the q structure of the upper mantle constraints from rayleigh wave amplitudes 1 the three dimensional shear attenuation or q structure of the upper mantle is still poorly understood despite the increasing accuracy and sophistication of velocity models of the same part of the earth here we present a set of three dimensional q models of the upper mantle based on amplitude measurement of minor and major arc rayleigh waves in the period range 70 170 s the models show that areas of low attenuation underlie continents to a depth of around 300 km and areas of high attenuation are associated with oceans and plate boundaries particularly in the top 200 km below 350 km the sensitivity of the data to attenuation structure decreases rapidly it is well known that the amplitudes of surface waves can be strongly influenced by factors other than attenuation in particular focusing due to elastic structure and errors in source mechanisms we consider the effects of focusing by discussing the implications of the results of selby and woodhouse 2000 comparisons with focusing predictions using phase velocity maps allow us to identify features due to focusing in maps of attenuation distribution the influence of the source on the observed attenuation distribution is investigated by including a source term in the model inversion we find that successfully combining the data at each frequency into one three dimensional model requires that this source term must vary with frequency suggesting that a simple correction to the scalar moment of each event cannot explain the observations although the effects of focusing and the source can be significant we find that the observed attenuation pattern is robust up to degree 8 however shorter wavelength structure can be strongly influenced by other controls finally we use one of the models to predict the degree 2 attenuation pattern for 250 s rayleigh waves the observed pattern suggests that existing normal mode observations may be explainable in terms of structure above 350 km depth

seismic tomography a window into deep earth abstract the goal of this paper is to provide an overview of the current state of the art in seismic tomography and trace its origins from pioneering work in the early 1970s to its present status as the pre eminent tool for imaging the earth s interior at a variety of scales due to length limitations we cannot hope to cover every aspect of this diverse topic or include mathematical derivations of the underlying principles rather we will provide a largely descriptive coverage of the methodology that is targeted at readers not intimately familiar with the topic the relative merits of local versus global parameterization ray tracing versus wavefront tracking backprojection versus gradient based inversion and synthetic testing versus model covariance are explored a variety of key application areas are also discussed including body wave traveltime tomography surface wave tomography attenuation tomography and ambient noise tomography established and emerging trends many of which are driven by the ongoing rapid increases in available computing power will also be examined including finite frequency tomography full waveform tomography and joint tomography using multiple datasets several practical applications of seismic tomography including body wave traveltime attenuation and surface waveform are presented in order to reinforce prior discussion of theory

thermal model of oceanic transform faults a thennal model of the oceanic transform fault which includes effects of the lateral heat conduction across the fault and the shear heating along the fault has been developed the results show that shear heating along the transform fault significantly raises the temperature along the fault the depths to isotherms of the thermal model were compared to the depths of earthquakes along transform faults by including the shear heating the limiting isotherm of the focal depths of atlantic transform earthquakes is 700 c 600 c if not including the shear heating which is close to the limiting temperature of the intraplate oceanic earthquakes if the transform earthquakes are limited by the 750 c isotherm then the transform earthquakes should be shallow events as predicted by our thermal model the model predicts the maximum depth of the 750 c isotherm increases with the length of the transform fault and decreases with the half slip rate both the effects of the lateral heat conduction across the transform fault and the shear heating along the fault generate topographic and geoid anomalies in a 30 to 60 km wide zone at the fault with magnitudes of the order of a few hundred meters and tens of centimeters respectively given the thermal structure of the transform fault the shear traction along the fault can be estimated the average shear traction per unit length of the transform fault is of the order of 1012 n m which is comparable to the magnitude of the major plate driving forces

global upper mantle structure from finite frequency surface wave tomography 1 we report global shear wave velocity structure and radial anisotropy in the upper mantle obtained using finite frequency surface wave tomography based upon complete three dimensional born sensitivity kernels because wavefront healing effects are properly taken into account finite frequency surface wave tomography improves the resolution of small scale mantle heterogeneities especially for deep anomalies that are constrained by the longest period surface waves in our finite frequency model ffsw1 the globally averaged radial anisotropy shows a transition from positive sh sv to negative anisotropy sv sh at about 220 km consistent with a change in the dominant mantle circulation pattern from predominantly horizontal flow at shallow depths to vertical flow at greater depths the radial anisotropy beneath cratons and the old pacific plate agrees well with previous studies however our model exhibits a strong negative radial anisotropy at depths greater than 120 km beneath mid ocean ridges a feature that is not present in previous upper mantle models more interestingly the depth extent of the ridge anomalies is distinctly different beneath fast and slow spreading centers anomalies beneath fast spreading centers are stronger but the strength decreases rapidly below 250 km in contrast beneath slow spreading centers such as the northern mid atlantic ridge and the red sea anomalies extend down at least to the top of the transition zone the different depth extent of the ridge anomalies suggests that the primary driving force of slow spreading seafloor may be different from that of fast spreading seafloor and that active upwelling beneath slow spreading ridges may play a major role in the opening of the seafloor

seismic evidence for sharp lithosphere asthenosphere boundaries of oceanic plates the mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics and thus the understanding of the processes at the lithosphere asthenosphere boundary lab is fundamental to understand how our planet works it is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the lab data from borehole broadband ocean bottom seismometers show that the lab beneath the pacific and philippine sea plates is sharp and age dependent the observed large shear wave velocity reduction at the lab requires a partially molten asthenosphere consisting of horizontal melt rich layers embedded in meltless mantle which accounts for the large viscosity contrast at the lab that facilitates horizontal plate motions

the deep structure of the north anatolian fault zone abstract multi scale full waveform inversion of complete continental and regional scale seismograms reveals the crustal and upper mantle signature of the north anatolian fault zone which shapes the neotectonics of turkey and the eastern mediterranean within the crust the fault zone is mostly bounded by several high velocity blocks suggesting that it developed along the edges of continental fragments with high rigidity below the crust the surface expression of the eastern and central parts of the north anatolian fault zone correlate with a pronounced low velocity band that extends laterally over 600 km around 100 km depth the low velocity band merges into the shallow anatolian asthenosphere thereby providing a link to the kirka afyon isparta volcanic field and the central anatolian volcanics we interpret the low velocity band beneath the north anatolian fault zone as the upper mantle expression of the tethyan sutures that formed 60 15 ma ago as a result of africa eurasian convergence the structurally weak suture facilitated the formation of the younger less than 10 ma crustal fault zone in this sense the north anatolian fault zone is not only a crustal feature but a narrow zone of weakness that extends into the upper mantle

