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

numerical simulation of 2 d seismic wave propagation in the presence of a topographic fluid solid interface at the sea bottom by the curvilinear grid finite difference method

in situ synchrotron radiation xrf study of ree phosphate dissolution in aqueous fluids to 800 c abstract the temporal evolution of the concentrations of la ce pr nd sm gd y pb th and u in the fluid during dissolution of synthetic lapo 4 monazite natural monazite and xenotime in aqueous hcl nacl solutions was studied in situ at temperatures from 25 to 800 c and pressures to about 2 gpa using hydrothermal diamond anvil cells and synchrotron radiation xrf analyses constant within error la concentrations in the fluid were attained in less than 50 min at temperatures 300 c and in less than 90 min at 200 c at 100 c the time required to reach a constant la concentration varied with the hcl molality from less than 3 h at 5 1 m hcl to 11 h at 1 m hcl the experiments indicate a significantly lower mobility of y gd and th compared to that of the lree particularly la over a large range of crustal p t conditions if controlled by interaction of monazite with acidic and chloridic fluids the corresponding change in the ree pattern is in close agreement with literature reports on natural monazites which underwent greisenization or sericitization the th pb ratio in the fluid increased with temperature and hcl concentration but was far below the th pb ratio in the monazite even at 600 c and 2 gpa the experimental results imply that monazites leached in acidic and chloridic fluids are characterized by a strong enrichment of th relative to the lree and pb

observations on attenuation and shear wave velocity in fine grained marine sediments compressional p wave attenuation shear s wave attenuation and shear s wave velocity measurements compiled for fine grained unconsolidated sediments show trends that do not support empirical relationships hamilton j acoust soc am 68 1313 1340 1980 in acoustics and ocean bottom f a s e specialize conf madrid 1987 commonly used for geoacoustic modeling the exception is compressional wave attenuation data from 10 hz to 500 khz that essentially follow a frequency dependence of f1 2 standard deviations p wave attenuation with depth is difficult if not impossible to predict given the variability in the data examination of several attenuation depth profiles indicates that those of mitchell and focke j acoust soc am 67 1582 1589 1980 may be the best choice for predicting p wave attenuation with depth at the present time the assumption that s wave and p wave attenuations are proportional hamilton j acoust soc am 60 334 338 1976c in acoustics and ocean bottom

laterally constrained inversion of ground roll from seismic reflection records seismic reflection data contain surface waves that can be processed and interpreted to supply shear wave velocity models along seismic reflection lines the coverage of seismic reflection data allows the use of automated multifold processing to extract high quality dispersion curves and experimental uncertainties in a moving spatial window the dispersion curves are then inverted using a deterministic laterally constrained inversion to obtain a pseudo 2d model of the shear wave velocity a monte carlo global search inversion algorithm optimizes the parameterization when the strategy is used with synthetic and field data consistent final models with smooth lateral variations are successfully retrieved this method constitutes an improvement over the individual inversion of single dispersion curves

seismic shear wave observations in a physical model experiment the observation and common depth point cdp processing of mode converted shear waves is demonstrated for real data collected in a physical model experiment the model submerged in water represented water depth scaled to 250 ft the first subsea reflector at 4000 ft and the last reflector at 7000 ft below the sea floor with a structural wedge at the center very efficient mode conversion from p to sv and back to p is anticipated for angles of incidence at the liquid solid interface sea floor between 35 and 80 degrees the model constructed of plexiglas and 3180 resin will support elastic shear wave propagation one anticipated problem internal reflections from the sides of the model was solved by tapering the sides of the model to 45 degrees off vertical the p wave reflection coefficient at an interface between plexiglas and water is 35 percent for vertical incidence but it diminishes to very nearly zero between 43 and 75 degrees thus by tapering the sides of the model any undesired intern

evolution of double diffusion convection in a felsic magma chamber abstract the onset of double diffusion convection ddc is modeled in a two dimensional case in respect to magma chambers the viscosity model for the melt takes into account the effects of temperature and concentration of the dissolved component h 2 o the upper boundary of the convecting magma chamber is assumed to be anhydrous and at constant temperature whereas the lower boundary is treated as being hydrous permeable with a temperature greater than that within the upper boundary the case of positive compositional and thermal buoyancy of melt is studied assuming a h 2 o diffusion coefficient small in comparison with thermal diffusivity the ddc has been modeled using a system of equations solved by the finite difference method on a square grid the convective pattern evolution has been studied for fixed boundary conditions as well as for cooling and degassing due to the higher viscosity in the upper zone the upper boundary layer is thicker than the lower one the variation of water concentration in this zone of the convective cell can be significant in nature the high gradient of water concentration can be responsible for the observed variations of water content in minerals crystallized from a granite melt e g biotite because of a high lewis number 100 temperature variations in the magma chamber decay much faster than the water concentration in this case the intensive convection can continue at a constant temperature due to the non zero water content in the chamber in principle the effect can be applied to the formation of magmatic bodies if the cooling and degassing system reaches a uniform temperature distribution prior to the crystallization temperature water content throughout the body may still remain variable

1 5d inversion of lateral variation of scholte wave dispersion reliable models of in situ shear wave velocities of shallow water marine sediments are important for geotechnical applications lithological sediment characterization and seismic exploration studies we infer the 2d shear wave velocity structure of shallow water marine sediments from the lateral variation of scholte wave dispersion scholte waves are recorded in a common receiver gather generated by an air gun towed behind a ship away from a single stationary ocean bottom seismometer an offset window moves along the common receiver gather to pick up a local wavefield a slant stack produces a slowness frequency spectrum of the local wavefield which contains all modes excited by the air gun amplitude maxima dispersion curves in the local spectrum are picked and inverted for the shear wave velocity depth profile located at the center of the window as the window continuously moves along the common receiver gather a 2d shear wave velocity section is generated in a synthetic example the smooth lateral variation of surficial shear wave velocity is well reconstructed the method is applied to two orthogonal common receiver gathers acquired in the baltic sea northern germany the inverted 2d models show a strong vertical gradient of shear wave velocity at the sea floor along one profile significant lateral variation near the sea floor is observed

separation of s wave and p wave reflections offshore western florida hard water bottom marine environments such as offshore western florida have presented particular problems in the acquisition and processing of seismic reflection data one problem has been the limited angle of incidence less than critical available to p wave penetration into the subsurface mode conversion from p wave to s waves sv however is quite efficient over a broad range of angles of incidence after the success of a previously reported physical model experiment an experimental line was acquired offshore western florida the 19 mile line located approximately 100 miles west of key west florida was shot and processed three key factors have contributed to the successful recording of mode converted s wave reflections 1 recognition of the effect of the group length on attenuation of energy arriving at large angles of incidence 2 tau p processing techniques that allow separation of energy by angle of incidence and 3 velocity filtering over a range of hyperbolic normal moveout nmo

imaging beneath a high velocity layer using converted waves high velocity layers hvls often hinder seismic imaging of deeper reflectors using conventional techniques a major factor is often the unusual energy partitioning of waves incident at an hvl boundary from lower velocity material using elastic physical modeling i demonstrate that one effect of this factor is to limit the range of dips beneath an hvl that can be imaged using unconverted p wave arrivals at the same time however partitioning may also result in p waves outside the hvl coupling efficiently with s waves inside by exploiting some of the waves that convert upon transmission into and or out of the physical model hvl i am able to image a much broader range of underlying dips this is accomplished by acoustic migration tailored via the migration velocities used for selected families of converted wave arrivals

direct estimation of shear wave interval velocities from seismic data conventional velocity analysis of seismic data is based on normal moveout of common depth point cdp traveltime curves analysis is done in a hyperbolic framework and therefore is limited to using the small angle reflections only muted data hence it can estimate the interval velocities of compressional waves only since mode conversion is negligible when small angle arrivals are concerned we propose a new method which can estimate the interval velocities of compressional and mode converted waves separately the method is based on slant stacking or plane wave decomposition pwd of the observed data seismogram which transforms the data from the conventional t x domain into the intercept time ray parameter domain since pwd places most of the compressional energy into the precritical region of the slant stacked seismogram the compressional wave interval velocities can be estimated using the best ellipse approximation on the assumption that the elliptic array velocity stacking velocity is app

