strong inland propagation of low frequency long waves in river estuaries tidal waves traveling into estuaries are modified by channel geometry and river flow the damping effect of river flow on incident astronomical tides is well documented whereas its impact on low frequency tides like msf and mm is poorly understood in this contribution we employ a numerical model to explore low frequency tidal behavior under varying river flow msf and mm are locally generated by frictional mechanisms inside an estuary and they are larger in amplitude far upstream in tidal rivers and persist landward of the point of tidal extinction increasing river flow nonlinearly modulates the longitudinal variations of msf and mm amplitudes this is dynamically explained by flow enhanced asymmetry in subtidal friction over the spring neap msf and perigee apogee mm cycles respectively estuaries act as frequency filters where low frequency waves decay at a smaller rate and propagate more inland than high frequency waves strong inland penetration of low frequency tides informs compound flood management

an introduction to wavelet transform tidal analysis methods continuous wavelet transforms cwts provide an approach to understanding the numerous tidal phenomena that deviate markedly from an assumed statistical stationarity or exact periodicity inherent in traditional tidal methods use of wavelets allows determination of the degree of non stationarity present in time series such as estuarine and shelf currents usually treated as stationary wavelets also provide a consistent analysis of tidal and non tidal variance a feature often essential for dynamical analyses of non stationary tides we summarize basic notions of the wavelet transform also known as a perfect reconstruction filter bank or a multire solution analysis contrast them with those of harmonic analysis and fourier transforms construct a continuous wavelet transform basis with a scale selection especially adapted to tidal problems describe possibilities for analysis of scalar and vector quantities define a criterion for knowledge of independence of process between adjoining scales and illustrate use of wavelet tools with several examples in contrast to the nearly periodic barotropic tide typical of coastal stations this paper analyses processes that are in part tidally driven but non stationary e g baroclinic tidal currents river tides continental shelf internal tides and some kinds of biological activity in the coastal ocean in all cases wavelet analysis provides a consistent linear analysis of tidal and non tidal variance and reveals features that harmonic analysis on a fourier transform approach could not elucidate

exploration of tidal fluvial interaction in the columbia river estuary using s_tide plain language summary numerous tidal phenomena including river tides internal tides and tides in ice covered bay are nonstationary which pose a great challenge for traditional tidal analysis methods based on the independent point scheme and cubic spline interpolation a new approach namely the enhanced harmonic analysis is developed to deal with nonstationary tides a matlab toolbox s tide developed from the widely used t tide is used to realize the approach the efficiency of s tide is validated by analyzing a set of hourly water level observations from stations on the lower columbia river in all stations the hindcast of s tide is more accurate than ns tide that is a powerful nonstationary tidal analysis tool adapted to river tides the changing mean water level and tidal constituent properties obtained by s tide are similar to those obtained by ns tide continuous wavelet transform and empirical mode decomposition and highly consistent with theory on river tides moreover different from ns tide that only can be applied to river tides enhanced harmonic analysis is free of dynamic content assuming only known tidal frequencies therefore s tide can be applied to all kinds of nonstationary tides theoretically though powerful s tide also has some limitations s tide cannot be used for prediction and too many independent points in s tide may induce computational memory overflow and unrealistic results based on the independent point scheme and cubic spline interpolation a new approach enhanced harmonic analysis was developed to deal with nonstationary tides enhanced harmonic analysis is realized by a matlab toolbox s tide which is developed from the widely used t tide s tide assumes only known tidal frequencies and theoretically can be applied to all kinds of nonstationary tides and stationary tides in this study s tide is applied to analyzing records of river rides that is one of the simplest kinds of nonstationary tides for which ample data are available the method is compared with other methods to show its efficiency

temporal and spatial variability of tidal fluvial dynamics in the st lawrence fluvial estuary an application of nonstationary tidal harmonic analysis predicting tides in upstream reaches of rivers is a challenge because tides are highly nonlinear and nonstationary and accurate short time predictions of river flow are hard to obtain in the st lawrence fluvial estuary tide forecasts are produced using a one dimensional model one d forced downstream with harmonic constituents and upstream with daily discharges using 30 day flow forecasts from lake ontario and the ottawa river although this operational forecast system serves its purpose of predicting water levels information about nonstationary tidal fluvial processes that can be gained from it is limited particularly the temporal changes in mean water level and tidal properties i e constituent amplitudes and phases which are function of river flow and ocean tidal range in this paper a harmonic model adapted to nonstationary tides ns tide was applied to the st lawrence fluvial estuary where the time varying external forcing is directly built into the tidal basis functions model coefficients from 13 analysis stations were spatially interpolated to allow tide predictions at arbitrary locations as well as to provide insights into the spatiotemporal evolution of tides model hindcasts showed substantial improvements compared to classical harmonic analyses at upstream stations the model was further validated by comparison with one d predictions at a total of 32 stations the slightly lower accuracy obtained with ns tide is compensated by model simplicity efficiency and capacity to represent stage and tidal variations in a very compact way and thus represents a new means for understanding tidal rivers

acoustic facies and depositional processes in the upper submarine canyon swatch of no ground bay of bengal abstract the swatch of no ground song is a canyon that incises the bengal shelf deeply over more than 100 km length landward of the shelf edge and 100 km west of the ganges brahmaputra meghna river mouth it acts as conduit for the fluvially discharged sediment that bypasses the shelf and reaches the deep sea fan what transport deposition and mass wasting processes contribute to the sediment export and what sediment structures and main pathways are associated with these processes is studied by closely spaced bathymetric hydrosweep swath sounder and parasound sediment echosounder profiles over the upper song an analogue side scan sonar profile completes the acoustic data set from the parasound sediment echosounder data three main acoustic facies types related to undisturbed normal deposition mass wasting and erosive transport are defined and mapped with respect to the hydrosweep bathymetry of the song generally nearly all facies types show an unusually high sediment echosounder signal penetration of 80 100 m indicating that unconsolidated high porosity sediments occur on the canyon floor flanks and banks additionally the acoustic facies distribution map yields that about half of the canyon floor is covered by undisturbed well stratified fine grained muddy and coarse grained graded beds they are deposited from a suspension plume transported to the canyon either during fine weather conditions by westward oriented tidal currents or by storm events that mobilize sediments on the inner shelf curved or inclined faults or growth faults are found at all steep flanks indicating that active mass wasting processes occur along all channels and gullies on both canyon flanks such mass wasting processes are probably initiated by severe storms earthquakes high sediment load or excess pore pressure and lead to slides slumps or mudflows they stop in regions with low inclination angle and form acoustically transparent deposits of various extents on the channel and gully floors and on the southwestern canyon thalweg current marks identified on the canyon floor by high backscatter amplitudes in the side scan sonar images indicate that low density turbidity currents episodically flow down the canyon they are generated in an area of very high sedimentation rates close to the canyon head by high energy conditions like severe storms or earthquakes additionally a small gravity driven flow along the main channel s obviously continuously erode the steeper northeastern branches and inhibit sediment deposition in the more gentle southwestern channel below 450 500 m water depth together with larger scale mudflows and low density turbidity currents this gravity driven flow contributes to an active growth of the channel levee system in the deep sea fan

