structure of large amplitude internal solitary waves the horizontal and vertical structure of large amplitude internal solitary waves propagating in stratified waters on a continental shelf is investigated by analyzing the results of numerical simulations and in situ measurements numerical simulations aimed at obtaining stationary solitary wave solutions of different amplitudes were carried out using a nonstationary model based on the incompressible two dimensional euler equations in the frame of the boussinesq approximation the numerical solutions which refer to different density stratifications typical for midlatitude continental shelves were obtained by letting an initial disturbance evolve according to the numerical model several intriguing characteristics of the structure of the simulated large amplitude internal solitary waves like for example wavelength amplitude and phase speed amplitude relationship as well as form of the locus of zero horizontal velocity emerge consistent with those obtained previously using stationary euler models the authors approach which tends to exclude unstable oceanic internal solitary waves as they are filtered out during the evolution process was also employed to perform a detailed comparison between model results and characteristics of large amplitude internal solitary waves found in high resolution in situ data acquired north and south of the strait of messina in the mediterranean sea from this comparison the importance of using higher order theoretical models for a detailed description of large amplitude internal solitary waves observed in the real ocean emerge implications of the results showing the complexity related to a possible inversion of sea surface manifestations of oceanic internal solitary waves into characteristics of the interior ocean dynamics are finally discussed

high angle wave instability and emergent shoreline shapes 2 wave climate analysis and comparisons to nature 1 recent research has revealed that the plan view evolution of a coast due to gradients in alongshore sediment transport is highly dependant upon the angles at which waves approach the shore giving rise to an instability in shoreline shape that can generate different types of naturally occurring coastal landforms including capes flying spits and alongshore sand waves this instability merely requires that alongshore sediment flux is maximized for a given deepwater wave angle a maximum that occurs between 35 and 50 for several common alongshore sediment transport formulae here we introduce metrics that sum over records of wave data to quantify the long term stability of wave climates and to investigate how wave climates change along a coast for long point a flying spit on the north shore of lake erie canada wave climate metrics suggest that unstable waves have shaped the spit and furthermore that smaller scale alongshore sand waves occur along the spit at the same locations where the wave climate becomes unstable a shoreline aligned along the trend of the carolina capes united states would be dominated by high angle waves numerical simulations driven by a comparable wave climate develop a similarly shaped cuspate coast local wave climates along these simulated capes and the carolina capes show similar trends shoreline reorientation and shadowing from neighboring capes causes most of the coast to experience locally stable wave climates despite regional instability

regional seismic stratigraphy and controls on the quaternary evolution of the cape hatteras region of the atlantic passive margin usa abstract seismic and core data combined with amino acid racemization and strontium isotope age data enable the definition of the quaternary stratigraphic framework and recognition of geologic controls on the development of the modern coastal system of north carolina u s a seven regionally continuous high amplitude reflections are defined which bound six seismic stratigraphic units consisting of multiple regionally discontinuous depositional sequences and parasequence sets and enable an understanding of the evolution of this margin data reveal the progressive eastward progradation and aggradation of the quaternary shelf the early pleistocene inner shelf occurs at a depth of ca 20 40 m beneath the western part of the modern estuarine system pamlico sound a mid to outer shelf lowstand terrace also early pleistocene with shelf sand ridge deposits comprising parasequence sets within a transgressive systems tract occurs at a deeper level ca 45 70 m beneath the modern barrier island system the outer banks and northern pamlico sound seismic and foraminiferal paleoenvironmental data from cores indicate the occurrence of lowstand strandplain shoreline deposits on the early to middle pleistocene shelf middle to late pleistocene deposits occur above a prominent unconformity and marine flooding surface that truncates underlying units and contain numerous filled fluvial valleys that are incised into the early and middle pleistocene deposits the stratigraphic framework suggests margin progradation and aggradation modified by an increase in the magnitude of sea level fluctuations during the middle to late pleistocene expressed as falling stage lowstand transgressive and highstand systems tracts thick stratigraphic sequences occur within the middle pleistocene section suggesting the occurrence of high capacity fluvial point sources debouching into the area from the west and north furthermore the antecedent topography plays a significant role in the evolution of the geomorphology and stratigraphy of this marginal system

numerical investigation of internal wave induced sediment motion resuspension versus entrainment we present numerical simulations of near bed instability induced by internal waves shoaling over topography using a model with an explicit representation of the sediment concentration we find that not all separation bubble bursting events lead to resuspension though all lead to significant transport out of the bottom boundary layer this transport can significantly enhance chemical exchange across the bottom boundary layer when resuspension occurs we find that it is largely due to two dimensional evolution of the separation bubble during the bursting process three dimensionalization occurs once the resuspended sediment cloud is transported out of the bottom boundary layer and hence redeposition is strongly influenced by three dimensional effects we derive a criterion for resuspension over a linearly sloping bottom in terms of two dimensionless parameters that encapsulate the sediment properties

internal waves and the generation of turbulence in the thermocline of a large lake high resolution thermistor chain data collected between 5 and 20 m in a large stratified freshwater lake lake constance at a water depth of 60 m reveal the frequent occurrence of large amplitude 2 i m vertical density inversions that indicate overturns in the pelagic thermoc1ine velocity data collected simultaneously with the temperature measurements indicate that the density inversions are mainly produced by shear instabilities a comparison between the timing of the passage of the basin scale internal kelvin wave and the density inversions demonstrates a pronounced phase relationship implying that the processes leading to the occurrence of turbulence and mixing are connected to the passage of the kelvin wave two different processes are identified during which density inversions were particularly common an increased number of density inversions and especially high dissipation rates of turbulent kinetic energy were observed when kelvin wave induced critical shear supported the generation of large kelvin helmholtz billows a particularly large number of density inversions was also associated with the passage of nonlinear high frequency waves of large amplitudes the density inversions typically occurred at the wave troughs which indicates breaking of these waves these observations indicate that self induced shear generated by the basin scale seiche and by high frequency internal waves leads to a significant amount of turbulence and mixing in the pelagic thermoc1ine

theory of radar imaging of internal waves radar images taken over ocean areas in particular those obtained by the synthetic aperture radar sar onboard the american seasat satellite in 19781 2 sometimes show features that seem to be surface manifestations of oceanic internal waves3 11 here i present a theory explaining the large radar signatures of internal waves in which the imaging is attributed to variations in the short scale surface roughness induced by current variations associated with internal waves

seismic signature of a permeable dual porosity layer of the key reservoir properties permeability seems to be the most elusive since the middle of the 90s various seismic attributes have been proposed to map permeability by using detailed analysis of the frequency content of reflected wavetrains some attributes are expected to show a relative increase of high frequency content with increased permeability other attributes assume the opposite actually both these trends were observed a possible explanation of these observations is here derived from an effective model of a permeable dual porosity layer enclosed by impermeable rocks for such a model the reflected wavetrain can be regarded as a sum of three components one of which is related to acoustic impedance contrasts another to extra compliance caused by p wave induced fluid flows between fractures and intergranular pores with a high aspect ratio and a third to the fluid flow induced inelastic attenuation in layered reservoirs all the components tend to be frequency dependent and the well k

