seismically inactive. In western Crete, the southern and western borders of this aseismic zone correlate strongly with the coastline of Crete. Presented on: Tectonophysics

The Pliocene–Quaternary Esen Cay Basin in southwestern Turkey has a key position in the southern Aegean to gain insight into both lateral and temporal changes in stresses exerted by plate convergence at the Hellenic–Cyprus arc junction. A tectonosedimentary study of the basin development in combination with a structural analysis helped to reveal internal basin deformation and adjacent basement kinematics in order to delineate 3D strain through time. In the Pliocene the basin originated as a fluviolacustrine basin situated in a depression related to a ramp-fold geometry in the Lycian nappe stack. During the late Pliocene, E–W extension caused the development of N–S normal faults, displacement along which caused the differentiation of the relief and deposition of local alluvial fan systems. The Pleistocene is also marked by widespread alluvial-fluvial sedimentation that is triggered by activity at 020° faults. This fault system resulted from WNW–ESE extension and caused disruption of the former basin floor by uplift and tilting of intrabasinal areas, which initiated development of new source areas for the fan sedimentation. The Holocene–Recent period is characterized by a complex combination of faults of which 070° sinistral strike-slip faults are the most important. Fault-slip analysis reveals that deformation occurred in transtension, explained by the addition of a sinistral shear component. This implies that stresses evolved from simple tensional to transtensional over the Pliocene–Quaternary period. The initial extension phase is explained by the kinematic effects of outward growth of the Hellenic forearc, comparable with observations from the island of Rhodes and the eastern Anaximander Mountains. The time-transgressive addition of a sinistral shear component was likely produced by the northeastward propagating transcurrent motions of forearc slivers sheared from the expanding forearc as has been previously inferred for Crete and Rhodes. The latter process is related to the incipient continental collision of an African promontory south of Crete. This implies a kinematic linkage between the studied domain in southwestern Turkey and the eastern Hellenic Arc.

WOS: 000186014500004, Following final closure of the Neotethyan Ocean during the late Miocene, deformation in central Turkey has led to crustal thickening and uplift to produce the Anatolian Plateau followed by westward extrusion of terranes by strike-slip. Widespread volcanism has accompanied this latter (neotectonic) phase, and palaeomagnetic study of the volcanism shows a coherent record of differential block rotations, indicating that the Anatolian region is not a plate (or 'platelet') sensu stricto but is undergoing distributed internal deformation. To evaluate the scale of neotectonic rotations in the transition zone near the western limit of tectonic escape and the border of the extensional domain in central-west Turkey, we have studied the palaeomagnetism at 82 sites in volcanic suites distributed along a similar to 140-km lineament with north-south trend and ranging in age from 18 to 8 Ma. Comparable deflection of magnetic remanence from the present field direction is identified along the full length of the lineament. A mean clockwise rotation of 12.3 +/- 4.2degrees is determined for this western sector of the Anatolian strike-slip province. Since similar rotations are observed in the youngest and oldest units, this cumulative rotation occurred after the late Miocene. When interpreted together with results elsewhere in Anatolia, it is inferred that the rotation is later than crustal thickening and uplift of the Anatolian Plateau and entirely a facet of the tectonic escape. Inclinations are mostly similar to 10degrees shallower than the predicted Miocene field and are considered to reflect the presence of a persistent inclination anomaly in the Mediterranean region. Larger rotations departing from the regional trend are also observed within the study region, but are confined to the vicinity of major faults, notably those bounding the Afyon-Aksehir Graben. The pattern of neotectonic declinations across Anatolia identifies strong anticlockwise rotation in the east near the Arabian pincer with progressive reduction in the amount of rotation towards the west; it becomes zero or slightly clockwise at the western extremity of the accreted terrane collage. Rotations also appear to become generally younger towards the south. Crustal deformation has therefore been distributed, and the net effect of terrane extrusion to the west and south has been to expand the curvature of the Tauride Arc. The westward radial expansion of the extruded terranes is inferred to combine with backroll on the Hellenic Arc to produce the contemporary extensional province in western Turkey. (C) 2003 Elsevier B.V. All rights reserved.

