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

new transfer functions for nutations of a nonrigid earth there are differences between the observed values of nutation and the computed ones based on the international astronomical union iau 1980 adopted nutation series these differences can be expressed in the frequency domain where they may reach several milliarc seconds a level that is too large for practical use this paper aims to resolve part of these differences by computing a new theoretical model accounting for additional geophysical effects a new transfer function is computed based on an earth initially in a nonhydrostatic equilibrium corresponding to the steady state associated with the present mantle convection the mantle mass anomalies are deduced from seismic tomography data and the flow induced boundary deformations are computed from internal loading for an earth made up of a viscous inner core a liquid outer core a viscous mantle and a solid lithosphere in this way a new core mantle boundary cmb flattening is obtained which gives the observed free core nutation fcn period furthermore the global earth dynamical flattening induced by the mass anomalies in the mantle associated with tomography and by the mass anomalies due to the computed boundary deformations is in agreement with the j2 form factor or the observed precession constant in addition to this nonhydrostatic initial state the rheology of the mantle is considered as inelastic the transfer function for nutation is then obtained by numerical integration of motion equations from the earth s center up to the surface to provide a model which is completely self consistent in order to validate our model the transfer function is convolved with new rigid earth nutations ocean corrections are applied and the final results are then compared with the observed nutations or with the international earth rotation service iers nutation series the residuals between our model and the observation are about 3 times smaller than those between the iau 1980 adopted model and the observation however our model still presents residuals above the observational error this is particularly true for the out of phase part of the residuals while the in phase part gives very small residuals improvement of about 1 order of magnitude a further step in this study is a refinement of the modeling of geophysical fluids core ocean and atmosphere

use of numerical models to study land based sedimentation and subsequent nearshore morphological evolution a beach sedimentation problem is presented this problem involves assessing the impact and importance of land based sediment sources erosion from gullies during intense rainfall and directly from cliffs by wave action on morphodynamic changes at a beach the site motivating the study is la barrosa beach spain the location is described and a discussion of possible approaches presented a schematized representation of a gully and beach is used a hybrid approach is adopted in which sediment deposition by run off and to a lesser extent cliff erosion is modelled using wave resolving hydrodynamic models it is found that significant amounts of sediment can be supplied by gully run off during storms for small run offs the swash can be involved in determining the region of deposition within the gully area with longer period motions favouring increased sediment deposition at gully sides simulations also show that swash motions can erode gully sides and the presence of a cross shore jet associated with the swash and gullies can also impact on sediment movement longer term wave averaged morphodynamic modelling without a swash zone indicates that run off deposits subsequently diffuse laterally whether under normal or oblique incidence these simulations also reveal the possibility of underlying crescentic bar shedding dynamics that may pertain during changes of wave conditions

the role of attenuation in 2d full waveform inversion of shallow seismic body and rayleigh waves abstractfull waveform inversion fwi of rayleigh waves is attractive for shallow geotechnical investigations due to the high sensitivity of rayleigh waves to the s wave velocity structure of the subsurface in shallow seismic field data the effects of anelastic damping are significant dissipation results in a low pass effect as well as frequency dependent decay with offset we found this by comparing recorded waveforms with elastic and viscoelastic wave simulation the effects of anelastic damping must be considered in fwi of shallow seismic rayleigh waves fwi using elastic simulation of wave propagation failed in synthetic inversion tests in which we tried to reconstruct the s wave velocity in a viscoelastic model to overcome this q values can be estimated from the recordings to quantify viscoelasticity waveform simulation in the fwi then uses these a priori values when inferring seismic velocities and density a source wavelet correction which is inevitable in fwi of field data can compensate a

mass flux and undertow in a surf zone abstract the mass of water carried shoreward by the breaking waves in a surf zone will in a two dimensional situation be compensated by a seaward return flow the undertow it is shown that the undertow is driven by the local difference between radiation stress and the set up pressure gradient which only balance each other in average over the depth turbulent shear stresses are required to maintain a steady situation comparison with measurements confirms the theoretical results

the influence of tides wind and waves on the redistribution of nourished sediment at terschelling the netherlands abstract a calibrated morphodynamic model of the barrier island of terschelling the netherlands grunnet n m walstra d j r ruessink b g 2004 process based modelling of a shoreface nourishment coastal eng 51 7 581 607 comprising the island and its two adjacent tidal inlet systems is applied to identify the relative contribution of tides wind and waves to the cross shore and alongshore redistribution of a 2 mm3 nourishment supplied to the nearshore zone along the island several model simulations with varying combinations of horizontal and vertical tide wind and wave forcing were designed to investigate the effect of each individual forcing on a large spatio temporal scale order of kilometres and months respectively as expected stirring and transport by waves and wave induced currents are predicted to be by far the dominant contributor to the net sediment transport along the coast of terschelling because of the strong obliquity of the winds and the relatively small tidal currents in front of the island 0 5 m s alongshore wind driven currents increase sediment transport rates and horizontal tides virtually have no net transport capacity this motivated a local model of the study area along the closed coast of terschelling not including tidal inlets and further simplifying tidal boundary definitions by omitting the horizontal tides morphodynamic simulations of the local model show virtually identical results as the larger model predictions the reduction in complexity in setting up a local model instead of a regional model coupled with the corresponding significant reduction in computational time points to an increasing applicability of complex process based models

aspherical structure of the core mantle boundary from pkp travel times maps of aspherical structure in the vicinity of the core mantle boundary have been constructed from a tomographic analysis of p df and p ab travel times in the distance range 150 180 these maps reveal long wavelength features not previously detected by mantle tomography the peak to peak amplitude of these features is on the order of 1 s in vertical travel time too large to be explained by conventional thermal boundary layer models or dynamically supported topography on the core mantle boundary we hypothesize the existence of one or more chemical boundary layers whose large scale accumulations on the surface of the core may in some ways be analogous to continents at the earth s surface

a mixed solution for a highly protected coast punta marina northern adriatic sea italy abstract spatial data collected over three years are presented to assess the impacts of a mixed intervention carried out in a low sandy microtidal highly protected beach punta marina italy coastal erosion started in the 1980s principally due to reduction of fluvial sediment discharges wave attack and both anthropic and natural subsidence the intervention consisted in a small beach nourishment shallow feeder berm construction and the placement of an artificial reef to retain the sand fill topo bathymetrical surveys with real time kinematic rtk gps multi beam surveys sediment samplings wave data records dive inspections and numerical simulations were undertaken over a 3 year monitoring period to analyse the process response mechanism of this intervention to assess the main factors affecting the performance of the mixed intervention and the possibility of using fine sediments for nourishment practices the results reveal a generally positive impact characterised by short term beach stability that was mostly due to the feeder berm effect the beach nourishment had a short but direct effect on the beach width while the feeder berm dissipated wave energy and successively fed the nearshore with eroded sediment on the other hand the artificial reef did not retain the sand but rather induced rip currents that increased eddy circulation and therefore promoted the loss of offshore sediment settlement and scouring problems were also observed and the structure s failure induced safety problems the results confirm that a feeder berm operation carried out with fine sediment represents a good solution although particular attention must be paid to the relationship between sediment grain sizes volume and location of the nourishment as they are the key factors for good performance finally the cross shore sediment transport represents a critical factor that controls the coastal evolution of beaches bounded by hard structures and assimilated to the littoral cell consequently it should be better integrated within the nourishment design and model setting

