seismogram synthesis for radially layered media using the generalized reflection transmission coefficients method theory and applications to acoustic logging a new method based on generalized reflection and transmission coefficients is proposed to calculate the synthetic seismograms in radially multilayered media this method can be used to efficiently simulate full waveform acoustic logs and crosswell seismic profiles in situations where we need to consider borehole effects the new formulation is tested by comparing our numerical results with previous available work and shows excellent agreement because of the use of the normalized hankel functions and the normalization factors this new algorithm for computing seismograms is stable numerically even for high frequency problems to show the applicability of this new approach to full waveform sonic logging we apply it to investigate the effects of complex invaded zones on the geometrical spreading and attenuation estimation for p waves we find that a damaged zone its velocity is slower than the unperturbed formation velocity exhibits a convergence effect on the p waves and a flushed zone velocity is faster than the unperturbed formation velocity exhibits a divergence effect on the p waves

steepest descent integration a novel method for computing wavefields radiated from borehole sources borehole sources which include chemical explosives air gun water gun piezoelectric transducers in the borehole generate seismic waves both in and outside the borehole modeling the wave field inside and outside the borehole is of key importance in acoustic logging crosshole tomography mining geophysics and deep sounding seismic for interpretation of amplitude information of real data and prediction of energy radiation pattern the classical methods for wavefield modeling inside the borehole such as real axis integration are challenged by highly oscillatory integrals outside the borehole we present a novel method called steepest descent integration sdi which evaluates the oscillatory wavenumber integration by numerically integrate along the steepest descent path the oscillation along the new integration path is extremely reduced the contribution of poles and branch cuts are added if they are located between the steepest descent path and the real axis the sdi is applicable to arbitrary freq

dense shelf water formation along the south west australian inner shelf 1 hydrological data from a repeated cross shore transect obtained using teledyne webb research slocum electric gliders offshore two rocks in south western australia over 13 months are presented the data revealed that formation of dense water inshore and its transport across the shelf as a near bed gravity current defined as dense shelf water cascade dswc was a regular occurrence particularly during autumn and winter months in autumn the dense water is mainly formed through changes in salinity resulting from evaporation whilst in winter temperature change through surface cooling was the dominant factor the mean wind speeds also decrease during the transition during autumn the speed of the dswc was estimated to be 0 01 0 02 m s 1 and similar to that measured in other selected regions globally the offshore transport from the shelf is a significant component of the alongshore wind driven transport

frequency domain simulation of logging while drilling borehole sonic waveforms numerical simulation of sonic logging while drilling lwd borehole measurements is challenging because of significant wave propagation effects due to the massive drilling collar occupying a large portion of the borehole in addition the internal structure of the lwd tool can have a significant impact on the measured dispersions of stoneley and quadrupole modes the collar is typically constructed with a set of inner periodic grooves which act as a mechanical filter to attenuate undesirable collar modes reliable numerical simulation and interpretation of lwd sonic waveforms requires that all features and dimensions of the drilling collar be included in the simulation model furthermore the presence of the drilling collar can prompt numerical instabilities due to backward propagating modes in the perfectly matched layer pml commonly used to truncate the computational domain this problem can be circumvented with the implementation of artificial viscoelastic attenuation in the collar whenever the simulations are intended to reproduce only wave propagation within the surrounding rock formations in addition reliable modeling of borehole wave propagation in the presence of high contrasts in material properties and the internal structure of the lwd collar requires a numerical method capable of accurately and stably resolving all spectral scales present in the model we implemented an automatic hp adaptive finite element method in the frequency domain combined with a pml technique to simulate lwd sonic logging measurements examples of the application verified the accuracy and reliability of the simulated borehole and formation propagation modes in the presence of casing and internal structures in the lwd collar the presence of steel casing and quality of casing formation bond significantly influence the propagation modes excited in a borehole however it is still possible to estimate the formation shear slowness using monopole and quadrupole sources regardless of the quality of cement bond in fast formations assessment of the formation compressional slowness was significantly impeded by the strong pipe mode estimation of formation shear slowness in slow formations is practically impossible due to the presence of casing and a strong annulus mode when the quality of casing bond is poor