utilization of multiple scattering the next big step forward in seismic imaging surface removal and internal multiple removal are explained by recursively separating the primary and multiple responses at each depth level with the aid of wavefield prediction error filtering this causal removal process is referred to as data linearization the linearized output primaries only is suitable for linear migration algorithms next a summary is given on the migration of full wavefields primaries multiples by using the concept of secondary sources in each subsurface gridpoint these secondary sources are two way and contain the gridpoint reflection and the gridpoint transmission properties in full wavefield migration a local inversion process replaces the traditional linear imaging conditions finally marchenko redatuming is explained by iteratively separating the full wavefield response from above a new datum and the full wavefield response from below a new datum the redatuming output is available for linear migration marchenko imaging or even better for full wavefield migration linear migration full wavefield migration and marchenko imaging are compared with each other the principal conclusion of this essay is that multiples should not be removed but they should be utilized yielding two major advantages i illumination is enhanced particularly in the situation of low signal to noise primaries and ii both the upper side and the lower side of reflectors are imaged it is also concluded that multiple scattering algorithms are more transparent if they are formulated in a recursive depth manner in addition to transparency a recursive depth algorithm has the flexibility to enrich the imaging process by inserting prior geological knowledge or by removing numerical artefacts at each depth level finally it is concluded that nonlinear migration algorithms must have a closed loop architecture to allow successful imaging of incomplete seismic data volumes reality of field data

tidal asymmetry in estuaries with mixed semidiurnal diurnal tides 1 tidal asymmetry in estuaries with mixed mainly semidiurnal tides arises from both the interaction of principal tides and the higher harmonics generated by distortions within the estuary the duration asymmetry in rise and fall of water level caused by principal tides on the west coast of the continental united states is ebb dominant and so the tide entering estuaries is also ebb dominant prior to any internal distortions within the estuary the interaction of higher harmonics with principal constituents either augments or cancels the duration asymmetry in the principal tides in estuaries where tidal elevation and velocity phase are near quadrature 90 out of phase the duration asymmetry in tidal elevation leads to asymmetries in tidal current magnitude asymmetry can be conveniently quantified in terms of the sample skewness 1 the normalized third sample moment about the mean an analytic approximation to the skewness shows that traditional metrics of asymmetry namely the ratio of constituent amplitudes and the relative constituent phase difference arise from calculating the third sample moment observations from three california estuaries of different morphologies are presented as an illustration of how skewness can be used to quantify asymmetry in real systems as in semidiurnal systems morphology is a good predictor of whether higher harmonics engender ebb dominance or flood dominance however asymmetry imposed by principal tides at the mouth must first be overcome and so there is a spatial evolution in the total asymmetry quantifying observations via skewness should be considered in addition to traditional metrics in estuaries with mixed tides

unravelling the causes of tidal asymmetry in deltas abstract tidal asymmetry in deltas is caused by both the intrinsic asymmetry resulting from the combination of astronomical tides and by nonlinear tidal interactions that occur in shallow water the relative importance of these sources of tidal asymmetry in delta channel networks have remained poorly studied partly due to the limitations of classical harmonic analysis ha in hindcasting nonstationary tides the pearl river delta prd is a multichannel system with rapidly changing bathymetry subject to severe human interventions this work applies a nonstationary harmonic model ns tide to hydrological data from 15 stations in the prd spanning the period 1961 2012 the spatiotemporal variation of multiple sources of tidal asymmetry is quantified by a skewness metric revealing how similar or dissimilar the development of alternative sources of tidal asymmetry develop in the delta subject to study a relative sensitivity coefficient rsc is introduced to decompose the contribution of tidal amplitude variations to multiple tidal asymmetries analytical results show the development of tides becoming gradually more asymmetric as they propagate into delta channel networks and how this depends on the river flow variation in the orientation of tidal asymmetries induced by different combinations of tidal constituents leads to a complex pattern of the overall tidal asymmetry in the prd our results show that tidal asymmetry in deltas can be significantly dependent on the river flow

tomography of diffraction based focusing operators diffractions carry the same kinematic information provided by common focus point operators cfpos thus cfpo and diffraction time trajectories may be used separately or combined into a single unified tomography for velocity analysis velocity estimation by tomography of cfpos reduces the depth velocity ambiguity compared to two way time tomography cfpo estimation is complicated where there are event discontinuities and diffractions this problem is overcome by using the kinematic information in diffractions in near offset common offset gathers the procedure is illustrated using synthetic data and a single channel field seismic profile from the blake ridge off the east coast of the united states the results show the effectiveness of the proposed method for estimation of velocity from single channel seismic data and for refinement of the velocity field from multichannel data both applications are costcompetitive

seismic monitoring of diffraction images for detection of local heterogeneities diffracted waves contain valuable information regarding both the structure and composition of the media they are in in seismic data processing however these waves are usually regarded as noise in this paper we present an attempt to use scattered diffracted waves for the detection of local heterogeneities the method is based on the detection of diffracted waves by concentrating the signal amplitudes from diffracting points on the seismic section this is done using a correlation procedure that enhances the amplitude of the seismic signal at the location of the diffractors on the common diffraction point section d section the new local time correction for diffraction traveltime curve parameterization is based on the radius of curvature of the diffracted wavefront and near surface velocity we use the idea of seismic monitoring for detection and delineating local objects which may occur within the subsurface resulting from human activity or fast geological processes the method consists of continuou

imaging discontinuities on seismic sections in routine seismic processing normal moveout nmo corrections are performed to enhance the reflected signals on common depth point or common midpoint stacked sections however when faults are present reflection interference from the two blocks and the diffractions from their edges hinder fault location determination destruction of diffraction patterns by poststack migration further inhibits proper imaging of diffracting centers this paper presents a new technique which helps in the interpretation of diffracting edges by concentrating the signal amplitudes from discontinuous diffracting points on seismic sections it involves application to the data of moveout and amplitude corrections appropriate to an assumed diffractor location the maximum diffraction amplitude occurs at the location of the receiver for which the diffracting discontinuity is beneath the source receiver midpoint since the amplitudes of these diffracted signals drop very rapidly on either side of the midpoint an appropriate amplitude correction must be applied also because the diffracted signals are present on all traces one can use all of them to obtain a stacked trace for one possible diffractor location repetition of this procedure for diffractors assumed to be located beneath each surface point results in the common fault point cfp stacked section which shows diffractor locations by high amplitudes the method was tested for synthetic data with and without noise it proves to be quite effective but is sensitive to the velocity model used for moveout corrections therefore the velocity model obtained from nmo stacking is generally used for enhancing diffractor locations by stacking finally the technique was applied to a field reflection data set from an area south of princess well in alberta

the offset midpoint travel time pyramid for p wave in 2d transversely isotropic media with a tilted symmetry axis for pre stack phase shift migration in homogeneous isotropic media the offsetmidpoint travel time is represented by the double square root equation the travel time as a function of offset and midpoint resembles the shape of cheops pyramid this is also valid for transversely isotropic media with a vertical symmetry axis in this study we extend the offset midpoint travel time pyramid to the case of 2d transversely isotropic media with a tilted symmetry axis the p wave analytical travel time pyramid is derived under the assumption of weak anelliptical property of the tilted transverse isotropy media the travel time equation for the dip constrained transversely isotropic model is obtained from the depth domain travel time pyramid the potential applications of the derived offset midpoint travel time equation include pre stack kirchhoff migration anisotropic parameter estimation and travel time calculation in transversely isotropic media with a tilted symmetry axis

