alternative waveform inversion for surface wave analysis in 2 d media in the context of near surface seismic imaging a few hundreds of metres we propose an alternative approach for inversion of surface waves in 2 d media with laterally varying velocities it is based on full waveform inversion fwi but using an alternative objective function formulated in the frequency wavenumber f k domain the classical fwi objective function suffers from severe local minima problems in the presence of surface waves it thus requires a very accurate initial model the proposed objective function is similar to the one used in classical surface wave analysis in this approach the data are first split using sliding windows in the time space t x domain for each window the amplitude of the f k spectrum is computed the objective function measures the least squares misfit between the amplitude of observed and modelled 2 d fourier transformed data sets we call this formulation the windowed amplitude waveform inversion w awi the w awi objective function reduces some local minima problems as shown here through numerical examples the global minimum basin is wider in the w awi approach than in fwi synthetic examples show that w awi may achieve convergence if the lowest data frequency content is twice higher than the one needed by fwi for elastic inversion w awi can be used to reconstruct a velocity model explaining surface waves this surface wave inversion procedure can be used to retrieve near surface model parameters in lateral varying media

the interplay of sedimentation and carbon accretion in riparian forests abstract sediment trapping and organic carbon oc accretion in soil are crucial ecosystem services of floodplain forests however interactions between the two processes have scarcely been analyzed at the ecosystem level this study aimed at quantifying oc accretion parameters cap including sedimentation rate oc concentration oc accretion over roughly the last 50 years on both sides of a dike in a danubian floodplain forest in austria additionally we determined soil oc stocks 0 100 cm in depth and modeled both cap and oc stocks in relation to environmental parameters overall mean sedimentation rate and oc accretion of the riparian forest were 0 8 cm y 1 and 3 3 t oc ha 1 y 1 and significantly higher in flooded riparian forest frf 1 0 cm y 1 and 4 1 t oc ha 1 y 1 than in diked riparian forest drf 0 3 cm y 1 and 1 5 t oc ha 1 y 1 in contrast mean oc concentration 0 05 t oc m 3 and oc stocks 238 t oc ha 1 were significantly higher in the drf than in frf 0 05 vs 0 04 t oc m 3 and 286 vs 201 t oc ha 1 modeling revealed tree species fluctuation of groundwater table and the distance to the river as valuable indicators for oc accretion rate the oc concentration and distance to the river were positively and sedimentation negatively correlated with oc stock the dike was consistently ruled out as a significant predictor variable consequently differences among frf and drf seem to be related rather to longer term processes during the last centuries than directly to the dike our findings highlight the relevance of sediment quality i e oc concentration for building up long term soil oc stocks whereas sediment quantity is the main driver of recent oc accretion rates

a note on tidal asymmetry in the severn estuary a one dimensional non linear numerical model is used to investigate the tidally averaged frictional stress and set up of water level due to tidal asymmetry in the severn estuary these quantities depend on the overtides in the region a linearized model of the overtides is applied to calculations of the m4 currents in order to delineate the mechanisms responsible for their generation the relative importance of individual non linear mechanisms to the tidally averaged stress and set up is determined these mechanisms are interactions between tidal flow and changes in depth or breadth over a cross section frictional interaction between the tidal flow and stokes drift interaction between the tidal fluctuations in water depth and frictional retardation and non linear advection

full waveform inversion of sh and love wave data in near surface prospecting we develop a two dimensional full waveform inversion approach for the simultaneous determination of s wave velocity and density models from sh and love wave data we illustrate the advantages of the sh love full waveform inversion with a simple synthetic example and demonstrate the method s applicability to a near surface dataset recorded in the village c achtice in northwestern slovakia goal of the survey was to map remains of historical building foundations in a highly heterogeneous subsurface the seismic survey comprises two parallel sh profiles with maximum offsets of 24 m and covers a frequency range from 5 hz to 80 hz with high signal to noise ratio well suited for full waveform inversion using the wiechert herglotz method we determined a one dimensional gradient velocity model as a starting model for full waveform inversion the two dimensional waveform inversion approach uses the global correlation norm as objective function in combination with a sequential inversion of low pass filtered field data this mitigates the non linearity of the multiparameter inverse problem test computations show that the influence of visco elastic effects on the waveform inversion result is rather small further tests using a monoparameter shear modulus inversion reveal that the inversion of the density model has no significant impact on the final data fit the final full waveform inversion s wave velocity and density models show a prominent low velocity weathering layer below this layer the subsurface is highly heterogeneous minimum anomaly sizes correspond to approximately half of the dominant love wavelength the results demonstrate the ability of two dimensional sh waveform inversion to image shallow small scale soil structure however they do not show any evidence of foundation walls

