The Hellenic subduction zone displays well-defined temporal and spatial variations in subduction rate and offers an excellent natural laboratory for studying the interaction among slab buoyancy, subduction rate, and tectonic deformation. In space, the active Hellenic subduction front is dextrally offset by 100–120 km across the Kephalonia Transform Zone, coinciding with the junction of a slowly subducting Adriatic continental lithosphere in the north (5–10 mm/yr) and a rapidly subducting Ionian oceanic lithosphere in the south (∼35 mm/yr). Subduction rates can be shown to have decreased from late Eocene time onward, reaching 5–12 mm/yr by late Miocene time, before increasing again along the southern portion of the subduction system. Geodynamic modeling demonstrates that the differing rates of subduction and the resultant trench offset arise naturally from subduction of oceanic (Pindos) lithosphere until late Eocene time, followed by subduction of a broad tract of continental or transitional lithosphere (Hellenic external carbonate platform) and then by Miocene entry of high-density oceanic (Ionian) lithosphere into the southern Hellenic trench. Model results yield an initiation age for the Kephalonia Transform of 6–8 Ma, in good agreement with observations. Consistency between geodynamic model results and geologic observations suggest that the middle Miocene and younger deformation of the Hellenic upper plate, including formation of the Central Hellenic Shear Zone, can be quantitatively understood as the result of spatial variations in the buoyancy of the subducting slab. Using this assumption, we make late Eocene, middle Miocene, and Pliocene reconstructions of the Hellenic system that include quantitative constraints from subduction modeling and geologic constraints on the timing and mode of upper plate deformation.

The new Environmental Seismic Intensity scale (ESI 2007), introduced by INQUA, incorporates the advances and achievements of palaeoseismology and earthquake geology and evaluates earthquake size and epicentre solely from the earthquake environmental effects (EEE). This scale is tested and compared with traditional existing scales for the 1981 Alkyonides earthquake sequence in the Corinth Gulf (Ms=6.7, Ms=6.4, Ms=6.3), the 1993 Pyrgos event (Ms=5.5) and the 2006 Kythira event (Mw=6.7). These earthquakes were of different magnitudes, focal mechanisms and focal depths and produced well-documented environmental effects. The ESI 2007 intensity values and the isoseismal pattern for the 1993 Pyrgos and the 2006 Kythira events are similar to those resulting from the traditional scales, demonstrating that for moderate intensity levels (VII and VIII) the ESI 2007 and the traditional scales comply well. In contrast, the 1981 Alkyonides earthquake sequence shows that there is an inconsistency between the ESI 2007 and the traditional scales both in the epicentral area, where higher ESI 2007 intensity values have been assigned, and for the far-field effects. The ESI 2007 scale offers higher objectivity in the process of assessing macroseismic intensities, particularly in the epicentral area, than traditional intensity scales that are influenced by human parameters. The ESI 2007 scale follows the same criteria-environmental effects for all events and can compare not only events from different settings, but also contemporary and future earthquakes with historical events. A reappraisal of historical earthquakes so as to constrain the ESI 2007 scale may prove beneficial for seismic hazard assessment by reducing the uncertainty implied in the attenuation laws, which constitute one of the most important seismic hazard parameters.