poststack velocity analysis by separation and imaging of seismic diffractions small geologic features manifest themselves in seismic data in the form of diffracted waves which are fundamentally different from seismic reflections using two field data examples and one synthetic example we demonstrate the possibility of separating seismic diffractions in the data and imaging them with optimally chosen migration velocities our criteria for separating reflection and diffraction events are the smoothness and continuity of local event slopes that correspond to reflection events for optimal focusing we develop the local varimax measure the objectives of this work are velocity analysis implemented in the poststack domain and high resolution imaging of small scale heterogeneities our examples demonstrate the effectiveness of the proposed method for high resolution imaging of such geologic features as faults channels and salt boundaries

diffraction imaging by uniform asymptotic theory and double exponential fitting seismic diffracted waves carry valuable information for identifying geological discontinuities unfortunately the diffraction energy is generally too weak and standard seismic processing is biased to imaging reflection in this paper we present a dynamic diffraction imaging method with the aim of enhancing diffraction and increasing the signal to noise ratio the correlation between diffraction amplitudes and their traveltimes generally exists in two forms with one form based on the kirchhoff integral formulation and the other on the uniform asymptotic theory however the former will encounter singularities at geometrical shadow boundaries and the latter requires the computation of a fresnel integral therefore neither of these methods is appropriate for practical applications noting the special form of the fresnel integral we propose a least squares fitting method based on double exponential functions to study the amplitude function of diffracted waves the simple form of the fitting function has no singularities and can accelerate the calculation of diffraction amplitude weakening coefficients by considering both the fitting weakening function and the polarity reversal property of the diffracted waves we modify the conventional kirchhoff imaging conditions and formulate a diffraction imaging formula the mechanism of the proposed diffraction imaging procedure is based on the edge diffractor instead of the idealized point diffractor the polarity reversal property can eliminate the background of strong reflection and enhance the diffraction by samephase summation moreover the fitting weakening function of diffraction amplitudes behaves like an inherent window to optimize the diffraction imaging aperture by its decaying trend synthetic and field data examples reveal that the proposed diffraction imaging method can meet the requirement of high resolution imaging with the edge diffraction fully reinforced and the strong reflection mostly eliminated

3 d seismic attributes using a semblance based coherency algorithm seismic coherency is a measure of lateral changes in the seismic response caused by variation in structure stratigraphy lithology porosity and the presence of hydrocarbons unlike shaded relief maps that allow 3 d visualization of faults and channels from horizon picks seismic coherency operates on the seismic data itself and is therefore unencumbered by interpreter or automatic picker biases we present a more robust multitrace semblance based coherency algorithm that allows us to analyze data of lesser quality than our original three trace cross correlation based algorithm this second generation semblance based coherency algorithm provides improved vertical resolution over our original zero mean crosscorrelation algorithm resulting in reduced mixing of overlying or underlying stratigraphic features in general we analyze stratigraphic features using as narrow a temporal analysis window as possible typically determined by the highest usable frequency in the input seismic data in the limit one may confidently apply our new semblance based algorithm to a one sample thick seismic volume extracted along a conventionally picked stratigraphic horizon corresponding to a peak or trough whose amplitudes lie sufficiently above the ambient seismic noise in contrast near vertical structural features such as faults are better enhanced when using a longer temporal analysis window corresponding to the lowest usable frequency in the input data the calculation of reflector dip azimuth throughout the data volume allows us to generalize the calculation of conventional complex trace attributes including envelope phase frequency and bandwidth to the calculation of complex reflector attributes generated by slant stacking the input data along the reflector dip within the coherency analysis window these more robust complex reflector attribute cubes can be combined with coherency and dip azimuth cubes using conventional geostatistical clustering and segmentation algorithms to provide an integrated multiattribute analysis

detailed morphology sedimentary structure and evolution of the continental margin of the western provencal basin south of france since the late miocene abstract seabeam bathymetry and high resolution seismic profiles allow the study of different sedimentary units existing off western provence and to establish their continuity throughout the continental margin from the shelf to the rise the morphology of the slope is greatly controlled by gravity processes leading to phenomena such as canyon piracy or channel avulsion this morphology quite accurately expresses the configuration of the old underlying sedimentary and tectonic structures the sedimentary structure of this domain is the result of the complex arrangement of lobes and ridges that originated from different continental sources and were deposited during different epochs of the plio quaternary knowledge of the old hydrographic networks draining provence during the different quaternary climatic stages allows palaeogeographic reconstructions to be proposed linking these sedimentary units to their continental sources

diffraction imaging by multifocusing correct identification of geologic discontinuities such as faults pinch outs and small size scattering objects is a primary challenge of the seismic method seismic response from these objects is encoded in diffractions our method images local heterogeneities of the subsurface using diffracted seismic events the method is based on coherent summation of diffracted waves arising in media that include interface discontinuities and local velocity heterogeneities this is done using a correlation procedure that coherently focuses diffraction energy on a seismic section by flattening diffraction events using a new local time correction formula to parameterize diffraction traveltime curves this time correction which is based on the multifocusing method depends on two parameters the emergent angle and the radius of curvature of the diffracted wavefront these parameters are estimated directly from prestack seismic traces the diffraction multifocusing stack dmfs can separate diffracted and reflected energy on a stacked section by focusing diffractions to the diffraction location and defocusing the reflection energy over a large area

river flow controls on tides and tide mean water level profiles in a tidal freshwater river 1 tidal rivers feature oscillatory and steady gradients in the water surface controlled by interactions between river flow and tides the river discharge attenuates the tidal motion and tidal motion increases tidal mean friction in the river which may act as a barrier to the river discharge time series of tidal water level amplitudes at five gauge stations along the river mahakam in indonesia and tidal flow velocity amplitudes at a discharge monitoring station were obtained applying wavelet analysis temporal variations in tidal damping coefficients for quaterdiurnal semidiurnal and diurnal tidal species were quantified from the observed amplitude profiles the analysis shows that tidal damping during the rising limb of a discharge wave differs from damping during the falling limb wavelet cross correlations between surface levels yielded empirical estimates of wave numbers an empirical relation between tidal damping and river flow is derived to describe subtidal bottom friction along an idealized tidal river resembling the mahakam the subtidal friction is decomposed into contributions from the river flow only from river tide interaction and from tidal asymmetry even for high river flow and low tidal velocity river flow enhances friction attributed to river tide interaction causing subtidal water level setup a simple multilinear regression model using subtidal bottom friction is employed to predict subtidal water levels at locations upstream with a relatively good agreement between predictions and observations the explicit expression shows the nonlinear dependence of subtidal friction on river flow velocity explaining the complex behavior of tidal mean surface level profiles

near bottom sedimentation processes revealed by echo character mapping studies northwestern mediterranean basin subbottom echoes recorded on 3 5 khz echo sounders in the northwestern mediterranean basin from 1978 to 1991 can be classified into five main categories of echo character 1 continental shelf cs echo character characterizes the continental platform and areas of shallow relief and commonly is related to consolidated sediments 2 hyperbolic h echo character is recorded from areas with rough bottom morphology echo type h1 corresponds to steep slopes echo type h2 reflects very coarse grained sediments deposited by energetic turbidity currents 3 bedded b echo character is widely observed throughout the study area and corresponds to terrigenous deposits distributed by turbidity currents echo type b1 is related to thin turbidites deposited on overbank portions of channel levees by lateral overflow of turbiditic currents moving down the channels echo type b2 corresponds to coarser turbiditic materials 4 rugged r echo character is observed in the axes of submarine canyons and channels and characterizes hard sea floor with coarse heterogeneous turbiditic deposits subjected to energetic gravity flow processes 5 transparent t echo character is ubiquitous in the study area and is attributed to mass movement deposits the widespread occurrence of those deposits testifies to the general instability of the study area types and distribution of echo character throughout the study area show the importance of gravity dominated depositional processes turbidity currents and mass wasting in this region this remobilization of siliciclastic sediments induced by high sediment rates steep slopes and halotectonics theoretically could create potential hydrocarbon reservoirs within the deep water portions of the continental margin