shear and baroclinic energy flux on the summer new england shelf observations are presented of internal wave properties and energy fluxes through a site near the 70 m isobath on the new england shelf in late summer data collected from a shipboard adcp and microstructure profiler over a three week period and projected onto dynamic vertical modes reveals large variations in the magnitude and vertical structure of internal waves baroclinic energy and shear were primarily associated with low mode near inertial and semidiurnal waves and at times high frequency solibores the energies in each mode varied by factors from 2 to 10 over several days and were not significantly correlated with one another the associated shear variance was concentrated in the thermocline however the strength and vertical range of shear varied significantly throughout the research period and depended sensitively on both the magnitude and evolving vertical mode content of the wave field shear during the quasi two layer solibores was strong enough to temporarily lower the 4 m richardson number below the threshold for shear instability energy flux through the site came primarily from the mode 1 internal tide in both linear and nonlinear solibore forms the average energy flux from the first five baroclinic modes was 130 w m 21 a comparison of energy fluxes from each mode and locally measured average dissipation rates suggests that near inertial and high mode waves were generated near the experimental site

equivalent viscoelastic solids for heterogeneous fluid saturated porous rocks differenttheoreticalandlaboratorystudiesonthepropagation ofelasticwavesinrealrockshaveshownthatthepresenceofheterogeneities larger than the pore size but smaller than the predominant wavelengths mesoscopic scale heterogeneities may producesignificantattenuationandvelocitydispersioneffectson seismic waves such phenomena are known as mesoscopic effects and are caused by equilibration of wave induced fluid pressure gradients we propose a numerical upscaling procedure to obtain equivalent viscoelastic solids for heterogeneous fluidsaturated rocks it consists in simulating oscillatory compressibility and shear tests in the space frequency domain which enable us to obtain the equivalent complex undrained plane wave and shear moduli of the rock sample we assume that the behavior of the porous media obeys biot s equations and use a finiteelementproceduretoapproximatethesolutionsoftheassociated boundary value problems also because at mesoscopic scales rock parameter distributions are generally uncertain and of stochastic nature we propose applying the compressibility and sheartestsinamontecarlofashion thisfacilitatesthedefinition of average equivalent viscoelastic media by computing the moments of the equivalent phase velocities and inverse quality factors over a set of realizations of stochastic rock parameters described by a given spectral density distribution we analyzed the sensitivity of the mesoscopic effects to different kinds of heterogeneities in the rock and fluid properties using numerical examples also theapplicationofthemontecarloprocedureallowed us to determine the statistical properties of phase velocities and inverse quality factors for the particular case of quasi fractal heterogeneities

geological characteristics and spatial distribution of paleo inlet channels beneath the outer banks barrier islands north carolina usa abstract nearly 200 km of high resolution ground penetrating radar gpr data were acquired along the outer banks barrier island system of north carolina usa gpr data combined with lithofacies and biofacies data reveal multiple depositional facies including inlet channel flood tide delta overwash peat and inner shelf previously undocumented paleo inlet channels constitute a significant portion of the shallow geologic framework between oregon inlet and cape hatteras gpr data reveal the complex stratigraphy associated with multiple sequences of cut and fill within inlet channels two types of paleochannels non migrating and migrating were classified based on geometry and fill patterns sediments and foraminifera collected from vibracores were correlated to gpr data to define the regional shallow stratigraphic framework channel fill facies are characterized by clinoform packages sometimes bounded by erosional surfaces indicating variable sediment transport directions from the ocean and sound sides channels are incised into older flood tide delta deposits corresponding to older inlet activity when barriers existed further seaward flood tide delta deposits are capped with marsh peat and overwash units migrating inlet facies occur under the widest portions of the island whereas narrow portions of the island are underlain by the non migrating inlet facies or flood tide delta overwash facies this geologic geomorphic relationship is attributed to the successional stage of island evolution during transgression and sediment transport processes associated with the different inlet types the radar facies lithofacies and biofacies provide a comprehensive dataset that will permit more precise identification of barrier island facies in the geologic record

permeability effects on the seismic response of gas reservoirs summary in this work we analyse the role of permeability on the seismic response of sandstone reservoirs characterized by patchy gas water saturation we do this in the framework of johnson s model which is a generalization of white s seminal model allowing for patches of arbitrary geometry we first assess the seismic attenuation and velocity dispersion characteristics in response to wave induced fluid flow to this end we perform an exhaustive analysis of the sensitivity of attenuation and velocity dispersion of compressional body waves to permeability and explore the roles played by the johnson parameters t and s v which characterize the shape and size of the gas water patches our results indicate that within the typical frequency range of exploration seismic data this sensitivity may indeed be particularly strong for a variety of realistic and relevant scenarios next we extend our analysis to the corresponding effects on surface based reflection seismic data for two pertinent models of typical sandstone reservoirs in the case of softer and more porous formations and in the presence of relatively low levels of gas saturation we observe that the effects of permeability on seismic reflection data are indeed significant these prominent permeability effects prevail for normal incidence and non normal incidence seismic data and for a very wide range of sizes and shapes of the gas water patches for harder and less porous reservoirs the normal incidence seismic responses exhibit little or no sensitivity to permeability but the corresponding non normal incidence responses show a clear dependence on this parameter again especially so for low gas saturations the results of this study therefore suggest that for a range of fairly common and realistic conditions surface based seismic reflection data are indeed remarkably sensitive to the permeability of gas reservoirs and thus have the potential of providing corresponding first order constraints

on the dynamics of internal waves in a nonlinear weakly nonhydrostatic three layer ocean aspects of the dynamics of internal solitary waves evolving in a three layer ocean are investigated using a new numerical multilayer model that solves the nonlinear weakly nonhydrostatic boussinesq equations and uses high resolution in situ data the model applications refer to two different phenomena frequently observed in the real ocean which can be described using a three layer model rather than a two layer model in the first application the influence of the strength of a shallow seasonal thermocline superimposed on a two layer permanent stratification on the structure of internal solitary waves is studied it is found that while for small to medium wave amplitudes a decrease in the strength of the thermocline yields an increase in the simulated wavelengths for large wave amplitudes this dependence is no longer monotonic in particular in the limiting case of a vanishing thermocline first mode internal solitary wave solutions of the three layer numerical model tend to the analytical internal solitary wave solutions of the miyata equations a two layer model in which the full nonlinearity of the shallow water theory up to first order phase dispersion is retained in the second application that refers particularly to high resolution observations made north and south of the strait of messina in the eurafrican mediterranean basin the generation of internal solitary waves by the evolution of surface and subsurface water jets is investigated the analysis of the in situ data shows in fact that from very energetic surface and subsurface jet like disturbances subject to strong turbulent mixing internal solitary waves emerge as robust quasi nondissipative oceanic features idealized flow conditions aimed at approximating possible initial stages of the observed water jets are imposed to force our numerical model in general good agreement is found between characteristics of observed and simulated wave fields our investigation identifies the observed water jets as peculiar features of the complex ocean dynamics and suggests that layered numerical models can represent helpful tools in understanding fundamental processes inherent in their intricate dynamics