retrieving 2d structures from surface wave data by means of space varying spatial windowing abstractsurface wave techniques are mainly used to retrieve 1d subsurface models however in 2d environments the 1d approach usually neglects the presence of lateral variations and because the surface wave path crosses different materials the resulting model is a simplified or misleading description of the site we tested a processing technique to retrieve 2d structures from surface wave data acquired with a limited number of receivers our technique was based on a two step process first we extracted several local dispersion curves along the survey line using a spatial windowing based on a set of gaussian windows with different shapes the window maxima span the survey line so that we were able to extract a dispersion curve from the seismic record for every window this provided a set of local dispersion curves each of them referring to a different subsurface portion this space varying spatial windowing provided a good compromise between wavenumber resolution and the lateral resolution of the obtain

exploring some issues in acoustic full waveform inversion the least squares error measures the difference between observed and modelled seismic data because it suffers from local minima a good initial velocity model is required to avoid convergence to the wrong model when using a gradient based minimization method if a data set mainly contains reflection events it is difficult to update the velocity model with the least squares error because the minimization method easily ends up in the nearest local minimum without ever reaching the global minimum several authors observed that the model could be updated by diving waves requiring a wide angle or large offset data set this full waveform tomography is limited to a maximum depth here we use a linear velocity model to obtain estimates for the maximum depth in addition we investigate how frequencies should be selected if the seismic data are modelled in the frequency domain in the presence of noise the condition to avoid local minima requires more frequencies than needed for sufficient spectral coverage we also considered acoustic inversion of a synthetic marine data set created by an elastic time domain finite difference code this allowed us to validate the estimates made for the linear velocity model the acoustic approximation leads to a number of problems when using long offset data nevertheless we obtained reasonable results the use of a variable density in the acoustic inversion helped to match the data at the expense of accuracy in the inversion result for the density

theoretical background for continental and global scale full waveform inversion in the time frequency domain summary we propose a new approach to full seismic waveform inversion on continental and global scales this is based on the time frequency transform of both data and synthetic seismograms with the use of time and frequency dependent phase and envelope misfits these misfits allow us to provide a complete quantification of the differences between data and synthetics while separating phase and amplitude information the result is an efficient exploitation of waveform information that is robust and quasi linearly related to earth s structure thus the phase and envelope misfits are usable for continental and global scale tomography that is in a scenario where the seismic wavefield is spatially undersampled and where a 3 d reference model is usually unavailable body waves surface waves and interfering phases are naturally included in the analysis we discuss and illustrate technical details of phase measurements such as the treatment of phase jumps and instability in the case of small amplitudes the frechet kernels for phase and envelope misfits can be expressed in terms of their corresponding adjoint wavefields and the forward wavefield the adjoint wavefields are uniquely determined by their respective adjoint source time functions we derive the adjoint source time functions for phase and envelope misfits the adjoint sources can be expressed as inverse time frequency transforms of a weighted phase difference or a weighted envelope difference in a comparative study we establish connections between the phase and envelope misfits and the following widely used measures of seismic waveform differences 1 cross correlation time shifts 2 relative rms amplitude differences 3 generalized seismological data functionals and 4 the l2 distance between data and synthetics used in time domain full waveform inversion we illustrate the computation of frechet kernels for phase and envelope misfits with data from an event in the west irian region of indonesia recorded on the australian continent the synthetic seismograms are computed for a heterogeneous 3 d velocity model of the australian upper mantle with a spectral element method the examples include p body waves rayleigh waves and s waves interfering with higher mode surface waves all the kernels differ from the more familar kernels for cross correlation time shifts or relative rms amplitude differences the differences arise from interference effects 3 d earth s structure and waveform dissimilarities that are due to waveform dispersion in the heterogeneous earth

