a geodynamic model of mantle density heterogeneity using cenozoic and mesozoic plate motion reconstructions we derive a model of present day mantle density heterogeneity under the assumption that subducted slabs sink vertically into the mantle the thermal buoyancy of these slabs is estimated from the observed thermal subsidence cooling of oceanic lithosphere slab velocities in the upper mantle are computed from the local convergence rate we assume that slabs cross the upper lower mantle interface and continue sinking into the lower mantle with a reduced velocity for a velocity reduction factor between 2 and 5 our slab heterogeneity model is as correlated with current tomographic models as these models are correlated with each other we have also computed a synthetic geoid from our density model for a viscosity increase of about a factor of 40 from the upper to lower mantle our model predicts the first 8 spherical harmonic degrees of the geoid with statistical confidence larger than 95 and explains 84 of the observed geoid assuming that the model c21 and s21 terms are absent due to a long relaxation time for earth s rotational bulge otherwise 73 of the geoid variance is explained the viscosity increase is consistent with our velocity reduction factor for slabs entering the lower mantle since downwelling velocities are expected to scale roughly as the logarithm of viscosity loge 40 3 7 these results show that the history of plate tectonics can explain the main features of the present day structure of the mantle the dynamic topography induced by this heterogeneity structure consists mainly of about 1 km amplitude lows concentrated along the active continental margins of the pacific basin our model can also be used to predict the time variation of mantle heterogeneity and the gravity field we find that the age of the geoid defined as the time in the past before which the geoid becomes uncorrelated with the present geoid is about 50 m y our model for the history of the degree 2 geoid which is equivalent to the history of the inertia tensor should give us a tool to study the variations in earth s rotation pole indicated in paleomagiietic studies

experimental assessment of the infiltration properties of a coarse soil medium in a dielectric infiltration test an accurate determination of the hydrological characteristics of porous media such as the values of the porosity and effective porosity are essential this is important to understand the transport processes of infiltration and the movement of water and contaminants in the porous media in this study a laboratory soil column experiment to estimate the porosity and effective porosity of toyoura standard sand samples using a dielectric method termed the frequency domain reflectometry with vector network analyzer fdr v was performed the fdr v device uses high frequency microwaves ranging from 0 1 to 3 ghz to measure the complex dielectric constants of the sample from the measured complex dielectric constant the two parameters of the soil samples then were derived using a proposed dielectric mixture model and tracer concentration model the effective porosity of the soil sample is measured at 0 311 with the fdr v dielectric method and 0 345 by the soil tracer column test comparing this with the calculated porosities of the soil sample the ratio of effective porosity is approximately 78 for the dielectric method and approximately 86 for the tracer concentration method these different values can be explained to be within the measurement range with regard to the measurement volume for the soil column these results indicate that measurement by the dielectric method using an fdr v device is an efficient and useful tool for estimating the hydrological parameters of porous media because of the dielectric response of earth materials

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

waveform modeling of shear wave splitting from anisotropic models in iceland 1 no quantitative model of seismic anisotropy beneath iceland has yet explained the observed shear wave splitting results in iceland in this study we explore the structure of mantle seismic anisotropy associated with plume ridge interaction beneath iceland by modeling synthetic waveforms using a pseudo spectral method first predicted sks waveforms are shown to produce shear wave splitting results for two anisotropic layers that are in generally agreement with analytic solutions next simple models in which anisotropy are imposed at different depths and geographic regions around iceland are used to examine different hypothesized effects of plume ridge interaction the model that is designed to represent crystallographic fabric due to mantle deformation associated with lithosphere spreading in western iceland and along axis channeled asthenospheric flow in eastern iceland can predict the distinct shear wave splitting observations on the east and west sides of the island last we analyze geodynamic models that simulate 3 d mantle flow and evolution of mineral fabric the predicted fast directions of shear wave splitting from the models with realistic spreading rate 10 km myr and broad range of plume viscosities are consistent with the observations in central and eastern iceland however because these models are symmetric about the ridge none of them can predict the observed shear wave splitting results in western iceland

lateral heterogeneity and azimuthal anisotropy in the north atlantic determined from ss s differential travel times to explore upper mantle heterogeneity beneath the north atlantic we have measured 70 ss s differential travel times using the waveform cross correlation method both the two way preliminary reference earth model prem and j b jeffreys bullen residuals exhibit a maximum variation of 17 s ranging from 10 to 7 and 9 to 8 s respectively the lack of correlation between ss s and s residuals along with the strong correlation between ss s and ss residuals suggests that ss s differential travel times eliminate source and receiver effects and sample the upper mantle anomalies near the ss bounce points without being strongly affected by lower mantle heterogeneities we find evidence for a strong local anomaly in the north atlantic residuals for bounce points immediately to the north of the azores gibraltar plate boundary average about 4 s faster than for the bounce points to the south of the boundary we infer that this velocity contrast exists in the lithosphere and continues below a depth of 200 km a series of linear multiple regression experiments demonstrate that variation in velocity with increasing age of the seafloor and azimuthal anisotropy are both significant contributors to the prem and j b residuals assuming that travel time delays are a linear function of the square root of the seafloor age we find the coefficient for age to be about 1 0 s m y this is smaller than but not significantly different from the corresponding slope for the s delays of intraplate earthquakes in the atlantic reported by j d duschenes and s c solomon 1977 and favors the presence of small amounts of water e g 0 1 in the upper mantle in modeling anisotropy we carry out an experiment using synthetic seismograms to examine the shear wave splitting phenomena in the anisotropic medium and investigate three possible forms for sh wave delay as a function of azimuth sinusoidal variations as a function of 2 4 and a combination of 4 predominant and 2 that mimics the delay expected in olivine crystals when the axis is aligned horizontally our regression models strongly prefer the predominance of a 4 to a 2 variation and the last type of anisotropy explains our data best from the preferred anisotropy model the olivine axis or the upper mantle shearing flow is inferred to be oriented n s the magnitude of the azimuthal variation suggests that anisotropy extends over a depth range of several hundred kilometers in the upper mantle

widespread volcanism in the greenland north atlantic region explained by the iceland plume in the classical concept a hotspot track is a line of volcanics formed as a plate moves over a stationary mantle plume defying this concept intraplate volcanism in greenland and the north atlantic region occurred simultaneously over a wide area particularly around 60 million years ago showing no resemblance to a hotspot track here we show that most of this volcanism can nonetheless be explained solely by the iceland plume interacting with seafloor spreading ridges global mantle flow and a lithosphere the outermost rigid layer of the earth with strongly variable thickness an east west corridor of thinned lithosphere across central greenland as inferred from new highly resolved tomographic images could have formed as greenland moved westward over the iceland plume between 90 and 60 million years ago our numerical geodynamic model demonstrates how plume material may have accumulated in this corridor and in areas east and west of greenland simultaneous plume related volcanic activities starting about 62 million years ago on either side of greenland could occur where and when the lithosphere was thin enough due to continental rifting and seafloor spreading possibly long after the plume reached the base of the lithosphere volcanism across the north atlantic region 62 million years ago is consistent with an iceland plume source despite the absence of a classic hotspot track suggest tomographic images and geodynamic models

constraints on north atlantic upper mantle anisotropy from s and ss phases several analyses of ssh sh differential travel times disagree on whether these data contain evidence for azimuthal anisotropy in the north atlantic upper mantle to explore possible explanations for these discrepant results we calculated the azimuthal variation in ssh sh travel times predicted by an anisotropic upper mantle model theoretical travel times were obtained by cross correlating s and ss phases on transverse component reflectivity synthetic seismograms we determined that predicted azimuthal travel time patterns are sensitive to the relative amplitudes of radial and transverse particle motions incident on the anisotropic medium if a large variation in the relative incident amplitudes exists in a dataset the overlap of different azimuthal travel time patterns may obscure anisotropic signatures we analyzed shear wave splitting in a dataset of 12 ss and 10 s phase observations to constrain the presence of anisotropy in the north atlantic upper mantle a comparison of ss splitting parameters with s and sks particle motions suggests that shear wave splitting apparent in the ss phases is at least partially due to anisotropy in the vicinity of their bounce points although contributions from anisotropy in the source and station regions cannot be ruled out observed ss splitting is consistent with an olivine model in which horizontal a axes are aligned at an average of n24 w in the central north atlantic 15 40 n and at an average of n23 e in the northern north atlantic 40 50 n