rayleigh to shear wave conversion at the tunnel face from 3d fd modeling to ahead of drill exploration for safe tunnel excavation it is important to predict lithologic and structural heterogeneities ahead of construction conventional tunnel seismic prediction systems utilize body waves p and s waves that are directly generated at the tunnel walls or near the cutter head of the tunnel boring machine tbm we propose a new prediction strategy that has been discovered by 3d elastic finite difference fd modeling rayleigh waves arriving at the front face of the tunnel are converted into high amplitude s waves propagating further ahead reflected or backscattered s waves are converted back into rayleigh waves which can be recorded along the sidewalls we name these waves rssr waves in our approach the front face acts as an s wave transceiver one technical advantage is that both the sources and the receivers may be placed behind the cutter head of the tbm the modeling reveals that the rssr waves exhibit significantly higher amplitudes than the directly reflected body waves the excavation damage zone causes dispersion of the rssr wave leading to multimodal reflection response for the detection of geologic interfaces ahead rssr waves recorded along the sidewalls are corrected for dispersion and stacked from the arrival times the distance to the s s reflection point can be estimated a recurrent application while the tunnel approaches the interface allows one to quantify the orientation of the reflecting interfaces as well our approach has been verified successfully in a field experiment at the piora adit of the gotthard base tunnel the distance to the piora fault zone estimated from stacked rssr events agrees well with the information obtained by geologic surveying and exploratory drilling

separation of p and sv wavefields from multi component seismic data in the τ p domain summary multi component seismic data contain richer information about the elastic parameters of the subsurface than do conventional single component data separation of the compressional and shear wavefields from multi component seismic data is crucial in estimating the subsurface elastic properties we present a p domain scheme to separate p and sv wavefields from multi component seismic data observed at the free surface and ocean bottom based on plane wave components with known horizontal slowness in p domain the whole p and sv wavefields are separated into the direction of observed p and sv wave oscillations by rotation of the horizontal and vertical components respectively the incident p and sv waves are extracted from the separated wavefields using plane wave partitions at the free surface and ocean bottom the parameters used in the separation are the local seismic wave velocities and the density at the receiver location numerical tests on synthetic data for plane layered models show good performance and accuracy of the scheme

extraction of p and s waves from the vertical component of the particle velocity at the sea floor at the boundary between two solid media in welded contact all three components of particle velocity and vertical traction are continuous through the boundary across the boundary between a fluid and a solid however only the vertical component of particle velocity is continuous while the horizontal components can be discontinuous furthermore the pressure in the fluid is the negative of the vertical component of traction in the solid while the horizontal components of traction vanish at the interface taking advantage of this latter fact the authors show that total p and s waves can be computed from the vertical component of the particle velocity recorded by single component geophones planted on the sea floor in the case when the sea floor is transversely isotropic with a vertical axis of symmetry the computation requires the five independent elastic stiffness components and the density however when the sea floor material is fully isotropic the only material parameter needed is the local shear wave velocity the analysis of the extraction problem is done in the slowness domain they show however that the s wave section can be obtained by a filtering operation in the space frequency domain the p wave section is then the difference between themore vertical component of the particle velocity and the s wave component a synthetic data example demonstrates the performance of the algorithm less

retrieving 2d structures from surface wave data by means of space varying spatial windowing abstractsurface wave techniques are mainly used to retrieve 1d subsurface models however in 2d environments the 1d approach usually neglects the presence of lateral variations and because the surface wave path crosses different materials the resulting model is a simplified or misleading description of the site we tested a processing technique to retrieve 2d structures from surface wave data acquired with a limited number of receivers our technique was based on a two step process first we extracted several local dispersion curves along the survey line using a spatial windowing based on a set of gaussian windows with different shapes the window maxima span the survey line so that we were able to extract a dispersion curve from the seismic record for every window this provided a set of local dispersion curves each of them referring to a different subsurface portion this space varying spatial windowing provided a good compromise between wavenumber resolution and the lateral resolution of the obtain

multichannel analysis of surface waves masw for offshore geotechnical investigations abstract multichannel analysis of surface wave masw surveys are commonly used onshore to produce shear wave velocity vs profiles this paper describes its use in offshore geotechnical investigations underwater masw umasw where the focus was on the upper 15 m of the sediment profile to aid the design of structures such as marine pipelines cable routes and shallow anchor systems umasw was shown to provide reliable data in irish offshore conditions in water depths of up to 50 m the receiver spacing and array length rather than the characteristics of the air gun seismic energy source were the primary control on signal penetration and resolution of individual sediment layers good resolution of the properties of the upper 5 m of sediment was found by reducing the receiver spacing to as low as 0 3 m a test site with a broad intertidal zone allowed coincident land marine and direct measurements to be compared and vs profiles obtained from umasw onshore masw and by seismic cone testing scptu were in good agreement vs profiles estimated from published correlations with cptu data in sandy sediments agreed well with the measured values inversion of data using different software packages showed only a minor variation in results

inversion of source generated noise in high resolution seismic data the immediate subsurface is often characterized by a layer of weathered bedrock or unconsolidated sediments typically this surficial layer has a very high poisson s ratio and an unusually strong impedance contrast at its lower boundary comparable for example to that observed at a hard seafloor within the offset range of high resolution seismic surveys the layer can be regarded as horizontal and seismic energy trapped within the layer generates horizontally propagating guided wave trains together with rayleigh waves guided waves pose serious problems to high resolution seismic imaging and are commonly referred to as source generated noise in a typical seismic shot gather rayleigh and guided waves define two cone shaped time offset windows that bound the optimum time offset window in which primary reflections can be observed

measuring lateral variability of sediment geoacoustic properties dispersion analysis of interface waves scholte stoneley rayleigh has been used extensively to determine geoacoustic models of near bottom ocean sediments in the traditional approach a single seismic trace is analyzed to obtain group velocity dispersion using the multiple filter technique a dispersion curve obtained in this manner reflects the averaged influence of the sediment acoustic properties over the entire path from source to receiver thus a geoacoustic model derived from this dispersion curve is not a true vertical section in the vicinity of the receiver unless the sediment properties do not change over the entire propagation path however when a linear array of receivers is used to obtain data simultaneously at a number of different ranges it is possible to derive both group and phase velocity dispersion curves that correspond to propagation over a short portion typically 5 m of the total path at many different ranges with this kind of data the range dependent variation of geoacoustic properties in the sediment may be assessed results are presented based on data obtained with a 24 receiver array and an explosive source both deployed on the seafloor analysis of data from a number of shallow water sites suggests that there is a considerable amount of lateral inhomogeneity even over very short ranges

relationship between p and s wave velocities and geological properties of near surface sediments of the continental slope of the barents sea seismic velocities v p and v s of compressional p and shear s waves are important parameters for the characterization of marine sediments with respect to their sedimentological and geotechnical properties p and s wave velocity data of near surface marine sediments upper 9 m of the continental slope of the barents sea are analysed and correlated to sedimentological and geotechnical properties the results show that the s wave velocity is much more sensitive to changes in lithology and mechanical properties than the p wave velocity which is characterized by a narrow range of values the correlation coefficients between s wave velocity and silt and clay content wet bulk density porosity water content and shear strength are higher than 0 5 while the correlation coefficients of p wave velocity and the same parameters are always lower than 0 4 although the relationship between v s and clay content has been widely described the data show that v s is better correlated with silt content than with clay content for the sediments of the area investigated however they show different trends while v s increases with increasing clay content it decreases with increasing silt content

on the use of the norwegian geotechnical institute s prototype seabed coupled shear wave vibrator for shallow soil characterization i acquisition and processing of multimodal surface waves summary pure shear wave data are only very rarely acquired for offshore site investigations and exploration here we present details of a novel seabed coupled shear wave vibrator and field data recorded by a densely populated multicomponent ocean bottom cable to improve shallow soil characterization the prototype shear wave vibrator uses vibroseis technology adopted for marine environments through its instalment on top of a suction anchor assuring seabed coupling in combination with self weight penetration the prototype is depth rated to 1500 m water depth and can be rotated while installed in the seabed the philosophy is to acquire fully complementary seismic data to conventional p and p to s converted waves in particular for 2 d profiling vsp vertical seismic profiling or monitoring purposes thereby exploiting advantages of shear waves over compressional waves for determining for example anisotropy small strain shear modulus and excess pore pressures effective stress the source was primarily designed for reservoir depths however significant energy is emitted as surface waves which provide detailedgeotechnicalinformationthroughmappingofshearwavevelocitiesinpotentiallyhigh resolution of the upper soil units to fully utilize pure shear wave content a proper analysis of surface waves is paramount due to the proximity of surface wave propagation speed with shear wave velocities the experiment was carried out in the northern north sea in 364 m water depth cable dragging was necessary to obtain close receiver spacing 2 5 m effective spacing with total line length of 600 m frequency waveform transforms reveal both scholte and love waves up to six surface wave modes are identified that is fundamental mode and several higher surface wave modes the occurrence of these two different dispersive surface wave types with well resolved higher modes allows for a unique analysis and inversion scheme for highresolution mapping of physical properties in the shallow subsurface as well as anisotropy which is discussed in an accompanying paper the data presented in this paper are thus a unique long and densely populated receiver array allows for multimodal love and scholte surface waves from the marine environment but challenging marine operations marine data set

