upper mantle anisotropy beneath the geoscope stations seismic anisotropy has been widely studied this last decade particularly by measuring splitting of vertically propagating core shear waves the main interest in this technique is to characterize upper mantle flow beneath seismic stations on the other hand the major restriction in this method is that a single station gives a single anisotropy measurement alternative methods have been developed in order to avoid this restriction an accurate determination of upper mantle seismic anisotropy beneath a seismic station may allow one by doing anisotropy correction to characterize remote or deeper anisotropy the geoscope network is ideal for this purpose because it is composed of a large set about 26 of high quality broadband seismometers globally distributed and because some of these stations have run for more than 10 years and most of them for more than 5 years we selected about 100 events at each site generally of magnitude mb 6 0 and we performed systematic measurements of the splitting parameters fast polarization direction and delay time t on sks skks and pks phases splitting on oceanic islands has been difficult to observe owing to the low quality of the signal but also perhaps owing to complex upper mantle structures beneath the stations station kip kipapa hawaii in the pacific is the only oceanic geoscope station with a clear anisotropy we determined well constrained splitting parameters for 10 of the 17 continental stations that may be explained by a single anisotropic layer the poor correlation between fast polarization directions and the absolute plate motion together with the apparent incoherence between the plate velocities and the observed delay times suggest that a simple drag induced asthenospheric flow alone fails to explain most of the observations for some stations located on or near major lithospheric structures tam tamanrasset algeria for instance we observe a good correlation between fast polarization directions and regional structures at station scz santa cruz california we found clear variations of the splitting parameters as a function of the event backazimuth compatible with two layers of anisotropy three stations can canberra hyb hyderabad india and ssb saint sauveur badole france seem to be devoid of detectable anisotropy

upper mantle flow in eastern europe we present and discuss estimates of shear wave splitting in the upper mantle of eastern europe based on sks techniques estimates of the direction of polarization of the fast split wave and the delay of the slow wave t are obtained at seven stations uzh kov and lvv within and near the carpathians sim sev and yal in the crimean peninsula and kiev in the russian plate fast directions at all stations are around 130 close to the values previously found in central europe in the carpathians similar values of t are observed within the pannonian depression where the subcrustal lithosphere if present is very thin and in the foredeep with a thick subcrustal lithosphere this similarity suggests that the observed anisotropy is not inherited from earlier orogenies and preserved in the lithosphere in the crimea the fast direction of anisotropy in the mantle is perpendicular to the strike of the crimean mountains of late jurassic cretaceous age contrary to the expected alignment of the fast direction with the strike of a collisional belt in general the data are consistent with a present day or recent large scale mantle flow in central and eastern europe parallel to the alpine belt

the ultraslow difference the speed at which mid ocean ridges grind out new ocean floor varies considerably the slowest spreading ridges are especially tough to study but the latest data show that they are especially intriguing

crustal thicknesses in se brazilian shield by receiver function analysis implications for isostatic compensation hypothesis are proposed to explain the data 1 a lower density by 30 40 kg m 3 i n the lithospheric mantle under the archean block of the sao francisco craton relative to the proterozoic lithosphere is responsible for maintaining the high elevations in the plateau area relatively low density and high p wave velocity are compatible with a depleted low feo composition for the archean lithosphere 2 alternatively if the density contrasts between archean and proterozoic lithospheres are smaller than the values above then the crust beneath the paranabasin must be more dense than that of the craton higher crustal density and high poisson s ratio would be consistent with magmatic underplating in the lower crust beneath the paranabasin as inferred from other studies index terms 7205 seismology continental crust 1242 9360 information related to geographic region south america 7218 seismology lithosphere and upper mantle keywords crust upper mantle brazil parana basin san francisco craton

toroidal mantle flow through the western u s slab window the circular pattern of anisotropic fast axis orientations of split sks arrivals observed in the western u s cannot be attributed reasonably to either preexisting lithospheric fabric or to asthenospheric strain related to global scale plate motion a plume origin for this pattern accounts more successfully for the anisotropy field but little evidence exists for an active plume beneath central nevada we suggest that mantle flow around the edge of the sinking gorda juan de fuca slab is responsible for creating the observed anisotropy seismic images and kinematic reconstructions of gorda juan de fuca plate subduction have the southern edge of this plate extending from the mendocino triple junction to beneath central nevada and flow models of narrow subducted slabs produce a strong toroidal flow field around the edge of the slab consistent with the observed pattern of anisotropy this flow may enhance uplift extension and magmatism of the northern basin and range while inhibiting extension of the southern basin and range

