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Funded by the EEC Sixth Framework Program, the SEAHELLARC project was aimed to evaluate, and better understand the causes, of the various natural geohazards (chiefly earthquakes and tsunamis), which frequently affect the western Peloponnese area and particularly its coastal domain; this region is one of the most seismically active of Greece and therefore of the Mediterranean Sea. Based on a set of new geophysical data, such as detailed swath bathymetry and high-resolution sub-bottom Chirp, we have distinguished and studied four contrasted domains along this area of the Peloponnese active continental margin underlined by intense crustal seismicity and marked by very contrasted and often sharp continental slopes; from east to west these are: (1) an area including the continental shelf and the upper slope; there sedimentary overload and destabilizations, syn-sedimentary faults, mass transport deposits and active sedimentary by-pass mechanisms are the main risk factors. (2) The middle to lower continental slopes, is mainly expressed by two, N-S trending, faultrelated, depressions, where active deformations, well recorded by actual tilting of the sedimentary blanket, occur. (3) West of this deep structural depressions exists a poorly sedimented ridge area (from which merges the small Strophades Islands) also showing N-S and E-W trending lineaments resulting in a dense network of fractures and scarps and leading too a particularly complex sub-marine morphology; this area, together with the westernmost deep domain (4), which bounds the continental margin, clearly records the effects of significant active tectonic. Our studies of the shallow and recent sedimentary cover of the continental margin off western Peloponnese, confirm that this active margin segment is an area where geohazards can be expected. In addition to fault ruptures, generated at depth by the specific tectonic framework, sedimentary collapses, particularly along the shelf break nearby Cape Katakolo, may trigger significant local tsunamis, which may in turn induce strong damages all along the nearby coasts up to the town of Pylos. [ABSTRACT FROM AUTHOR]

Abstract: The first high-resolution mapping of mud volcanoes and mud domes of the Central Mediterranean Ridge (Eastern Mediterranean) presented here is based on successive in situ observations from the Nautile submersible [MEDINAUT (1998) and NAUTINIL (2003) surveys] and near-bottom side-scan sonar data (MEDINETH cruise, 1999). Data were obtained over two types of clay-kinetic-related features previously identified south of Crete: the Olimpi field mud volcanoes and the Southern belt mud domes, characterized by highly contrasting morpho-acoustic characteristics. Using the new data we can better define the morphological and backscatter characteristics of both mud volcanoes and mud domes and illustrate their similarities and differences; and establish ground truth, in terms of the presence or not of mud flows, diagenetic carbonate pavements, active seepage and macro-and microbiology. This study reveals strong contrasts between: (1) large mud volcanoes, made of successive mud flows, and associated with diagenetic carbonates and fluid venting activity, and (2) smaller mud domes, characterized by steep slopes affected by sedimentary instabilities, and without any evidence of mud flow, specific fluid seepage activity, authigenic carbonate pavement, or biologic communities. From these results we demonstrate a strong variability of clay-kinetic structures from the central domain of the Mediterranean Ridge accretionary complex to its northern thrust boundary against the Cretan continental backstop. From an integration of the high-resolution results to the Mediterranean Ridge geologic and structural settings, a qualitative model is finally proposed to explain the mud volcano and mud dome emplacement. [Copyright &y& Elsevier]

The Florence Rise is a submarine feature extending from the island of Cyprus in the southeast to the Anaximander Mountains which form the northwestern end of the Cyprus Arc south of western Turkey. The eastern Florence Rise includes a topographic high near Cyprus while its central domain displays relatively low relief. Most of the major elements of relief appear to be bounded by faults, in the light of new geophysical data. An underlying ‘core’ ridge, likely made of pre-Pliocene nappes emplaced from the north, separates relatively undeformed sediments to the northeast from actively shearing sediments and seismic basement, to the southwest. A dextral arc-parallel wrench zone, at least 15 km wide, has created a lineated seafloor texture and accompanying flower structures within the central Florence Rise. Apparent Riedel type conjugate shears within this system cut across the Florence Rise and mark changes in the relief along the arc. Several mud volcanoes are observed within the wrench zone and along associated faults, indicating that overpressuring at depth is relieved by these faults. There is no evidence for any typical subduction along this arcuate trend, which is considered to act as the present boundary between the African and Anatolian–Aegean plates. In contrast, both the nature of faulting and the morphology of the Florence Rise seem to indicate some degree of transpressional coupling between the two plates, even though they appear disconnected by a tectonic boundary in the form of a major shear zone. [Copyright &y& Elsevier]