flow and solute transport through the soil matrix and macropores of a hillslope segment subsurface flow from various portions of a soil profile on a steep forested hillslope was evaluated by two sets of step change miscible displacement tests at different application rates and antecedent hydrologic conditions solutions of nacl 1000 mg l 1 cl were applied at steady state rates equivalent to 20 and 30 mm h 1 of standing water over the entire plot area using a line irrigation source located 1 5 m upslope lateral distance from an excavated soil pit subsurface flow and tracer breakthrough from five portions the organic rich soil layer including macropores the mineral soil matrix and three groups of macropores in the mineral soil layer of the soil profile were individually measured and analyzed using a convective dispersive model matrix flow dominated discharge from the soil pit during tracer tests 70 93 of total discharge however during wet periods with upslope drainage macropores including organic rich soil contributed proportionally more flow than during periods when upslope drainage was minimal outflow from macropores during the test with wet antecedent conditions had lower cl concentrations than drainage from the soil matrix suggesting dilution in macropores from upslope drainage effective pore volumes calculated for the flow averaged breakthrough data from the entire profile were much less 40 than the estimates measured by tensiometers of total volume of pore water suggesting that preferential flow significantly contributed to subsurface transport of tracer the pore volume for the entire profile increased only slightly with increasing application rate however the relative proportions of pore volumes calculated for individual portions varied proportionally to antecedent hydrologic conditions these changes are attributed to the expansion of individual macropores with surrounding soil and the lateral extension of macropore networks during wetter conditions

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

anisotropy in the oceanic lithosphere of the north western pacific basin summary a series of long range explosion seismological experiments has been conducted by the use of specially designed ocean bottom seismographs obss in the western pacific obs studies of apparent velocity measurements by the use of natural earthquakes have also been made the experiments have made clear that large scale p wave anisotropy exists in the entire thickness of the oceanic lithosphere the existence of the large scale anisotropy in the oceanic lithosphere has been demonstrated for the first time by seismic body wave studies previously anisotropy had been found only in the uppermost oceanic mantle in the eastern pacific the azimuth of the maximum velocity 8 6km s l is about 155 clockwise from north the direction is perpendicular to the magnetic lineation of the region however the direction differs from the direction of the present plate motion by about 30 so it appears that the anisotropy has been frozen at least since the change of the plate motion that occurred 40myr ago the frozen anisotropy should set important constraints on the mechanical properties of the lithosphere such as the viscosity and temperature of the lower lithosphere

application of the osl dating for stratigraphic correlation of late weichselian and holocene sediments in the lithuanian maritime region abstract the lithuanian maritime region of the baltic sea is notable for widely spread sandy sediments of different stages of baltic sea development from post glacial late weichselian to recently settled marine sediments the osl dating of about 70 sandy sediments was performed during the large scale 1 50 000 geological mapping of this region for some boreholes radiocarbon 14 c dating and palaeobotanical studies were also carried out a good agreement of the osl ages with 14 c dating results and palaeobotanical data has been revealed for marine lacustrine and aeolian sediments the overestimation of osl ages for baltic ice lake sediments is caused by a very rapid sedimentation and the resultant insufficient bleaching

applicability of unmanned aerial vehicles in research on aeolian processes surface dynamics and instabilities are characteristic of aeolian formation the method of surface comparison is regarded as the most appropriate one for evaluation of the intensity of aeolian processes and the amount of transported sand the data for surface comparison can be collected by topographic survey measurements and using unmanned aerial vehicles time cost for relief microform fixation and measurement executing topographic survey are very high the method of unmanned aircraft aerial photographs fixation also encounters difficulties because there are no stable clear objects and contours that enable to link aerial photographs to determine the boundaries of captured territory and to ensure the accuracy of surface measurements creation of stationary anchor points is irrational due to intense sand accumulation and deflation in different climate seasons in september 2015 and in april 2016 the combined methodology was applied for evaluation of intensity of aeolian processes in the curonian spit temporary signs marks were installed on the surface coordinates of the marks were fixed using gps and then flight of unmanned aircraft was conducted the fixed coordinates of marks ensure the accuracy of measuring aerial imagery and the ability to calculate the possible corrections this method was used to track and measure very small micro rank relief forms 5 10 cm height and 10 20 cm length using this method morphometric indicators of micro terraces caused by sand dunes pressure to gytia layer were measured in a non contact way an additional advantage of the method is the ability to accurately link the repeated measurements the comparison of 3d terrain models showed sand deflation and accumulation areas and quantitative changes in the terrain very clearly

hydrology of a forested hillslope during storm events abstract subsurface flow from a 0 47 ha hillslope subcatchment at the upper most reach of the west fork 38 ha of walker branch watershed was monitored throughout 1988 stormflow in the first order stream draining the west fork responded simultaneously with the initiation of subsurface flow through 0 to 2 5 m depth from the hillslope subsurface flow from the upper hillslope was only 1 3 of total precipitation for 1988 however individual storms yielded as much as 12 5 of precipitation as subsurface flow the west fork had 10 4 of precipitation observed as storm flow with an additional 29 as baseflow individual storms exhibited up to 71 of precipitation as storm flow in the west fork illustrating the significant increase in percent rain converted to subsurface flow in lower landscape positions as compared to upper hillslopes peak subsurface flow preceded peak streamflow and occurred primarily through the 1 0 2 5 m depth bt2 horizons due to perched water tables preferential flow from hillslopes through macro and mesopores was concluded to be the predominant stormflow mechanism the contributions of the various size pores was reasoned to be dependent upon the position within the soil profile and the stage of the hydrograph preferential flow occurred at extreme soil water conditions with the response due to perched water tables under wet conditions and believed to be due to hydrophobic conditions under extremely dry conditions intermediate soil water conditions resulted in infiltration into soil matrix pores precluding subsurface stormflow

shear wave splitting beneath the galapagos archipelago shear wave splitting measurements in the galapagos archipelago show a rapid change from consistently oriented anisotropy to no measurable anisotropy at the western edge of the archipelago delay times are 0 4 0 9 s and fast polarization directions are 81 109 e these directions are consistent with anisotropy resulting from shear of the asthenosphere by the overlying plate there is no indication of fossil lithospheric anisotropy in the plate spreading direction in contrast beneath the center of the archipelago the upper mantle is isotropic or weakly anisotropic the isotropic region coincides approximately with a volume of anomalously low upper mantle velocities suggesting that the presence of melt may weaken the effects of fabric on anisotropy or that melt preferred orientation generates a vertical fast polarization direction alternatively the complex flow field associated with a near ridge hotspot may result in apparent isotropy

on the orientation of tensile dikes in a ridge centered plume abstract we present three dimensional numerical models of the ascent of a plume under a spreading ridge and the concomitant melt generation and crust formation using a mantle viscosity which depends on pressure temperature melt content and optionally water content from the velocity field of these convection models we compute the viscous stress tensor in the mantle assuming that melt rich channels or melt filled dikes are oriented parallel to the maximum compressional stress we calculate the orientation of such dikes in the partially molten zone of the plume head and beneath the ridge for the central part of the plume we find dike orientations parallel to the ridge in shallow parts of the plume head while they are ridge perpendicular at greater depth the boundary between these two regimes is shifted downwards for a water rich plume which dehydrates upon melting the two regimes of different dike or melt channel orientations seem to be in good agreement with seismic observations on depth dependent seismic anisotropy indicating a preference of our wet model we find a modest focusing of melt towards the spreading center beneath normal ridge in both models but also in the fully dehydrated parts of the plume head in the model where water was included those are regions where upwelling is essentially passive in contrast the plume in the water free model and the only partly dehydrated parts of the plume in the water bearing model tend to develop a dike orientation which moves melt away from the spreading center these regions are characterized by active upwelling the defocusing of melt in actively upwelling plume mantle has radial symmetry about the plume axis i e an outward orientation of the dikes is not only visible in planes perpendicular to the ridge but also along the ridge