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

the evolution of the carpathians pannonian system interaction between neotectonics deep structure polyphase orogeny and sedimentary basins in a source to sink natural laboratory abstract the carpathians pannonian basin system provides a natural laboratory for analysing lithospheric to surface controls on tectonic topography development in a coupled source to sink environment to link processes taking place at depth and at the surface recent research focused on the interplay between basin evolution active tectonics topography evolution and intraplate folding mechanisms neotectonic processes control landscape development and natural hazards in particular the seismicity during the late stage late neogene quaternary evolution of both the carpathians pannonian basin system and its interaction with the adjacent dinarides and balkans the deep structure of the se carpathians exerts a strong control on the post collisional evolution of the system new constraints are available from seismic tomography deep seismic reflection and refraction profiling and detailed studies of the vreancea seismicity inherited orogenic fabric and structure of the active black sea sink has a strong influence on the localisation of the neogene sediment pathways a close relationship has been established between the timing and mechanisms of stress changes in the pannonian and transylvania basins and structural episodes in the surrounding thrust belts pointing to an intrinsic mechanical coupling with these basins the orogen and its foredeep basin inversion taking place during the pliocene quaternary times in the entire carpathians pannonian system is related to changes in the regional stress field leading to differential vertical movements associated with a laterally variable folding mechanism active in the entire system short crustal folding patterns alternate with lithospheric wavelengths in the se carpathians foreland east and south carpathians transylvania and pannonian basins the lateral variability is the result of a marked contrast in rheology between these areas directly related to the crustal configuration thermal properties and late stage collision kinematics with the carpathians foreland lateral variations in the properties of the downgoing plates largely control the collision mode in the carpathians and the post collisional evolution of the entire system

mantle flow deflected by interactions between subducted slabs and cratonic keels subducting slabs can influence mantle flow but the importance of neighbouring continental cratons is little understood geodynamical modelling constrained by seismic data that identify regions of mantle flow beneath the caribbean south american plate margin shows that the deep rooted south american craton acts to deflect and enhance mantle flow into a narrow channel

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

trench parallel flow beneath the nazca plate from seismic anisotropy shear wave splitting of s and sks phases reveals the anisotropy and strain field of the mantle beneath the subducting nazca plate cocos plate and the caribbean region these observations can be used to test models of mantle flow two dimensional entrained mantle flow beneath the subducting nazca slab is not consistent with the data rather there is evidence for horizontal trench parallel flow in the mantle beneath the nazca plate along much of the andean subduction zone trench parallel flow is attributale utable to retrograde motion of the slab the decoupling of the slab and underlying mantle and a partial barrier to flow at depth resulting in lateral mantle flow beneath the slab such flow facilitates the transfer of material from the shrinking mantle reservoir beneath the pacific basin to the growing mantle reservoir beneath the atlantic basin trenchparallel flow may explain the eastward motions of the caribbean and scotia sea plates the anomalously shallow bathymetry of the eastern nazca plate the long wavelength geoid high over western south america and it may contribute to the high elevation and intense deformation of the central andes

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

towards a mechanical model for the formation of the pannonian basin abstract new maps showing crustal and lithospheric thickness variations in the pannonian basin and the surrounding east alpine carpathian and dinaric mountains have been prepared on the basis of recent seismic seismologic and electromagnetic data a map presenting miocene faults of regional significance has been also constructed for the same region by using a wealth of recently available national and or more local studies it is suggested that observed crustal and lithospheric structural contrasts have been controlled primarily by neogene kinematic history of the region kinematic history is characterized by the following main patterns 1 1 indentation by adria and large scale backthrusting in the southern alps 2 2 eastward escape and extension of the eastern alps 3 3 extensional collapse in the pannonian basin area 4 4 formation of broad wrench fault systems along strike in the dinarides and southern carpathians and the western carpathians with dextral and sinistral shear respectively 5 5 compression and accretion of the external thrust and fold belt in the eastern carpathians these kinematic patterns are thought to be interrelated and all are manifestations of the late stage evolution of an overthickened orogenic wedge in order to arrive at a better understanding of the mechanism of extension which formed the pannonian basin deep crustal seismic profiles hydrocarbon exploration reflection lines and borehole data have been analyzed in the little hungarian plain this plain represents the transition zone between the alps and the pannonian lowlands and the results are illustrated by eight interpreted cross sections one result of regional importance is the clear recognition that the transdanubian central range at the southeastern flank of the little hungarian plain is composed of alpine pre senonian thrust sheets this finding marks the end of a century of debate the allochthony of the substrata of the pannonian basin can be now considered proven another result of more general interest is that these cross sections document the mode of lithospheric extension preexisting compressional detachment planes reactivate as low angle normal faults and lead to tectonic unroofing of deeply buried metamorphic terranes characterized by ductile flow along subhorizontal lineation

thickness of the central and eastern european lithosphere as seen by s receiver functions summary s receiver functions obtained from seismograms of teleseismic events recorded at 78 european permanent broad band stations are used to estimate the thickness of the european lithosphere our results provide new independent information about the lithospheric thickness beneath the precambrian platform of eastern europe and the phanerozoic platform of central europe detailed high resolution images of the lithosphere asthenosphere boundary lab reveal indications for a typical continental lithosphere of about 100 km thickness beneath a majority of stations within central europe whereas in the vicinity of the trans european suture zone tesz the lithosphere thickens to about 130 km a relatively thin lithosphere of 80 km was found beneath the upper rhine graben region suggesting that the cenozoic extension affects the whole lithosphere no clear signal from the lab was detected beneath the alps and carpathians the lab sp phase might be disturbed by complicated structure due to ongoing collision subduction in these regions or the data are not yet sufficiently dense a relatively thicker lithosphere of about 120 km was found beneath the sw part of the bohemian massif that was formed during the variscan orogeny we found an lab depth of about 190 km near a single station located in the vrancea area eastern carpathians which is characterized by the occurrence of intermediate deep earthquakes beneath the stations located in the precambrian platform of eastern europe the lab deepens to approximately 200 km even though the converted phase from the lab is not as sharp as found beneath other stations located in central europe or even is missing

