mapping upper mantle anisotropy beneath se france by sks splitting indicates neogene asthenospheric flow induced by apenninic slab roll back and deflected by the deep alpine roots the presence of two regional seismic networks in southeastern france provides us high quality data to investigate upper mantle flow by measuring the splitting of teleseismic shear waves induced by seismic anisotropy the 10 three component and broadband stations installed in corsica provence and western alps efficiently complete the geographic coverage of anisotropy measurements performed in southern france using temporary experiments deployed on geodynamic targets such as the pyrenees and the massif central teleseismic shear waves mainly sks and skks are used to determine the splitting parameters the fast polarization direction and the delay time delay times ranging between 1 0 and 1 5 s have been observed at most sites but some larger delay times above 2 0 s have been observed at some stations such as in northern alps or corsica suggesting the presence of high strain zones in the upper mantle the azimuths of the fast split shear waves define a simple and smooth pattern trending homogeneously wnw ese in the nice area and progressively rotating to nw se and to ns for stations located further north in the alps this pattern is in continuity with the measurements performed in the southern massif central and could be related to a large asthenospheric flow induced by the rotation of the corsica sardinia lithospheric block and the retreat of the apenninic slab we show that seismic anisotropy nicely maps the route of the slab from the initial rifting phase along the gulf of lion 30 22 ma to the drifting of the corsica sardinia lithospheric block accompanied by the creation of new oceanic lithosphere in the liguro provencal basin 22 17 ma in the external and internal alps the pattern of the azimuth of the fast split waves follows the bend of the alpine arc we propose that the mantle flow beneath this area could be influenced or perhaps controlled by the alpine deep penetrative structures and that the alpine lithospheric roots may have deflected part of the horizontal asthenospheric flow around its southernmost tip

seismic anisotropy tracing plate dynamics in the mantle elastic anisotropy is present where the speed of a seismic wave depends on its direction in earth9s mantle elastic anisotropy is induced by minerals that are preferentially oriented in a directional flow or deformation earthquakes generate two seismic wave types compressional p and shear s waves whose coupling in anisotropic rocks leads to scattering birefringence and waves with hybrid polarizations this varied behavior is helping geophysicists explore rock textures within earth9s mantle and crust map present day upper mantle convection and study the formation of lithospheric plates and the accretion of continents in earth history

including anisotropy in 3 d velocity inversion and application to marlborough new zealand summary two types of seismic velocity heterogeneity are often observed in a given region pronounced patterns of anisotropy shown by local earthquake shear wave splitting and seismic velocity structure imaged by local earthquake traveltimes we seek to combine these types of observations by including anisotropy in 3 d velocity inversion the fast polarization directions from local earthquake shear wave splitting are used to define an initial anisotropy model the ray paths are estimated for each of the shear wave splitting observations and the 3 d initial model is determined via an averaging process and a coherence analysis the initial magnitude of anisotropy at a node is dependent on the number of adjacent ray paths and the consistency of the shear wave splitting anisotropy measurements the traveltime inversion is parametrized with an isotropic component and two azimuthal anisotropy parameters for each node the ray paths are defined with approximate 3 d ray tracing and for each point along a ray path the velocity is defined as a function of the ray path azimuth at that point a blended approach is used to damp the perturbations to the magnitude of anisotropy and or perturbations to the fast direction tests with synthetic traveltime data show that the anisotropic velocity inversion method is reliable application to the marlborough region shows variations in anisotropy in the brittle crust ductile lower crust mantle and subducted slab the patterns are consistent with the shear wave splitting observations but show some additional features the maximum anisotropy is approximately 12 per cent oriented northeast between the awatere and wairau faults this high anisotropy may reflect deformation and extensive fracturing in a region of high total shear strain in the region of interaction of the ductile lower crust with the shallow subducting slab moderate anisotropy with east west orientation is imaged this is consistent with ductile deformation roughly parallel to the plate velocity

statistical properties of seismic anisotropy predicted by upper mantle geodynamic models 1 we study how numerically predicted seismic anisotropy in the upper mantle is affected by several common assumptions about the rheology of the convecting mantle and deformation induced lattice preferred orientations lpo of minerals we also use these global circulation and texturing models to investigate what bias may be introduced by assumptions about the symmetry of the elastic tensor for anisotropic mineral assemblages maps of elasticity tensor statistics are computed to evaluate symmetry simplifications commonly employed in seismological and geodynamic models we show that most of the anisotropy predicted by our convection lpo models is captured by estimates based on a best fitting hexagonal symmetry tensor derived from the full elastic tensors for the computed olivine enstatite lpos however the commonly employed elliptical approximation does not hold in general the orientations of the best fitting hexagonal symmetry axes are generally very close to those predicted for finite strain axes correlations between hexagonal anisotropy parameters for p and s waves show simple bilinear relationships such relationships can reduce the number of free parameters for seismic inversions if this information is included a priori the match between our model predictions and observed patterns of anisotropy supports earlier more idealized studies that assumed laboratory derived mineral physics theories and seismic measurements of anisotropy could be applied to study mantle dynamics the match is evident both in agreement between predicted lpo at selected model sites and that measured in natural samples and in the global pattern of fast seismic wave propagation directions

how deep can we find the traces of alpine subduction 1 slab like seismic velocity heterogeneities below the alpine chain interpreted as subducted lithosphere are imaged by tomographic studies down to only about 300 km depth a non negligible discrepancy therefore exists between tomographic and geological data the latter indicating at least 500 km of tertiary convergence at trench yet a recently published tomographic study detects a pronounced high velocity anomaly at the bottom of the upper mantle right below the alpine area combining tomographic images of the mantle geological findings and plate system kinematics we investigate how the presence of this feature in the transition zone below the alps can be traced back to the tertiary alpine subduction and possibly explain the observed discrepancy we propose that a part of the fast velocity body now residing just above the 660 km discontinuity once belonged to the alpine slab torn off by an event occurred at about 30 35 ma