2 d multiparameter viscoelastic shallow seismic full waveform inversion reconstruction tests and first field data application 2d full waveform inversion fwi of shallow seismic wavefields has recently become a novel way to reconstruct s wave velocity models of the shallow subsurface with high vertical and lateral resolution in most applications seismic wave attenuation is ignored or considered as a passive modelling parameter only in this study we explore the feasibility and performance of multi parameter viscoelastic 2d fwi in which seismic velocities and attenuation of p and s waves respectively and mass density are inverted simultaneously synthetic reconstruction experiments reveal that multiple crosstalks between all viscoelastic material parameters may occur the reconstruction of s wave velocity is always robust and of high quality the parameters p wave velocity and density exhibit weaker sensitivity and can be reconstructed more reliably by multi parameter viscoelastic fwi anomalies in s wave attenuation can be recovered but with limited resolution in a field data application a small scale refilled trench is nicely delineated as a low p and s wave velocity anomaly the reconstruction of p wave velocity is improved by the simultaneous inversion of attenuation the reconstructed s wave attenuation reveals higher attenuation in the shallow weathering zone and weaker attenuation below the variations in the reconstructed p and s wave velocity models are consistent with the reflectivity observed in a gpr profile

decomposition of multicomponent sea floor data into upgoing and downgoing p and s waves a method for decomposing multicomponent sea floor measurements into upgoing and downgoing p and s waves is presented we assume that a marine survey employing a marine source in the water layer is conducted over a plane layered medium from recordings of the pressure just above the sea floor and the particle velocity vector just below the sea floor decomposition filters can be determined by plane wave analysis the decomposition filter coefficients depend on the p and s wave velocities and the density at the sea bottom we show how to decompose the multicomponent measurements into upgoing and downgoing p and s vertical traction components vertical particle velocity components and horizontal particle velocity components the decomposition filters are applied with good results to synthetic data modeled in a plane layered medium

regional seismic phases across the ligurian sea lg blockage and oceanic propagation abstract the ligurian sea west mediterranean is an example of a narrow oceanic basin which stops lg wave propagation locating the exact point of lg extinction was one of the goals of the sisbalig ii seismological experiment which deployed both inland stations in provence and corsica and ocean bottom seismometers obs in the ligurian sea a precise analysis of all available regional seismological data using energy diagrams reveals the role of the provence margin in the lg phase extinction for seismic events occurring in the southwestern alps the extinction is not a progressive phenomenon along oceanic travel path but occurs in a narrow zone of about 20 km width in the vicinity of the provence margin the extinction is accompanied by the generation of two types of diffracted waves the mantle phase sn v s 3 5 km s 1 and very low velocity s waves appearing both near the provence margin and in the middle of the ligurian basin we performed numerical simulation of sh wave propagation in two dimensional 2d media to investigate the mechanisms of lg extinction the simulations confirm that simple crustal thinning at the continent ocean boundary alone cannot cause the observed extinction of lg waves although the change in moho depth does induce the diffraction of a part of the incident lg wavetrain into mantle waves giving rise to the sn phase on the other side of the basin the existence of soft oceanic sediments is a very important factor in explaining the extinction as a large part of the lg energy is transferred into slow s waves trapped in the sediments moreover comparison of synthetic seismograms and observed data shows that the observed two packets of low velocity waves are an indication of the asymmetry of the ligurian basin with the existence of two shallow basins with very low s velocity 1 0 km s 1 near the provence margin and in the middle of the ligurian sea however the attenuation of lg waves in the vicinity of the provence margin is more abrupt in the data than in the simulations this discrepancy could result from the complex geometry of the continent ocean transition zone and its possibly very diffractive nature two factors that could add to lg extinction at the margin and are impossible to take into account in models

physical modelling of a surface wave survey over a laterally varying granular medium with property contrasts and velocity gradients laboratory experiments using laser based ultrasonic techniques can be used to simulate seismic surveys on highly controlled small scale physical models of the subsurface most of the time such models consist in assemblies of homogeneous and consolidated materials to enable the physical modelling of unconsolidated heterogeneous and porous media the use of granular materials is suggested here we describe a simple technique to build a two layer physical model characterized by lateral variations strong property contrasts and velocity gradients we use this model to address the efficiency of an innovative surface wave processing technique developed to retrieve 2 d structures from a limited number of receivers a step by step inversion procedure of the extracted dispersion curves yields accurate results so that the 2 d structure of the physical model is satisfactorily reconstructed the velocity gradients within each layer are accurately retrieved as well confirming current theoretical and experimental studies regarding guided surface acoustic modes in unconsolidated granular media

retrieving lateral variations from surface wave dispersion curves surface wave analysis is usually applied as a 1d tool to estimate v s profiles here we evaluate the potential of surface wave analysis for the case of lateral variations lateral variations can be characterized by exploiting the data redundancy of the ground roll contained in multifold seismic data first an automatic processing procedure is applied that allows stacking dispersion curves obtained from different records and which retrieves experimental uncertainties this is carried out by sliding a window along a seismic line to obtain an ensemble of dispersion curves associated to a series of spatial coordinates then a laterally constrained inversion algorithm is adopted to handle 2d effects although a 1d model has been assumed for the forward problem solution we have conducted different tests on three synthetic data sets to evaluate the effects of the processing parameters and of the constraints on the inversion results the same procedure applied to the synthetic data was then tested on a field case both the synthetic and field data show that the proposed approach allows smooth lateral variations to be properly retrieved and that the introduction of lateral constraints improves the final result compared to individual inversions

ongoing hydrothermal activities within enceladus analysis of silicon rich nanometre sized dust particles near saturn shows them to consist of silica which was initially embedded in icy grains emitted from enceladus subsurface waters and released by sputter erosion in saturn s e ring their properties indicate their ongoing formation and transport by high temperature hydrothermal reactions from the ocean floor and up into the plume of enceladus hsiang wen hsu et al have analysed the silicon rich nanometre sized dust stream particles in the saturnian system using the cosmic dust analyser cda onboard the cassini spacecraft with the help of experiments and modelling the particles are interpreted as silica grains that were initially embedded in the icy plume emitted from subsurface waters on enceladus and released by sputter erosion in saturn s e ring their properties indicate their formation and transport by high temperature hydrothermal reactions from the ocean floor and up into the plume of enceladus detection of sodium salt rich ice grains emitted from the plume of the saturnian moon enceladus suggests that the grains formed as frozen droplets from a liquid water reservoir that is or has been in contact with rock1 2 gravitational field measurements suggest a regional south polar subsurface ocean of about 10 kilometres thickness located beneath an ice crust 30 to 40 kilometres thick3 these findings imply rock water interactions in regions surrounding the core of enceladus the resulting chemical footprints are expected to be preserved in the liquid and subsequently transported upwards to the near surface plume sources where they eventually would be ejected and could be measured by a spacecraft4 here we report an analysis of silicon rich nanometre sized dust particles5 6 7 8 so called stream particles that stand out from the water ice dominated objects characteristic of saturn we interpret these grains as nanometre sized sio2 silica particles initially embedded in icy grains emitted from enceladus subsurface waters and released by sputter erosion in saturn s e ring the composition and the limited size range 2 to 8 nanometres in radius of stream particles indicate ongoing high temperature 90 c hydrothermal reactions associated with global scale geothermal activity that quickly transports hydrothermal products from the ocean floor at a depth of at least 40 kilometres up to the plume of enceladus