surface kinematics in the alpine carpathian dinaric and balkan region inferred from a new multi network gps combination solution abstract the understanding of the intraplate tectonics of central europe requires a detailed picture of how stress is transferred from the interaction of the eurasian nubian and anatolian plates to the alpine carpathian pannonian and dinaric regions recent strain distribution is controlled by the adria horizontal push by the vrancea vertical slab pull and associated horizontal displacements and by the aegean anatolia extension and slab roll back we present a horizontal velocity field for the alpine carpathian pannonic dinaric and balkan regions resulting from a new combination of seven different gps networks formed from permanent and campaign stations dedicated velocity profiles in two specific regions are studied in detail one is the alpine pannonian region with a detailed picture of the ns indentation of the adria microplate into the southern alps in ne italy the deformation in the tauern window and the eastwards kinematics of a pannonian plate fragment the second study region includes transylvania the southern carpathians up to the aegean sea and albania where a major right lateral shear deformation exists as a consequence of the ne convergence of the apulia platform towards the dinarids and the ssw motion of macedonia western bulgaria and rumania related to the hellenic arc dynamics in the eastern mediterranean the profiles in the alpine pannonian area indicate that a velocity drop of 2 5 0 4 mm yr associated with the adria indentation concentrates on a segment of some 50 km south of the periadriatic fault the deformation becomes extensional by a similar amount just north of the periadriatic fault in the tauern window where the updoming of the tauern window implies vertical motion which could well be associated with surface extension in the ew profile we observe a sudden velocity change of 1 5 0 2 mm yr in 20 km corresponding to the right lateral lavant fault which seems to mark the border between dominant indentation kinematics to the west and dominant extrusion kinematics to the east three profiles are considered in southern and eastern europe one across the lower adriatic sea from apulia in italy to the southern dinarides which enables it to constrain the velocity drop associated with the subduction of the adria microplate into the dinarides to 3 2 0 5 mm yr in 140 km the second profile is longitudinal and constrains the velocity inversion of 7 4 1 0 mm yr in 350 km associated with right lateral shear faults in albania the third profile crosses the transylvania region with a shortening of 2 3 1 0 mm yr in 220 km and the wallachian moesian region up to the chalcidic peninsula in n greece this lower part of the profile implies an extensional stretch of the upper crust of 3 2 0 9 mm yr in 440 km culminating in the hellenic arc strain rate maps are presented in this regional scale showing the excellent agreement between fault plane solutions of crustal earthquakes and the eigenvectors of the gps derived two dimensional strain rate tensor three profiles are considered in the balkan and se carpathians one across the lower adriatic sea from apulia in italy to the southern dinarides which enables to constrain the velocity drop associated to the subduction of the adria microplate into the dinarides to 3 2 0 5 mm yr in 140 km the second profile is longitudinal and constrains the velocity inversion of 7 4 1 0 mm yr in 350 km associated to right lateral shear faults in macedonia a highly seismic region the third profile crosses the transylvania with a shortening2 3 1 0 mm yr in 220 km and the wallachian moesian region up to the chalcidic peninsula in n greece this lower part of the profile implies an extensional stretch of the upper crust of 3 2 0 9 mm yr in 440 km culminating in the hellenic arc

development of mantle seismic anisotropy during subduction induced 3 d flow 1 the dynamics of subduction can be indirectly constrained by studying the induced mantle flow however inferring the circulation of the mantle around subducting plates from the interpretation of shear wave splitting patterns remains elusive we calculated the strain induced lattice preferred orientation lpo developed in 3 d models of subduction where retreat motions are maximized and found that in the mantle layer entrained with the downgoing slab the seismic anisotropy is trench perpendicular and becomes trench parallel deeper where the toroidal flow accommodates slab retreat synthetic sks splitting shows that in the fore arc slab rollback favors trench parallel polarization of the fast shear wave component while plate advance enhances trench perpendicular seismic anisotropy the interference between these two competing mechanisms yields subslab delay times of 0 5 to 1 3 sec comparable with those observed at most natural subduction zones the magnitude of the subslab trench parallel splitting is independent of the rate at which the slab migrates instead it is proportional to the amount of retreat

a quantitative evaluation of the contribution of crustal rocks to the shear wave splitting of teleseismic sks waves abstract the seismic elastic properties of the crust have been modelled using hypothetical polycrystals with typical crustal compositions and commonly measured petrofabrics this modelling allows us to better evaluate and quantify the crustal contribution to splitting of teleseismic sks waves mafic rocks such as anorthosite or pyroxene bearing gabbros have complex s waves properties i e with small shear wave anisotropies

