the effects of ignored seabed variability in geoacoustic inversion geoacoustic inversion using a matched field inversion algorithm is a well established technique for estimating the geoacoustic parameters of the seabed this paper demonstrates how parameter estimation can be affected by unknown or wishfully ignored random range dependence of the true environment when the inversion model is for practicality assumed to be range independent simulations with controlled statistics were carried out using a simple shallow water model an isospeed water column over a homogeneous elastic halfspace the inversion parameters included water depth compressional speed in the seabed seabed density and compressional wave attenuation on average the environment is range independent some parameters are constant while other parameters are random with range independent means and variances a parabolic equation underwater acoustic propagation model is used to calculate the simulated data fields for the range dependent environment as well as to calculate the model fields for the range independent inversion model the adaptive simplex simulated annealing inversion algorithm is used to estimate the best fit solution it is found that ignoring the variability of even a single geoacoustic parameter leads to significant and correlated uncertainty bias and variance in the estimation of all inverted parameters results are presented for range variation of compressional sound speed and water depth

rheology of ices a key to the tectonics of the ice moons of jupiter and saturn the polymorphic varieties of water ice are important rock forming minerals in the outer solar system the voyager 1 and 2 missions have shown that most of the ice moons of jupiter and saturn have had some form of tectonic or internal activity understanding of the tectonics and building reasonable models of the interior of these planets depend on our knowledge of the theological properties and viscosity of high pressure and low temperature forms of ice

dated evidence of the interaction between humans and megafauna in the late pleistocene of sergipe state northeastern brazil abstract we present a radiocarbon date 12 742 12 562 cal bp for an eremotherium laurillardi tooth found in sergipe state northeastern brazil which shows anthropogenic marks our result provides additional information and reinforces the hypothesis that humans was present in south america earlier than accepted currently and interacted with megafauna during the late pleistocene in this region

a comparison of miocene and archean rhyolite hyaloclastites evidence for a hot and fluid rhyolite lava abstract in this paper we compare the geology and petrography of miocene and archean submarine rhyolite hyaloclastites the hyaloclastites are sparsely 10 or less plagioclase quartz and pyroxene phyric the hyaloclastites consist of a feeder dyke from which branch lava lobes and irregularly shaped lava pods the lava bodies consist of a holocrystalline core with microlitic texture grading outward into a flow layered rim zone and finally into obsidian the proportion of plagioclase and pyroxene microlites decreases outward some layers of the rim zone may be pumiceous vesicularity up to 50 vesicle size 1 mm or less but most of the lava has less than 5 vesicles one or a few cm long the obsidian shows perlitic fracture patterns the lava bodies grade through an in situ breccia into a hyaloclastite composed of angular obsidian granules and in many cases of fragments of lava lobes evidence for alteration at high temperature is as follows in the archean rhyolite hyaloclastites plagioclase microlites are overgrown by quartz albite spherulites furthermore parts of the miocene and archean hyaloclastite have been cemented and granules have been marginally replaced by quartz and albite hyaloclastite cemented at high temperature locally shows columnar joints at low temperatures obsidian has been hydrated and or has been replaced by clay minerals zeolites chlorite or prehnite chess board albite and fibroradial prehnite in archean hyaloclastite is possibly a pseudomorph after zeolites the sparsely porphyritic nature of the lava and the absence of microlites from the quenched glass suggests that the thyolite hyaloclastites extruded at high near liquidus temperature furthermore pumice is present only locally in the flow layered rim zone and in fragments derived from that zone these features suggest that vesiculation was inhibited by the weight of the water column high temperature and possibly the volatile h 2 o content explain the relatively low viscosity and shear strength of the lava and resulted in the flow morphology particular to this type of hyaloclastic rhyolite flows

range dependent seabed characterization by inversion of acoustic data from a towed receiver array the mapex2000 experiments were conducted in the mediterranean sea in march 2000 to determine seabed properties using a towed acoustic source and receiver array towed systems are advantageous because they are easy to deploy from a ship and the moving platform offers the possibility for estimating spatially variable range dependent seabed properties in this paper seabed parameters are determined using a matched field geoacoustic inversion approach with measured towed array data previous research has successfully applied matched field geoacoustic inversion techniques to measured acoustic data however in nearly all cases the inverted data were collected on moored vertical receiver arrays results here show that seabed parameters can also be extracted by inverting acoustic measurements from a towed array of receivers and these agree with those inverted using data received simultaneously on a vertical array these findings imply that a practical technique could be developed to map range dependent seabed parameters over large areas using a towed acoustic system an example of such a range dependent inversion is given using measurements from the mapex2000 experiments

terrestrial sea ice morphology considerations for europa abstract the galileo mission has returned the first high resolution 21 m pixel images of the surface of europa these images reveal structures with morphologies reminiscent of those seen on terrestrial sea ice although it is premature to make one to one analogies between sea ice and europa s surface a review of the types of surface features commonly formed on earth and of various sea ice processes can provide insight into the complex geology of europa for example deformation of terrestrial sea ice results from winds tides and currents and from thermally induced stresses the resulting features include fractures ranging in width from millimeters to kilometers pressure ridges shear ridges and rafted ice potential agents of deformation on europa are more likely to be limited to tidal flexing and possibly convection but could produce similar features and perhaps account for the ridges and fractures seen in many areas subtle differences in albedo and color in terrestrial sea ice result from differences in ice thickness and grain size attributed to factors such as the rate of ice crystal growth water turbulence age of the ice and deformation similar factors could account for differences observed in the bright icy plains of europa moreover salts in both the solid form and as brine vary in concentration and composition as a function of space and time on earth leading to differences in density and the strength of ice sheets salts are also suspected in the europan ice and could lead to similar differences enhancing the creation of topographic relief from density contrasts and the formation of fractures from brittle failure of the ice differences in the environments between europa and terrestrial sea ice in terms of parameters such as temperature gravity time and ice compositions suggest caution in drawing direct analogies future work by the planetary and sea ice communities must include understanding the terrestrial processes sufficiently for extrapolation to europa

a comparison of broadband and narrow band modal inversions for bottom geoacoustic properties at a site near corpus christi texas detailed comparison between narrow band and broadband techniques used in a series of acoustic experiments are presented with emphasis on a comparisons of the pressure field versus range predicted b comparisons of the bottom compressional wave speed model generated c the variance of the bottom model estimated and d the resolution of the bottom model generated the range dependence of the bottom medium and the seasonal dependence of the near surface sediment sound speed profile are observed and discussed