how many oceans meliata vardar and pindos oceans in mesozoic alpine paleogeography the timing of rifting and subduction in the meliata vardar and pindos zones of the hellenic dinaric carpathian region indicates that they cannot be considered remnants of a single ocean basin in contrast to several recently published mesozoic paleogeographies sea floor spreading in the meliata zone culminated in middle triassic ladinian time and ceased in the late triassic and subduction occurred from this time until late jurassic closure in contrast sea floor spreading in the vardar zone began in early jurassic time and culminated in the middle jurassic and subduction occurred from latest jurassic time in the pindos zone sea floor spreading was initiated in the early triassic with late jurassic and early tertiary subduction

pn observation and interpretation in washington abstract the travel time characteristics of p n waves in the state of washington were investigated using regional earthquakes as seismic sources and stations of the state wide university of washington telemetered network as receivers there is a significant difference in upper mantle velocity between eastern washington 8 20 0 02 km sec and western washington 7 79 0 02 km sec modifications of the time term method were used to find the dependence of p velocity on distance and azimuth to the source p n velocity in eastern washington depends on the distance to the source implying a velocity gradient with depth in the upper mantle no significant distance dependence was found for western washington azimuthal anisotropy was found for p n with a northwest direction of maximum velocity in eastern washington and a north northwest direction in western washington assuming no lateral crustal velocity gradients the p n refracting interface dips to the west approximately 0 8 in eastern washington and to the southeast approximately 3 2 in western washington contour maps of the station time terms indicate significant variations in crustal structure across the state the combination of low p n velocity and small moho dip beneath western washington suggests that the subducting lithospheric slab underlying the continental margin lies below the level of transition to upper mantle velocity over much of this region

sks splitting observed at romanian broad band seismic network abstract shear wave splitting results are presented for the broad band stations of the romanian seismic network for stations buc1 and crar located in moesian platform ias in east european platform tirr and cvd in central dobrudja black sea microplate tim and drgr in dacia tisza plate including apuseni mts burar bzs and gzr in or very close to the carpathian arc the fast directions are around 135 the mean delay values t of the slow wave are slightly greater for the stations placed in platform areas t 1 5 s than for the stations situated in the proximity of carpathians t 1 2 s for the mlr station located in the south western part of vrancea area at the carpathian bend the fast direction is 48 similar to voir station located in southern carpathians 70 km west of mlr at vri and plor located in the north eastern part of vrancea the fast axis is oriented approximately on north south direction with a possible dependence of the splitting parameters with back azimuth at least for some stations the splitting results are not consistent with vertical coherent lithospheric anisotropy

insights on the upper mantle beneath the eastern alps analyses of ps and sp receiver functions from datasets collected by permanent and temporary seismic stations image a seismic discontinuity due to a negative velocity contrast across the entire eastern alps the receiver functions show the presence of the discontinuity within the upper mantle with a resolution of tens of kilometers laterally it is deeper 100 130 km below the central portion of the eastern alps and shallower 70 80 km towards the pannonian basin and in the central alps comparison with previous studies renders it likely that the observed discontinuity coincides with the lithosphere asthenosphere boundary lab east of 15 e longitude while it could be associated with a low velocity zone west of 15 e

time lapse seismic tomography of an underground mining zone abstract in this study we determined p wave tomographic images of the yongshaba deposit an underground mining zone in guizhou province china by inverting arrival time data of micro seismic events and blasts recorded by a passive seismic array consisting of 28 sensors during january to april 2014 using an event location technique and a travel time tomography method that can handle complex seismic discontinuities the damping parameter used in the damped least squares method is determined with the help of trade off curve to reveal internal p wave velocity changes of the study area under severe mining activities a time lapse data partition scheme is used to assess the human influence on the underground structure we introduce a parameter to measure the relative velocity changes in different periods the resolution of the tomographic images and the robustness of the obtained features are examined by conducting a series of checkerboard resolution tests and a restoring resolution test our tomographic results obtained from the entire data set reveal a prominent low velocity low v zone and many obvious high velocity high v zones these features match well with the geological setting and the excavation plan carried out in the mine according to in site surveys the low v zone may reflect empty volumes stress releases and rock breaking and cracking caused by mining activities whereas the high v zones are probably the consequences of local stress concentrations caused by regional stress redistribution the time lapse tomographic images may reveal the process of stress concentrations caused by rock breaking due to the continuing excavations in the entire observation period indicating that the mining activities influenced the rock property and caused complex changes of the underground structure

stress strain rate and anisotropy in kyushu japan abstract seismic anisotropy the directional dependence of wave speeds may be caused by stress oriented cracks or by strain oriented minerals yet few studies have quantitatively compared anisotropy to stress and strain over large regions here we compare crustal stress and strain rates on the island of kyushu japan as measured from inversions of focal mechanisms gps and shear wave splitting over 85 000 shear wave splitting measurements from local and regional earthquakes are obtained from the nied network between 2004 and 2012 and on aso sakurajima kirishima and unzen volcano networks strain rate measurements are made from the japanese geonet stations jma determined s arrival times processed with the mfast shear wave splitting code measure fast polarisations related to the orientation of the anisotropic medium and time delays dt related to the path length and the percent anisotropy we apply the tessa 2 d delay time tomography and spatial averaging code to the highest quality events which have nearly vertical incidence angles separating the 3455 shallow depth 40 km earthquakes using square grids with 30 km sides for all the inversions the best correlations are observed between splitting from shallow earthquakes and stress axes of maximum horizontal stress shmax and correlate with a coefficient c of 0 56 significant at the 99 confidence level their mean difference is 31 9 axes of maximum compressional strain rate and shmax are also well aligned with an average difference of 28 but they do not correlate with each other meaning that where they differ the difference is not systematic anisotropy strength is negatively correlated with the stress ratio parameter determined from focal mechanism inversion c 0 64 significant at the 99 confidence level the anisotropy and stress results are consistent with stress aligned microcracks in the crust in a dominantly strike slip regime eigenvalues of maximum horizontal strain rate correlate positively with stress ratio c 0 43 significant at 99 confidence all three orientations are e w in central kyushu where the compressional strain rate is highest both splitting and stress suggest plate boundary parallel maximum principal stress just off the coast of kyushu where strain rate measurements are sparse south western kyushu has the largest difference between directions of strain rate and stress from shallow and deep earthquakes are not well aligned suggesting that the deep earthquake waveforms are not simply split in the crust causes for the anisotropy may be olivine crystals aligned by drag of the subducting philippine sea plate in the mantle and stress aligned microcracks in the crust