modelling shallow water wave generation and transformation in an intertidal estuary an experiment is described in which wave growth was measured in manukau harbour a new zealand estuary with relatively large fetches and extensive intertidal flats wave spectra were obtained from pressure sensors and current meters placed at six sites across the estuary the swan third generation spectral model was then used to simulate wave transformation during a part of the study period during which consistent south westerly winds blew along the instrument transect the simulations incorporated refraction by currents using output from a circulation model of the estuary measured wave variance spectra were compared with the model results and the contributions of the various processes represented by source terms within the model were compared it was found that along with whitecapping bed friction and exponential growth from wind input four wave nonlinear interactions played a dominant role some limitations were noted in the discrete interaction approximation which the swan model uses to compute the four wave nonlinear interaction term

nourishing the shoreface observations and hindcasting of the egmond case the netherlands abstract although beach nourishment policy in the netherlands is generally successful in maintaining the 1990 shoreline the efficiency of nourishments at several locations along the north sea coast is unacceptably low these locations are identified as erosion hotspots egmond aan zee is such a hotspot the bathymetric longshore irregularities make this coastal stretch highly susceptible to rip currents and horizontal circulations which transport large volumes of nourished sand to the sea in 1999 an alternative nourishment design was implemented this consisted of a shoreface nourishment at the outer bar at 7 5 m depth combined with a nourishment of the beach behind it high resolution bathymetric surveys carried out with the wesp revealed that the shoreface nourishment resulted in a significant shoreward migration of the outer bar during 1999 2001 after 2 years the system started to return to its natural dynamic equilibrium and lost the positive influence of the shoreface nourishment area shoreward movement of bars and increase of bar height which forms the first defense line of the mainland against the sea and positive contribution to the sand budget which increased as a result of the nourishment after 3 years may 1999 to april 2002 the sediment volume still had an increase of 477 500 m3 45 of the applied sand relative to may 1999 the shoreface nourishment area did not have a direct effect on the beach the shoreface nourishment area probably will have to be maintained to retain the sediment on the beach in the long run in egmond the shoreface nourishment started to disappear before the sediment could reach the beach the time scale of sediment feed to the beach zone probably is of the order of 5 10 years the shoreface nourishment seems to function as a reef creating a lee side effect that influences both cross shore and longshore sediment transport resulting in two main hypotheses firstly the longshore effect in which large waves break at the shoreface nourishment cause a calmer wave climate shoreward of the shoreface nourishment area and a reduction of the longshore current the shoreface nourishment partially blocks the wave driven longshore current secondly the cross shore effect in which shoaling waves generate onshore transport these hypotheses are supported by generated model results with both a process based profile model unibest tc and a process based coastal area model delft3d mor the unibest tc model was able to predict the detachment of the outer bar from the shoreface nourishment and to some extent the shoreward bar movements in the lee of the shoreface nourishment area the model found an increase in sediment confirming the shielding effect of the shoreface nourishment area the delft3d model found as a result of the shoreface nourishment area a decrease of the flow velocity and the wave height just shoreward of the shoreface nourishment area the model was able to predict the similar trend in sedimentation erosion pattern although the intensities were smaller in the lee of the shoreface nourishment area a clear sedimentation was found erosion was found south and seaward of the shoreface nourishment area the modeled profiles did not follow the measured profile changes the separation of the shoreface nourishment from the outer bar and the shoreward migration of the bars could not be accurately modeled because the cross shore transport caused by wave asymmetry is not taken into account in the standard version of delft3d these results were in line with the expectations

long wavelength s wave velocity structure throughout the mantle summary long wavelength s wave velocity anomalies are obtained for the entire mantle by inverting 6ooo long period 40 100s sh body waves and lo00 long period 100 500 s love waves in the shallow mantle the patterns of fast and slow velocity anomalies correlate well with age and tectonics in the depth range of 400 1000 km we find two antipodal fast velocity anomalies one in the western pacific and the other in south america they form a fairly strong i 2 anomaly moreover the 1 2 anomaly is the largest spherical harmonic component throughout the entire mantle except for in the layer of 1000 1300 km depth a fast velocity anomaly near the caribbean previously reported by several other investigators is found between the depths of 1000 and 1300km with diminishing amplitudes it can be traced to canada and the aleutians and may be related to old subducted slabs in the same depth interval similar size anomalies can be found in the middle of the pacific and in the indian ocean these could be checked by more detailed studies to judge the reliability of this study heterogeneity power has a peak at the surface and a secondary peak at the bottom of the mantle d consistent with the existence of chemical and or thermal boundary layers at the base of the mantle we also find a fast velocity anomaly which surrounds the pacific ocean this feature has been found by other researchers previously but its interpretation is difficult due to the trade off between velocity anomaly and core mantle boundary deformation

the equilibrium distribution of grain size fractions and its implications for cross shore sediment transport a conceptual model abstract the relative distribution of individual grain size fractions across the cross shore coastal profile of terschelling north sea displays a constant shape when average conditions are considered the shape of the distribution curve depends on the hydrodynamic processes acting in the littoral zone and if the curve is contemplated in a normalized relative form it can be considered as a permanent feature of the nearshore zone the normalized curve is an equilibrium distribution curve and it can be used in the prediction of the cross shore redistribution of sediments when the textural distribution of the supplied sediment is known sediment may be imported into the active profile by either natural or man induced processes such as e g nourishments the application of the conceptual model in the prediction of the sediment redistribution from the shoreface nourishment carried out in front of the island of terschelling indicates a predominant sediment transport from the nourished area towards the shoreline 58 and a subordinate cross shore transport in an offshore direction 17 about 25 of the supplied sediment remains in the nourished area comparison of these results with the volumetric estimations of the sediment transport based on the morphological evolution shows a good agreement and suggests that the method gives reliable results the method may become a simple additional and useful tool in predicting the behaviour and dispersion of naturally or artificially imported volumes of sediment the conceptual model is a typical black box model and it cannot replace the existing and future generations of generic coastal morphodynamic models or process related models such as 2dv coastal profile models in addition the application of this model is definitely limited to coastal environments that satisfy certain hydrodynamic and geological conditions that are related to e g a longshore uniformity in processes and the lack of influence of sedimentary outcrops

the impact of waves and tides on residual sand transport on a sediment poor energetic and macrotidal continental shelf 2019 the authors the energetic macrotidal shelf off south west england was used to investigate the influence of different tide and wave conditions and their interactions on regional sand transport patterns using a coupled hydrodynamic wave and sediment transport model residual currents and sediment transport patterns are important for the transport and distribution of littoral and shelf sea sediments morphological evolution of the coastal and inner continental shelf zones and coastal planning waves heavily influence sand transport across this macrotidal environment median 50 exceedance waves enhance transport in the tidal direction extreme 1 exceedance waves can reverse the dominant transport path shift the dominant transport phase from flood to ebb and activate sand transport below 120 m depth wave tide interactions encompassing radiation stresses stoke s drift enhanced bottom friction and bed shear stress refraction current induced doppler shift and wave blocking significantly and nonlinearly enhance sand transport determined by differencing transport between coupled wave only and tide only simulations a new continental shelf classification scheme is presented based on sand transport magnitude due to wave forcing tide forcing and nonlinear wave tide interactions classification changes between different wave tide conditions have implications for sand transport direction and distribution across the shelf nonlinear interactions dominate sand transport during extreme waves at springs across most of this macrotidal shelf at neaps nonlinear interactions drive a significant proportion of sand transport under median and extreme waves despite negligible tide induced transport this emphasizes the critical need to consider wave tide interactions when considering sand transport in energetic environments globally where previously tides alone or uncoupled waves have been considered

