seismic imaging of subduction zone metamorphism combined analysis of high resolution seismic images of the alaska and cascadia subduction zones reveals where metamorphic fl uids are released both images show the subducted oceanic crust as a dipping low velocity layer with a clear termination depth however in alaska the crust is thicker 15 20 km compared to 8 km and terminates at greater depth 120 km com pared to 40 km than in cascadia based on metamorphic reaction estimates and geodynamic models we demonstrate that the termination depth corresponds to eclogitization of the crust triggered by dehydration of water bearing minerals and that the location of this reaction is dependent on the thermal structure of the subducted slab

seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing water and hydrous minerals play a key role in geodynamic processes at subduction zones however there are few seismological constraints on the presence of water within the subducting plate audet et al model converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle their observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip this study models converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle the observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip water and hydrous minerals play a key part in geodynamic processes at subduction zones1 2 3 by weakening the plate boundary aiding slip and permitting subduction and indeed plate tectonics to occur4 the seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization5 6 7 however seismological observations bearing on the presence of water within the subducting plate itself are less well documented here we use converted teleseismic waves to obtain observations of anomalously high poisson s ratios within the subducted oceanic crust from the cascadia continental margin to its intersection with forearc mantle on the basis of pressure temperature and compositional considerations the elevated poisson s ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values combined with observations of a strong negative velocity contrast at the top of the oceanic crust our results imply that the megathrust is a low permeability boundary the transition from a low to high permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization these results may have important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip

growth faults and fault related structures of prograding terrigenous clastic continental margins abstract growth faults are the structural manifestation of the inherent tensional stress regime that is focused at the upwardly convex margin of a prograding continental platform extension and faulting may be triggered by either gravitational gliding or spreading extensional faulting results in both lateral translation and subsidence of the down faulted sediment mass consequently outer platform and upper slope facies are expanded and disproportionately preserved relative to paralic or deep water facies specific growth fault geometries and patterns are related in part to the depositional history and style of the prograding margin unusually continuous and low angle master faults are proposed to result from a history of rapid progradation of a deltaic depocenter onto an older retrograditional slope growth fault zones function as major conduits for large scale circulation of both ground waters and hydrocarbon fluids within the sedimentary prism

imaging crustal discontinuities and the downgoing slab beneath western crete the migration of teleseismic receiver functions yields high resolution images of the crustal structure of western crete data were collected during two field campaigns in 1996 and 1997 by networks of six and 47 short period three component seismic stations respectively a total of 1288 seismograms from 97 teleseismic events were restituted to true ground displacement within a period range from 0 5 to 7 s the application of a noise adaptive deconvolution filter and a new polarization analysis technique helped to overcome problems with local coda and noise conditions the computation and migration of receiver functions results in images of local crustal structures with unprecedented spatial resolution for this region the crust under crete consists of a continental top layer of 15 20 km thickness above a 20 30 km thick subducted fossil accretionary wedge with a characteristic en echelon fault sequence the downgoing oceanic moho lies at a depth of 40 60 km and shows a topography or undulation with an amplitude of several kilometres as a consequence of slab depth and distribution of local seismicity the mediterranean ridge is interpreted as the recent accretionary wedge

crustal strain in central greece from repeated gps measurements in the interval 1989 1997 summary a 66 station gps network spanning central greece first observed in 1989 has been occupied fully on three occasions june 1989 october 1991 and may 1993 subsets of this network bounding the gulf of korinthos have also been occupied in june 1995 october 1995 may 1996 and september october 1997 the first three occupations were processed using a fiducial gps methodology whereas later surveys were processed using code precise orbits combination of data from different surveys to yield smooth site velocities requires global network translations at each epoch to compensate for errors in the realization of the reference frame this method provides a posteriori estimates of the relative coordinate errors and reference frame noise only one earthquake the 1995 june 15 egion event has caused significant local coseismic displacement and its effects on the interseismic velocity field are removed using an elastic dislocation model we constrain the orientation of the 100 yr triangulation gps velocity estimates of davies et al 1997 using 14 sites common to the two networks the goodness of fit of this transformation indicates that the short term and 100 yr geodetic estimates of deformation are highly compatible we infer that short term geodetic studies are capable of determining longer term deformation rates provided that transient local effects can be modelled from the combined velocity field we estimate principal strains and rigid body rotation rates at points on a regular grid using data from neighbouring sites strain rates are high within the gulf of korinthos and much lower elsewhere the extension rate across the gulf of korinthos increases from east to west comparison of the extension rate with historical and recent rates of seismic release of strain reveals significant medium term seismic hazard in the western gulf of korinthos and may also indicate long term aseismic strain

delay times and shear wave splitting in the mediterranean region summary we measure sks splitting parameters and p and s delay times in the mediterranean region using broad band recordings from the temporary midsea array and permanent networks the midsea seismic array has substantially improved data coverage along the european mediterranean margins and in northern africa shear wave splitting is observed for 95 per cent of the stations with splitting times up to 2 s we propose five anisotropic domains based on the characteristics of the observations in the western part of the region we observe an alignment with plate motion suggesting an asthenospheric origin for anisotropy in the central and near eastern part the fast directions are less coherent laterally and influenced by extension and subduction processes along the dead sea fault the fast directions are parallel to the relative motion between arabia and africa which we attribute in part to coherent vertical deformation our measurements of teleseismic relative p and s wave delay times within the mediterranean region reach peak to peak values of 2 5 and 8 s respectively consistent with international seismological centre isc delay times we observe the earliest arrivals along the hellenic subduction zone and some of the latest along the dead sea fault we find that s wave delays are roughly three times as large as those of p waves from a slight frequency dependence of our cross correlation based delay time measurements we estimate mediterranean lateral heterogeneity to have a dominant size of one or more hundred kilometres we further determine that the anisotropy implied by our sks splitting measurements does not significantly bias the pattern of teleseismic delay times

multiparameter two dimensional inversion of scattered teleseismic body waves 3 application to the cascadia 1993 data set this is the third paper in a three part series that examines formal inversion of the teleseismic p wave coda for discontinuous two dimensional 2 d variations in elastic properties beneath dense arrays of three component broadband seismometers in this paper the method is applied to data from the incorporated research institutions for seismology program for array seismic studies of the continental lithosphere iris passcal cascadia 1993 experiment undertaken across central oregon two major features are imaged in the resulting model the continental moho becomes evident 150 km from the coast beneath the western cascades and extends through the eastern end of the profile at 35 40 km depth in the western portion of the model oceanic crust of the subducting juan de fuca plate dips shallowly 12 at the coast and more steeply 27 below the willamette valley and is evident to depths of 100 km beneath the high cascades the abrupt increase in plate dip at 40 km depth coincides with an apparent thickening of the oceanic crust followed by a diminution in its signature building on previous work we argue that these results are consistent with the consequences of prograde metamorphic reactions occurring within the oceanic crust progressive dehydration at lower grade facies conditions culminates in the transformation to eclogite producing a pronounced increase in the seismic velocity density and dip of the subducting plate and structural complexity in the overlying wedge

miocene chronostratigraphy paleogeography and play framework of the burgos basin southern gulf of mexico this study characterizes miocene chronostratigraphy and plays in the burgos basin and adjacent south texas within an area of approximately 39 700 km2 15 300 mi2 onshore and offshore to the 500 m 1640 ft isobath using greater than 40 000 linear kilometers 25 000 mi of two dimensional seismic lines 115 onshore wells 9 offshore wells and paleontological data we established a correlation framework of 9 key surfaces upper oligocene to lower pliocene representing major probably third order sequence boundaries and maximum flooding surfaces throughout the basin five of the burgos miocene surfaces coincide with regional chronostratigraphic surfaces from the veracruz and laguna madre tuxpan basins thus establishing a consistent correlation framework throughout much of the mexican gulf coast basin twenty miocene plays are defined by four age divisions lower miocene middle miocene upper miocene 1 and upper miocene 2 and four paleogeographic settings unexpanded and expanded shelf proximal slope and distal slope because of proven high productivity in salt bounded basins in the northern gulf of mexico the onlap of strata onto diapirs in the eastern burgos salt province was evaluated as a fifth setting the paleogeographic provinces and onlap areas exhibit characteristic seismic facies stratal geometries and structural relations a characterization of each one of these being key to the overall play evaluation this play framework provides the means for continuing exploration of miocene strata and evaluation of key play elements reservoir presence and quality seal trap source and migration and timing in this structurally complex underexplored basin the relative importance of these play elements varies systematically for each play especially between the onshore shelf plays and the offshore deep water plays where fault complexity and stratigraphic variability are greater

