on the hellenic subduction zone and the geodynamic evolution of crete since the late middle miocene abstract in recent syntheses of the geodynamic evolution of the aegean area the hellenic subduction zone and in particular its initiation plays a central role two basic aspects of the recent comprehensive model put forward by le pichon angelier and co workers are a initiation of subduction along the hellenic arc is inferred to have taken place approximately 13 ma ago whereas several others have suggested approximately 5 ma and b migration of the trench system to the south southwest giving rise to an extensional regime in the back arc region which led to general subsidence and formation of the present day aegean sea new data on the structure of the upper mantle underneath the aegean area indicate that the former aspect requires modification the seismic velocity structure indicating a northward dipping slab down to a depth of at least 600 km and the depth distribution of earthquake hypocenters can not be reconciled with straightforward initiation of subduction approximately 13 ma ago estimates of about 5 ma for the time of initiation of the present subduction zone are even more difficult to reconcile assuming 400 km as an upper bound for the effect of stretching of the aegean sea and of other processes contributing to the separation of crete from the eurasian mainland we arrive at an age for the hellenic subduction zone of at least 26 ma as to aspect b geological data of crete lend strong support to the idea that on crete compressional tectonics is of much greater importance than current models imply combining geophysical and geological data we propose a modification of the tectonic evolution for the cretan segment of the hellenic arc whereas the basic process of extension caused by a migrating trench system roll back in a land locked basin remains a very useful and sound concept the tectonics of the margins of a region subject to stretching in this case crete may be more complicated than hitherto thought in our model the documented fragmentation of crete into several basins which started about 12 ma ago is not attributed to initiation of subduction but to inception of the roll back process compressional tectonics on crete is taken to be associated with deformation of the crust resulting from the overall tensional stress regime

seismicity and active tectonics in the alboran sea western mediterranean constraints from an offshore onshore seismological network and swath bathymetry data seismicity and tectonic structure of the alboran sea were derived from a large amphibious seismological network deployed in the offshore basins and onshore in spain and morocco an area where the convergence between the african and eurasian plates causes distributed deformation crustal structure derived from local earthquake data suggests that the alboran sea is underlain by thinned continental crust with a mean thickness of about 20 km during the 5 months of offshore network operation a total of 229 local earthquakes were located within the alboran sea and neighboring areas earthquakes were generally crustal events and in the offshore domain most of them occurred at crustal levels of 2 to 15 km depth earthquakes in the alboran sea are poorly related to large scale tectonic features and form a 20 to 40 km wide nne ssw trending belt of seismicity between adra spain and al hoceima morocco supporting the case for a major left lateral shear zone across the alboran sea such a shear zone is in accord with high resolution bathymetric data and seismic reflection imaging indicating a number of small active fault zones some of which offset the seafloor rather than supporting a well defined discrete plate boundary fault moreover a number of large faults known to be active as evidenced from bathymetry seismic reflection and paleoseismic data such as the yusuf and carboneras faults were seismically inactive earthquakes below the western alboran basin occurred at 70 to 110 km depth and hence reflected intermediate depth seismicity related to subducted lithosphere

global anisotropy in the upper mantle inferred from the regionalization of phase velocities a data set of 2600 paths for rayleigh waves and 2170 paths for love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70 250 s the epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of earth a synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path to process such a large data set a new tomographic technique is designed a good correlation is found with surface tectonics in the whole period range for love waves and at shorter periods for rayleigh waves the directions of maximum velocities are also well correlated with plate tectonics motions for the 2 azimuthal term of rayleigh waves when the power spectrum of heterogeneities is computed it is found that for love waves the even orders are usually larger than the odd orders for rayleigh waves the degrees 2 and 6 dominate only at long periods suggesting a deep origin for these components

segmented african lithosphere beneath the anatolian region inferred from teleseismic p wave tomography summary lithospheric deformation throughout anatolia a part of the alpine himalayan orogenic belt is controlled mainly by collision related tectonic escape of the anatolian plate and subduction roll back along the aegean subduction zone we study the deeper lithosphere and mantle structure of anatolia using teleseismic finite frequency p wave traveltime tomography we use data from several temporary and permanent seismic networks deployed in the region approximately 34 000 p wave relative traveltime residuals measured in multiple frequency bands are inverted using approximate finite frequency sensitivity kernels our tomograms reveal segmented fast seismic anomalies beneath anatolia that corresponds to the subducted portion of the african lithosphere along the cyprean and the aegean trenches we identify these anomalies as the subducted aegean and the cyprus slabs that are separated from each other by a gap as wide as 300 km beneath western anatolia this gap is occupied by slow velocity perturbations that we interpret as hot upwelling asthenosphere the eastern termination of the subducting african lithosphere is located near the transition from central anatolia to the eastern anatolian plateau or arabian eurasian collision front that is underlain by large volumes of hot underplating asthenosphere marked by slow velocity perturbations our tomograms also show fast velocity perturbations at shallow depths beneath northwestern anatolia that sharply terminates towards the south at the north anatolian fault zone nafz the associated velocity contrast across the nafz persists down to a depth of 100 150 km hence our study is the first to investigate and interpret the vertical extent of deformation along this nascent transform plate boundary overall the resolved upper mantle structure of anatolia is directly related with the geology and tectonic features observed at the surface of the anatolian plate and suggest that the segmented nature of the subducted african lithosphere plays an important role in the evolution of anatolia and distribution of its tectonic provinces

is there a remnant variscan subducted slab in the mantle beneath the paris basin implications for the late variscan lithospheric delamination process and the paris basin formation abstract the paris basin northern france is a late paleozoic mesozoic intracratonic basin that settled upon the collapsed variscan collisional belt the lithospheric roots of the variscan orogenic system below the paris basin have been investigated using a european scale p wave velocity tomographic model tomography points out the existence of a significant high velocity anomaly in the upper mantle below the western part of the basin at 150 200 km depth the anomaly extends with a nw se trend along the buried northern france trace of the northern variscan suture zone i e the bray segment of the upper carboniferous lizard rhenohercynian lrh suture moreover the high velocity anomaly is spatially correlated with the prominent paris basin magnetic anomaly its downdip extent reaches depths greater than 200 km below the southern margin of the paris basin as suggested in previous tomographic studies below ancient suture zones these data argue for such anomaly being the remnant of a variscan subducted slab that escaped the extensive late orogenic delamination process affecting the lithospheric roots by late carboniferous early permian times and that was preserved stable over 300 ma at the base of the lithosphere on a general geodynamical perspective these results provide a new insight into the long term evolution of subducted lithosphere into the mantle in the case of the western european variscan orogenic belt they suggest that the subduction of the lrh slab below the previously thickened variscan crust and its final detachment from the orogenic root have played an important role in the collapse of the belt inducing thermal erosion and extension of the overriding lithosphere the spatial evolution of late orogenic extension across the belt and of subsequent thermal subsidence in the paris basin is suggested to result from the heterogeneous delamination of the lithospheric roots along strike and from the resultant pattern of asthenospheric rise

distribution of seismic velocities and attenuation in the crust beneath the north anatolian fault turkey from local earthquake tomography we investigate the crustal structure beneath the western part of the north anatolian fault zone nafz an area where at least five damaging earthquakes occurred during the twentieth century this study is based on local earthquake tomography using the data from aftershocks of the izmit event 17 august 1999 m 7 4 recorded by stations of permanent and temporary networks we derive the distribution of v p v s and the v p v s ratio based on the iterative inversion for both v p v s and v p v p v s using the lotos code innovatively in this study we perform an inversion for frequency dependent s wave attenuation 1 q s the reliability of the results is assessed through synthetic tests the distributions of the resulting seismic parameters v p v s v p v s and q s highlight important geodynamical features in the study area the low velocity and high attenuation patterns mostly correlate with the fracturing zones of the nafz low velocities are also observed beneath the main sedimentary basins e g adapazari duzce and kuzuluk high velocity and low attenuation patterns correlate with blocks presumed to be rigid kocaeli armutlu and almacik blocks the rupture traces of the largest earthquakes in this area pass generally in the transition areas between high and low velocities while moderate and weak seismicity is mostly concentrated in low velocity areas based on these results we propose and discuss the role that the almacik block could have played in producing the largest earthquakes in the study area in the twentieth century

towards absolute plate motions constrained by lower mantle slab remnants the movement of tectonic plates before the cretaceous period is poorly understood a global mantle tomography model suggests that the longitude of oceanic subduction zones up to 300 million years ago was offset by up to 18 compared with tectonic reconstructions for the same period