laterally constrained inversion of ground roll from seismic reflection records seismic reflection data contain surface waves that can be processed and interpreted to supply shear wave velocity models along seismic reflection lines the coverage of seismic reflection data allows the use of automated multifold processing to extract high quality dispersion curves and experimental uncertainties in a moving spatial window the dispersion curves are then inverted using a deterministic laterally constrained inversion to obtain a pseudo 2d model of the shear wave velocity a monte carlo global search inversion algorithm optimizes the parameterization when the strategy is used with synthetic and field data consistent final models with smooth lateral variations are successfully retrieved this method constitutes an improvement over the individual inversion of single dispersion curves

seismic imaging of complex onshore structures by 2d elastic frequency domain full waveform inversion quantitative imaging of the elastic properties of the subsurface at depth is essential for civil engineering applications and oil and gas reservoir characterization a realistic synthetic example provides for an assessment of the potential and limits of 2d elastic full waveform inversionfwiof wide aperture seismic data for recovering high resolution p and s wave velocity models of complex onshore structures fwi of land data is challengingbecauseoftheincreasednonlinearityintroducedbyfreesurface effects such as the propagation of surface waves in the heterogeneous near surface moreover the short wavelengths of the shear wavefield require an accurate s wave velocity starting modeliflowfrequenciesareunavailableinthedata weevaluated different multiscale strategies with the aim of mitigating the nonlinearities massively parallel full waveform inversion was implemented in the frequency domain the numerical optimization relies on a limited memory quasi newton algorithm that outperforms the more classic preconditioned conjugate gradient algorithm the forward problem is based upon a discontinuous galerkin dg method on triangular mesh which allows accuratemodelingoffree surfaceeffects sequentialinversionsofincreasingfrequenciesdefinethemostnaturallevelofhierarchyin multiscale imaging in the case of land data involving surface waves the regularization introduced by hierarchical frequency inversions is not enough for adequate convergence of the inversion a second level of hierarchy implemented with complexvalued frequencies is necessary and provides convergence of the inversion toward acceptable p and s wave velocity models amongthepossiblestrategiesforsamplingfrequenciesintheinversion successive inversions of slightly overlapping frequency groups is the most reliable when compared to the more standard sequential inversion of single frequencies this suggests that simultaneous inversion of multiple frequencies is critical when consideringcomplexwavephenomena

shallow structure characterization by 2d elastic full waveform inversion assessing the effectiveness of elastic full waveform inversion fwi algorithms when applied to shallow 2d structures in the presence of a complex topography is critically important by using fwi we overcome inherent limitations of conventional seismic methods used for near surface prospecting acoustic tomography and multichannel spectral analysis of surface waves the elastic forward problem formulated in the frequency domain is based on a mixed finite element p0p1 discontinuous galerkin method to ensure accurate modeling of complex topography effects at a reasonable computing cost the inversion problem uses an fwi algorithm to minimize the misfit between observed and calculated data based on results from a numerical experiment performed on a realistic landslide model inspired from the morphostructure of the super sauze earthflow we analyzed the effect of using a hierarchical preconditioning strategy based on a simultaneous multifrequency inversion of damped data to mitigate the strong nonlinearities coming from the surface waves this strategy is a key point in alleviating the strong near surface effects and avoiding convergence toward a local minimum using a limited memory quasi newton method improved the convergence level these findings are analogous to recent applications on large scale domains although limited sourcereceiver offset ranges low frequency content of the source and domination of surface waves on the signal led to some difficulties regarding the impact of data decimation on the inversion results we have learned that an inversion restricted to the vertical data component can be successful without significant loss in terms of parameter imagery resolution in our investigations of the effect of increased source spacing we found that a sampling of 4 m less than three times the theoretical maximum of one half wavelength led to severe aliasing