aegean crustal thickness inferred from gravity inversion geodynamical implications since oligo miocene times the aegean domain has undergone regional extension due to the southward retreat of the hellenic subduction zone boundary conditions have been more recently modified by the westward extrusion of anatolia a new map of the aegean crustal thickness inferred from gravity inversion is proposed here to better constrain the variations in space and time of crustal thinning that has accumulated since oligo miocene times moho topography is obtained by inversion of satellite marine gravity data data are first corrected for terrain anomalies and deep mantle effects african subducting slab they are then filtered between 50 and 300 km to avoid short wavelength intracrustal effects results are consistent with previous 2d geophysical studies seismic refraction receiver functions and show that an overall regional isostatic compensation of the crust holds for the aegean area with a mean crustal thickness of 25 km three different provinces north aegean cyclades and cretan sea can be identified thinner crust is observed both in the north aegean region ne sw trending of thinning with crustal thickness lower than 24 km and in the cretan sea crustal thickness of 22 23 km between these two regions the cyclades are marked by a rather flat moho at 25 km a two stage model of the aegean extension could well explain the observed crustal thickness variation from oligocene to middle miocene gravitational collapse of the hellenides due to the southward retreat of the african slab reduced the aegean continental crust from 50 km by reference to continental greece and anatolia to a mean value of 25 km at the scale of the whole aegean from upper miocene to present the westward extrusion of anatolia modified the extension and the associated crustal thinning in the north aegean domain during this second episode crustal thinning related to the southward retreat of the african slab tends to localize in the cretan sea the cyclades likely behave as a rigid block translated toward the south west without significant deformation in agreement with the gps velocity field and the lack of major earthquakes d 2004 elsevier b v all rights reserved

multiparameter two dimensional inversion of scattered teleseismic body waves 2 numerical examples in this paper we investigate the formal inversion of synthetic teleseismic p coda waves for subsurface elastic properties using a ray theoretic approach which assumes single scattering bostock et al this issue we consider a model comprising an idealized lithospheric suture zone whose geometrical configuration is drawn from previous deep crustal seismic studies two dimensional pseudospectral synthetic seismograms representing plane waves propagating through this model are preprocessed to extract an estimate of the scattered wave field generated by short wavelength structure these data are employed in a series of numerical simulations which examine the dependence of multiparameter inversion results on a range of input parameters in particular we demonstrate 1 the contrasting sensitivity which forward and backscattered waves display to structural recovery 2 the diminution of the problem null space accompanied by increased source coverage 3 improvements in model reconstruction achieved through simultaneous treatment of multiple scattering modes and 4 the robustness of the method for data sets with noise levels and receiver geometries that approach those of field experiments

correlated shear and bulk moduli to 1400 km beneath the mediterranean region we present a new model for the shear and compressional wave velocity structure of the mediterranean plate boundary region the model is obtained by a combined inversion of s and p data where we solve in one single step for shear wave and bulk sound velocity variations the ratios between the types of seismic velocities inferred from the combined inversion constrain the origin of heterogeneity our model is dominated by fast anomalies from subducted oceanic lithosphere we found that only a slight amount of bulk sound velocity heterogeneity is required to explain the combined set of p and s data thus compressional wave velocity anomalies are dominated by shear modulus heterogeneity and the ratio between bulk sound and shear wave velocity heterogeneity suggests a predominantly thermal origin 2006 elsevier b v all rights reserved

recommendations for a uniform chronostratigraphic designation system for phanerozoic depositional sequences many published sequence stratigraphic frameworks lack a systematic and consistent designation for both depositional sequences and key surfaces despite the original goal to provide a fully integrated stratigraphic architecture including diagnostic age information based on a system in use for more than 10 yr at exxonmobil we recommend methodologies for a chronostratigraphic designation system cds using more uniform and robust sequence stratigraphic designations after objectively defining important physical stratigraphic surfaces biostratigraphic and other age constraining information is used to designate surfaces and the packages of rocks they bound this leads to the establishment of a sequence chronostratigraphic framework for a local area of investigation outcrop section field region or basin only after demonstrating clear well documented ties to phanerozoic global coastal onlaps or cycle charts are these sequences and associated surfaces considered as global entities and designated as such higher frequency sequences and surfaces are also accommodated in this cds alternative designations for areas with limited or poor quality chronostratigraphic information are also discussed the cds has proven to have great use in all phanerozoic strata different tectonic settings and depositional environments especially when chronostratigraphic age constraints are robust we have used this system at regional and basinal scales in many geographic locations to help reduce uncertainty in identifying and correlating reservoirs sources and seal rocks predicting the local distribution and quality of reservoirs as well as seals within a producing field and near field wildcats is also facilitated by this system this system has demonstrated use in the correlation of outcrop sections within a basin or between basins rigorous use of the cds proposed here will permit meaningful regional and or interbasinal correlation that is difficult to carry out with the diverse systems currently in use this uniform designation scheme will also facilitate communication within a company and between institutions as well as among academic investigators

objective regionalization of rayleigh wave dispersion data by clustering algorithms an application to the mediterranean basin abstract the main target of the present study is an objective and automated regionalization of rayleigh wave dispersion data for the mediterranean basin without a priori seismotectonic constraints and to determine the corresponding regional shear velocity structures the database used is formed by almost 200 rayleigh wavetrains corresponding to 42 regional events with surface wave magnitude greater than 4 5 recorded at the mednet very broad band stations in the mediterranean area path averaged group velocities for the rayleigh wave fundamental mode are derived for each available epicentre station trajectory crossing the mediterranean basin after this a principal component analysis and a clustering process are applied to local group velocities obtained for 13 different periods from 10 to 70 s in order to classify the mediterranean basin into several homogeneous regions the stochastic inversion of the averaged group velocity dispersion curve obtained for each region provides the respective shear velocity structures down to a depth of 150 160 km the characteristics of these areas and their possible correlation with the main seismotectonic features of the mediterranean region are discussed the regional models reveal significant lateral changes in the elastic structure with the main differences concerning particularly the upper 35 40 km within this depth range low shear velocities varying from 2 8 to 3 9 km s 1 characterize the eastern mediterranean whereas higher velocities ranging from 3 0 to 4 2 km s 1 are deduced for the western mediterranean these results suggest a thicker crust in the eastern part but with a greater thickness of sedimentary layers however for depths of between 80 and 110 km lower shear velocities are obtained in the western part while higher shear velocities are derived for the eastern mediterranean sea in the aegean sea greece the south of italy sicily and tunisia this velocity pattern suggests an averaged thicker lithosphere under the latter areas as the top of the asthenosphere is detected at a mean depth of 75 km for the remaining regions this thicker lithosphere can be related to processes associated with the convergence of the eurasian and african plates and subduction under the calabrian and hellenic arcs