joint inversion for three dimensional s velocity mantle structure along the tethyan margin abstract for purposes of studying the lateral heterogeneity as well as for ultimately predicting seismograms for this region we construct a new 3 d s velocity model by jointly inverting a variety of different seismic data we jointly invert regional waveforms surface wave group velocity measurements teleseismic s arrival times and crustal thickness estimates from receiver functions refraction lines and gravity surveys these data types have complementary resolving power for crust and mantle structures vertical and lateral variations shallow and deep mantle features local and global structure therefore a joint inversion of these data sets might help unravel the complexity of this tectonically diverse area these measurements are made from a combination of mantle investigation of the deep suture between europe and africa midsea program for array seismic studies of the continental lithosphere passcal geoscope geofon global seismographic network gsn international deployment of accelerometeres ida mednet national networks and local deployments throughout the study region which extends from the western mediterranean region to the hindu kush and encompasses northeastern africa the arabian peninsula the middle east and part of the atlantic ocean for reference we have fitted the waveforms of regional s and rayleigh waves from over 3800 seismograms using partitioned waveform inversion we include over 3000 crustal thickness estimates from receiver functions gravity measurements and refraction profiles we include rayleigh wave group velocities for hundred thousands of paths transecting the region we have over 3000 teleseismic s arrival times measured through cross correlation and over 170000 from picks originally reported to the international seismological centre isc

slab rupture and delamination under the betics and rif constrained from receiver functions abstract we map the lithospheric structure under the westernmost mediterranean convergent setting interpreting p receiver functions obtained from a dense seismic network no orogenic root occurs under the eastern and great part of the central betics however the subducted south iberian continental lithosphere is found beneath the western betics where the iberian moho reaches depths of approximately 65 km dipping gently towards the se meanwhile at the rif strong crustal and lithospheric thickness contrasts occur across the nekor nw se sinistral fault that overlies the region of present slab tearing east of the nekor fault there is no orogenic root and the crust has been thinned to approximately 22 km whilst to the west the crust reaches 55 km thickness and the maghrebian continental lithosphere is attached to the lithospheric slab imaged by tomography under the alboran basin these data suggest that subduction rollback under the alboran and algerian basins together with continental slab tearing or detachment producing edge delamination under the betics and rif have been the main tectonic mechanisms driving extension magmatism and regional uplift in the westernmost mediterranean since the late miocene until present the surface expression of edge delamination and slab tearing is marked by regional uplift denudation of hp rocks in elongated core complex type domes late miocene volcanism in the eastern betics and rif and by large ne sw strike slip transfer faults like the alpujarras crevillente torcal or nekor faults that accommodate strong gradients in crustal displacements the iberian slab is still attached to the oceanic slab imaged under the alboran basin at the western betics where intermediate depth seismicity recent dextral strike slip faulting and folding could reflect slab tearing meanwhile active faulting and differential gps measured displacements would mark slab tearing beneath the rif coinciding with the trace of the sinistral nekor fault

crust and upper mantle of the western mediterranean constraints from full waveform inversion abstract we present a full waveform tomographic model of the western mediterranean crust and mantle constructed from complete three component recordings from permanent and temporary networks the incorporation of body and multi mode surface waves in the period range from 12 150 s allows us to jointly resolve crustal and mantle structures including the guadalquivir tajo and ebro basins at shallow depth as well as the western mediterranean subduction system in the transition zone no mantle plumes can be detected beneath the european cenozoic rift system including the massif central in addition to the well studied alboran slab a strong e w trending high velocity anomaly is present around 200 300 km depth beneath the algerian coast this previously undetected african slab is detached from the surface and broken into two segments it may be interpreted as the slab that caused the opening of the liguro provencal basin through successive roll back between 35 15 ma

mantle dynamics in the mediterranean the mediterranean offers a unique opportunity to study the driving forces of tectonic deformation within a complex mobile belt lithospheric dynamics are affected by slab rollback and collision of two large slowly moving plates forcing fragments of continental and oceanic lithosphere to interact this paper reviews the rich and growing set of constraints from geological reconstructions geodetic data and crustal and upper mantle heterogeneity imaged by structural seismology we proceed to discuss a conceptual and quantitative framework for the causes of surface deformation exploring existing and newly developed tectonic and numerical geodynamic models we illustrate the role of mantle convection on surface geology a coherent picture emerges which can be outlined by two almost symmetric upper mantle convection cells the downwellings are found in the center of the mediterranean and are associated with the descent of the tyrrhenian and the hellenic slabs during plate convergence these slabs migrated backward with respect to the eurasian upper plate inducing a return flow of the asthenosphere from the backarc regions towards the subduction zones this flow can be found at large distance from the subduction zones and is at present expressed in two upwellings beneath anatolia and eastern iberia this convection system provides an explanation for the general pattern of seismic anisotropy in the mediterranean first order anatolia and adria microplate kinematics and may contribute to the high elevation of scarcely deformed areas such as anatolia and eastern iberia more generally the mediterranean is an illustration of how upper mantle small scale convection leads to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the tethyan collision

aegean tectonics strain localisation slab tearing and trench retreat abstract we review the geodynamic evolution of the aegean anatolia region and discuss strain localisation there over geological times from late eocene to present crustal deformation in the aegean backarc has localised progressively during slab retreat extension started with the formation of the rhodope metamorphic core complex eocene and migrated to the cyclades and the northern menderes massif oligocene and miocene accommodated by crustal scale detachments and a first series of core complexes mccs extension then localised in western turkey the corinth rift and the external hellenic arc after messinian times while the north anatolian fault penetrated the aegean sea through time the direction and style of extension have not changed significantly except in terms of localisation the contributions of progressive slab retreat and tearing basal drag extrusion tectonics and tectonic inheritance are discussed and we favour a model 1 where slab retreat is the main driving engine 2 successive slab tearing episodes are the main causes of this stepwise strain localisation and 3 the inherited heterogeneity of the crust is a major factor for localising detachments the continental crust has an inherited strong heterogeneity and crustal scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation the dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate successive slab ruptures from the middle miocene to the late miocene have isolated a narrow strip of lithosphere still attached to the african lithosphere below crete the formation of the north anatolian fault is partly a consequence of this evolution the extrusion of anatolia and the aegean extension are partly driven from below asthenospheric flow and from above extrusion of a lid of rigid crust

subduction and the depth of convection in the mediterranean mantle 1 we tie together geological data paleotectonic reconstruction plate motion and tomographic analysis to unravel the history of subduction and back arc extension of the eastern and central mediterranean in these two regions extensional processes started contemporaneously around 30 myr ago but with marked differences in the eastern region the aegean basin opened slowly 1 cm yr behind a shallow dipping slab 40 45 the corresponding high velocity anomaly extends inside the upper mantle and can be also followed in the midmantle down to a depth of at least 1500 km its descent into the midmantle initiated most probably during the late cretaceous and the trench moved northeastward following the path of the eurasian plate and under the persistent push of the african plate conversely in the central mediterranean region subduction initiated later and the motion of the subducting slab is confined to the upper mantle causing punctuated and rapid episodes of back arc extension provencal and tyrrhenian basins behind a slab that dips steeply 75 we explore the causes that control how the slab subducted and interacted with the lower more viscous part of the mantle

evidence for slab rollback in westernmost mediterranean from improved upper mantle imaging this work is funded by the picasso project nsf grant ear 0808939 the deployment and data processing for spanish stations was funded by consolider ingenio 2010 project topo iberia csd2006 00041 as well as alert es cgl2010 19803 c03 02

surface expression of eastern mediterranean slab dynamics neogene topographic and structural evolution of the southwest margin of the central anatolian plateau turkey 1 the southwest margin of the central anatolian plateau has experienced multiple phases of topographic growth including the formation of localized highs prior to the late miocene that were later affected by wholesale uplift of the plateau margin our new biostratigraphic data limit the age of uplifted marine sediments at the southwest plateau margin at 1 5 km elevation to 7 17 ma and regional lithostratigraphic correlations imply that the age is 6 7 ma single grain ca tims u pb zircon analyses from a reworked ash within the marine sediments yield dates as young as 10 6 ma indicating a maximum age that is consistent with the biostratigraphy our structural measurements within the uplifted region and fault inversion modeling agree with previous findings in surrounding regions with early contraction followed by strike slip and extensional deformation during uplift focal mechanisms from shallow earthquakes show that the extensional phase has continued to the present broad similarities in the change in the tectonic stress regime after 8 ma and the onset of surface uplift after 7 ma imply that deep seated process es caused post 7 ma uplift the geometry of lithospheric slabs beneath the plateau margin pliocene to recent alkaline volcanism and the uplift pattern with accompanying normal faulting point toward slab tearing and localized heating at the base of the lithosphere as a probable mechanism for post 7 ma uplift of the southwest margin considering previous work in the region there appears to be an important link between slab dynamics and surface uplift throughout the anatolian plateau s southern margin

