deposition and modification of a flood layer on the northern california shelf lessons from and about the fate of terrestrial particulate organic carbon the 1995 flood of the eel river in northern california provided an opportunity to follow the short term history of riverine particulate matter on a continental shelf particulate organic carbon including both vascular plant debris and soil carbon was utilized as a tracer of the distribution and modification of the shelf flood deposit these components were sorted during initial emplacement of the deposit both in the river plume and in the benthic boundary layer during the 8 months following the flood lateral transport shallow burial and bioturbation contributed to spatial changes in the amount and character of carbon in the flood deposit study of the deposit suggests that this and previous flood layers may be preserved in the shelf and upper slope stratigraphic record as clay rich beds with relatively high carbon to nitrogen ratios and more negative 13c values than background non flood sediment concentrations of vascular plant debris are locally characteristic of such layers and may serve as distinctive stratigraphic markers investigation of organic carbon in the 1995 flood layer on the eel river shelf provides insight into the fate of terrestrial particulate carbon on continental margins in general flooding of the eel river and of similar river systems draining mountainous terrains introduces large quantities of terrestrial carbon to the marine environment and may favor the preservation of both terrestrial and marine carbon the abundant woody vascular plant debris discharged during floods is especially likely to survive oxidation and sulfate reduction in the shallower zones of the seabed this study reveals the dominant role that physical and biological processes may play in attenuating the terrestrial organic carbon signal on shelves over monthly to yearly time scales

prestack depth migration of dense wide angle seismic data abstract prestack depth migration of wide angle seismic data represents an extension of traditional imaging with near vertical incidence data because it includes a larger component of the recorded wave field to date however studies that have employed wide angle migration have suffered because only widely spaced data were available and because only very simple synthetic tests were performed although wide angle migration has the potential to increase our ability to image deep crustal structures particularly when closely spaced data are collected a thorough study of this technique has been lacking to address this we present a case study of prestack depth migration of relatively dense synthetic wide angle marine data the objectives are to identify potential benefits and limitations of this approach and answer such fundamental questions as how close the receiver spacing must be for a typical survey to image effectively with wide angle data this will facilitate the design of better seismic experiments our study employs kirchhoff prestack depth migration of variably spaced full wave field synthetic wide angle ocean bottom hydrophone obh data generated using a realistic velocity model based on the passive eastern margin of the united states we show how an increase in obh density improves the migration by increasing the lateral resolution and signal to noise ratio we also investigate the contribution of various offset ranges to the migrated image and show how the wider angle components contribute primarily to the deepest parts of the image with relatively low spatial frequency compared to the near vertical incidence components to investigate how errors in the velocity model affect imaging as a function of offset range we migrate the data using a velocity model derived from refraction and reflection traveltime inversion this example demonstrates the need to obtain an increasingly accurate model as increasingly wider angle data are migrated to effectively image structures in our 200 40 km synthetic velocity model an obh spacing of approximately 2 km is required

high resolution seismic imaging in deep sea from a joint deep towed obh reflection experiment application to a mass transport complex offshore nigeria we assess the feasibility of high resolution seismic depth imaging in deep water based on a new geophysical approach involving the joint use of a deep towed seismic device sysif and ocean bottom hydrophones obhs source signature measurement enables signature deconvolution to be used to improve the vertical resolution and signal to noise ratio the source signature was also used to precisely determine direct traveltimes that were inverted to relocate source and receiver positions the very high accuracy of the positioning that was obtained enabled depth imaging and a stack of the obh data to be performed the determination of the p wave velocity distribution was realized by the adaptation of an iterative focusing approach to the specific acquisition geometry this innovative experiment combined with advanced processing succeeded in reaching lateral and vertical resolution 2 5 and 1 m in accordance with the objectives of imaging fine scale structures and correlation with in situ measurements to illustrate the technological and processing advances of the approach we present a first application performed during the erig3d cruise offshore nigeria with the seismic data acquired over ng1 a buried mass transport complex mtc interpreted as a debris flow by conventional data evidence for a slide nature of a part of the mtc was provided by the high resolution of the obh depth images rigid behaviour may be inferred from movement of coherent material inside the mtc and thrust structures at the base of the mtc furthermore a silt layer that was disrupted during emplacement but has maintained its stratigraphic position supports a short transport distance

coagulation and transport of sediments in the gironde estuary the distribution of suspended particle size and concentration were measured along the gironde estuary france from the river seaward to the ocean the suspended particle size and volume concentration were measured using in situ holography and onboard optical techniques utilizing special procedures in order to avoid floc breakage sediments discharged by the rivers coagulate upon encountering the very low salinities 0 2 of the upper estuary confirmed with laboratory experiments and are then transported and deposited by currents in the remainder of the estuary this coagulation coupled with estuarine circulation produces a turbidity maximum which is offset between the surface and bottom waters the floc size maximum is oceanward of the turbidity maximum and is likewise offset along the estuary by about 30 km the estuary can be subdivided into the following zones 1 coagulation 2 hydrodynamic landward of the null point and 3 hydrodynamic seaward of the null point initial coagulation appears to be completed in coagulation zone 1 and particles are transported and settled with very little floc breakage and recoagulation in zones 2 and 3 only the floc settling velocities coupled with estuarine circulation control the concentration and size distributions of flocs in the water column and eventually control the deposition of sediments

depth image focusing in traveltime map based wide angle migration wide aperture prestack depth migration requires application of challenging and time consuming velocity analysis and depth focusing collectively referred to here as depth focusing we present an approach to depth focusing using 1 a detailed starting velocity model obtained by a 1 d transformation of the first arrival times followed iteratively by 2 interactive analysis of the common image gathers 3 computation of coherency attributes of the wavefield in the depth domain and 4 2 d traveltime tomography to update the background velocity model we employ two interactive method of migration velocities refinement in the first method similar to the common midpoint velocity spectrum approach residual velocity updates are picked directly from the common image gathers in another method analogous to the common velocity stacks we pick the velocity updates from the areas of maximum coherency in depth sections that are migrated using rescaled traveltime maps both types of migration velocity picks

prestack residual migration in the frequency domain prestack stolt residual migration can be applied to seismic images that are depth migrated using wavefield extrapolation techniques this method has significant advantages over other methods that estimate interval velocity functions for depth migration it is more accurate than methods that are based on focusing the stack of migrated images by a residual nmo operation so it provides a more accurate estimate of the correct migration velocities also it is conceptually simpler and easier to implement than traveltime tomography methods although the theory is developed assuming constant velocity the method can be used for depth migrated images produced with smoothly varying velocity models since the residually migrated images depend only on the ratio of the reference and updated velocities this method closely resembles stolt stretch techniques so it inherits the stolt method s speed and convenience the main applications of this method are in migration velocity analysis mva where it can be used to i

kirchhoff image propagation seismic imaging processes are in general formulated under the assumption of a correct macrovelocity model however seismic subsurface images are very sensitive to the accuracy of the macrovelocity model this paper investigates how the output of kirchhoff inversion migration changes for perturbations of a given 3 d laterally inhomogeneous macrovelocity model the displacement of a reflector image point from a perturbation of the given velocity model is determined in a first order approximation by the corresponding traveltime and slowness perturbations as well as the matrix of the beylkin determinant the required traveltime derivatives can be calculated with ray perturbation theory using this result a new computationally efficient kirchhoff inversion migration technique is developed to predict in parallel a series of subsurface images for perturbations of a given macrovelocity model during a single inversion migration process applied to the unmigrated seismic data these images are constructed by su

combining borehole and surface seismic data for velocity field estimation through slope tomography a joint traveltime and slope or slowness tomography method of marine surface reflections and walk away transmitted arrivals is investigated based on our previous developments of 2 d isotropic slope tomography dedicated to reflection data the transmitted arrivals are added into the inversion scheme the results of the transmitted arrival tomography are compared to those of the joint transmitted and reflected arrivals tomography on synthetic data moreover a quality control qc procedure is proposed finally walk away transmitted arrivals surface reflected arrivals and joint tomography of both arrivals are applied on real data sets from oseberg north sea these data include 2 d surface and walk away lines along the same direction the resulting velocity fields are used for pre stack depth migration allowing us to conclude that joint inversion leads to significantly improved images both in terms of focusing and event location a key point is that improvements are not restricted in the area covered by transmitted arrivals as the number of available borehole receivers is small this case study demonstrates the strong impact direct arrivals that may have on depth imaging

velocity analysis by iterative profile migration in conventional seismic processing velocity analysis is performed by using the normal moveout nmo equation which is based on the assumption of flat horizontal reflectors imaging by migration either before or after stack is done normally in a subsequent step using these velocities in this paper velocity analysis and imaging are combined in one step and migration itself is used as a velocity indicator because unlike nmo migration can be formulated for any velocity function migration based velocity analysis methods are capable of handling arbitrary structures i e those with lateral velocity variations in the proposed scheme each shot gather profile is migrated with an initial depth velocity model profile migration is implemented in the x domain but the actual implementation of profile migration is not critical as long as it is not done in a spatial wavenumber domain which would preclude handling of lateral velocity variations after migration with an initial velocity model the

suspended sediment concentration and calibre in relation to surface flow structure in squamish river estuary southwestern british columbia surface grabs of suspended sediments from boils and the background flow in squamish estuary revealed strong differences between the two environments boils exhibit higher sediment concentrations and larger particle sizes than the background flow the higher sediment concentrations and larger grain sizes in boils are related to tidal phase with maximum concentrations and sediment sizes occurring in the early decelerating phase of the tidal flow sediment concentrations and grain sizes in the background flow are comparatively invariant with tidal phase boils appear to play an important if not dominant role in suspending and transporting sand sized sediments in squamish estuary