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

seismic anisotropy reveals the long route of the slab through the western central mediterranean mantle abstract in the south eastern corner of the tyrrhenian basin in the central mediterranean sea a tight alignment of earthquakes along a well defined benioff zone marks one of the narrowest active trenches worldwide where one of the last fragment of the former tethys ocean is consumed seismic tomography furnishes snapshot images of the present day position of this slab and seismic anisotropy allows to reconstruct the past kinematics of the subduction process using seismic anisotropy fast directions as a proxy for the present and past mantle flow we look backward for the seismic traces of the slab motion through the western central mediterranean mantle from the starting locus of subduction toward its present day position the result of combining independent data sets provides a coherent pattern of anisotropy that illustrates an example of slab rollback from its initiation point to its present day position

first seismic evidence for continental subduction beneath the western alps the first discovery of ultrahigh pressure coesite in the european alps 30 years ago led to the inference that a positively buoyant continental crust can be subducted to mantle depth this had been considered impossible since the advent of the plate tectonics concepts although continental subduction is now widely accepted there remains debate because there is little direct geophysical evidence of a link between exhumed coesite at the surface and subducted continental crust at depth here we provide the first seismic evidence for continental crust at 75 km depth that is clearly connected with the european crust exactly along the transect where coesite was found at the surface our data also provide evidence for a thick suture zone with downward decreasing seismic velocities demonstrating that the european lower crust underthrusts the adriatic mantle these findings from one of the best preserved and long studied ultrahigh pressure orogens worldwide shed decisive new light on geodynamic processes along convergent continental margins

shear wave splitting in the eastern alps observed at the transalp network data from the temporary transalp seismic network were analysed to investigate the seismic anisotropy in the upper mantle beneath the eastern alps we operated mostly short period and some broadband stations in a dense linear array which transects the eastern alps at 12 e longitude recorded sks and skks phases with different backazimuths were used simultaneously to calculate the splitting parameters of delay time and fast axis direction for each seismic station while we found variations in the delay times between 0 8 and 2 0 s the determined fast axis directions prove to be rather consistent along the profile 60 70 n they coincide well with the trend of the eastern alps thus suggesting orogen parallel flow in the upper mantle our findings support the earlier proposed idea that the adriatic indenter which was forced northwards into the european plate during the late stage of the alpine orogeny triggered an escape movement to the less constrained pannonian basin to the east

eucrust 07 a new reference model for the european crust 1 we present a new digital model eucrust 07 for the crust of western and central europe and surroundings 35n 71n 25w 35e available results of seismic reflection refraction and receiver functions studies are assembled in an integrated model at a uniform grid 15 0 15 0 the model consists of three layers sediments and two layers of the crystalline crust besides depth to the boundaries we provide average p wave velocities in the upper and lower parts of the crystalline crust the new model demonstrates large differences in the moho depth compared to previous compilations over 10 km in some specific areas e g the baltic shield furthermore the velocity structure of the crust is much more heterogeneous than in previous maps eucrust 07 offers a starting point for numerical modeling of deeper structures by allowing correction for crustal effects beforehand and to resolve trade off with mantle heterogeneities citation tesauro m m k kaban and s a p l cloetingh 2008 eucrust 07 a new reference model for the european crust geophys res lett 35 l05313 doi 10 1029 2007gl032244

seasonality and meridional propagation of the mjo abstract the madden julian oscillation mjo is known to have a substantial impact on the variability of the asian australian summer monsoons an important but not well understood aspect of the mjo monsoon connection is the meridional propagation of bands of enhanced or reduced precipitation that are especially pronounced during the northern summer in this study the nature of the seasonality of the mjo is examined with a focus on the meridional propagation using both observations and simulations with an atmospheric general circulation model agcm a key result is that the agcm when forced with idealized eastward propagating equatorial dipole heating anomalies reproduces the salient features of the observed seasonality in the precipitation and wind fields associated with the mjo including meridional propagation into the indian and australian summer monsoon regions an analysis of the simulations and observations shows that the off equatorial precipitation anomalies are initiated by surface fricti

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

subduction of continental crust in the western alps as a result of recent deep reflection and refraction seismology the crustal structure of the western alps is now quite well defined however this raises the question of what is present below the moho such as a crustal eclogitic root this study attempts to estimate the volume of this eclogitic root on the basis of palinspastic reconstructions even with a minimum estimate of the crustal material involved in the subduction processes which took place during the alpine orogeny a significant eclogitized crustal root must be present down to depths of around 100 km below the po plain a maximum estimate suggests that a large part of this root could now be recycled in the asthenosphere

teleseismic shear wave splitting and deformations in central europe abstract we analyse the results of measurements of shear wave splitting due to azimuthal anisotropy in the upper mantle of central europe based on the sks technique the observations at seismograph stations in the eastern part of germany are combined with the published estimates of the parameters of azimuthal anisotropy at neighbouring locations these data are interpreted in terms of lattice preferred orientation of olivine which is caused by deformations in the upper mantle directions of polarization of the fast wave counted clockwise from north change from 50 70 in the western part of the region to 100 120 in the eastern part these directions are close to the trend of the hercynian fold belt and might suggest that anisotropy is frozen in the subcrustal lithosphere however the observed traveltime delays between the split waves are generally too large to be easily reconciled with the thermal and seismic estimates of thickness of the subcrustal lithosphere underneath central europe