reconstruction of tidal discharges in the st lawrence fluvial estuary the method of cubature revisited knowledge of tidal flows in rivers and estuaries is often scarce yet vital in determining flushing properties and sediment transport rates while many rivers still remain ungauged methodological difficulties often arise in gauged systems resulting in short flow records compared to historical water level data notwithstanding discharge reconstructions in estuaries are possible using indirect methods based on long term tidal data in this paper we revisit the method of cubature integrating the continuity equation for discharges at different sections the method consists in computing temporal changes in water volume from simultaneous tidal heights readings along the river and storage width estimations these water balance estimates remain challenging to produce because they require spatial interpolation of gappy tidal records and an accurate representation of inundated areas over time improvements on the method are made by using a 1d nonstationary tidal harmonic model that provides continuous tidal data along the estuary with no temporal or spatial gaps secondly a 2d finite element discretization is used to compute the time varying wetted surface area relying on detailed topographic data over intertidal flats the method is applied to the st lawrence fluvial estuary slfe and validated against discharge data collected along 9 cross sections of the river reaching relative rmse below 4 of the diurnal tidal discharge range at downstream locations and below 9 upstream one year reconstructions conducted in the slfe also show the potential of the method to reproduce the tidal discharge variability along the tidal river continuum for a wide range of temporal scales

deposition processes from echo character mapping along the western algerian margin oran tenes western mediterranean abstract the westernmost algerian margin south algero provencal basin depicts a few offshore active faults moderate to rare seismicity and generally very steep slopes 16 we classified and mapped 12 echo types according to their sub bottom acoustic facies observed on this margin on 2 5 2 khz chirp echo sounder data maradja 2003 cruise the echo character maps are interpreted in terms of sedimentary processes the b1 echo type parallel to subparallel high to low amplitude sub bottom reflections mainly in the deep basin corresponds to hemipelagic sedimentation r1 prolonged single echo with no sub bottoms and r2 small irregular overlapping hyperbolae echo types generally near or in canyon systems are associated with turbidity currents or more rarely to contour currents or mass transport deposits such as slumps slides and debris flows the transparent echo types t1 t5 and r3 chaotic lens of low amplitude reflections on top of higher amplitude often located at the foot of the slope or canyons walls typically indicate mass transport deposits like slides or turbidites large zones that display a large variety of echo types are evidenced in the study area and are generally associated with turbidity currents but could also be associated with bottom currents it appears that active tectonics plays a significant role in this part of the margin which presents a few active faults offshore but also a strong and relatively frequent seismicity onland the general pattern of the distribution of mass transport deposits is particular i e many but small slides all along the margin and suggests a probable triggering by recurrent earthquake shakings however active tectonics is not the only factor influencing the deposition pattern as some zones seem characterized by predominant strong turbidity currents transporting sediments far away from the foot of the margin whereas others depict retrogressive erosion features on the slope i e small slides scarps in gullies rather than transport by turbidity currents in particular the rivers sediment discharge fluxes and the geomorphologic characteristics of the margin seem to be very important factors too

seismic imaging of complex geometry forward modeling of sandstone intrusions abstract sandstone intrusions form large bedding discordant sandstones that intruded into finer grained less permeable host strata they form naturally sand propped hydraulic fractures that constitute a connected network of permeable conduits through which fluids escape to the earth s surface saucer shaped sandstone intrusions are among the largest volume intrusions and are commonly resolved on seismic data outcrop analogues of seismically resolved saucers shaped intrusions reveal that many attendant intrusions in particular dikes are undetected in seismic data seismic forward modeling of a detailed outcrop description of a saucer shaped intrusion demonstrates that intrusions steeper than 45 are undetected and that up to 40 of the entire volume of sandstone intrusions is not seismically imaged wedge geometry associated with discordant contacts between different lithologies causes constructive and destructive amplitude interference creating imaging artefacts of sandstone thickness and geometry comparison of the outcrop seismic models with 3d seismic data from volund oilfield demonstrate both the similarity of the saucer shaped intrusions and the distribution and quantity of dikes that may be undetected ca 78 using subsurface data lack of detection of dikes has direct implications on the valuation of upward migration of fluids and an overestimation of seal capacity this therefore has major implications when using seismic data to evaluate waste sequestration or to execute hydrocarbon or groundwater exploration and production

color encoding multifrequency acoustic data for near bottom studies in this paper we describe color encoding methods for combining acoustic data in widely separate spectral bands into composite displays these new display methods better image the near bottom is interval in fine grained depositional environments in fine grained depositional environments the water bottom is typically not a discrete surface but is a transition zone spanning 1 3 m this near bottom interval is not completely imaged by either fathometers or subbottom profilers alone multiple acoustic frequencies spanning both the fathometer and subbottom bands are needed for applications in which the details of the near bottom are critical such applications include surveys of water reservoirs scour around bridge piers and predredging surveys in harbors to make effective use of the multifrequency data we combine three or more signal frequencies into composite false color displays by adapting multispectral photography methods used in optical remote sensing one approach is to encode amplitudes of traces r

diffraction imaging by prestack reverse time migration in the dip angle domain prestack image volumes may be decomposed into specular and non specular parts by filters defined in the dip angle domain for space shift extended image volumes the dip angle decomposition is derived via local radon transform in depth and midpoint coordinates followed by an averaging over space shifts we propose to employ prestack space shift extended reverse time migration and dip angle decomposition for imaging small scale structural elements considered as seismic diffractors in models with arbitrary complexity a suitable design of a specularity filter in the dip angle domain rejects the dominant reflectors and enhances diffractors and other non specular image content the filter exploits a clear discrimination in dip between specular reflections and diffractions the former are stationary at the specular dip whereas the latter are non stationary without a preferred dip direction while the filtered image volume features other than the diffractor images for example noise and truncation artifacts are also present synthetic and field data examples suggest that diffractors tend to dominate and are readily recognizable averaging over space shifts in the filter construction makes the reflectors rejection robust against migration velocity errors another consequence of the space shift extension and its angle domain transforms is the possibility of exploring the image in a multiple set of common image gathers the filtered diffractions may be analyzed simultaneously in space shift scattering angle and dip angle image gathers by means of a single migration job the deliverables of our method obviously enrich the processed material on the interpreter s desk we expect them to further supplement our understanding of the earth s interior this article is protected by copyright all rights reserved