One of the objectives of the European project SEAHELLARC (SEismic and tsunami risk Assessment and mitigation scenarios in the western HELLenic ARC) was to identify the key elements controlling the geological structure of the Peloponnese continental margin in order to better understand the distribution of earthquakes in the area. Vintage multichannel seismic lines were reprocessed, interpreted and integrated with detailed morpho-bathymetric data and high-resolution single channel seismic data. According to the interpretation, most of the upper continental margin has been created within the former Alpine Gavrovo, Ionian and Apulian thrust units, including their Miocene to Quaternary cover and their Triassic salt-bearing formations. The Ionian thrust complex seems to have been continuously overthrusting the Apulian Ridge, itself characterised by strongly fractured acoustic basement features. Ductile and mobile Triassic evaporitic sequences are present in most of the major Ionian zone morpho-structures. The westward directed thrusts of the Ionian zone reached their final positions in Lower Pliocene and were followed by uplift of the ridges that is continuing in the present time. Previous compressional structures are being reactivated as normal faults with associated diapirism in the Triassic evaporites. NNE-SSW shear displacements related to trans-extensional motion may have activated "pull apart" basins with ENE-WSW normal faulting at their heads. This NNE-SSW dextral strikeslip motion agrees with the present anticlockwise rotation of the Peloponnese. The focal mechanism and the NNE-SSW distribution of aftershocks of a major earthquake in June 2008 along the Andravida fault define a major lineament that can be followed past the Katakolo Peninsula to the diapiric morpho-structures defining the eastern boundary of the Strophades basin. [ABSTRACT FROM AUTHOR]

The SEAHELLARC project, supported by the European Commission, aimed at evaluating and computing seismic hazard and risk, as well as modelling tsunamis for the town of Pylos, in the western Peloponnese and neighboring region. This paper describes the main scopes and results of the project. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the first “in situ” seafloor observations of fluid escape structures in a fault-controlled caldera-type depression of about 8 km diameter, named the Menes caldera, in the Eastern Mediterranean sea off Egypt (western province of the Nile Deep Sea Fan). A detailed analysis of seven Nautile dives, performed during the Nautinil cruise in 2003, focused on determining the nature, origin, importance, mechanisms and environmental impacts of the fluid escape processes from the geological observations. Seafloor maps, constructed from direct visual observations and video records made from the submersible, and sampling results, for three mud volcanoes of the caldera, Cheops, Chephren and Mykerinos show differences in activity but many common characteristics. The three volcanoes show a crater-like depression. The study reveals a strong contrast between Mykerinos, where no seepage activity was found, and the craters of Cheops and Chephren, where an intense activity of brine seepage was discovered. On Cheops, a dome of dark grey mud raises slightly above the brine surface in the central part of the brine lake, and shows numerous circular vents of 1–2 m diameter that become gradually colonized by microbial mats. Chephren hosts a deep (>200 m) and warm (45 °C) brine lake. Alternations of areas void of or covered with microbial mats at the surface of the Chephren brine lake indicate large surface disturbances that may result from the occurrence of several active vents at the bottom of the lake. A special feature at Chephren is a brine overflow at the western edge of the crater, also indicative of the very high activity of brine seepage. The Nautinil observations indicate that the Menes caldera in the Eastern Mediterranean is a highly active site of brine seepage. Growth faults rooted in pre-Messinian sediment layers provide pathways for warm fluids to escape pressurized source levels below the Messinian salt. [Copyright &y& Elsevier]

Tests the predicted effects on the transform margin crust of continental heating by the adjacent oceanic lithosphere. Seismic and gravity data from the Cote d'Ivoire-Ghana transform margin showing that the continental crust remains uniform in thickness as the continent-ocean boundary is approached; Implications of finding for thermal exchanges across the palaeotransform boundary.