crustal investigation of the hellenic subduction zone using wide aperture seismic data abstract we present the results of a wide aperture seismic onshore offshore study crete seismic experiment in the cretan region as part of the hellenic arc compressional system three seismic lines were carried out on and around the island of crete in order to investigate the crustal structure of the region up to 119 three component recording stations were deployed on each profile that observed seismic energy generated by a 48 l airgun array and eight 20 kg landshots a total of 6208 shots were fired upon completing the fieldwork the vertical components of all stations were evaluated 300 common receiver gather crg sections of the ocean bottom seismographs obs and land stations as well as 100 common source gather csg sections of the land shots and selected airgun shots were compiled and modeled in order to generate a 2d p wave velocity depth model for each profile the accuracy of the model depends on the depth and position along the profiles and does not exceed 5 for both depth and p wave velocity we identified strong lateral variations in crustal and sedimentary thickness mainly in a north south direction but also along strike east west the crust is continental and has a maximum thickness of 32 5 km below northern central crete its subdivision in an upper v p 5 8 6 3 km s locally up to 6 5 km s and a lower v p 6 4 6 9 km s part is justified by a first order discontinuity with v p velocity a contrast of up to 0 6 km s the eastern part of crete shows a significantly thinner crust of 24 to 26 km to the north the crustal thickness decreases to 15 km below the central cretan sea the prominent decrease of the moho depth north of central crete is interpreted to represent the northern end of a microcontinent that was subducted in oligocene times and later surfaced by buoyant escape stockhert et al 1999 thomson et al 1999 the p t t d history of the high pressure rocks of crete greece denudation by buoyant escape in exhumation processes normal faulting ductile flow and erosion ring u lister g willet s brandon m eds spec publ of the geol soc of london p 154 to the south and southwest of the island the continental crust gradually thins to a minimum of 17 km and at approximately 100 km off the southern coast of crete it is in contact with oceanic crust below the mediterranean ridge upper mantle velocities were determined to be 7 7 km s below the cretan sea and 8 0 km s south of crete below the continental cretan crust a 6 to 7 km thick layer with v p velocities between 6 6 and 7 1 km s was identified on each line and could be followed by reflections to a depth of 42 km it is decoupled from the overlying continental crust at central crete and is interpreted as oceanic crust presently under subduction towards the nne below the aegean sea

relationships between dynamically recrystallized grain size and deformation conditions in experimentally deformed olivine rocks new microstructural data on experimentally deformed wet and dry natural olivine rocks anita bay and aheim dunite together with the other reliable experimental data indicate that the experimental stress recrystallized grain size relationship in olivine rocks is largely independent of water content and temperature and is only slightly dependent on the flow properties of the material the experimental data cover a stress range of 30 300 mpa water contents from 30 ppm to 300 ppm and temperatures in the range 1100 1650 c local melt contents of up to 10 volume cannot be demonstrated to have a significant effect on the stress grain size relationship

variations in the crustal structure beneath western turkey summary we use teleseismic receiver functions to investigate the crustal structure at two locations in westernturkey using seismic data recorded on small arrays of temporary broad band seismographs the results from these analyses are compared with receiver function results from the gdsn station anto on the anatolian plateau in central turkey the crust is 30 km thick in the region of western turkey where active normal faulting reveals present day extension in the upper crust and alkali basaltic volcanism reveals recent extension within the subcrustal lithosphere the crust is 34 km thick further east where crustal extension is still evident but less pronounced in the anatolian plateau which is not currently extending the crust is 38 km thick the level of extension estimated from these measurements of crustal thickness implies a b factor of 1 2 this value agrees with the amount of extension estimated in the upper crust from the integrated seismic strain rate b factor of 1 3 from surface faulting b factor of 1 25 and from the amount of extension in the subcrustal lithosphere estimated from the volcanism b factor 2 all indicating that the extension is approximately uniformly distributed vertically throughout the lithosphere the moho transition in this region appears to thin slightly as the degree of extension increases westwards

the cretaceous sedimentary history of the pindos basin greece the cretaceous sedimentary rocks of the pindos zone in western greece document the evolution of a tethyan deep water basin new sedimentological and micropalaeontological studies reveal a complex basin history siliceous sediments with abundant radiolaria and organic rich facies prevailed up to the early late cretaceous within the sediment starved pre middle cenomanian marked black shale levels appear that are probably linked to oceanic anoxic events at the change from the late early to the early middle cenomanian the sedimentary regime altered abruptly the early late cretaceous is characterized by major calcareous redepositional events orbitoline horizons and often associated siliciclastic turbidite deposition submarine fan environments in the late late cretaceous carbonate supply increased rapidly resulting in the evolution of a carbonate slope and basin plain setting pelagic and allodapic limestones recorded basinwide blooms in planktonic foraminifera elevata event and a polyphase redepositional history that is interpreted to reflect the sensitivity of the basin to the tectonic evolution of apulia

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

p and s deep velocity structure of the hellenic area obtained by robust nonlinear inversion of travel times we derived a new model for the p and s velocity structure of the lithosphere in the subduction area of the hellenic arc and the aegean sea from the inversion of travel times of local events the inversion technique applied is nonlinear since three dimensional ray tracing is incorporated at the same time an appropriate preconditioning of the final linearized system is used in order to reduce ray density effects on the results the p s coherency is controlled by an additional damping of the vp vs ratio the study focuses mainly on the structure of the hellenic subduction in the southern aegean region interesting features and details of the subducted slab can be recognized in the final tomographic images on the western part the shallower section of the slab is dipping at a very small angle 10 this changes to approximately 25 for the deeper part of the subduction resulting in a prominent kink at a depth of about 70 km which is in accordance with the general characteristics of the associated benioff zone the smaller eastern part of the slab is not resolved with the same detail but a clearly steeper subduction zone can be recognized moreover detailed information about the crustal thickness variations are inferred from the velocity structure and correlate very well with the existing results from refraction experiments finally the results confirm the recent suggestion concerning the existence of a low velocity crustal layer at shallow depths 10 15 km in the accretionary prism of the alpine belt

the role of slab detachment processes in the opening of the western central mediterranean basins some geological and geophysical evidence abstract a review of the geological and geophysical data from the central and western mediterranean region and the present day upper mantle structure derived from tomographic studies are utilized in order to define the oligocene recent geodynamic evolution for the area in line with previous work we suggest that the miocene quaternary opening of the western and central mediterranean basins is the result of back arc extension due to the roll back toward the southeast of a northwestward subducting african slab in a geodynamic setting pinned between the alpine and betic collisional zones we find however that this general pattern is complicated by four different detachment events which occurred beneath the alps early oligocene the betic chain aquitanian northern africa langhian and the apennines late miocene pliocene we show that each of these events determines a major tectonic reorganization within the european plate

moho topography under central greece and its compensation by pn time terms for the accurate location of hypocenters the example of the gulf of corinth 1995 aigion earthquake abstract in this paper we expand over the whole of central greece the moho map centered on the gulf of corinth from tomographic inversion of pmp traveltime profile data recorded by several tens of temporary stations our approach is based on pn moho refracted waves from a large regional earthquake recorded by both temporary stations and the permanent hellenic network the moho map shows the large moho depth under the hellenides belt it also highlights the shallower moho domain towards the aegean sea south and east of the corinth gulf the domain of shallow moho is limited along a ne sw prolongation ahead of the north anatolian fault from the north aegean trough to the western tip of the gulf of corinth towards the gulf of patras the pn time terms provide corrections for the permanent stations that can be used together with the 1d velocity depth model for a first order compensation of lateral heterogeneity and contribute to the accurate and fast location of earthquake hypocenters as a test we relocated the 1995 aigion earthquake in this way using only the sparse data of the permanent stations hypocentral coordinates then shift close to those derived by a dedicated dense array deployed after the earthquake implying improvement of the routine location

