along arc segmentation and interaction of subducting ridges with the lesser antilles subduction forearc crust revealed by mcs imaging highlights we image the deep structure of the lesser antilles subduction zone by mcs profiles the complex deformation of the outer forearc crust is induced by subducting ridges we discuss also the effect of the subducting compressive nam sam plate boundary along strike variations of the seaward edge of the outer forearc crust are discovered the updip limit proxy of the seismogenic part reaches 20 km trenchwards than believed abstract we present the results from a new grid of deep penetration multichannel seismic mcs profiles over the 280 km long north central segment of the lesser antilles subduction zone the 14 dip lines and 7 strike lines image the topographical variations of i the subduction interplate decollement ii the top of the arcward subducting atlantic oceanic crust toc under the huge accretionary wedge up to 7 km thick and iii the trenchward dipping basement of the deeply buried forearc backstop of the caribbean upper plate the four northernmost long dip lines of this new mcs grid reveal several kilometre high topographic variations of the toc beneath the accretionary wedge offshore guadeloupe and antigua islands they are located in the prolongation of those mapped on the atlantic seafloor entering subduction such as the barracuda ridge this mcs grid also provides evidences on unexpected huge along strike topographical variation of the backstop basement and of the deformation style affecting the outer forearc crust and sediments their mapping clearly indicates two principal areas of active deformation in the prolongation of the major barracuda and tiburon ridges and also other forearc basement highs that correspond to the prolongation of smaller oceanic basement highs recently mapped on the atlantic seafloor although different in detail the two main deforming forearc domains share similarities in style the imaged deformation of the sedimentary stratification reveals a time and space dependent faulting by successive warping and unwarping which deformation can be readily attributed to the forearc backstop sweeping over the two obliquely oriented elongated and localized topographical ridges the induced faulting producing vertical scarps in this transport does not require a regional arc parallel extensional regime as proposed for the inner forearc domain and may support a partitioned tectonic deformation such as in the case of an outer forearc sliver a contrasted reflectivity of the sedimentary layering at the transition between the outer forearc and accretionary domains was resolved and used to define the seaward edge of the outer forearc basement interpreted as being possibly a proxy to the updip limit of the interplate seismogenic zone its mapping documents along arc variations of some tens of kilometres of the subduction backstop with respect to the negative gravity anomaly commonly taken as marking the subduction trench with the exception of the southernmost part the newly mapped updip limit reaches 25 km closer to the trench thus indicating a possible wider seismogenic zone over almost the whole length of the study area

formation and deformation of hyperextended rift systems insights from rift domain mapping in the bay of biscay pyrenees the bay of biscay and the pyrenees correspond to a lower cretaceous rift system including both oceanic and hyperextended rift domains the transition from preserved oceanic and rift domains in the west to their complete inversion in the east enables us to study the progressive reactivation of a hyperextended rift system we use seismic interpretation gravity inversion and field mapping to identify and map former rift domains and their subsequent reactivation we propose a new map and sections across the system illustrating the progressive integration of the rift domains into the orogen this study aims to provide insights on the formation of hyperextended rift systems and discuss their role during reactivation two spatially and temporally distinct rift systems can be distinguished the bay of biscay parentis and the pyrenean basque cantabrian rifts while the offshore bay of biscay represent a former mature oceanic domain the fossil remnants of hyperextended domains preserved onshore in the pyrenean cantabrian orogen record distributed extensional deformation partitioned between strongly segmented rift basins reactivation initiated in the exhumed mantle domain before it affected the hyperthinned domain both domains accommodated most of the shortening the final architecture of the orogen is acquired once the conjugate necking domains became involved in collisional processes the complex 3 d architecture of the initial rift system may partly explain the heterogeneous reactivation of the overall system these results have important implications for the formation and reactivation of hyperextended rift systems and for the restoration of the bay of biscay and pyrenean domains

structure of the lesser antilles subduction forearc and backstop from 3d seismic refraction tomography in 2007 the sismantilles ii experiment was conducted to constrain structure and seismicity in the central lesser antilles subduction zone the seismic refraction data recorded by a network of 27 obss over an area of 65 km 95 km provide new insights on the crustal structure of the forearc offshore martinique and dominica islands the tomographic inversion of first arrival travel times provides a 3d p wave velocity model down to 15 km basement velocity gradients depict that the forearc is made up of two distinct units a high velocity gradient domain named the inner forearc in comparison to a lower velocity gradient domain located further trenchward named the outer forearc whereas the inner forearc appears as a rigid block uplifted and possibly tilted as a whole to the south short wavelength deformations of the outer forearc basement are observed beneath a 3 to 6 km thick sedimentary pile in relation with the subduction of the tiburon ridge and associated seafloor reliefs north offshore dominica island the outer forearc is 70 km wide it extends as far as 180 km to the east of the volcanic front where it acts as a backstop on which the accretionary wedge developed its width decreases strongly to the south to terminate offshore martinique where the inner forearc acts as the backstop the inner forearc is likely the extension at depth of themesozoicmagmatic crust outcropping to the north in la desirade island and along the scarp of the karukera spur the outer forearc could be either the eastern prolongation of the inner forearc but the crust was thinned and fractured during the past tectonic history of the area or by recent subduction processes or an oceanic terrane more recently accreted to the island arc

variation of seismic coupling with slab detachment and upper plate structure along the western hellenic subduction zone abstract 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

3 d sediment basement tomography of the northern marmara trough by a dense obs network at the nodes of a grid of controlled source profiles along the north anatolian fault a 3 d tomographic inversion of first arrival times of shot profiles recorded by a dense 2 d obs network provides an unprecedented constraint on the p wave velocities heterogeneity of the upper crustal part of the north marmara trough nmt over a region of 180 km long by 50 km wide one of the specific aims of this controlled source tomography is to provide a 3 d initial model for the local earthquake tomography let hence in an original way the controlled source inversion has been performed by using a code dedicated to let after several tests to check the results trade off with the inversion parameters we build up a 3 d a priori velocity model in which the sea bottom topography the acoustic and the crystalline basements and the moho interfaces have been considered the reliability of the obtained features has been checked by checkerboard tests and also by their comparison with the deep penetration multichannel seismic profiles and with the wide angle reflection and refraction modelled profiles this study provides the first 3 d view of the basement topography along the active north anatolian fault beneath the marmara sea even beneath the deepest part of three sedimentary basins of nmt clear basement depressions reaching down 6 km depth below the sea level bsl have been found beneath these basins the north imrali basin located on the southern continental shelf is observed with a similar sedimentary thickness as its northern neighbours between central and cinarcik basins the central high rises up to 3 km depth below bsl its crest position is offset by 10 km northwestward relatively to the bathymetric crest on the contrary tekirdag and central basins appear linked forming a 60 km long basement depression beneath the bathymetric relief of western high low velocities are observed down to 6 km depth bsl and no basement high have been found the obtained 3 d vp heterogeneity model allows the consideration of the 3 d supracrustal heterogeneity into the future earthquake relocations in this region the topographic map of the pre kinematic basement offers the possibility to take into account the locking depth variations in future geohazard estimations by geomechanical modelling in this region