Multi-proxy analysis of two marine sediment cores (MS27PT and MD04-2726) from the Nile continental slope provides evidence of changes in Nile sediment discharge related to changes in Ethiopian African Monsoon (EAM) precipitation, and allows us to reconstruct changes in Nile River runoff, vegetation and erosion in the Nile headwaters. Sediment element composition and neodymium isotopic composition reveal significant changes in clastic sediment provenance, with sources oscillating between a Saharan aeolian contribution during the Last Glacial Maximum/deglacial transition and during the Late Holocene, and a Blue/Atbara Nile fluvial contribution during the African Humid Period (AHP). This study provides a new understanding of past environmental changes. Between 14.6 and 14.13 ka there was a major input of sediments from the Ethiopian Highlands, consistent with a stronger EAM at that time. Climate in the Nile basin was wetter between 14.8 and 8.4 ka, with a corresponding increase in Blue Nile water and sediment discharge via the main Nile into the Eastern Mediterranean. The gradual climatic transition from the AHP to the present-day dry climate was reflected in a decrease in Blue Nile sediment deposition and flood discharge between 8.4 and 3.7 ka, with aridity at a maximum between 3.7 and 2.6 ka. The onset of drier conditions in the Blue Nile basin seems to have begun before the 8.2 ka cooling event in the North Atlantic. We speculate that the climatic change from the wet AHP to the dry late Holocene may have been a result of a break in the low latitude dynamic equilibrium between climate, vegetation and erosion, which may in turn have affected the climate in higher latitudes. Reduced Nile flow may also have had an impact on Levantine Intermediate Water originating in the Eastern Mediterranean through an increase in intermediate water formation. [ABSTRACT FROM AUTHOR]

In order to define seismic hazard with sufficient accuracy required for engineering applications, we initiated a multidisciplinary geoscientific study offshore western Peloponnese, focusing on the Kyparissiakos Gulf. Multibeam swath bathymetry localised unstable coastal slopes, which were later investigated by high resolution seismic profiles. Sediments and crustal structures were studied by multi-channel seismic recordings and active larse-offsets seismic profiling. We established an onshore/offshore local seismic array that recorded 3500 micro-earthquakes in two months, and combined the results with historical and digital seismicity data in order to understand the active crustal deformation. These findings were further combined with geological mapping and tectonic observations from onshore Peloponnese and available offshore data. All this geologic and tectonic information was coupled with evidence from the analysis of historical and recent seismicity with the aim of identifying the seismogenic sources. We have defined nine seismogenic zones in western Peloponnese that are significantly different from those published in the literature. The new zonation addresses more accurately the deformation of the crust and sediments, and is the basis for a reliable seismic hazard analysis and seismic risk assessment. We identified a large area of the northern Peloponnese and the Ionian islands of Lefkas, Cephalonia, Zakynthos and Strophades, to be involved in a SW-ward oriented crustal extrusion, dominated by two major dextral deforming strike slip faults: Cephalonia and Andravida with their offshore prolongation. Some changes with respect to the Greek zonation in the literature have been introduced in the region surrounding the new nine seismogenic zones to reach a homogeneous cover of the whole Peloponnese. [ABSTRACT FROM AUTHOR]