Source parameters for 40 earthquakes with epicentres in the Aegean Sea and the surrounding lands have been determined using P and SH body waveform inversion of digital waveforms from the Global Seismograph Network (GSN). These results are combined with 145 previous solutions, 41 of which were determined by first motion polarities and 104 by waveform modelling. Thus, a new updated database of source parameters for earthquakes for the period 1953–1999 is available. These fault plane solutions confirm our previous knowledge about the seismotectonics of the Aegean Sea and the surrounding lands. They also provide strong evidence that the western part of the Peloponnese (Gulf of Patras to Gulf of Kyparissia) is mainly deforming by strike-slip faulting, parallel in strike to the Cephalonia Fault and are in favour of the models that suggest a connection of the North Anatolian Fault (NAF) zone with the transform zone of the Ionian Islands. The sedimentary arc (inner part of the Hellenic trench) is deforming by normal faulting with the T-axes trending ∼E–W. We did not determine any fault plane solutions at the eastern part of the Hellenic arc indicating pure strike-slip motions as expected from the presence of the Pliny and Strabo trenches. However, we did determine solutions that indicate normal faulting combined with a considerable strike-slip component. In the central Aegean Sea the newly determined focal mechanisms support the conclusion that the area, extending from the eastern coasts of Evia up to the coasts of Turkey, is exhibiting a clear strike-slip character. Thus, the effect of the propagating tip of the North Anatolian fault into the Aegean is very clearly pronounced. The focal mechanisms in the back-arc Aegean area confirm the existence of normal faulting with T-axes trending NNE–SSW in western Anatolia and NNW–SSE in Greece. A zone showing NNE–SSW extension that runs parallel to Northern Aegean branch of the NAF zone up to the Corinth Gulf is depicted from the mechanisms of few earthquakes.

Qβ for shear-waves is determined for the inner part of the Hellenic arc, the back-arc area, as a function of frequency in the range 0.6–16 Hz. We used 314 digital records from 32 earthquakes with magnitudes (Mw) ranging from 3.9 to 5.1. Epicentral distances ranged from 65 to 515 km. The data were obtained in 1997 during a 6-month operation of a digital portable network in Greece. The Qβ estimates were made for five frequency bands centred at 0.8, 1.5, 3.0, 6.0 and 12.0 Hz and the Qβ values obtained were 47, 79, 143, 271 and 553, respectively. The results show that Qβ for S-waves increases with frequency taking the form Qβ=55f 0.91 (or Qβ−1≃0.018f−0.91). The high attenuation and the strong frequency dependence found, which is close to the frequency dependence of coda Q for Greece, are characteristic of an area with high seismicity, rapid extension, and in agreement with other similar studies in Greece.

The Hellenic arc is the most active seismic region of the transition zone between the African and Eurasian plates. In this rapidly deforming region, the physical state of the crust and upper mantle may vary laterally and vertically. However, a detailed 3D model of the region is lacking. The reliable determination of fault plane solutions is crucial if such a model is to be produced. On this basis, fault plane solutions have been determined from recent microearthquakes and small events to assess their reliability for use in tectonic interpretation. A search algorithm on first motion data and amplitude ratios and also a waveform-matching scheme were employed on data from our temporal network, operated on the western part of the island of Crete. There, a network of 47 three-component digital stations with an aperture of 60 km and an average station spacing of 5 km was operated in 1997. The majority of the shallow microearthquakes under Crete for which fault plane solutions were determined have a near horizontal T -axis oriented essentially E–W. Differences between well determined fault plane solutions from the search algorithm and the waveform-matching technique were significant (strike up to 45°, dip up to 10°, and slip up to 50°). Second, data of small events within the Hellenic subduction zone were obtained from recently installed broadband stations at local and regional distances and inverted for a deviatoric seismic moment tensor. Available solutions from other sources such as the Harvard group, EMSC, or SED show drastic differences in part. Owing to still limited azimuthal station coverage, the resulting fault plane solutions of small events have generally not been well constrained. The observed large variation of fault plane solutions for micoearthquakes and small events poses a caveat to tectonic interpretation in case of using data from a few stations only.