high resolution seismic imaging of the western hellenic subduction zone using teleseismic scattered waves summary the active hellenic subduction system has long been considered an ideal setting for studying subduction dynamics because it is easily accessible and of limited spatial extent it has been the focus of numerous seismological studies over the last few decades but nonetheless the detailed structure of both the slab and the surrounding mantle remain poorly constrained in an intermediate depth range from 30 to 150 km the objective of this paper is to fill this gap the intermediate depth regime is of particular interest because it is pivotal for improving our understanding of the dynamic interaction between subducting lithosphere and the surrounding mantle an interdisciplinary effort aimed at addressing this challenge is currently undertaken by the multidisciplinary experiments for dynamic understanding of subduction under the aegean sea medusa project as part of the medusa initiative a temporary array consisting of 40 densely spaced broad band seismometers from the iris passcal pool has been deployed in southern greece we process the teleseismic data recorded by this array with a migration algorithm based on the generalized radon transform to obtain high resolution images of the subduction zone in 2 d the images reveal a sharp mohoroviy discontinuity moho at depths ranging from 30 km beneath the western margin of the aegean sea to 40 km beneath the central peloponnesus where it outlines the crustal root of the hellenides to the west of the hellenides the continental moho is not identified but we interpret a pronounced discontinuity imaged at 20 km depth as the contact between low velocity sediments and high velocity crystalline basement the images also show the subducted oceanic crust as a low velocity layer that plunges at a constant angle of 21 from west to east the oceanic crust exhibits low velocities to at least 90 km depth indicating that the bulk of fluid transfer from the subducted slab into the mantle wedge occurs below this depth a detailed comparison of images constructed for distinct backazimuthal illuminations reveals deviations in the geometry of the subducted slab these deviations are attributed to structural and or compositional changes taking place directly to the north of the medusa array and are consistent with the existence of a slab tear beneath the central hellenic shear zone

establishment of a continuous gps network across the kephalonia fault zone ionian islands greece abstract we report on the establishment of a continuous gps network across the kephalonia fault zone kfz central ionian islands greece the kfz is an important segment of the boundary zone between the rapidly moving aegean microplate and the apulian platform italy repeated gps measurements carried out between the northern ionian islands and the island of crete have shown rates of crustal motion of the aegean reaching 35 mm a oriented sw relative to southern italy the kfz coincides with a maximum shear strain rate 180 nano strain a and a very high level of seismicity in order to monitor the ongoing deformation across the kfz and correlate the strain accumulation with earthquakes a continuous gps network has been installed operating at a sampling rate of 5 s this paper describes the instrumental set up the data logging strategy and first preliminary results

crustal and upper mantle structure in the eastern mediterranean from the analysis of surface wave dispersion curves summary the dispersive properties of surface waves are used to infer earth structure in the eastern mediterranean region using group velocity maps for rayleigh and love waves from 7 to 100 s we invert for the best 1 d crust and upper mantle structure at a regular series of points assembling the results produces a 3 d lithospheric model along with corresponding maps of sediment and crustal thickness a comparison of our results to other studies finds the uncertainties of the moho estimates to be about 5 km we find thick sediments beneath most of the eastern mediterranean basin in the hellenic subduction zone and the cyprus arc the ionian sea is more characteristic of oceanic crust than the rest of the eastern mediterranean region as demonstrated in particular by the crustal thickness we also find significant crustal thinning in the aegean sea portion of the backarc particularly towards the south notably slower s wave velocities are found in the upper mantle especially in the northern red sea and dead sea rift central turkey and along the subduction zone the low velocities in the upper mantle that span from north africa to crete in the libyan sea might be an indication of serpentinized mantle from the subducting african lithosphere we also find evidence of a strong reverse correlation between sediment and crustal thickness which while previously demonstrated for extensional regions also seems applicable for this convergence zone

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

impact of regional variation in detrital mineral composition on reservoir quality in deep to ultradeep lower miocene sandstones western gulf of mexico abstract future exploration in lower miocene sandstones in the gulf of mexico will focus increasingly at depths greater than 4 5 km and reservoir quality will be a critical risk factor in these deep to ultradeep reservoirs the goal of this study was to understand the variation in reservoir quality of lower miocene sandstones across the western gulf of mexico to do this we examined regional variation in detrital mineral composition diagenesis and reservoir quality in five areas 1 louisiana 2 upper texas coast 3 lower texas coast 4 burgos basin mexico and 5 veracruz basin mexico using petrographic and petrophysical data from depths of 0 9 7 2 km there are strong variations in mineralogical composition within the study area lower miocene sandstones from offshore louisiana have an average composition of quartz 86 feldspar 12 and rock fragments 2 q 86 f 12 r 2 feldspar and rock fragment content increase southward as source areas shifted to include volcanic and carbonate rocks composition of samples from offshore texas ranges from q 67 f 24 r 9 in the upper texas coast to q 58 f 24 r 19 in the lower texas coast lower miocene sandstones from the onshore burgos basin northern mexico have an average composition of q 54 f 22 r 23 whereas sandstones from the veracruz basin southern mexico contain the highest proportion of rock fragments q 33 f 12 r 55 main diagenetic events in quartz rich lower miocene sandstones in louisiana were mechanical compaction and precipitation of quartz cement compactional porosity loss increased to the south with increasing rock fragment content calcite is the most abundant cement in the south and is strongly related to reservoir quality loss at moderate burial depths the best reservoir quality occurs in quartz rich sandstones in louisiana and decreases with increasing lithic content in texas and mexico porosity is higher in louisiana and upper texas than in lower texas and mexico at all depths and temperatures but at depths 5 km and temperatures 175 c porosity differences are lessened the lower miocene sandstone trend in the western gulf of mexico from louisiana to mexico is an example of the importance of variation in detrital mineralogy as a control on diagenesis and reservoir quality

crustal and upper mantle structure beneath the corinth rift greece from a teleseismic tomography study we report here the results of a tomographic lithospheric study in the area of the corinth and evvia rifts greece designed to constrain the mechanism of continental extension sixty seismological stations were deployed in the area for a period of 6 months and 177 teleseismic events were recorded by more than five stations and gave more than 2000 travel time residuals p and pkp phases which were inverted to image the velocity structure down to 200 km depth we use both a linear and a nonlinear method to invert the data set the main result is a long wavelength positive velocity anomaly located in the upper mantle which is interpreted as the subducted african lithosphere the subducted lithosphere is well defined from 7o km depth down to 200 km from synthetic tests as well as from the amplitude of the anomaly more than 7 we conclude that the subduction continues below 200 km in addition a second positive velocity anomaly of about 4 from the surface down to 40 km depth located north of the gulf of corinth has been found this is interpreted as the result of a crustal thinning of several kilometers 5 km shifted to the north from the gulf of corinth and trending obliquily nw se we suggest that this crustal thinning is mainly related to the miocene widespread extension in the aegean and that the quaternary corinth rift initiated where the crust was already thinned the different styles of deformation of the eastern and western part of the rift are consistent with this interpretation no clear velocity anomaly can be related to the evvia rift

high frequency miocene sequence stratigraphy offshore louisiana cycle framework and influence on production distribution in a mature shelf province the regressive miocene succession of offshore louisiana comprises 10 third order sequences and no fewer than 58 fourth order sequences which average approximately 1 1 and 0 19 m y in duration respectively comparable to durations measured in the gulf coast basin and basins worldwide upper lower to middle miocene distal third order sequences comprise mostly lowstand prograding wedge slope fan and basin floor fan deposits in contrast middle to upper miocene medial sequences record progressively more landward systems tracts 1 the lateral transition between on shelf incised valley fills and the proximal parts of basinward thickening lowstand prograding wedges and 2 cyclic on shelf highstand and transgressive systems tracts upper miocene inner shelf and marginal marine systems tracts and more abundant incised valleys dominate the thinner proximal third order sequences this genetic framework has a major influence on hydrocarbon distribution although a strong structural trapping component is present in the fields more than 90 of cumulative production originates where fourth order systems tracts stack to form third order lowstand systems tracts in all 10 third order sequences the development of a high frequency sequence framework for the prolific miocene succession and the discovery that hydrocarbons are pooled within the miocene third order lowstand systems tracts yield a focused model for the development of abundant undiscovered miocene reserves in the mature northern gulf of mexico shelf province

the hellenic subduction zone a tomographic image and its geodynamic implications new tomographic images of the hellenic subduction zone demonstrate slab penetration in the aegean upper mantle to depths of at least 600 km beneath greece the lower part of the slab appears to be detached at a depth of about 200 km whereas it still seems to be unruptured beneath the southern aegean schematically we derive minimum time estimates for the duration of the hellenic subduction zone that range from 26 to 40 ma this is considerably longer than earlier estimates which vary between 5 and about 13 ma