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

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

the kaapvaal craton seismic anisotropy petrophysical analyses of upper mantle kimberlite nodules a dense network of seismic stations has been deployed on the kaapvaal craton south africa to investigate the upper mantle seismic structures in order to bring independent petrophysical constraints we analyze a direct sampling of the cratonic upper mantle and determine the seismic properties of 48 mantle nodules brought up to the earth s surface by kimberlite eruptions seismic properties of these nodules are calculated from the olivine and pyroxene crystal preferred orientations and the single crystal elastic constants despite variations in the nodules compositions microstructures and crystallographic preferred orientations seismic anisotropy is rather homogeneous throughout the craton mean s wave anisotropy is weak 2 64 which is compatible with the small measured sks wave splitting mean delay time of 0 62 s

litho asthenospheric structures of northern italy as inferred from teleseismic p wave tomography abstract regional three dimensional inversions of teleseismic p wave travel time residuals recorded by high frequency regional and local seismic networks operating along the western alps and surrounding regions were carried out and lithosphere and upper mantle p wave velocity models down to 300 km were obtained residuals of more than 500 teleseismic events recorded by 98 fixed and temporary seismic stations have been inverted the comparison between real residuals and the ones obtained from tomographic model indicates that the method is able to solve the feature of the regional heterogeneities where the resolution is good coherent lithospheric and upper mantle structures are imaged in the shallower layers high and low velocity anomalies follow the structural behaviour of the alpine apenninic chains showing the existence of very strong velocity contrasts in the deepest layers velocity contrast decreases however two deep seated high velocity structures are observed the most extended in depth and approximately trending ne sw has been interpreted as a wreck of the oldest subduction responsible of the alpine orogenesis the second one connected to the northwestern sector of the apenninic chain appears to vanish at depths greater than 180 km and is probably due to still active apenninic roots cross sections depict the spatial trend of perturbations and in particular outline the sub vertical character of the alpine and apenninic anomalies under the ligurian sea the 3 d inversion confirms the uplift of the asthenosphere in agreement with the tectonic evolution of the basin

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

p wave anisotropic tomography of the alps the first tomographic images of p wave azimuthal and radial anisotropies in the crust and upper mantle beneath the alps are determined by joint inversions of arrival time data of local earthquakes and teleseismic events our results show the south dipping european plate with a high velocity high v anomaly beneath the western central alps and the north dipping adriatic plate with a high v anomaly beneath the eastern alps indicating that the subduction polarity changes along the strike of the alps the p wave azimuthal anisotropy is characterized by mountain chain parallel fast velocity directions fvds in the western central alps and ne sw fvds in the eastern alps which may be caused by mantle flow induced by the slab subductions our results reveal a negative radial anisotropy i e vph vpv in the low velocity mantle wedge which may reflect the subvertical plate subduction and its induced mantle flow the results of anisotropic tomography provide important new information on the complex mantle structure and dynamics of the alps and adjacent regions

tomographic imaging of the alaska subduction zone the alaska subduction zone is characterized by the pacific plate descending beneath the north american plate causing abundant seismic activity in the crust and along the wadati benioff zone down to a depth of approximately 200 km we have used 142 908 p wave arrival times from 12 237 shallow and intermediate depth earthquakes recorded by the alaska earthquake information center jointly run by the geophysical institute university of alaska fairbanks and u s geological survey in the period from january 1977 to november 1991 to investigate the three dimensional 3 d p wave velocity structure beneath central and southern alaska travel times and ray paths are accurately calculated by using an efficient 3 d ray tracing technique the nonlinear tomographic problem is solved by iteratively conducting linear inversions and the velocity structure and hypocentral locations are simultaneously determined we conducted two types of inversions one is an inversion with a laterally homogeneous starting model the others are what we call slab inversions in which we introduce into the initial model the high velocity subducting pacific plate as a priori information we found that the slab inversions gave a seismologically more plausible result and a final root mean square travel time residual significantly smaller than that of the inversion with the homogeneous starting model detailed p wave tomographic images are obtained for the crust and upper mantle down to a depth of 200 km with spatial resolutions of 30 60 km the tomographic image of the upper crust correlates well with the major surface geological features such as slow sedimentary basins and fast ultramafic bodies prominent low velocity anomalies exist in the crust and upper mantle beneath active volcanoes in the mantle wedge the low velocity anomalies dip toward the continental side and extend to a depth of about 150 km which are considered to be associated with the active volcanism in the alaska subduction zone the results suggest that the subducting pacific plate has a thickness of 45 55 km and a p wave velocity 3 6 higher than that of the surrounding mantle

slab break offs in the alpine subduction zone after the onset of plate collision in the alps at 32 34 ma the deep structure of the orogen is inferred to have changed dramatically european plate break offs in various places of the alpine arc as well as a possible reversal of subduction polarity in the eastern alps have been proposed we review different high resolution tomographic studies of the upper mantle and combine shear and body wave models to assess the most reliable geometries of the slabs several hypotheses for the tectonic evolution are presented and tested against the tomographic model interpretations and constraints from geologic and geodetic observations we favor the interpretation of a recent european slab break off under the western alps in the eastern alps we review three published scenarios for the subduction structure and propose a fourth one to reconcile the results from tomography and geology we suggest that the fast slab anomalies are mainly due to european subduction adriatic subduction plays no or only a minor role along the tauern window sections possibly increasing towards the dinarides the apparent northward dip of the slab under the eastern alps may be caused by imaging a combination of adriatic slab from the dinaric subduction system and a deeper lying european one as well as by an overturned retreating european slab

seismic anisotropy and large scale deformation of the eastern alps abstract mountain chains at the earth s surface result from deformation processes within the earth such deformation processes can be observed by seismic anisotropy via the preferred alignment of elastically anisotropic minerals the alps show complex deformation at the earth s surface in contrast we show here that observations of seismic anisotropy suggest a relatively simple pattern of internal deformation together with earlier observations from the western alps the sks shear wave splitting observations presented here show one of the clearest examples yet of mountain chain parallel fast orientations worldwide with a simple pattern nearly parallel to the trend of the mountain chain in the eastern alps the fast orientations do not connect with neighboring mountain chains neither the present day carpathians nor the present day dinarides in that region the lithosphere is thin and the observed anisotropy thus resides within the asthenosphere the deformation is consistent with the eastward extrusion toward the pannonian basin that was previously suggested based on seismicity and surface geology