statistical estimation of transmission loss from geoacoustic inversion using a towed array geoacoustic inversion estimates environmental parameters from measured acoustic fields e g received on a towed array the inversion results have some uncertainty due to noise in the data and modeling errors based on the posterior probability density of environmental parameters obtained from inversion a statistical estimation of transmission loss tl can be performed and a credibility level envelope or uncertainty band for the tl generated this uncertainty band accounts for the inherent variability of the environment not usually contained in sonar performance prediction model inputs the approach follows gerstoft et al ieee j ocean eng 31 299 307 2006 and is demonstrated with data obtained from the mapex2000 experiment conducted by the nato undersea research center using a towed array and a moored source in the mediterranean sea in november 2000 based on the geoacoustic inversion results the tl and its variability are estimated and compared with the measured tl

results from an autonomous underwater vehicle towed hydrophone array experiment in nantucket sound shallow water experiments have been conducted in nantucket sound with an autonomous underwater vehicle towed hydrophone array system in an area proximate to that of a previous experiment frisk and lynch j acoust soc am 86 1928 1939 1989 transmission loss was measured for frequencies between 220 and 1228 hz in an ocean waveguide under conditions of an isovelocity water column with an approximate depth of 13 m over a sandy silty bottom results obtained at 415 hz show classic isovelocity waveguide phenomena that include interference effects mode stripping due to modal attenuation and transmission loss proportional 15 to 10 log 10 r

spherulites quench fractures and relict perlite in a late devonian rhyolite dyke queensland australia abstract a late devonian rhyolite dyke displays perlitic and other fracture sets as well as textures generated by crystallisation of the glass the dyke is less than a metre wide and has sharp contacts with ignimbrite although originally glassy no glass is preserved aligned magnetite after pyroxene microlites and trains of small 0 5 1 mm spherical spherulites crystallised early at temperatures above the glass transition temperature and before formation of the fracture sets long subplanar fractures oriented perpendicular to the dyke walls extend almost the full dyke width and end by merging with adjacent long fractures short subplanar cross fractures are perpendicular to and terminate at the long fractures well defined perlitic fractures are present within the volumes of rock generally

mirages in shallow water matched field processing broadband matched field processing mfp derived estimates of 3d source location using data from hydrophone line arrays deployed in various geometries i e vertical horizontal and tilted 45 from vertical are presented in this paper these data were collected in two shallow water 100 200 m experiments off the coast of san diego results show that estimates of source range and depth remain surprisingly coherent in the presence of large mismatch in bathymetry but are offset from the true position by as much as 100 the offsets are independent of array geometry in contrast for estimates of source azimuth bathymetry mismatch typically causes a degradation in mfp correlation rather than an appreciable offset however errors in the assumed tilt from vertical of an array can lead to large offsets in the estimated source azimuth particularly as the nominal angle of the array from vertical becomes smaller predictions from a simple analytical model based on adiabatic normal modes in ideal waveguides provide good fits to the broadband mfp results

the impact of water column variability on horizontal wave number estimation and mode based geoacoustic inversion results the influence of water column variability on low frequency shallow water geoacoustic inversion results is considered the data are estimates of modal eigenvalues obtained from measurements of a point source acoustic field using a horizontal aperture array in the water column the inversion algorithm is based on perturbations to a background waveguide model with seabed properties consistent with the measured eigenvalues water column properties in the background model are assumed to be known as would be obtained from conductivity temperature and depth measurements the scope of this work in addressing the impact of water column variability on inversion is twofold range dependent propagation effects as they pertain to eigenvalue estimation are first considered it is shown that mode coupling is important even for weak internal waves and can enhance modal eigenvalue estimates second the effect of the choice of background sound speed profile in the water column is considered for its impact on the estim

high resolution geoacoustic inversion in shallow water a joint time and frequency domain technique high resolution geoacoustic data are required for accurate predictions of acoustic propagation and scattering in shallow water since direct measurement of geoacoustic data is difficult time consuming and expensive inversion of acoustic data is a promising alternative however the main problem encountered in geoacoustic inversion is the problem of uniqueness i e many diverse geoacoustic models can be made to fit the same data set a key and perhaps unique aspect of this approach is the combination of data analysis in both the space time and the space frequency domains this combination attempts to ameliorate the uniqueness problem by exploiting as much independent data as possible in order to meet the stringent requirements of high spatial resolution and uniqueness an entire method has been developed including a new measurement technique processing analysis technique and inversion strategy these techniques are described and then illustrated with a shallow water data set sound speed gradients in the upper few meters of the sub bottom appear to be much higher one order of magnitude than generally assumed and although often ignored a large density gradient was observed in the top layer that played an acoustically significant role

patterns of fracture and tidal stresses on europa abstract the hypothesis that lineaments on europa are fractures produced by tidal distortion and planetary volume change is examined by comparing the orientations of dark bands triple bands and cuspate ridges to fracture patterns predicted for tidal distortion due to orbital recession and orbital eccentricity if short reticulate dark band nnear the anti jove point are tension cracks which formed in response to tidal distortion they could only have been produced by orbital eccentricity long arcuate dark band and triple bands peripheral to the anti jove point orientations which suggest that they are strike slip faults which formed in response to orbital recession if cuspate ridges are compressional features their orientations and distribution suggest that they formed in response to combined orbital recession and a decrease in planetary volume stresses due to orbital eccentricit could have produced tension cracks near the anti jove point only if tensile failure occurred either prior to the accumulation of orbital recession stresses or after they had relaxed surface fracturing if a consequence of tidal deformation places important constraints on the orbital evolution of europa

range dependent sediment sound speed profile measurements using the image source method this paper presents a range dependent sediment sound speed profile measurement obtained using the image source method this technique is based on the analysis of the seafloor reflected acoustic wave as a collection of image sources which positions are linked with the thick nesses and the sound speed of the sediment stack the data used were acquired by the nurc in 2009 during the clutter09 experiment the equipment used was an autonomous undersea vehicle towing a 1600 3500 hz frequency band source and a 32 m horizontal line array of 32 hydrophones at 12 m above the seabed under the assumption of locally range independent seabed properties the moving horizontal array provides successive range independent sediment sound speed profiles along a track to obtain the range and depth dependent structure of the seafloor two key steps include recovery of the time varying unknown array shape from the data and spatial filtering of the successive sound speed profiles a comparison of the image source method result and seismic data along nearly the same 14 km track indicates that the seabed stratigraphy is correctly mapped by this method