evolution of titan s rocky core constrained by cassini observations 1 we model the thermal evolution of titan s core and search for solutions that are consistent with the mean moment of inertia yielded by the cassini huygens mission like previous studies we assume that titan s core is enriched in hydrated silicates however our modeling accounts for the possible dehydration of these minerals the resulting models are consistent with titan s moment of inertia if the inner dry silicate core remains smaller than 1300 km in radius this constraint is met if at least 30 of potassium was leached from the silicate during the hydration event i e the core is depleted in one of its major heat source in this scenario the core is currently undergoing dehydration

seismic attenuation from recordings of ambient noise abstractwe applied seismic interferometry to data from an ocean bottom survey offshore norway and found that ambient seismic noise can be used to constrain subsurface attenuation on a reservoir scale by crosscorrelating only a few days of recordings by broadband ocean bottom seismometers we were able to retrieve empirical green s functions associated with surface waves in the frequency range between 0 2 and 0 6 hz and acoustic waves traveling through the sea water between 1 0 and 2 5 hz we discovered that the decay of these surface waves cannot be explained by geometrical spreading alone and required an additional loss of energy with distance we quantified this observed attenuation in the frequency domain using a modified bessel function to describe the cross spectrum in a stationary field we averaged cross spectra of equally spaced station couples and sorted these azimuthally averaged cross spectra with distance we then obtained frequency dependent estimates of attenuation by minimizing the misfit

on the use of the norwegian geotechnical institute s prototype seabed coupled shear wave vibrator for shallow soil characterization ii joint inversion of multimodal love and scholte surface waves summary seismic data generated by a novel seabed coupled shear wave vibrator prototype and recorded by a densely populated multicomponent ocean bottom cable allowed several modes of propagation of love and scholte waves to be retrieved in a relatively wide frequency band both global dispersion curves and local dispersion curves are extracted in the frequency wavenumber f k domain and inverted with a multimodal joint scholte and love wave inversion algorithm monte carlo inversion is used for a estimating the global s wave velocity profile of the seabed sediments whereas laterally constrained inversion is used to detect lateral variations of the layer interface depths the results are in agreement and allowed consistent full waveform simulation to be performed the investigation depth is limited to around 40 m due to the low shear wave velocities within the shallow clay layer

frequency dependent multi offset phase analysis of surface waves an example of high resolution characterization of a riparian aquifer multi offset phase analysis of seismic surface waves is an established technique for the extraction of dispersion curves with high spatial resolution and consequently for the investigation of the subsurface in terms of shear wave velocity distribution however field applications are rarely documented in the published literature in this paper we discuss an implementation of the multi offset phase analysis consisting of the estimation of the rayleigh wave velocity by means of a moving window with a frequency dependent length this allows maximizing the lateral resolution at high frequencies while warranting stability at the lower frequencies in this way we can retrieve the shallow lateral variability with high accuracy and at the same time obtain a robust surface wave velocity measurement at depth in this paper we apply this methodology to a dataset collected for hydrogeophysical purposes and compare the inversion results with those obtained by using refraction seismics and electrical resistivity tomography the surface wave results are in good agreement with those provided by the other methods and demonstrate a superior capability in retrieving both lateral and vertical velocity variations including inversions our results are further corroborated by the lithological information from a borehole drilled on the acquisition line the availability of multi offset phase analysis data also allows disentangling a fairly complex interpretation of the other geophysical results

towards high resolution 3d marine seismic surveying using boomer sources the use of boomer sources for 3d seismic imaging of shallow marine structures was investigated in a feasibility study boomers show sufficient stability to be used in multichannel seismic surveys the acquisition of a high frequency densely sampled seismic data volume was successfully performed in the baltic sea a pleistocene fluvial channel system and shallow gas accumulations were revealed beneath the unconsolidated sediments which constitute the sea floor in the southern kiel bay

the present state of seismic data acquisition one view seismic data acquisition in the mid 1980s is briefly reviewed in terms of hardware the trend has been toward an increased number of data channels in both land and marine applications this has led to the development of digital telemetry systems positioning systems particularly for marine work have made use of artificial satellites the perceived need for s wave information has led to development of s wave sources such as the horizontal vibrator s waves in a few cases have been used to validate hydrocarbon indicators on seismic records there has been a distinct trend toward three dimensional 3 d seismic recording both on land and at sea and for both exploration and production applications

separation of p and s wavefields from wide angle multicomponent obc data for a basalt model wide angle multicomponent ocean bottom cable obc data should further enhance sub basalt imaging by using both compressional and converted shear wavefields the first step in analysing multicomponent obc data is to decompose the recorded wavefields into pure p and pure s wavefields and extract the upgoing p and s waves this paper presents a new scheme to separate p and s wavefields from wide angle multicomponent obc data in the p domain by considering plane wave components with a known horizontal slowness the p and s wavefields are separated into the directions of observed p and s wave oscillations using the horizontal and vertical components of the data the upgoing p and s waves are then extracted from the separated p and s wavefields the parameters used in the separation are the seismic wave velocities and the density at the receiver location which can be estimated from the first reflection phase observed on the horizontal and vertical components numerical tests on synthetic data for a plane layered model show good performance and demonstrate the accuracy of the scheme separation of wavefields from a basalt model is performed using synthetic wide angle multicomponent obc data the results show that both near offset and wide angle reflections and conversions from within and below basalt layers are enhanced and clearly identified on the separated wavefields

evidence of dispersion in an artificial water saturated sand sediment a laboratory experiment was conducted to measure the speed of sound in an artificial water saturated granular sediment composed of cleaned and sorted medium grained sand and degassed distilled water the experiment was conducted within a range of frequencies where dispersion is predicted by a number of existing models between 2 and 4khz the sound speed was inferred from measurements of the resonance frequencies of a thin walled cylindrical container filled with the material an elastic waveguide model was used to account for the effect of the finite impedance of the walls although this effect was found to be small from 20 to 300khz the sound speed was obtained directly from time of flight measurements within the sediment dispersion in close agreement with the williams effective density fluid model k l williams j acoust soc am 110 2276 2281 2001 was observed

field experiments to study seafloor seismoacoustic response results of a 5 year program to measure the seismoacoustic properties of unlithified sediments in the seafloor are presented a field technique utilizing an impulsive source and a geophone array located on the seafloor was used to obtain detailed travel time curves which permit a number of different kinds of analysis a new signal source powered by electrically detonated 8 gauge shotgun shells was used to focus energy into the bottom and eliminate much of the high frequency water borne noise that accompanies the usual explosive sources both interface waves and wide angle refractions were analyzed a variety of data inversion techniques including slant stacking and cross multiplication were used to obtain dispersion curves and constrained least squares inversion using partial derivatives was used to develop an iterative inversion method to obtain velocity and attenuation as a function of depth examples of data from a wide angle of different kinds of sediment ranging from soft holocene mud to stiff over

velocity analysis from large offset seismic records one of the most important problems in applied geophysics is to extract velocities of compressional and shear waves using the observed data collected at the earth s surface or in boreholes unfortunately in a typical seismic experiment we do not have enough information to uniquely recover seismic velocities as functions ofx y andz thus in the paper a simplified model of the earth a stack of horizontal homogeneous layers is considered and a critical discussion of modern techniques for processing reflection arrivals is presented

salt partitioning between water and high pressure ices implication for the dynamics and habitability of icy moons and water rich planetary bodies abstract water rich planetary bodies including large icy moons and ocean exoplanets may host a deep liquid water ocean underlying a high pressure icy mantle the latter is often considered as a limitation to the habitability of the uppermost ocean because it would limit the availability of nutrients resulting from the hydrothermal alteration of the silicate mantle located beneath the deep ice layer to assess the effects of salts on the physical properties of high pressure ices and therefore the possible chemical exchanges and habitability inside h 2 o rich planetary bodies we measured partitioning coefficients and densities in the h 2 o rbi system up to 450 k and 4 gpa rbi standing as an experimentally amenable analog of nacl in the h 2 o salt solutions we measured the partitioning coefficient of rbi between the aqueous fluid and ices vi and vii using in situ synchrotron x ray fluorescence xrf with in situ x ray diffraction we measured the unit cell parameters and the densities of the high pressure ice phases in equilibrium with the aqueous fluid at pressures and temperatures relevant to the interior of planetary bodies we conclude that rbi is strongly incompatible towards ice vi with a partitioning coefficient k d vi l 5 0 2 1 10 3 and moderately incompatible towards ice vii k d vii l 0 12 0 05 rbi significantly increases the unit cell volume of ice vi and vii by ca 1 this implies that rbi poor ice vi is buoyant compared to h 2 o ice vi while rbi enriched ice vii is denser than h 2 o ice vii these new experimental results might profoundly impact the internal dynamics of water rich planetary bodies for instance an icy mantle at moderate conditions of pressure and temperature will consist of buoyant ice vi with low concentration of salt and would likely induce an upwelling current of solutes towards the above liquid ocean in contrast a deep and or thick icy mantle of ice vii will be enriched in salt and hence would form a stable chemical boundary layer on top of the silicate mantle such a contrasted dynamics in the aqueous ice vi ice vii system would greatly influence the migration of nutrients towards the uppermost liquid ocean thus controlling the habitability of moderate to large h 2 o rich planetary bodies in our solar system e g ganymede titan calisto and beyond