application of rtm 3d angle gathers to wide azimuth data subsalt imaging the availability of wide azimuth data and the use of reverse time migration rtm have dramatically increased the capabilities of imaging complex subsalt geology with these improvements the current obstacle for creating accurate subsalt images now lies in the velocity model one of the challenges is to generate common image gathers that take full advantage of the additional information provided by wide azimuth data and the additional accuracy provided by rtm for velocity model updating a solution is to generate 3d angle domain common image gathers from rtm which are indexed by subsurface reflection angle and subsurface azimuth angle we apply these 3d angle gathers to subsalt tomography with the result that there were improvements in velocity updating with a wide azimuth data set in the gulf of mexico

hydrodynamic sorting and transport of terrestrially derived organic carbon in sediments of the mississippi and atchafalaya rivers abstract over the course of two years four cruises were conducted at varying levels of discharge in the lower mississippi and atchafalaya rivers mr and ar where grab samples were collected from sand and mud dominated sediments the tetramethylammonium hydroxide tmah thermochemolysis method was used to determine sources of terrestrially derived organic carbon oc in these two sediment types to examine the effects of hydrodynamic sorting on lignin sources in river sediments average lignin concentrations in the lower mr were 1 4 1 1 mg goc 1 at english turn et and 10 4 27 4 mg goc 1 at venice using these concentrations annual lignin fluxes to the gulf of mexico from tidal and estuarine mud remobilization at et and venice were 3 1 2 5 10 5 kg and 11 4 30 0 10 5 kg respectively much of the lignin derived materials in muddy sediments appeared to be derived from non woody grass like sources which should decay more quickly than the woody materials typically found in the sandy deposits the average total oc 1 93 0 47 of english turn sands yields an annual flux of 0 34 0 09 10 9 kg lignin flux in the english turn sands 3 6 2 6 mg gc 1 using the numbers above would be 12 2 9 4 10 5 kg the extensive amounts of sand sized woody materials coffee grinds found in the sandy sediments in both the ar and mr are likely derived from woody plant materials this is the first time it has been demonstrated that sandy sediments in the mr provide an equally important pathway compared to muds for the transport of terrestrially derived organic matter to the northern gulf of mexico using the ar average oc in sand 1 16 0 72 we estimated an annual flux of oc to the shelf of 0 13 0 07 10 9 kg lignin flux for ar sands was estimated to be 12 4 12 1 10 5 kg despite the high error associated with these numbers we observe for the first time that the flux of lignin in sandy sediments in the ar to the northern gulf of mexico is comparable to that found in the mr these results further support the likelihood of grain size related hydrodynamic sorting of terrestrially derived organic carbon in the lower mississippi and atchafalaya rivers suggesting that there is a distinct sandy sediment organic fraction contributed by major rivers to the global carbon cycle

dynamics of the turbidity maximum in king sound tropical western australia king sound is a 100 km long embayment located in tropical northwestern australia with a spring tidal range of 11 m this is the second largest tide in the world after the bay of fundy in canada intertidal areas cover about 800 km2 the upper reaches of the sound are turbid with fine suspended sediment concentration reaching 3 kg m 3 field studies of the dynamics of water and fine sediment were carried out in the dry seasons of 1997 and 1998 the tide was a propagating wave shoaling and dissipating by friction as it entered the sound this mode of propagation generated an asymmetric tidal current with a stronger current at flood than at ebb an evaporation driven salinity maximum zone was found in the upper reaches of the sound and this was also where the turbidity maximum occurred tidal pumping by the tidal asymmetry and possibly the biological filter formed by muddy marine snow trapped the fine sediment in the upper regions of king sound wind driven waves contributed significantly to entrainment of bottom fine sediment possibly through wave pumping of the sediment and not wave induced orbital velocities field data suggest that erosion of bottom fine sediment was proportional to the sixth power of the tidal current and the third power of the wave height

in situ estimations of the density and porosity of flocs of varying sizes in a submarine canyon abstract this paper introduces a new method to estimate in situ floc density and porosity of three particle size classes 0 45 10 10 63 and 63 250 m lisst 100 and catnet a novel on board filtration system of nested filters were used to measure suspended particle volume and mass concentrations of 32 and 3 size classes respectively two field experiments were conducted in 2004 and 2006 in the head region of gaoping submarine canyon gpsc to test this method in each experiment ctd and lisst 100 profiling and simultaneous water sampling were carried out on board r v ocean research iii in 2004 the water samples were filtered in the laboratory after the cruise using traditional methods catnet was used in 2006 and the seawater filtration was done on board assuming the observed suspended particles were all flocs composed of primary particles with assumed density of 2 65 g cm 3 and interstitial water with assumed density of 1 025 g cm 3 we estimated the volume of primary particles the volume difference between flocs measured from lisst 100 and primary particles is the interstitial pore space in flocs subsequently the porosity of a floc particle is the ratio of the volume of the interstitial pore space to that of the floc particle results for 2004 show erroneous values of estimated floc porosities which do not appear in 2006 the major difference is that the seawater was filtered immediately on board using catnet in 2006 after removing erroneous data related to after cruise filtering the averaged floc porosity and density in the three grain size classes were 47 0 64 0 85 9 and 1 89 1 61 1 25 g cm 3 respectively there is a trend that larger particles have lower density which is supported by literature the temporal variations of floc density and porosity of all three particle size groups were larger in the surface than near the bottom of the submarine canyon this vertical variability resulted from flocculation and biogenic processes in the surface of the coastal ocean and the terrestrial source of the gaoping river floc density is an important physical parameter to evaluate the settling flux of suspended sediments in estuarine and marine environments this approach provides direct in situ floc bulk densities of different grain size classes which has advantages over conventional methods

flocculation and sedimentation on the po river delta with the goal of improving understanding of the effect of flocculation on the formation of fine grained deposits on continental shelves hydrographic profiling in situ imaging of suspended matter and collection of surficial sediment samples were conducted at the po river delta in june 2001 these data show that during medium flow conditions 1920 m3 s sedimentation occurs rapidly immediately offshore of the main distributary po della pila rapid sedimentation is promoted by large rapidly sinking flocs forming in the river well upstream of the mouth the delivery of fine sediment to the seabed at the mouth of the po is sufficient to overwhelm the erosive effects of waves and currents leading to accumulation of mud in water depths as shallow as 4 m on cross shelf transects 2 km north and south of the mouth however suspended sediment supply from the river is reduced to the point that mud accumulates only seaward of the 8 m isobath along the central transect suspended sediment concentration decreases rapidly seaward of the 6 m isobath where the emergence of a more organic rich population of flocs along a mid water density interface is suggested energetic activity along the 15 m isobath likely promotes resuspension with the potential for removal of material from the delta further investigation of floc properties namely the relationship of floc size to settling velocity is necessary to establish the degree to which the suspension is flocculated during transport and deposition

depth characterization of shallow aquifers with seismic reflection part ii prestack depth migration and field examples it is common in shallow seismic studies for the compressional wave velocity in unconsolidated sediments to increase by a factor of four or more at the transition from dry or partial water saturation to full saturation under these conditions conventional nmo velocity analysis fails and leads to large depth and layer thickness estimates if the dix equation is assumed valid prestack depth migration psdm is a means of improving image accuracy a comparison of psdm with conventional nmo processing for three field examples from differing hydrogeologic environments illustrates that psdm can significantly improve image quality and accuracy

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

prestack time migration velocity analysis using remigration trajectories abstractwe have developed a prestack time migration tool for local improvement of the seismic migration velocity model the method is based on remigration trajectories that describe the position of an image point in the image domain for different source receiver offsets as a function of the migration velocity it determines kinematic migration parameters using local slope information of migrated seismic reflection events these parameters in turn are used to locally correct the velocity model the main advantage of this technique is that it allows us to carry out a moveout correction not just at a fixed point in a zero offset poststack time migrated gather but varying through all offsets of a common image gather taking into account the reflection point displacement in the midpoint direction in other words it provides for time migration velocity analysis from prestack data we have tested the feasibility of the method on synthetic data from four simple models and the sigsbee2b data our tests deter

an experimental study on the ripple dune transition flume experiments were conducted on different bed stages across the ripple dune transition as flow velocity increases an initially flat bed surface made of fairly uniform sandy material is gradually transformed into a two dimensional rippled bed with further increase in velocity two dimensional ripples are replaced by irregular linguoid ripples as the average velocity necessary for the ripple dune transition to occur is imposed on the bed surface these non equilibrium linguoid ripples are further transformed into larger two dimensional dunes for each of these stages across the transition a concrete mould of the bed was created and the flow structure above each fixed bed surface investigated an acoustic doppler velocimeter was used to study the flow characteristics above each bed surface detailed profiles were used along a transect located in the middle of the channel results are presented in the form of spatially averaged profiles of various flow characteristics and of contour maps of flow fields section view they clearly illustrate some important distinctions in the flow structure above the different bedform types associated with different stages during the transition turbulence intensity and reynolds stresses gradually increase throughout the transition two dimensional ripples present a fairly uniform spatial distribution of turbulent flow characteristics above the bed linguoid ripples induce three dimensional turbulence structure at greater heights above the bed surface and turbulence intensity tends to increase steadily with height above bed surface in the wake region a very significant increase in turbulence intensity and momentum exchange occurs during the transition from linguoid ripples to dunes the turbulent flow field properties above dunes are highly dependent on the position along and above the bed surface and these fields present a very high degree of spatial variability when compared with the rippled beds further investigations under natural conditions emphasizing sediment transport mechanisms and rates during the transition should represent the next step of analysis together with an emphasis on quadrant analysis copyright 2001 john wiley sons ltd