The Itea-Amfissa valley, separating Giona Mountain to the west from Parnassos Mountain to the east, is related to an extensional detachment observed along the eastern slopes of Giona. The detachment is traced for 30 km north of the Corinth Gulf and dips 25{degrees}-40{degrees} to the east, showing an east-west extension parallel to the Hellenic arc. The lower nappes of Pindos, Penteoria, Vardoussia and mainly the basal thrust of the Parnassos unit form part of the footwall, whereas the upper thrusts of the Parnassos unit and the Western Thessaly-Beotia nappe form part of the hanging wall. The eastern slopes of Giona are controlled by the detachment and several hundred metres of syn-tectonic breccia-conglomerates are observed at the top of the hanging wall rocks and are back-tilt towards the detachment plane. Two conglomeratic sequences are distinguished: the lower one consists of argillaceous matrix and abundant ophiolite detritus whereas the upper one bears carbonate matrix with carbonate detritus together with large olistholites of Mesozoic limestones. Based on calcareous nannofossils a middle Miocene age has been determined for the lower formation and a middle-upper Miocene age is probable for the upper. Planation surfaces cut on top of the sediments rise from south to north starting from sea level at Galaxidi to about 1400 m at Prosilio. The throw of the detachment is about 2.5-4.2 km measured mainly from the structural omission of the Alpine tectono-stratigraphic units. A contrast between the footwall and the hanging wall structure is described, with monoclinic sequence of the Parnassos nappe dipping to the west in the footwall but a complex synsedimentary horst and graben structure of sliding blocks of Alpine formations within the Miocene clastic sequences in the hanging wall. The detachment has been deformed by the east-west-trending steep normal faults that have created the Corinth rift during late Pliocene-Quaternary time showing a north-south extension. The Itea-Amfissa detachment forms the northern tip of the broader East Peloponnesus detachment, observed south of the Corinth rift structure from Feneos to Kyparissi. Similar geodynamic phenomena with large olistholites and breccia conglomerates are known from the Serravalian of Crete, related to the activity of the Cretan detachment.

The timing of tectonic emplacement of the ophiolites is analyzed in the four oceanic terranes of the Hellenides (H2, H4, H6, H8). The criteria for this analysis are based on: a) the post-emplacement sedimentary cover or intrusive rocks, b) the syn-emplacement tectonostratigraphic formations and c) the youngest rocks involved in the structure of the autochthon and the allochthon unit in each case. The timing becomes younger towards the more external tectonic units of the Hellenides with: (i) Late Eocene-Oligocene age in the external ophiolite belt of the Pindos-Cyclades oceanic terrane H2, (ii) Late Jurassic-Early Cretaceous age in the internal ophiolite belt of the Vardar/Axios oceanic terrane H4 , (iii) Post-Liassic-pre-Late Jurassic age in the ophiolites of Lesvos-Circum Rhodope oceanic terrane H6 and (iv) Pre-Late Jurassic age in the ophiolites of Volvi-Eastern Rhodope terrane H8. An ophiolite obduction model can be applied, with the ophiolitic nappes always emplaced on top of pre-Alpine continental terranes with Mesozoic shallow-water carbonate platforms. The geometry of the continental terranes drifting during the Mesozoic within the Tethys Ocean controls the number and dimensions of the Tethyan oceanic basins. Where a continental terrane dies out, the two adjacent oceanic basins merge into one larger basin. This seems to be the case of the Pelagonian terrane (H3), which is terminated north of Skopje, where the Pindos oceanic basin (H2) merges with the Vardar/Axios oceanic basin (H4).

The South Balkan extensional system consists of normal faults and associated sedimentary basins within southern Bulgaria, Macedonia, eastern Albania, northern Greece, and northwestern Turkey. Extensional tectonism began during the final convergence across the Vardar, Intra-Pontide, and Izmir-Ankara suture zones, where oceanic regions closed between continental Europe and continental fragments that make up the Pelagonian, Sakar, and western Anatolian tectonic units. Earliest extension of latest Cretaceous- middle Eocene age appears to have occurred within a regional convergent tectonic setting and may be related to an increase in gravitation potential energy within a thickening continental lithosphere. Following diachronous closure across the suture zone, from the middle Eocene to late Oligocene, the transition from a regionally convergent to a regionally extensional tectonic setting occurred and was associated with abundant magmatism and formation of sedimentary basins. Extension was associated with lithospheric thinning probably related to changes in geometry of the subducted slab, dynamics of the mantle wedge, and beginning of slab rollback along the Hellenic subduction zone. A short period of local and diachronous (?) shortening (during latest Oligocene-early Miocene time) occurred in the Thrace basin of northwestern Turkey and in some basins in western Bulgaria and eastern Macedonia. Regional extension began in middle Miocene time and was related to the regional extensional tectonic setting that has dominated the Aegean extensional region to the present. Trench rollback was the dominant dynamic process, but during late Miocene time it was modified by the formation of the western part of the North Anatolian fault zone that partially decoupled the South Balkan extensional system from the Aegean extensional region. During late Cenozoic time, east-west-striking normal faults and associated sedimentary basins in the eastern part of the South Balkan extensional system propagated westward in tandem with westward migration of north-south-striking normal faults and sedimentary basins from western Bulgaria into eastern Albania. This migration was caused by evolution of the Hellenic subduction zone as it increased its curvature during trench rollback and clockwise and counterclockwise rotation of crustal fragments in the west and east, respectively. After formation of the western part of the North Anatolian fault zone, extension within the eastern part of the South Balkan extensional system was related to southward movement of its lithosphere at a slower rate than the extension within the Aegean extensional region. Active extension and basin formation show two provinces of extension that are nearly at right angles to one another and their overlap in the central South Balkan extensional system: east-west extension in central Albania to eastern Macedonia and north-south extension from northwestern Greece and eastern Macedonia to eastern Bulgaria and northwestern Turkey.