simulating the evolution of coastal morphology and stratigraphy with a new morphological behaviour model geombest abstract a new morphological behaviour model is used to simulate evolution of coastal morphology associated with cross shore translations of the shoreface barrier and estuary the model encapsulates qualitative principles drawn from established geological concepts that are parameterized to provide quantitative predictions of morphological change on geological time scales order 10 3 years as well as shorter time scales applicable for long term coastal management order 10 1 to 10 2 years changes in sea level and sediment volume within the shoreface barrier and estuary drive the model behaviour further parameters defining substrate erodibility sediment composition and time dependent shoreface response constrain the evolution of the shoreface towards an equilibrium profile results from numerical experiments are presented for the low gradient autochthonous setting of north carolina and the steep allochthonous setting of the washington shelf simulations in the currituck region of north carolina examined the influence of sediment supply substrate composition and substrate erodibility on barrier transgression results demonstrate that the presence of a lithified substrate reduces the rate of barrier transgression compared to scenarios where an erodible sand rich substrate exists simulations of the washington coast 20 km north of the columbia river confirmed that the model can reproduce complex stratigraphy involving regressive and transgressive phases of coastal evolution results suggest that the first major addition of sediment to the shelf occurred around 12 900 years ago and resulted from the rapid addition of sediment volume from the columbia river attributed to the missoula floods this was followed by a period where little or no sediment was added 12 400 9100 bp and a third period when most sediment was added to the shelf 9100 bp to present from the columbia river comparing results from each setting demonstrates an indirect control that substrate slope has on shoreface transgression rates shoreface transgression is shown to be sensitive to the rate of estuarine sedimentation with the sensitivity increasing as substrate slope decreases

internal waves in the strait of messina studied by a numerical model and synthetic aperture radar images from the ers 1 2 satellites a new numerical two layer model is presented which describes the generation of internal tidal bores and their disintegration into internal solitary waves in the strait of messina this model is used to explain observations made by the synthetic aperture radar sar from the european remote sensing satellites ers 1 and ers 2 the analysis of available ers 1 2 sar data of the strait of messina and adjacent sea areas show that 1 northward as well as southward propagating internal waves are generated in the strait of messina 2 southward propagating internal waves are observed more frequently than northward propagating internal waves 3 sea surface manifestations of southward as well as northward propagating internal waves are stronger during periods where a strong seasonal thermocline is known to be present 4 southward propagating internal bores are released from the sill between 1 and 5 hours after maximum northward tidal flow and northward propagating internal bores are released between 2 and 6 hours after maximum southward tidal flow and 5 the spatial separation between the first two internal solitary waves of southward propagating wave trains is smaller in the period from july to september than in the period from october to june the numerical two layer model is a composite of two models consisting of 1 a hydrostatic generation model which describes the dynamics of the water masses in the region close to the strait s sill where internal bores are generated and 2 a weakly nonhydrostatic propagation model which describes the dynamics of the water masses outside of the sill region where internal bores may disintegrate into internal solitary waves due to a technique for movable lateral boundaries the generation model is capable of simulating the dynamics of a lower layer that may intersect the bottom topography the proposed generation propagation model depends on one space variable only but it retains several features of a fully three dimensional model by including a realistic channel depth and a realistic channel width it is driven by semidiurnal tidal oscillations of the sea level at the two open boundaries of the model domain numerical simulations elucidate several observed characteristics of the internal wave field in the strait of messina such as north south asymmetry times of release of the internal bores from the strait s sill propagation speeds and spatial separations between the first two solitary waves of internal wave trains

on the discrimination of radar signatures of atmospheric gravity waves and oceanic internal waves on synthetic aperture radar images of the sea surface synthetic aperture radar sar images acquired over the ocean frequently show sea wave like patterns that have wavelengths well above those of ocean surface waves and that are sea surface signatures of oceanic internal waves oiws or of atmospheric gravity waves agws however it is often difficult to decide whether they result from the first or the second kind of waves which has led many investigators to misinterpret sar images of the sea surface based on solitary wave and radar imaging theories of agws and oiws we present criteria that help distinguish between them however there are cases where these criteria which are based solely on the shape and structure of the features visible on the sar images yield ambiguous results in these cases one must resort to additional information on the generation of agws and oiws which are listed in this paper

reservoir permeability from seismic attribute analysis in case of porous fluid saturated medium the biot s poroelasticity theory predicts a movement of the pore fluid relative to the skeleton on seismic wave propagation through the medium this phenomenon opens an opportunity for investigation of the flow properties of the hydrocarbon saturated reservoirs it is well known that relative fluid movement becomes negligible at seismic frequencies if porous material is homogeneous and well cemented in this case the theory predicts an underestimated seismic wave velocity dispersion and attenuation based on biot s theory helle et al 2003 have numerically demonstrated the substantial effects on both velocity and attenuation by heterogeneous permeability and saturation in the rocks besides fluid flow effect the effects of scattering gurevich et al 1997 play very important role in case of finely layered porous rocks and heterogeneous fluid saturation we have used both fluid flow and scattering effects to derive a frequency dependent seismic attribute which is proportional to fluid mobility and applied it for analysis of reservoir permeability

fast inversion of formation permeability from stoneley wave logs using a simplified biot rosenbaum model this paper describes a fast algorithm for estimating formation permeability from stoneley wave logs the procedure uses a simplified biot rosenbaum model formulation the input to the inversion is the stoneley wave spectral amplitudes at each receiver position the bore hole fluid properties velocity and density the borehole caliper log the formation density and porosity from log data and the compressional and shear velocities for the interval of interest the model uses the borehole caliper and elastic properties to compute the stoneley wave excitation that is predicted amplitude without permeability effects as a function of frequency and the porosity and permeability to compute the fluid flow amplitude reduction this method also uses a reference depth of known permeability and compares amplitude variations at other depths relative to the reference depth the permeability value obtained from the inversion represents the best fit over all receivers and all relevant frequencies a processing example is shown to demonstrate the ability of this technique to extract formation permeability from stoneley wave logs