the relative importance of gravity induced versus current controlled sedimentation during the quaternary along the mideast u s outer continental margin revealed by 3 5 khz echo character abstract a detailed echo character map based on more than 50 000 km of 3 5 khz echograms reveals the relative importance of contour currents turbidity currents and mass wasting processes for the upper 50 100 m of sea floor sediments along the u s continental margin between southern georges bank and cape hatteras nineteen individual echo types are mapped and interpreted as deposits produced either by current controlled or gravity induced processes based on echo type distribution analysis of selected sediment core samples and the published results of other workers turbidity currents and mass wasting have apparently been the primary depositional agents throughout 60 of the region in contrast contour currents alone appear to have influenced only 10 of the region however combined processes i e non separable interaction between downslope and parallel to contour processes have influenced an estimated 25 of the margin the remaining 5 of the study area constitutes the outermost continental shelf echo types here reflect the influence of fluvial deltaic and shallow marine sedimentary processes changes in the relative distributions of various echo types with sea floor depth indicate that the dominant sedimentary processes change downslope and are significantly different within each physiographic province deposits formed by mass wasting dominate the continental slope where 50 of the sea floor is eroded and gullied by slides slumps and the heads of debris flows deposits developed under the influence of combined processes are most wide spread on the upper continental rise and cover 40 of the sea floor primarily in the form of deep sea channel levees modified by contour currents on the lower continental rise turbidites form more than 50 of the sea floor deposits the downslope deposits turbidity currents slumps debris flows etc were emplaced primarily during the pleistocene glacioeustatic sea level lowering moved beaches and rivers across the exposed continental shelf to the shelf edge where massive fluxes of terrigenous sediment could be delivered to the continental slope and rise by turbidity currents significant amounts of this sediment were transported through submarine canyons and leveed deep sea channels to the lower continental rise and formed the lower continental rise terrace a flat turbidite basin ponded behind the hatteras outer ridge southwest of the wilmington channel this glacially derived influx was diminished however depositional patterns indicate that downslope processes continued to be dominant at least as far south as cape hatteras where rapid deposition on the continental slope and uppermost continental rise created instabilities slope failure produced slumps slides and debris flows and provided an additional volumetrically important redistribution of sediment downslope the influence of contour currents is clearly observed only in those areas topographically shielded from the masking effects of downslope processes in particular along the seaward side of the buried chesapeake drift and the hatteras outer ridge

tidal fluvial interaction in the guadalquivir river estuary spatial and frequency dependent response of currents and water levels tidal fluvial interaction in the gre

post stack velocity analysis in the dip angle domain using diffractions interval velocity analysis in complex geological areas is often considered as an unresolved problem a novel approach to improve the velocity analysis process is to perform the analysis in a non conventional domain and to use seismic events that are usually ignored during standard data processing and imaging in this study a method to analyse diffraction data for migration velocity analysis in the time or depth domain is presented the method is based on the clear distinction between diffractions and reflections in the post migration dip angle domain the attractive possibility to perform the analysis using only stacked data as an input is demonstrated on synthetic and real data examples

diffraction imaging by focusing defocusing an outlook on seismic superresolution diffractions always need more advertising it is true that conventional seismic processing and migration are usually successful in using specular reflections to estimate subsurface velocities and reconstruct the geometry and strength of continuous and pronounced reflectors however correct identification of geological discontinuities such as faults pinch outs and small size scattering objects is one of the main objectives of seismic interpretation the seismic response from these structural elements is encoded in diffractions and diffractions are essentially lost during the conventional processing migration sequence hence we advocate a diffraction based data oriented approach to enhance image resolution as opposed to the traditional image oriented techniques which operate on the image after processing and migration even more it can be shown that at least in principle processing of diffractions can lead to superresolution and the recovery of details smaller than the seismic wavelength the so called reflection stack is capable of effectively separating diffracted and reflected energy on a prestack shot gather by focusing the reflection to a point while the diffraction remains unfocused over a large area muting the reflection focus and defocusing the residual wavefield result in a shot gather that contains mostly diffractions diffraction imaging applies the classical isotropic diffraction stack to these diffraction shot gathers this focusingmuting defocusing approach can successfully image faults small size scattering objects and diffracting edges it can be implemented both in model independent and modeldependent contexts the resulting diffraction images can greatly assist the interpreter when used as a standard supplement to full wave images

diffraction enhancement in prestack seismic data seismic diffractions are often considered noise and are intentionally or implicitly suppressed during processing diffraction like events include true diffractions wave conversions or fracture waves which may contain valuable information about the subsurface and could be used for interpretation or imaging using synthetic and field data we examine workflows to separate diffractions from reflections that allow enhancement of diffraction like signals and suppression of reflections the workflows consist of combinations of standard processing modules most workflows apply normal moveout corrections to flatten reflection hyperbolas which eases their removal we observe that the most effective techniques are the decomposition of seismic gathers into eigensections and flows based on radon transformations

slope instabilities from echo character mapping along the french guiana transform margin and demerara abyssal plain the french guiana transform margin and demerara abyssal plain have been recently surveyed in the framework of the extraplac french program of extension of the continental shelf guyaplac survey ifremer ifp shom ipev based on the interpretation of some of the data collected during the guyaplac survey simrad em12 multibeam bathymetric data backscatter imagery and 3 5 khz profiles the area can be divided into three morphostructural domains 1 the western guiana margin including a part of the demerara plateau an important bathymetric relief prolonging the continental platform off guiana and surinam this domain is bounded by 1a the nw se trending northern border of the demerara plateau which appears quite steep and corresponds to a transform segment of the margin 1b the n s eastern border of the demerara plateau which corresponds to a divergent segment of the margin the demerara plateau shows a segmented morphology lowslope gradients and a very rough surface ripples perpendicular to the slope direction nnw sse structural steps seem to correspond to collapses of 100 km long blocs towards the east slumps initiate along these directions the observed rough bathymetry seems to be related to creeping processes at a greater scale seismic data this part of the margin has been totally destabilized numerous imbricate transparent masses rooted at about 0 5 s t w t t belowseafloor thenw se trending northern border of the demerara plateau corresponds to a cliff like continental slope probably slightly smoother than other transform margins ghana co te d ivoire margin the n s eastern border of demerara plateau is characterized by numerous small scale imbricate slumps some of these failures seem to be emplaced in the prolongation of the nnw sse structural steps identified on the demerara plateau 2 the eastern guiana margin corresponds to a nw se oriented gullied transform margin segment the associated continental slope is very steep and characterized by numerous imbricate slumps and related debris lows some undulated masses probably corresponding to creeping sediments or to older mass wasting events are still imprinted on bathymetry this transform margin segment is nearly entirely destabilized and eroded 3 the demerara abyssal plain this domain is characterized eastwards by channels belonging to the amazon turbidite system and westwards at the foot of demerara continental slope by sediment waves probably created by contour currents to conclude it seems that there is a strong relationship between the structure transform and divergent segments and the emplacement of recurrent slope instabilities these are probably related to the steepness of the slopes but also to subsidence histories generating in some cases huge deep seated collapses of the whole margin fluid ascents are common everywhere in the area probably enhancing slope instability their origin is not constrained but the black shales or cretaceous organic rich layers could be good candidates

specular ray parameter extraction and stationary phase migration the kirchhoff type prestack depth migration operator is a diffraction stack of seismic reflection energies over seismic traces typically the diffraction stack is carried out over the full data aperture producing not only images of reflectors but also aliasing artifacts aliasing artifacts often break reflector continuity in images the stationary phase approximation to the migration operator shows that for image points on reflectors traces within the neighborhood of specular rays contribute most to the diffraction stack traces outside this vicinity introduce aliasing artifacts into the image especially in the case of coarse trace spacing and aperture truncation a new migration algorithm denoted as stationary phase migration is proposed to find the specular ray parameters and then to migrate the specular ray energies and reject nonspecular ray energies to yield images with less aliasing