seismic velocity model building in an area of complex geology southern alberta canada we developed velocity models to prestack depth migrate two seismic lines acquired in an area of complex mountainous geology in southern alberta canada initial processing in the time domain was designed to attenuate noise and enhance the signal in the data the prestack and poststack time migrated sections were poorly focused implying the velocity models would be inadequate for prestack depth migration the velocity models for prestack depth migration developed by flattening reflections on common image gathers ineffectively imaged the complex geology we developed our most effective velocity models by integrating the mapped surface geology and dips well formation tops geological cross sections and seismic velocity information into the interpretation of polygonal areas of constant velocity on several iterations of prestack depth migrated seismic sections the resulting depth processed sections show a more geologically realistic geometry for the reflectors at depth and achieve better focusing than either the time migrated sections or the depth sections migrated with velocity models derived by flattening reflections on offset gathers

joint ray born least squares migration and simulated annealing optimization for target oriented quantitative seismic imaging a seismic processing workflow based on iterative ray born migration inversion and target oriented postprocessing of the migrated image is developed for fine scale quantitative characterization of reflectors the first step of the workflow involves linear iterations of the ray born migration inversion the output of the first step is a true amplitude migrated image parameterized by velocity perturbations in a second step postprocessing of the migrated image is performed through a random search with a very fast simulated annealing vfsa algorithm the forward problem of the global optimization is a simple convolutional model that linearly relates a vertical profile of the band limited migrated image after depth to time conversion to a 1d velocity model composed of a stack of homogeneous layers of arbitrary velocity and thickness the aim of the postprocessing is to eliminate the limited bandwidth effects of the source from the migrated image for resolution improvement and enhanced geological interpre

migration of wide aperture onshore offshore seismic data central california seismic images of late stage subduction we conducted a high shot and receiver density onshore offshore seismic experiment in 1986 across the central california transform margin as part of the pacific gas and electric edge deep crustal geophysical survey the data set consists of land recordings of 406 marine air gun shots fired along a 70 km track across the santa maria basin the seismic vessel s track was collinear with 154 land seismic recorders deployed over 50 km across the sur obispo terrane and part of the salinian block the source receiver offsets range from 2 5 km to 120 km the unique recording geometry and high shot and receiver density permit imaging the deeper crustal structure of the california transform margin but pose serious challenges for conventional seismic imaging methods consequently we developed a unified approach to wide angle imaging which incorporates a tomography technique for obtaining initial migration velocity models and a prestack kirchhoff depth migration with depth focusing of the main reflectors for velocity model refinement and imaging this approach retains the velocity and dip information in the data and allows user control over the imaging process we applied this processing to subsets of the onshore offshore data to obtain an upper crustal velocity model and a 32 km long wide angle depth migrated image of the lower crust in the coastal region under the santa maria basin and the sur obispo terrane the migration image shows a part of an underplated oceanic crustal layer interpreted as the monterey plate meltzer and levander 1991 miller et al 1992 which dips coastward at depths of 18 to 28 km the plate appears to be kinked or imbricated beneath the coastline the image correlates well with existing wide angle seismic interpretations based on ray tracing walter and sharpless 1987 putzig 1988 howie et al 1993 the migrated lower crustal image has more structural information than is apparent in conventional ray based interpretations along the same crossing and adjacent profiles the crustal image demonstrates that automated imaging techniques applied to wide angle data can provide images of crustal structure comparable in fidelity to conventionally processed and migrated near vertical incidence data

applicability of artificial neural networks for obtaining velocity models from synthetic seismic data seismic velocity analysis is a crucial part of seismic data processing and interpretation which has been practiced using different methods in contrast to time consuming and complicated numerical methods artificial neural networks anns are found to be of potential applicability ann ability to establish a relationship between an input and output space is considered to be appropriate for mapping seismic velocity corresponding to travel times picked from seismograms accordingly a preliminary attempt is made to evaluate the applicability of anns to determine velocity and dips of dipping layered earth models corresponding to travel time data the study is based on synthetic data generated using inverse modeling approach for three earth models the models include a three layer structure with same dips and same directions a three layer model with different dips and same directions as well as a two layer model with different dips and directions an ann structure is designed in three layers namely input output and hidden ones the training and testing process of the ann is successfully accomplished using the synthetic data the evaluation of the applicability of the trained ann to unknown data sets indicates that the ann can satisfactorily compute velocity and dips corresponding to travel times the error intervals between the desired and calculated velocity and dips are shown to be acceptably small in all cases the applicability of the trained ann in extrapolating is also evaluated using a number of data outside of the range already known to ann the results indicate that the trained ann acceptably approximates the velocity and dips furthermore the trained ann is also evaluated in terms of capability of handling deficiency in input data where acceptable results were also achieved in velocity and dip calculations generally this study shows that velocity analysis using anns can promisingly tackle the challenge of retrieving an initial velocity model from the travel time hyperbolas of seismic data

focusing in prestack isochrone migration using instantaneous slowness information prestack migration finds increasing application in processing crustal seismic data however less effort has been made to incorporate slowness information in the imaging process the combination of slowness information with migration leads to an improved image in the depth domain especially by reducing migration artefacts and noise a slowness driven isochrone migration scheme is introduced for migration of 2 d seismic data instantaneous slowness information p x t is extracted from the data using correlation analysis in moving time and space windows slowness values resulting from spatial coherent energy signal and incoherent background noise are distinguished by the simultaneous evaluation of an instantaneous coherence criterion g x t in slowness driven isochrone migration this information is used for locally weighting the amplitude a x t smearing on the isochrone surface in particular slowness p and coherence criterion g determine position and sharpness of a gaussian weighting function the method is demonstrated using two synthetic data examples and is subsequently applied to two deep crustal data sets one wide angle along dekorp4 and one steep angle reflection seismic observation ktb8506 both data sets were collected in the surroundings of the ktb drill site oberpfalz as part of the german dekorp project

seismic wave equation demigration migration reverse time migration is a well known method based on a single scattering approximation it is designed to obtain seismic images in the case of a complex subsurface it can however be a very time consuming task because the number of computations is directly proportional to the number of processed sources in the context of velocity model building iterative approaches require that one derives a series of migrated sections for different velocity models we propose to replace the summation over sources by a summation over depth offsets or time delays defined in the subsurface for that we have developed a new relationship between two migrated sections obtained for two different velocity models starting from one of the two images we obtain a second section correctly and efficiently for each time delay we compute a generalized source term by extending the concept of exploding reflector to nonzero offset we obtain the final migrated section by solving the same wave equation in the perturbed model with the modified source term our work included testing the methodology on 2d synthetic data sets particularly when the initial and perturbed velocity models differ greatly

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

dynamics of a river channel confluence with discordant beds flow turbulence bed load sediment transport and bed morphology 1 river channel confluences play a major role in the dynamics of all fluvial systems and yet our understanding of bed load routing at these sites is very sparse the dynamics of confluences are a function of the momentum ratio between the combining flows and the three dimensional geometry of the junction recent experiments have shown that discordance in bed height between the confluent rivers increases turbulence intensity and enhances upwelling of flow within the confluence however the significance of these flow characteristics on sediment transport is still unknown to examine the relations between flow and sediment transport we have measured near bed flow turbulence bed load transport rates and changes in bed morphology for eight different flow conditions at a sand bed discordant confluence detailed analysis of the near bed flow patterns reveals that within the shear layer low mean flow velocities are combined with the highest values of reynolds shear stresses and that turbulence generation is associated with intense upward movements of flow high sediment transport rates are found at the edges of the shear layer region where horizontal vertical cross stresses uw are high these patterns match changes in bed morphology where erosion occurs along the shear layer the relation between the shear layer and sediment transport confirms the role of bed discordance on the dynamics of the confluence migration of the shear layer into the confluence as a result of a change in momentum ratio modifies local near bed flow characteristics sediment transport rates and the spatial distribution of deposition and erosion zones

tidal oscillation of sediment between a river and a bay a conceptual model a conceptual model of fine sediment transport between a river and a bay is proposed based on observations at two rivers feeding the same bay the conceptual model consists of river transitional and bay regimes within the transitional regime resuspension advection and deposition create a mass of sediment that oscillates landward and seaward while suspended this sediment mass forms an estuarine turbidity maximum at slack tides this sediment mass temporarily deposits on the bed creating landward and seaward deposits tidal excursion and slack tide deposition limit the range of the sediment mass to verify this conceptual model data from two small tributary rivers of san pablo bay are presented tidal variability of suspended sediment concentration markedly differs between the landward and seaward deposits allowing interpretation of the intratidal movement of the oscillating sediment mass application of this model in suitable estuaries will assist in numerical model calibration as well as in data interpretation a similar model has been applied to some larger scale european estuaries which bear a geometric resemblance to the systems analyzed in this study 2004 elsevier ltd all rights reserved