We use new on-land and offshore structural data and scaled analogue models to analyse the fault tectonic pattern at Nisyros Island (Greece), which has an active caldera that shows a complicated network of faults, fractures and volcano-tectonic structures. We measured 157 faults that show dominant dip-slip normal motions along planes mainly striking NE-SW, NNE-SSW, and NNW-SSE. Inside the caldera, dykes, necks and morphometric parameters of volcanic domes, explosion craters and fumarole pits indicate the control by NE-striking discontinuities on magma and gas paths. The NNW- and NE-striking faults bound a major block that underwent repeated downthrow and uplift movements during the late Pleistocene-Holocene. Experiments with scaled models of caldera resurgence and two magma chambers indicate the formation of an hourglass-shaped fault pattern, as seen in plan view, with an asymmetric increase in the fault offset and a widening of the fault divergence towards the volcano flank. All these data suggest that regional fault tectonics and stress state strongly guided magma upwelling and the emplacement of volcanic centres, whereas periodical bulging due to the overpressure of a second magma chamber located northwest of the caldera combined with faulting due to tectonic stresses, can account for the overall deformation field.

Kyparissiakos Gulf forms a 45 km long zone located at 70-80 km east from the Hellenic trench with a general direction NNW-SSE. Onshore studies show the existence of several neotectonic horsts and grabens bounded by E-W trending normal faults. Thrust sheets of the underlying Hellenides crop out within the horst areas and younger sediments, mostly Lower Pleistocene, have been deposited in the grabens. The age of the marine sediments is mostly Lower Pleistocene. Throw rate on the normal faults varies between 0.7 and >1.0 mm/yr, accommodating extension in the N-S direction. Subsidence rates during Early Pleistocene are between 0.1 and 0.3 mm/yr, whereas uplift rates during Middle Pleistocene-Present are between 0.18 and 0.50 mm/yr. Offshore data were obtained using bathymetric and air-gun litho-seismic profiles. The shelf has been disrupted by active faults with several meters of throw. Average Holocene throw rates are 0.4-0.6 mm/yr, but in some areas adjacent Filiatra and Olympia values greater than 3 mm/yr are detected. Holocene and Upper Pleistocene marine sediments thicken gradually to the north, as do the marine Lower Pleistocene sediments onshore. A NNW-SSE offshore longitudinal fault parallel to the Kyparissiakos coast with throw rate above 3 mm/yr is the dividing structure between the uplifted coastal area and the present-day gulf. This indicates a major change in paleogeography between Early and Middle Pleistocene. Present-day transition from E-W compression in the Hellenic Trench to E-W extension in the Kyparissiakos Gulf and to N-S extension in Western Peloponnesus is discussed. The development of E-W structures in Western Peloponnesus since Latest Pliocene may be related to the Central Hellenic Shear Zone, which accommodates differential GPS rates between Northern Greece and Southern Peloponnesus.