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

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

shear velocity structure of the tyrrhenian sea tectonics volcanism and mantle de hydration of a back arc basin the tyrrhenian sea in the mediterranean formed as the result of roll back of the adriatic and ionian subducting plates it is mostly underlain by strongly thinned continental lithosphere but contains two small oceanic basins in the southern tyrrhenian the youngest one located just behind the active magmatic arc its regional setting with dense station coverage provides a unique opportunity to derive a high resolution 3 d shear velocity model of this back arc basin and surrounding onshore areas using interstation rayleigh wave dispersion measurements our tomographic model extending to a depth of approximately 160 km displays a pronounced nearly ring shaped low shear velocity zone between 70 and 110 km depth which surrounds the older oceanic vavilov basin the sharp velocity decrease at 70 km depth can be explained by the transition from a relatively dry lithospheric mantle to more hydrous asthenospheric mantle material the tectonic evolution of the region and the correlation of the low velocity anomaly with subduction related volcanism indicate that the low velocity anomaly reflects hydrous mantle material in present or former mantle wedge regions we suggest that the absence of the low velocity zone beneath the vavilov basin is due to mantle dehydration caused by the creation of morb crust whereas temperature effects may dominate the asthenospheric shear velocity differences between various back arc basins we find that the variations in shear velocity structure within the tyrrhenian area are best explained by variations in mantle water content

reconstructing the alps carpathians dinarides as a key to understanding switches in subduction polarity slab gaps and surface motion palinspastic map reconstructions and plate motion studies reveal that switches in subduction polarity and the opening of slab gaps beneath the alps and dinarides were triggered by slab tearing and involved widespread intracrustal and crust mantle decoupling during adria europe collision in particular the switch from south directed european subduction to north directed wrong way adriatic subduction beneath the eastern alps was preconditioned by two slab tearing events that were continuous in cenozoic time 1 late eocene to early oligocene rupturing of the oppositely dipping european and adriatic slabs these ruptures nucleated along a trench trench transfer fault connecting the alps and dinarides 2 oligocene to miocene steepening and tearing of the remaining european slab under the eastern alps and western carpathians while subduction of european lithosphere continued beneath the western and central alps following the first event post late eocene nw motion of the adriatic plate with respect to europe opened a gap along the alps dinarides transfer fault which was filled with upwelling asthenosphere the resulting thermal erosion of the lithosphere led to the present slab gap beneath the northern dinarides this upwelling also weakened the upper plate of the easternmost part of the alpine orogen and induced widespread crust mantle decoupling thus facilitating pannonian extension and roll back subduction of the carpathian oceanic embayment the second slab tearing event triggered uplift and peneplainization in the eastern alps while opening a second slab gap still present between the eastern and central alps that was partly filled by northward counterclockwise subduction of previously unsubducted adriatic continental lithosphere in miocene time adriatic subduction thus jumped westward from the dinarides into the heart of the alpine orogen where northward indentation and wedging of adriatic crust led to rapid exhumation and orogen parallel escape of decoupled eastern alpine crust toward the pannonian basin the plate reconstructions presented here suggest that miocene subduction and indentation of adriatic lithosphere in the eastern alps were driven primarily by the northward push of the african plate and possibly enhanced by neutral buoyancy of the slab itself which included dense lower crust of the adriatic continental margin

a high resolution model for eurasia north america plate kinematics since 20 ma summary we derive the first chronologically detailed model of eurasia north america plate motion since 20 ma from ship and airplane surveys of the well expressed magnetic lineations along this slowly spreading plate boundary including previously unavailable dense russian magnetic data from the southern reykjanes ridge and northern mid atlantic ridge near the charlie gibbs fracture zone from more than 7000 crossings of 21 magnetic anomalies from anomaly 1n 0 78 ma to anomaly 6n 19 7 ma we estimate best fitting finite rotations and realistic uncertainties linear regressions of total opening distances versus their reversal ages at different locations along the plate boundary show that reversal boundaries are shifted systematically outwards from the spreading axis with respect to their idealized locations with the outward shift ranging from more than 5 km between iceland and the charlie gibbs fracture zone to 2 km elsewhere this outward displacement which is a consequence of the finite zone of seafloor accretion degrades estimates of the underlying plate motion and is thus removed for the ensuing kinematic analysis the corrected plate motion rotations reveal surprising previously unrecognized features in the relative motions of these two plates within the uncertainties motion was steady from 20 to 8 ma around a pole that was located 600 km north of the present pole with seafloor spreading rates that changed by no more than 5 per cent 1 mm yr 1 along the reykjanes ridge during this period seafloor spreading rates decreased abruptly by 20 2 per cent at 7 5 6 5 ma coinciding with rapid southward migration of the pole of rotation and a5 10 counter clockwise change in the plate slip direction eurasia north america plate motion since 6 7 ma has remained remarkably steady with an apparently stationary axis of rotation and upper limit of 2 per cent on any variations in the rate of angular rotation during this period based on the good agreement between seismotectonic constraints on present deformation in northeast asia and directions of motion that are predicted by our 6 7 ma to present pole we hypothesize that motion has remained steady to the present and attempt to test this hypothesis with published gps estimates for eurasia north america motion we find however that gps estimates that are tied to recent versions of the international geodetic reference frame and rely principally on station velocities from europe give implausible estimates of recent motion with the most recently published gps model predicting convergence along the southern gakkel ridge and in the laptev sea where seafloor spreading occurs an alternative gps estimate that is not tied to the international terrestrial reference frame and employs gps station velocities from northeastern asia is marginally consistent with our 6 7 0 ma motion estimate

shape and origin of the east alpine slab constrained by the alpass teleseismic model abstract during the last two decades teleseismic studies yielded valuable information on the structure of the upper mantle below the alpine mediterranean area subducted oceanic lithosphere forms a broad anomaly resting on but not penetrating the 670 km discontinuity more shallow slabs imaged below the alpine arc are interpreted as subducted continental lower lithosphere substantial advances in our understanding of past and active tectonic processes have been achieved due to these results however important issues like the polarity of subduction under the eastern alps and the slab geometry at the transition to the pannonian realm are still under debate the alpass teleseismic experiment was designed to address these open questions teleseismic waveforms from 80 earthquakes recorded at 75 temporary and 79 permanent stations were collected during 2005 and 2006 from these data a tomographic image of the upper mantle was generated between 60 km and 500 km depth crustal corrections additional station terms and ray bending caused by the velocity perturbations were considered a steeply to vertically dipping shallow slab below the eastern alps is clearly resolved down to a depth of 250 km it is interpreted as european lower lithosphere detached from the crust and subducted during post collision convergence between adria and europe below the pannonian realm low velocities or high mantle temperatures prevail down to 300 km depth consistent with the concept of a pannonian lithospheric fragment which underwent strike slip deformation relative to the european plate and extension during the post collision phase of the alpine orogeny between 350 km and 400 km depth a deep slab extends from below the central eastern alps to under the pannonian realm it is interpreted as subducted lithosphere of the alpine tethys at greater depth there is a continuous transition to the high velocity anomaly above the 670 km discontinuity

mapping the moho with seismic surface waves a review resolution analysis and recommended inversion strategies abstract the strong sensitivity of seismic surface waves to the moho is evident from a mere visual inspection of their dispersion curves or waveforms rayleigh and love waves have been used to study the earth s crust since the early days of modern seismology yet strong trade offs between the moho depth and crustal and mantle structure in surface wave inversions prompted doubts regarding their capacity to resolve the moho here we review surface wave studies of the moho with a focus on early work and then use model space mapping to establish the waves sensitivity to the moho depth and the resolution of their inversion for it if seismic wavespeeds within the crust and upper mantle are known then moho depth variations of a few kilometres produce large 1 perturbations in phase velocities however in inversions of surface wave data with no a priori information wavespeeds not known strong moho depth shear speed trade offs will mask 90 of the moho depth signal with remaining phase velocity perturbations 0 1 only in order to resolve the moho with surface waves alone errors in the data must thus be small up to 0 2 for resolving continental moho with larger errors moho depth resolution is not warranted and depends on error distribution with period an effective strategy for the inversion of surface wave data alone for the moho depth is to first constrain the crustal and upper mantle structure by inversion in a broad period range and then determine the moho depth in inversion in a narrow period range most sensitive to it with the first step results used as reference prior information on crustal and mantle structure reduces the trade offs and thus enables resolving the moho depth with noisier data such information should be used whenever available joint analysis or inversion of surface wave and other data receiver functions topography gravity can reduce uncertainties further and facilitate moho mapping