on crustal corrections in surface wave tomography summary mantle models from surface waves rely on good crustal corrections we investigated how far ray theoretical and finite frequency approximations can predict crustal corrections for fundamental mode surface waves using a spectral element method we calculated synthetic seismograms in transversely isotropic prem and in the 3 d crustal model crust2 0 on top of prem and measured the corresponding time shifts as a function of period we then applied phase corrections to the prem seismograms using ray theory and finite frequency theory with exact local phase velocity perturbations from crust2 0 and looked at the residual time shifts after crustal corrections residuals fall within the uncertainty of measured phase velocities for periods longer than 60 and 80 s for rayleigh and love waves respectively rayleigh and love waves are affected in a highly non linear way by the crustal type oceanic crust affects love waves stronger while rayleigh waves change most in continental crust as a consequence we find that the imperfect crustal corrections could have a large impact on our inferences of radial anisotropy if we want to map anisotropy correctly we should invert simultaneously for mantle and crust the latter can only be achieved by using perturbation theory from a good 3 d starting model or implementing full non linearity from a 1 d starting model

separating intrinsic and apparent anisotropy abstract seismic anisotropy plays a key role in studies of the earth s rheology and deformation because of its relation to flow induced lattice preferred orientation lpo of intrinsically anisotropic minerals in addition to lpo small scale heterogeneity produces apparent anisotropy that need not be related to deformation in the same way as intrinsic anisotropy quantitative interpretations of observed anisotropy therefore require the separation of its intrinsic and apparent components we analyse the possibility to separate intrinsic and apparent anisotropy in media with hexagonal symmetry typically used in surface wave tomography and sks splitting studies our analysis is on the level of the wave equation which makes it general and independent of specific data types or tomographic techniques we find that observed anisotropy can be explained by isotropic heterogeneity when elastic parameters take specific combinations of values in practice the uncertainties of inferred anisotropy are large enough to ensure that such a combination is always within the error bars it follows that commonly observed anisotropy can always be explained completely by a purely isotropic laminated medium unless all anisotropic parameters are known with unrealistic accuracy most importantly minute changes in the poorly constrained p wave anisotropy and the parameter can switch between the possible or impossible existence of an isotropic equivalent important implications of our study include 1 intrinsic anisotropy over tomographically resolved length scales is never strictly required when reasonable error bars for anisotropic parameters are taken into account 2 currently available seismic observables provide weak constraints on the relative contributions of intrinsic and apparent anisotropy 3 therefore seismic observables alone are not sufficient to constrain the magnitude of mantle flow 4 quantitative interpretations of anisotropy in terms of mantle flow require combined seismic geodynamic inversions as well as the incorporation of additional data such as topography gravity and scattered waves

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

adjoint tomography of the southern california crust using an inversion strategy based on adjoint methods we developed a three dimensional seismological model of the southern california crust the resulting model involved 16 tomographic iterations which required 6800 wavefield simulations and a total of 0 8 million central processing unit hours the new crustal model reveals strong heterogeneity including local changes of 30 with respect to the initial three dimensional model provided by the southern california earthquake center the model illuminates shallow features such as sedimentary basins and compositional contrasts across faults it also reveals crustal features at depth that aid in the tectonic reconstruction of southern california such as subduction captured oceanic crustal fragments the new model enables more realistic and accurate assessments of seismic hazard

full waveform tomography for radially anisotropic structure new insights into present and past states of the australasian upper mantle article i nfo we combine spectral element simulations and adjoint techniques in a non linear full seismic waveform tomography for the radially anisotropic structure of the australasian upper mantle our method allows us to explain 30 s waveforms in detail and it yields tomographic images with locally 2 lateral resolution in the course of 19 conjugate gradient iterations the total number of exploitable waveforms increased from 2200 to nearly 3000 the final model amsan 19 thus explains data that were not initially included in the inversion this is strong evidence for the effectiveness of the inversion scheme and the physical consistency of the tomographic model amsan 19 confirms long wavelength heterogeneities found in previous studies and it allows us to draw the following inferences concerning the past and present states of the australian upper mantle and the formation of seismic anisotropy 1 small scale neutral to low velocity patches beneath central australia are likely to be related to localised paleozoic intraplate deformation 2 increasing seismic velocities between the moho and 150 km depth are found beneath parts of proterozoic australia suggesting thermochemical variations related to the formation and fragmentation of a centralian superbasin 3 radial anisotropy above 150 km depth reveals a clear ocean continent dichotomy we find strong vshnvsv beneath the coral and tasman seas the anisotropy is strongest at the top of the inferred asthenospheric flow channel where strain is expected to be largest radial anisotropy beneath the continent is weaker but more variable localised patches with vshbvsv appear in accord with small scale intraplate deformation 4 the ocean continent dichotomy disappears gradually between 150 and 250 km depth where the continental lithospheric mantle and the oceanic asthenosphere pass into the underlying convecting mantle 5 significant anisotropy exists below 250 km depth its character can be explained by sublithospheric small scale convection and a change in the dominant glide system of olivine

imaging lateral heterogeneity in the northern apennines from time reversal of reflected surface waves summary prominent arrivals in the coda of seismograms from the wider alpine area can be associated with lateral reflections of love waves at the northern apennines mountain chain italy where structural heterogeneity causes an abrupt contrast in phase velocity we discuss an approach to image lateral heterogeneity from reflected surface waves using intermediate period threecomponent coda waveforms as sources for an adjoint wavefield that propagates the reflections backward in time we numerically compute three dimensional sensitivity kernels for the dependence of coda waveforms on p velocity s velocity and density based upon correlations between the adjoint and the regular forward wavefields we consider synthetic coda waveforms for a simplified model of the northern apennines as well as real coda observations from five moderate magnitude earthquakes m w 4 6 5 6 in the southern alps wave propagation is simulated using the spectral element method for which a 3 d regional earth model is used in the case of real data single and combined event sensitivity kernels provide clear images of the reflectivity associated with the northern apennines in kernels for density and s wave speed the kernels show that surface wave reflections occur near the axial zone of the mountain chain apart from the apennines the approach is able to image other smaller reflectivity patches from the coda waveforms like the ivrea zone in the southern alps our coda misfit kernels can be integrated in a gradient based waveform tomography where they could enhance the sharpness of the model at lateral discontinuities