reproducibility of uav based earth topography reconstructions based on structure from motion algorithms combination of uav based aerial pictures and structure from motion sfm algorithm provides an efficient low cost and rapid framework for remote sensing and monitoring of dynamic natural environments this methodology is particularly suitable for repeated topographic surveys in remote or poorly accessible areas however temporal analysis of landform topography requires high accuracy of measurements and reproducibility of the methodology as differencing of digital surface models leads to error propagation in order to assess the repeatability of the sfm technique we surveyed a study area characterized by gentle topography with an uav platform equipped with a standard reflex camera and varied the focal length of the camera and location of georeferencing targets between flights comparison of different sfm derived topography datasets shows that precision of measurements is in the order of centimetres for identical replications which highlights the excellent performance of the sfm workflow all parameters being equal the precision is one order of magnitude higher for 3d topographic reconstructions involving independent sets of ground control points which results from the fact that the accuracy of the localisation of ground control points strongly propagates into final results 2015 elsevier b v

directions of seismic anisotropy in laboratory models of mantle plumes 1 a recent expansion in global seismic anisotropy data provides important new insights about the style of mantle convection interpretations of these geophysical measurements rely on complex relationships between mineral physics seismology and mantle dynamics we report on 3 d laboratory experiments using finite strain markers evolving in time dependent viscous flow fields to quantify the range in expected anisotropy patterns within buoyant plumes surfacing in a variety of tectonic settings a surprising result is that laboratory proxies for the olivine fast axis overwhelmingly align tangential to radial outflow in plumes well before reaching the surface these remarkably robust and ancient anisotropy patterns evolve differently in stagnant translational and divergent plate tectonic settings and are essentially orthogonal to patterns typically referenced when prospecting for plume signals in seismic data results suggest a fundamental change in the mineral physics seismology circulation relationship used in accepting or rejecting a plume model

current plate velocities relative to the hotspots incorporating the nuvel 1 global plate motion model nuvel 1 is a new global model of current relative plate velocities demets et al 1990 which differ significantly from those of prior models here we incorporate nuvel 1 into hs2 nuvel1 a new global model of plate velocities relative to the hotspots hs2 nuvel1 was determined from the hotspot data and errors used by minster and jordan 1978 to determine am1 2 which is their model of plate velocities relative to the hotspots am1 2 is consistent with minster and jordan s relative plate velocity model rm2 here we compare hs2 nuvel1 with am1 2 and examine how their differences relate to differences between nuvel 1 and rm2 hs2 nuvel1 plate velocities relative to the hotspots are mainly similar to those of am1 2 minor differences between the two models include the following 1 in hs2 nuvel1 the speed of the partly continental apparently non subducting indian plate is greater than that of the purely oceanic subducting nazca plate 2 in places the direction of motion of the african antarctic arabian australian caribbean cocos eurasian north american and south american plates differs between models by more than 10 3 in places the speed of the australian caribbean cocos indian and nazca plates differs between models by more than 8 mm yr although 27 of the 30 rm2 euler vectors differ with 95 confidence from those of nuvel 1 only the am1 2 arabia hotspot and india hotspot euler vectors differ with 95 confidence from those of hs2 nuvel1 thus substituting nuvel 1 for rm2 in the inversion for plate velocities relative to the hotspots changes few euler vectors significantly presumably because the uncertainty in the velocity of a plate relative to the hotspots is much greater than the uncertainty in its velocity relative to other plates

seismic anisotropy beneath east greenland revealed by shear wave splitting 1 seismic anisotropy was investigated by measuring shear wave splitting at 7 broadband stations in eastern greenland splitting parameters fast polarization and time delay were determined for sks and skks phases fast polarizations are oriented roughly parallel to the east greenland coast at 5 stations while for two they are nearly perpendicular to the coast the anisotropy at 5 is unrelated to the spreading direction of the north atlantic or absolute plate motion the fast polarization direction can be related to tectonic fabric in the caledonides in the north suggesting that anisotropy is frozen in the lithosphere deformed coherently with depth another explanation of the coast parallel fast polarization is asthenospheric flow along the mid atlantic ridge at the time of opening of the ocean inducing fabric in the thickened lithosphere the time delays 0 5 1 3 s do however require that fabric to be strong or distributed over a substantial depth range

variations of shear wave splitting in greenland mantle anisotropy and possible impact of the iceland plume abstract seismic anisotropy was investigated by measuring shear wave splitting at 19 broadband stations in greenland we examined mostly sks and skks phases but also some pks and depth phases of sks e g psks ssks for deep events splitting parameters fast polarization and time delay were determined for these phases the fast polarizations at nine sites in southern greenland are quite uniformly oriented about n ne two sites in central northern greenland show a similar geometry to southern greenland similar fast polarizations in southern and central northern greenland suggest continuity of structural fabric beneath large parts of greenland this coherent pattern extends across a number of geological provinces of varying age and suggests a common cause of anisotropy not related to the bitwise formation of the greenland continental block four sites in an east west oriented belt crossing central greenland show varying fast polarizations and suggest a separate process causing the anisotropy there which may indicate that these processes are not currently active the overall pattern of anisotropy in our results with the exception of variations across central greenland is similar to results obtained from rayleigh waves the irregular geometry of splitting across central greenland may be related to the impact of the iceland plume at 60 ma reported splitting time delays range from 0 4 to 1 4 s with an average of 0 8 s which can generally not be explained by crustal anisotropy alone if confined to a lithosphere of thickness on the order of 100 km time delays of up to 1 4 s indicate anisotropy of up to about 6 assuming that the a crystallographic axis of olivine is preferentially contained in the horizontal plane we suggest that the anisotropy beneath greenland is located mainly in the upper mantle but some contributions from the crust and lower mantle may be present

slabs in the lower mantle results of dynamic modelling compared with tomographic images and the geoid abstract the recent increase in resolution of tomographic images of the earth s interior has enabled us to see slabs in the lower mantle on the other hand the distribution of slabs can be inferred from subduction history using a dynamical model of mantle flow comparison of tomographic images with model results can help to distinguish between alternative models of subduction history tomographic models and mantle flow models and thus improve our understanding of the earth here a simple dynamic model of subduction is used and some results are presented amounts and locations of subduction are inferred from published models of plate motion and plate boundaries for the past 120 ma the latter have been interpolated on 2 ma time intervals mantle flow driven by the density anomalies corresponding to subducted slabs is calculated with the method of hager and o connell for a viscosity structure that features an increase in viscosity from 4 10 20 pa below the lithosphere to 4 10 22 pa in the lower part of the lower mantle slabs are advected in the flow field in the model slabs sink on average about 1700 km through the mantle during 100 ma however the calculated average horizontal motion of slabs throughout most of the mantle is only about 600 700 km for slabs that have sunk to the lowermost mantle it is about 1000 km this is in accordance with the previously observed good correlation between subduction locations and lowermost mantle heterogeneities slabs sink fastest in regions with abundant subduction and little trench migration e g below east asia in the lowermost mantle predicted slab locations tend to lie in areas with high seismic velocities however there are large areas of fast seismic velocities where no slabs are predicted and which therefore presumably correspond to earlier subduction in some regions e g below japan our model approximately reproduces the observed shape of the slab in other regions where the agreement is poor the results can help to further constrain models of subduction history and associated mantle flow additionally the predicted geoid is computed and compared with the actual geoid predicted and observed geoid have similar magnitude and a number of features in common however an optimization of the fit is not attempted here since in order to do this also the hot upwellings from the lower boundary layer presumably in the form of plumes would have to be included

upper mantle seismic anisotropy and lithospheric decoupling the lithosphere underlying stable continental shield regions is thought to extend to a depth of 200 km compressional wave velocity models derived from a recent approximately ns refraction profile in northern australia include a pronounced high velocity zone at a depth of around 200 250 km conventional petrological interpretations in terms of mineralogical or compositional changes cannot readily explain this feature calculated velocities for the garnet pyrolite model using a derived geotherm fit the velocities above and below this high velocity zone but cannot account for the high velocity 8 6 km s 1 zone itself this feature is explained in terms of velocity anisotropy which might reflect mechanical decoupling of the continental lithosphere from the underlying mantle

shear wave splitting and implications for mantle flow beneath the melt region of the east pacific rise shear wave splitting across the fast spreading east pacific rise has been measured from records of sks and skks phases on the ocean bottom seismometers of the mantle electromagnetic and tomography melt experiment the direction of fast shear wave polarization is aligned parallel to the spreading direction delay times between fast and slow shear waves are asymmetric across the rise and off axis values on the pacific plate are twice those on the nazca plate splitting on the pacific plate may reflect anisotropy associated with spreading induced flow above a depth of about 100 km as well as a deeper contribution from warm asthenospheric return flow from the pacific superswell region