delay time tomography of the upper mantle below europe the mediterranean and asia minor summary the method of linearized delay time tomography is applied to retrieve the p velocity heterogeneity of the upper mantle in central europe the mediterranean and asia minor the upper mantle is parametrized in slowness cell functions with lateral dimensions of 1 the model parametrization includes event mislocation vectors and station delay time corrections in all 20 000 parameters describe the model delay time data selected from the isc data base 1964 1982 from regional events and from stations up to 90 of epicentral distance are used about 18 000 events and 937 stations contributed nearly 500 000 delay times we discuss the tomographic method the data processing the cell model employed the computation of the ray geometry the use of composite rays in tomography and the cell hit count the inversions are performed with two different iterative row action methods lsqr and sirt results obtained with the lsqr method will be shown only the spatial resolution is investigated with sensitivity analyses using two different synthetic velocity models a spike model and a model with harmonically varying velocity anomalies the spatial resolution is estimated to be high on the order of the cell size in the mantle below central and southeastern europe the mapped velocity heterogeneity exhibits primarily low velocities around a depth of 200 km and just above the transition from upper to lower mantle this indicates a systematic deviation of the reference model jeffreys bullen from the radially averaged earth structure which may violate the basic assumptions underlying the linearized approach a posteriori investigation of the data also indicates the presence of a low velocity zone and the existence of strong velocity depth gradients

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

constraints on mantle circulation around the deforming calabrian slab 1 combining tectonics with seismological and geochemical data we reconstruct the deformation history of the presently narrow calabrian slab and the path of mantle circulation during the last 10 ma we show that during the slab deformation the mantle laterally flowed inside the back arc region permitting its retrograde motion and giving a seismological and volcanological record after 1 2 myr

structure of the european upper mantle revealed by adjoint tomography the structure of the european crust and upper mantle is precisely known only in limited regions a new tomographic model for the entire european upper mantle identifies northeastward subduction of the adria plate beneath the dinarides mountains volcanism related to the upwelling eifel hotspot and mantle delamination beneath scandinavia

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

upper mantle structures beneath the carpathian pannonian region implications for the geodynamics of continental collision abstract the carpathian pannonian system of eastern and central europe represents a unique opportunity to study the interaction between surface tectonic processes involving convergence extension and convective overturn in the upper mantle here we present high resolution images of upper mantle structure beneath the region from p wave finite frequency teleseismic tomography to help constrain such geodynamical interactions we have selected earthquakes with magnitude greater than 5 5 in the distance range 30 95 which occurred between 2006 and 2011 the data were recorded on 54 temporary stations deployed by the south carpathian project 2009 2011 56 temporary stations deployed by the carpathian basins project 2005 2007 and 131 national network broadband stations the p wave relative arrival times are measured in two frequency bands 0 5 2 0 hz and 0 1 0 5 hz and are inverted for vp perturbation maps in the upper mantle our images show a sub vertical slab of fast material beneath the eastern alps which extends eastward across the pannonian basin at depths below 300 km the fast material extends down into the mantle transition zone mtz where it spreads out beneath the entire basin above 300 km the upper mantle below the pannonian basin is dominated by relatively slow velocities the largest of which extends down to 200 km we suggest that cold mantle lithospheric downwelling occurred below the pannonian basin before detaching in the mid miocene in the vrancea zone of se romania intermediate depth 75 180 km seismicity occurs at the ne end of an upper mantle high velocity structure that extends sw under the moesian platform oblique to the southern edge of the south carpathians at greater depths 180 400 km a sub circular high velocity anomaly is found directly beneath the seismicity this sub vertical high velocity body is bounded by slow anomalies to the nw and se which extend down to the top of the mtz no clear evidence of a residual slab is observed above the mtz beneath the eastern carpathians these observations suggest that intermediate depth seismicity in vrancea zone is unlikely to be due to slab tearing but rather could be explained by either gravitational instability or delamination of mantle lithosphere

messinian salinity crisis regulated by competing tectonics and erosion at the gibraltar arc the persistent shallow connection between the atlantic ocean and the mediterranean sea that caused the messinian salinity crisis may have been sustained by a balance between tectonic uplift and erosion due to inflow about six million years ago a series of geological factors drastically reduced the exchange of water between the atlantic ocean to the mediterranean sea through what is now the strait of gibraltar the resulting widespread salt precipitation in the mediterranean linked to a decrease in sea level of about 1 5 kilometres due to evaporation is known as the messinian salinity crisis the exact mechanism that caused the crisis remains uncertain here daniel garcia castellanos and antonio villasenor propose a competition between the obstruction of the gibraltar arc seaway by tectonic uplift and its erosional deepening by water inflow controlled by the resulting changes in sea level difference across the gibraltar arc as a possible mechanism for the crisis the messinian salinity crisis1 2 5 96 to 5 33 million years ago was caused by reduced water inflow from the atlantic ocean to the mediterranean sea resulting in widespread salt precipitation and a decrease in mediterranean sea level of about 1 5 kilometres due to evaporation3 the reduced connectivity between the atlantic and the mediterranean at the time of the salinity crisis is thought to have resulted from tectonic uplift of the gibraltar arc seaway and global sea level changes both of which control the inflow of water required to compensate for the hydrological deficit of the mediterranean1 4 however the different timescales on which tectonic uplift and changes in sea level occur are difficult to reconcile with the long duration of the shallow connection between the mediterranean and the atlantic5 needed to explain the large amount of salt precipitated here we use numerical modelling to show that seaway erosion caused by the atlantic inflow could sustain such a shallow connection between the atlantic and the mediterranean by counteracting tectonic uplift the erosion and uplift rates required are consistent with previous mountain erosion studies with the present altitude of marine sediments in the gibraltar arc6 7 and with geodynamic models suggesting a lithospheric slab tear underneath the region8 9 10 the moderate mediterranean sea level drawdown during the early stages of the messinian salinity crisis3 5 can be explained by an uplift of a few millimetres per year counteracted by similar rates of erosion due to atlantic inflow our findings suggest that the competition between uplift and erosion can result in harmonic coupling between erosion and the mediterranean sea level providing an alternative mechanism for the cyclicity observed in early salt precipitation deposits and calling into question previous ideas regarding the timing of the events that occurred during the messinian salinity crisis1

the slab puzzle of the alpine mediterranean region insights from a new high resolution shear wave velocity model of the upper mantle mediterranean tectonics since the lower cretaceous has been characterized by a multiphase subduction and collision history with temporally and spatially variable small scale plate con gurations a new shear wave velocity model of the mediterranean upper mantle mere2020 constrained by a very large set of over 200 000 broadband 8 350 s interstation rayleigh wave phase velocity curves illuminates the complex structure and fragmentation of the subducting slabs phase velocity maps computed using these measurements were inverted for depth dependent shear wave velocities using a stochastic particle swarm optimization pso algorithm the resulting three dimensional 3 d model makes possible an inventory of slab segments across the mediterranean fourteen slab segments of 200 800 km length along strike are identi ed we distinguish three categories of subducted slabs attached slabs reaching down to the bottom of the model shallow slabs of shorter length in downdip direction terminating shallower than 300 km depth and detached slab segments the location of slab segments are consistent with and validated by the intermediate depth seismicity where it is present the new high resolution tomography demonstrates the intricate relationships between slab fragmentation and the evolution of the relatively small and highly curved subduction zones and collisional orogens characteristic of the mediterranean realm

p and s wave upper mantle seismic velocity structure beneath the northern apennines new evidence for the end of subduction orogeny in the geologically young northern apennines is explained by the eastward retreat of a convergence zone in which adriatic lithosphere subducts to the west it is unclear however whether all of the lithosphere or only the lower portion has subducted since 15 ma when the convergence zone lay near corsica we combine teleseismic p and s wave arrival time data from the retreat seismic network 2003 2006 and surrounding permanent stations to estimate tomographic images of the upper mantle structure beneath the northern apennines we image a vertically oriented slab that that extends to only 300 km depth our slab termination is shallower than previous studies but is confirmed by resolution tests furthermore our images resolve the southern edge of the northern apennines slab at 43 n with no deep continuity with any slab segment to the south as earlier proposed our results suggest that only a 300 400 km strip of lithosphere has subducted since 15 ma beneath the northern tyrrhenian sea a length roughly equivalent to the distance from the present day west coast of corsica to the crest of the northern apennines although not a definitive indicator the largely aseismic vertical slab configuration and its limited extent coupled with other volcanic and geophysical indicators suggests the delamination scenario of bird 1979 in which only the lower portion of the continental lithosphere subducts