a review of numerical experiments on seismic wave scattering this paper reviews applications of the finite difference and finite element methods to the study of seismic wave scattering in both simple and complex velocity models these numerical simulations have improved our understanding of seismic scattering in portions of the earth where there is significant lateral heterogeneity such as the crust the methods propagate complete seismic wavefields through highly complex media and include multiply scattered waves and converted phases e g p tosv sv top body wave to surface wave the numerical methods have been especially useful in cases of moderate and strong scattering in complex media where multiple scattering becomes important progress has been made with numerical methods in understanding how near surface low velocity basin structures scatter surface waves and vertically incident body waves the numerical methods have proven useful in evaluating scattering of surface waves and body waves from topography of both the free surface and interfaces buried at depth numerical studies have demonstrated the importance of conversions from body waves to surface waves andvice versa when lateral heterogeneities and topographic relief are present in the uppermost crust recently several investigations have applied numerical methods to study seismic wave propagation in velocity models which vary randomly in space this stochastic approach seeks to understand the effects of small scale complexity in the earth which cannot be resolved deterministically these experiments have quantified the relationships between the statistical properties of the random heterogeneity and the measurable properties of high frequency 1 hz seismograms these simulations have been applied to the study of many features observed in actual high frequency seismic waves including the amplitude and time decay of seismic coda the apparent attenuation from scattering the dispersion of waveforms and the travel time and waveform variations across arrays of receivers

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

petrological constraints on seismic anisotropy the purpose of this paper is to investigate the correlations between anisotropic parameters for different orientations and mineralogies for realistic mineralogical and petrological models of the upper mantle such correlations make it possible to reduce the number of independent parameters required in seismic modelling of the upper mantle the variation with depth and with degree of random orientation is also investigated it is shown that the anisotropic combinations involved in an equivalent transversely isotropic medium azumithally averaged velocities with a vertical symmetry axis are strongly correlated but the combinations involved in azimuthal anisotropy are more weakly correlated comparison with available seismic data does not yet allow discrimination based on anisotropy between different petrological models it is shown that even if a proportion of random orientation is introduced it should be possible to achieve petrological discrimination from seismic data for some orientation configurations if the inverse problem is well posed i e takes account of the correlations between anisotropic parameters these correlations are incorporated in an inversion process to show that it is possible to explain the dataset used to derive the prem by alternative anisotropic models for the uppermost 220 km

global crustal thickness from neural network inversion of surface wave data summary we present a neural network approach to invert surface wave data for a global model of crustal thickness with corresponding uncertainties we model the a posteriori probability distribution of moho depth as a mixture of gaussians and let the various parameters of the mixture model be given by the outputs of a conventional neural network we show how such a network can be trained on a set of random samples to give a continuous approximation to the inverse relation in a compact and computationally efficient form the trained networks are applied to real data consisting of fundamental mode love and rayleigh phase and group velocity maps for each inversion performed on a 2 2 grid globally we obtain the a posteriori probability distribution of moho depth from this distribution any desired statistic such as mean and variance can be computed the obtained results are compared with current knowledge of crustal structure generally our results are in good agreement with other crustal models however in certain regions such as central africa and the backarc of the rocky mountains we observe a thinner crust than the other models propose we also see evidence for thickening of oceanic crust with increasing age in applications characterized by repeated inversion of similar data the neural network approach proves to be very efficient in particular the speed of the individual inversions and the possibility of modelling the whole a posteriori probability distribution of the model parameters make neural networks a promising tool in seismic tomography

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

shear wave velocity variations in the upper mantle beneath central europe summary a new model eur s91 of shear wave velocity variations in the upper mantle beneath central europe and surrounding regions down to a depth of 670km is presented the model is derived from the inversion of the waveforms of 217 seismograms using the partitioned waveform inversion method for the seismogram in the time window from the s wave arrival to the fundamental mode of the rayleigh wave the seismograms were mostly assembled from digitally recording long period and broad band stations in europe the resulting 3 d model accurately predicts most of the observed waveforms in a wide band of frequencies body waves were fit for frequencies up to 60mhz the fundamental rayleigh mode which at high frequencies is more prone to scattering and multipathing was generally low passed at 25 mhz the resolving power of the data set depends strongly on the density of available wave paths and varies as a function of geographical position small scale heterogeneities like the subducted lithosphere in the hellenic collision zone were imaged in the region with the highest density of wave paths which indicates an optimum resolution of better than 200 km the main new results of this study pertain to the transition between east and central europe we present new information about the structure below the tornquist teisseyre zone ttz the ttz is generally regarded as the boundary between the precambrian crust of the baltic shield russian platform and the younger crust of central europe our 3 d s velocity model reveals that below this line a sharp lateral boundary extends down to at least 140 km depth with high velocities beneath the baltic shield and russian platform contrasting to the low velocities beneath the younger regions of europe the observed velocity contrast across the ttz is largest between the pannonian basin and the russian platform where it is equal to 12 per cent at 80 km depth at depths of 300 400 km the ttz is underlain by a zone of low s velocity which indicates a local thinning of the deeply rooted high velocity structure or tectosphere that underlies most of eastern europe in addition to these new results on the transition region between east and central europe a number of features that are present in other tomographic results have been confirmed the precambrian provinces of europe are characterized by high s velocities low velocities are found beneath the pannonian basin the western mediterranean northern aegean sea turkey and a small region south west of the massif central the lithosphere beneath the paris basin has a positive s velocity anomaly the resolution of all these anomalies has been established with sensitivity tests