multiparameter waveform inversion of a large wide azimuth low frequency land data set in oman abstractseveral 3d seismic acoustic full waveform inversions fwis of offshore data sets have been reported over the last five years a successful updating of the long to intermediate wavelengths of the earth model by fwi requires good quality wide angle long offset low frequency data recent improvements in acquisition make such data sets available on land too we evaluated a 3d application on a data set recorded in north oman the data contain low frequencies down to 1 5 hz long offsets and wide azimuths the application of acoustic fwi on land remains complicated because of the elastic effects notably the strong ground roll and many acquisition and human activity related noises the presence of fast carbonate layers in this region induces velocity inversions difficult to recover from diving or postcritical waves we accounted for anisotropic effects as we include fwi in a classical structural imaging workflow with a dedicated processing of the data and a simultaneous inversion of the nmo veloc

new methodology for describing the equilibrium beach profile applied to the valencia s beaches abstract mathematical models used for the understanding of coastal seabed morphology play a key role in beach nourishment projects these projects have become the fundamental strategy for coastal maintenance during the last few years accordingly the accuracy of these models is vital to optimize the costs of coastal regeneration projects planning of such interventions requires methodologies that do not generate uncertainties in their interpretation a study and comparison of mathematical simulation models of the coastline is carried out in this paper as well as elements that are part of the model that are a source of uncertainty the equilibrium profile ep and the offshore limit corresponding to the depth of closure doc have been analyzed taking into account different timescale ranges the results have thus been compared using data sets from three different periods which are identified as present past and future accuracy in data collection for the beach profiles and the definition of the median grain size calculation using collected samples are the two main factors that have been taken into account in this paper these data can generate high uncertainties and can produce a lack of accuracy in nourishment projects together they can generate excessive costs due to possible excess or shortage of sand used for the nourishment the main goal of this paper is the development of a new methodology to increase the accuracy of the existing equilibrium beach profile models providing an improvement to the inputs used in such models and in the fitting of the formulae used to obtain seabed shape this new methodology has been applied and tested on valencia s beaches

on bar growth and decay during interannual net offshore migration abstract multiple bar systems often show a cyclic net offshore directed migration with return periods on the order of years generally a bar is generated near the shoreline grows in height and width while migrating offshore before finally decaying at the seaward limit of the surf zone based on a three year hindcast of a bar cycle at noordwijk netherlands and on additional synthetic runs using a wave averaged cross shore process model this study identifies the dominant mechanisms that govern the bar amplitude growth and decay during net interannual offshore migration the bar amplitude response is particularly sensitive to the water depth above the bar crest h xb and the angle of wave incidence these variables largely control the amount of waves breaking on the bar and the strength and cross shore distribution of the associated longshore current the longshore current has its maximum landward of the bar crest inducing additional stirring of sediment on the landward bar slope and trough the enhanced sediment concentration in the trough region shifts the cross shore transports peak landward of the bar crest forcing bar amplitude growth during offshore migration for increased h xb values wave breaking becomes less frequent consequently reducing the influence of the longshore current on sediment stirring therefore the resulting dominance of the cross shore current results in a sediment transport peak at the bar crest causing bar amplitude decay all four types of bar response viz all combinations of onshore offshore migration and bar amplitude growth decay can occur for a single wave height and wave period combination depending on h xb and additional hindcast runs in which the wave direction was assumed time invariant confirmed that h xb and largely control the transient bar amplitude response

linear evolution of a shoreface nourishment abstract the morphological evolution of a shoreface nourishment is investigated by interpreting the nourishment as a linear perturbation of the natural system the nourishment is projected onto the subset of linear eigenmodes with negative growth rates of the morphodynamical system the evolution of these linear modes then determines the temporal behaviour of the shoreface nourishment the method is presented and results are shown for shoreface nourishments of different length scales on a straight coast and subject to normal incidence shoreface nourishments are represented by their expansions according to the projection method on a 1 50 plane beach profile all nourishments are shown primarily to be diffusive features with long scale nourishments diffusing more slowly than shorter length scale nourishments long scale nourishments also exhibit a shoreward movement during their decay this all indicates that long length scale nourishments may be more beneficial in coastal engineering projects this study is a first step towards nonlinear projection to study shoreface nourishment behaviour

modeling the alongshore current on barred beaches mean alongshore currents observed on two barred beaches are compared with predictions based on the one dimensional time and depth averaged alongshore momentum balance between forcing by breaking waves wind and 10 100 km scale alongshore surface slopes bottom stress and lateral mixing the observations span 500 hours at egmond netherlands and 1000 hours at duck north carolina and include a wide range of conditions with maximum mean currents of 1 4 m s including rollers in the wave forcing results in improved predictions of the observed alongshore current structure by shifting the predicted velocity maxima shoreward and increasing the velocity in the bar trough compared with model predictions without rollers for these data wave forcing balances the bottom stress within the surfzone with the other terms of secondary importance the good agreement between observations and predictions implies that the one dimensional assumption holds for the range of conditions examined despite the presence of small alongshore bathymetric nonuniformities with stronger bathymetric variations the model skill deteriorates particularly in the bar trough consistent with earlier modeling and laboratory studies

processes controlling the development of a river mouth spit abstract spits are among the most dynamic features in the coastal zones their stability is very often the result of a fragile equilibrium between the availability of sediments and the forcing hydrodynamics due to the complex interactions between the processes shaping such geomorphologic features the investigation is difficult and requires separate analysis for each of the processes a typical example of a spit is sahalin which emerged one century ago at the mouth of the danube delta s southernmost distributary and has continuously evolved through elongation and lateral migration in order to investigate and quantify separately each of the main processes shaping a spit we divide our research in two stages first wave induced sediment transports were simulated and analyzed using a complex processes based on a numerical model for an idealised spit this schematized spit was based on the shape of a number of spits secondly the findings were used in a similar approach for a real case the sahalin spit results show convergence of the wave fields towards the spit and large transport rates for the dominant wave directions the sediment budget derived from the predicted transport and the historical maps of the spit show that the evolution of the spit is the result of a continuous interaction between along and cross shore sediment transport furthermore a good match was obtained between the volumes of sediment supplied to the spit system and those feeding the expansion of the spit the final output is a conceptual model that includes four stages submarine accumulation emerging evolution and merging with the mainland of the spit based on the findings from the present study as well as on the findings of previous authors although the model was constructed to explain the evolution of sahalin spit it is suggested that it can be applied more generally for spits formed in wave dominated deltas in a microtidal environment and with a wave climate dominated by one direction