late miocene to recent tectonic evolution of crete greece geological observations and model analysis abstract using a numerical model we focus on the late middle miocene to recent kinematic evolution of the cretan segment of the hellenic arc geological observations of crete are given a quantitative interpretation in terms of tectonic mechanisms controlling the evolution of the active arc boundary this was achieved by calculating intra plate stress fields for various possible distributions of forces and comparing the models with observations the models address specific questions concerning important changes in the observed horizontal stress patterns we deal with the question of what caused extension to initiate modelling results of the collapse of an earlier formed topography and extensional forces acting on the plate boundary are compared with a newly reconstructed tectonostratigraphy of crete our results suggest that arc normal pull is the dominant force that generates the late miocene extension in the cretan segment of the overriding plate although arc normal pull in combination with intra plate spreading forces cannot be excluded the observed transform motions in the pliny and strabo trenches led us to incorporate experiments with additional resistance on the eastern levantine segment of the hellenic arc the models performed with a transform resistance along the trenches are in agreement with the cretan deformation for the pliocene to recent period the stress fields for the short duration compressional periods around the middle late miocene and the miocene pliocene boundary are modelled by assuming resistive instead of tensional forces acting at the overriding margin

episodic back arc extension during restricted mantle convection in the central mediterranean abstract in the central mediterranean during the last 80 myr africa has been slowly converging toward eurasia with an average relative velocity of less than 1 cm yr 1 for 50 myr this slow convergence led to the build up of the alpine orogenic belt and to the initiation of consumption of the former tethys ocean in the last 30 myr however the whole central western mediterranean has been swept by rapid episodes of trench migration up to 6 cm yr 1 and back arc opening which consumed the whole former tethys ocean we combine plate tectonic history geological timing and laboratory modelling to reconstruct the subduction history and the evolution of the central mediterranean over the last 80 myr we find that the dynamic evolution of the subducting oceanic lithosphere can reconcile the rapid episodic back arc migration with the slow african convergence but only if the subduction process is restricted to the upper mantle

mesozoic break up of sw gondwana implications for regional hydrocarbon potential of the southern south atlantic abstract this work provides new palinspastic palaeofacies reconstructions of sw gondwana incorporating rotation of a falkland malvinas microplate we discuss the implications of this for the tectonic evolution of the southern south atlantic and hence for the regional hydrocarbon potential existing gondwana reconstructions display good fits of major continents but poorly constrained fits of microcontinents in most continental reconstructions the falkland malvinas plateau was assumed to be a rigid fragment of pre permian south american crust however it has been suggested on the basis of palaeomagnetic data that the falkland malvinas islands were rotated by 180 after 190 ma this rotation hypothesis has been successfully tested on the basis of devonian stratigraphy and palaeontology permian stratigraphy and sedimentology and late palaeozoic and early mesozoic structure making it unlikely that the plateau behaved as a rigid structure during breakup we have explored the consequences of accepting this hypothesis for the tectonic evolution of sw gondwana by compiling new palaeogeographic maps for the permian cretaceous of the southern atlantic area to achieve a realistic close fit we have devised a pre rift proxy for the ocean continent boundary for the south atlantic in order to produce the best fit it is necessary to subdivide south america into four plates the consequences of this are far reaching our work suggests that although sedimentary basins were initiated at different times three major tectonic phases can be recognised in regional terms these can be thought of as pre syn and post rift during the pre rift time until the late triassic the area was dominated by compressional tectonism and formed part of the gondwana foreland the falkland malvinas islands lay east of africa the falkland malvinas plateau was 33 shorter and patagonia was displaced east with respect to the rest of south america in part along the line of the gastre fault system potential source facies are dominantly post glacial black shales of late permian age deposited in lacustrine or hyposaline marine environments these rocks would also be an effective regional seal sandstones deposited in the late permian would be dominantly volcaniclastic with poor reservoir qualities triassic sandstones tend to be more mature there was significant extension from about 210 ma end triassic until the south atlantic opened at about 130 ma early cretaceous in the early syn rift phase extension was accompanied by strike slip faulting and block rotation later extension was accompanied by extrusion of large volumes of lava early opening of the south atlantic was oblique which created basins at high angle to the trend of the ocean on the argentine margin and resulted in microplate rotation in ne brazil intermittent physical barriers controlled deposition of upper jurassic cretaceous anoxic sediments during breakup some of these mudrock units are effective seals with likely regional extent during crustal reorganisation clastic sediments changed from a uniform volcaniclastic provenance to local derivation with variable reservoir quality in the late rift and early post rift phase continental extension changed from oblique to normal and basins developed parallel to the continental margins of the south atlantic this change coincides with the main rifting in the equatorial basins of brazil and the early impact of the santa helena plume it resulted in widespread development of unconformities the abandonment of the reconcavo tucano jatoba rift and the end of ne brazil plate rotation which remained attached to south america there was extensive deposition of evaporites concentrated in but not restricted to the area north of the rio grande rise walvis ridge widespread deposits can be used to define potential regional elements of hydrocarbon systems and to provide a framework for relating more local elements our main conclusion is that the regional hydrocarbon potential of the southern south atlantic has been constrained by the tectonic evolution

regional scale tectonic evolution and the seismic velocity structure of the lithosphere and upper mantle the mediterranean region we present a numerical modeling approach designed for the verification of tectonic reconstructions and for a quantitative analysis of the seismic velocity structure of the lower lithosphere and upper mantle in this forward modeling procedure we use published reconstructions of the tectonic evolution of a region to predict the thermal structure from which we calculate physical quantities like p wave velocity basin subsidence and basement heat flow we show an application of this approach to two reconstructions of the late mesozoic and cenozoic evolution of the mediterranean region the resulting synthetic velocity models are tested against seismological models of the mantle structure obtained independently by delay time tomography subsidence and heat flow predictions are compared with actual observations to further constrain the geological assumptions underlying the forward models the mantle models predicted from reconstructions of the evolution of the mediterranean region correlate with major features in the tomographic images from our model results we conclude that the present distribution of seismic velocities in the mediterranean region is largely determined by the tectonic evolution during at least the last 40 m y this means we can verify processes represented in different tectonic scenarios with the seismologically determined velocity structure seen from a different perspective the model results contribute to understanding the causes of the velocity structure imaged by delay time tomography by showing how the tectonic evolution results in this structure

revision of the timing magnitude and distribution of neogene rotations in the western aegean region to evaluate the dimension and the timing of the clockwise rotating domain and the nature of the structures that accommodate the rotating domain in the western aegean region paleomagnetic analyses were carried out in northern western and southwestern greece the results show that the rotating domain covers an area including the external albanides western mainland greece including evia and probably at least partly the peloponnesos smaller clockwise rotations on the order of 30 408 were reported previously from the chalkidiki peninsula and the islands of skyros and limnos previously two phases of approximately 258 of rotation were suggested the last one during the plio pleistocene our analysis shows that the western aegean domain rotated approximately 408 clockwise between 15 13 and 8 ma followed by an additional 108 after 4 ma the rotating domain is accommodated in the north by deformation associated with the scutari pec fault zone and in the west by the ionian thrust and the hellenic subduction zone to the south no rocks older than 10 ma are available so no conclusive data are obtained to the east of the rotating domain extensional detachment systems of the cyclades and rhodope areas were active during the rotation phase and may explain at least part of the differences in finite amounts of rotation between nonrotation or counterclockwise rotations observed in northern and eastern greece and the large clockwise rotations in western greece d 2004 elsevier b v all rights reserved

large scale waveform inversions of surface waves for lateral heterogeneity 2 application to surface waves in europe and the mediterranean linear surface wave scattering theory is used to reconstruct the lateral heterogeneity under europe and the mediterranean using surface wave data recorded with the network of autonomously recording seismographs nars the waveform inversion of the phase and the amplitude of the direct surface wave leads to a variance reduction of approximately 40 and results in phase velocity maps in the period ranges 30 40 s 40 60 s and 60 100 s a resolution analysis is performed in order to establish the lateral resolution of these inversions using the phase velocity perturbations of the three period bands a two layer model for the s velocity under europe and the mediterranean is constructed the s velocity perturbations in the deepest layer 100 200 km are much more pronounced than in the top layer 0 100 km which confirms that the low velocity zone exhibits pronounced lateral variations in both layers the s velocity is low under the western mediterranean while the s velocity is high under the scandinavian shield in the deepest layer a high s velocity region extends from greece under the adriatic to northern italy several interesting smaller features such as the massif central are reconstructed one of the spectacular features of the reconstructed models is a sharp transition in the layer between 100 and 200 km near the tornquist tesseyre zone this would indicate that there is a sharp transition at depth between central europe and the east european platform the waveform inversion of the surface wave coda leads to good waveform fits but the reconstructed models are chaotic this is due both to a lack of sufficient data for a good imaging of the surface wave energy on the heterogeneities and to an appreciable noise component in the surface wave coda