Airborne laser techniques have evolved during the last years and have been tested in several pilot projects which cover a wide range of geodetic applications. In this project, airborne laser altimetry was used to determine the sea level in coastal areas of Greece, and to connect satellite radar altimetry results over the deep sea with tide gauge stations at the coast. Because airborne laser altimetry is capable to provide sea surface heights at the decimeter to centimeter level, it allows for an independent validation of spaceborne radar altimetry results. Airborne laser data acquired along densely spaced tracks of a total of 30-h flight time were used to determine instantaneous sea surface heights of the Ionian Sea, Greece. Differential GPS and inertial platform data were utilized as ancillary information for the purpose of ensuring a precise trajectography of the aircraft. Emphasis was put on the assessment of errors and the reduction of the raw data to mean sea level by crossover analysis and the incorporation of tidal predictions. The airborne laser data yield a high-resolution sea surface over the coastal areas of the Ionian Sea. The most prominent feature is a steep gradient of the sea surface amounting to 15 m over a distance of 150 km. This slope can be followed all along the bathymetric relief between the Hellenic Arc and Hellenic Trench.

The western Hellenic arc has been commonly considered as a largely aseismic subduction zone, from the comparison of a small rate of shortening derived from the seismic moment release, with a large rate of convergence inferred from geology. Complete seismic coupling would instead be expected from models that consider a control by plate tectonic forces, because of the trenchward velocity of the Hellenic–Aegean upper plate now confirmed with GPS measurements. In the region of the Ionian Islands, a subduction interplate boundary has been recently imaged and its seismogenic downdip width suggested to be moderate, from reflection seismic profiling and local earthquake tomography. In the appropriate model for such an earthquake source region, which considers a single interplate fault and takes into account these features, the moderate seismic moment release is found consistent with complete seismic coupling of this subduction. The shallow downdip limit of the seismogenic zone can be interpreted as due to the interplate boundary being overlain there by the ductile deeper crust of the orogenically thickened Hellenides.

Historical and archaeological data are used to test geological claims that, in the fourth to sixth centuries AD, the Eastern Mediterranean experienced an unusual clustering of destructive earthquakes (the ‘Early Byzantine Tectonic Paroxsym’). A review of historical accounts of a notable earthquake at this time, that of 21 July AD 365, indicates that this event destroyed nearly all the towns in Crete and was followed by a tsunami which devastated the Nile Delta. The AD 365 event was also probably responsible for reported or observed destruction in ancient towns of west Cyprus and Libya. This earthquake is most likely to be identified with a Hellenic Arc subduction-zone event of ‘great’ (M>8) magnitude, as testified by up to 9 m of uplift in western Crete dated by previous geological studies to around this time. Historical and archaeological data also support the hypothesis that the fourth to sixth centuries AD was a period of abnormally high seismicity in the Eastern Mediterranean. The high seismicity rates of this period may reflect a reactivation of all plate boundaries in the region (Dead Sea Transform, East Anatolian Fault, North Anatolian Fault, Hellenic Arc, Cyprus Arc Fault).

Accurate locations of 961 shallow and intermediate depth earthquakes, which occurred between 1956 and 1995 in the Hellenic arc (34–39°N, 19–28°E), are used to define the plate boundaries in this area. Reliable fault plane solutions for 77 shallow and intermediate depth earthquakes are also used in order to define the interaction between the different plates in the arc. An ocean–continent type of interaction occurs on a curved surface, which is defined by the shallow branch (20–100 km) of the Wadati–Benioff zone. The intersection of this zone with the earth's surface is a curve which follows the convex (outer) side of the sedimentary arc (western Peloponnese–west of Cythera–south coast of Crete–east coast of Rhodes) and dips at low angle (∼30°) to the Aegean sea. Coupling between the subducted oceanic crust and the overriding of the Aegean lithospheric plate takes place on this surface. The deep branch (100–180 km) of the Wadati–Benioff zone is dipping freely (without coupling) at a high angle (∼45°) beneath the south Aegean trough and the volcanic arc. The high shallow seismicity ( h ≤20 km) which is observed in the southwestern convex (outer) side of the arc (Ionian sea) is attributed to the fast southwestward motion of the Aegean plate. Location of strong deep earthquakes ( h >100 km) in the fore-arc area of the southwestern part of the Hellenic arc (west of Cythera) indicates that oceanic crust is ‘destroyed’ in this part of the Hellenic trench due to roll-back of the descending lithospheric slab.