warm ocean is eroding west antarctic ice sheet 1 satellite radar measurements show that ice shelves in pine island bay have thinned by up to 5 5 m yr 1 over the past decade the pattern of shelf thinning mirrors that of their grounded tributaries the pine island thwaites and smith glaciers and ocean currents on average 0 5 c warmer than freezing appear to be the source the synchronised imbalance of the inland glaciers is the result of reduced lateral and basal tractions at their termini and the drawdown of grounded ice shows that antarctica is more sensitive to changing climates than was previously considered

acoustic wave propagation in a fluid filled borehole surrounded by a formation with stress relief induced anisotropy the stress relief associated with the drilling of a borehole may lead to an anisotropic formation in the vicinity of the borehole where the properties in the radial direction differ from those in the axial and tangential directions thus axial and radial compressional acoustic velocities are different and similarly the velocity of an axial shear wave depends on whether the polarization is radial or tangential a model was developed to describe acoustic wave propagation in a borehole surrounded by a formation with stress relief induced radial transverse isotropy rti acoustic full waveforms due to a monopole source are computed using the real axis integration method and dispersion relations are found by tracing poles in the kz plane an analytic expression for the low frequency stoneley wave is developed the numerical results confirm the expectations that the compressional refraction is mainly given by the axial compressional velocity while the shear refraction arrival is due to the shear wave wit

interpretation of resonance frequencies recorded during hydraulic fracturing treatments hydraulic fracturing treatments are often monitored by strings of geophones deployed in boreholes instead of picking discrete events only we here use time frequency representations of continuous recordings to identify resonances in two case studies this paper outlines an interpretational procedure to identify their cause using a subdivision into source path and receiver side effects for the first case study two main resonances are observed both at depth by the downhole geophones and on the surface by two broadband arrays the two acquisition networks have different receiver and path effects yet recorded the same resonances these resonances are therefore likely generated by source effects the amplitude pattern at the surface arrays indicates that these resonances are probably due to pumping operations in the second case study selective resonances are detected by the downhole geophones resonances coming from receiver effects are either lower or higher frequency and wave propagation modeling shows that path effects are not significant we identify two possible causes within the source area namely eigenvibrations of fractures or non darcian flow within the hydraulic fractures in the first situation 15 10 m long fluid filled cracks could generate the observed resonances an interconnected fracture network would then be required corresponding to mesoscale deformation of the reservoir alternatively systematic patterns in non darcian fluid flow within the hydraulic fracture could also be their leading cause resonances can be used to gain a better understanding of reservoir deformations or dynamic fluid flow perturbations during fluid injection into hydrocarbon and geothermal reservoirs co2 sequestration or volcanic eruptions

cross borehole observation of mode conversion from borehole stoneley waves to channel waves at a coal layer conversion of borehole stoneley waves to channel waves was observed in data from a seismic cross borehole experiment conducted between wellbores penetrating a thin coal layer at 2022 m depth near rifle colorado traveltime moveout observations show that borehole stoneley waves underwent partial conversion to channel waves at the coal layer the channel waves were detected directly in an adjacent borehole 35 m away at receiver positions within the coal stoneley waves subsequently produced by partial conversion of channel waves were also detected at receiver positions located up to 50 m above and below the coal layer in the adjacent borehole we infer the channel wave to be the first higher rayleigh mode by comparing the observed group velocity with theoretically derived dispersion curves identifying the conversion between borehole and stratigraphically guided waves is significant because coal penetrated by multiple wells may be detected without placing a transmitter or receiver in the coal itself

inversion based interpretation of borehole sonic measurements using semianalytical spatial sensitivity functions abstractone of the major challenges in the interpretation of sonic logs is the presence of bed boundary shoulder bed effects which can decrease the accuracy of the estimated elastic properties due to spatial averaging caused by the sonic receiver array across thin beds a reliable approach to account for shoulder bed effects in the interpretation of sonic logs is the implementation of forward modeling and inversion techniques we have developed an efficient inversion based interpretation method for the estimation of in situ rock formation elastic properties from sonic logs acquired in vertical wells the method uses semianalytical spatial sensitivity functions for fast forward modeling of sonic slowness logs and estimates formation elastic properties by iteratively matching the available logs with numerical simulations due to the intrinsic vertical resolution limits of sonic logs the inversion method requires predefined bed boundaries using other high resolution well logs we first developed a workfl