yellow shark spring 1995 inversion results from sparse broadband acoustic measurements over a highly range dependent soft clay layer in may 1995 saclantcen performed broadband 200 800 hz acoustic measurements in the giglio basin off the coast of italy as part of the yellow shark inversion experiments in this paper inversion of sparse broadband transmission loss tl measurements is investigated to determine bottom properties in strongly range dependent rd situations commonly encountered in shallow water the data are from the elba formiche transect where water depth varies from 65 m at the acoustic projector location to approximately 120 m at the 4 element vertical arrays deployed at ranges of 8 16 24 32 and 40 km along the transect the experimental site has a soft clay layer bottom which varies in thickness from 3 to 10 m with a sound speed less than the water column a modal analysis including coupling effect is given to explain the frequency bands for which high tl was observed as a function of range and depth the tl measurements were inverted by matching the rd fields with model results using parabolic equation modeling bottom geoacoustic parameters were varied in a marching search to fit the tl measured at the five ranges the experimental results demonstrate that rd bottom properties such as sound speed and thickness of the slow clay layer can be obtained from broadband tl measurements sparsely distributed in range and depth

experimental study of geo acoustic inversion uncertainty due to ocean sound speed fluctuations acoustic data measured in the ocean fluctuate due to the complex time varying properties of the channel when measured data are used for model based geo acoustic inversion how do acoustic fluctuations impact estimates for the seabed properties in may 1999 saclant undersea research center and tno physics and electronics laboratory fel conducted a shallow water experiment on the adventure bank off the southwest coast of sicily italy to assess the effects of a time varying ocean on acoustic propagation and geo acoustic inversion a favorable area for acoustic propagation was identified which had slight internal wave activity and a weakly range dependent bathymetry with sand like bottom properties oceanographic and acoustic measurements were performed continuously over a 3 day period broadband 0 2 3 8 khz acoustic signals from a bottom moored source were transmitted over fixed paths and received on a moored vertical hydrophone array during the transmissions extensive environmental measurements e g sound speed current sea surface waveheight etc were made to correlate the time varying environmental and acoustic data modeled acoustic data show time variability which agrees with the measurements results illustrate severe problems when modeling shallow water acoustic propagation at ranges beyond a few kilometers in the frequency band considered further the acoustic fluctuations in time caused erroneous time variability in inverted seabed properties

geoacoustic inversion using multipath pulse shape experimental data measured in a shallow water region of the mediterranean sea are used to show that the variation of received intensity with time is well described by existing expressions harrison and nielsen j acoust soc am 121 1362 1373 2007 these expressions indicate that the effect of the sea water sound speed profile can be neglected for times greater than the peak intensity arrival beyond this time intensity is shown to decay at a rate determined by the seabed acoustic properties in a manner very similar to that for an isovelocity water column it is shown that a method of determining seabed acoustic properties previously restricted to isovelocity water columns prior and harrison j acoust soc am 116 1341 1344 2004 can consequently be used in the presence of a sound speed profile the method relates the decay rate of smeared multipath arrivals to the angular derivative of seabed reflection loss two datasets are studied and the method is used to describe average seabed properties and to detect changes in seabed type the seabed descriptions thus derived are used to predict total received intensity as a function of source receiver separation agreement between the propagation measurements and predictions is shown to be within measurement uncertainties

reconstructing habitats in central amazonia using megafauna sedimentology radiocarbon and isotope analyses abstract a paleomegafauna site from central amazonia with exceptional preservation of mastodons and ground sloths allows for the first time a precise age control based on 14 c analysis which together with sedimentological and 13 c isotope data provided the basis to discuss habitat evolution within the context of climate change during the past 15 000 yr the fossil bearing deposits trapped within a depression in the paleozoic basement record three episodes of sedimentation formed on floodplains with an intermediate unit recording a catastrophic deposition through debris flows probably favored during fast floodings the integrated approach presented herein supports a change in humidity in central amazonia through the past 15 000 yr with a shift from drier to arboreal savanna at 11 340 50 14 c yr b p and then to a dense forest like we see today at 4620 60 14 c yr b p

hydrated salt minerals on europa s surface from the galileo near infrared mapping spectrometer nims investigation we reported evidence of heavily hydrated salt minerals present over large areas of europa s surface from analysis of reflectance spectra returned by the galileo mission near infrared mapping spectrometer nims mccord et al 1997a b 1998a b here we elaborate on this earlier evidence present spatial distributions of these minerals examine alternate water ice interpretations expand on our hydrated salts interpretation consider salt mineral stability on europa and discuss the implications extensive well defined areas on europa show distinct asymmetric water related absorption bands in the 1 to 2 5 m region radiative transfer modeling of water ice involving different particle sizes and layers at europa temperatures does not reproduce the distinctive europa water bands however ice near its melting temperature such as in terrestrial environments does have some characteristics of the europa spectrum alternatively some classes of heavily hydrated minerals do exhibit such water bands among plausible materials heavily hydrated salt minerals such as magnesium and sodium sulfates sodium carbonate and their mixtures are preferred all europa spectral features are present in some salt minerals and a very good match to the europa spectrum can be achieved by mixing several salt spectra however no single or mix of salt mineral spectra from the limited library available has so far been found to perfectly match the europa spectrum in every detail the material is concentrated at the lineaments and in chaotic terrain which are technically disrupted areas on the trailing side since the spectrum of the material on europa is nearly the same everywhere so far studied the salt or salt mixture composition may be nearly uniform this suggests similar sources and processes over at least a near hemispheric scale this would suggest that an extensive subsurface ocean containing dissolved salts is the source and several possible mechanisms for deposit emplacement are considered the hydrogen bonds associated with hydration of these salts are similar or greater in strength and energy to those in pure water ice thus once on the surface the salt minerals should be as stable to disruption as water ice at the europa temperatures and mechanisms are suggested to enhance the stability of both materials spectra obtained of mgso4 6h2o at 77 k show only small differences from room temperature spectra the main difference is the appearance of the individual absorptions composing the broad composite water features and associated with the several different h2o sites in the salt hydrate molecule this suggests that the europa absorption bands are also composites thus higher spectral resolution may reveal these diagnostic features in europa s spectrum the specific salts present and their relative abundances would be indicators of the chemistry and conditions of an ocean environment and areas of fresh heavy concentration of these minerals should make ideal lander mission sampling sites