partition of suspended and riverbed sediments related to the salt wedge in the lower reaches of a small mountainous river a month long comprehensive field experiment during the beginning of the flood season of a small mountainous river in southern taiwan was carried out in 2004 the major goal of the study was to investigate the effect of hydrodynamic sorting related to the salt water intrusion on the spatial variability of suspended and riverbed sediments and their coupling of different sizes the experiment included the deployment of an instrumented tetrapod near the river mouth with an upward looking adcp and two ctds mounted at 50 and 100 cm above the bed cmab respectively on three different days along the river turbidity salinity and temperature of the water column were profiled and water samples were taken from the surface and near the bed at different stations additionally one sediment sample was also taken from the riverbed suspended sediment concentrations ssc were analyzed for five different sizes i e 500 250 500 63 250 10 63 and 1 2 10 m by filtration for each riverbed sample the size composition was analyzed for the subsample that contained lithogenic and nonlithogenic components and the subsample having major nonlithogenic components organic matter carbonates and biogenic opal was removed the grain size frequency distributions of the riverbed samples were analyzed using a laser particle analyzer the results were grouped into the following size classes 473 249 473 62 249 10 62 and 10 m for comparison with those of the suspended sediments near the riverbed some suspended sediment samples were analyzed for poc and pon some riverbed samples were analyzed for toc statistical methods of linear regression and empirical orthogonal eigen function eof were used in the data analysis two layered estuarine circulation pattern was observed at the tetrapod site the tidally driven salt water intrusion is the major factor influencing the hydrodynamics of the gaoping river which in turn affect the longitudinal and vertical distribution of the suspended sediments and the longitudinal distribution of the riverbed sediments during the flood the intrusion front of the salt wedge creates a dynamic barrier upriver from this barrier the riverbed substrate is coarser composed of sediments mostly coarser than 249 m within the salt wedge the riverbed substrate is finer consisting of mostly mud 62 m the barrier creates a trap on the riverbed immediately seaward from the intrusion front retaining higher percentages of clay sized sediments and toc the barrier also creates partition in the terrestrial and marine sources of organic matter in the suspended and riverbed sediments within the salt wedge the major contributor of riverbed toc is the clay sized marine sediment transport upriver by the intruding seawater the terrestrial poc is a minor contributor to the riverbed toc the riverbed and suspended sediments are coupled most size classes in corresponding suspended and riverbed sediments have a reciprocal relationship negative feedback through resuspension and deposition on the water bed interface the only size class of 62 473 m on the riverbed and 63 250 m in the suspension are co varying positive feedback this size class contains largely a transient floc population that is formed and disintegrated in situ both on the riverbed and in the suspension in the course of a tidal cycle

winter storms induced high suspended sediment concentration along the north offshore seabed of the changjiang estuary abstract fine grained sediments suspended in coastal waters play an important role in submarine topography evolution and associated environment changes the convergence of suspended sediments concentrated near the seabed results in high sediment concentration and contributes significantly to sediment transport in order to investigate the mechanism triggering high suspended sediment concentration ssc we deployed a tripod to the seabed to obtain in situ bottom boundary layer measurements of sediment dynamics and a buoy to the sea surface to collect meteorological and wave data at the northern changjiang river mouth from december 20 2015 to january 20 2016 the high ssc e g 3 g l events were observed together with fluid mud thicknesses of 4 16 cm near the seabed during neap tides when cold air intrusion generated winter storms and strong waves further we found that the high ssc event was mainly resulted from wind waves and sediment resuspension supported by local benthic fluid mud which was associated with three stages at the setting up stage the winter storm brought long duration of strong waves e g significant wave height 1 5 m more than 15 h resulting in a maximum wave current combined bottom shear stress of 3 2 pa and the increase of ssc to 1 g l at the reinforcement stage the strong waves and bottom shear stress lasted for several hours and further increased the ssc to 3 g l at the final decay stage wind waves and the maximum wave current shear stresses decreased significantly with the disappearance of high ssc thus there was no high ssc event observed even with strong wind waves during spring tides because strong wave duration was too short for the reinforcement process the sediment source for the high ssc events was mainly from bottom fluid mud resuspension as well as the advection transport from the adjacent subaqueous changjiang river delta

shot and angle domain wave equation traveltime inversion of reflection data synthetic and field data examples abstractfull waveform inversion requires the accurate simulation of the dynamics and kinematics of wave propagation this is difficult in practice because the amplitudes cannot be precisely reproduced for seismic waves in the earth wave equation reflection traveltime tomography wt is proposed to avoid this problem by directly inverting the reflection traveltime residuals without the use of the high frequency approximation we inverted synthetic traces and recorded seismic data for the velocity model by wt our results demonstrated that the wave equation solution overcame the high frequency approximation of ray based tomography was largely insensitive to the accurate modeling of amplitudes and mitigated problems with ambiguous event identification the synthetic examples illustrated the effectiveness of the wt method in providing a highly resolved estimate of the velocity model a real data example from the gulf of mexico demonstrated these benefits of wt but also found the limitations in traveltime

particle dynamics of the surface intermediate and benthic nepheloid layers under contrasting conditions of summer monsoon and typhoon winds on the boundary between the taiwan strait and east china sea abstract two shipboard surveys of hydrographics and sediment dynamics were conducted off the mouth of minjiang the min river in july 2012 under contrasting summer monsoon and typhoon wind conditions observations included profiles of conductivity temperature depth fluorescence and suspended particle volume concentration and current velocity in addition water samples were taken for the analyses of mass concentration poc and chlorophyll of suspended sediment seafloor sediment samples were also taken for grain size analysis nepheloid layers nls were observed at surface intermediate and benthic depths snl inl bnl respectively the nl dynamics under the two wind conditions were mainly controlled by 1 the presence of the minjiang river plume and terrigenous material it carries 2 water column stability affected by wind current and waves 3 current induced resuspension of seafloor sediment and 4 physically coupled biological activities the wind field was the major forcing controlling the observed flow field and the upper water column stability in the typical summer condition southerly winds induced offshore directed currents enhancing the seaward dispersal of the minjiang river plume facilitating water column stratification thereby forming 3 nls in the water column phytoplankton growth was enhanced by terrigenous material and sunlight the suspension of the seafloor sediment was the one of the major sources for suspended particles in these nls furthermore the c n ratio of poc in the three nls is 5 72 almost identical to the redfield ratio indicating their predominant marine origin conversely under typhoon related northerly winds the offshore spread of the river plume was restricted the reduced riverine input and enhanced mixing resulted in the disappearance of the snl elevated turbidity in the inl was largely due to the presence of phytoplankton while the bnl was comprised of sediment resuspended off the seafloor and from horizontal advection our results suggest that the presence of the river plume from the minjiang at the study site sets the condition for the snl dynamics the dynamics of inl and bnl were dominated by the wind field and to a lesser degree the wave field and tidal current

the isochron ray in seismic modeling and imaging the isochron the name given to a surface of equal two way time has a profound position in seismic imaging in this paper i introduce a framework for construction of isochrons for a given velocity model the basic idea is to let trajectories called isochron rays be associated with iso chrons in an way analogous to the association of conventional rays with wavefronts in the context of prestack depth migration an isochron ray based on conventional ray theory represents a simultaneous downward continuation from both source and receiver the isochron ray is a generalization of the normal ray for poststack map migration i have organized the process with systems of ordinary differential equations appearing on two levels the upper level is model independent and the lower level consists of conventional one way ray tracing an advantage of the new method is that interpolation in a ray domain using isochron rays is able to treat triplications multiarrivals accurately as opposed to interpolation in the dep

image domain wavefield tomography with extended common image point gathers waveform inversion is a velocity model building technique based on full waveforms as the input and seismic wavefields as the information carrier conventional waveform inversion is implemented in the data domain however similar techniques referred to as image domain wavefield tomography can be formulated in the image domain and use a seismic image as the input and seismic wavefields as the information carrier the objective function for the image domain approach is designed to optimize the coherency of reflections in extended common image gathers the function applies a penalty operator to the gathers thus highlighting image inaccuracies arising from the velocity model error minimizing the objective function optimizes the model and improves the image quality the gradient of the objective function is computed using the adjoint state method in a way similar to that in the analogous data domain implementation we propose an image domain velocity model building method using extended common image point space and time lag gathers constructed sparsely at reflections in the image the gathers are effective in reconstructing the velocity model in complex geologic environments and can be used as an economical replacement for conventional common image gathers in wave equation tomography a test on the marmousi model illustrates successful updating of the velocity model using commonimage point gathers and resulting improved image quality

watershed control on the carbon loading of marine sedimentary particles abstract previous investigations of the factors governing organic carbon burial on continental margins have pointed toward the important apparently protective association of carbon with mineral particles these studies have also revealed dramatic transformations of carbon particle relationships at the land sea interface riverine particles in some settings lose a large portion of their loads of sorbed terrestrial carbon upon discharge to the ocean and gradually reload to similar levels with marine carbon the eel river in northern california and the adjacent continental shelf were selected as an ideal system to investigate the rates of these processes the river is episodically subject to large floods and the shelf stratigraphy preserves a record of the resultant large pulses of sediment and carbon input to the marine environment carbon isotopic carbon to nitrogen and carbon to surface area ratios of particles in flood deposits were expected to reflect the rapid unloading of terrestrial carbon from discharged particles whereas nonflood sediments that have accumulated at slower rates on the shelf were expected to carry higher loads of marine carbon our results indicate however that particles on the eel shelf have retained their loads of terrigenous carbon and that a significant portion of the particle sorbed carbon buried on the shelf is kerogen derived from the mesozoic tertiary franciscan complex we hypothesize that rates of uplift and mass wasting in the eel watershed and rates of particle delivery to and burial on the continental shelf are so rapid that kerogen is not completely oxidized and is recycled instead the loading of carbon on clay sized particles delivered to the shelf moreover is dependent on river discharge and may reflect the relative importance of different mass wasting processes during precipitation events of varying intensity the eel river system is likely to be representative of other small mountainous rivers and indicates that processes on land may play an important role in governing the amount and character of carbon being buried on the continental margins