seismic attenuation due to wave induced flow analytical expressions for three p wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework two of the models concern wave induced flow due to heterogeneity in the elastic moduli at mesoscopic scales scales greater than grain sizes but smaller than wavelengths in the first model the heterogeneity is due to lithological variations e g mixtures of sands and clays with a single fluid saturating all the pores in the second model a single uniform lithology is saturated in mesoscopic patches by two immiscible fluids e g air and water in the third model the heterogeneity is at microscopic grain scales broken grain contacts and or micro cracks in the grains and the associated fluid response corresponds to squirt flow the model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus crack porosity and or frequency is reduced to zero it is shown that squirt flow is incapable of explaining the measured level of loss 10 sup 2 q sup 1 10 sup 1 within the seismic band of frequencies 1 to 10 sup 4 hz however either of the two mesoscopic scale models easily produce enough attenuation to explain the field data

two dimensional time dependent hurricane overwash and erosion modeling at santa rosa island abstract a 2dh numerical model which is capable of computing nearshore circulation and morphodynamics including dune erosion breaching and overwash is used to simulate overwash caused by hurricane ivan 2004 on a barrier island the model is forced using parametric wave and surge time series based on field data and large scale numerical model results the model predicted beach face and dune erosion reasonably well as well as the development of washover fans furthermore the model demonstrated considerable quantitative skill upwards of 66 of variance explained maximum bias 0 21 m in hindcasting the post storm shape and elevation of the subaerial barrier island when a sheet flow sediment transport limiter was applied the prediction skill ranged between 0 66 and 0 77 in a series of sensitivity tests in which several hydraulic forcing parameters were varied the sensitivity studies showed that the variations in the incident wave height and wave period affected the entire simulated island morphology while variations in the surge level gradient between the ocean and back barrier bay affected the amount of deposition on the back barrier and in the back barrier bay the model sensitivity to the sheet flow sediment transport limiter which served as a proxy for unknown factors controlling the resistance to erosion was significantly greater than the sensitivity to the hydraulic forcing parameters if no limiter was applied the simulated morphological response of the barrier island was an order of magnitude greater than the measured morphological response

seasonal variation of solitary wave properties in lake constance 1 the properties of internal solitary waves isws depend on the stratification of the water body in most climatic regions the stratification in lakes and oceans varies during the year and hence the properties of the isws can also be expected to change over the seasons on the basis of a long term temperature time series recorded over 6 years this paper investigates seasonal changes in the characteristic properties of isws in lake uberlingen a subbasin of lake constance a large number of isws with amplitudes ranging from 3 m to 30 m were identified more than 15 of the leading isws of a wave train were associated with density inversions often indicating shear instabilities or trapped cores for all waves the propagation depth and the value of a nonlinearity index nlp providing the degree of nonlinearity were determined propagation depth being the rest height of the isotherm undergoing maximum displacement and nlp the ratio between wave amplitude and propagation depth the index nlp was found to be a good parameter for predicting the occurrence of inversions the statistical analysis of the wave properties derived from the observations revealed that the degree of nonlinearity of the isws changes with season complementary to the statistical analysis the seasonally averaged isw properties were compared with wave prototypes obtained numerically from the dubreil jacotin long djl and the stratified korteweg devries kdv models the simulations indicate that the typical stratification and its seasonal variation are responsible for the degree and the seasonality of nonlinearity of the isws

large amplitude internal solitary waves in the north equatorial countercurrent the analysis of high resolution oceanographic data referring to velocity measurements carried out by means of a vessel mounted acoustic doppler current profiler on 12 november 2000 in the equatorial atlantic at 44 w between 4 5 and 6 n reveals the presence of three large amplitude internal solitary waves superimposed on the velocity field associated with the north equatorial countercurrent necc these waves were found in the deep ocean more than 500 km off the continental shelf and far from regions of topographic variations they propagated toward the north northeast strongly inclined with respect to the main axis of the necc and perpendicular to the brazilian shelf as well as to the north brazil current and were characterized by maximum horizontal velocities of about 2 m s 1 and maximum vertical velocities of about 20 cm s 1 the large magnitudes of the measured velocities indicate that the observed waves represent disturbances evolving in a strongly stratified ocean the distance separating the waves about 70 km indicates that the observed features cannot be considered as elements of a single train of internal solitary waves the waves consist instead of truly disconnected pulselike intense solitary disturbances this behavior which strongly differs from that typically observed for trains of tidally generated internal solitary waves indicates that different mechanisms were possibly involved in their generation and or evolution

dynamic permeability of porous rocks and its seismic signatures in inhomogeneous porous media the mechanism of wave induced fluid flow causes significant attenuation and dispersion of seismic waves in connection with this phenomenon we study the impact of spatial permeability fluctuations on the dynamic behavior of porous materials this heterogeneous permeability distribution further complicates the ongoing efforts to extract flow permeability from seismic data based on the method of statistical smoothing applied to biot s equations of poroelasticity we derive models for the dynamic equivalent permeability in 1d and 3d randomly inhomogeneous media the low frequency limit of this permeability corresponds to the flow permeability governing fluid flow in porous media we incorporate the dynamic equivalent permeability model into the expressions for attenuation and dispersion of p waves also obtained by the method of smoothing the resulting attenuation and dispersion model is confirmed by numerical computations in randomly layered poroelastic structures the results suggest that the effect of wave induced fluid flow can be observed in a broader frequency range than previously thought the peak attenuation shifts along the frequency axis depending on the strength of the permeability fluctuations we conclude that estimation of flow permeability from seismic attenuation is only possible if permeability fluctuations are properly accounted for

phase shifted based numerical method for modeling frequency dependent effects on seismic reflections the significant velocity dispersion and attenuation has often been observed when seismic waves propagate in fluid saturated porous rocks both the magnitude and variation features of the velocity dispersion and attenuation are frequency dependent and related closely to the physical properties of the fluid saturated porous rocks to explore the effects of frequency dependent dispersion and attenuation on the seismic responses in this work we present a numerical method for seismic data modeling based on the diffusive and viscous wave equation dvwe which introduces the poroelastic theory and takes into account diffusive and viscous attenuation in diffusive viscous theory we derive a phase shift wave extrapolation algorithm in frequencywavenumber domain for implementing the dvwe based simulation method that can handle the simultaneous lateral variations in velocity diffusive coefficient and viscosity then we design a distributary channels model in which a hydrocarbon saturated sand reservoir is embedded in one of the channels next we calculated the synthetic seismic data to analytically and comparatively illustrate the seismic frequency dependent behaviors related to the hydrocarbon saturated reservoir by employing dvwe based and conventional acoustic wave equation awe based method respectively the results of the synthetic seismic data delineate the intrinsic energy loss phase delay lower instantaneous dominant frequency and narrower bandwidth due to the frequency dependent dispersion and attenuation when seismic wave travels through the hydrocarbon saturated reservoir the numerical modeling method is expected to contribute to improve the understanding of the features and mechanism of the seismic frequency dependent effects resulted from the hydrocarbon saturated porous rocks