magma generation by slab steepening and breakoff beneath a subduction accretion complex an alternative model for collision related volcanism in eastern anatolia turkey 1 eastern anatolia is regarded as one of the best examples of continental collision represented by a 2 km high plateau it displays shallow and diffuse seismicity indicating that the crust is still being actively deformed perhaps the most striking aspect of eastern anatolia is the volume and compositional variability of collision related volcanic products erupted during the neogene and quaternary time a number of models have been proposed for the genesis of this volcanism in the region however recent geophysical studies have revealed that a mantle lithosphere is almost completely absent beneath a greater portion of the region which makes us question the validity of the previous models in this paper we propose a new model for magma genesis slab steepening and breakoff beneath a large subduction accretion complex this model holds that a northward subducting oceanic lithosphere beneath the eastern anatolia accretionary prism gets steepened and eventually detached from the continental lithosphere of the bitlis poturge massif following the continent accretionary complex collision this brings the asthenospheric mantle in contact with the accretionary complex at shallow depths e g around 50 km resulting in rapid regional uplift and extensive melting which leads to collisional volcanism

seismic tomography of the southern california crust based on spectral element and adjoint methods we iteratively improve a 3 d tomographic model of the southern california crust using numerical simulations of seismic wave propagation based on a spectral element method sem in combination with an adjoint method the initial 3 d model is provided by the southern california earthquake center the data set comprises three component seismic waveforms i e both body and surface waves filtered over the period range 2 30 s from 143 local earthquakes recorded by a network of 203 stations time windows for measurements are automatically selected by the flexwin algorithm the misfit function in the tomographic inversion is based on frequency dependent multitaper traveltime differences the gradient of the misfit function and related finite frequency sensitivity kernels for each earthquake are computed using an adjoint technique the kernels are combined using a source subspace projection method to compute a model update at each iteration of a gradient based minimization algorithm the inversion involved 16 iterations which required 6800 wavefield simulations the new crustal model m 16 is described in terms of independent shear v s and bulk sound v b wave speed variations it exhibits strong heterogeneity including local changes of 30 per cent with respect to the initial 3 d model the model reveals several features that relate to geological observations such as sedimentary basins exhumed batholiths and contrasting lithologies across faults the quality of the new model is validated by quantifying waveform misfits of full length seismograms from 91 earthquakes that were not used in the tomographic inversion the new model provides more accurate synthetic seismograms that will benefit seismic hazard assessment

adaptively parametrized surface wave tomography methodology and a new model of the european upper mantle summary in this study we aim to close the gap between regional and global traveltime tomography in the contextofsurfacewavetomographyoftheuppermantleimplementingtheprincipleofadaptive parametrization observations of seismic surface waves are a very powerful tool to constrain the3 dstructureoftheearth suppermantle includingitsanisotropy becausetheysamplethis volumeefficientlyduetotheirsensitivityoverawidedepthrangealongtheraypath onaglobal scale surface wave tomography models are often parametrized uniformly without accounting for inhomogeneities in data coverage and as a result in resolution that are caused by effective under or overparametrization in many areas if the local resolving power of seismic data is not taken into account when parametrizing the model features will be smeared and distorted in tomographic maps with subsequent misinterpretation parametrization density has to change locally formodelstoberobustlyconstrainedwithoutlosinganyaccurateinformationavailable in the best sampled regions we have implemented a new algorithm for upper mantle surface wave tomography based on adaptive voxel parametrization with voxel size defined by both the hit count number of observations sampling the voxel and azimuthal coverage how welldifferentazimuthswithrespecttothevoxelarecoveredbythesource stationdistribution high image resolution is achieved in regions with dense data coverage while lower image resolution is kept in regions where data coverage is poorer this way parametrization is everywhere tuned to optimal resolution minimizing both the computational costs and the non uniqueness of the solution the spacing of our global grid is locally as small as 50 km we apply our method to identify a new global model of vertically and horizontally polarized shear velocity with resolution particularly enhanced in the european lithosphere and upper mantle we find our new model to resolve lithospheric thickness and radial anisotropy better than earlier results based on the same data robust features of our model include for example the trans european suture zone the panonnian basin thinned lithosphere in the aegean and western mediterranean possible small scale mantle upwellings under iberia and massif central subduction under the aegean arc and a very deep cratonic root underneath southern finland

automated multimode phase speed measurements for high resolution regional scale tomography application to north america summary a fully automated method for obtaining multimode phase speed measurements from a single seismogram has been developed and applied to a large data set of three component longperiod seismograms in north america constructing high resolution phase speed maps on a continental scale the method of our phase speed estimation is based on a fully non linear waveform inversion by yoshizawa kennett working with a global search method the neighbourhood algorithm the entire process of waveform fitting and the evaluation of the estimated phase speed have been fully automated employing several empirical quantitative measures assessing the quality of waveform fit and the relative contributions of each mode in a chosen time window the measured phase speed data undergo automatic screening for quality control comprising the threshold evaluation of their reliability and outlier detection and removal this new automated method has been applied to a large data set recorded at north american stations including the latest transportable stations of usarray using long period three component seismograms recorded during the past eight years we have successfully retrieved large numbers of regional surface wave paths including over 20000 paths for the fundamental mode rayleigh waves over a wide range of frequencies and over 10000 paths for the higher mode rayleigh as well as the fundamental mode love waves the consistentresultsoftheautomatedmeasurementproceduresuggestthatthemethodworkswell at regional distances allowing us to perform a high resolution mapping of multimode phase speeds in north america the results of the automated waveform analysis also indicate some intrinsic limitations in the higher mode phase speed measurements from a single seismogram particularly in the short period range mainly due to the overlapping of higher mode arrivals as well as coupling between mode branches despite such an innate difficulty in the higher mode dispersion measurements the automated method allows us to construct reliable multimode phase speed maps the current data set of ray paths is significantly biased towards the western half of north america resulting in non uniform horizontal resolution across the continent this issue will be resolved by the future migration of the usarray stations to cover the central and eastern united states the new automated method can be a useful tool for high resolution mapping of regional 3 d shear wave structure including possible anisotropy