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

seismicity of the hellenic subduction zone in the area of western and central crete observed by temporary local seismic networks temporary local seismic networks were installed in western crete in central crete and on the island gavdos south of western crete respectively in order to image shallow seismically active zones of the hellenic subduction zone more than 4000 events in the magnitude range between 0 5 and 4 8 were detected and localized the resulting three dimensional hypocenter distribution allows the localization of seismically active zones in the area of western and central crete from the mediterranean ridge to the cretan sea furthermore a three dimensional structural model of the studied region was compiled based on results of wide angle seismics surface wave analysis and receiver function studies the comparison of the hypocenter distribution and the structure has allowed intraplate and interplate seismicity to be distinguished high interplate seismicity along the interface between the subducting african lithosphere and the aegean lithosphere was found south of western crete where the interface is located at about 20 to 40 km depth an offset between the southern border of the aegean lithosphere and the southern border of active interplate seismicity is observed in the area of crete the offset varies laterally along the hellenic arc between about 50 and 70 km a southwards dipping zone of high seismicity within the aegean lithosphere is found south of central crete in the region of the ptolemy trench it reaches from the interface between the plates at about 30 km depth towards the surface in comparison the aegean lithosphere south of western crete is seismically much less active including the region of the ionian trench intraplate seismicity within the aegean plate beneath crete and north of crete is confined to the upper about 20 km between 20 and 40 km depth beneath crete the aegean lithosphere appears to be seismically inactive in western crete the southern and western borders of this aseismic zone correlate strongly with the coastline of crete

seismic evidence for deep water transportation in the mantle we report seismic evidence for the transportation of water into the deep mantle in the subduction zone beneath northeastern japan our data indicate that water is released from the hydrated oceanic crust at shallow depths approximately 100 kilometers and then forms a channel of hydrated mantle material on top of the subducting plate that is the pathway for water into the deep mantle our result provides direct evidence that shows how water is transported from the ocean to the deep mantle in a cold subduction zone environment

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km

constraints on the evolution and vertical coherency of deformation in the northern aegean from a comparison of geodetic geologic and seismologic data abstract we study the 3 d strain evolution of the northern aegean and the vertical coherency of deformation we observe that finite strain orientations in the mantle inferred from published shear wave sks fast polarization orientations mid to upper crustal stretching lineations in metamorphic core complexes of mainly miocene age and the gradient in regional crustal thickness variations are subparallel to one another this correlation suggests that the miocene phase of extension is imprinted in the anisotropic fabric i e lattice preferred orientation lpo of the lithospheric mantle and that the orientation of finite strain due to extension is nearly constant with depth the lateral variation of published seismic delay times shows a correlation with laterally varying finite strain in the crust inferred from topography and crustal thickness estimates this correlation suggests that lateral variations in finite crustal and mantle strain are correlated and may point at a pure shear extension mechanism involving the entire lithosphere we also present a new strain rate model for the northern aegean based on global positioning system gps velocities and additional geological constraints no length change orientations calculated from the model near the north anatolian fault naf and north aegean trough are not consistent with anisotropy orientations at depth present day extension orientations are systematically and significantly more n s oriented than the stretching lineations and sks splitting orientations we conclude that the current shear dominated surface deformation pattern is not yet reflected by significant anisotropy in the lithosphere based on some simple calculations we postulate that the present day deformation pattern cannot be older than 4 ma which is consistent with independent arguments on the timing of the propagation of the north anatolian fault into the aegean domain

uppermost mantle velocities and anisotropy beneath europe pn data collected within southern europe and the mediterranean are used to tomographically image variations in both seismic velocity and seismic anisotropy seismic anisotropy is an essential part of the inversion and without it several low velocity features within the uppermost mantle could not be properly imaged the technically active mantle of southern europe has much lower seismic velocities 7 6 8 1 km s than the more stable mantle of the sub african plate of the adriatic sea 8 3 km s however the most dramatic features within europe s uppermost mantle relate to the apennine dinaride and hellenide arcs these arcs all have extremely low 5 amounts of arc parallel anisotropy the tyrrhenian and aegean back arc regions also show low velocities 7 7 7 9 km s but less anisotropy the same may be true for the pannonian basin but the tomography has poorer resolution there a model explaining these observations focuses on subducted water metasomatizing the mantle wedge the addition of water causes melting creates arc volcanism lowers the seismic velocity and enhances the formation of anisotropy due to preferential olivine orientation for collisional arcs of the northern mediterranean arc parallel anisotropy has formed in response to compression across them and extension along them within back arc regions water is no longer a major factor instead convection associated with subduction and back arc extension controls the anisotropy

the kephalonia transform fault and the rotation of the apulian platform evidence from satellite geodesy this paper describes a collaborative gps project to determine recent crustal movements and deformations across the ne ionian sea this region is characterized by rifting in the african foreland pelagian sea subduction along the calabrian and west hellenic arcs rotation of the italian peninsula and distributed normal faulting in central greece from gps campaigns on the ionian islands and in nw greece performed in 1989 and 1991 a kinematic field is deduced which is controlled by the deep trough following the nw coast of kephalonia island it is concluded that this prominent bathymetric feature resembles an active fault system kephalonia fault which has the signature of a right lateral transform fault

3 d structure of the lithosphere in the aegean region summary p wave traveltime residuals from about 300 local and 400 teleseismic earthquakes recorded by the athens seismological network were used to study the structure of the lithosphere in the aegean region teleseismic data included readings from local stations which do not routinely report to the isc the large values of the residuals up to f3 s and their variation with azimuth and epicentral distance indicate significant velocity heterogeneity in the upper mantle p wave traveltime residuals were inverted simultaneously for both local and teleseismic earthquakes tomographic results which are best resolved at lithospheric depths reveal a heterogeneous lithosphere down to a depth of 100km or so a high velocity anomaly is found dipping at an average of 45 to the ne away from the hellenic trench and supports the hypothesis of subduction due to a cooler descending slab of oceanic composition an area of low velocities is observed at depths less than 80 km in the aegean back arc corresponding well with observed high heat flow values in the area in contrast an area of relatively higher velocity anomalies is resolved in the lithosphere underlying the sea of crete the tectonic structure of the crust and upper mantle in the eastern mediterranean area results from the complex interaction of several different geodynamic processes not all of which can be described by simple plate tectonic models at present the eurasian and african plates are converging at a rate of about lcmyr in an approximately n s direction minster jordan 1978 with the latter descending

controls on the evolution of passive margin salt basins structure and evolution of the salina del bravo region northeastern mexico we would like to thank cgg and tgs for permission to use seismic data nancy cottington drafted the diagrams cari breton constructed the geographic information system database eva silverfine ott edited the text the paper was greatly improved by reviews from chris jackson and an anonymous reviewer the project was funded by the applied geodynamics laboratory consortium consisting of the following companies anadarko bhp billiton bp cgg chevron condor ecopetrol emgs eni equinor exxonmobil fieldwood hess ion geophysical midland valley murphy nexen noble petrobras petronas pgs repsol rockfield saudi aramco shell spectrum geo stone talos tgs total west erngeco and woodside additional funding came from the jackson school of geosciences juan i soto also acknowledges the financial support provided by the ministry of education in spain with a salvador de madariaga fellowship publication was authorized by the director of the bureau of economic geology jackson school of geosciences the university of texas at austin