joint inversion of multichannel seismic reflection and wide angle seismic data improved imaging and refined velocity model of the crustal structure of the north ecuador south colombia convergent margin 1 improving seismic imaging of the crust is essential for understanding the structural factors controlling subduction zones processes we developed a processing work flow based on the combined analysis of multichannel seismic reflection mcs and wide angle wa reflection refraction data to derive both shallow and deep velocities suitable for prestack depth migration and to construct a blocky velocity model integrating all identifiable seismic phases contained in mcs and wa data we apply this strategy to the study of the north ecuador sw colombia subduction margin to improve the imaging and geostructural interpretation of a splay fault and surrounding outer and inner margin wedges results show improvements over tomographic inversion of wa data only such as 1 sediment velocity variation across the trench and margin slope that correlates with lateral lithologic changes tectonic compaction and effect of mass wasting processes 2 a two layer velocity structure of the inner wedge basement that is consistent with the crust of an oceanic plateau 3 a complex velocity structure of the outer wedge basement that consists of a deep high velocity 5 0 5 5 km s 1 core and a low velocity zone 3 8 5 0 km s 1 associated with the major splay fault 4 a 1 3 km thick low velocity 3 5 4 0 km s 1 subduction channel that extends beneath the margin outer wedge both the splay fault and subduction channel are expected to direct fluid flows and 5 downdip velocity increase 5 6 km s 1 in the subducting oceanic crust associated with a low 7 8 km s 1 upper mantle velocity possibly reflecting changes in rock nature or properties

erosion and sedimentation as processes controlling the bsr derived heat flow on the eastern nankai margin in 2000 a 3d mcs survey was carried out on the eastern nankai trough a strong and widespread bottom simulating reflector bsr was observed and mapped after a preserved amplitude 3d prestack migration of the seismic data we use this bsr to calculate a heat flow map over the 3d survey area this map presents some high and low heat flow areas that cannot be correlated to known active wedge faults and previously observed fluid venting sites since the heat flow anomalies are not correlated to known major faults or fluid venting sites large fluid circulation is not likely to explain the varying bsr derived heat flow distribution in order to explain this heat flow distribution quantitatively we calculate the rates of erosion and sedimentation that are necessary to create these anomalies these rates are in good agreement with observations on seismic profiles and are locally consistent with a sedimentation rate calculated from slope basin depth and reflect the distribution of erosion landsliding and deposition on the margin slope we therefore propose that the observed bsr derived heat flow anomalies are mainly due to active erosion and sedimentation and that heat flow distribution on the margin section of the 3d survey is controlled by surface processes fluid migration could occur where a bsr is absent but is probably episodic or limited where a bsr is present and does not affect the bsr derived heat flow in this part of the margin these surface processes are the consequence of the tectonic and seismic activity of the wedge and are influenced by the subduction of a wide oceanic ridge below the eastern nankai margin

sensitivity kernel based tomographic migration velocity analysis using reverse time migration angle image gathers abstractsensitivity kernel based tomographic migration velocity analysis tmva provides a means to better update the migration velocity model in complex media for actual seismic data with finite frequency bandwidth migration velocity updated from wave equation based tomography is more suitable and robust than ray based tomography for images obtained from reverse time migration rtm depth residuals in the rtm extracted angle image gathers offer a reliable source of velocity information we have developed cost effective means of calculating the angle domain sensitivity kernel and incorporated it into the tmva approach using rtm angle image gathers the angle domain sensitivity kernels are used to convert the depth residuals from rtm angle image gathers into velocity perturbations which were then used to refine the velocity model we derived an approximate analytical residual moveout function for measuring depth residuals of the rtm angle image gather in isotropic media and also devised a workflow for

seamount subduction at the north ecuadorian convergent margin effects on structures inter seismic coupling and seismogenesis at the north ecuadorian convergent margin 1 s 1 5 n the subduction of the rough nazca oceanic plate leads to tectonic erosion of the upper plate and complex seismogenic behavior of the megathrust we used three selected pre stack depth migrated multi channel seismic reflection lines collected during the sisteur cruise to investigate the margin structure and decipher the impact of the subducted atacames seamounts on tectonic erosion interseismic coupling and seismogenesis in the region of the 1942 mw7 8 earthquake this dataset highlights a subducted 30 40 km 30 40 km double peak seamount that belongs to the atacames seamount chain and that is associated with a deep morphologic re entrant containing mass transport deposits the seamount subduction uplifted the margin basement by 1 6 km and pervasively broke the margin by deep and intense reverse faulting ahead of the seamount a process that is likely to weaken considerably the margin in the seamount wake the basement reverse fault system rotated counter clockwise this faulted basement is overlain with slope sediment sliding along listric normal faults that sole out onto the bsr this superposition of deep tectonic contraction within the basement and shallow gravitational extension deformation within the sediment highlights the key role of gas hydrate on outer slope erosion in addition to long term regional basal erosion the margin basement has thinned locally by an extra 0 8 1 km in response to the subduction of the atacames seamount chain and hydrofracturing by overpressured fluids at the margin toe this pervasively and deeply fractured margin segment is associated with a seismically quiet and gps modeled low interseismic coupling corridor that terminates downdip near the 1942 epicenter and locked zone we suggest that the deeply buried double peak atacames seamount triggered the 1942 earthquake ahead of its leading flank this result supports previous studies proposing that subducted seamounts provide unfavorable conditions for locking the updip segment of the plate boundary limiting the updip extent of seismogenic zones but may favor large subduction earthquakes at greater depths

groundwater seawater interactions off the coast of southern taiwan evidence from environmental isotopes abstract we have conducted detailed hydrochemical surveys off the pingtung plain coast sw taiwan using environmental isotope compositions d 18 o 13 c dic tritium and 14 c as the main tracers to investigate groundwater seawater interactions in the region the 18 o values of seawater in this area show significant variability with heavy isotope enrichment relatively to groundwater the d and 18 o data also confirmed that submarine groundwater discharge sgd originated from meteoric water and were mixed with seawater due to an overdraft of groundwater seawater has intruded inwardly through the offshore outcrops for both the unconfined and confined aquifers at a depth of 300 m however 18 o depleted layer is found along deep parts of kaoping canyon this result provides evidence for sgd in this region this phenomenon is also reflected in depleted 13 c dic and lower 14 c values in deep canyon water than in adjacent seawater and indicating that the discharge zone extends over a considerable distance to the offshore area 25 km based on these three parameters 18 o 13 c dic and 14 c we used two end member mixing model to estimate that fresh submarine groundwater constitute the submarine fresh groundwater contributed about 3 and the estimated submarine fresh groundwater discharge was calculated as 4 5 10 9 m 3 per year this result is comparable with groundwater annual loss in the pingtung plain as documented by the isotopic composition of the collected samples detailed results show that sgd in the pingtung coastal zone raises a potential environmental concern and provides implication for the management of groundwater resource in the region

velocity model estimation for depth imaging comparison of three tomography methods on a 2d real data set the estimation of velocity models is still crucial in seismic reflection imaging as it controls the quality of the depth migrated image which is the basis of geological interpretation among the numerous existing methods for velocity determination tomographic methods are very attractive for their efficiency and ability to retrieve heterogeneities of the medium we present three tomographic methods in order to estimate heterogeneous velocity models from 2d prestack pp reflection data a traveltime tomography in the time migrated domain a traveltime and slope tomography in the non migrated time domain and a slope tomography in the depth migrated domain the first method traveltime tomography in the time domain is based on continuous picked events whereas the two slope tomographic methods one in the time domain and the other in the depth domain are based on locally coherent events with no assumptions about reflector geometry or the unknown velocity field the purpose of this paper is not to describe in detail the theoretical basis and implementation of the methods but to apply and compare their output using the same marine real data set based on the estimated velocity models the migrated images and the common image gathers from the three processing routes the relative strengths and weaknesses of the methods are discussed finally similarities are indicated and potential alternative approaches are proposed

on interfacial instability as a cause of transverse subcritical bed forms 1 recent experimental results suggest there are at least two distinct bed form initiation processes bed forms may be generated from local bed defects that are propagated down and across stream by flow separation processes when sediment transport is patchy and sporadic alternatively bed form development may occur over the whole bed at once when sediment transport is general and widespread herein we critically test a simple model for this latter bed form initiation mode that was originally presented by h k liu in 1957 but not tested because of the complex nature of the measurements required the theory is based on the idea that a moving sand bed might be likened to a dense fluid and that a hydrodynamic instability develops at the interface between the sediment transport layer and the near bed fluid leading to the organization of the transport system into laterally extended discrete bed forms our predicted initial bed form lengths are within 10 of the lengths observed in a series of flume experiments suggesting that transverse waveforms on sand beds sheared by unidirectional currents can be initiated as an interfacial hydrodynamic instability of kelvin helmholtz type when the current is sufficiently vigorous to produce general sediment movement that is to create a sediment transport layer that acts as a pseudofluid with density composed of solid and fluid components

nonlinear 3d tomographic least squares inversion of residual moveout in kirchhoff prestack depth migration common image gathers velocity model estimation with seismic reflection tomographyisanonlinearinverseproblem wepresentanewmethodforsolvingthenonlineartomographicinverseproblemusing 3d prestack depth migrated reflections as the input data i e our method requires that prestack depth migration psdmbeperformedbeforetomography themethodisapplicable to any type of seismic data acquisition that permits seismic imaging with kirchhoff psdm afundamental conceptofthemethodisthatwedissociatethepossiblyincorrect initialmigrationvelocitymodelfromthetomographicvelocity model we take the initial migration velocity model and the residual moveout in the associated psdm common image gathers as the reference data this allows us to consider themigrateddepthoftheinitialpsdmastheinvariantobservation for the tomographic inverse problem we can therefore formulate the inverse problem within the general framework of inverse theory as a nonlinear least squares data fitting between observed and modeled migrated depth the modeledmigrateddepthiscalculatedbyraytracinginthetomographic model followed by a finite offset map migration in the initial migration model the inverse problem is solved iteratively with a gauss newton algorithm we applied the method to a north sea data set to build an anisotropic layer velocitymodel