q tomography of the upper mantle using three component long period waveforms summary we present a degree 8 3 d q model qrlw8 of the upper mantle derived from three component surface waveform data in the period range 60 400 s the inversion procedure involves two steps in the first step 3 d whole mantle velocity models are derived separately for elastic sh transverse component and sv vertical and longitudinal component velocity models using both surface and body waveforms and the non linear asymptotic coupling theory nact approach in the second step the surface waveforms thus aligned in phase are inverted to obtain a 3 d q model in the depth range 80 670 km various stability tests are performed to assess the quality of the resulting q model and in particular to assess possible contamination from focusing effects we find that the 3 d patterns obtained are stable but the amplitude of the lateral variations in q is not well constrained because large damping is necessary to extract the weak q signal from data the model obtained agrees with previous results in that a strong correlation of q with tectonics is observed in the first 250 km of the upper mantle with high attenuation under oceanic regions and low attenuation under continental shields it is gradually replaced by a simpler pattern at larger depth at the depths below 400 km the q distribution is generally dominated by two strong minima one under the southern pacific and one under africa yielding a strong degree 2 pattern most hotspots are located above regions of low q at this depth ridges are shallow features in both velocity and q models

characteristics of ripple structures revealed in oh airglow images small scale ripple structures observed in oh airglow images are most likely induced by either dynamic instability due to large wind shear or convective instability due to superadiabatic lapse rate using the data set taken in the mesopause region with an oh all sky imager at yucca ridge field station colorado 40 7 n 104 9 w from september 2003 to december 2005 we study the characteristics and seasonal variations of ripple structures by analyzing the simultaneous background wind and temperature observed by the nearby sodium temperature wind lidar at fort collins colorado 40 6 n 105 w and a nearby medium frequency radar at platteville colorado 40 2 n 105 8 w we are able to statistically study the possible relation between ripples and the background atmosphere conditions characteristics and seasonal variations of ripples are presented in detail in this study the occurrence frequency of ripples exhibits clear seasonal variability with peak in autumn the occurrence of ripples shows a local time dependence which is most likely associated with the solar tides the lifetime and spatial scale of these ripples are typically 5 20 min and 5 10 km respectively and most of the ripples move preferentially either southward or northward however more than half of the observed ripples do not advect with background flow they have higher richardson numbers than those ripples that advect with background flow it is possible that they are not instability features but wave structures that are hard to be distinguished from the real instability features

a global tomographic model of shear attenuation in the upper mantle we present a global three dimensional model of shear attenuation in the upper mantle based on the measurement of amplitudes of low frequency 100 300s rayleigh waves observed at stations of the geoscope and iris networks attenuation coefficients are measured on r1 and r2 paths using a method which minimizes the effects of focussing due to propagation in a three dimensional elastic earth through a series of tests which in particular involve the computation of synthetic models of attenuation and focussing we demonstrate that long wavelength lateral variations in attenuation in the first 400 500 km of the mantle can indeed be resolved the model is obtained in a two step procedure the first step consists in the computation of maps of rayleigh wave attenuation at different periods using an inversion method without a priori parametrisation which involves the introduction of a correlation length chosen here at 3000 km to optimize the trade off between resolution and variance in the model in the second step after corrections for shallow structure an inversion with depth is performed assuming lateral heterogeneity is confined to depths between 80 and 650 km the resulting model presents lateral variations in qp that are correlated with tectonic features in particular ridges and shields in the first 250 km of the upper mantle below that depth the pattern shifts and becomes correlated with the hotspot distribution particularly so if the buoyancy strength of hotspots is taken into account two major low velocity zones appear to be located in the central pacific and beneath northern africa in the depth range 300 500 km this pattern seems to continue at greater depth but resolution becomes insufficient below 500 km to draw definitive conclusions the smooth lateral variations retrieved are on the order of 50 down to 400 km we propose an interpretation in terms of plume lithosphere ridge interaction in the upper mantle arguing for deflection of the bulk of hot upwelling material from plumes towards ridges which may be occurring between 200 and 300 km depth

inferring upper mantle structure by full waveform tomography with the spectral element method summary mapping the elastic and anelastic structure of the earth s mantle is crucial for understanding the temperature composition and dynamics of our planet in the past quarter century global tomography based on ray theory and first order perturbation methods has imaged long wavelength elastic velocity heterogeneities of the earth s mantle however the approximate techniques upon which global tomographers have traditionally relied become inadequate when dealing with crustal structure as well as short wavelength or large amplitude mantle heterogeneity the spectral element method on the other hand permits accurate calculation of wave propagation through highly heterogeneous structures and is computationally economical when coupled with a normal mode solution and applied to a restricted region of the earth such as the upper mantle sem importantly sem allows a dramatic improvement in accounting for the effects of crustal structure here we develop and apply a new hybrid method of tomography which allows us to leverage the accuracy of sem to model fundamental and higher mode long period 60 s waveforms we then present the first global model of upper mantle velocity and radial anisotropy developed using sem our model semum confirms that the long wavelength mantle structure imaged using approximate semi analytic techniques is robust and representative of the earth s true structure furthermore it reveals structures in the upper mantle that were not clearly seen in previous global tomographic models we show that semum favourably compares to and rivals the resolving power of continental scale studies this new hybrid approach to tomography can be applied to a larger and higher frequency data set in order to gain new insights into the structure of the lower mantle and more robustly map seismic structure at the regional and smaller scales

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

contrasts in lithospheric structure within the australian craton insights from surface wave tomography abstract contrasts in the seismic structure of the lithosphere within and between elements of the australian craton are imaged using surface wave tomography new data from the wacraton and tigger experiments are integrated with re processed data from previous temporary deployments of broad band seismometers and permanent seismic stations the much improved path coverage in critical regions allows an interpretation of structures in the west of australia and a detailed comparison between different cratonic regions improvements to the waveform inversion procedure and a new multi scale tomographic method increase the reliability of the tomographic images in the shallowest part of the model 75 km a region of lowered velocity is imaged beneath central australia and confirmed by the delayed arrival times of body waves for short paths within the cratonic lithosphere there is clearly structure at scale lengths of a few hundred kilometres resolution tests indicate that path coverage within the continent is sufficient to reveal features of this size in the upper part of our model in western australia differences are seen beneath and within the archaean cratons at depths greater than 150 km faster velocities are imaged beneath the yilgarn craton than beneath the pilbara craton in the complex north australian craton a fast wavespeed anomaly continuing to at least 250 km is observed below parts of the craton suggesting the possibility of archaean lithosphere underlying areas of dominantly proterozoic surface geology