structure of the earth oceanic crust and uppermost mantle the past four years have witnessed the introduction of a variety of new instruments and methods for the study of the seismic structure of the oceanic crust and lithosphere the application of these and existing tools has led to the discovery of a number of new phenomena and to a fuller understanding of the genesis and evolution of the oceanic ithosphere borehole seismic instrumentation has become more widely employed ocean bottom seismographs while generally decreasing in number have become significantly more reliable and useful and multichannel seismic systems have been employed in innovative experiments ranging from studies of fracture zones to the regular detection of magma chambers beneath rise axes the techniques available for the analysis of seismic data have become more sophisticated waveforms collected in seismic experiments can now be used directly in constructing and evaluating seismic velocity models and travel time data are regularly inverted directly for structure trial and error modeling has become increasingly unimportant marine seismologists are becoming increasingly involved in understanding the coupling between the ocean and the underlying oceanic lithosphere this has led to a more complete understanding of seafloor noise processes and the partitioning of energy between acoustic and elastic waves

nonlinear inversion for ocean bottom properties high resolution methods based on simulated annealing and full wave sound propagation models are developed for nonlinear inversion for ocean bottom properties simulated annealing is used to search the high dimensional parameter space of ocean bottoms for the parameter set corresponding to the best replica field the parabolic equation method is used to solve range dependent inversion problems for data taken by lynch et al from a range dependent region of the gulf of mexico j acoust soc am 89 648 665 1991 this approach achieves excellent agreement between the theoretical and measured acoustic pressures the recovered sediment parameters suggest that a sound speed boundary layer exists in the upper part of the sediment and that the depth of an interface in the sediment is range dependent for locally range independent problems inversion is performed in wave number space large efficiency gains are possible with this approach because the number of wave number samples required for inversion is mu

geoacoustic inversion on the new jersey margin along and across the shelf this paper presents results of a range independent perturbative inverse approach applied to data from the shallow water experiment 2006 the inversion technique is based on a linearized relationship between sound speed in the sediment and modal eigenvalues horizontal wave numbers were estimated from data collected from two distinct source receiver tracks oriented along and across the shelf the specific inversion algorithm used is based on qualitative regularization and uses known information about the environment to constrain the solution locations of the r reflector and other layering information are used as a priori information for the inversion to emphasize the layered structure of the sediment

matched field geoacoustic inversion with a horizontal array and low level source this paper applies geoacoustic inversion to acoustic field data collected on a bottom moored horizontal line array due to a continuous wave towed source at a shallow water site in the barents sea the source transmitted tones in the frequency band of 30 160hz at levels comparable to those of a merchant ship with resulting signal to noise ratios of 9 15db bayesian inversion is applied to cross spectral density matrices formed by averaging spectra from a sequence of time series segments snapshots quantifying data errors including measurement and theory errors is an important component of bayesian inversion to date data error estimation for snapshot averaged data has assumed either that averaging reduces errors as if they were fully independent between snapshots or that averaging does not reduce errors at all this paper quantifies data errors assuming that averaging reduces measurement error dominated by ambient noise but does not reduce theory modeling error providing a physically reasonable

eigenray finding and time series simulation in a layered bottom ocean a ray theory approach for simulating the propagation of broadband signals interacting with a layered ocean bottom is presented the range invariant environment consists of the ocean and an arbitrary number of bottom layers each bottom layer has profiles of compressional and shear wave velocity attenuation and density eigenrays including those with multiple interactions and refractions in the ocean and bottom layering are found using a thorough and efficient algorithm based on an analysis of the sound velocity profile and the dependence of ray path geometry on the snell invariant the time series at a receiver due to an arbitrary source waveform is obtained by constructing a frequency domain transfer function from the eigenray characteristics several example applications demonstrate the potential use of this approach and show that reflection from relatively simple layering can severely distort a received time series

an evaluation of the accuracy of shallow water matched field inversion results in this article the accuracy of geo acoustic and geometric parameter estimates obtained through matched field inversion mfi was assessed multi frequency mfi was applied to multi tone data 200 600 hz received at a 2 km source receiver range the acoustic source was fixed and the signals were received at a vertical array simultaneously with the acoustic transmissions a ctd conductivity temperature and depth chain was towed along the acoustic track a genetic algorithm was used for the global optimization whereas a normal mode model was applied for the forward acoustic calculations acoustic data received at consecutive times were inverted and the stability of the inverted parameters was determined also the parameter estimates were compared with independent measurements such as multi channel seismic surveys for geo acoustic parameters the obtained uncertainty in the inversion results was assumed to have two distinct origins the first origin is the inversion method itself since each optimization will come up with some solution close to the exact optimum parameter coupling and the fact that some parameters hardly influence the acoustic propagation further contribute to this uncertainty the second is due to oceanographic variability both contributions were evaluated through simulation the contribution of oceanographic variability was evaluated through synthetic inversions that account for the actual sound speed variations as measured by the towed ctd chain

frequency based noise coherence function extension and application to passive bottom loss estimation accurate modeling of acoustic propagation in the ocean waveguide is important to sonar performance prediction particularly in shallow waters a crucial contribution to the total transmission loss is the bottom refection loss which can be estimated passively by beamforming the natural surface noise acoustic field recorded by a vertical line array of hydrophones however the performance in this task of arrays below 2 m of length is problematic for frequencies below 10 khz it is shown in this paper that when the data are free of interference from sources other than wind and wave surface noise data from a shorter array can be used to approximate the coherence function of a longer array this improves the angular resolution of the estimated bottom loss often making use of data at frequencies above the array design frequency application to simulated and experimental data shows that the technique rigorously justified for a halfspace bottom is effective also on more complex bottom types dispensing with