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

crustal anisotropy beneath pacific ocean islands from harmonic decomposition of receiver functions crustal anisotropy beneath ocean islands can be attributed to preferentially aligned minerals cracks or dike structures stacked with harmonic weighting receiver functions from permanent ocean island stations display evidence of strong and distinct anisotropy parameters in the underlying crust and underplated layer we analyze data for 11 iris gsn stations in the pacific ocean we observe the prevalence of two lobed receiver function rf amplitude variations with back azimuth consistent with slow tilted axis anisotropy in most cases the anisotropy is accommodated in the underplated crust synthetic modeling of a representative station indicates that the strength of anisotropy of vp 10 and vs 5 is possible the strike direction of the inferred symmetry axis tends to align with plate motion with some scatter at stations in the northwest pacific i e kwaj tara and wake the strike direction of the symmetry axis aligns with plate motion at the time of volcano emplacement beneath station poha and the closest stations to the present day hawaiian hotspot alignment of the symmetry axis is almost orthogonal to the plate motion we attribute the crustal anisotropy to the preferred alignment of dike structures that transported asthenospheric magma toward the seafloor volcanic edifice our results suggest that the thermal plume origin for ocean islands must be supplemented by tectonic stress heterogeneities that allow magma to penetrate the lithosphere via fractures magma transport fractures should align normal to the least compressive direction which are predicted by theoretical models to align approximately with plate motion at the time of emplacement

post glacial stratigraphy and palaeoenvironment of the northern part of the curonian spit western lithuania a complex study including palynological and diatom analysis palaeontological investigation of molluscan fauna carbonates analyses and radiocarbon dating was performed in the northern part of the curonian spit western lithuania environmental changes were reconstructed during the late glacial and holocene cold and dry climate unstable soils open habitats of tundra vegetation spread in the surroundings of the northern part of the curonian spit during the younger dryas birch was dominant the relatively deep baltic ice lake with a freshwater planktonic diatom complex existed during the preboreal and the beginning of boreal forest birch and pine was not dense and wetland development occurred in coastal areas forest spread rapidly in response to significant warming during boreal time a shallow freshwater ancylus lake nearshore environment existed in the area of the northern part of the present curonian spit the surrounding forest was dominated by broad leaved species especially elm lime and oak during the atlantic alder and hazel occurred everywhere pine forest was still widely represented in the area on sandy soils subsequently the shallow litorina sea basin existed around the area spruce forest spread in the early subboreal climate was warm and relatively dry and intensive soil formation took place shallow brackish postlitorina sea lagoonal environmental conditions existed in the first half of subboreal aeolian sand with buried soil formation started to accumulate at the end of subboreal and the northern part of the curonian spit became land

observations of laterally inhomogeneous anisotropy in the continental lithosphere elastic anisotropy may be an important factor when seismic data are used to determine the structure composition and dynamics of the earth s interior1 2 azimuthal anisotropy has been found in the oceanic and although less definitely in the continental lithosphere from field experiments where the pn wave velocity was observed to vary with direction3 5 these studies suggest a 180 periodicity in travel time variations as the only criterion of the presence of azimuthal anisotropy this criterion however may fail to distinguish between anisotropy and lateral inhomogeneity of the isotropic medium a new method for measuring azimuthal anisotropy has been described recently6 based on the phenomenon of shear wave splitting in anisotropic media which suggests three criteria instead of one to identify azimuthal anisotropy we have now applied this method to the records of permanent seismograph stations in southern germany our results provide strong evidence for the presence of azimuthal anisotropy in the lithosphere of the region and reveal pronounced lateral variations in the parameters of anisotropy on a scale of about 200 km

the anisotropic and rheological structure of the oceanic upper mantle from a simple model of plate shear summary we have developed a channel flow model that dynamically couples plate motion and mantle stress with a composite rheology diffusion creep and dislocation creep to study the rheological and anisotropic structures of the oceanic upper mantle a semi analytic approach is used to solve for mantle stress and viscosity allowing fast calculations and exploration of a wide range of rheological parameters mantle stress in our model is due to shearing by a moving plate by comparing mantle stress with a transition stress for dislocation creep we identify regions where either diffusion creep or dislocation creep is active deformation by dislocation creep results in a mineral fabric that may be responsible for observed seismic anisotropy our study suggests that there is an important relation between plate motion seismic anisotropy mantle viscosity and transition stress using laboratory results for rheological parameters we find that dislocation creep exists only in a layer at certain depths in the upper mantle for a plate velocity of 10 cm yr 1 an asthenospheric viscosity of 10 19 pa s and an asthenospheric transition stress of 0 1 mpa our model predicts a 200 km thick dislocation creep layer which is broadly consistent with the observations of seismic anisotropy for a plate velocity of 10 cm yr 1 and an asthenospheric transition stress of 0 1 mpa the asthenospheric viscosity needs to be greater than 5 10 18 pa s to produce any dislocation creep deformation and the

using time domain reflectometry to characterize shallow solute transport in an oak woodland hillslope in northern california usa the natural heterogeneity of water and solute movement in hillslope soils makes it difficult to accurately characterize the transport of surface applied pollutants without first gathering spatially distributed hydrological data this study examined the application of time domain reflectometry tdr to measure solute transport in hillslopes three different plot designs were used to examine the transport of a conservative tracer in the first 50 cm of a moderately sloping soil in the first plot which was designed to examine spatial variability in vertical transport in a 1 2m 2 plot a single probe per meter was found to adequately characterize vertical solute travel times in addition a dye and excavation study in this plot revealed lateral preferential flow in small macropores and a transport pattern where solute is focused vertically into preferential flow pathways the bypass flow delivers solute deeper in the soil where lateral flow occurs the second plot designed to capture both vertical and lateral flow provided additional evidence confirming the flow patterns identified in the excavation of the first plot the third plot was designed to examine lateral flow and once again preferential flow of the tracer was observed in one instance rapid solute transport in this plot was estimated to occur in as little as 3 of the available pore space finally it was demonstrated that the soil anisotropy although partially responsible for lateral subsurface transport may also homogenize the transport response across the hillslope by decreasing vertical solute spreading copyright 2002 john wiley sons ltd

seismic anisotropy of oceanic upper mantle shear wave splitting methodologies and observations we develop methodologies to obtain accurate measurements of shear wave splitting and apply these techniques to examine the pattern of oceanic upper mantle anisotropy to obtain high quality estimates of receiver splitting at island stations we devise a stacking method that finds the optimum splitting parameters and 95 error region for teleseismic shear wave phases from a suite of earthquake events to obtain additional measurements in oceanic regions we develop techniques to measure splitting parameters and errors for ss phases that sample upper mantle anisotropy at their bounce points however we find the data are often of low resolution and anomalous characteristics are sometimes found that make splitting difficult to interpret ten second splitting of ss is observed across the banjo seismic array but we cannot unambiguously attribute this signal to mantle anisotropy at the bounce the receiver splitting methods are used to assess the adequacy of a two anisotropic layer model for the pacific region with fast polarization azimuth in the lithosphere oriented in the fossil spreading direction and in the asthenosphere oriented in the absolute plate motion direction this model has been proposed to explain surface wave data in the pacific ocean but our splitting results demonstrate that oceanic anisotropy patterns are more heterogeneous than would be predicted while the island splitting measurements could reflect the influence of individual hotspot upwellings hotspot effects do not appear to be universally dominant we propose that splitting observations alternatively indicate broad scale differences in the underlying character of oceanic upper mantle anisotropy associated with coherant patters of lithospheric structure and asthenospheric flow in particular splitting surface wave models and regional studies all support a model where lithospheric anisotropy throughout the south pacific has been erased or reoriented toward the absolute plate motion direction whereas more limited observations in the north pacific indicate that the fossil lithospheric signature appears to be preserved