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

a plate tectonics oddity caterpillar walk exhumation of subducted continental crust since plate tectonics began on earth grandiose subduction factories have continually shaped the continents accreting continental blocks and new crust at the convergent plate boundaries an enigmatic product of subduction factories is the high pressure to ultrahigh pressure hp uhp metamorphic crustal rocks regurgitated to earth s surface sometimes from depths as great as 200 km the aegean backarc domain comprises two continental blocks that underwent hp metamorphism during the subduction of the african plate here we use thermomechanical numerical simulations to show that subduction of small continental lithosphere blocks separated by oceanic domains induces variations in the slab buoyancy giving rise to episodic rollback exhumation cycles the single self consistent numerical model successfully reproduces the major structural patterns and pressure temperature time paths of hp rocks across the aegean we suggest that the caterpillar walk of exhuming hp rock units revealed by our simulations is a fundamental mechanism behind hp exhumation globally

geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings the tyrrhenian sea and surroundings abstract information on the physical and chemical properties of the lithosphere asthenosphere system las can be obtained by geophysical investigation and by studies of petrology geochemistry of magmatic rocks and entrained xenoliths integration of petrological and geophysical studies is particularly useful in geodynamically complex areas characterised by abundant and compositionally variable young magmatism such as in the tyrrhenian sea and surroundings a thin crust less than 10 km overlying a soft mantle where partial melting can reach about 10 is observed for magnaghi vavilov and marsili which belong to the central tyrrhenian sea backarc volcanism where subalkaline rocks dominate similar characteristics are seen for the uppermost crust of ischia a crust about 20 km thick is observed for the majority of the continental volcanoes including amiata vulsini roccamonfina phlegraean fields vesuvius vulture stromboli vulcano lipari etna and ustica a thicker crust is present at albani about 25 km and at cimino vico sabatini about 30 km the structure of the upper mantle in contrast shows striking differences among various volcanic provinces volcanoes of the roman region vulsini sabatini alban hills sit over an upper mantle characterised by vs mostly ranging from about 4 2 to 4 4 km s at the alban hills however slightly lower vs values of about 4 1 km s are detected between 60 and 120 km of depth this parallels the similar and rather homogeneous compositional features of the roman volcanoes whereas the lower vs values detected at the alban hills may reflect the occurrence of small amounts of melts within the mantle in agreement with the younger age of this volcano the axial zone of the apennines where ultrapotassic kamafugitic volcanoes are present has a mantle structure with high velocity lid vs 4 5 km s occurring at the base of a 40 km thick crust beneath the campanian volcanoes of vesuvius and phlegraean fields the mantle structure shows a rigid body dipping westward a feature that continues southward up to the eastern aeolian arc in contrast at ischia the upper mantle contains a shallow low velocity layer vs 3 5 4 0 km s just beneath a thin but complex crust the western aeolian arc and ustica sit over an upper mantle with vs 4 2 4 4 km s although a rigid layer vs 4 55 km s from about 80 to 150 km occurs beneath the western aeolian arc in sardinia no significant differences in the las structure are detected from north to south the petrological geochemical signatures of italian volcanoes show strong variations that allow us to distinguish several magmatic provinces these often coincide with mantle sectors identified by vs tomography for instance the roman volcanoes show remarkable similar petrological and geochemical characteristics mirroring similar structure of the las the structure and geochemical isotopic composition of the upper mantle change significantly when we move to the stromboli campanian volcanoes the geochemical signatures of ischia and procida volcanoes are similar to other campanian centres but sr pb isotopic ratios are lower marking a transition to the backarc mantle of the central tyrrhenian sea the structural variations from stromboli to the central vulcano and lipari and western aeolian arc are accompanied by strong variations of geochemical signatures such as a decrease of sr isotope ratios and an increase of nd pb isotope and lile hfse ratios the dominance of mafic subalkaline magmatism in the tyrrhenian sea basin denotes large degrees of partial melting well in agreement with the soft characteristics of the uppermost mantle in this area in contrast striking isotopic differences of plio quaternary volcanic rocks from southern to northern sardinia does not find a match in the las geophysical characteristics the combination of petrological and geophysical constraints allows us to propose a 3d schematic geodynamic model of the tyrrhenian basin and bordering volcanic areas including the subduction of the ionian adria lithosphere in the southern tyrrhenian sea and to place constraints on the geodynamic evolution of the whole region

relationship between kamen volcano and the klyuchevskaya group of volcanoes kamchatka data on the geology petrography mineralogy and geochemistry of rocks from kamen volcano central kamchatka depression are presented and compared with rocks from the neighbouring active volcanoes the rocks from kamen and ploskie sopky volcanoes differ systematically in major elemental and mineral compositions and could not have been produced from the same primary melts the compositional trends of kamen stratovolcano lavas and dikes are clearly distinct from those of klyuchevskoy lavas in all major and trace element diagrams as well as in mineral composition however lavas of the monogenetic cones on the southwestern slope of kamen volcano are similar to the moderately high mg basalts from klyuchevskoy and may have been derived from the same primary melts this means that the monogenetic cones of kamen volcano represent the feeding magma for klyuchevskoy volcano rocks from kamen stratovolcano and bezymianny form a common trend on all major element diagrams indicating their genetic proximity this suggests that bezymianny volcano inherited the feeding magma system of extinct kamen volcano the observed geochemical diversity of rocks from the klyuchevskaya group of volcanoes can be explained as the result of both gradual depletion over time of the mantle n morb type source due to the intense previous magmatic events in this area and the addition of distinct fluids to this mantle source

lithosphere tearing at step faults response to edges of subduction zones abstract slab edges are a relatively common feature in plate tectonics two prominent examples are the northern end of the tonga subduction zone and the southern end of the new hebrides subduction zone near such horizontal terminations of subduction trenches ongoing tearing of oceanic lithosphere is a geometric consequence we refer to such kinks in the plate boundary as a subduction transform edge propagator or step other steps are the north and south ends of the lesser antilles trench the north end of the south sandwich trench the south end of the vrancea trench and both ends of the calabria trench volcanism near steps is distinct from typical arc volcanism in some cases slab edges appear to coincide with mantle plumes using 3d mechanical models we establish that step faults are stable plate tectonic features in most circumstances in the probably rare cases that the resistance to fault propagation is high slab break off will occur relative motion along the transform segment of the plate boundary often is non uniform and the step is not a transform plate boundary in the rigid plate tectonics sense of the phrase step propagation may result in substantial deformation rotation topography and sedimentary basins with a very specific time space evolution surface velocities are substantially affected by nearby steps

shallow anisotropy in the mediterranean mantle from surface waves 1 we present new evidence for the existence of the love rayleigh discrepancy in the mediterranean region and constrain the average polarization anisotropic structure of the mediterranean mantle we analysed regional rayleigh and love waveforms recorded at 3 component broadband seismic stations none of the 3 component seismograms could be fit with a single 1d isotropic and smooth velocity model however satisfactory fits for individual rayleigh and love waveforms could often be obtained using realistic 1d velocity models we used these 1d path average velocity structures to derive 3d s velocity models for the mediterranean region our results show that love waves require higher velocities about 200 m s compared to rayleigh waves between 30 and 120 km depth we relate the observed anisotropy to lattice preferred orientation of crystallographic axes of elastically anisotropic minerals such as olivine

thrust regime and transpression regime tectonics in the tauern window eastern alps below the penninic nappes of the tauern window the deepest level of the alpine thrust system is exposed in the parautochthonous sedimentary sequence of helvetic facies

the african plate a history of oceanic crust accretion and subduction since the jurassic we present a model for the jurassic to present evolution of plate boundaries and oceanic crust of the african plate based on updated interpretation of magnetic gravity and other geological and geophysical data sets location of continent ocean boundaries and age and geometry of old oceanic crust jurassic and cretaceous are updated in the light of new data and models of passive margin formation a new set of oceanic palaeo age grid models constitutes the basis for estimating the dynamics of oceanic crust through time and can be used as input for quantifying the plate boundary forces that contributed to the african plate palaeo stresses and may have influenced the evolution of intracontinental sedimentary basins as a case study we compute a simple model of palaeo stress for the late cretaceous time in order to assess how ridge push slab pull and horizontal mantle drag might have influenced the continental african plate we note that the changes in length of various plate boundaries especially trenches do not correlate well with absolute plate motion but variations in the mean oceanic crust age seem to be reflected in acceleration or deceleration of the mean absolute plate velocity