false pyroclastic textures in altered silicic lavas with implications for volcanic associated mineralization there is strong emphasis in recent literature that zn cu pb massive sulfide deposits associated with felsic volcanism the kuroko type deposits are directly related to submarine calderas formed by large submarine pyroclastic eruptions altered silicic volcanic rocks with the appearance of welded and nonwelded pyroclastic flow deposits volcaniclastic debris flows and massive to thin bedded tuffaceous rocks form a major component of a silurian succession that hosts zn cu pb massive sulfide deposits at benambra southeastern australia however critical evaluation of rock textures indicates that these silicic volcanic rocks are mainly lavas and associated autoclastic facies with remarkably deceptive false pyroclastic and volcaniclastic textures including apparent pumice fiamme and glass shards intercalated sediments indicate that most of the silicic volcanics were emplaced in subaqueous settings ranging from relatively shallow water to deep marine the false textures were produced mainly in originally glassy lava by the combined effects of devitrification perlitic fracture and pervasive hydrothermal alteration these processes are related to the emplacement and cooling history of individual lavas and to a regional essentially synvolcanic hydrothermal system tectonic foliation of the more altered and mechanically weakened rocks has led to partial dismembering of phenocrysts and groundmass fabrics thereby further enhancing clastic appearance subsequent to recognition of widespread false pyroclastic textures at benambra similar features have been identified in three other australian massive sulfide districts these results suggest that a reinvestigation of host rocks is warranted at other deposits where submarine pyroclastics are documented noncaldera settings combining subsidence in an extensional volcano tectonic basin passive submarine lava effusion within the basin and ambient sedimentation derived from basin margins including resedimented pyroclastic debris may be more relevant models in a number of massive sulfide districts

demonstration of the invariance principle for active sonar active sonar systems can provide good target detection potential but are limited in shallow water environments by the high level of reverberation produced by the interaction between the acoustic signal and the ocean bottom the nature of the reverberation is highly variable and depends critically on the ocean and seabed properties which are typically poorly known this has motivated interest in techniques that are invariant to the environment in passive sonar a scalar parameter termed the waveguide invariant has been introduced to describe the slope of striations observed in lofargrams in this work an invariant for active sonar is introduced this active invariant is shown to be present in the time frequency structure observed in sonar data from the malta plateau and the structure agrees with results produced from normal mode simulations the application of this feature in active tracking algorithms is discussed

europa initial galileo geological observations abstract images of europa from the galileo spacecraft show a surface with a complex history involving tectonic deformation impact cratering and possible emplacement of ice rich materials and perhaps liquids on the surface differences in impact crater distributions suggest that some areas have been resurfaced more recently than others europa could experience current cryovolcanic and tectonic activity global scale patterns of tectonic features suggest deformation resulting from non synchronous rotation of europa around jupiter some regions of the lithosphere have been fractured with icy plates separated and rotated into new positions the dimensions of these plates suggest that the depth to liquid or mobile ice was only a few kilometers at the time of disruption some surfaces have also been upwarped possibly by diapirs cryomagmatic intrusions or convective upwelling in some places this deformation has led to the development of chaotic terrain in which surface material has collapsed and or been eroded

bayesian inversion of reverberation and propagation data for geoacoustic and scattering parameters this paper applies nonlinear bayesian inference theory to quantify the information content of reverberation and short range propagation data both individually and in joint inversion to resolve seabed geoacoustic and scattering properties the inversion of reverberation data alone is shown to poorly resolve seabed properties because of strong multi dimensional correlations between parameters inversion of propagation data alone is limited by different correlations but better constrains the geoacoustic parameters however propagation data are insensitive to scattering parameters such as lambert s scattering coefficient in each case the parameter correlations are inherent in the physics of the forward problem reverberation and propagation and cannot be overcome by processing or inversion techniques rather the inversion of more informative data is required this is accomplished here by joint inversion of reverberation and propagation data weighted according to their respective maximum likelihood error estimates joint inversion of reverberation and propagation data collected on the malta plateau strait of sicily resolves both geoacoustic and scattering properties and achieves smaller uncertainties for all parameters than obtained by the inversion of either data set alone

the determination of geoacoustic models in shallow water a technique for determining geoacoustic models in shallow water is described for a horizontally stratified ocean and bottom the method consists of measuring the magnitude and phase versus range of the pressure field due to a cw point source and numerically hankel transforming these data to obtain the depth dependent green s function versus horizontal wavenumber in shallow water the green s function contains prominent peaks at horizontal wavenumbers corresponding to the eigenvalues for any trapped and virtual modes excited in the waveguide a geoacoustic model for the bottom is obtained by computing the theoretical green s function for various values of the bottom parameters and determining the parameter set which provides the best agreement with the experimental green s function particularly in the positions and relative magnitudes of the modal peaks comparisons are also made between the measured and theoretically computed pressure field magnitudes the technique is demonstrated using experimental data at 140 hz and 220 hz

joint estimation of water column and sediment acoustic properties from broadband towed array data using modal inverse method broadband data collected on a towed horizontal array of length 2375m during a geophysical survey are used to perform joint inversion for the water column and sediment acoustic parameters using modal inverse technique s d rajan j f lynch and g v frisk j acoust soc am 82 998 1017 1987 to perform the inversion based on modal wave numbers we first obtain the pressure field as a function of range at a discrete set of frequencies from the broadband data the sources of errors and their impact on the estimation of modal wave number from such data are discussed due to the possibility of large errors in the estimation of the modal wave numbers of the higher order modes the inversion was performed using the modal wave numbers of the dominant lower order modes the resolution estimates indicate that the wave speeds in the water column and top three sediment layers have resolution lengths that are approximately 1 5 times the layer thicknesses with respect to deeper sediment layers the resolu

inversion for geometric and geoacoustic parameters in shallow water experimental results experimental results on the estimation of both geometric and geoacoustic parameters in shallow water are presented genetic algorithms are used for estimation of the forward model parameters the estimated parameters are then used by a standard bartlett processor for source localization a stationary source at a range of 5 6 km and a moving source at ranges from 5 8 7 7 km were successfully localized in range and depth using a single frequency bartlett processor the results indicate that global estimation of the forward model parameters significantly improves source localization performance