The morphotectonic structure of the North Aegean Basin is studied on the basis of a new detailed swath bathymetric survey. The resulting bathymetric map is presented in reduction with 20-m isobaths. The slope analysis gives an accurate scheme of the geometry of the basin and distinction of several sub-basins (approximately 20). The overall basin geometry is a rectangular tetrahedron shaped by the major slope discontinuity separating the continental platform from the continental slope. The area distribution with depth shows a maximum at depths between 300 and 450 m along the sub-horizontal edge of the continental platform and at depths between 1000 and 1200 m at the basinal areas of the sub-basins. The separation of the western part of the North Aegean Basin from the eastern part (Saros Bay) is very clear in the area between Limnos and Thasos, with a maximum depth of 490 m. The 3.2% of the basin area is characterized by slope values >20%, which correspond to active fault zones. Their trend is NE-SW (N46o) and NW-SE (N136o). Some secondary E-W faults are also present within the basin with morphological expression only on the orientation of slopes <1%, reflecting deformation of the flat-lying deep parts of the basin’s interior. The overall geometry and inferred kinematics of the basin show an increase of both the vertical and horizontal components of the movement at the SW corner of the basin, where an opening of 40 km and a subsidence of 1600 m are contrasted to an opening of 20 km and a subsidence of 1000 m at the NE margin. The GPS data of the area showing an opening of 30 mm/yr are compatible with the above cumulative deformation for a neotectonic period of 4-5 Ma.

Statistical estimates of earthquake magnitudes are unreliable when based on very few historical data. Additional sources of information, such as geological data, are then necessary to update estimates of seismicity parameters. The Bayesian probability theory is a tool to combine prior information of seismicity obtained from geological data with historical observations. This theory is tested in the case of the Inner Messiniakos fault zone, southern Greece, for the estimation of the probability of occurrence of strong earthquakes. Prior estimates of seismicity are developed from slip rate measurements, obtained from offsets of geological formations, on the basis of both onshore and offshore neotectonic data. The analysis emphasizes the importance of the input seismicity parameters, particularly the significance of the upper bound magnitude in the estimation of the seismic potential of active faults

We present the results of a wide-aperture seismic onshore–offshore study (Crete Seismic Experiment) in the Cretan region as part of the Hellenic arc compressional system. Three seismic lines were carried out on and around the island of Crete in order to investigate the crustal structure of the region. Up to 119 three-component recording stations were deployed on each profile that observed seismic energy generated by a 48-l airgun array and eight 20-kg landshots. A total of 6208 shots were fired. Upon completing the fieldwork, the vertical components of all stations were evaluated; 300 Common-Receiver-Gather (CRG) sections of the ocean bottom seismographs (OBS) and land stations as well as 100 Common-Source-Gather (CSG) sections of the land shots and selected airgun shots were compiled and modeled in order to generate a 2D P-wave velocity–depth model for each profile. The accuracy of the model depends on the depth and position along the profiles and does not exceed 5% for both depth and P-wave velocity. We identified strong lateral variations in crustal and sedimentary thickness mainly in a north–south direction but also along strike (east–west). The crust is continental and has a maximum thickness of 32.5 km below northern central Crete. Its subdivision in an upper (vp = 5.8–6.3 km/s, locally up to 6.5 km/s) and a lower (vp = 6.4–6.9 km/s) part is justified by a first-order discontinuity with vp-velocity a contrast of up to 0.6 km/s. The eastern part of Crete shows a significantly thinner crust of 24 to 26 km. To the North, the crustal thickness decreases to 15 km below the central Cretan Sea. The prominent decrease of the Moho depth north of central Crete is interpreted to represent the northern end of a microcontinent that was subducted in Oligocene times and later surfaced by ‘buoyant escape’ (Sto¨ckhert et al., 1999; Thompson et al., 1999). The P–T–t–D history of the high-pressure rocks of Crete, Greece: denudation by buoyant escape. In: Exhumation Processes: Normal Faulting, Ductile Flow and Erosion. Ring, U., Lister, G.,Willet, S., Brandon, M. (Eds.), Spec. Publ. of the Geol. Soc. of London,p. 154]. To the south and southwest of the island, the continental crust gradually thins to a minimum of 17 km and atapproximately 100 km off the southern coast of Crete, it is in contact with oceanic crust below the Mediterranean Ridge. Upper mantle velocities were determined to be 7.7 km/s below the Cretan Sea and 8.0 km/s south of Crete. Below the continental Cretan crust, a 6- to 7-km-thick layer with vp-velocities between 6.6 and 7.1 km/s was identified on each line and could be followed by reflections to a depth of 42 km. It is decoupled from the overlying continental crust at central Crete and is interpreted as oceanic crust presently under subduction towards the NNE below the Aegean Sea.