upper mantle structure beneath the alpine orogen from high resolution teleseismic tomography 1 to understand the evolution of the alpine orogen knowledge of the actual structure of the lithosphere asthenosphere system is important we perform high resolution teleseismic tomography with manually picked p wave arrival times from seismograms recorded in the greater alpine region the resulting data set consists of 4199 relative p wave arrivals and 499 absolute p wave arrivals from 76 teleseismic events corrected for the contribution of the alpine crust to the travel times the three dimensional 3 d crustal model established from controlled source seismology data for that purpose represents the large scale alpine crustal structure absolute p wave arrival times are used to compute an initial reference model for the inversion tests with synthetic data document that the combination of nonlinear inversion high quality teleseismic data and usage of an a priori 3 d crustal model allows a reliable resolution of cells at 50 km 50 km 30 km hence structures as small as two cells can be resolved in the upper mantle our tomographic images illuminate the structure of the uppermost mantle to depth of 400 km along strike of the alps the inversion reveals a high velocity structure that dips toward the se beneath the adriatic microplate in the western and central alps in the eastern alps we observe a northeastward dipping feature subducting beneath the european plate we interpret this feature in the western and central alps as subducted mainly continental european lower lithosphere for the east we propose that parts of the vardar oceanic basin were subducted toward the ne forcing continental adriatic lower lithosphere to subduct northeastward beneath the european plate

upper mantle s velocity structure of north america we have inverted fundamental and higher mode rayleigh waveforms from 685 vertical component broadband seismograms with wave paths over north america to obtain an image of the upper mantle s velocity structure down to 660 km among the well resolved features of the new model are 1 a high velocity root beneath the north american craton which extends no deeper than 250 km except near the archean core of the craton where depths of 350 km are reached 2 a weak band of low velocity along the eastern margin of the north american craton which reaches into the transition zone 3 a low velocity slab window beneath the western united states down to a depth of 300 km 4 areas of low uppermost mantle velocity beneath the cascade volcanoes the yellowstone hotspot track the colorado plateau the sierra madre occidental and the grabens bordering the jalisco block and 5 a pronounced band of high velocities in the transition zone coinciding with the expected location of the subducted trailing fragments of the farallon plate we introduce several improvements to the method of partitioned waveform inversion which was used to compute the new model rather than to correct for an estimated depth to the mohorovicic discontinuity we leave the crustal thickness as a free though yet poorly resolved parameter in the inversion we also improve the windowing and filtering operator used to select uncontaminated waveforms

surface wave dispersion measurements from ambient seismic noise analysis in italy summary we present the surface wave dispersion results of the application of the ambient noise method to broad band data recorded at 114 stations from the istituto nazionale di geofisica e vulcanologia ingv national broad band network some stations of the mediterranean very broadband seismographic network mednet and of the austrian central institute for meteorology and geodynamics zamg vertical component ambient noise data from 2005 october to 2007 march have been cross correlated for station pairs to estimate fundamental mode rayleigh wave green s functions cross correlations are calculated in 1 hr segments stacked over periods varying between 3 months and 1 5 yr rayleigh wave group dispersion curves at periods from 8 to 44 s were determined using the multiple filter analysis technique the study region was divided into a 0 2 0 2 grid to invert for group velocity distributions checkerboard tests were first carried out and the lateral resolution was estimated to be about 0 6 the resulting group velocity maps from 8 to 36 s show the significant difference of the crustal structure and good correlations with known geological and tectonic features in the study region the po plain and the southern alps evidence lower group velocities due to soft alluvial deposits and thick terrigenous sediments our results also clearly showed that the tyrrhenian sea is characterized with much higher velocities below 8 km than the italian peninsula and the adriatic sea which indicates a thin oceanic crust beneath the tyrrhenian sea

transalp deep crustal vibroseis and explosive seismic profiling in the eastern alps abstract the transalp consortium comprising institutions from italy austria and germany carried out deep seismic reflection measurements in the eastern alps between munich and venice in 1998 1999 and 2001 in order to complement each other in resolution and depth range the vibroseis technique was combined with simultaneous explosive source measurements additionally passive cross line recording provided three dimensional control and alternative north south sections profits were obtained by the combination of the three methods in sectors or depths where one method alone was less successful the transalp sections clearly image a thin skinned wedge of tectonic nappes at the northern alpine front zone unexpected graben or half graben structures within the european basement and thick skinned back thrusting in the southern frontal zone beneath the dolomite mountains a bi vergent structure at crustal scale is directed from the alpine axis to the external parts the tauern window obviously forms the hanging wall ramp anticline above a southward dipping deep reaching reflection pattern interpreted as a tectonic ramp along which the penninic units of the tauern window have been up thrusted the upper crystalline crust appears generally transparent the lower crust in the european domain is characterized by a 6 7 km thick laminated structure on the adriatic side the lower crust displays a much thicker or twofold reflective pattern the crustal root at about 55 km depth is shifted around 50 km to the south with respect to the main alpine crest

tomographic images of the upper mantle below central europe and the mediterranean results from delay time tomography of the european mediterranean upper mantle are discussed and where possible interpreted in terms of geodynamic processes slab like positive velocity anomalies of which the locations correlate well with deeper seismicity are found beneath spain the tyrrhenian basin and the aegean these structures are interpreted as images of subducted slabs large aseismic regions with positive velocity anomalies are found beneath the western mediterranean italy the alps dinarides the pannonian basin northern greece and the aegean these anomalies can also be linked to subducted lithosphere from the anomaly patterns it is deduced that subduction occurred below the western mediterranean and along both sides of the adriatic micro plate beneath the dinarides and northern greece the velocity structures suggest detachment of the slab from the surface

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

neogene and quaternary rollback evolution of the tyrrhenian sea the apennines and the sicilian maghrebides reconstruction of the evolution of the tyrrhenian sea shows that the major stage of rifting associated with the opening of this basin began at similar to10 ma it involved two episodes of back arc extension which were induced by the rollback of a west dipping subducting slab the first period of extension 10 6 ma was prominent in the northern tyrrhenian sea and in the western part of the southern tyrrhenian sea the second period of extension mainly affected the southern tyrrhenian sea began in the latest messinian 6 5 ma and has been accompanied by subduction rollback at rates of 60 100 km myr 1 slab reconstruction combined with paleomagnetic and paleogeographic constraints indicates that in the central apennines the latest messinian 6 5 ma arrival of a carbonate platform at the subduction zone impeded subduction and initiated a slab tear and major strike slip faults these processes resulted in the formation of a narrow subducting slab beneath the ionian sea that has undergone faster subduction rollback and induced extreme rates of back arc extension

linking the alps and apennines subduction systems new constraints revealed by high resolution teleseismic tomography abstract we report a new model of the upper mantle structure beneath italy obtained by means of p wave teleseismic tomography besides the recent and remarkable development of the italian seismic network a high model resolution has been achieved improving the inversion method upon the ach method used in previous investigations and picking high quality arrival times with the multi channel cross correlation technique the finer details of our vp model yield new insights into the heterogeneous structure of the adria continental lithosphere involved in the collision between the africa and europe plates a wide low vp anomaly located in the northern adria mantle facing the alpine high vp slab supports the idea that the adria lithosphere has been hydrated and thinned during the alpine subduction we argue that this mantle softening may have played a key role in favoring the subsequent delamination of the adria lithosphere in the northern apennines we hypothesize that delamination of continental lithosphere previously thinned in a back arc setting may be considered a key process to favor subduction polarity reversal and recycling of continental material into the mantle circulation conversely in the central southern apennines the velocity structure is consistent with the existence of a deeper oceanic slab that flattens at the base of the upper mantle in agreement with the widely accepted geodynamic evolution of the central mediterranean by slab retreat and back arc spreading the oceanic slab is discontinuously detached from the surface plate suggesting a different structure of the adria lithosphere which resists subduction instead of favoring delamination