shear wave anisotropy across the geothermal field of milos aegean volcanic arc summary the drilled geothermal reservoir of milos island aegean sea greece is densely sampled by seismic waves from local earthquakes occurring at depths of 4 6 km recorded by numerous three component seismographs during the eight months of observation seismic activity on the island occurred in the form of a few swarms located in three different areas the focal mechanisms of all earthquakes share an area of dilatational quadrants indicating a nearly vertical maximum compressive stress this implies an extensional field consistent with the regional tectonics of the aegean sea shear wave splitting is widely observed most of the observed leading shear wave polarizations are aligned around the n s direction and they are parallel to the structural trends of faults observed at the surface the other seismograms show a leading shear wave polarized along a n40de direction these polarizations are observed particularly at stations located between the geothermal drillholes indicating probably the orientation of microfractures aligned in the geothermal reservoir by the present day stress field variations of the anisotropy magnitude are deduced from the study of shear wave delays in the vicinity of geothermal drillholes and their distribution appears to correlate with the limits of a fractured medium detected by p and s velocity anomalies

exploring the usability of isotopically anomalous oxygen in bones and teeth as paleo co2 barometer fluctuations in atmospheric pco2pco2 may have played the key role in global climate throughout earth s history for the quantification of past variations in atmospheric pco2pco2 several geological proxy approaches and geochemical models have been developed here we evaluate a new co2 proxy approach that is based on the triple oxygen isotope composition 16o 17o 18o of skeletal apatite of terrestrial mammals our approach utilizes the relation between an anomaly in 17o of tropospheric air o2 and atmospheric pco2pco2 the anomaly is transferred from inhaled air o2 to skeletal apatite of mammals hence triple oxygen isotope data of mammalian bioapatite provide information regarding pco2pco2 during the animal s lifetime the approach was calibrated with a detailed mass balance model that was verified by analyses on a set of recent mammals we evaluate the potential of this new independent terrestrial paleo co2 proxy in a case study including eocene to miocene samples the present investigation provides promising results that are in good agreement with existing proxy and model data the uncertainty intrinsic to the proxy is mainly due to uncertainties in physiological parameters

north marmara trough architecture of basin infill basement and faults from psdm reflection and obs refraction seismics abstract the reflection and refraction seismic data collected during the seismarmara leg 1 survey in the sea of marmara provide detailed imaging of sedimentary record and fault activity with deep penetration into its basement first a detailed analysis of pre stack depth migrated seismic lines crossing the central basin enable us to discuss the space and time relations of the large and smaller nested basins of the inner depression as well as the diversity of style and rate of activity of motion at the diverse basin border faults second forward modeling of obs refraction arrival times reveals the effect of compaction on the sedimentary pile whereas its layering imaged by mcs as seismic reflectors rather recorded the tectonic evolution another major result of the refraction modeling is the identification of the crystalline basement the latter is imaged about 1 or 2 km deeper than the base of the layered sedimentary sequence imaged on the coincident mcs profiles this basement exhibits sharp topography across the central high the kumburgaz basin and the eastern tip of the cinarcik north imrali basin in an unexpected way with respect to the sea bottom depressions we furthermore imaged several large tilted basement blocks which separate the deep basins as between the cinarcik and imrali basins despite the varying width of the nmt and the sizes of the tilted blocks we propose that the imaged finite deformation results from a similar process of partitioning deformation over more than one or even two faults across the nmt that may have changed activity with time and space

propagation of a lithospheric tear fault step through the western boundary of the calabrian accretionary wedge offshore eastern sicily southern italy the rollback of a segmented slab of oceanic lithosphere is typically accompanied by vertical lithospheric tear fault s along the lateral slab edge s and by strike slip movement in the upper plate defined as a step fault subduction tear edge propagator the neogene evolution of the central mediterranean is dominated by the interaction between the slow africa eurasia convergence and the se ward rollback of the ionian slab that leads to the back arc opening of the tyrrhenian sea here we present post stack time migrated and pre stack depth migrated archimede 1997 multichannel seismic lines that were acquired offshore eastern sicily at the foot of the malta escarpment first we identify the recent deformation along the lateral ramp of the calabrian accretionary wedge towards the east the calabrian wedge is formed by the accretion of the post evaporitic sediments above a decollement at the base of the messinian evaporites at the latitude of syracuse 50 km east of the malta escarpment a major n150 degrees e trending crustal scale and vertical fault slices through the entire accretionary wedge this fault cuts by several kilometers through the pre evaporitic messinian sediments and into the basement the vertical offset along this vertical fault decreases from north to south and the fault is no longer observed on the seismic lines 50 km se of the alfeo seamount a previously published moho depth isocontour map offshore sicily and the recent gps data combined with the presence of strike slip movements ne onshore sicily allow us to identify this 200 km long crustal scale fault as the surface expression of a step fault the presence of syntectonic pleistocene sediments on top this crustal scale fault suggests a recent lithospheric vertical movement of the step fault in response to the rollback of the ionian slab and to the se ward advance of the calabria peloritan block

single bubble marine source offers new perspectives for lithospheric exploration abstract we present deep penetration seismic time sections obtained in the last two years with the single bubble pulse generating method using marine seismic airguns whole crustal penetration and resolution have been obtained on the ionian quasi oceanic basin and its margin on the continental crust of the aegean sea on the continental margins and oceanic basin of the gulf of biscay we show that this method is more efficient than others in radiating the lower frequencies returned by deep structure without loosing resolution hence it allows deep crustal imaging from relatively low power academic ships and if the method is applied to powerful industrial vessels it may open the subcrustal lithosphere to imaging