the 5500 km long boundary flow off western and southern australia 1 the path of the shelf edge flow off southwestern australia is documented using results from satellite altimetry and sea surface temperature sst and a climatogical in situ analysis during austral winter a continuous current is shown to extend from its origin at north west cape to the southern tip of tasmania a distance of 5500 km satellite sst observations and surface buoy tracks confirm the location and continuity of the current trajectory while the leeuwin current is forced by the strong alongshore pressure gradient associated with the meridional portion of the western australian coastal boundary our results suggest that the essentially zonal shelf edge flow along the southern australian coast arises from the setup of coastal sea level by onshore ekman flow driven by the winter westerly wind and possibly a further alongshore pressure gradient the timing of these two different forcing mechanisms means that the west coast pressure gradient delivers the leeuwin current to the south coast just as the winds reverse and are thus able to maintain the eastward passage of the current the shelf edge flow consists of two main water masses a low salinity warm water type of tropical origin associated with the leeuwin current and a high salinity warm water inflow formed on the western end of the great australian bight continental shelf a naming convention is proposed the leeuwin current representing flow from north west cape to the great australian bight gab the south australian current between the eastern gab and western bass strait and the zeehan current off western tasmania

ocean mixing beneath pine island glacier ice shelf west antarctica ice shelves around antarctica are vulnerable to an increase in ocean driven melting with the melt rate depending on ocean temperature and the strength of flow inside the ice shelf cavities we present measurements of velocity temperature salinity turbulent kinetic energy dissipation rate and thermal variance dissipation rate beneath pine island glacier ice shelf west antarctica these measurements were obtained by ctd adcp and turbulence sensors mounted on an autonomous underwater vehicle auv the highest turbulent kinetic energy dissipation rate is found near the grounding line the thermal variance dissipation rate increases closer to the ice shelf base with a maximum value found 0 5 m away from the ice the measurements of turbulent kinetic energy dissipation rate near the ice are used to estimate basal melting of the ice shelf the dissipation rate based melt rate estimates is sensitive to the stability correction parameter in the linear approximation of universal function of the monin obukhov similarity theory for stratified boundary layers we argue that our estimates of basal melting from dissipation rates are within a range of previous estimates of basal melting

full wave acoustic logging in an irregular borehole a new boundary integral equation formulation for wave propagation in a borehole of irregular cross section represents the wave field diffracted at the borehole rock interface by the radiation from a distribution of surface sources applied along the borehole wall the wave fields in the borehole fluid and in the elastic rock are then expressed using the discrete wavenumber method application of boundary conditions at discretized locations along the borehole wall leads to a linear system of equations whose inversion yields the required source distribution we have used the method to investigate the effect of changes in borehole diameter on the pressure wave field inside the borehole when the change is smooth records obtained ahead of the discontinuity location are not affected by its presence in the case of a steep variation however a significant amount of the stoneley wave energy is reflected when the borehole diameters are different at the source and receiver levels the microseismograms obtained

secondary shear waves from source boreholes previous studies of radiation from point sources in fluid filled boreholes have most often been based on far field stationary phase analysis in these papers the explicit contribution of the borehole itself acting as a waveguide has not been properly considered with a few exceptions in general these studies accurately describe s wave radiation in high velocity rocks such as granites and limestones and p wave radiation in most rocks and experiments have confirmed this however tube waves directly influence the external wavefield and in fact create a shear wave wake outside the borehole due to constructive interference of tube wave emission if a velocity condition is met this constructive interference or wake is generated when the tube wave velocity is greater than the shear wave velocity when this happens a tube wave complex pole invalidates the mathematical assumptions for stationary phase analysis and the stationary phase predictions do not agree with experimentally derived radiation patterns the shape and properties of these secondary shear waves are calculated and shown to have identical properties to mach waves of aerodynamics and seismology for instance these waves are geometrically conical and the aperture of the cone and the moveout velocity can be calculated this paper also demonstrates the important effect that casing hasmore on the mach waves and provides predictions about when these waves are likely to be observed finally evidence of mach waves in data sets is examined and it is shown how these waves have been confused with receiver borehole tube waves less