diffraction imaging in depth high resolution imaging is of great value to an interpreter for instance to enable identification of small scale faults and to locate formation pinch out positions standard approaches to obtain high resolution information such as coherency analysis and structure oriented filters derive attributes from stacked migrated images since they are image driven these techniques are sensitive to artifacts due to an inadequate migration velocity in fact the attribute derivation is not based on the physics of wave propagation diffracted waves on the other hand have been recognized as physically reliable carriers of high or even super resolution structural information however high resolution information encoded in diffractions is generally lost during the conventional processing sequence indeed migration kernels in current migration algorithms are biased against diffractions we propose here methods for a diffraction based data oriented approach to image resolution we also demonstrate the different behaviour of diffractions compared to specular reflections and how this can be leveraged to assess characteristics of subsurface features in this way a rough surface such as a fault plane or unconformity may be distinguishable on a diffraction image and not on a traditional reflection image we outline some characteristic properties of diffractions and diffraction imaging and present two novel approaches to diffraction imaging in the depth domain the first technique is based on reflection focusing in the depth domain and subsequent filtering of reflections from prestack data the second technique modifies the migration kernel and consists of a reverse application of stationary phase migration to suppress contributions from specular reflections to the diffraction image both techniques are proposed as a complement to conventional full wave pre stack depth migration and both assume the existence of an accurate migration velocity

3d seismic reflection imaging of volcanic hosted massive sulfide deposits insights from reprocessing halfmile lake data new brunswick canada three dimensional seismic reflection data from the halfmile lake area new brunswick canada was reprocessed over an 18 km2 grid to improve the seismic signatures of a 5 million ton volcanic hosted massive sulfide vhms deposit located at 1200 m depth known as the deep zone as well as key host rock structures we chose a prestack dip moveout dmo and poststack migration processing sequence to preserve the possible diffraction signature of the deep vhms zone despite the high level of source generated noise and large statics caused by near surface conditions our processing results revealed improved 3d seismic images for shallow and deep structures many of the imaged structures were easily correlated with known lithological con tacts constrained by boreholes and petrophysical measurements a short flat lying segment of high amplitude reflection at about 800 m depth in the unmigrated cube was interpreted to originate from a small portion of the lower vhms zone the dmo stack was characterized by a l

instantaneous spectral attributes to detect channels channels filled with porous rock and encased in a nonporousmatrixconstituteoneofthemoreimportantstratigraphic exploration plays although attributes such as coherence can be used to map channel width they are relatively insensitive to channel thickness in contrast spectral decomposition can beusedtomapsubtlechangesinchannelthickness thepeak spectral frequency derived by using the short window discrete fourier transform swdft is an excellent tool for mapping such changes along an interpreted horizon we show that by use of instantaneous spectral attributes we can generateequivalentmapsforcompleteseismicvolumes because we are often interested in mapping high reflectivity channelsencasedinalower reflectivitymatrix wefindthata composite plot of the peak frequency and the above average peak amplitude accentuates highly tuned channels finally by generating a composite volume using peak frequency peakamplitude andcoherence wecanestablishnotonlythe channelthickness butalsoitswidth wedemonstratethevalueofsuch3dvolumetricestimatesthroughapplicationto1 a marine survey acquired over tertiary channels from the gulfofmexicoand2alanddatasurveyacquiredoverpaleozoic channels from the central basin platform west texas united states the channels in both marine and land surveys canbehighlightedthroughcomposite volumeanalysis

temporal variations of tides on the west coast of great britain summary temporal variations of tides are investigated by analysing tidal observations from five ports on the west coast of great britain variations considered here are those occurring in the semi diurnal species daily in the tidal constituents resolved from analyses of 29 day sets over a period of two years 1980 81 and in the tidal constituents resolved from 1 yr sets over a period of 19 yr the time variations of tidal constituents are mainly due to inseparable terms grouping with the principal term due to the short length of data and the insufficiency of the procedures to account for them surges and surge tide interaction are affecting the resolution of tides time variations of constituents of the diurnal species induced by non tidal forces are spatially consistent the use of equilibrium relationships to account for modulations of principal constituents by waves separable in an 18 61 yr nodal cycle improves the analysis however the modulation is smaller in the real tide than in the equilibrium tide when the application of this principle is extended to a wider frequency band to cover constituents which cannot be resolved from one month of observations it may produce the opposite effect these problems start compounding with decreasing length of data i e increasing band width of resolution functional approximations of interaction coefficients bi admittance of non linear tides similar to the response admittance of linear tides are computed for semi diurnal fourth diurnal and sixth diurnal bands these functional estimates may be used to interpolate unseparable constituents to improve the quality of analyses the results are consistent with the fact that the response of the sea does not change in a narrow frequency band covering a nodal cycle of the moon the change in the equilibrium relationship between the principal term and its nodal term can be interpreted in terms of the damping effect of bottom friction

full azimuth subsurface angle domain wavefield decomposition and imaging part i directional and reflection image gathers we present a new subsurface angle domain seismic imaging systemforgeneratingandextractinghigh resolutioninformation about subsurface angle dependent reflectivity the system enables geophysicists to use all recorded seismic data in a continuousfashiondirectlyinthesubsurfacelocalangledomainlad resulting in two complementary full azimuth common imageangle gather systems directional and reflection the complete setofinformationfrombothtypesofanglegathersleadstoaccurate high resolution reliable velocity model determination and reservoir characterization the directional angle decomposition enables the implementation of specular and diffraction imaging in real 3d isotropic anisotropic geological models leading to simultaneous emphasis on continuous structural surfaces and discontinuous objects such as faults and small scale fractures structural attributes at each subsurface point e g dip azimuth andcontinuity canbederiveddirectlyfromthedirectionalangle gathers the reflection angle gathers display reflectivity as a function of the opening angle and opening azimuth these gathers are most meaningful in the vicinity of actual local reflecting surfaces wherethereflectionanglesaremeasuredwithrespectto the derived background specular direction the reflection angle gathers are used for automatic picking of full azimuth angle domainresidualmoveoutsrmowhich togetherwiththederived background orientations of the subsurface reflection horizons provide a complete set of input data to isotropic anisotropic tomography the full azimuth angle dependent amplitude variations are used for reliable and accurate amplitude versus angle andazimuthavazanalysisandreservoircharacterization the proposed system is most effective for imaging and analysis below complex structures such as subsalt and subbasalt high velocity carbonate rocks shallow low velocity gas pockets and others in addition it enables accurate azimuthal anisotropic imaging and analysis providing optimal solutions for fracture detectionandreservoircharacterization