seismic structure and the active hellenic subduction in the ionian islands in the region of the ionian islands of western greece the active margin of the hellenic domain passes from oceanic subduction in the south to continental collision in the north linked by the right lateral cephalonia transform fault a slightly landward dipping interface revealed at 13 km depth by a single previous line in the channel between cephalonia and zante has been suggested as the interplate subduction boundary new marine multichannel reflection profiles and obs refraction and wide angle reflection data confirm the reflector as a regional feature these data evidence its extension to the south where large low angle thrust earthquakes occur offshore to zante the new profiles establish a coincidence between the focal depths of these large subduction events and the imaged bright reflective level confirming its tentative interpretation as the interplate boundary which generally appears with a positive reflection polarity in this context the ionian islands outcrop corresponds to a shallowing of the interplate boudary from south to north in the south offshore zante the interplate boundary comprises a stratified zone that may be considered as the sedimentary cover of the ionian basin oceanic like crust which forms the lower plate here the shallower position and single cycle reflection character of the interplate further north suggest that the lower plate could there be the apulian paleomargin to that basin

3 d architecture and plio quaternary evolution of the paola basin insights into the forearc of the tyrrhenian ionian subduction system

linking long term gully and river channel dynamics to environmental change using repeat photography northern ethiopia abstract in the highlands of northern ethiopia gully occurrence is linked to poverty driven unsustainable use of the land in a vulnerable semi arid and mountainous environment where intensive rainfall challenges the physical integrity of the landscape trends in gully and river channel erosion and their relation to triggering environmental changes can proffer valuable insights into sustainable development in northern ethiopia in order to assess the region wide change in gully and river channel morphology over 140 years a set of 57 historical photographs taken in tigray and clearly displaying gully cross sections were precisely repeated from 2006 till 2009 ninety two percent of the gully and river sections n 38 increased in cross sectional area during the studied period especially after 1975 two repeatedly photographed catchments of lake ashenge and atsela allowed a detailed study of gully development from 1936 until 2009 a conceptual hydrogeomorphic model was devised for these catchments and validated for the northern ethiopian highlands three major phases can be distinguished in the hydrological regime of the catchments in the first phase between 1868 or earlier and ca 1965 the relatively stable channels showed an oversized morphology inherited from a previous period when external forcing in environmental conditions had caused the channels to shape in the second phase ca 1965 ca 2000 increased aridity and continued vegetation clearance accelerated the channel dynamics of the gully and river system the third phase ca 2000 present started after the large scale implementation of soil and water conservation measures in 2009 23 of the gully and river sections were stabilizing this paper validates previous research indicating severe land degradation in the second half of the 20th century additionally it demonstrates that the recent erosive cycle started around 1965 and that at the present time improved land management stabilizes headwater streams

seismic characterization of basalt flows from the faroes margin and the faroe shetland basin high quality seismic profiles across the faroes volcanic continental margin and the adjacent continental shelf show contrasting styles of basalt emplacement across two major structural boundaries at the rifted continental margin the basalts form prominent seaward dipping reflector sequences up to 5 km thick the same basalts after they had travelled in a landward direction across the elevated subaerial faroes shelf produced prominent landward dipping foresets where they flowed across the paleo coastline into the deep water of the faroe shetland basin in both cases we are able to image details of the internal structure of the basalts as a result of using a low frequency airgun source capable of penetrating through the basalt sequence together with long offset recordings from ocean bottom seismometers and a 12 km long deep towed hydrophone streamer

the triple oxygen isotope composition of the earth mantle and understanding δo17 variations in terrestrial rocks and minerals abstract it has been shown in numerous studies that terrestrial rocks and minerals fall on a line with slope 0 52 in a o 17 vs o 18 diagram in this study we present new data on the triple isotope composition of the earth mantle crustal materials and low t aqueous precipitates crustal materials show distinct variations in o 17 suggesting that the concept of a single terrestrial mass fractionation is invalid on small scale observable variations in individual fractionation slopes are interpreted as temperature effects we show that the earth mantle is isotopically homogeneous and confirm the recent finding that the earth mantle has a negative o 17 the difference in o 18 and o 17 between seawater and oceanic crust is discussed with respect to the effects of low and high temperature water rock interaction

deep structure of the armorican basin bay of biscay a review of norgasis seismic reflection and refraction data the bay of biscay is bounded to the north by the north biscay margin which comprises the western approaches and armorican segments in the 1970s and 1980s most researchers considered this margin typical of a non volcanic passive margin it is characterized by a striking succession of tilted blocks beneath which occurs the s reflector and the continent ocean boundary is abrupt this paper examines the armorican segment and is based on a study of all early seismic profiles together with new multichannel reflection and refraction seismic data norgasis cruise an important result is the discovery of a 80 km wide ocean continent transition zone that coincides with the armorican basin a deep sedimentary basin it is characterized by a high velocity lower crustal layer 7 4 7 5 km s 1 overlain by sediments the other results are 1 the main crustal thinning occurs exclusively under the narrow continental slope 2 the tilted blocks and the s reflector are observed only at the base of the continental slope in the narrow domain called the neck area 3 the north biscay ridge is a large oceanic plateau present only off the nw armorican margin rather than a long ridge elongated off the whole north biscay margin

triple oxygen isotopes in biogenic and sedimentary carbonates abstract the 17 o anomaly 17 o of natural waters has been shown to be sensitive to evaporation in a way analogous to deuterium excess with evaporated bodies of water e g leaf waters lake waters animal body waters tending to have lower 17 o than primary meteoric waters in animal body water 17 o relates to the intake of evaporated waters evaporative effluxes of water and the 17 o value of atmospheric o 2 which itself carries signatures of global carbon cycling and photochemical reactions in the stratosphere carbonates have the potential to record the triple oxygen isotope compositions of parent waters allowing reconstruction of past water compositions but such investigations have awaited development of methods for high precision measurement of 17 o of carbonate we describe optimized methods based on a sequential acid digestion reduction fluorination approach that yield 17 o data with the high precision 0 010 1 needed to resolve subtle environmental signals we report the first high precision 17 o dataset for terrestrial carbonates focusing on vertebrate biogenic carbonates and soil carbonates but also including marine invertebrates and high temperature carbonates we determine apparent three isotope fractionation factors between the o 2 analyte derived from carbonate and the parent waters of the carbonate these in combination with appropriate temperature estimates from clumped isotope thermometry or known or estimated body temperatures are used to calculate the 18 o and 17 o of parent waters the clearest pattern to emerge is the strong 17 o depletion in avian dinosaurian and mammalian body water from analyses of eggshell and tooth enamel relative to meteoric waters following expected influences of evaporated water e g leaf water and atmospheric o 2 on vertebrate body water parent waters of the soil carbonates studied here have 17 o values that are similar to or slightly lower than global precipitation our results suggest that 17 o will have useful application to paleoenvironmental studies of continental environments where the effects of evaporation are important and where vertebrate body water may record an isotopic signal of evaporated water sources and atmospheric oxygen