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

lithospheric structure of the aegean obtained from p and s receiver functions combined p and s receiver functions from seismograms of teleseismic events recorded at 65 temporary and permanent stations in the aegean region are used to map the geometry of the subducted african and the overriding aegean plates we image the moho of the subducting african plate at depths ranging from 40 km beneath southern crete and the western peloponnesus to 160 km beneath the volcanic arc and 220 km beneath northern greece however the dip of the moho of the subducting african plate is shallower beneath the peloponnesus than beneath crete and rhodes and flattens out beneath the northern aegean observed p to s conversions at stations located in the forearc indicate a reversed velocity contrast at the moho boundary of the aegean plate whereas this boundary is observed as a normal velocity contrast by the s to p conversions our modeling suggests that the presence of a large amount of serpentinite more than 30 in the forearc mantle wedge which generally occurs in the subduction zones may be the reason for the reverse sign of the p to s conversion coefficient moho depths for the aegean plate show that the southern part of the aegean crustal thickness of 20 22 km has been strongly influenced by extension while the northern aegean sea which at present undergoes the highest crustal deformation shows a relatively thicker crust 25 28 km this may imply a recent initiation of the present kinematics in the aegean western greece crustal thickness of 32 40 km is unaffected by the recent extension but underwent crustal thickening during the hellenides mountains building event the depths of the aegean moho beneath the margin of the peloponnesus and crete 25 28 and 25 33 km respectively show that these areas are also likely to be affected by the aegean extension even though the cyclades crustal thickness of 26 30 km were not significantly involved in this episode the aegean lithosphere asthenosphere boundary lab mapped with s receiver functions is about 150 km deep beneath mainland greece whereas the lab of the subducted african plate dips from 100 km beneath crete and the southern aegean sea to about 225 km under the volcanic arc this implies a thickness of 60 65 km for the subducted african lithosphere suggesting that the aegean lithosphere was not significantly affected by the extensional process associated with the exhumation of metamorphic core complexes in the cyclades

study of the crustal thickness and the subducting lithosphere in greece from gravity data the area of greece has experienced a complex tectonic history dominated by the subduction of the african plate beneath eurasia in this study the variations of the crustal thickness in the area of greece were obtained by means of the multiple source werner deconvolution mswd method applied to gravity data thicknesses of 40 49 km are estimated beneath the hellenides mountain belt to the west eastward thinning of the crust to thicknesses ranging from 25 km in the north to 30 km in the south is seen in the aegean region these results are in good agreement with recent seismological results demonstrating that the mswd method successfully treated the problem using the crustal model we derived we computed the gravity effect of the crust and extracted it from the bouguer anomaly we also extracted the gravity effect of the subducting lithosphere from the bouguer anomaly producing a residual map where most of the original gravity variation has been successfully removed the remaining anomalies appear related to near surface features and an area of low velocity mantle in the central aegean sea

neogene tectonic stratigraphic and play framework of the southern laguna madre tuxpan continental shelf gulf of mexico neogene shelf slope canyon and slope to basin floor transition plays in the southern laguna madre tuxpan lm t continental shelf reflect a variety of structural and stratigraphic controls including gravity sliding and extension compression salt evacuation and lowstand canyon and fan systems the neogene in the lm t area was deposited along narrow shelves associated with a tectonically active coast affected by significant uplift and erosion of carbonate and volcanic terrains this study characterizes 4 structurally defined trends and 32 neogene plays in a more than 50 000 km2 19 300 mi2 area linking the veracruz and burgos basins the caonero trend in the southern part of the lm t area contains deep seated basement faults caused by laramide compression many of these faults are directly linked to the interpreted mesozoic source rocks providing potential pathways for vertically migrating hydrocarbons in contrast the lankahuasa trend north of the caonero trend contains listric faults which detach into a shallow horizon this trend is associated with thick pliocene shelf depocenters the dominant plays in the faja de oro nyade trend in the central part of the lm t area contain thick lower and middle miocene successions of steeply dipping slope deposits reflecting significant uplift and erosion of the carbonate tuxpan platform these slope plays consist of narrow channel fill and levee sandstones encased in siltstones and mudstones plays in the north end of the lm t area in the southern part of the burgos basin contain intensely deformed strata linked to salt and shale diapirism outer shelf slope and proximal basin floor plays in the lamprea trend are internally complex and contain muddy debris flow and slump deposits risk factors and the relative importance of play elements vary greatly among lm t plays reservoir quality is a critical limiting play element in many plays especially those in the caonero trend directly downdip from the trans mexican volcanic belt as well as carbonate rich slope plays adjacent to the tuxpan platform in contrast trap and source are low risk play elements in the lm t area because of the abundance of large three way and four way closures and the widespread distribution of organic rich upper jurassic tithonian age source rock the potential for hydrocarbon migration in lm t plays is a function of the distribution of deep seated faults inferred to intersect the primary mesozoic source their distribution is problematic for the lankahuasa trend where listric faults sole out into the paleocene seal is poorly documented for lm t plays although the presence of overpressured zones and thick bathyal shales is favorable for seal development in middle and lower miocene basin and slope plays

crustal thickness variations in the aegean region and implications for the extension of continental crust 1 we installed 5 broadband and 45 short period temporary seismic stations distributed partly as a dense 100 km long n s linear array and partly as a regional network throughout the menderes massif of western turkey in order to study crust upper mantle structure and seismicity in this study we have combined teleseismic waveform data from these stations with data from several permanent seismic stations to determine crustal thickness variations in the aegean region receiver function studies at seven broadband stations using the h stacking method have yielded crustal thicknesses and vp vs ratios over a broad region of the aegean a more detailed crustal image was obtained in the central menderes massif where we applied common conversion point stacking to receiver functions obtained from the n s linear array the results show a general trend of westward crustal thinning from 36 km in central anatolia to 28 30 km in the central menderes massif to 25 km beneath the aegean sea the results also indicate that crustal thinning in the aegean is not uniform in the n s extensional direction the crust is thinner in the central menderes massif 28 30 km of crustal thicknesses and the cycladic massif 25 26 km than in surrounding regions where crustal thicknesses are 32 34 km the long lived elevated moho under the metamorphic core complexes suggests that the lower crust in the aegean region is at least 3 times more viscous than that in the basin and range province where the moho is much flatter

mid cretaceous onlap history of the market weighton structural high northeast england the mid cretaceous sediments of northeast england were deposited at the western margin of the southern north sea basin with sedimentation occurring in a range of tectonic settings detailed analysis of the areal distribution and sedimentary facies of aptian to earliest cenomanian sediments has allowed the pattern of onlap onto the market weighton structural high and changes in relative sea level to be documented successive onlap episodes during the early aptian late aptian and early albian culminated in the final flooding of the structure during the late albian varicosum subzone sea level curves generated from coastal onlap patterns are difficult to relate to published global sea level curves due to the high frequency of the fluctuations in relative sea level observed despite this detailed correlation and analysis of sedimentological events suggest that even the most expanded basinal succession is relatively incomplete this study has also shown that the change from dominantly syn tectonic to dominantly post tectonic sedimentation style occurred in the late early albian

s velocity structure and radial anisotropy in the aegean region from surface wave dispersion summary the lithospheric structure of the aegean region is investigated by analysis of rayleigh wave fundamental mode dispersion measurements isotropic 1 d models for almost 100 two station ray paths across the region display distinct variations in the moho depth and crustal s wave velocities the descending slab of the subducting african plate can be resolved down to 120 km depth beneath the volcanic arc three different regions are distinguished in terms of moho depth 1 the forearc with large crustal thicknesses between 38 and 48 km and an average of 43 km 2 the northern aegean with an average moho depth of 28 km and 3 the southern aegean central volcanic arc i e cyclades and sea of crete with an even thinner crust of around 25 km lateral variations in structure between 25 and 55 km depth indicate a marked difference between the western and eastern forearc collocated with pronounced changes in trench and slab geometry as well as published deformation rates s velocities between 25 and 55 km depth are low everywhere beneath the forearc but increase from the peleponnesus to crete an abrupt change occurs between western and central crete in terms of the visibility of the aegean moho and the seismic structure of the lithospheric mantle wedge an aegean mantle wedge with s velocities above 4 4 km s 1 is only observed to the east of central crete whereas to the west velocities of less than 4 0 km s 1 occur down to the plate contact these low velocities above the slab may indicate the presence of a melange of metamorphic rocks at the depths a low velocity asthenospheric layer is observed beneath the sea of crete and the cyclades below 40 km depth between the thinned lithosphere above and the slab below the observed radial anisotropy in the northern part of the aegean is likely to be due to preferred orientation of anisotropic minerals within the lower crust possibly caused by lateral ductile flow associated with recent lithospheric extension