estimation of seabed shear wave velocity profiles using shear wave source data this paper estimates seabed shear wave velocity profiles and their uncertainties using interface wave dispersion curves extracted from data generated by a shear wave source the shear wave source generated a seismic signature over a frequency range between 2 and 60 hz and was polarized in both in line and cross line orientations low frequency scholte and love waves were recorded dispersion curves of the scholte and love waves for the fundamental mode and higher order modes are extracted by three time frequency analysis methods both the vertically and horizontally polarized shear wave velocity profiles in the sediment are estimated by the scholte and love wave dispersion curves respectively a bayesian approach is utilized for the inversion differential evolution a global search algorithm is applied to estimate the most probable shear velocity models marginal posterior probability profiles are computed by metropolis hastings sampling the estimated vertically and horizontally polarized shear wave

scholte wave tomography for shallow water marine sediments summary we determine the 3 d in situ shear wave velocities of shallow water marine sediments by extending the method of surface wave tomography to scholte wave records acquired in shallow waters scholte waves are excited by air gun shots in the water column and recorded at the seafloor by ocean bottom seismometers as well as buried geophones our new method comprises three steps 1 we determine local phase slowness values from slowness frequency spectra calculated by a local wavefield transformation of common receiver gathers areal phase slowness maps for each frequency used as reference in the following step are obtained by interpolating the values derived from the local spectra 2 we infer slowness residuals to those reference slowness maps by a tomographic inversion of the phase traveltimes of fundamental scholte wave mode 3 the phase slowness maps together with the residuals at different frequencies define a local dispersion curve at every location of the investigation area from those dispersion curves we determine a model of the depth dependency of shear wave velocities for every location we apply this method to a 1 km2 investigation area in the baltic sea northern germany the phase slowness maps obtained in step 2 show lateral variation of up to 150 per cent the shear wave velocity models derived in the third step typically have very low values 60 80 m s 1 in the top four meters where fine muddy sands can be observed and values exceeding 170 m s 1 for the silts and sands below that level the upper edge of glacial till with shear wave velocities of 300 400 m s 1 is situated approximately 20 m below sea bottom a sensitivity analysis reveals a maximum penetration depth of about 40 m below sea bottom and that density may be an important parameter best resolvable with multimode inversion

the river harbour of ostia antica stratigraphy extent and harbour infrastructure from combined geophysical measurements and drillings abstract we performed a combined geophysical and geoarchaeological survey of the harbour of ancient ostia italy to investigate the extent of the former harbour basin the sedimentary infill and possible building remains around the harbour besides geoarchaeological results the paper highlights the advantage of combining vibracore drilling with different geophysical prospection methods which are sensitive to different physical soil parameters geophysical methods applied were electrical resistivity tomography ert ground penetrating radar gpr and seismics with shear and compressional waves the extent and shape of the harbour basin were determined by ert profiling the ert profiles were compiled into a 3d model showing that the early lagoonal harbour basin was at least 100 m 50 m wide its southern border was confirmed by gpr measurements clearly imaging the former land water transition and the onset of ancient onshore building construction at its eastern border a consolidated horizon could be mapped in 2 3 m depth by compressional wave tomography this horizon most likely represents a cemented ramp a small part of which had been excavated in a previous study the sedimentary fill of the former harbour basin was investigated by a combination of vibracoring ert and seismics the ert profiles serve for inter and extrapolating the vibracore stratigraphy from the coring locations over the whole harbour area it turned out that one sedimentary unit which is important for the harbour development could not be resolved by ert but clearly shows up in seismic velocity depth profiles instead it is a thin coarse grained high energy layer in 1 2 m depth which was caused by a tsunami according to a previous study this layer separates two harbour phases an older lagoonal harbour phase underneath and a younger fluvial harbour phase above it the high energy layer represents a thin band of 100 increased shear wave velocity compared to the more fine grained layers in which it is embedded this study is the first to show that tsunami type sedimentary layers may be mapped by shear wave profiling

seabed property estimation from ambient noise recordings part i compliance and scholte wave phase velocity measurements the ability to derive a near surface shear velocity profile from ambient noise records is useful for seismic applications such as shear wave statics estimation and geohazard prediction measurements of seafloor compliance and scholte wave velocity and amplitude are all related to the near surface shear velocity profile i analyzed a data set of 33 minutes of continuous noise records recorded by an ocean bottom cable deployed in 273 m deep water for seafloor compliance and scholte waves i failed to observe seafloor compliance because of limitations in the record length i have detected scholte waves on the inline and vertical component geophones and love waves on the crossline component using f k spectra both the scholte and love wave phase velocities can be explained by a simple 1d isotropic near surface model the scholte waves may have been excited by acoustic energy from the recording vessel while no satisfactory excitation mechanism has been found for the love waves

shallow water sediment properties derived from high frequency shear and interface waves low frequency sound propagation in shallow water environments is not restricted to the water column but also involves the subbottom thus as well as being important for geophysical description of the seabed subbottom velocity attenuation structure is essential input for predictive propagation models to estimate this structure bottom mounted sources and receivers were used to make measurements of shear and compressional wave propagation in shallow water sediments of the continental shelf usually where boreholes and high resolution reflection profiles give substantial supporting geologic information about the subsurface this colocation provides an opportunity to compare seismically determined estimates of physical properties of the seabed with the ground truth properties measurements were made in 1986 with source detector offsets up to 200 m producing shear wave velocity versus depth profiles of the upper 30 50 m of the seabed and p wave profiles to lesser depths measurements in 1988 were made with smaller source devices designed to emphasize higher frequencies and recorded by an array of 30 sensors spaced at 1 m intervals to improve spatial sampling and resolution of shallow structure these investigations with shear waves have shown that significant lateral and vertical variations in the physical properties of the shallow seabed are common and are principally created by erosional and depositional processes associated with glacial cycles and sea level oscillations during the quaternary when the seabed structure is relatively uniform over the length of the profiles the shear wave fields are well ordered and the matching of the data with full waveform synthetics has been successful producing velocity attenuation models consistent with the subsurface lithology indicated by coring results both body waves and interface waves have been modeled for velocity attenuation as a function of depth with the aid of synthetic seismograms and other analytical techniques some results give strong evidence of anisotropy and lateral heterogeneity in shear velocity of the upper 5 10 m of sediments and of extremely high velocity gradients in the topmost 1 2 m possibly exceeding 30 s 1

elasticity and dislocations in ice x under pressure abstract we determine the compressibility the elasticity and the slip systems for ice x in the 100 350 gpa pressure range from first principles calculations our results show that ice x has a high elastic anisotropy which increases by more than two orders of magnitude over this pressure range we use the peierls nabarro model to compute the dislocation structure for the most likely glide systems we obtain that the easiest slip systems are 1 1 1 1 1 0 at low pressures and 1 0 0 1 1 0 at higher pressure this suggests that the mantle of large icy planets may have different rheological properties at shallow and at deep conditions in contrast the mantle of smaller icy planets would be more homogeneous from a rheological point of view

application of a complete workflow for 2d elastic full waveform inversion to recorded shallow seismic rayleigh waves abstractthe s wave velocity of the shallow subsurface can be inferred from shallow seismic rayleigh waves traditionally the dispersion curves of the rayleigh waves are inverted to obtain the local s wave velocity as a function of depth two dimensional elastic full waveform inversion fwi has the potential to also infer lateral variations we have developed a novel workflow for the application of 2d elastic fwi to recorded surface waves during the preprocessing we apply a line source simulation spreading correction and perform an a priori estimation of the attenuation of waves the iterative multiscale 2d elastic fwi workflow consists of the preconditioning of the gradients in the vicinity of the sources and a source wavelet correction the misfit is defined by the least squares norm of normalized wavefields we apply our workflow to a field data set that has been acquired on a predominantly depth dependent velocity structure and we compare the reconstructed s wave velocity model with the result