a theoretical study on formation shear radial profiling in well bonded cased boreholes using sonic dispersion data based on a parameterized perturbation model abstractinterpretation of sonic data can be challenging in the presence of a steel casing that has a strong influence on elastic waves propagating along a borehole the cement annulus behind the casing together with drilling induced near wellbore alteration causes radial heterogeneity in the propagating medium it is necessary to study the influence of such heterogeneities on borehole waves and estimate the radial extent of near wellbore alteration in terms of radial variation of velocities away from the casing to this end we based our study on the model of a fluid filled well bonded cased borehole surrounded by a cylindrically layered formation the formation is isotropic and purely elastic and can be either fast or slow borehole monopole and dipole dispersions for this kind of model can be obtained from a root finding mode search routine a modified perturbation model based on hamilton s principle is used to predict changes in borehole dispersions caused by formation heterogeneities a two layer for

ice sheet grounding line dynamics steady states stability and hysteresis 1 the ice sheet ice shelf transition zone plays an important role in controlling marine ice sheet dynamics as it determines the rate at which ice flows out of the grounded part of the ice sheet together with accumulation this outflow is the main control on the mass balance of the grounded sheet in this paper we verify the results of a boundary layer theory for ice flux in the transition zone against numerical solutions that are able to resolve the transition zone very close agreement is obtained and grid refinement in the transition zone is identified as a critical component in obtaining reliable numerical results the boundary layer theory confirms that ice flux through the grounding line in a two dimensional sheet shelf system increases sharply with ice thickness at the grounding line this result is then applied to the large scale dynamics of a marine ice sheet our principal results are that 1 marine ice sheets do not exhibit neutral equilibrium but have well defined discrete equilibrium profiles 2 steady grounding lines cannot be stable on reverse bed slopes and 3 marine ice sheets with overdeepened beds can undergo hysteresis under variations in sea level accumulation rate basal slipperiness and ice viscosity this hysteretic behavior can in principle explain the retreat of the west antarctic ice sheet following the last glacial maximum and may play a role in the dynamics of heinrich events

synthetic full waveform acoustic logs in cased boreholes a general expression is derived for the dispersion relations and the impulse response of a radially layered borehole the model geometry consists of a central fluid cylinder surrounded by an arbitrary number of solid annuli a thomson haskell type propagator matrix is used to relate stresses and displacements across the layers although the model is completely general the geometries considered here are restricted to those of a cased hole layers of steel cement and formation surround the innermost fluid layer synthetic microseismograms containing all body and interface waves are calculated for a variety of model parameters formation body wave arrivals are relatively unaffected by the presence of a casing they may however be hard to identify if cement velocities are close to or larger than those of the formation the stoneley and pseudo rayleigh wave arrivals are strongly influenced by the casing parameters they respond to the combined effects of the steel the cement and the formation

cased borehole effects on downhole seismic measurements both approximate and exact formulations for the interaction of an incident elastic wave with a cased borehole are presented in the approximate method simple and explicit formulae are derived for the pressure in fluid at low frequencies in the exact method elastic potentials in each annulus are presented as a superposition of fundamental solutions to the helmholtz equations continuity of displacements and stresses across layer boundaries are used to determine unknown coefficients a global matrix algorithm is employed to compute simultaneously these coefficients in individual layers calculations show that in cased boreholes the borehole effects on downhole seismic measurements are more significant than in open boreholes a strong resonance occurs in the fluid for sv wave incidence from a soft formation this resonance is prominent even at very high frequencies because the tube wave velocity is raised well above the formation shear velocity by the steel pipe at a particular angle of incidence of a plane p wave the pressure in the fluid is near zero at low frequencies the cased borehole screening phenomenon for hard formations and frequencies above 1 khz the cased borehole influence on a downhole geophone measurement is significant especially at grazing incidence for soft formations both the pressuremore in the fluid and the solid displacement on the borehole wall show strong dependence on frequency and angle of incidence even at low frequencies less

bottom boundary layer flow and salt injection from the continental shelf to slope 1 austral winter oceanographic measurements from the northwest australian continental shelf reveal salty water forming evaporatively inshore moving across the wide shelf near the bottom and into the adjacent open ocean when the shelf edge alongshore flow is equatorward the salt tongue is absent during more normal conditions when the poleward leeuwin current is present we hypothesize that the flow reversal enables shelf wide bottom boundary layer ekman transport and thus creates the shelf edge convergence that accounts for the observed salt tongue this flow is absent under sustained normal conditions because of buoyancy arrest in the bottom boundary layer