Finite element modeling of the central–eastern Mediterranean region has been carried out to show that the recent/present deformation pattern of this zone, inferred from neotectonic observations and seismic strain rates, may be satisfactorily reproduced as effect of the relative motion of Africa and eastern Anatolia with respect to Eurasia. Numerical modeling involved 2D elastic elements in a plane-stress approximation. The model is constituted by a mosaic of poorly deformable blocks separated by much more deformable decoupling zones, representing consuming boundaries, extensional zones and transcurrent discontinuities, whose location and geometry have been deduced by neotectonic, morphological and seismological information. The calculated displacement field obtained with the modeling parametrization which allows to match the observed strain regimes is compatible with geodetic observations in the study area, but for the Hellenic Arc, where geodetic velocities are higher than those predicted by modeling. This discrepancy could be considerably reduced by adopting a higher deformability of the model in the Hellenic trench, but this condition would contrast with the Plio-Quaternary deformation pattern of the southern Aegean zone, which suggest a considerable slowdown of western Crete since the late Pliocene. Furthermore, geodetic velocities are considerably higher than the motion rates derived by moment tensor analysis in the Hellenic trench and in the internal Aegean area and cannot easily account for the low Quaternary deformation observed in the southern Aegean zone. The above discrepancy could be due to a difference between the “instantaneous” kinematic behavior of the Aegean zone, indicated by geodetic measurements, and the average behavior over longer time intervals, inferred from geological and seismological strain indicators.

Geotectonic, seismotectonic and in-situ stress measurements in Greece indicate a zonation parallel to the active Hellenic arc. The raised question is, whether a similar zonation is characteristic of the geoelectrical structure and if the experimental ratio, R, of the time-averaged absolute values of the electric field variations comprises a competent indicator for the distinction of electric zones. In the present work, the magnetotelluric (MT) impedance tensor, measured at different sites in Greece, is further analyzed assuming that results from the galvanic distortion of the regionally induced electric field at a homogeneous or horizontally layered Earth due to near surface local inhomogeneities. From the comparison of the calculated ratio, R, with the respective experimental values, it is concluded that this ratio is strongly depended on local inhomogeneities.Furthermore, the geoelectrical anisotropy at these sites is investigated using the magnetotelluric representation of Mohr circles. Through this analysis, generalized local and regional strike-directions are estimated at each site, assuming a regional 2D-geoelectric structure aggravated by near surface local 3D-bodies of anomalous conductivity. The concepts of local and regional strikes are clarified in cases where the impedance tensor is singular, i.e. strong polarization of the measured electric field exists. It is concluded that the local strike is solely defined from the influence of the local inhomogeneities. On the contrary, the regional strike-direction is compatible, in a generalizing sense, with the direction designated by the major axes of the isoseismal curves drawn for earthquakes with epicenters in the vicinity of the measuring site. (C) 2000 Elsevier Science Ltd. All rights reserved.