mapping seismic anisotropy of the lithospheric mantle beneath the northern and eastern bohemian massif central europe abstract we evaluate 3d body wave anisotropic parameters shear wave splitting fast s polarizations and delay times of the split slow shear waves and directional terms of relative p wave residuals from data of passive seismic experiment bohema ii 2004 2005 data from 34 temporary stations increased substantial density of observations in the bohemain massif bm and allowed us to scan in detail the upper mantle structure of its northern and eastern parts for the first time we delimit domains of the mantle lithosphere in this part of the bm and infer 3d self consistent models of their fabrics by a joint inversion of the body wave anisotropic parameters fabrics of the northern and north eastern parts of the bm are approximated best by peridotite aggregates with the a c foliations dipping approximately to the n and ne respectively whereas a model with the westerly dipping a lineation fits best the fabric of the south eastern domain the saxothuringian fabric nw of the eger rift extends to the east across the elbe fault zone and continues along this zone to the southeast beneath the cretaceous basin the south eastward continuation of the elbe fault zone seems to be related to the boundary between two different fabrics of the northern and southern brunovistulian domains below the moravo silesian zone this study shows an underthrusting of the brunovistulian micro plate beneath the eastern rim of the bm and indicates that its northern and southern fragments might have originally belonged to baltica and to gondwana respectively according to a zone of distinctly decreased anisotropic signals the brunovistulian micro plate extends at least about 100 km westward beneath the moldanubian with these new findings we update the domain like mantle structure of the bm and compare the results with inferences from the upper mantle velocity tomography and depth changes of the lithosphere asthenosphere boundary retrieved in a detailed model from relative residuals and from the receiver functions inferences on anisotropic structure beneath the permanent observatories included in different experiments are stable and are validated by the bohema ii experiment

tertiary tectonic evolution of the external east carpathians romania abstract paleostress calculation and analysis of mesoscopic structures are integrated with depth interpreted geological profiles based on seismic studies and well correlation to derive a tertiary tectonic model for the east carpathians following early miocene and older orogenic phases the first tectonic event that affected the studied area is characterised by a wsw ene oriented shortening of middle miocene late burdigalian in age resulting deformations induced ene ward thrusting of tarcau and marginal units as well as the internal part of the subcarpathian nappe a second shortening event with an e w to wsw ene contraction direction took place in the late miocene sarmatian characterised by further foreland thrusting of the subcarpathian nappe and out of sequence deformation in the tarcau and marginal folds nappes along strike differences in deformation mechanisms are controlled by the friction coefficients along the main detachment layers by the lateral variations in the wedge thickness and by the involvement in the northern part of the thrusting system of the thick competent east european platform tear faulting occurred in both tectonic events the main resulting structure being the triangle zone developed south of the trotus valley the latest miocene latest sarmatian early pliocene is characterised by a strike slip stress field with nne ssw compression and wnw ese tension axis left lateral faults being dominant the last deformation which affected the studied area is characterised by nnw sse shortening during the pliocene major deformations taking place mainly in the sw most bending zone

on the relation between seismic anisotropy and finite strain because seismic anisotropy in the upper mantle is due primarily to lattice preferred orientation lpo of olivine crystals induced by deformation observations of anisotropy can provide constraints on mantle deformation and flow in this paper we use a previously published theory for deformation induced lpo ribe and yu 1991 to quantify the relation between seismic anisotropy and deformation for two model compositions a pure olivine dunite aggregate and a harzburgite comprising 70 olivine and 30 enstatite analytical and numerical solutions of the governing equations show that the predicted lpo and hence also the seismic anisotropy depends only on the finite strain and not on the deformation path by which that strain is produced the magnitude of the anisotropy depends only on the ratios c1 c2 and c2 c3 where c1 c2 c3 are the lengths of the principle axes of the finite strain ellipsoid and the directions of maximum and minimum compressional wave velocity vp coincide with the axes c1 and c3 respectively we calculate the percent anisotropies for compresional and shear waves propagating along the three principle axes of the finite strain ellipsoid as functions of the axial ratios c1 c2 and c2 c3 for our two model compositions however inferences of the magnitude of finite strain obtained using these results are likely to be minimum estimates because our theory neglects the effects of dynamic recrystallization finally we present as a byproduct of this study a new direct method for calculating the finite strain produced by an arbitiary deformation history