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

travel times and station corrections for p waves at teleseismic distances approximately 3300 shallow focus earthquakes and 1000 seismic stations have been used in a study of p wave travel times and station residuals including azimuthal effects the events were selected from a catalog containing 160 000 earthquakes and those having uniform distance and azimuthal coverage were systematically relocated and used to refine p wave travel times and station corrections station corrections are provided for 994 seismic stations the station corrections involve three terms the static effect and two cosine terms with appropriate phase shifts they exhibit general consistency over broad geographic areas and where coverage is dense often show abrupt changes from one geological province to another the cos 2 terms appear to be due to upper mantle anisotropy and they correlate with the stress direction in the crust

storm driven cyclic beach morphodynamics of a mixed sand and gravel beach along the mid atlantic coast usa abstract the morphodynamics of a mixed sand and gravel beach in delaware were investigated based on 18 almost monthly beach profile surveys at 46 locations from 2009 to 2011 60 sediment cores and 550 surface sediment samples collected at various alongshore and cross shore transects three different atmospheric disturbances occurred within a 3 month window during the study period 1 a distal hurricane 2 an energetic winter storm and 3 nor ida a long lasting and extremely energetic event resulting from the collision of a hurricane and winter storm the storm induced beach changes and post storm recovery following each of the three storms are evaluated a distinctive beach cycle was identified consisting of a built up berm profile and depleted nearly planar storm profile the time scale of the beach cycle relates to the frequency and intensity of storm impact and duration of inter storm recovery instead of simple seasonality the initiation of post storm recovery occurs during the subsiding phase of the storm attributable to the reduction in wave height and steepness transitioning to accretionary swells the sediment characteristics of the storm deposit associated with nor ida demonstrated substantial cross shore variation ranging from sandy gravel and gravelly sand within the storm swash zone near the pre storm dune edge to well sorted medium to coarse sand seaward of the storm swash zone storm deposits along mixed sand and gravel beaches demonstrate a variety of sedimentological characteristics in addition the studied beaches lacked a sandbar under all wave conditions a new beach cycle model is proposed for the non barred mixed sand and gravel beach

observations of waves and currents during barrier island inundation overwash and inundation on barrier islands can transport sediment onshore leading to vertical accretion these processes could ensure barrier island growth in times of sea level rise but wave and current fields during overwash and inundation are not well understood field data of water levels waves and currents were collected on a barrier island in the netherlands to investigate the hydrodynamics during island inundation observations show that even in shallow water depths 0 5 m wave energy was not completely dissipated as waves propagated from the north sea onshore additionally locally generated wind waves entered the field area from the wadden sea and propagated offshore infragravity waves were an important part of the wave field particularly onshore of the beach crest they were observed to be onshore progressive and displayed a bore like shape when water depths were shallow wave breaking was the dominant dissipation mechanism for high frequency waves as well as for infragravity waves which is in agreement with prior research on infragravity wave energy dissipation on mild sloping closed boundary beaches a large scale offshore directed water level gradient between the wadden sea and the north sea side caused by elevated water levels in the wadden sea during the storms frequently drove an offshore flow if it was large enough to exceed the cross shore gradient due to wave setup in addition elevated water levels in the wadden sea decreased current velocities due to a decrease in water level gradients this study highlights the influence of back barrier processes on the hydrodynamics during inundation

transition zone width and implications for modeling surfzone hydrodynamics the surfzone associated with a wave breaking on a plane slope may be subdivided into three regions the transition zone the inner zone and the swash zone the transition zone is the region just shoreward of the point of wave breaking and is characterised by rapid wave decay and also by constant wave setdown and thus constant radiation stress in this paper an empirical expression for the width of this zone is developed from monochromatic wave data two techniques are proposed for the consideration of this phenomenon in the numerical modelling of surfzone hydrodynamics for random waves the implications of a zone of nearly constant radiation stress inside the breakpoint are examined with respect to wave induced current generation both cross shore and longshore and sediment transport prediction comparisons are made to both field and laboratory data from plane and undulating profiles

the hellenic subduction zone a tomographic image and its geodynamic implications new tomographic images of the hellenic subduction zone demonstrate slab penetration in the aegean upper mantle to depths of at least 600 km beneath greece the lower part of the slab appears to be detached at a depth of about 200 km whereas it still seems to be unruptured beneath the southern aegean schematically we derive minimum time estimates for the duration of the hellenic subduction zone that range from 26 to 40 ma this is considerably longer than earlier estimates which vary between 5 and about 13 ma

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

the systematic contribution of transporting mechanisms to the cross shore sediment transport in water depths of 3 to 9 m the systematic contributions of short waves infragravity waves and mean flows to the cross shore sediment transport were studied with direct measurements of instantaneous near bed sediment concentrations and velocities as well as with an energetics based sediment transport model using measured time series of near bed cross shore flow as input the study was conducted at four cross shore positions in the multiple bar system of terschelling netherlands during three field campaigns each with a five week duration the data were collected in 3 to 9 m water depth during a wide range of conditions from low energy non breaking conditions to almost fully saturated breakers the height over depth ratio hs h was applied at all four measuring stations as a local conditional parameter all model predictions were grouped into hs h classes with a width of 0 02 to highlight the generality of the data the energetics approach predicted that the suspended load dominated over the bedload at all four stations both the sediment flux measurements as well as the model predictions showed that the largest contributors to the gross suspended sediment transport were made by the short waves and the undertow inducing an onshore and offshore transport respectively their contributions to the gross suspended transport were about 40 to 50 under surf zone conditions bound infragravity waves were observed and predicted to result in an offshore directed transport that was of subordinate magnitude compared to the observed and estimated magnitudes by the short waves and the undertow however as these transports almost cancelled out because of their about equal magnitude but opposite sign the suspended transport by bound infragravity waves may not be ignored and may rather paradoxically have a relatively large influence on the net suspended sediment transport hydrodynamical processes that do not seem to be of importance to the onshore and offshore sediment transport in 3 to 9 m water depth in the long run are mean flows under non breaking conditions and free infragravity motions a direct comparison between measured sediment fluxes and the model predictions suggests that simple energetics models are suitable for predicting cross shore sediment transport in 3 to 9 m water depth

the predictability of cross shore bed evolution of sandy beaches at the time scale of storms and seasons using process based profile models deterministic and probabilistic profile models have been compared with hydrodynamic and morphodynamic data of laboratory and field experiments on the time scale of storms and seasons the large scale laboratory experiment is a pure 2d case and offers and ideal test case for cross shore profile models as disturbing alongshore non uniformities are absent the field experiments are performed at the egmond site the netherlands during the eu coast3d project and represent storm time scale oct nov 1998 as well as seasonal time scale conditions may 1998 sep 1999 the objective of the paper is to present information of coastal processes on these time scales and to assess the predictive capabilities coastal process based profile models with respect to hydrodynamics and morphodynamics at sandy beaches on the time scales of storms and seasons profile models can quite accurately errors smaller than 10 represent the cross shore significant wave height distribution in the surf zone if the wave breaking model is properly calibrated the wave breaking coefficient should be a function of local wave steepness and bottom slope for most accurate results profile models can reasonably represent the cross shore and longshore currents undertow in a pure 2d case and in 3d field conditions profile models including cross shore mixing effects and breaker delay effects do not produce better predictions of the longshore and cross shore current velocities profile models using default settings can quite reasonably simulate the behaviour of the outer and inner bars on the storm time scale the behaviour of the beach cannot be modelled with sufficient accuracy on the storm time scale profile models can reasonably simulate the post storm onshore bar migration provided that the near bed orbital velocities and wave asymmetry related sand transport are represented in a sufficiently accurate way using non linear wave theories profile models cannot simulate the beach recovery processes on the post storm time scale because these essentially 3d processes are not sufficiently known to be included in the models profile models using default settings cannot simulate the behaviour of the outer and inner bars and the beach on the seasonal time scale the behaviour of the outer bar on the seasonal time scale can only be represented properly after tuning using measured bed profiles the simulation of the inner bar and beach morphology on the seasonal time scale could not be improved by tuning

the 3 d shear wave structure in the mantle by overtone waveform inversion ii inversion of x waves r waves and g waves summary the 3 d upper mantle structure from the surface of the earth to a depth of about 1000 km is obtained by inverting waveforms of fundamental and higher mode surface waves minor and major arc waves of r waves g waves and x waves higher mode wave packets are used as basic data two features of the solution seem fairly robust one is the shallow structure in the upper few hundred kilometres which is strongly correlated with the age of the crust the second feature is the deep fast velocity anomaly near the western pacific indonesia philippines and mariana region and its antipodal region of south america both of which are subduction zones which forms a strong l 2 pattern simple slab models with 100 km thicknesses of 10 per cent faster velocity material do not explain such large scale fast velocity anomalies this may indicate large scale deformation of the 670 km discontinuity piling up of slabs in the upper mantle or thickening lithosphere in the lower mantle or large horizontal motions of subducted material these results are stable whether an earth model 1066a or prem is used as a starting model