a numerical simulation of the acoustic and elastic wavefields radiated by a source on a fluid filled borehole embedded in a layered medium the authors present a method of calculation to simulation the propagation of acoustic and elastic waves generated by a borehole source embedded in a layered medium the method is formulated as a boundary element technique where the green s functions are calculated by the discrete wavenumber method the restrictive assumptions are that the borehole is cylindrical and that its axis runs normal to the layer interfaces the physics of the method rely on huygens s principle that states that a diffracting boundary the borehole wall in the present case can be represented as a distribution of secondary sources the borehole is discretized into small cylindrical elements and each element is represented by three sources a volume source representing the wavefield diffracted in the fluid and two surface forces that give rise to the elastic wavefield radiated outside the borehole the strength of each source is obtained by solving the linear system of equations that describes the boundary conditions at the borehole wall the method is used to generate synthetic acoustic log s and to investigate the wavefield radiated into the formation the simulations considered display the stoneley wave reflections at the bed boundaries and show the importance of the diffraction that takes place wheremore the borehole wall intersects the layer interfaces less

response of an oceanic bottom boundary layer on a slope to interior flow part i time independent interior flow abstract the behavior of oceanic boundary layers on a sloping bottom in the presence of stratification is investigated by the method of direct numerical simulations the navier stokes equations are decomposed into mean and turbulent components with the mean equations involving a slope burger number s n2sin2 f2 where n is the buoyancy frequency is the bottom slope angle and f is the coriolis parameter the influence of the turbulent fluctuations is parameterized as eddy coefficients of viscosity and diffusivity two regimes are considered the first is for cases where the eddy coefficients are constant in time but variable in space and the interior flow is allowed to adjust to the boundary mixing the numerical results agree with analytic theory for two limiting cases the first case is when the mixing extends into the fluid interior and the second is when the mixing is limited to a slab region the second regime involves cases in which the eddy coefficients are determined from a gradient richard

recent dramatic thinning of largest west antarctic ice stream triggered by oceans a growing body of observational data suggests that pine island glacier pig is changing on decadal or shorter timescales these changes may have far reaching consequences for the future of the west antarctic ice sheet wais and global sea levels because of pig s role as the ice sheet s primary drainage portal we test the hypothesis that these changes are triggered by the adjoining ocean specifically we employ an advanced numerical ice flow model to simulate the effects of perturbations at the grounding line on pig s dynamics the speed at which these changes are propagated upstream implies a tight coupling between ice sheet interior and surrounding ocean

widespread rapid grounding line retreat of pine island thwaites smith and kohler glaciers west antarctica from 1992 to 2011 we measure the grounding line retreat of glaciers draining the amundsen sea sector of west antarctica using earth remote sensing ers 1 2 satellite radar interferometry from 1992 to 2011 pine island glacier retreated 31 km at its center with most retreat in 2005 2009 when the glacier ungrounded from its ice plain thwaites glacier retreated 14 km along its fast flow core and 1 to 9 km along the sides haynes glacier retreated 10 km along its flanks smith kohler glaciers retreated the most 35 km along its ice plain and its ice shelf pinning points are vanishing these rapid retreats proceed along regions of retrograde bed elevation mapped at a high spatial resolution using a mass conservation technique that removes residual ambiguities from prior mappings upstream of the 2011 grounding line positions we find no major bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin 2014 american geophysical union all rights reserved

downhole geophysical logging downhole geophysical logging is the method of making geophysical measurements in drill holes and interpreting these measurements for evaluation of geological properties of the subsurface the downhole measurements can be made with great spatial resolution with a single sonde containing both source and receivers which are separated by 10 cm to tens of meters measurements can be repeated every few centimeters as the sonde moves upward or downward in the borehole this technique is called well logging it is also possible to make downhole measurements with the sensor in the borehole at depth and the source at the surface when the sensor package is moved to a different depth the source signal is repeated when these measurements are made with seismic waves the process is called vertical seismic profiling vsp in vsp the surface source can be any appropriate system that would generate a seismic pulse dynamite air gun or a sinusoidal wave vibroseis and the downhole sensor can be a hydrophone or borehole geophone vertical seismic profiling is a rapidly expanding technique and some of its applications are described in a series of recent books gal perin 1974 hardage 1983 balch lee 1984 toksoz stewart 1984 another method of downhole measurement is possible when closely spaced drill holes are available with the source placed in one drill hole and the detector receiver in another this technique called cross