comments on an anthropogenic modification in an eremotherium tooth from northeastern brazil over150yearsago peterw lundproposedthatlatequaternaryextinct megafauna henceforth just megafauna and homo sapienscoexisted in brazil lund 1844 but only recently his hypothesiswas supported by direct radiocarbon dating on megafauna bones neves and pilo 2003 hubbe et al 2007 2009 2011 these datesshowed that in some brazilian regions at least some speciessurvived until the beginning of the holocene and became extinctafter the arrival of the rst human groups besides the chronolog ical evidence which indicates that humans and megafauna lived inthe same region at the same time there are also claims that theymayhaveinteractedmoreactivelybasedonthe ndingofsingle orvery few bones or bone fragments associated with human occu pation levels near archeological material or showing marks thatsuggest their usage by humans however based on the meticulousrevision provided by prous 2002 it is possible to rule out most ofthese cases due to theircontroversial nature in fact few of those ifany can be held as solid evidence of this close interaction notconsidering scavengingon bones from a long ago deceased animal prous and fogaca 1999 recently dantas et al in press reported the nding of a singletooth fragment of the ground sloth eremotherium in sergipe state northeastern brazil that according to the authors presentsanthropogenic marks that favor the coexistence of this species andh sapiens however in our opinion their work does not providesolid evidence of an interaction of this nature and therefore theaim of this comment is to discuss the validity of their nding asreliable evidence of megafauna more speci cally eremotherium and humans coexistence in sergipe the coexistence and notablythe close interaction between the former and the later may haveimportant implications to the understanding of the initial humanoccupation of south america hence this kind of nding should notbe taken as granted but rather should be analyzed with rigorouscriteria in the following comments we question the interpretationof the marks seen in the tooth as human made cutmarks based on1 thenatureandlocationofthecutmarksand2 thearchaeologicalandpaleontologicalcontextof the nding furthermore wediscussreasons why the conclusions based on this nding could beseverely distorted dantas et al in press 1 described the marks found on thereported tooth as an effort to build a triangular object based onthe material the location of the marks and the scant informationprovided e g it is notclear if morebones fromeremotheriumwerefound if there are more bones from other species with marks whichother species were found it is hardtoaccept that the marksobserved are the result of human intervention on the tooth themarks are described by dantas et al in press 1 as being humanbecause they have parallel grooved striations narrower anddeeper which follow the curvature of the tooth along apical andlateral borders unfortunately these characteristics are unclear tous in the pictures presented by the authors fig 2f shows onlystriations fig 2g appear to show microwear striations when thescaleofthephoto 0 1mm istakenintoaccount andfig 2hshowsa network of shallow striations that crisscross the surface in everydirection in summary it is not possible to see the diagnosticfeatures in the pictures presented by the authors to justify theirconclusions of an anthropogenic origin for them added to the diagnostic dif culties of the marks in this tooth their occurrence is not in accordance to the standard patternsobserved for food processing in ethnographic and archaeologicalcontexts e g walker 1978 lupo 2002 lyman 2005 martinez 2009 thus diminishing the possibility of butchering marks onthis tooth indeed dantas et al in press never claimed thesemarks were the result of butchering however it is very hard to

insights into holocene megafauna survival and extinction in southeastern brazil from new ams 14 c dates abstract the extinction of late quaternary megafauna in south america has been extensively debated in past decades the majority of the hypotheses explaining this phenomenon argue that the extinction was the result of human activities environmental changes or even synergism between the two although still limited a good chronological framework is imperative to discuss the plausibility of the available hypotheses here we present six new direct ams 14 c radiocarbon dates from the state of sao paulo brazil to further characterize the chronological distribution of extinct fauna in this part of south america the new dates make evident that ground sloths toxodonts and saber toothed cats lived in the region around the pleistocene holocene transition and in agreement with previous studies also suggest an early holocene survival for the ground sloth catonyx cuvieri taken together with local paleoclimatic and archaeological data the new dates do not support hunting or indirect human activities as a major cause for megafauna extinction although more data are required parsimony suggests that climatic changes played a major role in this extinction event

u series dating and taphonomy of quaternary vertebrates from brazilian caves abstract the geochronology and taphonomy of internationally important fossil bearing cave deposits were studied both in the semi arid northern bahia area and the subtropical southeastern lagoa santa area of brazil taphonomic analysis suggests that the processes responsible for bone accumulation in the brazilian caves vary between sites and taphonomic bias can therefore be significant in causing differences in faunal composition in the toca da boa vista caves the presence of single articulated skeletons and the entrance related distribution indicate that random penetration of animals is the main mechanism of fossil accumulation a process that biases the assemblage to smaller species and takes place over extended time periods in nearby toca dos ossos cave transport by runoff in the cave river is predominant and biases the fauna remains to larger more robust bones and species deposition probably also occurred only at times of enhanced runoff giving a more contemporaneous assemblage similar processes were responsible for emplacement of the copious fossil remains in the more humid lagoa santa area where terrigenous fossil deposits are found intercalated by massive speleothem calcite layers in this area runoff under a drier climate probably accounts for the sediment emplacement inside caves in both areas the mode of emplacement implies bias in the fossil record resulting in fossil assemblages that do not mirror surface faunas limiting palaeoenvironmental reconstruction mass spectrometric u series analysis of speleothem calcite overlaying fossil remains gives minimum ages for fossil deposition these ages confirm the previous view that many of the deposits derive from the late glacial but also show that much older material some 350 000 yr is also present the habitat requirements of critical fossil species such as bats and monkeys strongly suggest that they derive from much wetter periods when forest cover was present in the currently semi arid northern bahia area taphonomy exerts a major control on the diversity and mode of emplacement of cave fossil deposits in eastern brazil and thus detailed sedimentological and hydrological studies coupled with a sound geochronological approach are essential in quantifying the relative importance of each taphonomic processes before faunal and palaeoecological interpretations can be attempted

the impact of ocean sound speed variability on the uncertainty of geoacoustic parameter estimates this paper investigates the influence of water column variability on the estimates of geoacoustic model parameters obtained from matched field inversions the acoustic data were collected on the new jersey continental shelf during shallow water experiments in august 2006 the oceanographic variability was evident when the data were recorded to quantify the uncertainties of the geoacoustic parameter estimates in this environment bayesian matched field geoacoustic inversion was applied to multi tonal continuous wave data the spatially and temporally varying water column sound speed is parametrized in terms of empirical orthogonal functions and included in the inversion its impact on the geometric and geoacoustic parameter estimates is then analyzed by the inter parameter correlations two different approaches were used to obtain information about the variation of the water sound speed one used only the profiles collected along the experimental track during the experiment and the other also included observations collected over a larger area the geoacoustic estimates from both the large and small sample sets are consistent however due to the diversity of the oceanic sound speed more empirical orthogonal functions are needed in the inversion when more sound speed profile samples are used

estimation of seabed reflection loss properties from direct blast pulse shape l the decay rate of a smeared multipath arrival received many water depths from a broadband source has been shown to be closely related to bottom reflection loss properties smith j acoust soc am 50 332 336 1971 harrison j acoust soc am 114 2744 2756 2003 this suggests a simple way of measuring bottom properties with active sonars the method is demonstrated with experimental data measured in a shallow water region of the mediterranean sea seabed properties are deduced directly by the method in the form of the rate of change of reflection loss with respect to angle close to grazing agreement is shown between the results of the method and the results of matched field inversions carried out in the same area good agreement is also shown between measurements and predictions of propagation loss made using seabed properties deduced via the method