the estimation of shear wave statics using in situ measurements in marine near surface sediments shear wave statics in marine seismic exploration data are routinely too large to be estimated using conventional techniques near surface unconsolidated sediments are often characterized by low values of v s and steep velocity gradients minor variations in sediment properties at these depths correspond to variations in the shear wave velocity and will produce significant static shifts it is suggested that a significant proportion of the shear wave statics solution can be estimated by performing a separate high resolution survey to target near surface unconsolidated sediments love wave shear wave refraction and geotechnical measurements were individually used to form high resolution near surface shear wave velocity models to estimate the shear wave statics for a designated survey line comparisons with predicted statics revealed that shear wave statics could not be estimated using a velocity model predicted by substituting geotechnical measurements into empirical relationships empirical relationships represent a vast simplification of the factors that control v s and are therefore not sufficiently sensitive to estimate shear wave statics refraction measurements are potentially sensitive to short wavelength variations in sediment properties when combined with accurate navigational data statics estimated from love wave data are less sensitive and sometimes smoothed in appearance since interpreted velocity values represent an average both laterally and vertically over the receiver array and the frequency depth sensitivity range respectively for the survey site statics estimated from near surface irregularities using shear wave refraction measurements represent almost half the total statics solution more often this proportion will be greater when bedrock relief is less

the scientific ancestry and historiography of the silurian system the historical background to murchison9s massive work of synthesis of 1839 the silurian system is considered with special reference to shropshire one of its most critical areas of investigation the question of why there has always seemed to be such a great chronological gap between the onsets of industrialization and of geological investigations subjects often thought to be intricately linked is posed evidence is given for the considerable amount of pre murchisonian investigation of the geology in the area it proves to be often of a notable quality particularly after 1810 with new focus on the ordering of stratigraphical sequences it becomes clear that murchison was often unwilling to acknowledge properly his debts whether factual or conceptual to those who had gone before him murchison9s work as a 9silurian9 historian proves of noticeably lower quality than his work as a stratigrapher

velocity dispersion in water saturated granular sediment recent experiments in the gulf of mexico have yielded a wealth of information on the environmental conditions and geoacoustic response of a uniform sand stratum immediately beneath the seafloor a comparison of p wave velocities measured at low 125 hz and high 11 50 khz frequencies in this layer indicates that there is a significant amount of velocity dispersion that occurs in the interval between these extremes this narrow band dispersion which is not consistent with the often used assumption of a nearly constant q model is in accordance with the predictions of the biot theory it results from viscous damping in the fluid as it moves relative to the skeletal frame other recent field data that support this conclusion are presented

biogeomorphological implications of microscale interactions between sediment geotechnics and marine benthos a review abstract at the foundations of biogeomorphological processes in the sea lie interactions between the activities of marine benthic animals and the geotechnical properties of their sedimentary environments the potential significance of these interactions which take place at a microscale level of millimetres to metres for the large scale geomorphology of the seabed has rarely been appreciated in the context of this review large scale is defined as greater than 50 m to hundreds of kilometres the present review addresses this link drawing examples from a wide range of marine environments including estuaries the intertidal zone continental shelves and slopes and the deep sea it firstly considers sediment stabilisation slope failure sediment mixing biodeposition sediment compaction and hydrodynamic effects this is followed by a consideration of two extremes of the ecological pyramid the effects of marine meiofauna and marine vertebrates the final section draws attention to the central role of faunal mucus and extracellular polymeric material ecpm in many of the microscale interactions that we describe the implications of these microscale biological processes and features are discussed in terms of their influence on and control of the large scale geomorphology of the seabed

how does the shear wave structure of the seabed affect the seismic wavefield summary much modelling of the seismic wavefield is undertaken with an acoustic approximation in which the influence of shear waves is neglected although such calculations can predict the correct traveltimes for compressional p wave propagation they can he very misleading with respect to the distribution of seismic amplitudes especially at larger offsets at the seabed the acoustic approximation predicts total reflection for p waves incident beyond the critical angle however once the presence of shear waves in the solid material below the sea floor is taken into account p waves in the sea water incident beyond the critical angle can give rise to transmitted s waves with a consequent major change in the propagation pattern such effects are very important for areas with high velocities at the sea floor as commonly occurs in tropical waters such as the north west shelf of australia the character of the water borne noise in these conditions depends on whether the shear wavespeed at the seabed lies above or below the p wave velocity in the sea water above for high shear velocities two distinct sets of critically reflected multiples can be produced to give a very energetic noise train trapped in the water column conversion of p to s in transmission at the sea floor can often be important and give rise to significant arrivals on the outer traces from long marine cables further the conversion of energy to s waves reduces the energy available for p wave multiples and dramatically reduces the influence of waterbottom multiples compared with a purely acoustic situation synthetic seismogram calculations for large offsets and equivalent calculations in the slowness times domain with selective control of the level of multiples and conversion at each interface provide a convenient tool for characterizing the expected water borne energy and the influence of converted shear waves on the pressure field recorded in the water

resolving meso scale seabed variability using reflection measurements from an autonomous underwater vehicle seabed geoacoustic variability is driven by geological processes that occur over a wide spectrum of space time scales while the acoustics community has some understanding of horizontal fine scale geoacoustic variability less than o 100 m and large scale variability greater than o 103 m there is a paucity of data resolving the geoacoustic meso scale o 100 103 m measurements of the meso scale along an ostensibly benign portion of the outer shelf reveal three classes of variability the first class was expected and is due to horizontal variability of layer thicknesses this was the only class that could be directly tied to seismic reflection data the second class is due to rapid changes in layer properties and or boundaries occurring over scales of meters to hundreds of meters the third class was observed as rapid variations of the angle frequency dependent reflection coefficient within a single observation and is suggestive of variability at scales of meter or less though generally assumed to be negligible in acoustic modeling the second and third classes are indicative of strong horizontal geoacoustic variability within a given layer the observations give early insight into possible effects of horizontal geoacoustic variability on long range acoustic propagation and reverberation

detection of sharp lateral discontinuities through the analysis of surface wave propagation surface wave sw techniques are mainly used to retrieve 1d velocity models and are therefore characterized by a 1d approach which might prove unsatisfactory when relevant 2d effects are present in the investigated subsurface in the case of sharp and sudden lateral heterogeneities in the subsurface a strategy to tackle this limitation is to estimate the location of the discontinuities and to separately process seismic traces belonging to quasi 1d subsurface portions we have addressed our attention to methods aimed at locating discontinuities by identifying anomalies in sw propagation and attenuation the considered methods are the autospectrum computation and the attenuation analysis of rayleigh waves aarw these methods were developed for purposes and or scales of analysis that are different from those of this work which aims at detecting and characterizing sharp subvertical discontinuities in the shallow subsurface we applied both methods to two data sets synthetic data from a finite element method simulation and a field data set acquired over a fault system both presenting an abrupt lateral variation perpendicularly crossing the acquisition line we also extended the aarw method to the detection of sharp discontinuities from large and multifold data sets and we tested these novel procedures on the field case the two methods are proven to be effective for the detection of the discontinuity by portraying propagation phenomena linked to the presence of the heterogeneity such as the interference between incident and reflected wavetrains and energy concentration as well as subsequent decay at the fault location the procedures we developed for the processing of multifold seismic data set showed to be reliable tools in locating and characterizing subvertical sharp heterogeneities

geophysical investigations of habitability in ice covered ocean worlds geophysical measurements can reveal the structures and thermal states of icy ocean worlds the interior density temperature sound speed and electrical conductivity thus characterize their habitability we explore the variability and correlation of these parameters using 1 d internal structure models we invoke thermodynamic consistency using available thermodynamics of aqueous mgso 4 nacl as seawater and nh 3 pure water ice phases i ii iii v and vi silicates and any metallic core that may be present model results suggest for europa that combinations of geophysical parameters might be used to distinguish an oxidized ocean dominated by mgso 4 from a more reduced ocean dominated by nacl in contrast with jupiter s icy ocean moons titan and enceladus have low density rocky interiors with minimal or no metallic core the low density rocky core of enceladus may comprise hydrated minerals or anhydrous minerals with high porosity cassini gravity data for titan indicate a high tidal potential love number k 2 0 6 which requires a dense internal ocean ocean 1 200 kg m 3 and icy lithosphere thinner than 100 km in that case titan may have little or no high pressure ice or a surprisingly deep water rock interface more than 500 km below the surface covered only by ice vi ganymede s water rock interface is the deepest among known ocean worlds at around 800 km its ocean may contain multiple phases of high pressure ice which will become buoyant if the ocean is sufficiently salty callisto s interior structure may be intermediate to those of titan and europa with a water rock interface 250 km below the surface covered by ice v but not ice vi

surface wave analysis for static corrections in mineral exploration a case study from central sweden in mineral exploration increased interest towards deeper mineralizations makes seismic methods attractive one of the critical steps in seismic processing workflows is the static correction which