seismic layer 2a variations in the lucky strike segment at the mid atlantic ridge from reflection measurements 1 the sismomar experiment carried out seismic measurements of the slow spreading lucky strike segment of the mid atlantic ridge located approximately 300 km south of the azores platform we present results from a segment scale reflection study of seismic layer 2a that is centered on the lucky strike volcano and covers the central 54 km of the 70 km long segment and extends 30 km on both sides of the ridge axis our study allows new conclusions about the role of tectonic magmatic and hydrothermal processes in shaping the upper crustal structure of the lucky strike segment the seismic reflection measurements show an almost constant layer 2a two way time within the median valley and an abrupt layer 2a two way time decrease off axis this two way time decrease is caused by a layer 2a velocity increase on the order of 1 km s the uniform two way time in the median valley results from a constant thickness layer 2a which could be caused by the existence of a porosity threshold linked to the lithologic lava dike boundary the regularity of the layer 2a 2b interface within the median valley indicates that layer 2a is built entirely inside the median valley the off axis velocity increase is consistent with hydrothermal alteration and the aging of the crust

environmental change geomorphic processes and land degradation in tropical highlands abstract the international symposium highland2006 held in mekelle ethiopia from 21 to 25 september 2006 was the second time that ethiopia could host a major international scientific event on geomorphological processes highland2006 created a forum for those conducting research on the impacts of environmental change on geomorphic processes and land degradation in east african highlands as well as in similar regions around the globe discussions of results and exchange of experiences during indoor sessions as well as excursions have resulted in this distinctive set of scientific papers the two main questions addressed in this special issue through case studies in tropical mountain areas on all continents are 1 how have environmental changes impacted the type and intensity of geomorphic processes in tropical mountains since late pleistocene times the answer to this question is strongly linked to our knowledge on changes in climate vegetation cover human activities hydrology hillslope and fluvial processes for such environments 2 which factors control the intensity of land degradation its on site and off site impacts in tropical mountains this question addresses the role of natural and anthropogenic factors in the degradation of the vegetation cover and in controlling the intensity of hydrological processes soil erosion landsliding reservoir sedimentation and flooding in parallel with this special catena issue a number of selected papers on land degradation and its mitigation in tropical highlands are presented in a special issue of soil tillage research

deep seismic reflection and refraction profiling along the aquitaine shelf bay of biscay summary the 300 km ecors bay of biscay profile was carried out along the aquitaine shelf and comprised a complete set of experiments including zero offset and 7 5 km constant offset vertical seismic reflection and six expanding spread profiles large offset recordings were fundamental for the definition of the layered lower crust and the moho while esps provided decisive complementary information for the geological interpretation these data show a strong variation in crustal thickness from about 20 km beneath the rifted parentis basin a failed arm of the oceanic bay of biscay up to 35 km to the north below the armorican shelf in the hercynian domain and to the south below the cantabria shelf in the vicinity of the pyrenean deformation front the results have important implications for the behaviour of the crust during the formation of rifted sedimentary basins and during continental collision

roots of etna volcano in faults of great earthquakes abstract results from several seismic methods allow us to sketch the deep structure of etna and its ionian margin under etna a volume of high velocity material is found in a structurally high position the emplacement of this suggests spreading of the surrounding medium just offshore down to the east normal faults penetrate through the upper crust the deeper crustal structure beneath appears upwarped from the basin towards etna juxtaposed with the crust of sicily a thinner crust reaches from the ionian basin under etna and the mantle is upwarped in such a structure magma can then be viewed as a melted lens capping a mantle upwarp at shallow depth rather than in an intracrustal chamber this reduces the conflict between estimates of its volume from excess output of volatiles and short residence times a link in time is indicated between volcanic and seismic activity at a large scale over the millennium the reported ends of episodes of high output rates of magma are followed by the reported occurrences of magnitude 7 earthquakes which caused destruction in southeastern sicily several steep active normal fault have been imaged to a depth of 10 km the crust up to 30 km offshore of the cities of catania and augusta which may be fault planes for such large earthquakes they expand and prolongate the system of the timpe faults on the eastern flank of etna thus linking large scale tectonics offshore with the volcano etna developed together with normal faulting upwarp and spreading during the recent evolution of the former ionian subduction activation of the material at depth at the lateral edge of the slab by vertical motion with extension above could produce the peculiar type of etna magmatism

specific sediment yield in tigray northern ethiopia assessment and semi quantitative modelling abstract sediment deposition in reservoirs is a serious off site consequence of soil erosion in tigray northern ethiopia so far insufficient and less reliable sediment yield data have been collected for northern ethiopia nor are there any adaptable methodologies for sediment yield assessment in the country as a whole which could be used when designing new reservoirs this study addresses those problems by 1 undertaking reservoir sediment deposition measurements and 2 by calibrating and adapting the pacific southwest inter agency committee psiac and the factorial scoring model fsm sediment yield assessment models to ethiopian conditions field rating of catchment characteristics and the sediment yield data from the reservoir survey were used for calibration and validation of the models our reservoir survey indicates that specific sediment yield ssy varies significantly between catchments i e 487 t km 2 year 1 to 1817 t km 2 year 1 with an average of 1054 446 t km 2 year 1 since the variability of ssy is high between the studied reservoirs care should be taken in the study area to adopt representative ssy values during reservoir and soil water conservation planning the psiac ssy prediction is found to fit well with observed ssy without adjustment while the fsm was found to have after modifying the description of factors and incorporating new controlling factors a good fit between the predicted and observed ssy studies of the relationship between the known sediment yield rates and the catchment conditions using semi quantitative approaches such as psiac and fsm can be of substantial benefit in extrapolating data for areas where no detailed information is available in a cheap and quick way however calibration and modification of such models may be necessary if they are to be used beyond the region where they were developed