epmantle a 3 d transversely isotropic model of the upper mantle under the european plate summary we present a new 3 d transversely isotropic shear wave velocity model of the european and mediterraneanuppermantleobtainedbyanalysisofsurfacewaves datausedarefundamentalmode rayleigh and love group velocity measurements in the period range 35 170 s taken on seismograms recorded by european stations for regional earthquakes the tomographic inversion to map the 3 d earth structure is split into two steps first we regionalize the group velocity dispersion measurements obtaining distinct geographical group velocity maps at different periods then each local dispersion curve is inverted separately to find the shear wave velocity structure at depth the inversion benefits from using ap rioriinformation from a 3 d global mantle model s20rts and a new detailed european crustal model epcrust to constrain the shallower layers the inversion scheme follows a non linear iterative algorithm by which rayleigh and love group slowness are inverted simultaneously for the best fitting isotropic voigt shear wave speed 2 vsv 1 vsh and radial anisotropy parameter vsh vsv final merging of the vs profiles results in a new higher resolution 3 d model of european upper mantle we find that western europe and mediterranean sea are mainly characterized by relatively low velocities strongly contrasting with the fast roots of the eastern european craton many regional scale structures are also evident in the model thus providing insights into the complex geodynamic framework of the european continent most prominent are the low velocity west mediterranean spreading basins and european cenozoic rift system and seismically fast features connected to subduction of adria microplate hellenic arc and calabrian arc radial anisotropy does not vary very significantly with respect to the prem profile as available data only resolve lateral variations to a limited degree due to trade off with velocity epmantle has the potential to provide a reliable seismological reference for the upper mantle structure in the broad european region

tomographic constraints on the geodynamic evolution of the italian region in this paper we present p wave tomographic images of the mantle beneath italy obtained by inverting 6000 teleseismic p and pkp wave arrival times accurately repicked recorded in the time period 1988 1994 by the stations of the national seismic network of the istituto nazionale di geofisica we pay great attention in the data selection and picking procedure of seismic phases to obtain a very high quality data set the data were inverted with the well established aki christofferson husebye tomographic technique different reference models and residuals computation have been tried to verify the stability of the results the high quality of the repicked arrival times allows us to enhance the definition of the deep structures beneath both the alps and the apennines looking for their lateral and vertical continuity down to 800 km depth the main finding of this study is a continuous high velocity body located between 250 and 670 km depth beneath the entire apenninic system dipping toward the tyrrhenian area which continues upward segmented in two main anomalies in the northern apenninic and the calabrian arcs we interpret this high velocity feature as the subducted oceanic lithosphere between the eurasian and african plates dipping down to the upper lower mantle boundary beneath the tyrrhenian sea the retrieved images of the lithosphere subducting beneath apennines are reliable in terms of thickness about 80 90 km and p wave velocity contrast 2 4 higher than the normal mantle furthermore our tomographic images which focus on the deep geometry and continuity of the velocity structures provide new keys to understanding the geodynamic evolution of the italian region the segmentation of the high velocity slab upward suggests a complex evolution of the arc trench system and the initially continuous subduction of the ionian adriatic plate progressively developed in subordinate arcs probably due to lateral heterogeneity of the subducting lithosphere

toward a generalized plate motion reference frame an absolute plate motion apm model is required to address issues such as the thermochemical evolution of earth s mantle all apm models have to rely on indirect inferences including those based on hot spots and seismic anisotropy each with their own set of uncertainties here we explore a seafloor spreading aligned reference frame we show that this reference frame fits azimuthal seismic anisotropy in the uppermost mantle very well the corresponding euler pole is close to those of hot spot reference frames ridge motion minimizing models and geodynamic estimates of net rotation and predicts clear trench motion patterns we conclude that a net rotation pole guided by the spreading aligned model at 64 e 61 s with moderate rotation of 0 2 0 3 myr could indeed represent a standard comprehensive reference frame for present day plate motions with respect to the deep mantle

subduction rollback slab breakoff and induced strain in the uppermost mantle beneath italy differences in seismic anisotropy revealed by split sks waves that traverse the upper mantle beneath the italian region reveal four areas of internally coherent anisotropic strength providing evidence for mantle strain partitioning when compared to uppermost mantle structure imaged by tomography the sequence of these areas displays a straightforward parallelism under proper assumptions the correspondence between areas of coherent splitting degree and areas of coherent velocity perturbations offers new insights into the late evolution of subduction in italy and their effect on mantle strain

the lithosphere asthenosphere system in fennoscandia abstract we present a summary of the available information on rayleigh wave dispersion data for the fennoscandian region the observations have been combined to produce regional dispersion relations which have then been subjected to the hedgehog inversion procedure the results are presented on a map outlining the thickness of the lid and the shear velocities in both the lid and the asthenosphere channel lid thickness up to around 135 km is found in the bothnia north central finland area with if any weak shear velocity contrast to the underlying layer the surrounding areas are characterized by lid thickness up to around 75 km a stronger low velocity zone to lid contrast may be found in the caledonian and baltic sea area 0 25 0 45 km s taking into account moho depth data and the aforementioned results a map of the lithosphere asthenosphere system was derived

three dimensional s wave structure of the upper mantle beneath turkey from surface wave tomography summary a 3 d upper mantle structure beneath turkey is investigated using phase speeds of fundamental mode rayleigh waves employing a conventional two station method with high density seismic networks in turkey we analyse 289 seismic events with moment magnitude 5 5 and greater and with focal depth shallower than 100 km between 2006 and 2008 waveform data are derived from 164 three component broad band seismic stations operated by two national seismic networks at first rayleigh wave phase speed maps are obtained from the inversion of two station phase speeds using about 1000 3000 paths depending on the period of rayleigh waves the three dimensional s wave model is then obtained in the depth range from 40 to 180 km using the phase speed maps in the period range from 25 to 120 s our model reveals the fast anomalies in the north of cyprus associated with the subducted portion of the african oceanic lithosphere from the cyprus trench we identify a vertical discontinuity of the fast anomaly associated with the cyprus slab starting at 60 80 km depth which may represent a minor tear of the cyprus slab we observed that the western part of the cyprus slab is getting closer to the edge of the hellenic slab beneath the isparta angle ia and antalya basin our model also indicates a slow wave speed anomaly beneath the ia and antalya basin probably due to hot materials of asthenosphere rising from a tear of the subducted african oceanic lithosphere that is a slab tear between the cyprus and the hellenic subductions in the eastern part of turkey a widespread slow anomaly appears in the model that corresponds to the eastern anatolian accretionary complex eaac our model shows a fast anomaly beneath the eaac that can be interpreted as the detached portion of the subducted arabian lithosphere

belt bending driven by lateral bending of subducting lithospheric slab geophysical evidences from the northern apennines italy abstract many of the mountain belts displaying a curved shape are oroclines i e are produced after progressive bending of an originally straight fold and thrust belt the bending process was previously explained as a consequence of several possible events taking place in the crustal orogenic wedge such as occurrence of obstacles non coaxial deformation and movements on wrench faults recent paleomagnetic results from the northern apenninic arc document that this belt is properly an orocline and results from late messinian early pliocene bending of a messinian straight belt foredeep system tomographic images in turn show the presence of a high velocity body interpreted as subducted slab in the upper mantle beneath the northern apennines between 35 and 670 km depth down to 100 km this body displays an arcuate shape which closely mirrors the geological outlines while it appears to be straight and parallel to the messinian pre rotated belt at depth we explore here the possibility that the arcuate shape of the northern apennines is a consequence closely following in time of much deeper processes than previously suggested i e the lateral bending of the subducting adriatic plate

the lithosphere in central europe seismological and petrological aspects abstract the lithosphere thickness in the variscan belt of central europe varies between about 60 and 150 km with typical values of 100 120 km our estimates derived from directionally independent representative p wave residuals are in good agreement with magnetotelluric determinations of a layer with increased conductivity in the upper mantle the large scale anisotropies of the subcrustal lithosphere beneath four seismological stations determined from spatial variations of relative p residuals vary between 6 5 and 15 2 for p velocities the s wave anisotropies determined from sks polarizations vary between 2 2 and 6 7 these values are in reasonable agreement with the anisotropies of peridotites determined in laboratory systematic spatial variations of the directional terms of relative residuals in dependence on azimuths and incidence angles suggest the existence of large dipping anisotropic structures in the subcrustal lithosphere the residual patterns at most stations in the saxothuringicum rhenohercynicum and in the massif central imply northwesterly orientated dips of the anisotropic structures while stations in the moldanubicum the alpine foredeep and most of the alps north of the insubric line suggest southeasterly orientated dips in our interpretation the dipping anisotropic structures may represent paleosubductions which retain olivine preferred orientations originating from an ancient oceanic lithosphere the variscides of central europe may thus represent a collision zone characterized by two systems of paleosubductions divergent relative to the suture between the moldanubicum and the saxothuringicum

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