on perturbations of harmonic constants in the thames estuary summary a long series of southend sea level observations extending over a period of 51 years 1929 79 is analysed using the harmonic method of tidal analysis the harmonic method of tidal analysis and prediction works on the assumption that the relationship of nodal terms with their respective principal terms in the physical tide is the same as in the equilibrium tide it is concluded that although this assumption is very useful in accounting for those terms which are not separable from a given length of observations it is not always fully valid as a result a systematic error is introduced in tidal analysis and prediction it is observed that small secular trends are present in amplitudes and phase lags of some principal tidal constituents in the diurnal band amplitudes of o1 and k1 are almost constant but the phase lag of k1 is increasing and the phase lag of o1 is decreasing in the semi diurnal band amplitudes of m2 s2 and k2 are increasing while the phase lag of m2 is decreasing and the phase lag of k2 is increasing the influence of these secular trends in amplitudes is to increase the tidal range and extreme levels this is confirmed by increases in the range of tide in the last one and a half centuries statistically no significance can be attached to trends in phase lags because standard errors are large a comparison of old records with tides synthesized by modern constituents for london bridge suggests that the phase of the tide was almost stable there from 1683 to 1835 then a large change occurred after 1835 similar changes are noted in the tidal range the nature of these changes indicates that they are partly due to increased input at southend resulting from secular trends in tidal harmonics and partly due to man made alterations embankment bank raising and deepening of the estuary

recent depositional patterns of the nile deep sea fan from echo character mapping the nile deep sea fan was surveyed in 1998 using swath multibeam bathymetry backscatter imagery and 3 5 khz and seismic profiling on the basis of this new data set the fan has been divided into three main provinces western central and eastern recent sedimentary patterns as deduced from echo character mapping show that gravity induced sedimentary deposits are predominant and are expressed through either slides debris flows or turbidites turbidity processes are particularly active in the westernmost province through a well developed network of deep sea channels this network controls turbiditic flows that subsequently overflow levees mass wasting processes are extremely efficient all over the nile deep sea fan in the upper central province a broad allochthonous tongue of mass flow deposits generated by slope destabilizations may have led to channel avulsions and migrations in the eastern province a northwest southeast deformed belt resulting from combined deep seated and salt related tectonics contains large proportions of destabilized sediments i e originating from destabilization processes such as mass movements probably settled by recent tectonic activity this article highlights 1 the influence of both thin skinned and thick skinned tectonics on sedimentary distribution and 2 the predominance of gravity induced sediments turbidites slides and mass flows in such submarine fans the distribution of debris flows and sedimentary deposits settled by turbidity currents appears fundamental in predicting reservoir geometry and economic potential

subtidal flow division at a shallow tidal junction 1 tides influence distribution of river discharge at tidally affected channel junctions at the apex of a channel network in an indonesian delta observations of flow division suggest that tidally averaged flow division depends on the tidal range to understand the mechanisms governing the subtidal flow division an idealized hydrodynamic junction model inspired by the observations has been set up the barotropic model consists of two exponentially converging tidal channels that connect to a tidal river at the junction and solves the nonlinear shallow water equations by varying the depth length e folding length scale of the channel width and hydraulic roughness in one of the two tidal channels the sensitivity of the subtidal flow division to those four parameters was investigated for depth length and e folding length scale differences between channels the effect of tides is generally to enhance unequal subtidal flow division that occurs in the case of river flow only in contrast for hydraulic roughness differences the tidal effect partly cancels the inequality in river flow division the tidal effect may even reverse the horizontal flow circulation that would occur in the absence of tides

interaction of fluctuating river flow with a barotropic tide a demonstration of wavelet tidal analysis methods wavelet transforms provide a valuable new tool for analysis of tidal processes that deviate markedly from an assumption of exact periodicity inherent in traditional harmonic analysis a wavelet basis adapted to nonstationary tidal problems is constructed and employed to analyze the modulation of the external tide in a river by variations in streamflow interaction of a surface tide with river flow is the best available demonstration of the continuous wavelet transform cwt methods developed it is the simplest and perhaps the only nonstationary tidal process for which both sufficient data and dynamical understanding exist to allow detailed comparisons between cwt analyses and analytical predictions of the response of tides to nontidal forcing variations at upriver locations of low frequency elevation river stage zr and three tidal species are deduced from cross sectionally integrated equations for landward propagation in a channel of constant cross section with quadratic friction the log of the amplitude of the diurnal d1 semidiurnal d2 and quarterdiurnal d4 elevations should vary at far upriver locations with the square root of the river flow qr and river stage zr should depend on the square of river flow convergent geometry and species species frictional interactions modify these predictions somewhat cwt analyses show that the predicted amplitude behavior for the tidal species is approximately correct best results are obtained for the dominant dynamically simplest processes zr and d2 in the past further progress in understanding river tides has been limited by a lack of data analysis tools data analysis tools are now clearly better than the available analytical solutions

reconstruction of spatially continuous water levels in the columbia river estuary the method of empirical orthogonal function revisited abstract accurate water level measurements in tidal rivers are vital and essential for water resources management coastal engineering and hydrodynamic research however the number of tide gauging stations in tidal rivers is far from adequate in this paper we revisit the method of empirical orthogonal function eof which is widely used in geophysics for spatial temporal data different from previous studies which used eof as a data analysis method here eof is used as a data interpolation method to reconstruct spatially continuous water levels in the fluvial estuary the eof interpolation eofi decomposes spatial temporal water levels into spatial patterns and temporal patterns and then eofi spatially integrates tidal heights using the interpolated spatial patterns between the stations eofi is simple to understand and easy to implement while its results are highly accurate moreover different from numerical modeling which needs the bathymetry river shorelines and river flow data eofi only needs the water level data in summary although eofi has some limitations it has the potential to be widely used in reconstructing water levels and other spatial temporal parameters

a comparison of diffraction imaging to incoherence and curvature detecting small subsurface features such as faults fracture swarms steep reef edges and channel edges is a routine task in seismic interpretation common seismic attributes used for this task such as curvature and incoherence are derived from conventional images containing both reflections and diffractions an emerging alternative approach is to interpret these edge features using the diffraction imaging technique which images diffracted energy separately a diffraction imaging volume is generated by separating specular reflections from diffractions in an unmigrated volume followed by migration of those diffractions different methods can be used to separate diffractions from reflections on unmigrated data in a case history they are separated with a plane wave destruction pwd filter an evaluation of diffraction imaging performance is applied to a 3d seismic data set from the cooper basin of australia diffraction imaging horizon maps are compared with corresponding maps made from incoherence and curvature volumes the resolution and the ability to detect faults fractures and channel edge features are compared the results show that diffraction imaging provides superior vertical and spatial resolution over conventional incoherence and curvature attributes for mapping faults and stratigraphy

plio pleistocene evolution of the var deep sea fan off the french riviera abstract the var deep sea fan was deposited during the pliocene and quaternary seaward progradation of the var delta within a steep sided flat floored basin formed during the messinian salinity crisis the prominent palaeo var canyon was cut on the slope at the same time following the early pliocene transgression var sediments were initially trapped in the coastal ria formed by sea level incursion of the head of the messinian valley by middle pliocene time gilbert type deltas had prograded to the break of slope modern coastline allowing coarse sediment to reach the basin quaternary coastal uplift and sediment supply from the glaciated alps resulted in a supply of coarse sediment to the fan by the braided var river throughout the quaternary even during sea level highstands such as the present in the earliest pliocene hemipelagic clays accumulated while coarse sediment was trapped in the var ria through the rest of the pliocene a leveed fan valley extended southward from the var canyon which periodically switched locations through avulsion to the east at about the beginning of the quaternary this eastward spillover channel became the main distributary and re occupation of the older south trending channels was blocked by rapid levee progradation and aggradation of mud waves by overbanking of turbidity flows on the var sedimentary ridge during the quaternary channel shifting to the north occurred the quaternary var fan has an unusually steep concave longitudinal profile compared with most passive margin fans the laurentian fan has a similar profile to the var both have a high levee and a gravel and pebble floored fan valley that is essentially a bypass zone compared with the aggradational channel levee systems with lower levees in most passive margin fans this is a consequence of the constant supply of coarse sand gravel and pebbles to the fan even during highstands of sea level the erosive capability of this coarse sediment in ignitive turbidity currents resulted in flushing out of the upper and middle fan valley system thick muddy turbidity currents probably resulting from slumping caused by canyon incision produced the prominent mud waves on the levee the concave longitudinal profile led to rapid sediment deposition at critical points in the valley system as a result of turbidity flow expansion this in turn promoted the development of a left hook in the valley system