upwelling and convergence in the middle atlantic bight shelfbreak front convergent and upwelling circulation within the shelfbreak front in the middle atlantic eight are detected using a dye tracer injected into the bottom boundary layer at the foot of the front from the three day displacement and dispersion of two dye injections within the front we infer lagrangian isopycnal diapycnal velocities and diffusivities of 2 x 10 2 m s 4 x 10 6 m s and 9 m 2 s 6 x 10 6 m 2 s these results substantiate model predictions of chapman and lentz 1994 and previous dye tracer observations by houghton 1997

borehole seismic source radiation in layered isotropic and anisotropic media boundary element modeling in modeling waves radiated from a borehole seismic source in layered isotropic or anisotropic media the commonly used numerical methods e g finite difference and finite element encounter difficulties because of the large scale difference between the borehole diameter and the formation extent to get around this problem we apply the indirect boundary element method to establish a general algorithm for modeling source radiation from open and cased boreholes in layered transversely isotropic ti media the essence of the algorithm is to use discrete secondary sources unknowns on both sides of the borehole wall formation cement interface to represent the influence of the interface on wave scattering so that wave propagation inside and outside the borehole can be carried out by green s functions the discrete distribution of the secondary sources is determined by matching boundary conditions on the borehole wall comparison with the discrete wavenumber method validates the implementation applications to fluid filled open and cased boreholes in three layer media demonstrate the creation of guided modes in low velocity layers presence of anisotropy complicates the guided modes as a result of dispersion and p and sv waves coupling in homogeneous ti media presence of casing and cement enhances the visibility of the guided modes

modeling ice shelf cavities in a z coordinate ocean general circulation model 1 processes at the ice shelf ocean interface and in particular in ice shelf cavities around antarctica have an observable effect on the solutions of basin scale to global coupled ice ocean models despite this these processes are not routinely represented in global ocean and climate models it is shown that a new ice shelf cavity model for z coordinate models can reproduce results from an intercomparison project of earlier approaches with vertical or isopycnic coordinates as a proof of concept ice shelves are incorporated in a 100 year global integration of a z coordinate model in this simulation glacial meltwater can be traced as far as north as 15 s the observed effects of processes in the ice shelf cavities agree with previous results from a coordinate model notably the increase in sea ice thickness however melt rates are overestimated probably because the parameterization of basal melting does not suit the low resolution of this configuration

characteristics of waveforms recorded by azimuthally spaced hydrophones of sonic logging tool for incident plane waves abstractthe borehole acoustic reflection survey bars is a method for imaging near borehole structures using waveforms acquired by a sonic logging tool signals from a monopole or dipole source are reflected from geologic interfaces and recorded by arrays of the hydrophones of the same tool due to the nearly 1d configuration of the source and hydrophones bars provides only 2d images in which the dimensions are the axis of the well and the distance from the center of the well we have developed methods for identifying the azimuthal direction of the reflector which is not given by the bars image by using the differences of the signals recorded by hydrophones at varying azimuths we have conducted a theoretical analysis for incident plane waves as follows analytic solutions in the frequency domain are numerically computed at discrete frequencies and converted to time domain synthetics using the fast fourier transform for a newly derived model that includes the effect of the tool in the fluid filled bo

a numerical investigation of head waves and leaky modes in fluid filled boreholes although synthetic borehole seismograms can be computed for a wide range of borehole conditions the physical nature of shear and compressional head waves in fluid filled boreholes is poorly understood this paper presents a series of numerical experiments designed to explain the physical mechanisms controlling head wave propagation in boreholes these calculations demonstrate the existence of compressional normal modes equivalent to shear normal modes or pseudo rayleigh waves with sequential cutoff frequencies spaced between the cutoff frequencies for the shear normal modes major contributions to head wave spectra occur in discrete peaks at frequencies just below mode cutoff for both compressional and shear modes this result is confirmed by calculations with synthetic waveforms at frequencies corresponding to mode cutoff and by branch cut integrals designed to yield independent spectra for the compressional mode for soft formations where shear velocity falls below acoustic velocity in the borehole