seismic anisotropy in the eastern united states deep structure of a complex continental plate we have analyzed shear wave splitting recorded by portable and permanent broadband and long period stations located in the eastern united states teleseismic shear waves sks skks and pks were used to retrieve the splitting parameters the orientation of the fast wave polarization plane and the delay time t in total 120 seismic events were processed allowing for more than 600 splitting measurements within the appalachians stations located in the western external part are characterized by t 1s and trending n50 70 e in the south and central regions and n30 40 e in the north closely following the trend of the orogenic belt in these areas the transition region between north and central is characterized by t 1 1 3 s and by e w trending that are at a high angle to the regional geologic trend measurements at two stations located in the eastern internal part of the belt indicate very weak anisotropy the large scale pattern of anisotropy is not consistent with that predicted for simple asthenospheric flow beneath the plate splitting along the southern and eastern margins of the continent is consistent with that expected for grenvillian deformation an alternative model of asthenospheric flow around the cratonic keel cannot be ruled out within the cratonic core the correlation between t and lithospheric thickness suggests a lithospheric anisotropy smaller length scale variations also argue for a significant contribution of lithospheric structures the fabric responsible for shear wave splitting may have formed during tectonic episodes that affected the eastern united states i e the grenville and appalachian orogenies and the subsequent rifting of the north atlantic ocean our observations in the western appalachians suggest that the anisotropy may be preserved since the grenvillian orogeny the absence of detectable splitting in the two stations in the eastern appalachians is attributed to the igneous intrusions related to the atlantic rifting the measurements in the transition between the northern and central southern appalachians constitute an intriguing anomaly whose e w have little obvious relation to the regional surface geology we suggest two possible causes 1 the local dominance of asthenospheric flow motivated by the proximity of a pervasive low velocity anomaly and 2 lithospheric deformation in a transcontinental strike slip fault zone active during the appalachian collision

deep structure of japan subduction zone as derived from local regional and teleseismic events we have determined a detailed three dimensional p wave velocity structure of the japan subduction zone to 500 km depth by inverting local regional and teleseismic data simultaneously we used 45 318 p wave arrivals from 1241 shallow and deep earthquakes which occurred in and around the japan islands the arrival times are recorded by the japan university seismic network which covers the entire japan islands densely and uniformly we also used 4211 travel time residuals from 100 teleseismic events which are read from seismograms recorded by seismic stations in northeastern japan in comparison with the previous results obtained from only local and regional events the present result for the area around the lower plate boundary and the mantle below the plate is determined more reliably because of the addition of 7035 data from 100 teleseismic events and 41 very deep earthquakes in the crust and uppermost mantle low velocity zones are clearly visible beneath active volcanoes in the mantle wedge the low velocity zones generally parallel with the slab and exist continuously to a depth of about 200 km which is consistent with the petrological geochemical and geodynamic studies we consider that the existence of volcanism related low velocity anomalies in the mantle wedge is a general seismological characteristic of subduction zones in light of all the available tomographic results for many subduction zones in the world the pacific slab beneath japan is imaged more clearly than in previous studies as a high velocity zone with a thickness of 80 90 km and a p wave velocity 4 6 higher than the normal mantle lower velocity anomalies are found in the mantle below the slab

seismic anisotropy and mantle flow from the great basin to the great plains western united states shear wave splitting and p sks and s travel time residuals are calculated for teleseismic arrivals recorded on the colorado plateau great basin program for array seismic studies of the continental lithosphere passcal portable broadband seismic deployment and for permanent stations in the western united states little shear wave splitting is observed for broadband recordings in the northern colorado plateau the rocky mountains or the central great basin the transition between the colorado plateau and the great basin is marked by moderate shear wave splitting 1 0 s and unusually late teleseismic phase arrivals this suggests material with a higher content of mantle melt or volatiles than regions to either side splitting in the transition between the colorado plateau and great basin is part of a pattern of fast polarizations that align in a semicircle surrounding a central great basin region of null no splitting measurements away from the california plate boundary splitting to the north and south of our study region aligns roughly parallel to the absolute plate motion of the north american plate no simple spatial relation of splitting with geological and geophysical features such as mountain ranges velocity anomalies gravity magnetics or heat flow is evident in most of the western united states however splitting in the great basin is compatible with asthenospheric flow the smallest shear wave splitting delay times coincide with the eureka low in heat flow also having low s velocity at 300 km depth we suggest that the circumferential pattern of fast polarization directions ringing a central region of nulls in the great basin is caused by mantle flow by the interaction of mantle up welling and the absolute motion of the north american plate

continuity of the alpine slab unraveled by high resolution p wave tomography the question of lateral and or vertical continuity of subducted slabs in active orogens is a hot topic partly due to poorly resolved tomographic data the complex slab structure beneath the alpine region is only partly resolved by available geophysical data leaving many geological and geodynamical issues widely open based upon a finite frequency kernel method we present a new high resolution tomography model using p wave data from 527 broadband seismic stations both from permanent networks and temporary experiments this model provides an improved image of the slab structure in the alpine region and fundamental pinpoints for the analysis of cenozoic magmatism u hp metamorphism and alpine topography our results document the lateral continuity of the european slab from the western alps to the central alps and the downdip slab continuity beneath the central alps ruling out the hypothesis of slab break off to explain cenozoic alpine magmatism a low velocity anomaly is observed in the upper mantle beneath the core of the western alps pointing to dynamic topography effects a ne dipping adriatic slab consistent with dinaric subduction is possibly observed beneath the eastern alps whereas the laterally continuous adriatic slab of the northern apennines shows major gaps at the boundary with the southern apennines and becomes near vertical in the alps apennines transition zone tear faults accommodating opposite dipping subductions during alpine convergence may represent reactivated lithospheric faults inherited from tethyan extension our results suggest that the interpretations of previous tomography results that include successive slab break offs along the alpine zagros himalaya orogenic belt might be proficiently reconsidered

anisotropic pn tomography in the western united states pn travel times are affected not only by lateral variations in crust and mantle velocity but also by significant amounts of laterally varying anisotropy to investigate uppermost mantle anisotropy a tomography algorithm was reformulated to include lateral variations in both velocity and horizontal anisotropy and it was applied to pn travel time data from the western united states results show that anisotropy is as important in explaining the travel time residuals as are the velocity variations a detailed resolution study examined the trade off between the velocity variations and the anisotropy variations and showed that both could be resolved for regions with good ray path coverage pn anisotropy beneath the western united states has maximum amplitudes of 0 3 km s 7 5 when resolved on a length scales of around 3 the orientations of pn anisotropy often correlate well with those inferred from shear wave splitting results this correlation suggests that orientation of mantle anisotropy does not change significantly with depth for many regions the orientation of the pn anisotropy can be correlated with some of the tectonic processes which occur within the western united states for example the fast direction of pn anisotropy parallels the northeast direction of subduction of the juan de fuca plate beneath the northwest pacific coast suggesting that there the anisotropy is related to subduction driven deformation the fast direction of pn anisotropy also parallels the strike of the san andreas fault system in central california indicating that shear strains along the plate boundary may be responsible for the anisotropy there within the great basin the pn anisotropy varies substantially and both partial melting and small scale convection within the uppermost mantle could be responsible for these anisotropy variations