throughflow and solute transport in an isolated sloping soil block in a forested catchment a 3m wide by 9m long by 1m deep soil block on a forested hillslope near orono me was isolated by excavation of encircling trenches a sprinkler system for application of water and potassium bromide tracer was constructed over the plot outflow was collected at six locations with troughs experiments were conducted at application rates of 2 5 5 and 10 cm h 1 pulses of tracer were applied subsequent to attainment of steady flow and breakthrough curves were measured at all outflow points recession limbs of outflow hydrographs exhibited distinct breaks when plotted on semilogarithmic axes indicating drainage from at least two distinguishable pore size classes or flow pathways solute breakthrough curves were dominated by a single peak travel times of solute were inversely related to the application rate a secondary peak in the outflow curve which is inconsistent with transport theories for a homogeneous soil was observed in all cases this second peak is unexplained but is conceptually consistent with the notion of transport in at least two pore size classes an undisturbed soil core diameter of 30 cm and length of 40 cm was sprinkled at the same rates as was the soil block using methylene blue as tracer in the last run drainage hydrographs and visual examination of dye stains in the block indicated also at this smaller scale that flow and transport are controlled by preferred paths in the soil paths that cannot be morphologically distinguished from the surrounding soil matrix theoretical explanations of processes on such hillslopes need to account for this fact

seismic anisotropy and shear wave splitting associated with mantle plume plate interaction geodynamic simulations of the development of lattice preferred orientation in the flowing mantle are used to characterize the seismic anisotropy and shear wave splitting sws patterns expected for the interaction of mantle plumes and lithospheric plates models predict that in the deeper part of the plume layer ponding beneath the plate olivine a axes tend to align perpendicular to the radially directed plume flow forming a circular pattern reflecting circumferential stretching in the shallower part of the plume layer plate shear is more important and the a axes tend toward the direction of plate motion predicted sws over intraplate plumes reflects the asymmetric influence of plate shear with fast s wave polarization directions forming a pattern of nested u shapes that open in the direction opposing both plate motion and the parabolic shape often used to describe the flow lines of the plume predictions explain sws observations around the eifel hot spot with an eastward not westward moving eurasian plate consistent with global studies that require relatively slow net westward rotation of all of the plates sws at the hawaiian hot spot can be explained by the effects of plume plate interaction combined with fossil anisotropy in the pacific lithosphere in ridge centered plume models the fast polarization directions angle diagonally toward the ridge axis when the plume is simulated as having low viscosity beneath the thermal lithosphere such a model better explains sws observations in northeast iceland than a model that incorporates a high viscosity layer due to dehydration of the shallow most upper mantle

shear wave splitting around the eifel hotspot evidence for a mantle upwelling summary we present the results of a shear wave splitting analysis across the eifel hotspot in westcentral europe our data set includes 18 permanent european broadband stations and 102 temporary eifel broadband and short period stations we observe variations in splitting at most permanent stations but are not able to model them reliably with unique dipping axis or two layer anisotropy models we prefer instead a single layer model with a horizontal fast axis to approximate the first order anisotropy which varies smoothly between stations we observe a first order parabolic pattern in fast polarization azimuth around the hotspot which suggests that a lattice preferred orientation lpo of olivine fast axes exists in the asthenosphere as a result of the interaction between the slowly wsw moving eurasian plate and a mantle upwelling beneath the eifel volcanic fields the minority of the variation not explained by this model correlates with rapid lateral changes in splitting and is interpreted as a result of additional anisotropy and or the effects of dynamic recrystallization associated with lpo development in the region of corner flow near the conduit our parabolic asthenospheric flow paf interpretation is consistent with eifel geological tomographic receiver function global absolute plate motion electrical conductivity anisotropy and geochemical studies as well as with splitting studies in the great basin and around hawaii we suggest that the eifel upwelling is sporadic and a result of a low excess upwelling temperature and or varying crustal stresses that periodically shift and facilitate eruption the paf pattern we observe neither suggests nor rules out anisotropy in the conduit associated with a wet eifel upwelling we use our optimum pa f model parameters to calculate a eurasian plate speed of 12 km ma 1 w hich is consistent with the recent hs3 nuvel1a speed of 19 14 km ma 1

the magnitude symmetry and origin of upper mantle anisotropy based on fabric analyses of ultramafic tectonites summary seismic anisotropy within the upper mantle originates from the preferred orientation of highly anisotropic single crystals the symmetry and magnitude of anisotropy depend upon 1 the volume percentages of the minerals constituting the upper mantle 2 the degree and symmetry of preferred orientation of each mineral and 3 the alignment of the minerals crystallographic axes relative to one another the nature of upper mantle anisotropy can be examined by studying mineral orientations within ultramafic rocks which were once part of the mantle petrofabric data for olivine and pyroxene have been used to obtain velocity anisotropy patterns over large regions of ultramafic rocks from the samail ophiolite oman the troodos ophiolite cyprus the bay of islands ophiolife newfoundland the twin sisters ultramafic washington usa the dun mountain ophiolite new zealand the red hills ophiolite new zealand and the red mountain ophiolite new zealand the compressional wave anisotropy calculated for these massifs ranges from 3 to 8 per cent in excellent agreement with observed seismic anisotropy in the upper continental and oceanic mantle the symmetry varies from orthorhombic to axial with the axial symmetry axis corresponding to the olivine a axes maxima and subparallel to spreading directions in oceanic upper mantle pyroxene a b and c axes maxima generally parallel olivine b c and a axes respectively and anisotropy decreases with increasing pyroxene content shear wave splitting is predicted for all propagation directions within the upper mantle symmetry is also orthorhombic or axial with the minimum difference in velocity between the two shear waves parallel to the maximum compressional wave velocity

rayleigh wave phase velocities in the pacific with implications for azimuthal anisotropy and lateral heterogeneities summary the lateral distribution of fundamental mode rayleigh wave phase velocities in the pacific has been calculated in order to determine the variation in velocity as a function of the age of the oceanic plate the importance of azimuthal anisotropy and the presence of secondary lateral heterogeneities the data set used in this study consists of phase velocity measurements in the period range 20 125 s for 178 paths traversing the pacific both the pure path and spherical harmonic inversion techniques are used in this investigation with an emphasis placed on determining the effectiveness and resolving power of these methods in calculating the velocity distribution in an oceanic regime the first order velocity age relation which dominantly characterizes surface wave dispersion in an oceanic environment can be adequately modelled by either the pure path or spherical harmonic techniques azimuthal anisotropy is the dominant second order effect and is best developed in regions less than 80 myr in age in this age zone the faster direction of wave propagation is either in the direction of fossil seafloor spreading or in the direction of present day absolute plate motion in the western pacific there is a correlation with paleo relative motion fossil seafloor spreading for periods less than 50 s lateral velocity heterogeneities which are not related to the age of the oceanic plate are found by pure path inversions and are correlated with regions associated with shallow residual depth anomalies this effect slow velocities with respect to the velocity age model monotonically decreases as a function of period and is indicative of a shallow origin age independent anomalies were also modelled by the application of the pure path and spherical harmonic methods in a sequential inversion