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

mountain building strike parallel motion and mantle anisotropy abstract geophysical and geological evidence indicates that tectonic movements parallel to the strike of orogenic belts and suture zones are the most important mode of displacement during continental collision and oblique subduction several hundred to a few thousand kilometers of displacement may have occurred this way resulting in a pervasive ductile deformation of the lithosphere consequently both crustal and mantle fabrics may reflect these movements and their study using both geological and geophysical methods could supply important clues to lithosphere behavior during mountain building on the basis of kinematic analysis of ductilely deformed crustal rocks in zones of movement a variety of tectonic models have been proposed which differ in 1 1 the timing of strike parallel motions early before or during continental accretion or late after accretion was completed 2 2 the geometric pattern of strike parallel displacement zones low angle or high angle and 3 3 the location of orogen parallel movement zones in outboard terranes on the subducting plate along the suture zone or within the continental hangingwall large scale displacements parallel to mountain belts also suggest that they occurred along lithospheric faults rooted in the upper mantle although few studies have been carried out from this view point thermal structural and petrological data support the conclusion that lithospheric faults involving the upper mantle may be discriminated from crustal faults rooted in some crustal decoupling zone where available data on mantle flow beneath orogenic belts are in agreement with mountain parallel displacements inferred from crustal studies this has an important bearing on the seismic anisotropy pattern which can be predicted in the lithospheric mantle below mountain belts the fast velocity direction which is parallel to the flow direction should therefore be recorded parallel to the strike of the belt

tectonic significance of changes in post subduction pliocene quaternary magmatism in the south east part of the carpathian pannonian region the south eastern part of the carpathian pannonian region records the cessation of convergence between the european platform moesia and the tisza dacia microplate plio quaternary magmatic activity in this area in close proximity to the vrancea zone shows a shift from normal calc alkaline to much more diverse compositions adakite like calc alkaline k alkalic mafic na alkalic and ultrapotassic suggesting a significant change in geodynamic processes at approximately 3 ma we review the tectonic setting timing petrology and geochemistry of the post collisional volcanism to constrain the role of orogenic building processes such as subduction or collision on melt production and migration the calc alkaline volcanism 5 3 3 9 ma marks the end of normal subduction related magmatism along the post collisional c limani gurghiu harghita volcanic chain in front of the european convergent plate margin at ca 3 ma in south harghita magma compositions changed to adakite like calc alkaline and continued until recent times 0 03 ma interrupted at 1 6 1 2 ma by generation of na and k alkalic magmas signifying changes in the source and melting mechanism we attribute the changes in magma composition in front of the moesian platform to two main geodynamic events 1 slab pull and steepening with opening of a tear window adakite like calc alkaline magmas and 2 renewed contraction associated with deep mantle processes such as slab steepening during post collisional times na and k alkalic magmas contemporaneous post collisional volcanism at the eastern edge of the pannonian basin at 2 6 1 3 ma was dominated by na alkalic and ultrapotassic magmas suggesting a close relationship with thermal asthenospheric doming and strain partitioning related to the adriatic indentation similar timing magma chamber processes and volume for k alkalic shoshonitic magmas in the south apuseni mountains 1 6 ma and south harghita area at a distance of ca 200 km imply a regional connection with the inversion tectonics

patterns in seismic anisotropy driven by rollback subduction beneath the high lava plains received 24 march 2011 revised 25 may 2011 accepted 31 may 2011 published 8 july 2011 1 we present three dimensional laboratory modeling of the evolution of finite strain and compare these to shear wave splitting observations in the northwest u s under the high lava plains hlp we show that relationships between mantle flow and anisotropy are complicated in subduction zones and factors such as initial orientation of the olivine fast axis style of subduction and time evolving flow are important due to increased horizontal shear systems with a component of rollback subduction have simple trench normal strain alignment within the central region of the backarc mantle wedge while those with more simple longitudinal sinking are often variable and complex in the hlp splitting observations are consistent with rollback driven laboratory results citation druken k a m d long and c kincaid 2011 patterns in seismic anisotropy driven by rollback subduction beneath the high lava plains geophys res lett 38 l13310 doi 10 1029 2011gl047541

deep seismic expression of an ancient plate boundary in europe seismological results on the structure of the upper mantle below europe reveal a marked contrast in seismic properties between precambrian and younger parts of europe the precambrian craton in eastern europe is characterized by high shear wave velocities which can be explained by low temperatures the transition to low seismic velocities below phanerozoic europe coincides with the crustal boundary zone of the craton and exists to depths of at least 140 kilometers despite the long and complex tectonic history of the plate boundary zone the transition is remarkably sharp which rules out any significant lateral transport of asthenospheric material across the suture zone

slab in the wrong place lower lithospheric mantle delamination in the last stage of the eastern carpathian subduction retreat a model with a new type of delamination of the lower lithospheric mantle is proposed to explain the pliocene to recent tectonic evolution of the eastern carpathians we suggest that after the continental collision in middle miocene time break off of the west dipping subducting slab occurred at a depth of 70 km slab break off propagated horizontally toward the east inducing lithospheric delamination and movement of the vrancea slab into its present position delamination was followed by rapid asthenospheric rise resulting in magma generation and the explosive alkaline basaltic magmatism of the persani mountains contamination of the former subduction related magmatic reservoirs with the alkalic basaltic material and differentiation processes produced the harghita calc alkaline and shoshonitic rocks the asthenospheric rise induced crustal uplift which is the triggering mechanism for extension and formation of the brasov gheorghieni hinterland basins the extension was accommodated by shortening and folding in the foreland the vertical vrancea slab appears in our model as a segment of delaminated lower lithospheric mantle that is seismically active due to the ongoing pull of the eclogitized oceanic crust the model explains the displaced and shallow position of the slab relative to the eastern carpathian suture zone