investigation of wave growth and decay in the swan model three regional scale applications abstract wave growth and decay characteristics in a typical wave action model simulating waves nearshore swan are investigated in this paper this study is motivated by generally poor agreement between model results and measurements for a regional scale model of a two day period during the sandyduck 97 experiment wherein there is consistent underprediction of lower frequency 0 05 0 19 hz energy two separate methods are presented for improving predictions of low frequency energy 1 by altering the weighting of the relative wavenumber term that exists in the whitecapping formulation and 2 by disallowing the breaking of swell the sandyduck 97 simulation is repeated with the proposed modifications using the first modification a slight improvement is seen and with the second modification an apparent problem with nonphysical dissipation of swell by the model is corrected the modifications are then applied to two other test cases one in lake michigan and the other in the mississippi bight both

barrier formation on an actively prograding delta system the red river delta vietnam abstract an extensive barrier spit system 20 to 30 km long developed on the delta front platform of the ba lat delta within a relatively short period 10 20 years however it was not evident whether the formation was related to river floods typhoons or calm weather conditions or to cross shore or alongshore sediment transport mechanisms therefore a process based numerical model that simulates sediment transport and morphologic changes by waves tides wind and river flow is used to analyze the processes that govern this barrier formation the mechanism that initiates the barrier formation is concluded to be onshore transport by wave asymmetry of sediment previously transported seaward in the buoyant river plume the main mechanism that counteracts the barrier formation is probably destruction of the barrier by river flow during the subsequent transformation from a subaqueous barrier into a sub aerial barrier spit system overwashes and alongshore sediment transport become increasingly important this spit system therefore appears to be dominated by alongshore processes even though its initial formation is more strongly regulated by cross shore processes the importance of cross shore processes results in a minor contribution of typhoons to the initial formation of these barriers typhoons are not very important to destruction of barriers as well because wave energy is gradually dissipated over the gentle offshore profile which in turn results from river plume sedimentation

a worldwide comparison of predicted s wave delays from a three dimensional upper mantle model with p wave station corrections abstract this paper is a comparison on a worldwide scale between p station corrections deduced from isc residuals dziewonski and anderson and synthetic s station corrections computed using a three dimensional upper mantle model obtained from mantle wave data woodhouse and dziewonski the upper mantle s velocity model is described by a spherical harmonic expansion up to degree 8 the p station corrections are smoothed using a similar expansion in order that the two data sets can be compared correlations between p station corrections t p and synthetic s station corrections t s relevant to various depths of integration indicate that a station correction contains information about structures down to at least 670 km for this depth of integration the correlation coefficient of the two data sets is 0 59 the slope a of the relation t s a t p b obtained for the worldwide distribution of stations is in good agreement with results of previous regional studies using direct readings of p and s arrival times a 3 61 0 13 an analysis of regional variations of the relation t s a t p b is carried out on the basis of two published global tectonic patterns okal jodan results for oceanic regions are not reliable due to the lack of data on continental areas a significant difference appears between mountains a 2 7 0 3 and shields a 4 5 0 4 for okal s pattern a 5 7 1 5 for jordan s pattern the largest a value for shields rules out an explanation by partial melting as proposed in previous studies thermal heterogeneities lead to low a values undulations of the lithosphere asthenosphere boundary appear to be the most feasible explanation of the high slope beneath shields they are also able to explain the range of variation of the station corrections the lowest values of the station corrections correspond to a total vanishing of the low velocity zone beneath the oldest shields for mountains the mean values of the station corrections as well as the low a value can be accounted for by a slight increase of poisson s ratio together with a significant density increase

the behaviour of a multiple bar system in the nearshore zone of terschelling the netherlands 1965 1993 abstract the behaviour of a multiple bar system in the nearshore zone of the island of terschelling the netherlands is investigated on the time scale of years using a data set of soundings the data set covers the period from 1965 to 1993 the behaviour is analysed in terms of bar crest position and in terms of morphometric parameters such as bar crest depth height width and volume two or three breaker bars are permanently present in the study area each individual bar passes through three stages during its existence 1 generation close to the shore 2 seaward migration and 3 degeneration at the outer margin of the nearshore bar zone the key factor controlling the behaviour of the inner bars is the crest depth of the outer bar three different couplings between the behaviour of the individual bars have been observed 1 bar stage changes due to the degeneration of the outer bar 2 prevention of the transition of an inner bar from the first to the second stage caused by the appearance from alongshore of a new outer bar having a small crest depth and 3 difference in mean annual seaward migration rate caused by the possible presence of a more seaward positioned bar it is hypothesized that the crest depth of the outer bar governs the relative importance of processes inducing shoreward and seaward migration in the inner nearshore bar zone and therefore controls the behaviour of the nearshore bar zone on the time scale of years

nearshore placement of a sand dredged mound abstract as a part of the dredging operations and environmental research doer program movable bed physical model experiments were performed at the u s army engineer research and development centre s erdc large scale sediment transport facility lstf to investigate the fate and evaluate the benefits of nearshore placed dredged material the resulting bathymetry was measured with detailed surveys the migration of the mound was quantified and comprehensive observations of hydrodynamics were obtained the potential suitability of dredged material placement in the nearshore surf zone was demonstrated after 10 h of oblique wave attacks it has been shown that as the mound was located at the edge of the surf zone very likely wave breaking induced horizontal circulation may be dominant a downdrift accretion of the submerged beach was observed which is due to the transport of part of the sediment suspended by breakers at the mound and captured by the longshore currents the experiments provided useful validation data for numerical morphological models

subduction zone calibration and teleseismic relocation of thrust zone events in the central aleutian islands abstract teleseismically determined epicenters for thrust zone earthquakes in the central aleutian islands are systematically mislocated by about 40 km to the north relative to local network solutions we attribute the mislocation to travel time anomalies produced by the higher p wave velocity in the subducting slab these travel time anomalies can be estimated by seismic ray tracing through a thermally modeled velocity structure for the slab observed teleseismic station residuals and slab travel time anomalies computed from local network hypocenters plotted as a function of event distance to the center of curvature of the island arc show good agreement this distance versus residual relationship can be used to validate the local network hypocenters and to constrain the length of subducting lithosphere computed slab source corrections when incorporated in a standard location program reduce teleseismic mislocations to 20 km the addition of empirical station corrections reduces the mislocation to about 10 to 15 km depth and origin time estimates can be further improved through use of better station corrections a local station within 2 and depth phases

alongshore variability of the multiple barred coast of terschelling the netherlands abstract the alongshore variability of the behaviour of a multiple bar system in the nearshore zone along the barrier island of terschelling the netherlands is investigated using a bathymetric data set with an alongshore extent of 12 km sampled annually for 28 yr the spatial and temporal variability of bar behaviour is quantified in terms of bar crest position in relation to morphometric parameters such as bar depth height width and volume along the entire study area the bars were generated close to the shore migrated seaward and eventually degenerated at the outer margin of the nearshore the interannual migrational patterns of the nearshore sandbars are analysed in terms of time of residence migration rates and return periods within the life cycle of a bar the cross shore nearshore bar behaviour was found to vary alongshore for instance cross shore migration rates gradually increased from 35 to 70 m yr from one end of the study area to the other concurrently the duration of net seaward migration increased from 9 to 15 yr the return period and total life span of bars were however found to be alongshore uniform on the order of 10 12 yr and 22 yr respectively morphological characteristics of the nearshore bar zone such as slope and width also exhibit gradually alongshore varying patterns a strong causal association is established between nearshore slope and both bar migration rates and duration of net seaward migration it is hypothesised that alongshore increasing wave heights at the seaward end of the bar zone is coupled with a corresponding increase in nearshore slope the presence of an important updrift ebb tidal shoal is identified as key controlling factor in the variability of bar behaviour along the adjacent shoreline of terschelling