We present a number of data for the Pyrgos (W.Peloponnessos, Greece), which took place on 26 March1993 and caused considerable damage in the town ofPyrgos and the surrounding area. The local geologicaland neotectonic conditions are also outlined; they aremainly characterized by complex stratigraphicstructure and outcrop pattern, together with a largenumber of large active fault zones and/or isolatedfaults. The detailed damage recording in themeizoseismal area, which was based on the EMS-92,showed significant differentiation of damage from oneurban unit to another, regardless of the foundationformation. The correlation of the existing dataconfirmed the decisive impact of faults and fault zoneon intensity distributions. It was also clear that,the larger a fault zone, the greater was thedifference in intensity across that structure.

Seismic and bathymetric profiles within the Argolic Gulf permitted the study of its neotectonic structure. The morphological data were analysed in the form of a morphological mean slope map on which the morphological discontinuities and the planar surfaces were distinguished. The neotectonic structure of the gulf is mainly created by the following fault sets grouped:(i) in two NW-SE zones of major border normal faults, separating the alpine basement from the sedimentary fill of the basin,(ii) in several E-W transcurrent faults which create horizontally escaping neotectonic blocks and,(iii) normal faults, some of which probably with oblique-slip motion, forming minor neotectonic blocks especially within the continental platform.The overall geomorphological and neotectonic structure and other characteristics of the post-alpine sedimentation show an asymmetry with more intence phenomena along the western margin of the gulf. The continental platform is highly fractured and Holocene vertical block movements of the order of 20 - 30 m are detected.

The tectonic structure and evolution of Kythira is in general similar to that of the Cyclades with a difference in the chronologic succession of the alpine and post alpine geodynaaic processes which have ended in the Cyclades in contrast to Kythira where they are still in evolution. A basic distinction has to be lade between the early phase of compressional tectonism which built up the alpine nappe pile and the late phase of extensional character which denudates the non metamorphic units froa the crests of the anticlinal domes of the underlying netanorphic units. During this late phase the decollement and sliding of the non metanorphic units along their contact with the underlying metamorphic units is dominant under the important effect of gravity, the normal faults being limited above the main overthrusts.

The structure and geotectonic evolution of the medial tectonometamorphic belt is described. The main tectonic units are classified to parts of continental plates and of oceanic plates. A younger age of tectonism (Late Eocene) is detected at the base than at the top (Early Cretaceous) of the belt. The tectonic evolution of the belt includes two convergent zones of plate movement, one during Late Jurassic-Early Cretaceous between the Serbomacedonian and the Pelagonian microcontinents with obduction of the Axios oceanic lithosphere onto the Pelagonian giving rise to the Internal Hellenides and another during Late Cretaceous-Eocene that included a subduction zone with blueschists generation and a subsequent collision of the microcontinents of the Pelagonian and the Lydo-Karian (Menderes), giving rise to the External Hellenides. Since Miocene times the previous paleogeographic-geotectonic units were consolidated to an unique structure.

The tectonic analysis of faults must include the geometric, kinematic, dynamic and temporal analyses. The results of the analysis must be coherent, with the σ2 axis parallel to the intersectionof a conjugate set of faults, whereas the slip lines must be perpendicular to it. Because of rejuvenation phenomena this relation is not always observed. Instead, the slip direction is observed to be oblique or subparallel to the intersection in the case of the activated faults during the earthquakes of 1981 in Kaparelli-Platees and in the case of the main fault set of Andros island in the Cyclades. Three areas are presented with inactive faults, active and inactive faults and active faults from NE Peloponnese. Finally, the generally active fault pattern of southern Greece is given and also a correlation of the fault pattern with the seismicity of the area, pointing out the existence of a relatively aseismic area with NHW-SSE trending faults in between two areas of high seismicity with B-W to ENE-KSW trending faults.