new type of olivine fabric from deformation experiments at modest water content and low stress a new type of olivine fabric was found by high strain simple shear deformation experiments in the presence of trace amounts of water at 0 5 2 2 gpa and 1470 1570 k in this fabric called e type fabric the olivine 100 axis is subparallel to the shear direction and the 001 plane is parallel to the shear plane this geometry suggests that the 100 001 slip system makes the dominant contribution to total strain this fabric is dominant at a modest water content 200 coh 1000 h 10 6 si at low stresses and high temperatures some mylonites from peridotite massifs show this type of olivine fabric which suggests the presence of water during the shear localization the seismic anisotropy caused by this fabric is qualitatively similar to that by dry fabric a type but the magnitudes of anisotropy are different between the two types for horizontal flow the amplitude of vsh vsv anisotropy is weaker but the amplitude of shear wave splitting is stronger for the e type fabric than for the a type dry fabric seismic anisotropy in the oceanic upper mantle may be due to the olivine e type fabric

shear wave splitting measurements problems and solutions abstract we compare sensitivity and reliability of three basic techniques of shear wave splitting analysis cross correlation of wave components minimization of covariance matrix eigenvalues and minimizing energy on the transverse component of both synthetic and real data point out some problems and propose solutions we discuss major difficulties of evaluating shear wave splitting parameters which are not always obvious in routine processing and can sometimes lead to false results and wrong interpretations we describe effects of pre processing of digital records of shear waves e g filtering and setting lengths of analyzed signals and discuss reliability of results to minimize outliers in evaluated splitting parameters for reliable evaluation of splitting of medium quality sks wave forms which are valuable mainly in temporary deployments of stations we recommend a careful band pass filtering of the signal using a window length not shorter than the dominant period inspecting the signal noise ratio on t component and the particle motion the transverse minimization method provides usually more robust and stable solutions than the other two methods in the conclusion we suggest how to proceed in evaluation of splitting parameters to ensure reliable solutions even for medium or low quality shear waveforms recorded frequently during temporary field measurements

the influence of deformation history on the interpretation of seismic anisotropy 1 seismic anisotropy in the mantle is primarily caused by the lattice preferred orientation lpo of olivine which forms and evolves in response to progressive plastic deformation the style of lpo and its rate of evolution depend on the effects of physiochemical conditions on the microphysics of deformation and recovery here we integrate results from laboratory experiments and naturally deformed shear zones to evaluate how variability in the evolution of olivine lpo modifies existing strategies for interpreting seismic anisotropy we concentrate on two particular effects first we show that olivine a and e type lpos evolve with opposite senses of rotation producing a wide spectrum of angular relationships between the orientation of fast seismic wave propagation and the direction of flow second we show that the presence of a pre existing lpo introduces a lag between changes in deformation kinematics and alignment of the seismic fast direction with the shear direction the combination of these two factors affects the inference of deformation kinematics from seismic anisotropy and the interpretation of shear wave splitting parameters

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 and mantle flow seismic anisotropy in the mantle is primarily due to deformation induced lattice preferred orientation lpo of olivine crystals the aim of this paper is to better understand how such lpo is produced by flow and to learn whether observations of seismic anisotropy can be used to infer the local direction of flow within the mantle the basis of the work is a two dimensional theory which describes how lpo evolves during an arbitrary time dependent deformation ribe 1989 i investigate the evolution of lpo beneath ocean ridges above subducted slabs and in thermal convective flows the ocean ridge model predicts that the seismic anisotropy produced at a fast spreading ridge should be greater in magnitude than that produced at a slow spreading ridge and that the fast axis should be more nearly horizontal the subduction zone model predicts that strong seismic anisotropy should be produced above subducted slabs with the fast axis aligned with the slab regardless of the subduction angle the evolution of lpo in typical convective flows is extremely complex and depends strongly on such factors as the mode of heating and the surface boundary conditions in general there is no simple relation between the lpo and the local flow direction in any of the models considered the attempt to use seismic anisotropy to map flow patterns on a global scale is therefore probably unwarranted however the lpo does become aligned with the flow direction when the flow is a progressive simple shear such a flow occurs in limited portions of the mantle beneath the lithosphere at a fast spreading ridge above subducted slabs and in boundary layers beneath rigid surfaces such as continents observations of seismic anisotropy may therefore indicate the sense of shear at shallow depths in the mantle

shear wave splitting observations in the lower great lakes region evidence for regional anisotropic domains and keel modified asthenospheric flow 1 fast axis directions obtained from shear wave splitting analysis of core refracted shear waves reveal several distinct anisotropic domains in the lower great lakes region we used data from 27 broadband seismograph stations extending across a low velocity anomaly in the lithospheric mantle observed splitting times vary from 0 4 to 1 4 s with a mean of 0 7 s a subset of the splitting vectors across a failed rift are oriented parallel to one arm of the rift zone most others show a coherent pattern of fast directions close to the direction of plate motion but oblique to surface tectonic belts within the area of the low velocity anomaly our observations are most simply explained by single layer anisotropy induced by asthenospheric flow spatial variability in the direction and magnitude of splitting are consistent with a flow regime influenced by basal topology of the lithospheric keel