teleseismic imaging of subaxial flow at mid ocean ridges traveltime effects of anisotropic mineral texture in the mantle summary deformation of peridotite caused by mantle flow beneath an oceanic spreading centre can result in the development of seismic anisotropy traveltime anomalies and shearwave splitting will develop as seismic energy propagates through such an anisotropic region thus providing a signature of the deformation field at depth in this study we investigate the nature of deformation associated with mantle upwelling for two models of flow in the upper 100 km of the mantle the finite strain fields of the passive upwelling model versus the buoyancy enhanced upwelling model are quite different this suggests that mineral aggregates deform differently in the two models thus developing seismic signatures that are distinguishable numerical estimates of the corresponding mineral textures are made using polycrystal theory for olivine with four operative slip systems the activation of a slip system is determined for each grain on the basis of the local critical resolved shear stress the computed grain deformation reflects a balance between stress equilibrium for the aggregate as a whole and strain continuity between neighbouring grains within the aggregate this approach enables a direct link to be made between the model flow fields and the resulting texture development given these mineral orientation distributions elastic parameters are calculated and wavefronts are propagated through the anisotropic structure traveltimes for teleseismic body waves are computed using ray theory and amplitudes are estimated for an across axis profile extending 100 km from the ridge axis relative p wave residuals of up to 1 s are predicted for the buoyant model with on axis arrivals being earliest since near vertical velocities are fastest beneath the axis on axis p wave arrivals for the passive model are half a second earlier than arrivals 60 km off axis and relative delays continue to increase slowly as distance from the ridge increases s wave splitting of almost a second is predicted for the buoyant model whereas less than a half second of splitting is determined for the passive model

global upper mantle structure from long period differential travel times we have made over ten thousand measurements of pp p and ss s differential travel times from long period global digital seismograph network recordings of all events with mb 5 5 which occurred during the years 1976 to 1986 we have obtained reasonable global coverage with very good sampling of several regions of the world the residuals range from 5 to 5 s for pp p and 12 to 12 s for ss s and reveal a large scale pattern of heterogeneity when plotted at the reflected phase s bounce point our experiments indicate that lower mantle structure and source receiver structure can each contribute approximately 0 5 s to our measured pp p residuals so there is considerable signal to be explained the pattern observed in the pp p measurements is similar to the pattern observed in the ss s measurements with the ss s residuals 2 to 4 times larger in magnitude comparisons of our measured residuals to those predicted by the upper mantle models of woodhouse and dziewonski show that the overall patterns are quite similar but the amplitude of the model residuals is roughly a factor of 2 too small comparisons with the predictions of a whole mantle model of tanimoto again shows that the predicted pattern of residuals is reasonably consistent with the observations but now the predicted residuals are too large by about a factor of 2 this variation in predicted amplitudes is probably mainly due to differences in the near surface structure of the models we have also binned our measurements according to the tectonic regionalization gtr1 of jordan and find a qualitative correlation of average residual with tectonic region in particular precambrian shields show a strong anomaly and there is a correlation of residual size with the age of oceanic crust at the bounce point for all tectonic regions the ratio of ss s to pp p residuals is approximately 2 this ratio is consistent with a thermal origin for the observed signal finally our measurements show no compelling evidence for azimuthal anisotropy which might be related to fossil spreading direction or the direction of absolute plate motion such a signal is probably overwhelmed by the large signal from three dimensional structure

shear wave polarization anisotropy in the upper mantle beneath honshu japan shear wave polarization anisotropy in the wedge portion of the upper mantle between a subducting plate and the earth s surface is investigated using three component seismograms of intermediate depth and deep earthquakes recorded at 14 local stations in honshu japan eighty nine high quality seismograms were selected from a period of 3 years the data used in this study are restricted such that incidence angles are smaller than the critical angle of 30 to the earth s surface in order to avoid phase shifts in the shear wave train to find directions of the maximum and minimum velocities in split shear waves where shear waves are resolved into two phases with the maximum time separation each set of the two horizontal component seismograms is rotated in the horizontal plane the split shear waves thus obtained are again recombined after the correction of anisotropy and the anisotropy corrected particle motion is compared with the focal mechanism for a cross check of the observed anisotropy directions of the maximum axes are plotted on azimuthincidence angle stereograms at each station the stereograms and the cross sections of seismic ray paths show that 1 the anisotropic material is distributed at intermediate location between earthquake sources and receiving stations and 2 the anisotropic region is separated into two parts one in the north of the present study area with the polarization of the maximum velocity shear wave trending 0 to 30 from the north north anisotropy and the other in the south with it trending 90 to 120 south anisotropy the maximum time delays between the two shear waves along a vertical seismic ray is about l s for both the anisotropic regions the horizontal extent of the anisotropic area in the north is 50 km at depths of 50 to 150 km perhaps prevalent in west honshu however the depth of anisotropic material is not well constrained because of insufficient coverage of seismic ray paths and angles if we assume the vertical extent of the anisotropic material to be 100 km the maximum velocity contrast would be 4 if we adopt a crack alignment model for the observed anisotropy cracks are inferred to be distributed vertically trending 0 to 30 in the north and 90 to 120 in the south if we assume an olivine alignment model olivine crystals are inferred to be aligned in the north with the a axis of the slip direction trending 0 to 30 and the slip plane normal to the b axis being vertical and in the south anisotropy with the axis trending 90 to 120 and the slip plane being horizontal

azimuthal anisotropy and phase velocity beneath iceland implication for plume ridge interaction abstract we have determined the pattern of azimuthal anisotropy beneath iceland from shear wave splitting and rayleigh wave tomography using seismic data recorded during the icemelt and hotspot experiments the fast directions of shear wave splitting are roughly n s in western iceland and nnw sse in eastern iceland in western iceland azimuthal variations in rayleigh wave phase velocity show that fast directions are close to the plate spreading direction at short periods of 25 40 s and roughly parallel to the mid atlantic ridge at longer periods of 50 67 s beneath the rift zones in central iceland we find a ridge parallel fast direction at periods of 25 40 s and significantly weaker azimuthal anisotropy at periods of 50 67 s the 2 d variation of isotropic phase velocity at periods of 33 67 s indicates that the lowest velocities are beneath the rift zones in central iceland rather than above the plume conduit in southeast iceland while ridge parallel alignment of melt films might contribute to anisotropy above 50 km depth beneath the rift zones the overall observations are consistent with a model in which plume influenced hot buoyant mantle rises beneath the mid atlantic ridge at depths greater than 50 km and is preferentially channeled along the ridge axis at the base of the lithosphere beneath iceland the shear wave splitting results are attributed primarily to a n s mantle flow at depths greater than 100 km

upper mantle s wave speed heterogeneity and anisotropy beneath the north atlantic from regional surface wave tomography the iceland and azores plumes summary we present a high resolution sv wave velocity and azimuthal anisotropy model for the upper mantle beneath the north atlantic and surrounding region derived from the analysis of over 3000 fundamental and higher mode rayleigh waveforms much of the data set comes from global and national digital seismic networks but to improve the path coverage we have also deployed a number of instruments at coastal sites in northwest europe iceland and eastern greenland the dense path coverage wide azimuthal distribution substantial higher mode content and the relatively short path lengths in the data set have enabled us to build an upper mantle model for the region with a horizontal resolution of a few hundred kilometres extending to 400 km depth three major hotspots iceland azores and eifel exist within the region of the model and slow upper mantle velocities are associated with each of these areas the best depth resolution in our model occurs in nw europe and in this area low sv velocities in the vicinity of the eifel hotspot extend to approximately 400 km depth major negative velocity anomalies exist in the north atlantic upper mantle beneath both iceland and the azores hotspots both anomalies are above 200 km depth 5 7 per cent slow with respect to prem and are elongated along the mid atlantic ridge low velocities extend to the south of iceland beneath the reykjanes ridge where other geophysical and geochemical observations have indicated the presence of hot plume material a similar but somewhat weaker feature exists beneath the kolbeinsey ridge north of iceland where there is also supporting evidence for the presence of hot plume material this observation might also be associated with a plume beneath jan mayen the low velocity structure beneath the azores hotspot is also elongated along the mid atlantic ridge the fast propagation direction of horizontally propagating sv waves in the atlantic south of iceland correlates well with the east west ridge spreading direction at all depths and changes to a direction close to ns in the vicinity of iceland