nearshore sediment pathways and potential sediment budgets in embayed settings over a multi annual timescale abstract embayed beaches constitute a large proportion of the world s rocky coastlines but there is a paucity of studies focusing on the longshore sediment exchange between embayed beaches separated by rocky stretches of coast here we investigate the nearshore sediment transport dynamics along a 15 km stretch of the embayed coastline of north cornwall sw england using delft3d numerical simulations coupled wave and tide are conducted to compute major circulation modes and sediment fluxes including order of magnitude for sediment bypassing between bays for a wide range of modal and extreme wave conditions results indicate that extreme events cause i multi embayment circulation and mega rip formation where an alongshore current is deflected offshore 0 7 m s 1 at 20 m depth in the down wave sectors ii large bypassing rates 103 104 m3 day 1 bypassing and iii exchanges extending to depths that exceed the base of the headlands accretionary phases over moderate high swell periods were associated with clockwise intra embayment circulation with simulated currents inducing redistribution towards the south in the long embayments 103 m3 day 1 longshore this circulation mode is combined with significant bypassing rates around the shallower and wider headlands 102 103 m3 day 1 predictions of sediment fluxes along the lower shoreface are based on the correlation between the modelled sediment fluxes and offshore wave conditions r 0 92 providing insights into the potential sediment budget over multi annual timescales hindcasted yearly bypassing rates around the headlands range between 103 and 105 m3 y 1 under an assumption of unlimited sediment supply with the bulk of the transport occurring mainly during high energy events hence the magnitude of the computed potential sediment fluxes presented here has implications for coastal evolution at longer timescales 10 years especially along sediment starved coastlines

the initial morphological response of the sand engine a process based modelling study abstract sand nourishments are presently widely applied to maintain or enhance coastal safety and beach width over the last decades global sand nourishment volumes have increased greatly and the demand for nourishments is anticipated to increase further in coming decades due to sea level rise with the increase in nourishment size and the request for more complex nourishment shapes an adequate prediction of the morphodynamic evolution is of major importance yet neither the skill of current state of the art models for such predictions nor the primary drivers that control the evolution are known this article presents the results of a detailed numerical modelling study undertaken to examine the model skill and the processes governing the initial morphological response of the sand engine and the adjacent coastline the process based model delft3d is used to hindcast the first year after completion of the mega nourishment the model reproduces measured water levels velocities and nearshore waves well the prediction of the morphological evolution is consistent with the measured evolution during the study period with brier skill scores in the excellent range the model results clearly indicate that the sand eroded from the main peninsular section of the sand engine is deposited along adjacent north and south coastlines accreting up to 6 km of coastline within just one year analysis of model results further show that the erosional behaviour of the sand engine is linearly dependent on the cumulative wave energy of individual high energy wave events with the duration of a storm event being more dominant than the maximum wave height occurring during the storm the integrated erosion volume due to the 12 events with the highest cumulative wave energy density accounts for about 60 of the total eroded volume of the peninsula indicating that the less energetic wave events with a higher probability of occurrence are also important for the initial response of the sand engine a structured model experiment using the verified delft3d model indicates that wave forcing dominates the initial morphological response of the sand engine accounting for approximately 75 of the total erosion volume in the first year the vertical tide is the second most important factor accounting for nearly 17 of the total erosion volume with surge wind and horizontal tide playing only a minor role

modeling the growth and migration of sandy shoals on ebb tidal deltas coherent sandy shoals that migrate toward the downdrift coast are observed on many ebb tidal deltas in this study processes that cause the growth and migration of shoals on ebb tidal deltas are identified moreover the effect of the incident wave energy and the tidal prism of an inlet on the migration speed of these shoals is investigated for this a numerical morphodynamic model with an idealized geometric setup is employed the model computes the bed level evolution due to local erosion and deposition of sand driven by tides and waves analysis of model results shows that shoals grow when there is a local imbalance between the bathymetry and the wave conditions which in this study was imposed by manually breaching the ebb tidal delta or by adding storms to the wave forcing there are thresholds for shoal formation that depend on the distribution of the sand and the incident wave energy wave refraction over the shoals leads to focusing of wave energy and increased wave energy dissipation around the location of the local minimum water depth this generates residual currents over the shoal and increased skin friction toward the local minimum water depth which together create a sand transport pattern that induces the growth and migration of the shoal sand transport due to asymmetric waves contributes to keeping the shoal a coherent structure the shoal migration speed increases with increasing incident wave energy and decreasing tidal prism this is because tidal residual currents oppose the wave driven residual currents that cause shoal migration

two dimensional full wavefield inversion of wide aperture marine seismic streamer data summary a 2 d full wavefield inversion method is presented for the processing of wide aperture data the diversity of information contained within such datasets may be handled in a complete manner by first matching the traveltimes of the main events and then progressing to waveform fitting of the data through explicit full wavefield modelling our wavefield inversion scheme is based upon a finite difference solution of the 2 d elastic wave equation in the time distance domain the strength of adopting such an approach is the ability to generate all possible wave types within a given 2 d model multiples converted waves etc and thus to simulate and accurately model complex seismic wavefields the aim of the inversion is to find the 2 d p wave velocity model that minimizes the least squared difference between the observed and synthetic data across the full range of offsets following extensive testing on synthetic data the wavefield inversion scheme has been applied to wide aperture real marine seismic streamer datasets we present results from the synthetic testing and the wavefield inversion of wide aperture real data out to 12 km offset that was recorded on a single streamer even though current computational restrictions allow only a small subsection of the data to be analysed these examples demonstrate the potential value of wide aperture 2 d full wavefield inversion

measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy 3 inversion lateral heterogeneity in the earth s upper mantle is investigated by inverting dispersion curves of long period surface waves 100 330 s models for seven different tectonic regions are derived by inversion of regionalized great circle phase velocity measurements from our previous studies we also obtain a representation of upper mantle heterogeneities with no a priori regionalization from the inversion of the degree 6 spherical harmonic expansion of phase and group velocities the data are from the observation of about 200 paths for love waves and 250 paths for rayleigh waves for both the regionalized and the spherical harmonic inversions corrections are applied to take into account lateral variations in crustal thickness and other shallow parameters these corrections are found to be important especially at low spherical harmonic order the trench region and fast velocities down to 250 km under shields below 200 km under the oceans both s velocity and s anisotropy support a model of small scale convection in which cold blobs detach from the bottom of the lithosphere when its age is large enough the spherical harmonic models clearly demonstrate a posteriori the relation between surface tectonics and s velocity heterogeneities in the first 250 km all shields are fast most ridges are slow below 300 km a belt of fast mantle follows the pacific subduction zones however at greater depths large scale heterogeneities that seem to bear no relationship to surface tectonics are observed the most prominent feature at 450 km is a fast velocity region under the south atlantic ocean smaller scale heterogeneities that are not related to surface tectonics are also mapped at shallower depths an anomalously slow region centered in the south central pacific is possibly linked to intense hot spot activity a very fast region southeast of south america may be related to subduction of old pacific plate between 200 and 400 km a belt of sv sh anisotropy follows part of the ridge and subduction systems indicating vertical mantle flow in these regions the spherical harmonic results open new horizons for the understanding of convection in the mantle perspectives for the improvement of the models presented are discussed