Abstract: The Florence Ridge, part of the western Cyprus arc, is a compressional relief that was eroded during the Messinian salinity crisis while deposition of salt occurred North (Antalya basin) and South (Herodotus abyssal plain). In order to better assess the impact of salt-tectonics in the Florence Ridge region deformations, we conducted a morpho-structural analysis of available multibeam and seismic data (Simed and Prismed II campaigns). It is indeed a crucial issue to distinguish crustal and gravity driven structures in the compressional to strike-slip belts of the eastern Mediterranean. Along the Antalya basin, we mainly observed multi-directional tectonic rafts typical of gravity gliding above salt. On the Florence Ridge itself, the base of salt evolves laterally to a Messinian erosional surface that erodes a series of stacked nappes. This surface is involved in recent faulting. South of the Florence Ridge, a nearly 100km wide fold belt characterizes the Herodotus abyssal plain. Three different zones parallel to the Florence Ridge appear within this fold belt. Those are respectively from North to South zones A, B and C. Zone A is characterized mainly by small-wavelength folding and faulting. Approaching Zone B, a long extensional graben deforms the seafloor. Zone B stands ~100 to 200m higher than zones A and C. There, salt welding seems common. In the easternmost zone B deep sub-circular bathymetric depressions are associated with extremely thick and fan-shaped depocenters probably emplaced in relation with active sub-salt thrusts. Many evidences suggest post-Messinian uplift in this zone. Zone C shows medium to high wavelength salt-cored folds. Wavelength of those folds increase approaching the distal Nile deep-sea fan. Within zone C, a nearly undeformed domain exists approaching the Eratosthenes seamount. ‘En echelon’ folds bound this flat domain suggesting lateral salt extrusion at the junction between zone C and the distal Nile deep-sea fan. To conclude, numerous evidences argue for a post-Messinian reactivation of the pre-Messinian Florence Ridge accretionary wedge (numerous folds, uplifted zones). The salt, as on the nearby Mediterranean Ridge, decouples deep and surface deformations and even allow the development of isolated grabens and associated salt ridges in the heart of the Florence compressional zone. We propose in this case that local basal slope of salt increase related to basement fault activity triggered gravity gliding and thus extensional deformation despite the regional compressional regime. Finally, this study shows that the eastern Nile deep-sea fan, submitted to extremely vigorous salt tectonics seems to have collided with the Florence Ridge fold belt and to have generated a “salt extrusion” zone. [Copyright &y& Elsevier]

In the Nile deep-sea fan, thin-skinned deformation detaching on a layer of Messinian salt has generated an upslope to downslope progression from growth faults, to polygonal minibasins bounded by salt ridges, to buckle folds. Such progression is common in salt-bearing passive margins, where gravity spreading of the salt–sediment system causes proximal thin-skinned extension on the shelf and upper slope, and distal contraction along and in front of the lower slope. In the Eastern Nile deep-sea fan, this structural progression seems to be restricted to a corridor bounded by NW–SE-trending lineaments more than 200 km in length. These are associated with salt ridges and record strike–slip movements. In the absence of a large grid of deep-penetrating seismic data accurately imaging the basement, different likely hypotheses have been advanced about the origin of this corridor: (1) it may result from possible deep-seated tectonics related to the Rift of Suez, combined with salt-related deformation or, (2) by complex interaction between the overburden's gravity spreading and pre-existing pre-Messinian paleo-topographic features, particularly the possible buttressing effect of a seamount located North of the eastern Nile deep-sea fan. In order to understand how this corridor could have been generated, we used a series of physical experiments to test the effect on three-dimensional spreading of a sediment lobe of the following parameters: (1) active, crustal, oblique extension, (2) a dormant subsalt graben, (3) a passive buttress, such as a seamount and (4) complex paleo-topographic features along the Egyptian margin affecting initial salt distribution. These experiments show that the presence of a distal buttress, combined with a complex Messinian topography best explain the complex deformational pattern observed in the eastern Nile deep-sea fan. [ABSTRACT FROM AUTHOR]

Abstract: Based on an unusual data set comprises bathymetric data, backscatter imagery, seismic-reflection and Chirp profiles, and sediment cores, the Late Quaternary lobe at the mouth of the youngest turbidite channel off the western Nile deep-sea fan was investigated. The large-scale construction of the lobe through time and space is mainly controlled by 1) a pre-existing topography inherited from the downslope movement of Messinian evaporites, and 2) the type and nature of gravity flows delivered to the basin floor. The margins of the lobe are defined by high-backscatter acoustic facies that contrasts strongly with the low-backscatter facies from the surrounding abyssal-plain deposits. Within the lobe, low-backscatter facies characterise the main channel-levee systems and lobate bodies immediately beyond the end of the channels. Cores reveal that the high-backscatter facies corresponds to a series of extensive but thin debris-flow deposits with a fingered margin. These debrites comprise a muddy-sand matrix and dispersed clasts with diameter of 5 to 10cm. The lower backscatter facies at channel mouths corresponds to alternations of thin sandy turbidites and muddy hemipelagites. Extensive thin debris flows therefore traversed surprisingly low gradients to reach the distal fringes of the lobe complex but are never found in the lobate bodies just beyond the channel mouths. Although the Nile deep-sea fan is considered as a silt/mud-rich accumulation, sand-prone deposits exist within the lobe. This sand/mud segregation results either from the presence of channelized features in the lobe and/or from the hydrodynamic process of particle transport by debris flows and turbulent flows. [ABSTRACT FROM AUTHOR]