reconciling the geological history of western turkey with plate circuits and mantle tomography abstract we place the geological history since cretaceous times in western turkey in a context of convergence subduction collision and slab break off to this end we compare the west anatolian geological history with amounts of africa europe convergence calculated from the atlantic plate circuit and the seismic tomography images of the west anatolian mantle structure western turkish geology reflects the convergence between the sakarya continent here treated as eurasia in the north and africa in the south with the anatolide tauride block atb between two strands of the neotethyan ocean convergence between the sakarya and the atb started at least 95 90 myr ago marked by ages of metamorphic soles of ophiolites that form the highest structural unit below sakarya these are underlain by high pressure low temperature metamorphic rocks of the tavsanli and afyon zones and the oren unit which in turn are underlain by the menderes massif derived from the atb underthrusting of the atb below sakarya was since 50 ma associated with high temperature metamorphism and widespread granitic magmatism thrusting in the menderes massif continued until 35 ma after which there is no record of accretion in western turkey plate circuits show that since 90 ma 1400 km of africa europe convergence occurred of which 700 km since 50 ma and 450 km since 35 ma seismic tomography shows that the african slab under western turkey is decoupled from the african plate this detached slab is a single coherent body representing the lithosphere consumed since 90 ma there was no subduction re initiation after slab break off atb collision with europe therefore did not immediately lead to slab break off but instead to delamination of subducting lithospheric mantle from accreting atb crust while staying attached to the african plate this led to asthenospheric inflow below the atb crust high temperature metamorphism and felsic magmatism slab break off in western turkey probably occurred 15 myr ago after which overriding plate compression and rotation accommodated ongoing africa europe convergence slab break off was accommodated along a vertical ne trending subduction transform edge propagator step fault zone accelerating southwestward slab retreat of the aegean slab the se aegean slab edge may have existed already since early miocene times or before but started to rapidly roll back along the southeastern aegean step in middle miocene times penetrating the aegean region in the pliocene

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

attenuation of broadband p and s waves in tonga observations of frequency dependent q teleseismic broadband recordings of intermediate and deep focus earthquakes are used to quantify both compression q and shear q wave attenuation within the lau backarc basin a spectral ratio method is employed to measure differential attenuation t between the depth phases ss pp and sp and the direct s and p phases over the frequency band 0 05 and 0 5 hz we use a stacking algorithm to combine the spectra of several phase pairs from a single event having similar azimuth and range to obtain more robust t measurements these estimates are then used to compute the average q above the focal depth q and q are measured directly from the ss s and pp p phase pairs respectively however the interpretation of t measured from sp p requires assumptions about the ratio q q we find an empirical ratio of q q 1 93 for this region and use it to compute q and q from the q sp observations

non linear crustal corrections in high resolution regional waveform seismic tomography summary we compare 3 d upper mantle anisotropic structures beneath the north american continent obtained using standard and improved crustal corrections in the framework of non linear asymptotic coupling theory nact applied to long period three component fundamental and higher mode surface waveform data our improved approach to correct for crustal structure in high resolution regional waveform tomographic models goes beyond the linear perturbation approximation and is therefore more accurate in accounting for large variations in moho topography within short distances as observed for instance at ocean continent margins this improved methodology decomposes the shallow layer correction into a linear and non linear part and makes use of 1 d sensitivity kernels defined according to local tectonic structure both for the forward computation and for the computation of sensitivity kernels for inversion the comparison of the 3 d upper mantle anisotropic structures derived using the standard and improved crustal correction approaches shows that the model norm is not strongly affected however significant variations are observed in the retrieved 3 d perturbations the largest differences in the velocity models are present below 250 km depth and not in the uppermost mantle as would be expected we suggest that inaccurate crustal corrections preferentially map into the least constrained part of the model and therefore accurate corrections for shallow layer structure are essential to improve our knowledge of parts of the upper mantle where our data have the smallest sensitivity

east anatolian high plateau as a mantle supported north south shortened domal structure an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl017858 shtml http atlas geo cornell edu turkey publications sengor et al 2003 htm

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

mapping lateral variations in upper mantle attenuation by stacking p and pp spectra 1 we study the lateral variations in p wave attenuation in the upper mantle at frequencies between 0 16 and 0 86 hz by analyzing the spectra from 18 000 p and 14 000 pp arrivals we select seismograms from shallow earthquakes at epicentral distances of 40 80 for p waves and 80 160 for pp waves each spectrum is the product of source receiver and propagation response functions as well as local source and receiver side effects we correct each spectrum for average source and attenuation models since there are multiple receivers for each source and multiple sources for each receiver we can approximate the source and receiver side terms by stacking the appropriate p log spectra the resulting source specific response functions include any remaining source spectrum and near source q structure the receiver stacks include the site response and near receiver q structure we correct the pp log spectra for the appropriate source and receiver side stacks since attenuation in the lower mantle is small the residual log spectrum approximates attenuation in the upper mantle near the pp bounce point and is used to estimate we constrain the anomalies to the top 220 km of the mantle as suggested by previous q studies and translate the measurements to variations in 1000 q the patterns of more and less attenuating regions generally correlate with previously published shear attenuation models and surface tectonics continents are usually less attenuating than the global average whereas oceanic regions tend to be more attenuating there are interesting exceptions to this tectonic pattern such as an attenuating region beneath southern africa

seismic evidence for small scale heterogeneity throughout the earth s mantle details in the amplitude structure of short period precursors to the seismic core phase pkp can be used to constrain the depth extent of mantle scattering the simplest model consistent with the observations invokes small 8 km weak r m s velocity perturbations of 1 random heterogeneities uniformly distributed throughout the mantle the data do not support previously proposed models that place an increase in the concentration of scattering sites near the base of the mantle and instead place an upper limit on the amplitude of any short wavelength topography at the core mantle boundary

a tomographic image of the shallow crustal structure in the eastern marmara 1 we present a 2 d tomographic seismic velocity image in eastern marmara region along a n s trending 120 km long seismic refraction profile which traverses the northern branches of north anatolian fault naf and tectonically active cinarcik basin in the sea of marmara the 2 d velocity model which is constrained down to upper crustal depth of 7 km shows significant heterogeneities in the upper crust displayed by well constrained velocity anomalies the seismicity observed following the 17 august 1999 izmit earthquake concentrates in three distinct zones and takes place near the inferred low velocity zones and below high velocity anomalies obtained from tomographic inversion this correlation is interpreted as a result of intensely sheared zones of deformation imposed by strike slip motion of the northern branches of the north anatolian fault