north aegean crustal deformation an active fault imaged to 10 km depth by reflection seismic data three multichannel seismic profiles imaged a normal fault to at least 10 km depth in the north aegean trough and thermaikos basin the fault is active and recent forming a scarp at sea bottom and crossing the quaternary deltaic front on the northern slope of the trough controlled to the south by the north anatolian fault prestack depth migration imaged the fault as a seismic reflector cutting steeply across the sedimentary rocks and flattening in the basement from the seismic image the n100 e strike of the fault scarp and the orientations of the three profiles the true fault dip is constrained to an average 20 in the basement a low angle dip the throw and age estimated from the geometry in the sedimentary rocks document recent onset of the motion that must have occurred at a high rate both the direction and the rate of slip are consistent with the instantaneous motion as measured by space based geodesy which shows the fault to be forming by pure normal slip large earthquakes that have occurred in the basin may relate to such normal faults whereas the north anatolian fault with its current strike slip earthquakes appears to slip here under low resolved shear stress

observation and interpretation of δ17o variations in terrestrial rocks response to the comment by miller et al on the paper by pack herwartz 2014

characterizing and identifying structural domains at rifted continental margins application to the bay of biscay margins and its western pyrenean fossil remnants we use the bay of biscay and western pyrenees as a natural laboratory to develop and apply an approach to characterize and identify distinctive rifted margin domains in offshore and onshore settings the bay of biscay and western pyrenees offer access to seismically imaged drilled and exposed parts of one and the same hyperextended rift system offshore we use gravity inversion and flexural backstripping techniques combined with seismic interpretation to provide estimates of accommodation space crustal thickness and lithosphere thinning onshore we focus on key outcrops of the former rift domain to describe the nature of sediment and basement rocks and of their interface this qualitative and quantitative characterization provides diagnostic elements for the identification of five distinct structural domains at magma poor rifted margins and their fossil analogues proximal necking hyperthinned exhumed mantle and oceanic domains this new approach can be used to reconcile offshore and onshore observations and to aid interpretation when only local observations are available onshore remnants can be placed in an offshore rifted margin context enabling the prediction of first order crustal architecture for the interpretation of offshore seismic reflection sections geological insights into rift structures and basement nature can be suggested based on onshore analogies

identification and inversion of converted shear waves case studies from the european north atlantic continental margins summary wide angle shear wave arrivals converted from compressional to shear waves at crustal interfaces enable crustal vp vs ratios to be determined which provide valuable constraint on geological interpretations analysis of the converted shear wave phases represents the next logical step in characterizing the crustal structure and composition following multichannel seismic structural imaging and tomographic inversion of the wide angle compressional wave phases in this offshore study across two passive margins extending from stretched continental to fully oceanic crust the high data density 2 10 km ocean bottom seismometer obs spacing and a consistent efficient conversion interface produced shear wave data sets suitable for traveltime inversion the shear waves were recorded by three orthogonal geophones in each obs arrival phases visible to 180 km offset were identified using their arrival times moveout velocities and particle motions across the north atlantic volcanic rifted continental margins studied breakup was accompanied by the eruption of large volumes of basalts of the north atlantic igneous province the interface between post volcanic sediments and the top of the basalts provides the dominant conversion boundary across the oceanic crust and the continent ocean transition however the shear wave data quality was significantly diminished at the continental ends of the profiles where the thick basalt flows and hence this conversion interface feathers out and crustal attenuation increases initial modelling of the converted shear wave phases was carried out using a layer based approach with arrivals converted on the way up used to constrain the vp vs ratio of the post volcanic sedimentary sequence beneath each obs to produce a model with continuous crustal s wave velocities the compressional wave velocities beneath the sediment top basalt interface were transformed into starting shear wave velocities using a constant value of vp vs and the inversion carried out by specifying the appropriate ray path once the data set had been fully interpreted correction of the traveltimes to effective symmetric ray paths enabled us to apply a regularized grid inversion such inversions are less subjective than the layer based approach and yield more robust minimum structure results with quantifiable errors except in the vicinity of a known subbasalt low velocity zone encountered on the faroes margin monte carlo analyses were performed for this approach the average model from multiple inversions using randomized starting models and traveltimes shows the structure required by the traveltimes and the model standard deviation gives an estimate of uncertainty model and inversion parametrizations were fully tested and optimum parameters chosen for compressional and shear wave inversions this allows after appropriate model smoothing an estimate to be made of the spatial variation of the vp vs ratio within the crust there are marked gradients in vp vs and vp vs ratio across the continent ocean transition which may result from intrusion of high magnesium mafic igneous material into the crystalline continental crust the vp vs ratio used in conjunction with vp also provides constraints on the subbasalt lithologies forming the low velocity zone we conclude from such an analysis that this zone is unlikely to be composed entirely of igneous hyaloclastite material some proportion of clastic sedimentary rocks is likely to be present the vp vs and vp properties of the units underlying the low velocity zone are inconsistent with crystalline

plough marks as a tool to assess soil erosion rates a case study in axum ethiopia abstract from the antiquity the hilly landscape around the city of axum in northern ethiopia has been terraced and extensively used for agriculture purposes impacts of the ard plough on protruding and or buried boulder at a depth less than the tillage depth produce scratches on their sides or their top the spatial relationship among plough marks and rock surface orientations gives information on the ploughing direction whereas the relative height from the present ground surface to the top of the marks and information on the age of cultivation can be used to assess soil loss rates parameters to define plough mark orientation were defined and measured in the field on boulders with plough marks within a study terrace located in an archaeological area with an approx of 2040 year age these parameters are height from the ground dip slope and frequency the measurements also show that the initial terrace slope was steeper than the present one confirming the effectiveness of the traditional terracing practice in soil conservation because of the low soil erosion rates assessed over a so large time interval for the main time intervals of the axumite history corresponding to the rise and fall of the axumite civilization and to variable conditions of human pressure on the land the maximum erosion rates inferred are of the order of 3 4 mg ha 1 y 1 this result is compared with erosion rates calculated with other methods reported in literature e g psiac and field measurement on terraces in the same region leading to values coinciding with those obtained by the plough marks method