alongshore currents and mesoscale variability near the shelf edge off northwestern australia 1 shelf break conditions and alongshore flow off northwestern australia are studied during the strongly evaporative conditions of austral winter 2003 present results along with those of previous authors confirm that a poleward fresh leeuwin current core is normally found near the shelf break salinity increases alongshore toward the southwest although there is no obvious shelf break front there is a persistent offshore upward tilting of isopycnals in the depth range of 100 150 m repeated mesoscale surveys were made at the shelf edge during 8 days when the shelf break flow was equatorward waters offshore of the shelf break contain a rich baroclinic ageostrophic eddy field with typically 10 km length scales and the eddy patterns in the upper 60 m are uncorrelated with those below 90 m the two depth horizons yield energy transfers from mean to eddy potential energy and appear to represent distinct finite amplitude instabilities on upper ocean and 180 m mean velocity cores respectively a linear stability model supports the existence of the two vertically separated instability types

glaciological and oceanographic evidence of high melt rates beneath pine island glacier west antarctica satellite imagery indicates that the floating terminus of pine island glacier has changed little in extent over the past two decades data on the velocity and thickness of the glacier reveal that calving of 28 4 gt a 1 accounts for only half of the ice input near the grounding line the apparently steady configuration implies that the remainder of the input is lost by basal melting at a mean rate of 12 3 m a 1 ocean circulation in pine island bay transports 1 c waters beneath the glacier and temperatures recorded in melt laden outflows show that heat loss from the ocean is consistent with the requirements of the calculated melt rate the combination of iceberg calving and basal melting lies at the lower end of estimates for the total accumulation over the catchment basin drawing into question previous estimates of a significantly positive mass budget for this part of the ice sheet

compressional and shear wave logging in open and cased holes using a multipole tool we have found in field observations that the multipole sonic logging tool can effectively measure formation p wave and s wave data in a cased hole the multipole tool containing both monopole and quadrupole source receiver systems was originally designed to log p and s waves directly in all lithologies for an open borehole the monopole source receiver system p wave operates at 7 10 khz as compared with 15 25 khz for a conventional sonic tool while the quadrupole source receiver system s wave operates at 3 7 khz these lower operating frequencies enable the signals to penetrate the well casing and cement more effectively than signals from a conventional sonic tool as a result the formation p and s waves recorded by the multipole tool are generally much stronger than the unwanted waves which travel along the well casing and cement formation arrivals can be easily identified and separated from the casing arrivals for a wide range of lithologies logs run before and after the wells were cased

3 d seismic endoscopy multiscale analysis and dynamic azimuthal filtering of borehole waves summary we previously proposed a method of seismic endoscopy and a related prototype tool to acquire directional information and to produce three dimensional 3 d seismic images in a cylindrical volume surrounding a borehole with an investigation radius of several metres basic imaging algorithms were developed where the azimuthal move out amo process is combined to a timescale method to refocus directional information and analyse the surrounding medium further processing tools however were necessary for separating the various types of waves recorded the present paper describes a multiscale and dynamic azimuthal filtering to separate the far field waves from borehole or tube waves generated by the pipe we call this filter stoneley move out smo because it characterizes stoneley waves associated with the tube it is then possible to reconstruct details of the far field by an inverse wavelet transform the comparison with classical methods such as the covariance method is discussed applications on noisy synthetic and experimental data are presented

homomorphic processing of the tube wave generated during acoustic logging we have developed a new method to process the tube wave which is generated during acoustic logging to obtain estimates for its wavenumber attenuation coefficient amplitude and phase at every frequency to improve the accuracy of the estimates the method can use data from multiple sources and data collected at successive depths in the borehole this new method has several advantages over other methods that are currently used to process acoustic logging data the new method can obtain accurate estimates of the wavenumber and amplitude from only a few receivers the receivers can be irregularly spaced and no spurious estimates are generated nonetheless this new method has one disadvantage compared to others it can only estimate the parameters for one high amplitude wave like the tube wave also like all other existing methods the new method obtains only reasonable estimates for the attenuation coefficient when data from many receivers are processed