3d surface wave estimation and separation using a closed loop approach surface waves in seismic data are often dominant in a land or shallow water environment separating them from primaries is of great importance either for removing them as noise for reservoir imaging and characterization or for extracting them as signal for near surface characterization however their complex properties make the surface wave separation significantly challenging in seismic processing to address the challenges we propose a method of three dimensional surface wave estimation and separation using an iterative closed loop approach the closed loop contains a relatively simple forward model of surface waves and adaptive subtraction of the forward modelled surface waves from the observed surface waves making it possible to evaluate the residual between them in this approach the surface wave model is parameterized by the frequency dependent slowness and source properties for each surface wave mode the optimal parameters are estimated in such a way that the residual is minimized and consequently this approach solves the inverse problem through real data examples we demonstrate that the proposed method successfully estimates the surface waves and separates them out from the seismic data in addition it is demonstrated that our method can also be applied to undersampled irregularly sampled and blended seismic data

full waveform inversion of sh and love wave data in near surface prospecting we develop a two dimensional full waveform inversion approach for the simultaneous determination of s wave velocity and density models from sh and love wave data we illustrate the advantages of the sh love full waveform inversion with a simple synthetic example and demonstrate the method s applicability to a near surface dataset recorded in the village c achtice in northwestern slovakia goal of the survey was to map remains of historical building foundations in a highly heterogeneous subsurface the seismic survey comprises two parallel sh profiles with maximum offsets of 24 m and covers a frequency range from 5 hz to 80 hz with high signal to noise ratio well suited for full waveform inversion using the wiechert herglotz method we determined a one dimensional gradient velocity model as a starting model for full waveform inversion the two dimensional waveform inversion approach uses the global correlation norm as objective function in combination with a sequential inversion of low pass filtered field data this mitigates the non linearity of the multiparameter inverse problem test computations show that the influence of visco elastic effects on the waveform inversion result is rather small further tests using a monoparameter shear modulus inversion reveal that the inversion of the density model has no significant impact on the final data fit the final full waveform inversion s wave velocity and density models show a prominent low velocity weathering layer below this layer the subsurface is highly heterogeneous minimum anomaly sizes correspond to approximately half of the dominant love wavelength the results demonstrate the ability of two dimensional sh waveform inversion to image shallow small scale soil structure however they do not show any evidence of foundation walls

shear wave velocity structure of the shallow sediments in the bohai sea from an ocean bottom seismometer survey abstractto investigate the seismic velocity structure of the shallow sediments in the bohai sea of china we conducted a shear wave velocity inversion of the surface wave dispersion data from a survey of 12 ocean bottom seismometers obss and 377 shots of a 9000 in3 air gun with obs station spacing of approximately 5 km and air gun shot spacing of approximately 190 m high quality scholte wave data were recorded by the obss within 0 4 5 km offset we retrieved the scholte wave phase velocity dispersion for the fundamental mode and first overtone in the frequency band of 0 9 3 0 hz with the phase shift method and inverted for the shear wave velocity structure of the shallow sediments with a damped iterative least squares algorithm pseudo 2d shear wave velocity profiles with a depth of approximately 400 m revealed coherent features of relatively weak lateral velocity variation we also estimated the uncertainty in shear wave velocity structure based on the pseudo 2d profiles from six trial inversions wi

determination of poisson s ratio from pre critical wide angle seismic reflection data from the babel project summary the pre critical wide angle seismic reflection data collected during the babel survey using multireceiver spreads contain high amplitude p wave and modeconverted s wave reflected arrivals the two phases can be partially separated and their signal to noise ratio emphasized by exploiting the multifold nature and the increased sensitivity of velocity analysis afforded by these data to produce zero offset corrected stacked sections using these sections a method has been developed to derive estimates of poisson s ratio by optimizing the cross correlation of p wave and s wave arrivals and hence to constrain petrological models of the crust sampled by these data although the apparently high degree of temporal and spatial resolution of reflected arrivals that are visible within the stacked sections must be reduced to achieve a satisfactory degree of correlation robustness the results shed some light on crustal petrology and concur with existing estimates of poisson s ratio for the baltic shield

kinetics of antigorite dehydration a real time x ray diffraction study antigorite dehydration has been studied in situ using time resolved x ray diffraction xrd in the 1 1 5 5 gpa pressure range the sequence of xrd spectra reveals that the high temperature stability limit of antigorite is decreased by 50 100 c under h2o unsaturated conditions the decomposition of antigorite into the high temperature products forsterite enstatite proceeds via an intermediate assemblage of forsterite and a talc like phase observed within a temperature interval of 130 20 c the analysis of the transformation time data using the avrami model suggests that the breakdown of antigorite and the talc like phase is kinetically controlled by surface growth processes at the edges of grains the overall transformation rates are 10 to 100 times faster than those observed in water saturated experiments and show that the h2o activity is a strong driving force for dehydration the breakdown of antigorite in subducting oceanic mantle with such kinetics would result in a fluid discharge rate of the order of 10 6 to 10 8 s 1 this is faster than the viscous relaxation of serpentinites and could lead to brittle failure or weakening of pre existing faults this provides an explanation for the seismicity in the lower plane of double seismic zones

new tools for studying seafloor geotechnical and geoacoustic properties three new tools designed to measure certain geotechnical and geoacoustic properties of the sediments just beneath the seafloor are described one tool is a source receiver system designed to generate and receive sh waves or love waves the source applies a torsional impulse to a small circular area of the seafloor and a linear array of gimballed geophones is used to measure horizontal motion perpendicular to the axis of the array energy to generate the torsional pulse is supplied by a rotating flywheel that is suddenly brought to rest the dispersion of love waves produced by this method is used as the basis for a least squares inversion to obtain shear wave velocity as a function of depth a second source receiver system generates vertically polarized shear waves or scholte waves by applying a vertical impulse to the sediment over a small circular area of the bottom in this case the receiving array utilizes gimballed geophones that respond to the vertical motion of the seafloor and the scholte wave di

marine pssp reflections with a bottom velocity transition zone marine shear wave reflection methods using the conventional data acquisition system i e source and receiver in water rely on two mode conversions at the water bottom to produce shear reflections such as pssp some theoretical considerations and the results of a marine check shot survey conducted in the gulf of mexico demonstrate that the difficulty in observing pssp events is attributable to weak p s and s p conversion at the bottom in regions with very low shear velocity a few hundred ft s or less sediments at the bottom for a simple water bottom with a low shear wave velocity water over a uniform half space the ps conversion factor is proportional to vs and the sp conversion factor is proportional to vs2 where vs is the bottom shear velocity for vs 1500ft s their product gives pssp reflections that can be comparable in amplitude to typical pppp events for vs 500ft s the pssp events should be about 30 db weaker and probably not visible for typical gulf of mexico sediments with a shear velo

kinetics and mechanism of antigorite dehydration implications for subduction zone seismicity properties of serpentine minerals are thought to influence the occurrence and location of intermediate depth seismicity in subduction zones which is often characterized by two dipping planes separated by 30 km defining a double seismic zone the seismicity of the lower plane is believed to be provoked by the dehydration of serpentine since the experimentally determined stability limit for antigorite matches hypocenter locations this requires that the fluid produced by dehydration is released much faster than the typical time scale of ductile deformation mechanisms here we measured the kinetics of antigorite dehydration in situ at high pressure and high temperature by time resolved synchrotron x ray diffraction in a closed system antigorite dehydrates in two steps during step 1 it partially breaks down into olivine and a hydrous phyllosilicate closely related to the 10 a phase the modal abundance of the intermediate assemblage is described by 66 wt antigorite 19 wt olivine 12 wt 10 a phase during step 2 at higher temperature the remaining antigorite and the 10 a phase fully dehydrate from the analysis of reaction progress data we determined that the major release of aqueous fluid occurs during step 2 at a fast rate of 10 4 mfluid 3 mrock 3 s 1 this exceeds by orders of magnitude the typical time scale of deformation by ductile mechanisms of any mineral or rock in the subducting slab or in the overlying mantle wedge these results suggest that the fast dehydration of antigorite may well trigger the seismicity of the lower plane of the double seismic zone