Abstract: Multiproxy analyses were performed on core MS27PT recovered in hemipelagic sediments deposited on the Nile margin in order to reconstruct Nile River palaeohydrological fluctuations during the last 100,000 years. The strontium and neodymium isotope composition of the terrigenous fraction and the major element distribution reveal large and abrupt changes in source, oscillating between a dominant aeolian Saharan contribution during arid periods and a dominant Nile River contribution during pluvial periods. Iron content shows a strong correlation with strontium and neodymium isotopes. This allows the use of a high-resolution continuous Fe record as a proxy of Blue Nile sediment input over the last 100,000 years. The detailed Fe record, with approximately 10 years resolution during pluvial periods, is consistent with subtropical African records of well-dated lake level fluctuations and thus constitutes a first continuous high resolution record of the East African monsoon regime intensity over Ethiopia. The detailed Fe record shows the two main known pluvial periods attributed to strengthening of the African monsoon over Ethiopia, the Nabtian period from 14 to 8ka cal BP and the Saharan period from 98 to 72ka BP. For the first time, the last glacial period (Marine Isotope Stage (MIS) 2, 3 and 4) is documented with a continuous record showing large oscillations between high and low East African palaeo-monsoon regimes. The end of the Nabtian period occurred at 8 ka in core MS27PT, i.e. much earlier than on the East Equatorial African region where it ended around 5.5ka. We interpret this as evidence that the southward shift of the rain belt occurred 3000 years earlier over the Eastern Ethiopian Highland and propose that the gradual southward migration of the rain belt was associated with highly variable intensity and longer rainy seasons from 8 to 5ka. During the last glacial period, two wet periods are present around 60–50ka BP and 38–30ka BP. These two humid periods are in phase with the rise of atmospheric CH4 concentrations suggesting that wetland tropical African area was one of the sources of the atmospheric CH4 during the MIS 3. During the Last Glacial Maximum and MIS 4, high Saharan aeolian influxes in phase with records of aeolian dust deposited in East Antarctica are documented. This study highlights the importance of reconstructions of monsoon rainfall fluctuation at high temporal resolution to better understand the link between low- and high-latitude climate variability at millennial timescales. [Copyright &y& Elsevier]

The SEAHELLARC project, supported by the European Commission, aims at evaluating and computing seismic hazard and risk, as well as modelling tsunamis for the town of Pylos, in the western Peloponnese. For this purpose, a new seismogenic zonation has been developed for the Pylos area, and broader region, and the most updated seismic hazard assessment is provided. The present paper describes preliminary seismic hazard computations performed with the scope of testing the improvements made during the project. In particular, the influence of an updated version of the Greek earthquake catalogue and of a new seismogenic zonation for the Pylos region are presented. The difference obtained for the expected ground motion, with a 475-year return period, in the town of Pylos is not significantly big (it only decreases from 0.63 to 0.56 g using literature data or the new ones, respectively). Conversely, greater differences concern the Island of Zakinthos. [ABSTRACT FROM AUTHOR]

Abstract: We report on a multidisciplinary study of cold seeps explored in the Central Nile deep-sea fan of the Egyptian margin. Our approach combines in situ seafloor observation, geophysics, sedimentological data, measurement of bottom-water methane anomalies, pore-water and sediment geochemistry, and 230Th/U dating of authigenic carbonates. Two areas were investigated, which correspond to different sedimentary provinces. The lower slope, at ∼2100 m water depth, indicates deformation of sediments by gravitational processes, exhibiting slope-parallel elongated ridges and seafloor depressions. In contrast, the middle slope, at ∼1650 m water depth, exhibits a series of debris-flow deposits not remobilized by post-depositional gravity processes. Significant differences exist between fluid-escape structures from the two studied areas. At the lower slope, methane anomalies were detected in bottom-waters above the depressions, whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities. Carbonate U/Th age dates (∼8 kyr BP), pore-water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past. In contrast, large (∼1 km2) carbonate-paved areas were discovered in the middle slope, with U/Th isotope evidence for ongoing carbonate precipitation during the Late Holocene (since ∼5 kyr BP at least). Our results suggest that fluid venting is closely related to sediment deformation in the Central Nile margin. It is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of ‘fossil’ carbonate ridges, whereas pervasive diffuse flow prevails at the unfailed middle slope. [Copyright &y& Elsevier]