spatial and temporal constraints on sources of seismic anisotropy evidence from the scottish highlands 1 routine sks splitting analyses of seismic anisotropy usually suffer from limitations in station density that hinder attempts to place spatial constraints on anisotropic fabrics data from a 20 km station spacing network in scotland show that splitting parameters vary considerably t 0 45 1 5 s 49 128 over short 10 20 km length scales improved spatial constraints then lead to tighter temporal constraints on the anisotropic sources asthenospheric fabrics due to tertiary rifting and present day plate motions do not strongly influence our results that instead correlate with lithospheric scale trends inferred from surface geology splitting observations track scotland s tectonic history from the precambrian emplacement of crustal basement and through the activation of large scale faulting and thrusting during the caledonian orogeny the shallow lithosphere beneath scotland has preserved a fossil anisotropic signature up to hundreds of millions of years after it was formed

development of shape and lattice preferred orientations application to the seismic anisotropy of the lower crust abstract we review the physical basis of the development of fabrics in plastic and viscous flow and illustrate the typical fabrics formed by these processes in the main rock forming silicates of the lower crust feldspar quartz pyroxene and amphibole the orientation process in plastic deformation where a single slip is dominant is recalled and the role of the constraint of neighbouring grains is emphasized the fabric development of anisometric crystals in viscous flow is discussed as a function of the main controlling parameters shear strain aspect ratio and interference between crystals the same sense of fabric asymmetry is introduced by plastic and viscous flow between the flow plane and the shape preferred orientation and hence coherent kinematic analysis can be undertaken in both modes of flow in order to assess the role of such fabrics in the seismic laminations of the lower continental crust we have calculated the seismic p wave properties of typical fabrics for hypothetical monomineralic and polymineralic rocks the calculations show that the strongest anisotropies develop in monomineralic rock with values between 5 and 16 compared with 5 and 8 for typical rock compositions the strongest anisotropies for layered monomineralic rocks generated by fabrics is only 6 compared to the 14 suggested by model studies of the observed seismic laminations we suggest that other effects such as compositional layering and or constructive interference of seismic waves are responsible for augmenting the apparent anisotropy

contrast in stream channel response to major storms in two mountainous areas of california the generally catastrophic effects of major storms on the geometry of intermediate and high order channels in northwestern california contrast with localized storm related channel changes found in the santa cruz mountains sediment delivery in northwestern california during storms overwhelms transport capacities throughout the length of most intermediate and high order channels and causes long lasting changes in geometry in contrast sediment delivery during storms in the santa cruz mountains overwhelms transport capacities only in localized reaches this contrast in channel behavior is at least partially caused by contrasts in the style of landsliding found in the two areas

modeling olivine cpo evolution with complex deformation histories implications for the interpretation of seismic anisotropy in the mantle relating seismic anisotropy to mantle flow requires detailed understanding of the development and evolution of olivine crystallographic preferred orientation cpo recent experimental and field studies have shown that olivine cpo evolution depends strongly on the integrated deformation history which may lead to differences in how the corresponding seismic anisotropy should be interpreted in this study two widely used numerical models for cpo evolution d rex and vpsc are evaluated to further examine the effect of deformation history on olivine texture and seismic anisotropy building on previous experimental work models are initiated with several different cpos to simulate unique deformation histories significantly models initiated with a preexisting cpo evolve differently than the cpos generated without preexisting texture moreover the cpo in each model evolves differently as a function of strain numerical simulations are compared to laboratory experiments by boneh and skemer 2014 in general the d rex and vpsc models are able to reproduce the experimentally observed cpos although the models significantly over estimate the strength of the cpo and in some instances produce different cpo from what is observed experimentally based on comparison with experiments recommended parameters for d rex are m 10 5 and 0 3 and for vpsc 10 100 numerical modeling confirms that cpo evolution in olivine is highly sensitive to the details of the initial cpo even at strains greater than 2 these observations imply that there is a long transient interval of cpo realignment which must be considered carefully in the modeling or interpretation of seismic anisotropy in complex tectonic settings

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

styles of extension in the pannonian basin abstract structural interpretation of reflection seismic profiles reveals distinct modes of upper crustal extension in the pannonian basin while some subbasins in the pannonian basin complex show little extension planar rotational normal faults others are characterized by large magnitude of extension detachment faults metamorphic core complexes gravitational collapse of the intra carpathian domain combined with subduction zone roll back is thought to be the driving mechanism of the neogene back arc extension the very heterogeneously distributed extension is accommodated by transfer faults which bound regions characterized by different polarity direction or amount of extension in cross section these transfer faults are characterized by flower structures typical for strike slip faults seismic stratigraphic interpretations indicate that the non marine post rift sedimentary fill of the pannonian basin can be described in terms of sequence stratigraphy the exceptionally good seismic sequence resolution allows recognition of third order and also fourth order depositional sequences which may reflect the interplay of tectonics and eustasy and milankovitch scale climatic variations respectively