sediment dynamics in a submarine canyon a case of river sea interaction this paper presents findings from a 1 month field experiment conducted during the flood season of 2000 on the southern coast of taiwan to examine the delivery of lithogenic siliciclastic sediment to kao ping submarine canyon from the nearby kao ping river and shelf sources and the transport of suspended lithogenic and nonlithogenic particles near the canyon floor collected time series data included simultaneous measurements of coastal winds salinity temperature flow field suspended sediment concentration ssc and size composition of suspended particles at the river mouth and inside the submarine canyon as well as results from seawater and sediment trap data other collected data included river discharge and sediment load and hydrographic measurements along and across the axis of the canyon during the experiment two significant episodic river sediment discharge events occurred relating to a typhoon and extreme precipitation conditions the findings show that theoretically the time difference between sand and clay siliciclastic grains to settle from the sea surface to the canyon floor is on the order of hours to months analogous to a sorting process river plume dynamics and the coastal wind field largely control the delivery of terrigenous fine grained sediment to the canyon inside the canyon the behavior of suspended lithogenic and nonlithogenic particles of different sizes can be differentiated into a coarse grained group sand which forms the drop in population and a fine grained group mud which forms the standing population each group has distinct spectral characteristics the coarse grained group is delivered directly to the canyon by the river effluent and by wave resuspension of the shelf substrate during the study period the net transport of suspended particles near the canyon floor was landward mostly by tidal currents whose direction was also modulated by spring neap tide both lithogenic and nonlithogenic particles contribute to high mass fluxes exceeding 700 g m 2 day 1 in the lower part of the canyon this river sea system represents a type of systems that consist of three geographically separated dynamic entities the river plume the shelf and the canyon under fair weather conditions the river plume and shelf processes are coupled through the tide and wind field the river and canyon form a direct source to sink link via coarse grained siliciclastic sediment during the flood season in both continuous and pulsed fashion in the typhoon season the shelf becomes a pulsed source region for coarse grained sediment

a constrained parametric inversion for velocity analysis based on cfp technology a method of velocity analysis based on the common focusing point cfp method is presented the two important aspects of the method are the use of the cfp domain and the use of a new parameterization a vertical velocity gradient to describe the lateral velocity variation within a layer the layer velocity is defined with only two parameters an average velocity 0 and a vertical velocity gradient layer velocity parameterization using 0 and assumes that the lithology of the layer is constant and that the overburden and fluid pressure increase linearly with depth this type of parameterization is suitable for areas with gross changes in lithology clastic carbonate salt and for rock in hydrostatic equilibrium a layer based model is required for these areas the salt dome data example presented belongs to this type of area so the layer based model with the defined parameterization produced a very good subsurface velocity model the method is based on the principle of equal traveltime between the

residual migration velocity analysis in the plane wave domain over the last few years migration velocity analysis methods have been developed for 2 d and 3 d models by extending the assumptions and approximations used for rms velocity models computational requirements for these analyses have increased dramatically because top down layer stripping migration is needed to derive interval velocities directly instead of using rms velocities and then converting into interval velocities we establish exact equations for 1 d and 2 d residual velocity analysis in the depth plane wave domain and use these in an iterative and interactive migration velocity analysis program the new method updates interval velocities directly in a top down residual difference correction for all layers after prestack depth migration instead of top down layer stripping migration followed by residual analysis this makes the new method a suitable tool for migration velocity analysis especially for 3 d surveys we test the method on synthetic and field data the field data results show that a reasonable velocity model is obtained and most common image gathers are correctly imaged using no more than four iterations

the fluid dynamics of river dunes a review and some future research directions 1 dunes are present in nearly all fluvial channels and are vital in predicting flow resistance sediment transport and deposition within many rivers progress in understanding the fluid dynamics associated with alluvial dunes has been significant in the last 15 years and has witnessed huge advances in field laboratory and numerical investigations progress has been made in detailing the principal features of mean and turbulent flow over asymmetric dunes that possess flow separation in their leesides and how these forms affect both downstream boundary layer structure and stress partitioning over the dune additionally the links between sediment transport over dunes and instantaneous coherent flow structures are being increasingly understood with the feedback of dune three dimensionality upon flow and sediment dynamics over these bed forms beginning to be recognized as vital such research now provides an outstanding background for beginning to address areas of greater complexity that will enable a fuller understanding of these important natural features this review paper summarizes the principal features of mean and turbulent flow over alluvial sand dunes five areas are then highlighted and discussed as a possible focus for future research 1 the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field 2 the influence of three dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress 3 flow field modification resulting from bed form superimposition and amalgamation 4 the scale and topology of dune related turbulence and its interactions with sediment transport and the flow surface and 5 the influence of suspended sediment on the dune flow field and dune morphology

residual depth moveout and velocity determination for parametric media for the case when prestack depth migration has been performed with inaccurate velocities it can be shown that second order approximations can be used to predict the residual depth moveout of common image and angle domain common image gathers corrections may be made in terms of offset and common reflection angles that can be estimated from the migrated data using moveout analysis schemes the residual moveout determined can be used to improve the signal to noise ratio of the migrated data and to determine the variation of parameters of well known formation dependent velocity laws away from borehole positions although the method is developed for small offsets reflection angles and velocity differences realistic examples may be used to demonstrate that satisfactory approximations to the residual moveout curve can be obtained over a relatively wide range of offsets or reflection angles and for moderate velocity differences a zero offset inversion was applied to the estimated residual radii of curvature this inversion was performed layerwise for each layer the velocity was assumed to vary according to a known depth varying and a laterally varying component to be determined iterative applications of the suggested approach have rendered satisfactory results for several representative velocity models for each application appropriate initial models were provided applications to initial models with large velocity differences and to seismic data with large offsets have to be investigated

time migration velocity analysis by image wave propagation of common image gathers image wave propagation or velocity continuation describes the variation of the migrated position of a seismic event as a function of migration velocity image wave propagation in the common image gather cig domain can be combined with residual moveout analysis for iterative migration velocity analysis mva velocity continuation of cigs leads to a detection of those velocities in which events flatten although image wave continuation is based on the assumption of a constant migration velocity the procedure can be applied in inhomogeneous media for this purpose cigs obtained by migration with an inhomogeneous macrovelocity model are continued starting from a constant reference velocity the interpretation of continued cigs as if they were obtained from residual migrations leads to a correction formula that translates residual flattening velocities into absolute time migration velocities in this way the migration velocity model can be improved iteratively until a satisfactory result is reached wi

full wavefield inversion of wide aperture sh and love wave data summary reverse time linearized inversion is implemented for synthetic wide aperture sh and love wave data including multiple reflections to estimate the s wave velocity in a two dimensionally inhomogeneous medium complete wide aperture wavefields in which triplications pre and post critical reflections and surface waves love waves are present can be imaged by reverse time inversion to estimate the sh velocity distribution the algorithm operates on common source gathers and involves cross correlation of the source and recorded wavefields to define the steepest descent direction to update the velocity at each point on a finite difference grid effects of noise can be reduced by stacking information from different sources

prestack kirchhoff time migration of 3d coal seismic data from mining zones conventional seismic data processing methods based on post stack time migration have been playing an important role in coal exploration for decades however poststack time migration processing often results in low quality images in complex geological environments in order to obtain high quality images we present a strategy that applies the kirchhoff prestack time migration pstm method to coal seismic data in this paper we describe the implementation of kirchhoff pstm to a 3d coal seam meanwhile we derive the workflow of 3d kirchhoff pstm processing based on coal seismic data the processing sequence of 3d kirchhoff pstm includes two major steps 1 the estimation of the 3d root mean square rms velocity field 2 kirchhoff prestack time migration processing during the construction of a 3d velocity model dip moveout velocity is served as an initial migration velocity field we combine 3d kirchhoff pstm with the continuous adjustment of a 3d rms velocity field by the criteria of flattened common reflection point gathers in comparison with post stack time migration the application of 3d kirchhoff pstm to coal seismic data produces better images of the coal seam reflections

along arc structural variation of the plate boundary at the japan trench margin implication of interplate coupling 1 at the japan trench convergent margin many large interplate earthquakes of greater than m7 5 frequently occur their epicenters have uneven distribution mostly located in the northern area to investigate the relationship between this distribution and tectonic structures we have conducted multichannel seismic surveys since 1996 our data show two kinds of interplate sedimentary units a wedge shaped unit and a channel like unit both units have a lower p wave velocity than the basal part of the overriding island arc crust the wedge shaped unit having a velocity of 2 3 km s is widely distributed over the forearc region in the northern area its thickness decreases with depth becoming several hundred meters at a depth of 12 km the channel like unit having a velocity of 3 4 km s is observed in the southern area extending in the downdip direction its thickness reaches 2 km at a depth of 12 km if the low velocity of these units results from the existence of fluid as many authors assume the units being thick implies higher fluid content assuming constant porosity considering that fluid reduces basal friction and with an assumption that fluid available at a specific interface is proportional to the total fluid content in the sediment the thickness variation of the units would cause different degrees of coupling at the plate boundary along the arc this may provide one explanation for the regional disparity in the interplate earthquake occurrence in the margin furthermore we attempt to call attention to the possibility that the channel like sediment works as a shear stress releaser