three dimensional velocity structure and resolution of the core mantle boundary region from whole mantle inversions of body waves the nature of the core mantle boundary cmb has important implications for deep earth processes particularly those which have their origin in the lower mantle or outer core the possibility of the existence of lateral p wave velocity variations in the outermost core is explored here by obtaining models of three dimensional cmb region velocity structure using an inversion of waveform data the numerical inversions involve determination of the three dimensional structure of the earth s outermost core and lower mantle using over 5000 long period seismic waveforms collected from global digital seismic networks spheroidal modes with periods between 33 and 100 s were selected to model the body wave portion of seismograms recorded from global earthquakes first order perturbations in s wave velocities in 11 mantle layers 200 350 km thick and p wave velocities in one outermost core layer comprise the least squares solutions to the inverse problem although the statistical f test supports the additional layer in the inversions this layer is not required by the f ratio to occur in the outermost core pattern retrieval resolution tests in which synthetic data constructed from an initial synthetic earth model are inverted for model parameters are used to compare parameters for one region to those of another in which some coefficient power smearing is suspected depth resolution tests indicate that the best radial resolution at the cmb is 500 km thus this method does not produce the resolution required for outermost core lateral velocity variation analysis an examination of the limitations of this approach demonstrates the need for waveform inversion techniques which more accurately predict raypaths in the deep mantle improvements in radial resolution are needed before whole mantle velocity models can begin to distinguish whether significant heterogeneity related to core mantle interactions occurs in the cmb region

analysis of submerged bar nourishment strategies in a wave dominated environment using a 2dv process based model the present study aims to analyze the effects of different submerged bars nourishment strategies using a 2dv process based morphodynamical model a two barred beach profile typical of the french mediterranean micro tidal storm dominated coastline is chosen as a reference profile two different kinds of modified beach profiles are considered i only the outer bar is nourished the inner bar being unchanged ii both bars are nourished three typical wave forcing regimes are considered the behavior of the natural profile is first investigated under the 3 wave forcing regimes then the behavior of the various nourished profiles is analyzed in terms of wave dynamics and bars behavior on the basis of the model results the outer bar only nourishment strategy appears to be preferable

two dimensional velocity models from wide angle seismic data by wavefield inversion summary modern wide angle surveys are often multi fold and multi channel with densely sampled source and receiver spacings such closely spaced data are potentially amenable to multi channel techniques involving wavefield propagation methods such as those commonly used in reflection data processing however the wide angle configuration requires techniques capable of handling very general wave types including those not commonly used in reflection seismology this is a situation analogous to that faced in cross borehole seismics where similar wave types are also recorded in a real cross borehole example we compare pre stack migration traveltime tomography and wavefield inversion we find that wavefield inversion produces images that are quantitative in velocity as are the tomograms but are of significantly higher resolution the wavefield inversion results have a resolution comparable to that of the qualitative pre stack migration images we seek to extend this novel development to the larger scale problem of crustal imaging an essential element of the approach we adopt is its formulation entirely within the temporal frequency domain this has three principal advantages 1 we can choose to decimate the data by selecting only a limited number of frequency components to invert thus making inversion of data from large numbers of source positions feasible 2 we can mitigate the notorious non linearity of the seismic inverse problem by progressing from low frequency components in the data to high frequency components and 3 we can include in the model any arbitrary frequency dependence of inelastic attenuation factors q and indeed solve for the spatial distribution of q an initial synthetic test with an anomaly located within the middle crust yields a velocity image with the correct structural features of the anomaly and the correct magnitude of velocity anomaly this is related to the fact that the reconstruction is obtained from forward scattered waves under these conditions the method thus behaves much like tomography a second test with a deeper more extensive anomaly yields an image with the correct velocity polarity and the correct location but with a deficiency in low and high wavenumbers in this case this is because the reconstruction is obtained from backscattered waves under these conditions the method behaves not like tomography but like migration a more extensive test based on a large wide angle survey in south eastern california and western arizona demonstrates a real potential for high resolution imaging of crustal structures although our results are limited by the acoustic approximation and by the relatively low frequencies that we can model today the images are sufficiently encouraging to warrant future research the problem of local minima in the objective function is the most significant practical problem with our method but we propose that appropriate layer stripping methods can handle this problem

spectra of mantle shear wave velocity structure summary we applied the stochastic method of gudmundsson davies clayton 1990 which was applied to isc p wave data to teleseismic isc s wave data to obtain an independent estimate of mantle structure we inverted the variance of s wave traveltime residuals of bundles of rays to obtain a description of the spectrum of lateral heterogeneity as a function of depth through the mantle the technique yields robust estimates of the traveltime scattering power the product of a characteristic scalelength of heterogeneity and the mean square of slowness perturbations we can estimate the characteristic scalelength half width from the autocovariance which can be reconstructed from the spectra hence by division we can estimate the root mean square slowness by extrapolating the variance of bundles of rays to bundles of zero cross sectional area we can also estimate the scale incoherent signal which is a plausible estimate of the noise in the data which is removed from the data we find that most of the structure generating shear wave traveltime residuals is located in the uppermost mantle about half of the structure is short scale harmonic degree 1 50 the large scale structure 1 50 has a half width of about 500 km in the upper half of the mantle this s wave half width is consistent with the p wave half widths determined by gudmundsson et al 1990 the s wave half width in the lower half of the mantle is poorly constrained it varies from 500 to 3000km which spans the better constrained value of 1200 km found by gudmundsson et al 1990 for p waves the incoherent scatter suggests that the signal to noise ratio of the s wave data set is around 1 5 assuming that the compressional and shear wave velocity variations are correlated then the signal weighted value of the ratio d in y ld in y is 2 as also found in normal mode studies this is much larger than the value of 0 8 1 4 suggested by laboratory experiments undertaken at atmospheric pressure there is no evidence of periodicity in the traveltime autocovariance this suggests little or no periodicity in the underlying convection the short half width through most of the mantle suggests high rayleigh number convection with its attendant small scale structures the power decreases by an order of magnitude or more in going from the upper mantle to the lower mantle the same as found by gudmundsson et al 1990 for p waves this large difference suggests either a change in convective regime and or a difference in the temperature sensitivity of elastic constants in both layers the increased short scale structure at the top of the mantle suggests that a large part of the seismic signature at this boundary is compositional since one would expect a red spectrum for a thermal boundary layer the derived spectra between 1 10 and i 50 are similar in shape to spectra from the mantle convection simulations of glatzmaier 1988 with a rayleigh number of 106 107 which would suggest layered convection if the comparison is valid

a 2 d synthetic study of global traveltime tomography a 2 d synthetic test study of global traveltime inversion for deep seated earth structure has been undertaken this was done by generating traveltime residual data using reasonable models for earth structure the data were then inverted by similar methods to those applied in global studies of earth structure our results indicate that models of the aspherical structure in the lower mantle based on traveltime data are only partially successful and only at the largest scales harmonic degree 3 and that maps of the core mantle boundary based on traveltimes are unsuccessful