rollover drowning and discontinuous retreat distinct modes of barrier response to sea level rise arising from a simple morphodynamic model we construct a simple morphodynamic model to investigate the long term dynamic evolution of a coastal barrier system experiencing sea level rise using a simplified barrier geometry the model includes a dynamic shoreface profile that can be out of equilibrium and explicitly treats barrier sediment overwash as a flux with barrier behavior primarily controlled by the maximum potential overwash flux and the rate of shoreface response the modeled barrier system demonstrates four primary behaviors height drowning width drowning constant landward retreat and a periodic retreat height drowning occurs when overwash fluxes are insufficient to maintain the landward migration rate required to keep pace with sea level rise on the other hand width drowning occurs when the shoreface response rate is insufficient to maintain the barrier geometry during overwash driven landward migration during periodic barrier retreat the barrier experiences oscillating periods of rapid overwash followed by periods of relative stability as the shoreface resteepens this periodic retreat which occurs even with a constant sea level rise rate arises when overwash rates and shoreface response rates are large and of similar magnitude we explore the occurrence of these behaviors across a wide range of parameter values and find that in addition to the maximum overwash flux and the shoreface response rate barrier response can be particularly sensitive to the sea level rise rate and back barrier lagoon slope overall our findings contrast with previous research which has primarily associated complex barrier behavior with changes in external forcing such as sea level rise rate sediment supply or back barrier geometry

can barrier islands survive sea level rise quantifying the relative role of tidal inlets and overwash deposition barrier island response to sea level rise depends on their ability to transgress and move sediment onto and behind the barrier either through flood tidal delta deposition or via overwash our understanding of these processes over decadal or longer timescales however is limited here we use a recently developed barrier island model brie to better understand the interplay between tidal dynamics overwash fluxes and sea level rise on barrier coasts and barrier island stratigraphy model results suggest that in microtidal environments with large alongshore sediment transport fluxes tidal inlets are ephemeral and migrate rapidly these conditions lead to effective deposition of flood tidal deltas and allow inlets to constitute most of the landward sediment flux whether barrier islands can survive sea level rise depends on the combined landward sediment flux from overwash and flood tidal delta deposition likely making barrier islands with artificially stabilized inlets via jetty construction or maintenance dredging more vulnerable to sea level rise

barrier dynamics and landward migration with holocene sea level rise barrier beaches islands and spits have become the subject of mounting interest1 2 due to human development on these land forms it is commonly thought that barrier beaches continuously migrate landward in response to sea level rise often by over wash processes maintain mass through time and that these processes are occurring at a rate commensurate with human 100 yr time frames while some barriers are naturally migrating quite rapidly3 4 other barriers decidedly are not here i present data which illustrate that many us atlantic coast barriers are not evolving over the short term in accordance with generally accepted hypotheses and argue that the presumed norm may actually be the exception

a long term decadal scale evolution model for microtidal barrier systems abstract a model is presented to simulate the long term decadal evolution of microtidal spit barrier systems the model has been derived from the analysis of coastal processes taking place along the trabucador la banya complex in the ebro delta spanish mediterranean coast it is composed of two submodels to simulate the evolution of the seaside and bayside barrier shorelines the outer coast submodel is of the one line type but formulated in curvilinear coordinates to reproduce the evolution of strongly curved coasts which is a common configuration for spits the model makes use of a long term parameterization of the longshore sediment transport rate which is formulated in terms of a morphological wave and a local transport constant the inner coast submodel is based on a morphological equilibrium approach it considers the overwash transport to be the dominant driving term contributing to the sediment budget of the inner coast it makes use of the concept of critical barrier width to estimate the conditions under which overwash is able to contribute to bayside shoreline accretion the model has been verified calibrated for the trabucador la banya system and it has been used to simulate its evolution under different climatic scenarios

finite frequency kernels for wave propagation in porous media based upon adjoint methods s u m m a r y we determine finite frequency kernels for wave propagation in porous media based upon adjoint methods these sensitivity kernels may be obtained based upon two numerical simulations for each source one calculation for the current model and a second adjoint calculation that uses time reversed signals at the receivers as simultaneous fictitious sources the adjoint equations for a porous medium are identical to the usual biot equations with the exception of the adjoint source term which involves time reversed measurements of the differences between simulations and data isotropic poroelastic wave propagation is governed by eight primary model parameters which appear in the original biot equations these parameters include four moduli the shear modulus of the frame plus three bulk moduli we consider two alternative parameterizations one involving density normalized moduli corresponding to squared wave speeds and a second involving the poroelastic shear and compressional wave speeds the alternative parameterizations lead to density sensitivity kernels that are small reflecting the fact that the traveltime of a poroelastic wave is governed by wave speed not density we systematically investigate and illustrate the sensitivity of the fast and slow compressional waves and the shear wave to the poroelastic model parameters using a 2 d spectral element method the poroelastic sensitivity kernels presented herein form the basis of tomographic imaging and inversion in porous media

seismic signatures of permeability in heterogeneous porous media in homogeneous poroelastic systems the permeability tensor practically does not influence propagating seismic waves in the low frequency range 0 1000 hz see e g schmitt 1989 gelinsky and shapiro 1996 in this paper we show that this situation changes in heterogeneous systems such as layered or fractured sediments due to the heterogeneities of poroelastic structures the attenuation of p waves is influenced by the permeability in an enhanced way we show however that such a seismic permeability can differ very strongly from the hydraulic permeability

propagation speeds of strongly nonlinear near surface internal waves in the strait of georgia 1 a novel aerial observational method for studying internal features in the coastal ocean is developed and tested in a study of large nonlinear internal solitary like waves photogrammetrically rectified oblique photo images from a circling aircraft are used to track a number of internal wave packets for periods of up to one hour in the strait of georgia british columbia canada combining these sequences with coincident water column data allows us to obtain a more complete view of the spatial structure of internal waves highly accurate measurements of wave propagation speeds and directions are possible the applicability of various weakly nonlinear theories in modeling propagation of the observed large amplitude waves is tested the measured wave speeds enable us to differentiate between classic internal wave models the linear kdv korteweg de vries and bo benjamin ono models are applied with and without background shear after background shear effects are included it is found that a continuously stratified bo equation can predict propagation speeds within observational error and that this is not true for other theories the technique may be useful in future studies of oblique internal wave interactions