Abstract: Understanding the recent formation of a sedimentary system such as a deep-sea turbidite system (DSTS) requires an accurate stratigraphic control on deposits. Due to the important terrigeneous input which disrupts the sedimentary record, DSTS is an environment where stratigraphic control is difficult to assess. Most of the time, traditional stratigraphic tools are not accurate enough. This has led to a rather limited number of studies concerning stratigraphy in DSTS. In this study, we examine several hemipelagic long piston cores collected from the Nile DSTS (eastern Mediterranean), in order to understand the recent evolution of the complex sedimentary system in this area. The first aim of this study is to show how to obtain a reliable timeframe in DSTS. Indeed, we provided a detailed ecostratigraphical scheme based on planktonic foraminiferal distribution, oxygen isotope records and lithostratigraphy (sapropels and tephra) of three cores where the sedimentation is least disturbed. We have identified 29 foraminiferal ecozones during the last 250,000 years BP, with an approximately 2000-year time resolution. The time span of each ecozone was constrained by the oxygen isotope record, 14C AMS radiometric data, tephrochronology and the sapropel chronology. These high-resolution ecostratigraphical time subdivisions have been applied in discontinuous mixed hemipelagic/turbiditic sequences of a levee record. This example shows how to date gravity events, formation and time periods of sedimentary accumulations. [Copyright &y& Elsevier]

Abstract: During the NAUTINIL cruise (September–October 2003), mud volcanoes and pockmarks located in four selected areas of the Nile deep-sea fan (caldera, central, eastern, North Alex) were investigated at water depths ranging from 500 to 3019m. Authigenic carbonate crusts were observed directly by a submersible in each of these fluid-venting areas, in close association with specific chemosynthetic biological communities. Authigenic carbonates occur typically as pavements, slabs and mounds on the seafloor, but are also present as millimeter- to centimeter-size concretions dispersed within sediments. Mineralogical analyses of carbonate crusts and concretions indicate that aragonite and high-Mg calcite represent the most dominant carbonate phases. Low-Mg calcite, dolomite and ankerite also occur as minor components. Petrographic observations of carbonate crusts and concretions show that they are composed mainly of microcrystalline carbonate cement, with minor amounts of detrital minerals, lithoclasts and bioclasts. Aragonite is present as microcrystalline cement or acicular crystals infilling bioclasts and voids. Pyrite occurs as framboids or cubic crystals, which are often associated with authigenic carbonates, thereby indicating that sulfate reduction was active during carbonate precipitation. Numerous millimeter- to centimeter-size euhedral gypsum crystals have been observed within carbonate crusts and concretions, and as isolated crystals in sediments recovered from the eastern province. In this area, precipitation of gypsum is related to the presence of rising sulfate-rich fluids, which originate from the dissolution of underlying Messinian evaporites. Millimeter-size barite concretions have also been discovered in sediment from the central province and precipitated from ascending fluids, which are enriched in barium due to the dissolution of biogenic and/or authigenic barite below the depth of sulfate depletion. The oxygen and carbon isotopic compositions of the carbonates display very large ranges, from −0.67‰ to 4.15‰ Vienna PeeDee Belemnite (V-PDB) and from −42.14‰ to 3.10‰ V-PDB, respectively. Most carbonates exhibit δ 18O values around 3‰, indicating that they have precipitated in isotopic equilibrium with bottom seawater. In contrast, two carbonate concretions from the caldera and the eastern areas are characterized by lower δ 18O values (−0.67‰ V-PDB and 0.98‰ V-PDB), which may reflect a contribution from 18O-poor (continental?) water or, most likely, a local high heat flow. A few carbonate crusts exhibit slightly positive δ 13C values, which indicate that seawater was the main source of carbon for those carbonates. Authigenic carbonates are typically depleted in 13C, revealing that the major carbon source for those carbonates derives from anaerobic oxidation of methane driven by microbial consortia of archaea and sulfate reducing bacteria. [Copyright &y& Elsevier]