normal mode constraints on shear and compressional wave velocity of the earth s inner core abstract free oscillation data are used to determine the average compressional and shear wave velocity structure of the earth s inner core and place tight constraints on their values the new data reinforce the argument for a solid inner core and the best data fit is obtained for average inner core velocities close to the prem reference model s 3 55 0 05 km s p 11 15 0 05 km s these values limit the time windows in which inner core shear waves like pkjkp may be observed inner core velocities for hcp and bcc iron at inner core conditions from ab initio molecular dynamics simulations and diamond anvil cell experiments are found to be incompatible with the seismological data in particular for the shear wave velocity when light elements are taken into account the misfit is worse than for a fluid inner core model the discrepancy between seismic and mineral physical values for the inner core shear wave velocity may be explained by an inner core temperature in excess of 6500 k the existence of fluid inclusions in the inner core the effect of viscoelastic weakening or crystal defects

quantifying transient mantle convective uplift an example from the faroe shetland basin the icelandic mantle plume generated maximum uplift in early paleogene times the faroe shetland basin which fringes the north atlantic margin of europe was close to the center of early paleogene icelandic plume activity three dimensional seismic reflection data from the faroe shetland basin reveal sedimentary geometries that allow a phase of transient uplift to be accurately reconstructed and quantified close to the paleocene eocene boundary circa 56 ma rapid uplift resulted in fluvial incision into marine sediments this unconformity was buried by nonmarine sediments recording the decay of transient uplift relief on the unconformity was 550 m constraining the minimum amount of surface uplift some 60 m of this uplift can be attributed to the isostatic response to erosional unloading tectonic uplift of over 490 m peaked and decayed within 3 ma rates of water loaded tectonic subsidence following peak uplift are several times greater than maximum expected postrift subsidence rates the amplitude and duration of this transient effect is best explained by a mantle convective phenomenon we suggest that a region of hot plume material flowed laterally beneath the lithosphere producing transient uplift which decayed when plume material was advected farther away our analysis suggests that under certain circumstances stratigraphic records can yield valuable quantitative information about aspects of mantle convective circulation

heterogeneity of the uppermost mantle beneath russian eurasia from the ultra long range profile quartz the 3850 km long deep seismic sounding profile quartz crosses six major geologic provinces in eurasia and is sourced by 3 nuclear and 48 chemical explosions we present the first interpretation of the entire data set using two dimensional 2 d ray tracing and inversion resolution analysis and 1 d amplitude modeling our interpretation shows a 42 km thick high velocity crust under the baltic shield a 29 km thick crust and high velocity upper mantle under the mezenskaya depression 52 km thick crust with high velocity lower crust and uppermost mantle under the urals and 40 km thick crust under the west siberian basin deepening to 45 km under the altay sayan fold belt high velocity 8 4 km s uppermost mantle is found under the mezenskaya depression and under the east flank of the urals one almost continuous upper mantle boundary occurs at 65 to 80 km depth and another with an approximately 40 km thick lvz occurs at 120 to 140 km depth the shallow upper mantle blocks and the two extensive interfaces indicate strong upper mantle heterogeneity resolution analysis based on direct multivariate model perturbations artificial neural network and principal component analysis indicate the depth uncertainty of the 410 km discontinuity within 6 km and also its trade off with dip and velocities above and below the discontinuity decreased near critical amplitudes of reflections from the 410 km and 660 km discontinuities indicate that these boundaries are most likely represented by gradient zones about 15 20 km thick lithosphere thins asthenospheric velocity decreases and the 410 km discontinuity dips to the se approaching the himalayan orogenic belt

full wave seismic data assimilation theoretical background and recent advances the seismological inverse problem has much in common with the data assimilation problem found in meteorology and oceanography using the data assimilation methodology i will formulate the seismological inverse problem for estimating seismic source and earth structure parameters in the form of weak constraint generalized inverse in which the seismic wave equation and the associated initial and boundary conditions are allowed to contain errors the resulting euler lagrange equations are closely related to the adjoint method and the scattering integral method which have been successfully applied in full 3d full wave seismic tomography and earthquake source parameter inversions i will review some recent applications of the full wave methodology in seismic tomography and seismic source parameter inversions and discuss some challenging issues related to the computational implementation and the effective exploitation of seismic waveform data

the global attenuation structure of the upper mantle 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive a new global three dimensional model of shear wave attenuation in the upper mantle the amplitude observations span a range of periods between 50 and 250 s and are derived from earthquakes with mw 6 0 that occurred between 1993 and 2005 four separate factors may influence an amplitude anomaly intrinsic attenuation along the raypath elastic focusing effects along the raypath uncertainties in the strength of excitation and uncertainties in the response at the station in an earlier paper dalton and ekstrom 2006a dependence of the retrieved attenuation structure on these terms was shown to be significant and an approach was developed to invert the amplitudes simultaneously for each term the new three dimensional attenuation model qrfsi12 which is the subject of this paper is derived using this method the model contains large lateral variations in upper mantle attenuation 60 to 100 and exhibits strong agreement with surface tectonic features at depths shallower than 200 km at greater depth qrfsi12 is dominated by high attenuation in the southeastern pacific and eastern africa and low attenuation along many subduction zones in the western pacific resolution tests confirm that the change in pattern of attenuation above and below 200 km depth can be determined with confidence using the fundamental mode data set the new model is highly correlated with global models of shear wave velocity particularly in the uppermost mantle suggesting that the same factors may control both seismic attenuation and velocity in this depth range however forcing the lateral perturbations in attenuation to match those found in global velocity models decreases the data variance reduction which suggests that subtle differences between patterns of attenuation and velocity are robust