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

models of lithosphere and asthenosphere anisotropic structure of the yellowstone hot spot from shear wave splitting 1 teleseismic shear wave splitting measured at 56 continuous and temporary seismographs deployed in a 500 km by 600 km area around the yellowstone hot spot indicates that fast anisotropy in the mantle is parallel to the direction of plate motion under most of the array the average split time from all stations of 0 9 s is typical of continental stations there is little evidence for plume induced radial strain suggesting that any contribution of gravitationally spreading plume material is undetectably small with respect to the plate motion velocity two stations within yellowstone have splitting measurements indicating the apparent fast anisotropy direction is nearly perpendicular to plate motion these stations are 30 km from stations with parallel to plate motion the 70 rotation over 30 km suggests a shallow source of anisotropy however split times for these stations are more than 2 s we suggest melt filled stress oriented cracks in the lithosphere are responsible for the anomalous orientations within yellowstone stations southeast of yellowstone have measurements of oriented nnw to wnw at high angles to the plate motion direction the archean lithosphere beneath these stations may have significant anisotropy capable of producing the observed splitting

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

calculating splitting parameters for plume type anisotropic structures of the upper mantle summary we apply a forward propagator method to calculate shear wave splitting parameters for general 3 d weakly anisotropic upper mantle structures the approach is valid under the assumption that the ray paths of the two quasi shear qs waves can be approximated by a common reference ray within an isotropic background medium along the reference ray the incremental splitting is expressed in terms of qs polarizations and slownesses in the direction of propagation using a ray theory ansatz we show that the resulting shear wave seismogram is equivalent to the coupling ray theory of coates chapman 1990 under the assumption of smoothly varying anisotropy here we use the forward propagator method to calculate apparent shear wave splitting parameters that can be compared directly with observations of teleseismic shear wave splitting a comparison with finite difference calculations is used to assess the validity of the method as an application we consider shear wave splitting due to a plume type anisotropic upper mantle structure the anisotropy is assumed to result from the preferred alignment of orthorhombic olivine we show examples of waveforms and splitting parameters as functions of backazimuth and angle of incidence anisotropic effects for sks are weak at stations near the central upwelling due to the combined effects of initial polarization and olivine a axis orientation here the splitting parameters are irregular and fast axis directions may vary by up to 70 depending on the vertical incidence angle at larger distances splitting parameters slowly converge towards values expected for homogeneous media the results suggest that direct evidence for mantle plumes from shear wave splitting is more likely to come from obs stations at some distance away from the central upwelling at shallower incidence the apparent splitting parameters for s exhibit a 90 periodicity as functions of the initial polarization of the incident shear wave provided that the ray path is kept fixed our results show that this is a general characteristic of shear wave splitting in inhomogeneous anisotropic media the effect can be used to identify complex anisotropic regions within the earth s mantle

pollen biostratigraphy and environmental pattern of snaigupėlė interglacial late middle pleistocene western lithuania abstract stratigraphical subdivision of the pleistocene formations in the areas affected by the numerous glaciations is still rather complicated and contradictory in many cases interglacial sediments are of primary importance for the stratigraphical subdivision of this stratum the palynological signature of interglacial sediments has often been used for determination of their chronostratigraphical position interglacial organic sediments consisting of peat and sapropelite were intersected in eight boreholes in western lithuania 19 50 34 5 m bsl 55 40 30 55 41 47 n 21 08 03 21 10 17 e palynological record suggests the deposition of the investigated sediments during the lateglacial and the first half of the interglacial including climatic optimum the spread of shrub herb vegetation with the patchy occurrence of betula and possibly pinus during the lateglacial was recorded deposition of silt and sand with low input of organic matter indicates rather severe climatic conditions betula and pinus dominated forest with presence of larix were typical of the early beginning of the interglacial deposition of sapropelite and peat indicates increasing organic input ongoing climatic amelioration coincided with the rapid development of a mixed forest with numerous broad leaved trees e g ulmus quercus and tilia during the first half of the interglacial further changes of the vegetation structure indicate migration of alnus and picea that may have been related with increasing humidity sediments from mardasavas section that contains a similar palynological record were 230 th u dated at 202 4 38 6 22 9 ka tsd method and 220 6 35 3 20 5 ka l l method gaigalas a arslanov kh a maksimov f e kuznetsov v yu chernov s b 2007 uranium thorium isochron dating results of penultimate late mid pleistocene interglacial in lithuania from mardasavas site geologija 57 21 29 the reconstructed pattern of the flora structure e g presence absence and abundance of certain characteristic taxa suggest the deposition of the investigated sediments during the warm climatic interval that can be tentatively correlated with the first half of the snaigup l lubavian uecker schoningen or gorkinskij interglacial attributed to late middle pleistocene or to marine isotope stage 7 mis 7 of the north atlantic pro rata

temperature and melting of a ridge centred plume with application to iceland part ii predictions for electromagnetic and seismic observables summary the dynamic and melting processes of a ridge centred plume have been investigated in a companion paper by ruedas et al hereafter referred to as paper i in a set of 3 d numerical fluid dynamic models with varying plume excess temperatures and melt extraction thresholds in paper i the modelled thickness of the generated crust has been compared to observations of the icelandic crust using the results of those plume models magnetotelluric mt transfer functions and seismic velocity anomalies are predicted in this paper together with paper i a dynamically consistent set of geophysical observables of a ridge centred plume is presented and applied to iceland temperature partial melting and the connectivity of the melt phase influence the electrical conductivity of crust and mantle rocks the temperature and melt fraction of our plume models are used to calculate 3 d conductivity models for mt modelling for the melt geometry ellipsoidal inclusions with appropriate aspect ratios were assumed to control melt connectivity the resulting transfer functions are compared to each other and to models not including a plume to separate signals from the ridge and the plume they may be applied to observed mt measurements if the plume head contains only 1 per cent of melt the plume signal cannot be distinguished from the ridge signal at least 3 per cent melt is needed for such distinction the other predicted observables calculated from the different numerical models are seismic velocity anomalies the temperature induced vp and vs anomalies were estimated including anharmonic and anelastic effects as well as the water induced increase of dislocation mobility that lowers seismic velocities realistic melt geometries as observed in laboratory experiments were used to calculate the effect of partial melts on the seismic velocities vs anomaly distributions are synthesized from the different plume models and compared to seismic observations to reconcile seismic anomalies of the plume head and plume stem a wet plume stem overlain by a partially molten dehydrated plume head is favoured the combined interpretation of available observations crustal thicknesses paper i and seismic results with our dynamic plume models paper i leads to a favoured plume model with 135 k excess temperature and a vertical velocity of approximately 13 cm yr 1 at 200 km depth with 1 per cent melt extraction threshold and a melting zone of approximately 500 km width and 100 km depth extent

the effect of the large scale mantle flow field on the iceland hotspot track abstract fluid dynamical simulations were carried out in order to investigate the effect of the large scale mantle flow field and the depth of the plume source on the structure of the iceland plume through time the time dependent location and shape of the plume in the earth s mantle was calculated in a global model and it was refined in the upper mantle using a 3d cartesian model box global flow was computed based on density heterogeneities derived from seismic tomography plate motion history served as a velocity boundary condition in both models hotspot tracks of the plume conduits and the plume head were calculated and compared to actual bathymetry of the north atlantic if a plume source in the lowermost mantle is assumed the calculated surface position of the plume conduit has a southward component of motion due to southward flow in the lower mantle depending on tomography model assumed plume age and buoyancy the southward component is more or less dominating plume models having a source at the 660 km discontinuity are only influenced by flow in the upper mantle and transition zone and hence rather yield westward hotspot motion many whole mantle plume models result in a v shaped track which does not match the straight greenland iceland faroe ridge models without strong southward motion such as for a plume source at 660 km depth match actual bathymetry better plume tracks were calculated from both plume conduits and plume heads a plume head of 120 k anomalous temperature gives the best match between plume head track and bathymetry