lithosphere asthenosphere interaction at the southeastern carpathian arc bend implications for anisotropy abstract the vrancea region in the southeastern carpathians romania represents a unique case among the seismic areas in the world taking into account the extreme concentration and persistence of seismicity and the tectonic stress field subduction in a post collisional phase is still active in a narrow area located at the sharp bend of the mountain belt our goal is to show that the particular shape of the shear wave splitting can be interpreted in the light of the decoupling and slab retreat processes which hypothetically induce a specific configuration of the upper mantle flow shear wave splitting of sks phases shows a relatively coherent pattern outside the epicentral area suggesting a prominent ne sw anisotropy in agreement with previous estimations performed in central and eastern europe and following the trends of the deformation field as outlined by the gps measurements a clear change is pointed out inside the vrancea area where strike parallel polarization is emphasized toward the nw wedge side the polarization turns to a strike perpendicular direction in agreement to an upwelling asthenospheric flow in the back arc region i e polarization aligned to the local strike of the slab these shear wave splitting attributes are not consistent with conventional models of 2 d mantle flow near subduction zones nor with a sub vertical down dipping flow driven by the sinking of the slab they correlate well with lateral inhomogeneities outlined by the tomography image heat flow seismic wave attenuation and thermal field we suggest that the eastward slab retreat and decoupling between the underlying asthenosphere and the slab itself have induced strike parallel mantle flow likely favoring detachment of the slab along the arcuate mountain belt these processes are directly related to the strong anisotropy observed in the se carpathians the anisotropy and gps data suggest a strong coupling of the surface and mantle processes

vertical coherence of deformation in lithosphere in the eastern himalayan syntaxis using gps quaternary fault slip rates and shear wave splitting data we present 59 new sks skks and combine them with 69 previously published data to infer the mantle deformation field in se tibet the dense set of anisotropy measurements in the eastern himalayan syntaxis ehs are oriented along a ne sw azimuth and rotate clockwise in the surround regions we use gps measurements and geologic data to determine a continuous surface deformation field that is then used to predict shear wave spitting directions at each station comparison of splitting observations with predictions yields an average misfit of 11 7 illustrating that deformation is vertically coherent consistent with previous studies within the central ehs in areas directly surrounding the namche barwa metamorphic massif the average misfit of 11 stations increases to 60 8 and vertical coherence is no longer present the complexity of the mantle anisotropy and surface observations argues for local alteration of the strain fields here associated with recent rapid exhumation of the indian crust

kinematics of retreating subduction along the carpathian arc romania kinematic axes and resultant vectors of displacement along the carpathian arc and the apuseni mountains aid in the reconstruction of retreating subduction along the carpathians the recent vertical position of the subducted slab below the vrancea area of the eastern carpathians represents the final rollback stage of a small fragment of oceanic lithosphere formerly situated between the moesian and east european plates the ages and locations of the eruption centers of the andesitic volcanic chain along the carpathian arc in the overriding plate as well as the thrust directions are used as markers to reconstruct the rollback area of the subducted slab between the moesian and east european plates

relation between surface velocity field and shear wave splitting in the south island of new zealand 1 the relative motion between the pacific and australian plates across the central south island of new zealand as measured by repeated gps measurements is distributed over a region more than 80 km wide the surface distribution of velocity is fit almost equally well by a model in which deformation of the lower lithosphere is concentrated into very narrow slip zones below one or two major faults and by a model in which the lower lithosphere deforms in a broad shear zone observations of the splitting of sks waves permit distinction between the two models on the basis of the finite strain they predict deformation in the deep lithosphere that was limited to narrow shear zones would not produce measurable splitting hence any splitting observed should not correlate with surface tectonics however the distribution of fast propagation directions revealed by observations of shear wave splitting do reflect surface tectonics in particular the orientations of fast propagation directions are consistent with the finite strain calculated by assuming that the distribution of velocity at depth within the lithosphere resembles the distribution of velocity measured at the surface by gps the observed distribution of splitting can be reproduced with an rms misfit of 15 provided that the velocity field is integrated over at least the time interval since significant convergence across the southern alps began at about 6 5 ma

shear wave splitting in the records of the german regional seismic network estimates of the parameters of shear wave splitting in the records of sks and skks of the new german regional seismograph network grsn for one layer model show large azimuthal variations at some stations of the network it is found that the variations are compatible with the presence of two anisotropic mantle layers in the region of the south german triangle sgt the fast direction in the upper layer is between n s and ne sw close to the previously reported estimates of the fast direction in the sub crustal lithosphere of the sgt the fast direction in the lower presumably asthenospheric layer is close to e w the estimates of the effective fast direction for one layer model at the stations of the grsn confirm the previously noted tendency of the fast direction of mantle anisotropy in central europe to change from 50 70 in the western part of the region to 100 120 in the eastern part a correlation of this change with a bending of the present day direction of maximum horizontal stress in the crust suggests that anisotropy in the asthenosphere of central europe can be related to the alpine orogeny