two stage growth of the calabrian accretionary wedge in the ionian sea central mediterranean constraints from depth migrated multichannel seismic data new structural images of the calabrian accretionary wedge are presented from depth migrated multichannel seismic data a combined interpretation swath mapping bathymetry allows us to identify five morphological domains on the basis of their tectonic style 1 beneath the undeformed abyssal plain a set of deep nw vergent reverse faults cuts the ionian oceanic crust and thick pre messinian sediments 2 towards the nw the low taper post messinian wedge overlying a shallow nw dipping decollement at the base of the messinian evaporites and exhibiting strong tectonic thickening 3 beneath the flat central transition zone a backthrust marks the contact between the post and pre messinian wedges here the decollement dip increases 3 cutting through deeper sediments to reach 10 km depth 4 beneath the pre messinian calabrian wedge some steep landward dipping features are imaged where underplating may occur 5 beneath the inner plateau a fore arc basin lies above the top of the calabrian continental basement imaged at 8 km depth the architecture of the calabrian accretionary complex is very similar to the mediterranean ridge both systems consist of a an external low taper post messinian wedge overlying a thick undeformed section of underthrust mesozoic sediments and b an internal pre messinian wedge where the decollement steps down and where the underthrust section is presumably underplated we perform area balancing and show that since the messinian the calabrian accretionary wedge has undergone extremely rapid outward growth at an average rate of 30 km ma which makes it the fastest growing accretionary wedge over the past 5 ma highlights relation between the pre and post messinian juxtaposed wedges contact between these wedges along a major backthrust the 130 km long outer calabrian prism a huge salt bearing body one of the fastest growing wedges 2 0 cm year in recent earth history 170 km amount of post messinian subduction subduction rate 3 4 cm year

crustal thinning on the aquitaine shelf bay of biscay from deep seismic data in recent years an increasing amount of new scientific data on the structure and nature of the whole continental crust has been acquired from deep seismic profiling the bay of biscay profile was recorded in 1984 at sea along the aquitaine platform for the french ecors group in association with hispanoil it collected a unique set of two ship multi channel seismic data with constant offset and expanded spread profiles in a complex geological area the data are of very good quality and contain clear moho and lower crust reflections as seen under most parts of western europe where similar experiments have been conducted1 4 this profile provided for the first time the most convincing evidence for an anomalously thin crust below a rifted basin the parentis basin which is directly connected to the oceanic area of the bay of biscay it gives new constraints for understanding the formation of extensional sedimentary basins

crustal structure of the ionian margin of sicily etna volcano in the frame of regional evolution abstract crustal imaging could be achieved on normal incidence reflection profiles offshore eastern sicily by using industrial grade reflection seismic with improved marine sources thick recent sediments a reflective pile including the mesozoic deposits a transparent upper crust and a band of low frequency reflections attributed to the lower crust are imaged in the seismic sections the structure of the crust and its thickness show features inherited from the mesozoic evolution as a passive margin by which ionian basin crust was formed around the hyblean continental promontory of africa to constitute the southern plate in the later convergence with europe the seismic images are also marked by the lithospheric deformation due to the neogene overriding of the northern part of this paleomargin by the calabro peloritan block of european continental crust this transpressive motion may have been guided along the northern part of this paleomargin where the seismic profiles evidence a hinge line between the northward upslope of the moho of that old passive margin and its downslope to the present slab under the tyrrhenian sea etna volcano is located at the intersection of this mantle upwarp by a zone of active sea bottom normal faults which cut across the formerly constructed compressional belt the onset of its volcanic activity is roughly coeval with that of the cessation of interplate thrusting and could hence be related to a change of the coupling of the ionian slab this slab is now probably disconnected from the overriding plate and rolled back in front of the expanding hot tyrrhenian asthenospheric dome with the mobilisation of a viscous mantle material at depth an active lithospheric fault is here imaged which cuts over more than 100 km into the ionian basin the fault runs from the tyrrhenian margin in the sse direction of etna updip of the southwestern lateral edge of this slab leaving north eastward the extruded calabrian block and on its south westward edge the uplifted crust and mantle structures of etna along it the crust including the mesozoic and deeper layers has sagged vertically in the segment in front of the slab with a finite throw across the fault increasing from the basin towards etna

methoni mw 6 8 rupture and aftershocks distribution from a dense array of obs and land seismometers offshore sw hellenic subduction abstract along the south western offshore hellenic subduction zone the overriding aegean upper plate above the mediterranean oceanic lithosphere generates uncommon large earthquakes on the offshore megathrust fault the largest subduction thrust event for half a century has been the 14 february 2008 methoni earthquake mw 6 8 that occurred offshore of the southwest coast of peloponnesus we conducted micro seismicity experiments around the rupture area and forearc domain between peloponnesus and crete using ocean bottom seismometers obs jointly with land based seismological stations our first experiment in 2006 had revealed an association of the matapan trough a 400 km long forearc basin with local seismicity clustering and a possible gap in activity over the later methoni rupture area here we present new data of post methoni seismic activity recorded during a time span of 11 months beginning in october 2008 within the period of proposed afterslip on the megathrust by an extended and dense seismic array consisting of up to 33 obs a minimum 1d velocity model was constructed for the region to provide better constraints on absolute locations and double difference relocation was applied to produce an enhanced image of the spatial distribution of hypocenters the high resolution earthquake locations confirm correlation of the matapan trough with local seismicity as a regional feature also filling up the previously observed gap over the methoni rupture area we constrain seismicity to be located mainly within the upper plate hypocenters are also resolved above the updip and downdip edges of the rupture area respectively seismic activity provides hints of upper plate structures which were activated in response to post seismic deformation spreading within the forearc crust our findings highlight the characteristics of a megathrust domain which is related with a highly deformable overriding plate and controlled by a segmented lower plate topography

a first deep seismic survey in the sea of marmara deep basins and whole crust architecture and evolution abstract increased source strength streamer length and dense spatial coverage of seismic reflection profiles of the seismarmara leg 1 allow to image the deep structure of the marine north marmara trough nmt on the strike slip north anatolian fault naf west of the destructive izmit 1999 earthquake a reflective lower crust and the moho boundary are detected they appear upwarped on an e w profile from the southern central basin eastwards towards more internal parts of the deformed region thinning of the upper crust could use a detachment suggested from an imaged dipping intracrustal reflector that would allow upper crustal material to be dragged from beneath it and above the lower crust accounting for the extensional component but also southwest motion of the southern margin of the nmt sections across the eastern half of the nmt crossing the cinarcik and imrali basins reveal several faults that are active reaching into the basement and have varying strike and proportions of normal and strike slip displacement they might be viewed as petals of a large scale negative flower structure that spreads over a width of 30 km at surface and is rooted deeper in the lithosphere under the central basin a very thick sediment infill is revealed and its extensional bounding faults are active and imaged as much as 8 km apart down to 6 km depth we interpret them as two deep rooted faults encompassing a foundering basement block rather than being merely pulled apart from a jog in a strike slip above a decollement the deep basin lengthening would account for only a modest part of the proposed 60 km finite motion since 4 myr along the same direction oblique to the nmt that sidesteps the shear motion from its two ends thus differential motion occurred much beyond the deep basins like subsidence involving the nmt bounding faults and the intracrustal detachments the complex partitioned motion localized on active faults with diverse natures and orientations is suggested to represent the overburden deformation induced from horizontal plane simple shear occurring in depth at lithospheric scale and in front of the north anatolian fault when it propagated through the region