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

where can seismic anisotropy be detected in the earth s mantle in boundary layers during the last 30 years considerable evidence of seismic anisotropy has accumulated demonstrating that it is present at all scales but not in all depth ranges we detail which conditions are necessary to detect large scale seismic anisotropy firstly minerals must display a strong anisotropy at the microscopic scale and or the medium must be finely layered secondly the relative orientations of symmetry axes in the different crystals must not counteract in destroying the intrinsic anisotropy of each mineral and there must be efficient mechanisms of orientation of minerals and aggregates finally the strain field must be coherent at large scale in order to preserve long wavelength anisotropy part of shallow anisotropy can be related to the past strain field frozen in anisotropy however the deep anisotropy is due to the present strain field all these conditions are fulfilled only in boundary layers of convective mantle we review in this paper the seismic data sets which provide insight into the location at depth of large scale anisotropy from the d layer up to the lithosphere in addition to the well documented seismic anisotropy in the lithosphere and asthenosphere there is new evidence of seismic anisotropy in the upper 400 660 km and lower 660 900 km transition zones and in the d layer nonetheless the bulk of the lower mantle seems close to isotropy if we assume the hypothesis that seismic anisotropy is associated with boundary layers in convective systems these observations strongly suggest that the transition zone is a boundary layer which makes the pasage of matter between the upper and the lower mantle difficult however this general statement does not rule out flow circulation between the upper and lower mantles finally the geophysical mineral physics and geological applications are briefly reviewed an intercomparison between surface wave anisotropy and body wave anisotropy data sets is presented we discuss the scientific potential of seismic anisotropy and how it makes it possible to gain more insight into continental root deformation and geodynamics processes

reconciling plate tectonic reconstructions of alpine tethys with the geological geophysical record of spreading and subduction in the alps article a new reconstruction of alpine tethys combines plate kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution from sea floor spreading through subduction to collision in the alps unlike previous models which relate the fate of alpine tethys solely to relative motions of africa iberia and europe during opening of the atlantic our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record the motions of these microplates adria iberia alcapia alkapecia and tiszia relative to both africa and europe during late cretaceous to cenozoic time involved the subduction of remnant tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces 1 131 84 ma intra oceanic subduction of the ligurian part of alpine tethys attached to iberia coincided with eo alpine orogenesis in the alcapia microplate north of africa these events were triggered primarily by foundering of the older 170 131 ma neotethyan subduction slab along the ne margin of the composite african adriatic plate subduction was linked by a sinistral transform system to e w opening of the valais part of alpine tethys 2 84 35 ma subduction of primarily the piemont and valais parts of alpine tethys which were then attached to the european plate beneath the overriding african and later adriatic plates nw translation of adria with respect to africa was accommodated primarily by slow widening of the ionian sea 3 35 ma recent rollback subduction of the ligurian part of alpine tethys coincided with western alpine orogenesis and involved the formation of the gibraltar and calabrian arcs rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable retreating adriatic and african slabs during slow convergence of africa and europe the upper european iberian plate stretched to accommodate this slab retreat in a very mobile fashion while the continental core of the adriatic microplate acted as a rigid indenter within the alpine collisional zone the subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the alps and apennines as well as beneath parts of the pannonian basin the adriatic sea the ligurian sea and the western mediterranean the predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10 30 indicating that parts of slabs may be superposed within the mantle transition zone and or that some of this subducted lithosphere became seismically transparent

the arc of the western alps in the light of geophysical data on deep crustal structure recently two international deep seismic campaigns in the western and central alps etude continentale et oceanique par reflexion et refraction sismique progetto strategico crosta profonda ecors crop roure et al 1996b and national research program 20 nrp 20 pfiffner et al 1997 have been completed here we present a synoptic interpretation of the wealth of geophysical data about deep crustal structure of the alps collected during the past 40 years including the two above mentioned geophysical projects the tectonic reinterpretation of the ecors crop high resolution seismic transect is based on an evaluation of the deep crustal structure by integrating new and literature data on surface geology combined with previously published interpretations regarding the central alps schmid et al 1996 this study reveals substantial differences in geometry and kinematics between transects across the western and central alps respectively at depth the transition between the central and western alps is marked by the western limits of an adriatic lower crustal wedge shaped structure and the northeastern limits of a similar structure made of european lower crustal material at the surface it coincides with a corridor of dextral strike slip along the tonale and simplon lines in addition the thickness of the seismogenic zone shows a remarkable variation from over 40 km beneath the penninic realm of the western alps to less than 20 km in the central alps the formation of the western alpine arc was initiated during convergence and collision before 35 myr ago when the adriatic micro plate moving northward with respect to the european foreland caused sinistral transpression in the western alps while the central and eastern alps underwent head on convergence and collision during the post collisional stage i e after 35 myr ago the arcuate shape of the western alps was accentuated by wnw directed movement and anticlockwise rotation of the adriatic microplate decoupled from the central and eastern alps along the tonale simplon dextral shear zone this led to wedging of lower crustal slices both in the western alps and in the central alps the new tectonic interpretation of the ecors crop transect allows a kinematic model to be established for crustal shortening in the western alps during the past 35 myr the ivrea mantle plays the role of a backstop in our tectonic model we distinguish three episodes of post collisional crustal shortening along the ecors crop transect from 35 to 30 ma the brianconnais basement was back thrusted over the gran paradiso units leading to 30 km of crustal shortening first episode in the early miocene movements concentrated mainly along the penninic frontal thrust and resulted in about 60 km shortening second episode post 12 ma shortening within the external massifs is associated with folding in the jura mountains when the crust was shortened by an additional 30 km third episode