europa stratigraphy and geological history of the anti jovian region from galileo e14 solid state imaging data a tidal bulge and associated deformation are predicted to occur in europa s anti jovian region voyager data showed polygonal low albedo bands in this region it was demonstrated that when the low albedo material comprising these bands was removed the margins could be reconstructed suggesting that fracturing and lateral separation has occurred higher resolution galileo images of a 300 000 km2 portion of the anti jovian region permit recognition and mapping of a variety of features and documentation of the geological history we identify background ridged plains several distinctive types of bands and ridges lenticulae and regions of chaotic terrain these images are at relatively low incidence angles thus albedo variations predominate over topography this presents a challenge to morphologically based mapping but does not preclude development of a regional stratigraphy stratigraphic relationships show that dark bands crosscut the bright ridged plains and are themselves disrupted by lenticulae and chaos suggesting a geological history beginning with background ridged plains followed by a period dominated by band formation with the most recent history predominantly characterized by formation of lenticulae and chaos the paucity of impact craters in this region indicates that the entire sequence of units is geologically recent

is europa surface cracking due to thermal evolution we propose that some of the surface features of europa may have originated by processes within a model planet in which hydrated silicates are stable

geoacoustic inversion in time domain using ship of opportunity noise recorded on a horizontal towed array a time domain geoacoustic inversion method using ship noise received on a towed horizontal array is presented the received signal containing ship noise as a source of opportunity is time reversed and then back propagated to the vicinity of the ship the back propagated signal is correlated with the modeled signal which is expected to peak at the ship s location in case of a good match for the environment this match is utilized for the geoacoustic parameter inversion the objective function for this optimization problem is thus defined as the normalized power focused in an area around the source position using a matched impulse response filter a hybrid use of global and local search algorithms i e ga and powell s method is applied to the optimization problem applications of the proposed inversion method to mapex 2000 noise experiment conducted north of the island of elba show promising results and it is shown that the time domain inversion takes advantage of dominant frequencies of the source si

passive fathometer processing ocean acoustic noise can be processed efficiently to extract green s function information between two receivers by using noise array processing techniques it has been demonstrated that a passive array can be used as a fathometer siderius et al j acoust soc am 120 1315 1323 2006 here this approach is derived in both frequency and time domains and the output corresponds to the reflection sequence from this reflection sequence it is possible to extract seabed layering in the ocean waveguide most of the energy is horizontally propagating whereas the bottom information is contained in the vertically propagating noise extracting the seabed information requires a dense array since the resolution of the bottom layer is about half the array spacing if velocity sensors are used instead of pressure sensors the array spacing requirement can be relaxed and simulations show that just one vertical velocity sensor is sufficient

geoacoustic inversion for the seabed transition layer using a bernstein polynomial model this paper develops an inversion method for the seabed transition layer at the water sediment interface often found in muddy sediments which provides density and sound speed profiles that were previously not resolvable the resolution improvements are achieved by introducing a parametrization that captures general depth dependent gradients in geoacoustic parameters with a small number of parameters in particular the gradients are represented by a sum of bernstein basis functions weighted by unknown coefficients compared to previous forms found in the literature the bernstein based parametrization can represent a wider range of depth dependent geoacoustic profiles using fewer parameters which leads to reduced uncertainty and improved resolution in addition the bernstein basis is the most stable polynomial representation in that small perturbations to the unknown coefficients result in small localized perturbations to the geoacoustic profile thereby providing an efficient exploration of the parameter space using markov chain methods in nonlinear inversion geoacoustic profiles at four mud sites on the malta plateau are studied with the proposed approach results show exceptional resolution of density profiles estimated with low uncertainty and clear sensitivity to sediment features of centimeter scale

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

range dependent geoacoustic inversion of vertical line array data using matched beam processing this paper describes the results of range dependent geoacoustic inversion using vertical line array data obtained from the 4th matched acoustic properties and localization experiment conducted in the east sea of korea the narrowband multitone continuous wave signal from the towed source was analyzed to estimate the range dependent geoacoustic properties along the radial track the primary approach is based on the sectorwise inversion scheme the inversion region up to 7 5 km from the vertical line array was divided into several segments and the subinversions for each segment were performed sequentially to reduce the dominance of low angle arrivals which bears little information for the bottom segment in question matched beam processing with beam filtering was used for the cost function the performance of proposed algorithm was tested using simulated data for an environment representative of the experimental site the inversion results for the experimental data were consistent with the geophysical database and were validated from matched field source localization using frequencies different from those used in the inversion

archaeology of the pleistocene holocene boundary in brazil abstract after a short history of brazilian research about pleistocene peopling the late pleistocene early holocene changes of climate and resources are discussed claims for a very ancient presence of man before 13 000 bp itaborai toca da esperanca pedra furada and lapa vermelha sites are polemic because putative structures and artifacts could have been made by natural processes in central and northeastern brazil some sites dated between 14 000 and 10 000 bp provide clear evidence of human activities and coexistence with huge pleistocene mammals in a synthesis of our present knowledge about the 12 000 8000 bp period biological aspects of the lagoa santa people and their subsistence are discussed the main regional traditions are umbu with bifacial projectile points and humaita with heavy implements in the southern part of brazil in the central and northeastern regions the itaparica tradition is characterized by typical retouched flakes and limaces although projectile points are generally thought to be absent in the earliest levels of this tradition some have been found in boquete cave in amazonia some cultural aspects seem to have been the same as in central brazil

shallow water waveguide characterization using the hankel transform a coherent processing technique is proposed for the characterization of shallow water channels for a horizontally stratified ocean and bottom the method consists of measuring the magnitude and phase versus range of the pressure due to a cw point source and hankel transforming this data to obtain the depth dependent green s function versus horizontal wave number the green s function contains all the information about the channel necessary to solve the forward problem including the nature of the discrete and continuous spectra and the plane wave reflection coefficient of the bottom characteristics of the green s function can also be used to infer acoustic properties of the bottom results for simple examples are presented using synthetic data and implications for the nonstratified case are discussed