the effect of a submarine canyon on the river sediment dispersal and inner shelf sediment movements in southern taiwan abstract this study examines the influence of a submarine canyon on the dispersal of sediments discharged by a nearby river and on the sediment movement on the inner shelf the study area includes the head region of the kao ping submarine canyon whose landward terminus is located approximately 1 km seaward from the mouth of the kao ping river in southern taiwan within the study area 143 surficial sediment samples were taken from the seafloor six hydrographic surveys along the axis of the submarine canyon were also conducted over the span of 1 yr three different approaches were used in the analysis of grain size distribution pattern they include 1 a combination of filtering and the empirical orthogonal eigen function eof analysis technique 2 the mclaren model and 3 the transport vector technique the results of the three methods not only agree with one another they also complement one another this study reveals that the kao ping submarine canyon is relatively a stratified and statically stable environment the hydrographic characteristics of the canyon display seasonal variability controlled primarily by the temperature field and the effluent of the kao ping river the hydrographic condition and the bottom topography in the canyon suggest the propagation of internal tides during the flood season summer of the kao ping river the submarine canyon acts as a trap and conduit for mud exchange between the kao ping river and offshore near the head of the canyon there is a region of sediment transport convergence this region is also characterized by high mud abundance on the seafloor that coincides with the presence of high suspended sediment concentration ssc spots in the bottom nepheloid layer outside the submarine canyon on the shelf where the evidence of wave reworking is strong the northwestward alongshore transport dominates over the southeastward transport which is a common theme on the west coast in southern taiwan

field studies of estuarine turbidity under different freshwater flow conditions kaipara river new zealand abstract we present a first interpretation of three days of measurements made in 2013 from the tidal reaches of the kaipara river new zealand under both low and high freshwater inputs and a neap tidal cycle during the first day we occupied two stations that were approximately 6 km apart in a tidal reach that runs for 25 km from the river mouth to the upstream limit of tidal influence during the second day longitudinal surveys were conducted over a distance of 6 km centred on the upstream station the data reveal a turbidity maximum in the form of a high concentration plug of suspended mud that was advected downstream on the ebbing tide past the upper hb measurement station and which exchanged sediment with the seabed by settling at low slack water and by resuspension in the early flooding tide the data suggest that fine sediment is transported landwards and trapped in the upper part of the tidal reach under these low flow conditions on the third day of measurements we repeated the experiments of the first day but later in the year for a much higher freshwater flow this interpretation of our data set highlights the potential contribution of a range of processes to the generation of the observed suspended sediment signals including resuspension of local bed sediment advection by the tidal current settling of suspended sediment over a long timescale compared to the advection timescale advection of longitudinal gradients in suspended sediment and suppression of vertical mixing by density stratification of the water column the level of temporal and spatial detail afforded by these measurements allows a much clearer understanding of the timing and importance of vertical stratification on the transport of suspended particulate matter than is generally possible using fixed point sensors

vertical seismic profile migration velocity analysis via residual moveout in receiver domain common image gathers abstractthe success of imaging vertical seismic profile vsp data critically depends upon obtaining and using an accurate subsurface velocity model first arrival time tomography can be used to derive velocities above the receivers reflection time tomography can be used to derive velocities below the receivers but it requires reflection time picking and association with appropriate horizons we described an alternative faster way to perform velocity analysis by assessing the residual moveout after migrating walk away vsp data we have derived residual moveout equations for migrated common receiver gathers assuming a constant velocity model with a single horizontal reflector the observed residual moveout in common image gathers in the receiver domain will be aligned and flat if the migration velocity is correct if the residual moveout is not flat by digitizing the extreme point on the unstacked migrated traces in each common receiver gather we could invert for the velocity of the target layer usin

impact of user parameters in inversion velocity analysis abstract migration velocity analysis is a method devoted to the evaluation of both reflectivity and background velocity models associated with the high and low wavenumber components of the model respectively inversion velocity analysis is one of its improved versions leading to more stable background velocity updates still the impact of the user parameters should be understood for an optimal update of the background velocity we show that a sign reversal of the background velocity gradient could occur when the selected surface offset range or the space lag range is too small we derive the theoretical limits and check their consistency through simulations in a simple model with a single interface these guidelines determine the necessary ranges of surface offsets and space lags for a proper update of the background velocity model we discuss their applicability on the marmousi model artefacts in the retrieved background velocity model are observed when the guidelines are not satisfied

from the highest to the deepest the gaoping river gaoping submarine canyon dispersal system abstract there are many different source to sink dispersal systems around the world and the gaoping river gpr gaoping submarine canyon gpsc provides an example especially as a canyon captured system the gpr a small mountainous river having an average gradient of 1 150 and the gpsc which links the river catchment to the deep sea basin represent two major topographic features around sw taiwan together they constitute a terrestrial to marine dispersal system that has an overriding impact on the source to sink transport of sediment in this region the gpsc extents from the mouth of the gpr through the shelf and slope and into the northeastern manila trench a distance of about 260 km it is a major conduit for the transport of terrestrial sediment and carbon to the south china sea and the landward transport of particles of marine and biological origin in the gpsc the dominant mode of suspended sediment transport is tidal oscillations and the net direction is up canyon in contrast sediment transport associated with episodic gravity driven events is down canyon the steady sedimentation of the tidal regime results in hemipelagic mud across the canyon floor whereas the gravity driven hyperpycnal regime causes turbidite erosion and deposition along the canyon thalweg typhoon induced river floods often lead to hyperpycnal plumes at the river mouth which directly and indirectly ignite hyperpycnal turbidity currents in the canyon forming an effective agent for transporting large amounts of terrestrial organic material modern and fossil carbon to the south china sea basin therefore the gpr gpsc represents a source to sink system in which terrestrial sediment in a mountainous catchment is promptly removed and transported to the deep sea by episodic gravity flows this is also a pathway by which modern terrestrial organic carbon is quickly and effectively delivered to the deep sea

seismic demigration migration in the curvelet domain curvelets can represent local plane waves they efficiently decompose seismic images and possibly imaging operators we study how curvelets are distorted after demigration followed by migration in a different velocity model we show that for small local velocity perturbations the demigration migration is reduced to a simple morphing of the initial curvelet the derivation of the expected curvature of the curvelets shows that it is easier to sparsify the demigration migration operator than the migration operator an application on a 2d synthetic data set generated in a smooth heterogeneous velocity model and with a complex reflectivity demonstrates the usefulness of curvelets to predict what a migrated image would become in a locally different velocity model without the need for remigrating the full input data set curvelets are thus well suited to study the sensitivity of a prestack depth migrated image with respect to the heterogeneous velocity model used for migration

a thirteen year record of bathymetric changes in the north passage changjiang yangtze estuary article i nfo the mouths of major rivers in the world have always been important waterways and as a result subject to significant human intervention therefore it is necessary to understand the coupling of natural processes and human intervention in the sediment movement and deposition to determine long term morphodynamic evolution in the mouth regions of major rivers a multivariate technique was used to analyze high resolution bathymetric data from the north passage of changjiang yangtze river which is the vital shipping channel in the mouth region and for the entire changjiang waterway our findings show that there are two modes of bathymetric changes the first mode represents 85 of the variability which includes the deposition in the peripheral groin fields along the shipping channel and deepening of the shipping channel which is primarily due to the channel maintenance the second mode represents 6 of the variability of the river mouth shoal seaward migration and size reduction attributable to the declining sediment discharge of the changjiang

migrating around in circles part ii this paper proposes 1 simulating a zero offset zo section from common offset co sections of different offsets and 2 a possibility to find the best velocity to do this simulation more precisely the paper discusses the kinematic aspects of a common reflection point crp stack for an unknown velocity model

floc properties in the turbidity maximum of a mesotidal estuary during neap and spring tidal conditions in order to improve the understanding of how fine cohesive matter behaves during different tidal conditions within an estuary turbidity maxima high quality in situ data is of a prime requirement as part of the european commission cosinus project a series of measurements were carried out in the upper reaches of the tamar estuary to investigate how flocculated mud properties vary within the turbidity maximum zone floc populations were sampled at regular intervals using the optical inssev instrument the floc data was supplemented by simultaneous time series of near bed profiles of turbulent shear stress and suspended particulate matter the proportion of macroflocs 160 m changed significantly across the turbidity maximum before the passage of the turbidity maximum the total floc mass tended to be equally divided between the macroflocs and microflocs on neaps whilst on springs the macroflocs contributed 60 70 at spring tides a peak near bed spm concentration of 6 g l 1 was measured in the turbidity maximum this was over an order of magnitude higher than observed at neaps the turbulence measurements showed significant drag reduction at spm concentration gradients above 3 6 kg m 4 within the turbidity maximum the macrofloc proportion rose rapidly until they contributed at least 75 of the floc dry mass during neap conditions and at spring tides this reached in excess of 90 96 an abundance of fast settling macroflocs from spring tides accounted for a time series average of 83 of the mass settling flux where as during neap tides the macroflocs contributed 15 less to the settling flux rate this was partly due to a time series averaged macrofloc settling velocity of 3 9 mm s 1 from the spring tidal data 2 1 mm s 1 higher than for neap tide conditions during the turbidity maximum passage at springs macroflocs reached 2 2 mm in diameter these flocs had settling velocities of up to 16 6 mm s 1 but effective densities were less than 50 kg m 3 which means they would be prone to break up when settling to a region of high shear at the opposite and of the scale low turbidity and quiescent slack water conditions severely restricted floc production