seismoacoustic signatures of fracture connectivity wave induced fluid flow wiff between fractures and the embedding matrix as well as within connected fractures tends to produce significant seismic attenuation and velocity dispersion while wiff between fractures and matrix is well understood the corresponding effects related to fracture connectivity and the characteristics of the energy dissipation due to flow within fractures are largely unexplored in this work we use oscillatory relaxation simulations based on the quasi static poroelastic equations to study these phenomena we first consider synthetic rock samples containing connected and unconnected fractures and compute the corresponding attenuation and phase velocity we also determine the relative fluid displacement and pressure fields in order to gain insight into the physical processes involved in the two manifestations of wiff in fractured media to quantify the contributions of the two wiff mechanisms to the total seismic attenuation we compute the spatial distribution of the local energy dissipation finally we perform an exhaustive sensitivity analysis to study the role played by different characteristics of fracture networks on the seismic signatures we show that in the presence of connected fractures both p wave attenuation and phase velocity are sensitive to some key characteristics of the probed medium notably to the lengths permeabilities and intersection angles of the fractures as well as to the overall degree of connectivity of the fracture network this in turn indicates that a deeper understanding of these two manifestations of wiff in fractured media may eventually allow for the extraction of some of these properties from seismic data

complexities in barrier island response to sea level rise insights from numerical model experiments north carolina outer banks using a morphological behavior model to conduct sensitivity experiments weinvestigate the sea level rise response of a complex coastal environment to changes ina variety of factors experiments reveal that substrate composition followed in rankorder by substrate slope sea level rise rate and sediment supply rate are the mostimportant factors in determining barrier island response to sea level rise we find thatgeomorphic threshold crossing defined as a change in state e g from landward migratingto drowning that is irreversible over decadal to millennial time scales is most likely tooccur in muddy coastal systems where the combination of substrate composition depth dependent limitations on shoreface response rates and substrate erodibility mayprevent sand from being liberated rapidly enough or in sufficient quantity to maintain asubaerial barrier analyses indicate that factors affecting sediment availability such aslow substrate sand proportions and high sediment loss rates cause a barrier to migratelandward along a trajectory having a lower slope than average barrier island slope therebydefining an effective barrier island slope other factors being equal such barrierswill tend to be smaller and associated with a more deeply incised shoreface therebyrequiring less migration per sea level rise increment to liberate sufficient sand to maintainsubaerial exposure than larger less incised barriers as a result the evolution of larger lessincised barriers is more likely to be limited by shoreface erosion rates or substrateerodibility making them more prone to disintegration related to increasing sea level riserates than smaller more incised barriers thus the small deeply incised north carolinabarriers are likely to persist in the near term although their long term fate is less certainbecause of the low substrate slopes that will soon be encountered in aggregate results point to the importance of system history e g previous slopes sediment budgets etc in determining migration trajectories and therefore how a barrier island will respondto sea level rise although simple analytical calculations may predict barrier responsein simplified coastal environments e g constant slope constant sea level rise rate etc our model experiments demonstrate that morphological behavior modeling is necessary toprovide critical insights regarding changes that may occur in environments havingcomplex geometries especially when multiple parameters change simultaneously

p wave seismic attenuation by slow wave diffusion effects of inhomogeneous rock properties recent research has established that the dominant p wave attenuation mechanism in reservoir rocks at seismic frequencies is because of wave induced fluid flow mesoscopic loss the p wave induces a fluid pressure difference at mesoscopic scale inhomogeneities larger than the pore size but smaller than the wavelength typically tens of centimeters and generates fluid flow and slow diffusion biot waves continuity of pore pressure is achieved by energy conversion to slow p waves which diffuse away from the interfaces in this context we consider a periodically stratified medium and investigate the amount of attenuation and velocity dispersion caused by different types of heterogeneities in the rock properties namely porosity grain and frame moduli permeability and fluid properties the most effective loss mechanisms result from porosity variations and partial saturation where one of the fluids is very stiff and the other is very compliant such as a highly permeable sandstone at shallow depths saturated with small amounts of gas around 10 saturation and water grain and frame moduli variations are the next cause of attenuation the relaxation peak moves towards low frequencies as the background permeability decreases and the viscosity and thickness of the layers increase the analysis indicates in which cases the seismic band is in the relaxed regime and therefore when the gassmann equation can yield a good approximation to the wave velocity

time spatial variability observed in velocity of propagation of the internal bore in the strait of gibraltar 1 some aspects of the time spatial variability of the phase speed of the internal bore generated almost every tidal cycle in camarinal sill are revised using a set of high resolution experimental data collected in two different positions of the strait during may 2003 this variability is mainly driven by the intense tidal currents comparable with the intrinsic propagation velocity of the first mode baroclinic bore it is shown that the importance of the diurnal tide in the strait of gibraltar induces a considerable diurnal inequality on the bore velocity with an observed maximum difference of 0 7 ms 1 between the speed of two consecutives bores propagating along the eastern part of the strait a regularly spatial pattern has been also found the internal bore reaches its maximum velocity in tarifa narrows a theoretical estimation predicts an extreme phase speed of 2 6 ms 1 during our period of study

fluid pressure diffusion effects on the excess compliance matrix of porous rocks containing aligned fractures the presence of sets of open fractures is common in most reservoirs and they exert important controls on the reservoir permeability as fractures act as preferential pathways for fluid flow therefore the correct characterization of fracture sets in fluid saturated rocks is of great practical importance in this context the inversion of fracture characteristics from seismic data is promising since their signatures are sensitive to a wide range of pertinent fracture parameters such as density orientation and fluid infill the most commonly used inversion schemes are based on the classical linear slip theory lst in which the effects of the fractures are represented by a real valued diagonal excess compliance matrix to account for the effects of wave induced fluid pressure diffusion fpd between fractures and their embedding background several authors have shown that this matrix should be complex valued and frequency dependent however these approaches neglect the effects of fpd on the coupling between orthogonal deformations of the rock with this motivation we considered a fracture model based on a sequence of alternating poroelastic layers of finite thickness representing the background and the fractures and derived analytical expressions for the corresponding excess compliance matrix we evaluated this matrix for a wide range of background parameters to quantify the magnitude of its coefficients not accounted for by the classical lst and to determine how they are affected by fpd we estimated the relative errors in the computation of anisotropic seismic velocity and attenuation associated with the lst approach our analysis showed that in some cases considering the simplified excess compliance matrix may lead to an incorrect representation of the anisotropic response of the probed fractured rock

seismic characterization of thin beds containing patchy carbon dioxide brine distributions a study based on numerical simulations we studied the seismic attenuation and velocity dispersion effects produced by wave induced fluid flow in weakly consolidated sandstones containing patchy carbon dioxide co2 brine distributions the analysis also focuses on the velocity pushdown because of the presence of this gas as well as on the role of the wave induced fluid flow mesoscopic effects on the amplitude variation with angle ava seismic response of thin layers containing co2 such as those found at the utsira sand sleipner field offshore norway we found that this loss mechanism may play a key role on conventional surface seismic data suggesting that further data analysis may provide useful information on the characteristics of the fluid distributions in these environments numerical experiments let us observe that although mesoscopic effects can be very significant in this kind of media the seismic response of a given isolated thin layer computed considering such effects is very similar to that of a homogeneous elastic thin layer with a compressional velocity equal to that of the original porous rock averaged in the effective data bandwidth this suggests that the thin bed prestack spectral inversion method published by the authors could be used to estimate representative compressional velocities and layer thicknesses in these environments in effect results using realistic synthetic prestack seismic data show that isolated co2bearing thin beds can be characterized in terms of their thicknesses and representative compressional velocities this information can be qualitatively related to co2 saturations and volumes thus the prestack spectral inversion method could find application in the monitoring of the evolution of co2 plumes at injection sites similar to that at the sleipner field