sandbar and beach face evolution on a prototype coarse sandy barrier abstract on steep beaches the cross shore movement of sand in response to erosive storm waves and accretive swell waves can lead to temporal changes between a barred winter profile and a non barred summer profile with a pronounced berm in the upper swash zone despite recent improvements in predicting berm formation and evolution within process based morphodynamic models substantial demand for improvement in understanding swash processes and associated surf swash sand exchange remains here we analyze bed level data collected on a near prototype 4 5 m high and 75 m wide sandy beach median grain diameter d50 430 m with a lagoon situated at its landward side in particular we distinguish between surf swash sand exchange time scale of tens of minutes to hours the net effect of single and multiple swash events on the entire beach face time scale of a few seconds to hours and instantaneous bed variability at 3 cross shore locations within individual swashes during erosive waves hs 0 8 m tp 8 s sand on the initially 1 15 planar profile was predominantly eroded from the inner surf zone to be deposited in the outer surf zone as a sandbar indicating minimal surf swash sand exchange subsequent accretive waves hs 0 6 m tp 12 s caused substantially larger surf swash sand exchange the pre existing sandbar migrated onshore and decayed with the sand ending up on the beach face in a prominent up to 0 7 m high steep 1 6 berm we found the dynamics of the berm to be governed primarily by wave conditions and the antecedent morphology with ground water gradients of additional importance when morphodynamic feedback between swash flow and the berm is small the observed bed level change within a swash and averaged over a swash event could be substantial several centimeters during all wave conditions but the net i e averaged over multiple swash events bed level change was strongly suppressed because erosive and accretionary swashes nearly balanced in addition the local beach face slope could be instantaneously 25 steeper or shallower than the median slope or the initial or final slope we anticipate that our data will stimulate new model development as to increase the range of conditions and settings in which morphodynamic models can be applied realistically and reliably

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

the use of low frequencies in a full waveform inversion and impedance inversion land seismic case study velocity model building and impedance inversion generally suffer from a lack of intermediate wavenumber content in seismic data intermediate wavenumbers may be retrieved directly from seismic data sets if enough low frequencies are recorded over the past years improvements in acquisition have allowed us to obtain seismic data with a broader frequency spectrum to illustrate the benefits of broadband acquisition notably the recording of low frequencies we discuss the inversion of land seismic data acquired in inner mongolia china this data set contains frequencies from 1 5 80 hz we show that the velocity estimate based on an acoustic fullwaveform inversion approach is superior to one obtained from reflection traveltime inversion because after full waveform inversion the background velocity conforms to geology we also illustrate the added value of low frequencies in an impedance estimate

a search for anomalies in the lowermost mantle using seismic bulletins abstract for deep events and epicentral distances around 75 the bulletins of the international seismological centre bisc contain many secondary arrivals between p and pcp the reflection from the core mantle boundary cmb which cannot be explained by current spherical symmetric earth models assuming that these arrivals in the p coda are reflections from p velocity anomalies in the lower mantle we calculate the associated reflection points geographical coordinates and distance from the cmb and map both strength relative density of reflection points in bins in the lower mantle and distance of the reflectors from the cmb on a global scale the regions with these anomalous bins cover 3 of the 50 of the lowermost mantle that can be analysed with this data set the most significant regions with anomalous bins values in parentheses give a preliminary estimate of the distance of the reflector from the cmb are under the north atlantic ridge 250 km northern central siberia 230 km japan 180 km the central mid atlantic ridge 310 and 260 km and off the coast of ecuador 340 km the presence of reflectors in one of these regions has already been confirmed by detailed seismic studies using waveform data from arrays and networks a slight 2 3 p velocity contrast is sufficient to produce measurable reflection amplitudes in the distance range of 70 80 ten percent of the lower mantle sampled by this study is covered by bins with no or very few secondary arrivals in the p coda the most significant regions with such a normal lower mantle are under central america the caroline and marshall islands in the eastern pacific the area of hawaii and the easter islands and the northern atlantic identification of the regions with anomalous bins serves to locate the areas of the lowermost mantle which should be analysed further by using the full information content of seismograms the study of the travel time the amplitude and the form of the wavefield recorded preferably at seismic arrays dense networks will allow the determination of the anomalous velocity structure of the core mantle transition zone in more detail the most promising areas for such a study are given here but further anomalies are likely to exist

process based modeling of kilometer scale alongshore sandbar variability subtidal nearshore sandbars may exhibit cyclic net offshore migration during their multi annual lifetime along many sandy coasts although this type of behavior can extend continuously for several kilometers alongshore variations in cross shore bar position and bar amplitude are commonly observed alongshore variability is greatest when bars display km scale disruptions indicative of a distinct alongshore phase shift in the bar cycle an outer bar is then attached to an inner bar forming a phenomenon known as a bar switch here we investigate such large scale alongshore variability using a process based numerical profile model and observations at 24 transects along a 6 km section of the barred beach at noordwijk the netherlands when alongshore variability is limited the model predicts that the bars migrate offshore at approximately the same rate i e the bars remain in phase only under specific bar configurations with high wave energy levels is an increase in the alongshore variability predicted this suggests that cross shore processes may trigger a switch in the case of specific antecedent morphological configurations combined with storm conditions it is expected that three dimensional 3d flow patterns augment the alongshore variability in such instances in contrast to the observed bar behaviour predicted bar morphologies on either side of a switch remain in different phases even though the bars are occasionally located at a similar cross shore position in short the 1d model is not able to remove a bar switch this data model mismatch suggests that 3d flow patterns are key to the dissipation of bar switches

the three dimensional shear wave structure in the mantle by overtone waveform inversion i radial seismogram inversion summary the three dimensional 3 d shear wave structure of the mantle down to the depth of about 900 km is obtained by inverting waveforms of radial component seismograms radial component seismograms contain large amplitude overtone signals which circle the earth as wave packets and are sometimes called x1 x2 x3 we use data which contain r1 x1 and x2 and filtered between 2 and 10mhz it is shown that unless each seismogram is weighted all seismograms are not fitted uniformly only data from large earthquakes are fitted and the final velocity anomalies are biased by the small number of large earthquake data resolution is good at shallow depths becomes worse in the intermediate depth range between about 400 and 500 km and then becomes better at greater depth ranges 600 900km even though we use only spheroidal mode data velocity anomalies in the shallow structure show excellent correlation with the age of the surface rocks of the earth in the deeper regions between about 600 and 900km south america shows a fast velocity anomaly which may indicate the slab penetration beyond 700 km there another region which shows a fast velocity anomaly is the mariana trench but other subduction regions do not show such features

process based modelling of a shoreface nourishment abstract a state of the art process based model is applied to hindcast the morphological development of a shoreface nourishment along the barrier island of terschelling the netherlands the applied morphodynamic model is delft3d for fully three dimensional flow and sediment transport in coastal environments owing to a complex geomorphological setting of the study area the curvi linear model includes adjacent tidal inlets and covers 40 70 km with an increasing grid size resolution towards the nourishment site in the center of the island in 1993 a total of 2 mm3 of sand was supplied to the nearshore bar zone off terschelling filling up the trough between the middle and outer bar by spring 1994 most of the nourished sediment had been redistributed onshore and welded onto the middle bar where it remained in the following years the morphodynamic model is applied to the prediction of this rapid nearshore profile behaviour the calibration of the model against an extensive set of full scale hydrodynamic data at several locations throughout the nearshore bar zone shows a good representation of the measured hydrodynamics morphodynamic results show a dependency on spatial scale on the scale of precise bed level evolution with respect to bar migration and growth model predictions are poor as the nearshore bars are predicted to flatten out resorting to bulk volumes integrated over larger spatial scales the model clearly has skill in predicting the overall effects of the nourishment the lack of phase shift between sediment transport and bathymetry is identified as the key controlling factor for the poor sandbar predictions