layered azimuthal anisotropy of rayleigh wave phase velocities in the european alpine lithosphere inferred from ambient noise abstract passive seismic imaging of the earth is a rapidly developing field of study recent advances in noise cross correlation techniques allow imaging of isotropic surface wave and shear wave velocities in areas where earthquake numbers and distributions are insufficient to implement traditional earthquake based tomography furthermore advances in the theory underpinning surface wave inversion have led to depth dependent mapping of seismic anisotropy in the lithosphere and upper asthenosphere we show that by merging these two rapidly advancing fields we can invert noise based phase velocity measurements for azimuthally anisotropic phase speed thereby providing a highly resolved image of layered azimuthal anisotropy in continental crust we apply this new algorithm in the western alps an area of complex lithospheric structure alpine crustal thickening results from continental collision indentation of the ivrea mantle into the middle crust of the european plate rollback of the european lithospheric mantle and crustal slicing we find that anisotropy beneath the central alps is stratified in two layers one with an orogen parallel fast direction above 30 km depth and another with a strong orogen perpendicular fast direction at greater depth although our resolution is reduced outside the central alps we map orogen parallel anisotropy in the crust of the northern alpine foreland we interpret the results in the central alps as first order evidence for a model of azimuthal anisotropy in which 1 near vertical emplacement of crustal slices following detachment of the lithospheric mantle from the crust gives rise to orogen parallel fast directions of wave propagation in the crust and 2 dominantly horizontal tectonics in the thickened crustal root and uppermost mantle yield orogen perpendicular fast directions at greater depth

slab detachment under the eastern alps seen by seismic anisotropy we analyze seismic anisotropy for the eastern alpine region by inspecting shear wave splitting from sks and skks phases the eastern alpine region is characterized by a breakdown of the clear mountain chain parallel fast orientation pattern that has been previously documented for the western alps and for the western part of the eastern alps the main interest of this paper is a more detailed analysis of the anisotropic character of the eastern alps and the transition to the carpathian pannonian region sk k s splitting measurements reveal a rather remarkable lateral change in the anisotropy pattern from the west to the east of the eastern alps with a transition area at about 12 e we also model the backazimuthal variation of the measurements by a vertical change of anisotropy we find that the eastern part of the study area is characterized by the presence of two layers of anisotropy where the deeper layer has characteristics similar to those of the central alps in particular sw ne fast orientations of anisotropic axes we attribute the deeper layer to a detached slab from the european plate comparison with tomographic studies of the area indicates that the detached slab might possibly connect with the lithosphere that is still in place to the west of our study area and may also connect with the slab graveyard to the east at the depth of the upper mantle transition zone on the other hand the upper layer has nw se fast orientations coinciding with a low velocity layer which is found above a more or less eastward dipping high velocity body the anisotropy of the upper layer shows large scale nw se fast orientation which is consistent with the presence of asthenospheric flow above the detached slab foundering into the deeper mantle

across fault velocity gradients and slip behavior of the san andreas fault near parkfield a long lasting question in earthquake physics is why slip on faults occurs as creep or dynamic rupture we compute passive measurements of the seismic p wave velocity gradient across the san andreas fault near parkfield where this transition of slip mode occurs at a scale of a few kilometers unbiased measurements are obtained through the application of a new bayesian local earthquake tomographic code that avoids the imposition of any user defined initial velocity contrast across the fault or any damping scheme that may cause biased amplitude in retrieved seismic velocities we observe that across fault velocity gradients correlate with the slip behavior of the fault the p wave velocity contrast decays from 20 in the fault section that experience dynamic rupture to 4 in the creeping section suggesting that rapid change of material properties and attitude to sustain supra hydrostatic fluid pressure are conditions for development of dynamic rupture low vp and high vp vs suggest that fault rheology at shallow depth is conversely controlled by low frictional strength material

mantle dynamics and seismic anisotropy abstract observations of seismic anisotropy yield some of the most direct constraints available on both past and present day deformation in the earth s mantle insight into the character of mantle flow can also be gained from the geodynamical modeling of mantle processes on both global and regional scales we highlight recent progress toward understanding mantle flow from both observations and modeling and discuss outstanding problems and avenues for progress particularly in the integration of seismological and geodynamical constraints to understand seismic anisotropy and the deformation that produces it to first order the predictions of upper mantle anisotropy made by global mantle circulation models match seismological observations well beneath the ocean basins but the fit is poorer in regions of greater tectonic complexity such as beneath continental interiors and within subduction systems in many regions of the upper mantle models of anisotropy derived from surface waves are seemingly inconsistent with shear wave splitting observations which suggests that our understanding of complex anisotropic regions remains incomplete observations of anisotropy in the d layer hold promise for improving our understanding of dynamic processes in the deep earth but much progress remains to be made in characterizing anisotropic structure and relating it to the geometry of flow geochemical heterogeneity or phase transitions major outstanding problems related to understanding mantle anisotropy remain particularly regarding the deformation and evolution of continents the nature of the asthenosphere subduction zone geodynamics and the thermo chemical state of the lowermost mantle however we expect that new seismological deployments and closer integration of observations with geodynamical models will yield rapid progress in these areas

belt parallel mantle flow beneath a halted continental collision the western alps constraining mantle deformation beneath plate boundaries where plates interact with each other such as beneath active or halted mountain belts is a particularly important objective of mantle tectonics that may bring a depth extent to the earth s surface observation such mantle deformation can be mapped at scale lengths of several tens of kilometers through the analysis of seismological data and particularly by mapping seismic anisotropy from the splitting analysis of vertically propagating sks waves that largely reflect the strain induced crystal preferred orientations of the rock forming minerals within the upper mantle in the present study we analyse data from approximately 50 broadband seismic stations covering the western alps and we provide a coherent picture of upper mantle anisotropy beneath the belt the large scale anisotropy pattern is characterized by fast split directions that closely follow the trend of the belt moreover the maximum anisotropy magnitude is not located beneath the internal zones of the belt but instead beneath external units all suggests that the anisotropy is likely dominated by sublithospheric mantle deformation we propose that the observed anisotropy pattern can be explained by recent or active mantle flow around the eurasian slab presently plunging beneath the inner parts of the alps