stochastic waveguide in the lithosphere indonesian subduction zone to australian craton summary earthquakes occurring in the indonesian subduction zone recorded in the cratonic regions of northern australia have long high frequency coda associated with both p and s waves similar behaviour is seen for earthquakes within australia on paths within the cratonic regions the complex character of the coda and its rapid spatial variation indicate that the high frequency waves have travelled within a zone of strong multiple scattering with very high intrinsic q there are subtle variations in the nature of the coda that can be described through a coda q the variations in coda are associated with the position along the arc and the nature of the transition from the subduction zone to the continental lithosphere the character of the coda observations can be captured with numerical simulations in models derived from seismic tomography for northern australia and the neighbouring subduction zone incorporating lower crustal and mantle heterogeneity with much longer horizontal than vertical correlation length high frequency calculations to high frequency 16 hz for long propagation distances up to 1500 km have been carried out using finite difference modelling on the earth simulator the variations in coda properties can be associated with the way in which the seismic energy gets ducted into the stochastic waveguide associated with the lithosphere the most efficient transfer occurs where continental lithospheric material is adjacent to the earthquake zone

subduction zone guided waves and the heterogeneity structure of the subducted plate intensity anomalies in northern japan 1 the subducting pacific plate acts an efficient waveguide for high frequency signals and often produces anomalously large intensity on the eastern seaboard of northern japan during deep earthquakes the waveform records in the region of high intensity show a low frequency f 2 hz later arrivals with a long coda this behavior is not explained by a simple subduction zone model comprising a high velocity plate with low attenuation from the analysis of observed broadband waveforms and numerical simulation of seismic wave propagation in the pacific subduction zone we demonstrate that the high frequency guided waves traveling in the subducting plate arise from the scattering of seismic waves by heterogeneity in plate structure our preferred model of the heterogeneity has elongated scatterers parallel to the plate margin described by a von karmann function with a downdip correlation length of about 10 km and much shorter correlation length of about 0 5 km in thickness the standard deviation of wave speed fluctuations from the averaged background model is about 2 this new heterogeneous plate model generates significant scattering of seismic waves with wavelengths shorter than correlation distance in thickness but low frequency waves with long wavelengths can easy tunnel through such lamina structure the result is frequency selective propagation characteristics with a faster low frequency phase followed by large and high frequency signals with very long coda a low wave speed channel effect from the former oceanic crust at the top of the subducting slab is not necessary to explain the observed dispersed signals and the very long high frequency coda three dimensional simulations using the earth simulator supercomputer for modeling of high frequency seismic wave propagation in the pacific subduction zone including plate heterogeneity clearly demonstrate the scattering waveguide effects for high frequency seismic waves traveling in the plate the region of large intensity for the heterogeneous model migrates away from the hypocenter into northern japan with an elongated zone along the pacific coast almost comparable to the observations from deep events in the pacific plate

global upper mantle tomography with the automated multimode inversion of surface and s wave forms summary we apply the automated multimode inversion of surface and s wave forms to a large global data set verify the accuracy of the method and assumptions behind it and compute an s vvelocity model of the upper mantle crust 660 km the model is constrained with 51 000 seismograms recorded at 368 permanent and temporary broadband seismic stations structure of the mantle and crust is constrained by waveform information both from the fundamentalmode rayleigh waves periods from 20 to 400 s and from s and multiple s waves higher modes in order to enhance the validity of the path average approximation we implement the automated inversion of surface and s wave forms with a three dimensional 3 d reference model linear equations obtained from the processing of all the seismograms of the data set are inverted for seismic velocity variations also relative to a 3 d reference in this study composed of a 3 d model of the crust and a one dimensional 1 d global average depth profile in the mantle below waveform information is related to shear and compressional velocity structure within approximate waveform sensitivity areas we use two global triangular grids of knots with approximately equal interknot spacing within each a finely spaced grid for integration over sensitivity areas and a rougher spaced one for the model parametrization for the tomographic inversion we use lsqr with horizontal and vertical smoothing and norm damping we invert for isotropic variations in s and p wave velocities but also allow for s wave azimuthal anisotropy in order to minimize errors due to possible mapping of anisotropy into isotropic heterogeneity the lateral resolution of the resulting isotropic upper mantle images is a few hundred kilometres varying with data sampling we validate the imaging technique with a spectral element resolution test inverting a published global synthetic data set computed with the spectral element method using a laterally heterogeneous mantle model we are able to reconstruct the synthetic model accurately this test confirms both the accuracy of the implementation of the method and the validity of the jwkb and path average approximations as applied in it reviewing the tomographic model we observe that low s v velocity anomalies beneath mid ocean ridges and backarc basins extend down to 100 km depth only shallower than according to some previous tomographic models this presents a close match to published estimates of primary melt production depth ranges there in the seismic lithosphere beneath cratons unambiguous high velocity anomalies extend to 200 km pronounced low velocity zones beneath cratonic lithosphere are rare where present south america tanzania they are neighboured by volcanic areas near cratonic boundaries the images of these low velocity zones may indicate hot material possibly of mantle plume origin trapped or spreading beneath the thick cratonic lithosphere

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

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

insights into the kinematics of a volcanic caldera drop probabilistic finite source inversion of the 1996 bardarbunga iceland earthquake article i nfo the accurate modelling and prediction of volcanic eruptions depends critically on information concerning the interaction between the caldera and the underlying magma chamber knowledge concerning the kinematics of a caldera in the course of an eruption is therefore essential here we provide detailed seismological constraints on the kinematics of a volcanic caldera drop and the geometry of a caldera ring fault for this we performed a finite source inversion of the september 29 1996 bardarbunga iceland earthquake that was caused by caldera subsidence our methodology is based on spectral element simulations of seismic wave propagation through a realistic model of the icelandic crust and upper mantle a particularly robust feature is the initiation of the rupture in the north western part of the ring fault that is about 10 km in diameter from there it spread to the other fault segments within about 3 s without invoking super shear propagation sensu stricto we can explain this unusually fast rupture propagation by the triggering of fault segments through p waves that propagated across the caldera our results favour outward dipping fault segments in the western half of the ring fault while the eastern half is preferentially inward dipping this variability may reflect structural heterogeneities or an irregular magma chamber geometry the individual segments of the caldera ring fault radiated approximately equal amounts of energy this indicates that the caldera dropped coherently as one single block the work presented here is intended to aid in the design of realistic models of magma chamber and caldera dynamics

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