high resolution subducting slab structure beneath northern honshu japan revealed by double difference tomography the high resolution seismic velocity structure of the subducting slab beneath northern honshu japan has been obtained by double difference tomography capitalizing on the existence of two planes of seismicity the upper plane lies in the region with average to high vp vs ratios 1 72 1 85 which may correspond to the transformations of metabasalt and metagabbro to blueschist the lower plane is associated with very low vp vs ratios 1 6 1 7 in sharp contrast with high vp vs ratios 1 8 1 85 in the region between the two planes these features may be explained by forsterite enstatite h2o formation from serpentine dehydration in the lower plane and partial hydration of the region between the two planes our results provide direct constraints for petrologic modeling of the subducting slab

structural styles and depositional history of north and south padre island ocs areas offshore south texas abstract north and south padre island ocs areas were studied using 2 d seismic reflection data check shot data well logs and paleontological reports six salt structures occur beneath the present shelf edge shale occurs in over pressured ridges beneath fault footwalls we found that growth faults in the study area are similar in style to that of growth faults in the brazos ocs area however they differ in maximum expansion periods the clemente tomas fault system late oligocene early miocene is located above an over pressured shale ridge the corsair fault system early middle miocene formed due to a large sediment influx that forced salt to withdraw basinward the wanda fault system formed during the late miocene due to further salt withdrawal we defined five depositional sequences from the miocene 18 0 16 3 13 4 10 5 and 6 2 ma nine mini basins are in the study area and they are connected by three main sediments pathways mechanism of the basin formation is controlled by the nature of depocenter shift depocenters formed by salt withdrawal and sediment influx do not shift on the other hand depocenters shift is controlled by fault expansion and sediment influx we generated five stratigraphic cross sections using detailed well log correlation to show the sand andmore shale sequences discontinuities in these sequences are common due to subsidence and the large number of faults in the study area presence of faults and shale bodies may cause formation of structural traps less

active faults deformation rates and quaternary paleogeography at kyparissiakos gulf sw greece deduced from onshore and offshore data abstract kyparissiakos gulf forms a 45 km long zone located at 70 80 km east from the hellenic trench with a general direction nnw sse onshore studies show the existence of several neotectonic horsts and grabens bounded by e w trending normal faults thrust sheets of the underlying hellenides crop out within the horst areas and younger sediments mostly lower pleistocene have been deposited in the grabens the age of the marine sediments is mostly lower pleistocene throw rate on the normal faults varies between 0 7 and 1 0 mm yr accommodating extension in the n s direction subsidence rates during early pleistocene are between 0 1 and 0 3 mm yr whereas uplift rates during middle pleistocene present are between 0 18 and 0 50 mm yr offshore data were obtained using bathymetric and air gun litho seismic profiles the shelf has been disrupted by active faults with several meters of throw average holocene throw rates are 0 4 0 6 mm yr but in some areas adjacent filiatra and olympia values greater than 3 mm yr are detected holocene and upper pleistocene marine sediments thicken gradually to the north as do the marine lower pleistocene sediments onshore a nnw sse offshore longitudinal fault parallel to the kyparissiakos coast with throw rate above 3 mm yr is the dividing structure between the uplifted coastal area and the present day gulf this indicates a major change in paleogeography between early and middle pleistocene present day transition from e w compression in the hellenic trench to e w extension in the kyparissiakos gulf and to n s extension in western peloponnesus is discussed the development of e w structures in western peloponnesus since latest pliocene may be related to the central hellenic shear zone which accommodates differential gps rates between northern greece and southern peloponnesus

the geometry of the wadati benioff zone and lithospheric kinematics in the hellenic arc abstract accurate locations of 961 shallow and intermediate depth earthquakes which occurred between 1956 and 1995 in the hellenic arc 34 39 n 19 28 e are used to define the plate boundaries in this area reliable fault plane solutions for 77 shallow and intermediate depth earthquakes are also used in order to define the interaction between the different plates in the arc an ocean continent type of interaction occurs on a curved surface which is defined by the shallow branch 20 100 km of the wadati benioff zone the intersection of this zone with the earth s surface is a curve which follows the convex outer side of the sedimentary arc western peloponnese west of cythera south coast of crete east coast of rhodes and dips at low angle 30 to the aegean sea coupling between the subducted oceanic crust and the overriding of the aegean lithospheric plate takes place on this surface the deep branch 100 180 km of the wadati benioff zone is dipping freely without coupling at a high angle 45 beneath the south aegean trough and the volcanic arc the high shallow seismicity h 20 km which is observed in the southwestern convex outer side of the arc ionian sea is attributed to the fast southwestward motion of the aegean plate location of strong deep earthquakes h 100 km in the fore arc area of the southwestern part of the hellenic arc west of cythera indicates that oceanic crust is destroyed in this part of the hellenic trench due to roll back of the descending lithospheric slab

unusual mantle poisson s ratio subduction and crustal structure in central alaska 1 subduction zones alter the upper plate in a variety of ways including metasomatism via slab derived fluids and accretion of exotic terranes these processes should produce distinctive seismic signatures as seismic velocities are sensitive to compositional variations a new method is developed to estimates depths to interfaces and poisson s ratio vp vs ratio for dipping layered structures by stacking teleseismic receiver functions it also estimates crustal vp vs and thickness using this method we analyze a broadband data set from the central alaska subduction zone to seek evidence for mantle wedge composition crustal thickness varies from 27 to 45 km and crustal vp vs indicates an intermediate to mafic composition expected for these accreted island arc terranes inversions for mantle structure confirm the presence of a 15 20 km thick low velocity zone atop of the downgoing plate to 130 km depth perhaps subducted crust of an exotic terrane vp vs in the mantle wedge allows for 15 15 serpentinization where the slab is 80 km deep and the wedge is cold where the slab is deeper vp vs for the mantle wedge is unusually low 1 7 this value is lower than predicted for any common mantle mineral and may indicate significant quantities of quartz provided that past physical properties measurements are not grossly in error these results suggest that the mantle wedge in subduction zones can occasionally differ substantially in bulk composition from normal subcrustal mantle perhaps because collisions of exotic terranes cause tectonic mixing of crustal material into the mantle