does subduction polarity changes below the alps inferences from analogue modelling the surface expression of a lateral polarity change of continental mantle lithosphere subduction has been studied by using lithosphere scale physical models key parameters investigated were the degree of lateral coupling between adjacent domains of opposing subduction polarity the width of the zone separating the domains and the lithosphere geometry and rheology the model results illustrate an asymmetric lithospheric structure induced by deformation of the downgoing plates which have been separated by a narrow transition zone a wide and symmetric orogenic wedge overlying a region of thickened mantle lithosphere and hampered subduction characterizes this transition zone in addition interaction between the neighboring subduction domains caused downbending of the upper plates and resulted in the lateral termination of crustal structures and lowering of surface topography the lateral extent of interaction between the domains strongly depends on the degree of coupling between the domains the rheology of the mantle lithosphere and the amount of bulk shortening the modelling results have major implications on the interpretation of seismic and tomographic data from the european alps in terms of the crust and lithosphere geometries it appears that an observed lateral change of subduction polarity at mantle depth can explain the variations of wedge build up between the western central and eastern alps

p wave anisotropic tomography beneath northeast japan we determined a 3 d p wave anisotropic tomography beneath northeast japan by using first p arrival times the travel time inversion is parameterized with an isotropic component and two anisotropic parameters for each grid node by assuming p wave azimuthal anisotropy with hexagonal symmetry axis distributed horizontally the geometries of the conrad and moho discontinuities and the upper boundary of the subducting pacific plate are taken into account in the model our extensive synthetic tests show that the anisotropic velocity inversion method is reliable our results show that low velocity zones exist below active volcanoes in the crust in the fore arc mantle wedge and in the central portion of the mantle wedge above the high velocity pacific slab which are similar to the previous tomographic images anisotropic velocity variations are revealed in the crust mantle wedge and the subducting pacific slab the anisotropic patterns are complex and different in the upper and lower crust in the mantle wedge the fast direction of p velocity is generally trench parallel in the fore arc area while it becomes trench normal in the back arc area which agree well with the shear wave splitting results the trench parallel fast direction is revealed beneath the volcanic front which may suggest the existence of complex 3 d mantle flows in the mantle wedge the fast velocity direction in the subducting pacific slab is mostly n s which is likely due to the original fossil anisotropy of the pacific plate formed at the mid ocean ridge our result also suggests that the anisotropy is weak in the upper crust and the average amplitude of the velocity anisotropy in the mantle is no larger than 4

seismic anisotropy beneath tibet evidence for eastward extrusion of the tibetan lithosphere strong seismic anisotropy beneath tibet has recently been reported from the study of sks shear wave splitting the fast split waves are generally polarized in an easterly direction close to the present day direction of motion of the tibetan crust relative to stable eurasia as deduced from holocene slip rates on the major active faults in and around tibet this correlation may be taken to suggest that the whole tibetan lithosphere is being extruded in front of indenting india and that the anisotropic layer is the deforming asthenosphere that accommodates the motion of the tibetan lithosphere relative to the fixed mantle at depth uncertainties about this motion are at present too large to bring unambiguous support to that view assuming that this view is correct however a simple forward model is used to compute theoretical delay times as a function of the thickness of the anisotropic layer the observed delay times would require a 50 100 km thick anisotropic layer beneath south central tibet and an over 200 km thick layer beneath north central tibet where particularly hot asthenosphere has been inferred this study suggests that the asthenospheric anisotropy due to present absolute block motion might be dominant under actively deforming continents

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

defining parameters for eckhardt s digital baseflow filter digital filters are useful tools for assessing the contribution of groundwater to total river flow several of those filters have been proposed in the last decades one of the last contributions on this subject was given by ekchardt 2005 who proposed a more general form of a digital baseflow filter and showed that some of the most used filters are special cases of this general form this new filter has the inconvenience of having two parameters one of them may be obtained directly from recession analysis but the other maximum baseflow index bfimax is routinely estimated by a priori defined values according to the predominant geological characteristics of the drainage basin in this short communication we propose a method to estimate bfimax by a backwards filtering operation the method was applied using data from 15 gauging stations in brazil with a varied range of groundwater contribution to streamflow results of the new estimation method for the bfimax parameter are coherent with the values which would be adopted by considering geological characteristics of the river basins copyright 2012 john wiley sons ltd

p and s velocity anomalies in the upper mantle beneath europe from tomographic inversion of isc data we present a new tomographic model for p and s velocity anomalies beneath europe 30 n 55 n 5 w 40 e extending in depth up to 700 km and constrained by inversion of data from the international seismological center isc catalogue the algorithm uses the traveltimes from events located in the study area recorded by all available worldwide stations as well as times from teleseismic events recorded by european stations the events from the isc catalogue have been relocated and combined into composite events all the traveltimes were corrected for crustal structure using the reference model eucrust 07 the resulting velocity anomalies show similar large scale patterns as observed in previous studies but have a higher resolution which allows detection of some features in more detail for example it is now possible to assess the depth extension of the small slow velocity body beneath the eifel region and eger graben the p and the s model show a good consistency in the uppermost 200 km below most of the european area and in some parts even in the deeper layers e g beneath the apennines and the hellenic arc the new model provides clear images of some principal features which were previously detected in a limited number of studies while the comparison between p and s velocity anomalies provides novel constraints to address on their nature e g the gap in the adriatic plate subducted below the central southern apennines in this paper we pay special attention to testing the reliability of the results the random noise effect is evaluated using a test with independent inversion of two data subsets with odd even events the spatial resolution is estimated using different checkerboard tests furthermore we present a synthetic model with realistic patterns which reproduces after performing forward and inverse modelling the same shape and amplitudes of the anomalies as in the case of the real data inversion in this case the parameters of the model can be used to assess the amplitudes of p and s anomalies that is critical for evaluation of other petrophysical parameters temperature density composition etc in the upper mantle 2009 the authors journal compilation 2009 ras