the late holocene geomorphic history of the ethiopian highlands supportive evidence from may tsimble abstract alluvial sedimentary archives contain important geochronological and paleo environmental information on past geomorphic processes in semi arid regions for north ethiopia in particular flashflood sediments transported by ephemeral streams can provide interesting chronological information on late holocene land degradation whether or not impacted by climate or land cover changes upstream here we compare geomorphic records with independent regional records of rainfall regime changes land use cover changes and macrohistory supported by optically stimulated luminescence osl dates for fluvial activity at a sediment sequence in the may tsimble catchment in the northeastern highlands we identified two degradation periods over the past 4000 years one broadly from 1500 500 bce and one from 500 ce onwards at least one prior incision phase is responsible for the stabilized gullies that can be seen on photographs around 1900 and another incision phase is dated to the late 20th century based on all datasets we re interpret the geomorphic history of the highlands land degradation is dominantly determined by a human impact although the impact of this human influence does get amplified during dry spells

triple oxygen isotope mass balance for the earth s oceans with application to archean cherts abstract the oxygen isotope composition of the earth s oceans is buffered by high and low t exchange with the lithosphere we present a triple oxygen isotope mass balance model for the earth s oceans the model is based on triple oxygen isotope measurements of rocks from various reservoirs including high and low t alteration products the modern ocean water composition can be well matched if the ratio between continental weathering and high t seafloor alteration is 25 higher than previously assumed the mass balance suggests that putative precambrian low 18o ocean water would fall on a trend with slope 0 51 passing through modern ice free world seawater exemplified application to a published phanerozoic and archean chert data suggest precipitation in cool oceans with modern like 18o followed by diagenetic alteration with involvement of meteoric water

moho crustal architecture and deep deformation under the north marmara trough from the seismarmara leg 1 offshore onshore reflection refraction survey abstract understanding further the nature and evolution at lithospheric scale of the sea of marmara on the north anatolian fault needs constraints on the deep crustal and moho spatial variation this has been probed here with offshore onshore and obs ocean bottom seismometer refraction seismics in addition to coincident mcs marine multichannel reflection seismic profiles over the whole north marmara trough the diverse strikes of mcs profiles in a dense grid allow to avoid misinterpretation of late echoes in the deep basin as moho reflections and attribute them to sidesweeps moho is instead positively identified from reversed observations of first arrival head and refracted waves at the top of the mantle obtained at large offset by land stations a significant and sharp reduction in its depth on the order of 5 km occurs beneath both the eastern and western rims of the north marmara trough with a more progressive crustal thinning from the south the wide angle reflections on obs and land stations document in addition to moho the top of a lower crustal reflective layer which is also sampled by mcs profiles and appears to follow moho topography the dense grid of mcs profiles along the southwestern margin of the north marmara trough reveals a dipping reflector through the upper crust with tilted basement blocks on top this low angle fault is suggested as a normal sense detachment extending in depth towards the reflective lower crust the upwarp of the moho and lower crustal layer towards the north marmara trough suggests that crustal thinning occurs mostly in the upper crustal part with lateral transport of the material towards wsw in the footwall of the detachment and possibly other features to the south in the motion of anatolia with respect to stable eurasia oblique to the north marmara trough thinning can be accommodated in an asymmetric partitioning of the displacement on several branching faults at lithospheric scale

a first coincident normal incidence and wide angle approach to studying the extending aegean crust abstract the aegean sea is a broad area of submerged continental crust undergoing active extension to varying degrees a combined near normal incidence and wide angle seismic recording programme was conducted in the western aegean sea in 1993 with the principal objective of testing the popular hypothesis that lower crustal deformation particularily extension is expressed as a seismically layered lower crust llc across the southern margin of the cretan trough i e north cretan offshore margin a llc was indicated by wide angle arrivals that was not apparent on either the coincident near normal in cidence profile or on older low frequency refraction records north of the northern margin of the cretan trough beneath the cyclades a domain of strong reflectivity is recorded from the middle to lower crust here the near normal incidence sections also show this typical llc reflectivity on the wide angle sections a distinct interface is suggested in addition at a larger depth than that previously assumed for the moho discontinuity the structural images and interpretations derived from the new seismic data so far do not clearly support either a pure shear crustal stretching or an asymmetric simple shear extension model for the aegean sea our results appear to be consistent with a tectonic model where middle crust mobilised by flow coincides spatially with upper crust that has been thinned by active extension of an orogenically thickened crust and expressed near the surface as an exhumed metamorphic core complex

two ship deep seismic soundings in the basins of the eastern mediterranean sea pasiphae cruise summary new results from a two ship refraction and oblique reflection deep seismic cruise are presented to discuss the nature of the crust in the ionian sirte and herodotus abyssal plains these expanding spread profiles were processed and analysed in both the x t and p domains arrival times of reflected and refracted branches are matched by ray tracing in both domains in spite of a shallow evaporitic sequence messinian evaporites deposited on top of a thick sedimentary pile responsible for velocity inversions on many profiles we obtain excellent velocity control down to moho depth pmp and pn 8 4 8 6 km s 1 arrivals are observed the three basins have a relatively thin crust 8 to 11 km overlain by a thick sedimentary cover up to 10km in the herodotus abyssal plain the moho boundary and main crustal units identified in the basins can be followed beneath the calabrian prism to the west and beneath the mediterranean ridge to the east the crustal structure is of oceanic type for both the ionian and sirte basins where typical oceanic layer 2 and 3 are recognized the thin crust of the herodotus basin may be interpreted either as oceanic or thinned continental crust about 10 km thick the top of the crust of the herodotus basin is much deeper therefore the herodotus basin is probably significantly older than the ionian basin triassic versus early cretaceous in age