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

teleseismic arrivals at a mid ocean ridge effects of mantle melt and anisotropy recent observational evidence of upwelling mantle anisotropy at a slow spreading center has motivated the modeling of teleseismic arrivals at mid ocean ridges the models consider a variety of types of anisotropy and heterogeneity where the emphasis is to ascertain whether or not travel times can be used to discriminate between the existence of partial melt and anisotropy two mechanisms for anisotropy in the upwelling asthenosphere are considered one due to the preferential alignment of the fast axes of olivine crystals in the direction of mantle flow and the other due to the preferential alignment of cracks that feed melt towards the spreading axis the results indicate that p waves are most sensitive to even modest amounts of flowinduced asthenospheric anisotropy while s waves are most sensitive to the presence of mantle melt multiple s wave arrivals are predicted for many models most notably the ones with anisotropy due to crack alignment where very large s wave separations develop the model which best fits existing data requires a higher degree of crystal alignment anisotropy in the upwelling asthenosphere than in the lithosphere this effect has been predicted in studies of the evolution of crystal alignment anisotropy in polycrystalline aggregates

straightforward reconstruction of 3d surfaces and topography with a camera accuracy and geoscience application topographic measurements for detailed studies of processes such as erosion or mass movement are usually acquired by expensive laser scanners or rigorous photogrammetry here we test and use an alternative technique based on freely available computer vision software which allows general geoscientists to easily create accurate 3d models from field photographs taken with a consumer grade camera the approach integrates structure from motion sfm and multi view stereo mvs algorithms and in contrast to traditional photogrammetry techniques it requires little expertise and few control measurements and processing is automated to assess the precision of the results we compare sfm mvs models spanning spatial scales of centimeters a hand sample to kilometers the summit craters of piton de la fournaise volcano with data acquired from laser scanning and formal close range photogrammetry the relative precision ratio achieved by sfm mvs measurement precision observation distance is limited by the straightforward camera calibration model used in the software but generally exceeds 1 1000 i e centimeter level precision over measurement distances of 10s of meters we apply sfm mvs at an intermediate scale to determine erosion rates along a 50 m long coastal cliff seven surveys carried out over a year indicate an average retreat rate of 0 70 0 05 m a 1 sequential erosion maps at 0 05 m grid resolution highlight the spatio temporal variability in the retreat with semivariogram analysis indicating a correlation between volume loss and length scale compared with a laser scanner survey of the same site sfm mvs produced comparable data and reduced data collection time by 80

inversion of teleseismic p wave particle motions for crustal structure in fennoscandia abstract we test a model of the earth s crust by transforming the observed vertical component of the teleseismic p wave record into the synthetic radial component and comparing this with the observed radial component the optimum model can be found by minimizing the rms difference between the synthetic radial component and the observed one for a number of records in the time intervals several tens of seconds long we applied this method to long period records of norsar and some other seismograph stations in fennoscandia the search for the optimum models was performed by trial and error and by application of the iterative procedure based on the general method of solution of the ill posed inverse problems tikhonov and arsenin in comparison with the conventional spectral ratio analysis our techniques are more flexible and demonstrate a higher resolving power it is found that in the norsar siting area the crustal thicknesses are regulated by the variations of thickness of the granite layer which dominates in the crust this observation explains peculiarities of the gravity field in the oslo graben region a similar relation between the parameters of the crust is found in the eastern part of fennoscandia

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

seismic anisotropy in the crust at the mid atlantic plate boundary in south west iceland summary seismograms of microearthquakes recorded on stations of the sil network in south western iceland exhibit strong shear wave splitting and are consistent with being caused by aligned parallel cracks in the uppermost crust splitting times of 0 1 0 3 s are observed with the larger values 0 2 0 3 s occurring beneath stations in the highly heated western volcanic zone and the smaller values 0 1 s in the younger less fractured south iceland seismic zone five of the stations have a fast shear wave polarization azimuth of n30 e n40 e7 parallel to the axis of the western volcanic zone i e the mid atlantic ridge in iceland and in the direction of maximum horizontal compression defined by fault dyke and fissure strikes and microearthquake focal mechanisms station gyg in the north western part of the network has the significantly different azimuth of n70 e this is parallel to one of the local strike slip fault trends and is probably due to a heated rock fabric caused by those faults

the mantle flow field beneath western north america although motions at the surface of tectonic plates are well determined the accompanying horizontal mantle flow is not we have combined observations of surface deformation and upper mantle seismic anisotropy to estimate this flow field for western north america we find that the mantle velocity is 5 5 1 5 centimeters per year due east in a hot spot reference frame nearly opposite to the direction of north american plate motion west southwest the flow is only weakly coupled to the motion of the surface plate producing a small drag force this flow field is probably due to heterogeneity in mantle density associated with the former farallon oceanic plate beneath north america

shear wave splitting across the iceland hot spot results from the icemelt experiment 1 we report on observations of upper mantle anisotropy from the splitting of teleseismic shear waves sks skks and pks recorded by the icemelt broadband seismometer network in iceland in a ridge centered hot spot locale mantle anisotropy may be generated by flow induced lattice preferred orientation of olivine grains or the anisotropic distribution of magma splitting measurements of teleseismic shear waves may thus provide diagnostic information on upper mantle flow and or the distribution of retained melt associated with the iceland mantle plume in eastern iceland fast polarization directions lie between n10 w and n45 w and average n24 w delay times between the fast and slow shear waves are generally 0 7 1 35 s in western iceland in contrast the fast polarization directions while less well constrained yield an average value of n23 e and delay times are smaller 0 2 0 95 s we propose that splitting in eastern iceland is caused by a 100 to 200 km thick anisotropic layer in the upper mantle the observed fast directions in eastern iceland however do not correspond either to the plate spreading direction or to a pattern of radial mantle flow from the center of the iceland hot spot we suggest that the relatively uniform direction and magnitude of splitting in eastern iceland situated on the eurasian plate may therefore reflect the large scale flow field of the north atlantic upper mantle we hypothesize that the different pattern of anisotropy beneath western iceland part of the north american plate is due to the different absolute motions of the two plates by this view splitting in eastern and western iceland is the consequence of shear by north american and eurasian plate motion relative to the background mantle flow from absolute plate motion models in which the eurasian plate is approximately stationary and the north american plate is moving approximately westward the splitting observations in both eastern and western iceland can be satisfied by a background upper mantle flow in the direction n34 w and a velocity of 3 cm yr in a hot spot reference frame this inference can be used to test mantle flow models in particular it is inconsistent with kinematic flow models which predict southward flow or models where flow is dominated by subduction related sources of mantle buoyancy which predict westward flow our observations are more compatible with the flow field predicted from global seismic tomography models which in particular include the influence of the large scale lower mantle upwelling beneath southern africa while the hypothesized association between our observations and this upwelling is presently speculative it makes a very specific and testable prediction about the flow field and hence anisotropy beneath the rest of the atlantic basin index terms 7218 seismology lithosphere and upper mantle 8120 tectonophysics dynamics of lithosphere and mantle general 8155 tectonophysics plate motions general keywords iceland anisotropy hot spot plate motion shear wave splitting mantle flow

sks splitting in the western indian ocean from land and seafloor seismometers plume plate and ridge signatures we present sks splitting measurements in the western indian ocean recorded on 20 land and 57 seafloor seismometers deployed by the rhum rum experiment reunion hotspot and upper mantle reunions unterer mantel we discuss our splitting observations within their geodynamic settings and compare them to sks splitting parameters predicted from an azimuthally anisotropic rayleigh wave tomography model that includes the rhum rum data we find that anisotropic directions poorly correlate with the present day motion of the somali plate which at 2 6 cm yr may be too slow to cause strongly sheared fabric in the asthenosphere fast split directions between la reunion and the central indian ridge cir trend e w and provide strong first seismological evidence for near horizontal flow in the asthenosphere that connects the reunion mantle upwelling with the cir supporting a long standing hypothesis on plume ridge interaction in the vicinity of the reunion hotspot we observe a seismic anisotropy pattern indicative of a parabolic asthenospheric flow controlled by the reunion mantle upwelling and its consecutive asthenospheric spreading we furthermore observe ridge normal along the cir and ridge parallel along the southwest indian ridge swir both mainly attributed to asthenospheric mantle flows in the mozambique channel between east africa and madagascar we attribute e w trending to frozen lithospheric structures recording the paleo orientation of the spreading ridges that enabled madagascar s separation away from africa based on the synopsis of this and previous sks splitting studies at mid ocean ridges we propose that ridge normal may develop at fast and intermediate spreading ridges e g cir and east pacific rise and ridge parallel could be characteristic to slow spreading ridges e g swir mid atlantic ridge and the paleo ridges in the mozambique channel