variability in cohesive sediment settling fluxes observations under different estuarine tidal conditions the mass settling flux which is defined as the product of the concentration and the settling velocity is of prime importance with respect to both stratified and well mixed estuarine conditions the determination of these fluxes for applied modelling purposes in high energy tidal estuarine environments is very problematic this is because the muddy sediments which dominate in estuaries flocculate producing a variety of sizes and settling velocities and this flocculation process is not understood well enough to be fully described theoretically by drawing on examples of floc spectra acquired in situ using the inssev system this study explains how mass settling fluxes in the near bed region can vary by three or four orders of magnitude in meso and macro tidal estuaries throughout a single tidal cycle a floc population representative of dilute suspension conditions on a neap tide indicated only 35 of the floc mass was macroflocs 160 m however the macrofloc settling velocity 2 4 mm s 1 three times faster than the microflocs which meant the former fraction contributed 57 of the 205 mg m 2s 1 settling flux both highly concentrated 4 6 g l 1 and very turbulent spring tide conditions 1 6 n m 2 produced a bi modal distribution in terms of the floc size and dry mass with the former 54 of the mass was contained within the 240 480 m size fraction with a further 25 of the dry floc mass in the flocs over 480 m in diameter these large flocs had settling velocities between 4 8 mm s 1 which meant 99 5 of the settling flux 33 5 g m 2s 1 was accredited to the macroflocs the high turbulence environment saw the dry floc mass distribution shift 60 40 in favour of the microflocs the microfloc settling velocity was 1 45 mm s 1 0 35 mm s 1 faster than the larger macrofloc fraction in terms of the total mass settling flux 0 9 g m 2 s 1 this translates into the microflocs contributing 70 during high turbulence at slack water the flux only reached 12 mg m 2 s 1 and macrofloc growth was mainly attributed to differential settling continuous floc observations made over a complete tidal cycle revealed that the asymmetrical distribution of the tidal energy generated throughout the spring conditions in the tamar estuary demonstrated a distinct control on the flocculation process the less turbulent ebb produced 86 of the total tidal cycle mass settling flux of which only 8 of the settling flux was outside the turbidity maximum an attempt to simulate these large settling fluxes by using a constant settling rate of 0 5 mm s 1 under estimated the tidal cycle settling flux by 78 with less than 15 of the total flux being estimated during the advection of the turbidity maximum on the ebb in contrast using a faster constant settling velocity parameter of 5 mm s 1 representative of the macrofloc fraction resulted in a mass flux over estimate of 116 for the tidal cycle duration

sources and distribution of organic matter in a river dominated estuary winyah bay sc usa abstract the sources and distribution of organic matter om in surface waters and sediments from winyah bay south carolina usa were investigated using a variety of analytical techniques including elemental stable isotope and organic biomarker analyses several locations along the estuary salinity gradient were sampled during four different periods of contrasting river discharge and tidal range the dissolved organic carbon doc concentrations of surface waters ranged from 7 mg l 1 in the lower bay stations closest to the ocean to 20 mg l 1 in the river and upper bay samples there was a general linear relationship between doc concentrations and salinity in three of the four sampling periods in contrast particulate organic carbon poc concentrations were significantly lower 0 1 3 mg l 1 and showed no relationship with salinity the high molecular weight dissolved om hmw dom isolated from selected water samples collected along the bay displayed atomic carbon nitrogen ratios c n a and stable carbon isotopic compositions of organic carbon 13coc that ranged from 10 to 30 and from 28 to 25 respectively combined such compositions indicate that in most hmw dom samples the majority of the om originates from terrigenous sources with smaller contributions from riverine and estuarine phytoplankton in contrast the c n a ratios of particulate om pom samples varied significantly among the collection periods ranging from low values of 5 to high values of 20 overall the trends in c n a ratios indicated that algal sources of pom were most important during the early and late summer whereas terrigenous sources dominated in the winter and early spring in winyah bay bottom sediments the concentrations of the mineral associated om were positively correlated with sediment surface area the c n a ratios and 13coc compositions of the bulk sedimentary om ranged from 5 to 45 and from 28 to 23 respectively these compositions were consistent with predominant contributions of terrigenous sources and lesser but significant inputs of freshwater estuarine and marine phytoplankton the highest terrigenous contents were found in sediments from the river and upper bay sites with smaller contributions to the lower parts of the estuary the yields of lignin derived cuo oxidation products from winyah bay sediments indicated that the terrigenous om in these samples was composed of variable mixtures of relatively fresh vascular plant detritus and moderately altered soil om based on the lignin phenol compositions most of this material appeared to be derived from angiosperm and gymnosperm vascular plant sources similar to those found in the upland coastal forests in this region a few samples displayed lignin compositions that suggested a more significant contribution from marsh c3 grasses however there was no evidence of inputs of spartina alterniflora a c4 grass remains from the salt marshes that surround the lower sections of winyah bay

imaging complex structure in shallow seismic reflection data using prestack depth migration prestack depth migration psdm analysis has the potential to significantly improve the accuracy of both shallow seismicreflectionimagesandthemeasuredvelocitydistributions inastudydesignedtoimagefaultsinthealvordbasin oregon at depths from 25 1000 m psdm produced a detailed reflection image over the full target depth range in contrast poststack time migration produced significant migration artifacts in the upper 100 m that obscured reflection events and limited the structural interpretation in the shallow section additionally an abrupt increase from 2500 to 3000 m s in the psdm velocity model constrained the interpretation of the transition from sedimentary basin fill to basementvolcanicrocks psdmanalysisrevealedacomplex extensional history with at least two distinct phases of basin growthandamidbasinbasementhighthatformsthedivision betweentwomajorbasincompartments

smiles and frowns in migration velocity analysis reliable seismic depth migrations require an accurate input velocity model inaccurate velocity estimates will distort point diffractors into smiles or frowns on a depth section for both poststack and prestack migrated sections high velocities cause deep smiles while low velocities cause shallow frowns on migrated gathers however for prestack images in the offset domain high velocities cause deep frowns while low velocities cause shallow smiles if the velocity is correct there will be no variation in the depth migration as a function of offset and no smiles or frowns in the offset domain we explain migration responses both mathematically and graphically and thereby provide the basis for depth migration velocity analysis

migration velocity analysis from locally coherent events in 2 d laterally heterogeneous media part ii applications on synthetic and real data we demonstrate a method for estimating 2 d velocity models from synthetic and real seismic reflection data in the framework of migration velocity analysis mva no assumption is required on the reflector geometry or on the unknown background velocity field provided that the data only contain primary reflections diffractions in the prestack depth migrated volume locations where the reflectivity exhibits local coherency are automatically picked without interpretation in two panels common image gathers cigs and common offset gathers cogs they are characterized by both their positions and two slopes the velocity is estimated by minimizing all slopes picked in the cigs we test the applicability of the method on a real data set showing the possibility of an efficient inversion using 1 the migration of selected cigs and cogs 2 automatic picking on prior uncorrelated locally coherent events 3 efficient computation of the gradient of the cost function via paraxial ray tracing from the picked events to the surface and 4 a gradient type optimization algorithm for convergence

loss of organic matter from riverine particles in deltas abstract in order to examine the transport and burial of terrigenous organic matter along the coastal zones of large river systems we assessed organic matter dynamics in coupled river delta systems using mineral surface area as a conservative tracer for discharged riverine particulate organic matter pom most pom in the rivers studied n 6 is tightly associated with suspended mineral material e g it is sorbed to mineral surfaces average organic loadings in the amazon river 0 67 0 14 mg c m 2 the river for which we have the largest dataset are approximately twice that of sedimentary minerals from the amazon delta 0 35 mg c m 2 stable carbon isotope analysis indicate that approximately two thirds of the total carbon on the deltaic particles is terrestrial the combined surface normalized isotope distinguished estimate is that 70 of the amazon fluvial pom is not buried in the delta consistent with other independent evidence aller et al 1996 losses of terrestrial pom have also been quantified for the river delta systems of columbia in the usa fly in new guinea and huange he in china if the losses of riverine pom observed in these river delta systems are representative of rivers worldwide then the surface constrained analyses point toward a global loss of fluvial pom in delta regions of 0 1 x 1015 g c y 1

avo analysis by offset limited prestack migrations of crustal seismic data abstract the physical causes of reflections from the crystalline crust are still a matter of debate the polarity of the wavelet and the amplitude versus offset avo dependence of seismic reflection data can help to reveal the nature of a reflector in contrast to seismic data from sedimentary environments however it is very difficult to get polarity and avo information from crystalline basement data reflections in prestack data are typically weak incoherent and often obscured by numerous diffractions there is however a better chance of obtaining reliable avo information from prestack migrated data after true amplitude processing as the migration process unravels the jumble of reflections and diffractions and improves the signal noise ratio important steps in this processing sequence are careful editing followed by surface consistent amplitude corrections for source and receiver coupling to the ground migration velocity models can be obtained from refraction seismics and or from migration velocity analyses the migration itself is of kirchhoff type and applied to cof gathers cof common offset to get one migrated section for each cof these cof migrated images can then be used to get avo functions for specific reflections examples from the dekorp near vertical reflection line ktb8502 show some strong reflections from beneath a granite body at about 9 to 11 km depth both the positive and negative reflection coefficients of the reflectors are consistent with an interval velocity model obtained from migration velocity analyses avo functions from these reflections include offsets from zero to 12 km and reflection angles from zero to about 30 absolute reflection coefficients are surprisingly small with maximum values of 0 015 two layer modelling has been done to match the avo dependence of these reflections