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

sedimentary geology as a key to understanding the tectonic evolution of the mesozoic early tertiary paikon massif vardar suture zone n greece abstract this paper demonstrates how sedimentary evidence can provide a key to elucidating the regional tectonic and palaeoceanographic significance of a complex partly metamorphic terrane in this case the paikon massif the paikon massif is located centrally within the vardar axios zone of n greece and is critical to the reconstruction of neotethys in the e mediterranean region the massif is here restored as a single tectono stratigraphic unit of jurassic to early tertiary age that originated along the margin of a continental unit known as the serbo macedonian zone in this area a mesozoic oceanic basin the almopias ocean opened in the triassic between the serbo macedonian continent to the ne and another continental unit the pelagonian zone to the sw initial deep water deposition along the northwesterly passive margin of the almopias ocean is represented within the paikon massif by metamorphosed redeposited carbonates and hemipelagic sediments gandatch formation above this the jurassic paikon volcanic group comprises two volcanogenic units of island arc type livadia and kastaneri formations the arc developed along the sw margin of the serbo macedonian continent in response to ne subduction of the almopias ocean the subduction also resulted in the opening of a related back arc basin in mid late jurassic represented by the guevgueli ophiolite now to the ne of the paikon massif the massif underwent ductile deformation and inferred hp lt metamorphism during late jurassic time related to subduction beneath the serbo macedonian active margin exhumation took place rapidly by kimmeridgian time followed by a shallow water transgression khromni limestones subsequent emergence and fluvial deposition ghrammos formation reflect a regional extensional or transtensional event following a marine transgression influenced by eustatic sea level rise and tectonic subsidence aptian albian a carbonate platform developed throughout the paikon massif cretaceous transgressive limestones short lived emergence turonian was followed by deepening in the campanian maastrichtian and pelagic carbonate deposition buff pelagic carbonates overlying terrigenous turbidites tchouka flysch form part of an early tertiary foredeep in a regional contractional setting late stage shortening resulted in bivergent thrusting and folding to form the paikon massif as a large anticlinal pop up structure near the axis of the suture zone localised transpression and neotectonic extension complete the picture

seismicity depth pattern seismic energy and b value depth variation in the hellenic wadati benioff zone abstract the statistics of the vertical distribution of the foci of earthquakes which occurred in the hellenic wadati benioff zone during the period 1964 1982 show that the seismicity pattern energy and b value of the frequency magnitude relation vary with depth in a specific manner the seismicity patterns of the western and the eastern flanks of the hellenic subduction zone vary with depth in a similar manner whereas the seismic energies and b value depth variations for these two flanks of the subduction zone do not show such a similarity

periodic instabilities during compression or extension of the lithosphere 1 deformation modes from an analytical perturbation method we argue that the plastic rheology of the lithosphere rather than its recoverable elastic properties is responsible for the systematic development of periodic instabilities during compression or extension we use a linear perturbation model with analytical solutions to calculate the instability modes for various rheologies the growth of such periodic instabilities is enhanced by the highly nonlinear stress strain rheologies encountered in the brittle layers of the lithosphere on the contrary ductile layers deforming according to high temperature creep flow laws tend to inhibit these instabilities for oceanic domains we assume that the only brittle layer is the upper part of the lithosphere in compression the only valid instability is a buckling whose wavelength is around 4 times the thickness of the brittle layer calculated wavelengths and growth rates are consistent with observations available for the indian ocean for continental domains a reasonable assumption is the existence of two plastic layers one in the upper crust the other in the upper mantle for moho temperatures between 450 c and 600 c in compression and extension two instabilities develop a long wavelength instability involving the whole lithosphere coupling mode and a short wavelength instability involving the crust and controlled by the upper brittle layer intrinsic crustal mode in compression the coupling mode is a whole lithosphere buckling with a wavelength about 4 times the thickness of the active lithosphere the two plastic layers plus the intermediate ductile layer in extension the coupling mode is a boudinage of opposite phase in the two plastic layers and a folding of the intermediate ductile layer the intrinsic crustal mode is a crustal buckling in compression crustal boudinage in extension neither deflects the moho the intrinsic crustal mode is favored by an increase in thermal gradient and by a decrease in strength of the ductile lower crust

grain size sensitive seismic wave attenuation in polycrystalline olivine 1 in order to investigate the processes responsible for the attenuation of seismic shear waves in the earth s upper mantle four olivine polycrystals ranging in mean grain size d from 3 to 23 m have been fabricated characterized and mechanically tested in torsion at high temperatures and seismic frequencies both the shear modulus which governs the shear wave speed vs and the dissipation of shear strain energy q 1 have been measured as functions of oscillation period to temperature t and for the first time grain size at sufficiently high t all four specimens display similar absorption band viscoelastic behavior adequately represented for 1000 t 1200 or 1300 c and 1 to 100 s by the expression q 1 a tod 1 exp e rt with a 7 5 102 s m 0 26 and e 424 kj mol 1 this mildly grain size sensitive viscoelastic behavior of melt free polycrystalline olivine is attributed to a combination of elastically and diffusionally accommodated grain boundary sliding the latter becoming progressively more important with increasing t and or to extrapolation to the larger mm cm grain sizes expected in the earth s upper mantle yields levels of dissipation comparable with those observed seismologically implying that the same grain size sensitive processes might be responsible for much of the observed seismic wave attenuation the temperature sensitivity of vs is increased substantially by the viscoelastic relaxation allowing the lateral variability of wave speeds to be associated with relatively small temperature perturbations

modeling the influence of moho topography on receiver functions a case study from the central hellenic subduction zone 1 pseudospectral 2d modeling of wave propagation provides a fresh look at receiver function data from the hellenic subduction zone it is shown that distinct moho topography which is suggested for this complex subduction environment from various geophysical data sets can provide a conclusive explanation for previously observed inverted moho phases in the forearc as well as for a complex sequence of apparently dipping conversions in the volcanic arc prominent effects of strongly dipping discontinuities include the change of sign in ps phases refracted past the vertical and multiple p reflections that cannot be separated from ps conversions during receiver function processing unambiguous identification of these phenomena can be hampered by poor azimuthal coverage of the data still in regions where discontinuity topography can reasonably be expected its effects should be considered when interpreting receiver functions as results might be spurious otherwise

the aegean sea we summarize briefly the main features of a kinematic model of evolution of the aegean area since 13 ma the formation of the aegean sea by extensional tectonics is related to the subduction of the mediterranean floor below the hellenic arc we then make a quantitative estimate of vertical movements in the aegean area on the basis of geological data and demonstrate that the outer arc was built since the beginning of this episode of subduction by vertical uplift the easiest way to explain the uplift is by underplating finally we discuss briefly the dynamics of the subduction marginal sea formation processes in this continental collision framework

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

complex patterns of fluid and melt transport in the central andean subduction zone revealed by attenuation tomography abstract we present a high resolution 3 d model of p wave attenuation q p 1 for the central andean subduction zone data from 1500 mostly intermediate depth 60 250 km earthquakes recorded at three temporary seismic networks covering the forearc arc and backarc around 23 s were used for tomographic inversion the forearc is characterised by uniformly high q p values indicating low temperature rocks in accordance with low surface heat flow values prominent low q p anomalies are found beneath the magmatic arc and the backarc in the crust and mantle continuous regions of low q p connect earthquake clusters at 100 km and 200 km depth with zones of active volcanism in the arc and backarc fluids fluxed from the subducted oceanic lithosphere into the overlying mantle wedge where they induce melting explain our observations we propose that low q p regions indicate source and ascent pathways of metamorphic fluids and partial melts ascent of fluids and melts as imaged by seismic q p are not vertical as is often implicitely assumed instead sources of fluids are located at different depth levels and ascent paths are complex and exhibit significant variation within the study area the largest quaternary backarc volcano cerro tuzgle is fed by mantle melts which are imaged as a plume of low q p material that reaches to the strong earthquake cluster at 200 km depth

the mediterranean ridge a mass balance across the fastest growing accretionary complex on earth depth migration of seismic reflection profiles across the mediterranean ridge accretionary complex between the african and eurasian blocks illustrates profound variations in the geometry and internal structure along strike structural interpretations of four cross sections together with bathymetric and acoustic surface information and drilling data are used to volumetrically balance the amount of subduction versus accretion with time results suggest the existence of three distinct scenarios with a jump in decollement in the west intense backthrusting in the central part between libya and crete and transcurrent tectonism in the east the onset of accretion coincides with exhumation of thrust sheets 19 ma followed by rapid sediment accretion with thick evaporite bearing incoming successions facilitating outward growth of the wedge the minimum rate of accretion 20 25 of the total sediment supply is observed in the central portion where the ridge suffers maximum deformation here the indenting leading edge of the african plate apparently forces the sediment into subduction or local underplating in contrast an estimated 40 60 of the available sedimentary input was accreted in the western domain where collision is less accentuated the results support the hypothesis that highly destructive forearc collisional events like slab break off and exhumation of thrust sheets can be followed by periods of accretion and continuous growth of accretionary wedges