geometry of tidal inlet systems a key factor for the net sediment transport in tidal inlets the net transport of sediment between the back barrier basin and the sea is an important process for determining the stability of tidal inlet systems earlier studies showed that in a short basin tidal flats favor peak ebb currents stronger than peak flood currents implying export of coarse sediment while shallow basins favor stronger flood currents the new elements considered in this study are 1 arbitrary basin lengths 2 a narrow inlet that connects the basin to the sea 3 an asymmetric tidal forcing and 4 radiation damping the objective is to gain fundamental insight in how the geometry of a tidal inlet system affects the net sand transport in a tidal inlet for this purpose a width averaged and depth averaged analytical model was constructed it is found that the length of a back barrier basin controls the effect that nonlinear hydrodynamic processes have on the tidal asymmetry and consequently controls whether the currents in the inlet are flood dominant or ebb dominant furthermore the cross sectional area of the inlet controls the ratio between the net sediment transports that results from tidal asymmetry and that caused by the interaction of the principal tide with the residual current finally it is shown that the effect of an asymmetric tidal forcing on the net sand transport depends on the length of the back barrier basin with respect to the tidal wavelength in that basin

low frequency reflections from a thin layer with high attenuation caused by interlayer flow the 1d interlayer flow or white s model is based on biot s theory of poroelasticity and explains low frequency seismic wave attenuation in partially saturated rocks by wave induced fluid flow between two alternating poroelastic layers each saturated with a different fluid we have developed approximate equations for both the minimum possible value of the quality factor q and the corresponding fluid saturation for which q is minimal the simple approximate equations provide a better insight into the dependence of q on basic petrophysical parameters and allow for a fast assessment of the minimal value of q the approximation is valid for a wide range of realistic petrophysical parameter values for sandstones partially saturated with gas and water and shows that values of q can be as small as two we ap plied the interlayer flow model to study the reflection coefficient of a thin i e between 6 and 11 times smaller than the incident wavelength layer that is partially saturated with gas and water

seismic wave attenuation and dispersion due to wave induced fluid flow in rocks with strong permeability fluctuations oscillatory fluid movements in heterogeneous porous rocks induced by seismic waves cause dissipation of wave field energy the resulting seismic signature depends not only on the rock compressibility distribution but also on a statistically averaged permeability this so called equivalent seismic permeability does not however coincide with the respective equivalent flow permeability while this issue has been analyzed for one dimensional 1d media the corresponding two dimensional 2d and three dimensional 3d cases remain unexplored in this work this topic is analyzed for 2d random medium realizations having strong permeability fluctuations with this objective oscillatory compressibility simulations based on the quasi static poroelasticity equations are performed numerical analysis shows that strong permeability fluctuations diminish the magnitude of attenuation and velocity dispersion due to fluid flow while the frequency range where these effects are significant gets broader by comparing the acoustic responses obtained using different permeability averages it is also shown that at very low frequencies the equivalent seismic permeability is similar to the equivalent flow permeability while for very high frequencies this parameter approaches the arithmetic average of the permeability field these seemingly generic findings have potentially important implications with regard to the estimation of equivalent flow permeability from seismic data

poroelastic analysis of permeability effects in thinly layered porous media the mechanism of wave induced fluid flow which causes significant attenuation and dispersion of seismic waves in heterogeneous porous media opens a potential opportunity to estimate fluid mobility properties from seismic data however the permeability effects on seismic data vary for different reservoir environments so rules of thumb are difficult to establish two types of reservoir models were selected one represents shallow unconsolidated low impedance reservoirs the other represents deep consolidated high impedance reservoirs using analytic equations and wave propagation numerical studies permeability effects were investigated on the magnitude and phase of normal incident reflection coefficients from an interface between an upper nondispersive medium and a lower thinly layered porous medium the study found that permeability can affect reflection amplitudes significantly for high impedance reservoirs magnitude of the reflection coefficient decreases when permeability increases however for low impedance reservoirs reflection magnitude increases as permeability increases

seismic attenuation due to patchy saturation 1 in porous rocks saturated in patches by two immiscible fluids seismic compression causes the fluid with the larger bulk modulus to respond with a larger change in fluid pressure than the fluid with the smaller bulk modulus which results in fluid movement and seismic attenuation for virtual rock samples having fluid distributions obtained using the invasion percolation model attenuation is determined using finite difference numerical experiments based on the laws of poroelasticity analytical models are also proposed to explain the numerical results when oil invades water the equilibration is controlled by the geometry of the invading oil which has a narrow range of small diffusion lengths resulting in a single relaxation frequency at high frequencies and not much seismic band attenuation when water invades oil the defending oil controls the equilibration and a power law emerges for how attenuation varies with frequency due to the fractal nature of how saturation is varying with scale in the defending oil for air invading water the geometry of the defending water controls the equilibration and a large amount of attenuation is observed over a wide range of frequencies including the seismic band due to the wide range in water patch sizes however when water invades air the narrow fingers of invading water control the equilibration and there is a single relaxation frequency at high frequencies that does not result in much seismic band attenuation

numerical analysis of wave induced fluid flow effects on seismic data application to monitoring of co2 storage at the sleipner field 1 in this work we analyze how patchy distributions of co2 and brine within sand reservoirs may lead to significant attenuation and velocity dispersion effects which in turn may have a profound impact on surface seismic data the ultimate goal of this paper is to contribute to the understanding of these processes within the framework of the seismic monitoring of co2 sequestration a key strategy to mitigate global warming we first carry out a monte carlo analysis to study the statistical behavior of attenuation and velocity dispersion of compressional waves traveling through rocks with properties similar to those at the utsira sand sleipner field containing quasi fractal patchy distributions of co2 and brine these results show that the mean patch size and co2 saturation play key roles in the observed wave induced fluid flow effects the latter can be remarkably important when co2 concentrations are low and mean patch sizes are relatively large to analyze these effects on the corresponding surface seismic data we perform numerical simulations of wave propagation considering reservoir models and co2 accumulation patterns similar to the co2 injection site in the sleipner field these numerical experiments suggest that wave induced fluid flow effects may produce changes in the reservoir s seismic response modifying significantly the main seismic attributes usually employed in the characterization of these environments consequently the determination of the nature of the fluid distributions as well as the proper modeling of the seismic data constitute important aspects that should not be ignored in the seismic monitoring of co2 sequestration problems