inversion for sediment geoacoustic properties at the new england bight this article discusses inversions for bottom geoacoustic properties using broadband acoustic signals obtained from explosive sources two different inversion schemes for estimating the compressional wave speeds and attenuation are presented in this paper in addition to these sediment parameters source receiver range is also estimated using the arrival time data the experimental data used for the inversions are sus charge explosions acquired on a vertical hydrophone array during the shelf break primer experiment conducted south of new england in the middle atlantic bight in august 1996 the modal arrival times are extracted using a wavelet analysis in the first inversion scheme arrival times corresponding to various modes and frequencies from 10 to 200 hz are used for the inversion of compressional wave speeds a hybrid inversion scheme based on a genetic algorithm ga is used for the inversion in an earlier study potty et al j acoust soc am 108 3 973 986 2000 have used this hybrid scheme in a range independent environment in the present study results of range dependent inversions are presented the sound speeds in the water column and bathymetry are assumed range dependent whereas the sediment compressional wave speeds are assumed range independent the variations in the sound speeds in the water column are represented using empirical orthogonal functions eofs the replica fields corresponding to the unknown parameters were constructed using adiabatic theory in the second inversion scheme modal attenuation coefficients are calculated using modal amplitude ratios the ratios of the modal amplitudes are also calculated using time frequency diagrams a ga based inversion scheme is used for this search finally as a cross check the computed compressional wave speeds along with the modal arrival times were used to estimate the source receiver range the inverted sediment properties and ranges are seen to compare well with in situ measurements and historical data

converted wave seismic exploration methods multicomponent seismic recording measurement with vertical and horizontal component geophones and possibly a hydrophone or microphone captures the seismic wavefield more completely than conventional single element techniques in the last several years multicomponent surveying has developed rapidly allowing creation of converted wave or p s images these make use of downgoing p waves that convert on reflection at their deepest point of penetration to upcoming s waves survey design for acquiring p s data is similar to that for p waves but must take into account subsurface vp vs values and the asymmetric p s ray path p s surveys use conventional sources but require several times more recording channels per receiving location some special processes for p s analysis include anisotropic rotations s wave receiver statics asymmetric and anisotropic binning nonhyperbolic velocity analysis and nmo correction p s to p p time transformation p s dip moveout prestack migration with two velocities and wa

separation of p and s waves in combined p and sv observations with vertical and in line horizontal geophones recognition and separation of the individual p and s arrivals may form a considerable problem due to the geophone receiving characteristics p and s waves are observed on both horizontal and vertical geophones a new method of separating p and s waves is presented that inverts the geophone records for the receiving characteristics thereby separating the two wavetypes the filter coefficients are determined from the near surface p and s wave velocity and from the geometry of the geophone groups the p s separation filter was tested on synthetic data with good results even ps and sp converted reflections which are completely coinciding for horizontal reflectors could be well separated the filter appears to be stable and to have low sensitivity to noise in the data or to errors in the near surface p and s wave velocity the filter is superior to other separation methods which were applied to the same dataset for comparison this method can also be applied to vsp data

does titan s long wavelength topography contain information about subsurface ocean dynamics abstract the long wavelength topography of titan is characterized by relatively small amplitudes about 1 km peak to peak an anomalous equatorial bulge the poles are about 300 m lower than the equator and small gravity anomalies indicating a high degree of compensation in the past years the nature of titan s non hydrostatic topography has been addressed in several studies the topography has been interpreted in terms of isostatic or viscous models and discussed in connection with tidal heating in the ice shell and surface erosion here we present a model of the shape evolution of titan s ice shell driven by tidal heating in the shell and spatial variations of the heat flux from a subsurface ocean the model is obtained by solving a general set of equations coupling the viscoelastic flow of ice with the thermal evolution of the ice shell and phase transitions at the ice water interface the equations are solved in a domain with radially varying material properties and moving boundaries the motion of the boundaries is a consequence of ice flow within the shell melting and crystallization at the bottom boundary and erosion and deposition at the surface our model suggests that titan s anomalous topographic bulge can be explained by lateral variations of ocean heat flux of the order of 0 1 1 mw m 2 provided that the heat flux is stable over a period of at least 10 myr and the ice shell has a sufficiently high viscosity exceeding 1016 pa s at the base of the shell such a high value of viscosity implies that either the ice grains are coarse 10 mm or the temperature of the ocean is significantly by more than 40 k lower than the melting temperature of pure water ice the heat flux pattern predicted on top of the ocean is consistent with a flow characterized by upwelling of warm water in polar regions and downwelling of cold water at low latitudes the negative correlation between the topography and geoid at degree 3 reported in a previous study but not confirmed at higher degrees yet is shown to be compatible with erosion and deposition occurring at a rate of 0 01 0 1 mm yr 1 our results underline the importance of gravity and topography measurements for understanding titan s surface and deep interior processes

modelling sound propagation in the southern ocean to estimate the acoustic impact of seismic research surveys on marine mammals summary modelling sound propagation in the ocean is an essential tool to assess the potential risk of air gun shots on marine mammals based on a 2 5 d finite difference code a full waveform modelling approach is presented which determines both sound exposure levels of single shots and cumulative sound exposure levels of multiple shots fired along a seismic line band limited point source approximations of compact air gun clusters deployed by r v polarstern in polar regions are used as sound sources marine mammals are simulated as static receivers applications to deep and shallow water models including constant and depth dependent sound velocity profiles of the southern ocean show dipole like directivities in case of single shots and tubular cumulative sound exposure level fields beneath the seismic line in case of multiple shots compared to a semi infinite model an incorporation of seafloor reflections enhances the seismically induced noise levels close to the sea surface refraction due to sound velocity gradients and sound channelling in near surface ducts are evident but affect only low to moderate levels hence exposure zone radii derived for different hearing thresholds are almost independent of the sound velocity structure with decreasing thresholds radii increase according to a spherical 20 log10 r law in case of single shots and according to a cylindrical 10 log10 r law in case of multiple shots a doubling of the shot interval diminishes the cumulative sound exposure levels by 3 db and halves the radii the ocean bottom properties only slightly affect the radii in shallow waters if the normal incidence reflection coefficient exceeds 0 2

an ultrahigh resolution 3 d survey of the shallow subsurface on the continental shelf of new jersey regional seismic surveys have identified a wedge of late quaternary sediment extending 150 km south from the hudson river apron along the edge of the continental shelf off new jersey the bottom of the sediment wedge is defined by a prominent reflector that is assumed to be an erosional surface carved during a lowstand of sea level probably corresponding to the wisconsin maximum glaciation about 18 000 years ago an extremely high resolution 3 d seismic reflection survey of the southern part of the wedge figure 1 was carried out in 1993 as part of the strataform strata formation on margins initiative funded by the u s office of naval research

individual and joint 2 d elastic full waveform inversion of rayleigh and love waves we investigate the performance of the individual 2 d elastic full waveform inversion fwi of rayleigh and love waves as well as the feasibility of a simultaneous joint fwi of both wave types the fwi of surface waves can provide a valuable contribution to near surface investigations since they are mainly sensitive to the s wave velocity and hold a high signal to noise ratio in synthetic reconstruction tests we compare the performance of the individual wave type inversions and explore the benefits of a simultaneous joint inversion in these tests both individual wave type inversions perform similarly well given that the initial p wave velocity model is accurate enough in this case the joint fwi further improves the result for an inaccurate initial p wave velocity model we observe artifacts in the results of the rayleigh wave fwi and the joint fwi subsequently we recorded a near surface field dataset to verify the results by a realistic example in the field data application the love wave fwi is superior to the rayleigh wave fwi possibly due to the initial p wave velocity model also in this case the joint fwi further improves the inversion result