a comparison of phase inversion and traveltime tomography for processing near surface refraction traveltimes with phase inversion one can estimate subsurface velocities using the phases of first arriving waves which are the frequency domain equivalents of the traveltimes phase inversion is modified to make it suitable for processing traveltimes from near surface refraction surveys the modifications include parameterizing the model correcting the observed phases and selecting the complex frequency this modified phase inversion is compared to traveltime tomography for two comparisons using computer simulated traveltimes the difference between the estimated and correct models the residual mean and the residual standard deviation are smaller for the phase inversion than they are for the traveltime tomography for a comparison using field data from an s wave refraction survey both methods estimate models that are consistent with the known geology nonetheless the phase inversion model includes small scale features in the bedrock that are geologically plausible the residual mean and the residual standard deviation are smaller for the phase inversion than they are for the traveltime tomography

the spatial variability of overbank sedimentation on river floodplains abstract river floodplains are important landforms and information on rates and patterns of overbank sediment deposition is essential for understanding their development such information is also needed for validating existing overbank floodplain flow and sediment transport and deposition models the use of bomb derived 137cs for documenting rates of overbank sediment deposition on river floodplains offers the potential for assembling data for a large number of points on a floodplain and therefore for investigating the spatial patterns involved this approach also overcomes some of the operational and sampling problems encountered in traditional monitoring techniques the study reported uses 137cs measurements on sediment cores to investigate the spatial variability of sediment deposition on selected floodplain reaches of five british lowland rivers attention is given both to the overall reach and to more detailed investigations of small areas the observed spatial patterns of sediment deposition are interpreted in terms of the major controls involved which include the floodplain microtopography and morphology the relationship between the grain size composition of deposited sediment and sedimentation rate is also considered

2 d multiparameter viscoelastic shallow seismic full waveform inversion reconstruction tests and first field data application 2d full waveform inversion fwi of shallow seismic wavefields has recently become a novel way to reconstruct s wave velocity models of the shallow subsurface with high vertical and lateral resolution in most applications seismic wave attenuation is ignored or considered as a passive modelling parameter only in this study we explore the feasibility and performance of multi parameter viscoelastic 2d fwi in which seismic velocities and attenuation of p and s waves respectively and mass density are inverted simultaneously synthetic reconstruction experiments reveal that multiple crosstalks between all viscoelastic material parameters may occur the reconstruction of s wave velocity is always robust and of high quality the parameters p wave velocity and density exhibit weaker sensitivity and can be reconstructed more reliably by multi parameter viscoelastic fwi anomalies in s wave attenuation can be recovered but with limited resolution in a field data application a small scale refilled trench is nicely delineated as a low p and s wave velocity anomaly the reconstruction of p wave velocity is improved by the simultaneous inversion of attenuation the reconstructed s wave attenuation reveals higher attenuation in the shallow weathering zone and weaker attenuation below the variations in the reconstructed p and s wave velocity models are consistent with the reflectivity observed in a gpr profile

3d elastic full waveform inversion of surface waves in the presence of irregular topography using an envelope based misfit function full waveform inversion fwi is a powerful method for estimating the earth s material properties we demonstrate that surface wave driven fwi is well suited to recovering near surface structures and effective at providing shear wavespeed starting models for use in conventional body wave fwi we illustrate the method with a synthetic example based on the seam phase ii foothills model to accurately model surface waves in the presence of complex tomography we used a spectral element wave propagation solver we started first with an envelope based objective function to invert for shallow large scale heterogeneities then using the recovered model of the subsurface we applied a waveform difference inversion to obtain higher resolution models envelope misfit functions were found to be effective in minimizing cycle skipping issues for surface wave inversions which are useful for constraining complex near surface features

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

detecting near surface objects with seismic waveform tomography three shallow high velocity rubble filled targets are imaged using waveform tomography in an engineering scale clay embankment at seven sisters falls manitoba canada to locate targets buried at approximately 7 m as a blind test of geophysical imaging methods previous studies use near offset reflection methods to image the targets however this test uses waveform tomography of the long offset refracted arrivals to image p velocity and seismic attenuation the targets are invisible to standard traveltime tomography using weight drop data with frequencies of 20 150 hz the subwavelength targets are resolved in the velocity images and complementary images of seismic q are produced the interpreted target locations are consistent with limited survey information from the embankment construction multiple quality control efforts paired with a very good fit between model and observed data indicate the reliability of the results