permeability dependence of seismic amplitudes can permeability be determined from seismic data this question has been around since maurice biot working for shell in the 1950s introduced the idea that seismic waves induce fluid flow in saturated rocks due to fluid pressure equilibration between the peaks and troughs of a compressional wave or due to grain accelerations in the case of a shear wave biot 1956 established a frequency dependent analytical relation between permeability and seismic attenuation however laboratory sonic log crosswell vsp and surface seismic have all demonstrated that biot s predictions often greatly underestimate the measured levels of attenuation dramatically so for the lower frequency measurements yet if an unresolved link truly exists between seismic amplitudes and permeability the potential benefit to the oil industry is enormous for this reason the department of energy doe brought together 15 participants from industry national laboratories and universities to concentrate for two days on whether permeability information is conceivably contained in and retrievable from seismic data the present article represents much of the workshop discussion which took place 5 6 december 2001 in berkeley california but is not strictly limited to it not all connections between hydrological and seismic properties are considered three dimensional seismic images and time lapse seismic monitoring are routinely used by reservoir engineers in constructing and constraining their reservoir model such imaging applications of seismic surveys to hydrological modeling are not discussed furthermore in fractured reservoirs it is reasonable to postulate that any locally determined seismic anisotropy defines a symmetry class for the geologic material that must also be satisfied by the permeability tensor neither are such material symmetry constraints discussed the focus here is only on whether the permeability of the rocks through which seismic waves propagate directly influences the decay of the wave amplitudes with distance key to addressing this question is an up to date discussion of the likely attenuation

sensitivity of 3d 3c synthetic seismograms to anisotropic attenuation and velocity in reservoir models abstractanisotropic attenuation in fluid saturated reservoirs with high fracture density may be diagnostic for reservoir characterization wave induced mesoscale fluid flow is considered to be the major cause of intrinsic attenuation at exploration seismic frequencies we perform tests of the sensitivity of anisotropic attenuation and velocity to reservoir properties in fractured hti media based on the mesoscale fluid flow attenuation mechanism the viscoelastic t matrix a unified effective medium theory of global and local fluid flow mechanisms is used to compute frequency dependent anisotropic attenuation and velocity for ranges of reservoir properties including fracture density orientation fracture aspect ratio fluid type and permeability the 3d 3c staggered grid finite difference anisotropic viscoelastic modeling with a crank nicolson scheme is used to generate seismograms using the frequency dependent velocity and attenuation computed by the viscoelastic t matrix a standard linear solid mo

squirt flow in fully saturated rocks we estimate velocity frequency dispersion and attenuation in fully saturated rocks by employing the squirt flow mechanism of solid fluid interaction in this model pore fluid is squeezed from thin soft cracks into the surrounding large pores information about the compliance of these soft cracks at low confining pressures is extracted from high pressure velocity data the frequency dependence of squirt induced pressure in the soft cracks is linked with the porosity and permeability of the soft pore space and the characteristic squirt flow length these unknown parameters are combined into one expression that is assumed to be a fundamental rock property that does not depend on frequency the appropriate value of this expression for a given rock can be found by matching our theoretical predictions with the experimental measurements of attenuation or velocity the low frequency velocity limits as given by our model are identical to those predicted by gassmann s formula the high frequency limits may sign

the sulu sea internal soliton experiment abstract we present the results of a comprehensive study of large amplitude internal solitons generated in the sulu sea in the philippines by intense tidal flow over a sharp bathymetric feature surface signatures of these waves have been observed in images from the dmsp landsat and nimbus 7 satellites and the space shuttle sir a synthetic aperture radar a two week experiment was conducted in the sulu sea in may 1980 from r v oceanograher during which a three mooring phased array of current meters and thermistors was implanted near the wave source and at 82 km and 200 km from the source seventeen soliton packets were observed whose properties underwent significant change as they propagated across the sea vertical profiles of density temperature and acoustic backscatter as well as radar and photographic surface signatures were obtained from the ship data from satellites moorings and the ship give unprecedented information on the spatial and temporal characteristics of solitary waves which ha

event based stratigraphic simulation of wave dominated shallow marine environments abstract the presence of event beds in the shallow marine stratigraphic record indicates formation is governed by high magnitude low frequency processes rather than low magnitude high frequency processes in this paper a 2 d multiple grain size process response model barsim is presented which uses event deposition to simulate stratigraphic response to changes in sea level and sediment supply barsim uses variable time steps to simulate individual storm event and fair weather periods deposition during storm conditions solely consists of reworked shoreface sediment while fair weather deposits consist of reworked shoreface sediment combined with sediment supplied by littoral drift and suspension simulations using variations in sea level sediment supply both amount and grain size and wave height regime result in distinct depositional patterns stratal geometry and bed characteristics model results indicate that both wave height regime and grain size of supplied sediment have considerable effect on shoreface morphology and stratal characteristics unraveling coastal evolution from the shallow marine stratigraphic record may therefore be more difficult than previously assumed as both variables are expected to vary over geologic time scales

barrier island aggradation via inlet migration mustang island texas abstract after establishing its present location around 9 5 ka mustang island aggraded stacking over 20 m of barrier island sand in the same location throughout mustang island s history tidal inlets shifted within nearly the same location from 7 5 ka to the present leaving 10 15 m thick deposits of clean well sorted quartz sand deposited within only a few centuries these deposits lack some of the sedimentary features normally associated with tidal inlets such as tidal couplets and shell hash the lack of such features is attributed to the uniform nature of the deposits cut by the inlets during the island s relatively long period of aggradation mustang island was able to maintain an aggradation character throughout most of the holocene due to the sediment eroded from three sources pleistocene headlands the transgressive colorado river delta of texas and the ois 3 shoreline of the central texas shelf each of these sources was exposed to waves and accompanying longshore drift during the island s early history when sea level rose quickly but was flooded or capped by transgressive muds by the time sea level rise slowed during the middle holocene

evidence for the influence of atlantic ionian stream fluctuations on the tidally induced internal dynamics in the strait of messina abstract on 24 and 25 october 1995 high resolution oceanographic measurements were carried out in the strait of messina by using a towed conductivity temperature depth chain and a vessel mounted acoustic doppler current profiler during the period of investigation the surface water of the tyrrhenian sea north of the strait sill was heavier than the surface water of the ionian sea south of the strait sill as a consequence during northward tidal flow surface water of the ionian sea spread as a surface jet into the tyrrhenian sea whereas during southward tidal flow heavier surface water of the tyrrhenian sea spread after having sunk to a depth of about 100 m as a subsurface jet into the ionian sea both jets had the form of an internal bore which finally developed into trains of internal solitary waves whose amplitudes were larger north than south of the strait sill these measurements represent a detailed picture of the tidally induced internal dynamics in the strait of messina during the period of i