Since the early 1970s, most geodynamic models proposed for the Eastern Mediterranean consider that the initiation of extension in the Aegean, during the late Middle Miocene or later, was a direct consequence of the westward extrusion of Anatolia away from the Arabia–Eurasia collision front. In the late 1990s, a few models have taken into account the increasing evidence for an earlier initiation of Aegean extension, arising mostly from the analysis of deformation within the various Alpine metamorphic complexes of the area. Based largely on our own investigations, we first present a review of the data that reliably constrain the minimum age for the initiation of extension in these complexes. It shows that regional-scale extension with a pattern of stretching orientations similar to that of the Pliocene–Pleistocene was already strongly active in the Aegean before the onset of Arabian indentation into Eurasia (Lower Miocene vs. Middle or Upper Miocene). This implies that the initiation of Aegean extension did not result from the lateral extrusion of Anatolia. Instead, extension may have started, owing to a process of gravity spreading of the continental lithosphere that had previously been thickened during Alpine collision. The main arguments favouring this interpretation are presented, and a preliminary scenario is proposed for the Neogene evolution of the Eastern Mediterranean, in which lateral extrusion of Anatolia occurred lately during southward spreading of the Aegean lithosphere. In order to test this hypothesis further, physical experiments simulating the horizontal spreading of a continental lithosphere toward a free boundary have been carried out. The analysis of various elements of the deformation field (displacements, strain, rotations, fault pattern and kinematics), both in the experiments and in the Aegean domain, reveals an excellent agreement between the two. Not only do early stages of Aegean extension appear to fit the gravity spreading hypothesis, but so does the recent to present internal deformation of the Aegean. Transverse (≈E–W) active shortening observed in the northern Aegean is commonly taken as one of the most striking pieces of evidence that Aegean extension results from the lateral extrusion of Anatolia. The experiments indicate that such transverse shortening may equally develop as a result of pure gravity spreading, associated with a pattern of faults and rotations that compares well with that of the northern Aegean. Pure dextral shearing along some strands of the North Aegean Trough fault system, and the related development of an asymmetric pattern of faults in the northern Aegean, are eventually the only features that evidently arise from the extrusion of Anatolia, since less than 3 Ma. Finally, we argue that during the early stages of Aegean extension, since at least 21 Ma and until ca. 11 Ma, the distribution of extensional strain on a regional scale has been controlled by the distribution of earlier thickening. Post-thickening thermal weakening, through partial melting of deep levels of the crust, probably accounts for the localization of extensional strain within the areas of thick crust. Restoring the Aegean in its most likely configuration at the onset of bulk crustal extension suggests that (1) the extensional strain rate remained roughly constant, or has eventually decreased, since the onset of Aegean extension, and (2) the amounts of extension before and after 16 Ma have been roughly equal.

In this paper we present the most recent observations of crustal motion across the entire West Hellenic Arc (WHA). These are based on repeated GPS measurements carried out in the period from 1993 to 1998. The results are presented in terms of trajectories and rates, relative to Eurasia. Within these five years southwestern Greece has moved to the southwest by an average rate of 30 mm/a, increasing from 10 mm/a at the island of Lefkada, in the center of the Ionian islands, to nearly 40 mm/a along the southwest part of the Peloponnesus and to 35 mm/a on the islands of Crete and Gavdhos. The data provide strong evidence that distributed shear strain starts at the Kephalonia Fault Zone (KFZ), were an anomalously high earthquake activity is also observed. A striking interruption of the motion is seen at the island of Strofades, at the southwest leading edge of the WHA, where a south-oriented displacement of 12 cm was detected, coincident with the M = 6.4 Strofades earthquake of Nov. 18, 1997.

Using a numerical model, we focus on the late Middle Miocene to Recent kinematic evolution of the Cretan segment of the Hellenic Arc. Geological observations of Crete are given a quantitative interpretation in terms of tectonic mechanisms controlling the evolution of the active arc boundary. This was achieved by calculating intra-plate stress fields for various possible distributions of forces and comparing the models with observations. The models address specific questions concerning important changes in the observed horizontal stress patterns. We deal with the question of what caused extension to initiate. Modelling results of the collapse of an earlier formed topography and extensional forces acting on the plate boundary are compared with a newly reconstructed tectonostratigraphy of Crete. Our results suggest that arc-normal pull is the dominant force that generates the Late Miocene extension in the Cretan segment of the overriding plate, although arc-normal pull in combination with intra-plate spreading forces cannot be excluded. The observed transform motions in the Pliny and Strabo trenches led us to incorporate experiments with additional resistance on the eastern (Levantine) segment of the Hellenic Arc. The models performed with a transform resistance along the trenches are in agreement with the Cretan deformation for the Pliocene to Recent period. The stress fields for the short duration compressional periods around the Middle–Late Miocene and the Miocene–Pliocene boundary are modelled by assuming resistive instead of tensional forces acting at the overriding margin.