crustal image of the ionian basin and its calabrian margins abstract previous seismic investigation of the crustal structure in the ionian basin has been limited to shallow penetration seismics of the 1970 s characterized by inadequate source power and low fold earlier obs and esp seismic refraction experiments have not been able to firmly resolve one of the principal scientific problems for this region which is whether the ionian basin is floored by oceanic crust or by highly attenuated continental crust a second elusive problem is the nature of the transition of the boundaries between the ionian basin and its margins in this paper we describe and interpret new deep seismic reflection and wide angle data collected in the western ionian sea and the calabria region of italy one of the principal features of our multichannel reflection data beneath the ionian basin is a band of layered high amplitude reflections near the base of the crust this band shows a quasi monochromatic ca 8 to 10 hz frequency and a traveltime thickness of 1 to 1 5 s these images contrast with the well known reflection patterns of mesozoic oceanic crust investigated in the atlantic ocean there is evidence that the low frequency band dips down towards the edge of the malta escarpment me where landward dipping reflectors separate continental and intermediate type crust in the central tract of the me the increased traveltimes of the lower crustal reflectors and moho from the basin towards the southern and eastern margins of southern calabria could be partially due to the velocity pull down effect of the sedimentary pile of the arc although a true dip of 15 to 18 over 60 km distance can be substantiated moreover the reflecting band maintains its reflectivity and thickness until its abrupt termination beneath the ionian continuation of the calabrian compressional crustal structures the coincident acquisition of wide angle seismic data and marine reflection seismic data provided a landward extension of the survey which will complement existing geologic information on the deep framework of the ionian basin and its calabrian margin

crustal velocity structure of the lucky strike segment of the mid atlantic ridge at 37 n from seismic refraction measurements we estimate the seismic structure of the slow spreading lucky strike segment of the mid atlantic ridge located approximately 300 km south of the azores platform using seismic reflection and seismic refraction data acquired in june 2005 as a part of the seismic study for monitoring of the mid atlantic ridge sismomar survey the three dimensional velocity model shows an upper crustal low velocity anomaly running parallel to the ridge axis which is limited by the median valley bounding faults the velocity models also show a low velocity anomaly underlying the axial melt lens reflector located at the segment center below the lucky strike volcano this lower crustal low velocity region can be explained by elevated temperatures and possibly small amounts of melt the lower crustal low velocity anomaly and the axial melt lens reflector constrain the geometry of the magma chamber responsible for the construction of the lucky strike volcano the presence of this magma chamber and thick crust at the segment center are consistent with a focused melt supply to the segment center

late quaternary changes in climate and land cover in the northern horn of africa and adjacent areas abstract most studies of landscape dynamics in the ethiopian highlands offer linear relations of population pressure and periodic droughts as causes of environmental degradation such views rely on limited historical information of one or two centuries which is inadequate for understanding the longer term effects of climatic shifts on landscape dynamics and environmental change in the highlands in this study we conducted a meta analysis of long term climate and biogeographic change and landscape dynamics during the holocene using multi proxy evidence from lacustrine n 10 marine n 5 geomorphic n 13 and vegetation n 7 records from the highlands and the wider horn of africa and western indian ocean region based on the datasets we discern late pleistocene dry phases in the region during the last glacial maximum the heinrich 1 event and the younger dryas additionally we recognize at least six dry phases during the holocene after 6500 bce 4900 bce 3700 bce 1000 bce 450 ce and 1750 ce the hydroclimatic shifts seem associated with changing equatorial atlantic and western indian ocean sea surface temperatures further the results show nonlinear relations between major holocene climate shifts and grassland expansions in the highlands our findings challenge conventional cause effect explanations of human population growth and land degradation and point instead to potentially strong but unexplored feedbacks between climate changes human activity and landscape dynamics over longer and short term periods

reflection refraction seismics in the gulf of corinth hints at deep structure and control of the deep marine basin abstract the gulf of corinth is a natural laboratory for the study of seismicity and crustal deformation during continental extension seismic profiling along its axis provides a 24 fold normal incidence seismic reflection profile and wide angle reflection refraction profiles recorded by sea bottom seismometers obs and land seismometers at wide angle incidence the land receivers document the moho at 40 km depth under the western end of the gulf north of aigion rising to 32 km depth under the northern coast in the east of the gulf both refraction and normal incidence reflection sections image the basement under the deep marine basin that has formed by recent extension the depth to the base of the sedimentary basin beneath the gulf constrained by both methods is no more than 2 7 km with 1 km of water underlain by no more than 1 7 km of sediment less than what was expected from past modeling of uplift of the south coast in the east of the gulf unlike the flat sea bottom the basement and sedimentary interfaces show topography along this axial line several deeps are identified as depocenters which suggest that this axial line is not a strike line to the basin it appears instead to be controlled by several faults oblique to the s60 e overall trend of the south coast of the gulf their more easterly strikes being consistent with the instantaneous direction of extension measured by earthquake slip vectors and by gps

a miocene tectonic inversion in the ionian sea central mediterranean evidence from multichannel seismic data it is widely accepted that the central and eastern mediterranean are remnants of the neo tethys however the orientation and timing of spreading of this domain remain controversial here we present time migrated and pre stack depth migrated nw se oriented archimede 1997 lines together with the prismed01 1993 profile to constrain the evolution of the ionian basin our interpretation allows us to identify a large scale set of sw ne striking reverse faults beneath the ionian abyssal plain these primarily nw vergent faults are characterized by a spacing comprised between 10 to 20 km and a dip ranging from 60 to 65 degree sign following very recent paleogeographic reconstructions we propose that the set of n degree sign 55 features initially formed as normal faults during the nw se trending seafloor spreading of the ionian basin after its late triassic early jurassic rifting based on geometric comparisons with the intraplate deformation observed beneath the central indian ocean we show that the inherited oceanic normal faults were reactivated under compression as reverse faults well developed tortonian syntectonic basins developed nw of the major faults and the base of the messinian evaporites mobile unit is slightly folded by the activity of the faults we show that 3 4 km of total shortening occurs over a 80 km wide area beneath the ionian abyssal plain resulting in a bulk shortening of 3 5 5 we propose a link between the tortonian early messinian inversion of the fault pattern and a plate tectonic reorganization prior to the main phase of back arc opening of the tyrrhenian domain