robust estimates of 3d reflector dip and azimuth much of seismic stratigraphy is based on the morphology of seismic textures the identification of reflector terminations and subtle changes in dip and azimuth allows us to infer coherent progradational and transgressive packages as well as more chaotic slumps fans and braided stream complexes infill of karsted terrains gas seeps and of course faults and angular unconformities a major difficulty in estimating reflector dip and azimuth arises at discrete lateral and vertical discontinuities across which reflector dip and azimuth change the smearing across these boundaries produced by traditional dip and azimuth estimations is avoided by using temporally and spatially shifted multiple windows that contain each analysis point this more robust estimation of dip and azimuth leads to increased resolution of well established algorithms such as coherence coherent amplitude gradients and structurally oriented filtering more promising still is the analysis of high resolution dip and azimuth through vol

impacts of columbia river discharge on salmonid habitat 1 a nonstationary fluvial tide model 1 this is the first part of a two part investigation that applies nonstationary time series analysis methods and the st venant equations to the problem of understanding juvenile salmonid access to favorable shallow water habitat in a tidal river habitat access is a function of river stage tidal range and the distribution of bed elevation part 1 models nonstationary tidal properties species amplitudes and phases and tidal range part 2 models low frequency river stage in the lower columbia river and reconstructs historical water levels using the tidal model from part 1 to incorporate the nonstationary frictional effects of variable river discharge into the tidal model we decompose the tidal wave into tidal species and calculate daily tidal range our one dimensional tidal model is based on analytic wave solutions to the linearized st venant equation and uses six coefficients per tidal species to represent the upstream evolution of the frictionally damped tidal wave the form of the coefficients is derived from the st venant equations but their values are determined objectively from the data about 50 station years of surface elevation data collected 1981 2000 below bonneville dam 235 km from the ocean were processed with a wavelet filter bank to retrieve time series of tidal species properties a min max filter was used to estimate daily tidal range tidal range diurnal and semidiurnal amplitudes were predicted with mean root mean square errors 30 mm which is significantly more accurate than predictions obtained from harmonic analysis thus despite the compact form of our solution we model nonstationary fluvial tidal properties with a high level of accuracy

full resolution 3d gpr imaging noninvasive 3d ground penetrating radar gpr imaging with submeter resolution in all directions delineates the internal architecture and processes of the shallow subsurface full resolution imaging requires unaliased recording of reflections and diffractions coupled with 3d migration processing the gpr practitioner can easily determine necessary acquisition trace spacing on a frequency wavenumber f k plot of a representative 2d gpr test profile quarter wavelength spatial sampling is a minimum requirement for full resolution gpr recording an intensely fractured limestone quarry serves as a test site for a 100 mhz 3d gpr survey with 0 1 m 0 2 m trace spacing this example clearly defines the geometry of fractures in four different orientations including vertical dips to a depth of 20 m decimation to commonly used half wavelength spatial sampling or only 2d migration processing makes most fractures invisible the extra data acquisition effort results in image volumes with submeter resolution both

sedimentation processes in the northwest pacific basin revealed by echo character mapping studies bottom echoes recorded from the northwest pacific basin on high frequency 3 5 and 12 khz echograms can be classified into five general types four types are related to sedimentation processes the two most widely recorded echo types roughly correlate with the sediment type of the uppermost sub sea floor type 1 a and b echoes distinct with continuous parallel subbottoms are generally recorded from the northwest portion of the basin where sediments consist of siliceous ooze with inter beds of volcanic ash type ii echoes distinct with continuous subbottoms in the top 10 to 20 m and semitransparent with discontinuous subbottoms below characterize the southeastern portion of the basin where brown red clays with interbeds of chert predominate type iii echoes are characterized by unconformable migrating or truncated subbottoms occasionally with zones of regular overlapping hyperbolas they represent erosional depositional bed forms created by the flow of thermohaline induced bottom currents that is contour currents presumably the pacific bottom water pbw most of the regions returning type iii echoes are of local extent and are at the bases of seamounts ridges and other topographic obstructions that locally accelerate current flow a few zones of type iii echoes are of regional extent one extensive type iii zone is along the southern boundary of the north pacific basin where the pbw enters from the south through wide gaps in the topography another extensive zone is west of the emperor seamount chain the timing and duration of episodes of the sediment reworking indicated by the type iii echoes are uncertain hydrographic measurements and bottom photographs indicate only weak or sluggish pbw flow throughout the basin at present perhaps most of the sediment reworking occurred during pleistocene and older glacial phases when oceanic water masses may have circulated faster than at present type iv echoes are prolonged incoherent or fuzzy echoes returned from small 5 to 25 km localized slump debris flow deposits these deposits often are observed at the bases of very gentle knolls 100 m relief the majority of the deposits occur in areas of siliceous sediment type i echoes apparently the physical properties of these sediments render them relatively unstable and hence more susceptible to failure than the brown clays

separation and imaging of seismic diffractions using migrated dip angle gathers abstractcommon reflection angle migration can produce migrated gathers either in the scattering angle domain or in the dip angle domain the latter reveals a clear distinction between reflection and diffraction events we derived analytical expressions for events in the dip angle domain and found that the shape difference can be used for reflection diffraction separation we defined reflection and diffraction models in the radon space the radon transform allowed us to isolate diffractions from reflections and noise the separation procedure can be performed after either time migration or depth migration synthetic and real data examples confirmed the validity of this technique

least squares migration of incomplete reflection data a least squares migration algorithm is presented that reduces the migration artifacts i e recording footprint noise arising from incomplete data instead of migrating data with the adjoint of the forward modeling operator the normal equations are inverted by using a preconditioned linear conjugate gradient scheme that employs regularization the modeling operator is constructed from an asymptotic acoustic integral equation and its adjoint is the kirchhoff migration operator we tested the performance of the least squares migration on synthetic and field data in the cases of limited recording aperture coarse sampling and acquisition gaps in the data numerical results show that the least squares migrated sections are typically more focused than are the corresponding kirchhoff migrated sections and their reflectivity frequency distributions are closer to those of the true model frequency distribution regularization helps attenuate migration artifacts and provides a sharper better frequency distribution of estimated reflectivity the least squares migrated sections can be used to predict the missing data traces and interpolate and extrapolate them according to the governing modeling equations several field data examples are presented a ground penetrating radar data example demonstrates the suppression of the recording footprint noise due to a limited aperture a large gap and an undersampled receiver line in addition better fault resolution was achieved after applying least squares migration to a poststack marine data set and a reverse vertical seismic profiling example shows that the recording footprint noise due to a coarse receiver interval can be suppressed by least squares migration