gas driven water volcanism and the resurfacing of europa we have analyzed the problem of how pathways are created for the resurfacing by water or volatiles for a europa model in which there is an ocean underlying a thin ice shell 10 km thickness open cracks propagating downward cannot reach the ocean unless the relative tension in the ice is both very high 100 bar and applied very rapidly 10 4 10 5sec there is no known way to satisfy these criteria water filled cracks propagating upward can approach the surface for relative tensions of 5 10 bar comparable to the stresses induced by the eccentricity tide exsolution of plausible gas species co 2 co ch 4 so 2 can then occur at the crack tip the application of linear elastic fracture mechanics shows that the gas filled portion of the crack pinches off from the water filled portion and may rise rapidly to the surface entraining some water many of these cracks may end up as intrusions rather than extrusions because of partial freeze out of co 2 and water on the walls of the crack the resulting eruption is initially gas dominated but may include a subsequent less extended eruption of foam there may not be a direct relationship between the resurfacing process described here and the currently known geologic features observed on the surface the main problem with this or any model for tapping the ocean is the propagation of cracks through the soft ice immediately overlying the ocean

analyzing lateral seabed variability with bayesian inference of seabed reflection data this paper considers bayesian inversion of seabed reflection coefficient data for multi layer geoacoustic models at several sites with the goal of studying lateral variability of the seabed rigorous uncertainty estimation is carried out to resolve lateral variability of the sediments from inherent inversion uncertainties the uncertainty analysis includes bayesian model selection comprehensive quantification of data error statistics and a markov chain monte carlo approach to transforming data uncertainties to model uncertainties model selection is addressed using the bayesian information criterion to ensure parsimony of the parametrizations data error statistics are quantified by estimating full covariance matrices from data residuals with posterior statistical validation a metropolis hastings sampling algorithm is used to compute posterior probability densities four experiment sites are considered along a track located on the malta plateau mediterranean sea and the inversion results are compared to cores taken at each site differences between profile marginal probability distributions at adjacent sites are quantified using the bhattacharyya coefficient differences that exceed the estimated geoacoustic uncertainties are interpreted as spatial variability of the seabed the results are compared to an interpretation of geologic features evident in a chirp sub bottom profiler section

bayesian geoacoustic inversion of ship noise on a horizontal array this paper applies geoacoustic inversion to low frequency narrow band acoustic data from a quiet surface ship recorded on a bottom moored horizontal line array in shallow water a bayesian matched field inversion method is employed which quantifies geoacoustic uncertainties and allows for meaningful comparison of inversion results from different data sets geoacoustic inversion results for ship noise data are compared with inversion results for multitone data from a towed controlled source collected in the same experiment and with independent geophysical measurements to increase the information content of low level ship noise data the effect of including multiple independent data segments in the inversion is investigated and shown to significantly reduce geoacoustic parameter uncertainties geoacoustic uncertainties are also shown to depend on ship range and orientation with increased uncertainties for long ranges and for the ship stern oriented away from the array

inversion for range dependent water column sound speed profiles on the new jersey shelf using a linearized perturbative method the environment of the new jersey shelf is characterized by high spatial and temporal variability of water column properties caused by intrusions of warm salty water from the continental slope these intrusions cause fluctuations in the water column sound speed profile which can have significant effects on acoustic propagation in shallow water in this work a linearized perturbative inverse technique is applied to estimate range dependent water column sound speed profiles this method utilizes estimates of horizontal wave numbers to determine sound speed as a function of depth this technique is appropriate for the range dependent shallow water environment as horizontal wave numbers can be measured semilocally 1 2 km aperture and their values are a direct measurement of the local environmental parameters difficulty is encountered in application of the perturbative inverse technique because the wave number data are insensitive to some portions of the waveguide and as a result the solution can deviat

a coupled mode solution for acoustic propagation in a waveguide with stepwise depth variations of a penetrable bottom a coupled mode solution is formulated for the problem of acoustic propagation in a cylindrically symmetric ocean divided in range into a finite number of adjoining pekeris waveguides of differing water depths attenuation is included in the bottom and the problem is discretized by assigning a pressure release boundary condition at a depth which is sufficiently far removed to prevent significant energy from returning to the water this formulation includes backscatter from the depth variations of the water column and full coupling between a finite number of modes propagating in the water column and in the bottom numerical results based on an implementation of this solution are presented

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

earliest art in the americas incised image of a proboscidean on a mineralized extinct animal bone from vero beach florida abstract a fragmented fossil bone incised with the figure of a proboscidean was recently found at vero beach florida near the location where late pleistocene fauna and human bones were recovered from 1913 to 1916 this engraving may represent the oldest and only existing example of terminal pleistocene art depicting a proboscidean in the americas because of the uniqueness rarity and potential antiquity of this specimen caution demanded that a variety of tests be used in an attempt to verify its authenticity the mineralized bone was identified as mammoth mastodon or giant sloth rare earth element analysis was consistent with the fossil bone being ancient and originating at or near the old vero site 8 ir 9 forensic analysis suggests the markings on the bone are not recent optical microscopy results show no discontinuity in coloration between the carved grooves and the surrounding material indicating that both surfaces aged simultaneously scanning electron microscopy sem revealed that the edges of the inscription are worn and show no signs of being incised recently or that the grooves were made with metal tools in addition the backscattered sem images suggest there is no discontinuity in the distribution of light and heavy elements between the scribed region and the surrounding bone indicating that both surfaces aged in the same environment this is very different from an intentional mark made on the bone for comparison energy dispersive x ray spectroscopy edxs shows that the surface contains significant amounts of calcium phosphorus oxygen and carbon typical of a mineralized bone surface examination of a cast and mold of the incised bone by reflectance transformation imaging rti also provided no evidence that the engraving was made recently all of these results are consistent with the mammoth engraving being authentic

extremely fast supercooling of water in the anti jovian hemisphere of europa a speculative model for the fracturing pattern and ascent of brines along cracks the anti jovian hemisphere of europa the hemisphere opposite the one facing jupiter displays a complex array of fractures including roughly concentric and arcuate ones the geometry of this intriguing pattern on the icy surface of europa resembles the textural features displayed by perlitic volcanic glass we argue that fast cooling of a rhyolitic magma may serve as an analogue for fast supercooling of water leading to formation of amorphous ice glassy water we envisage two possible scenarios for ice melting and subsequent extremely fast supercooling 1 massive subglacial volcanic activity or 2 a large impact on the anti jovian hemisphere we suggest that extremely fast formation of amorphous ice on europa would result in a fracture pattern geometrically equivalent to that observed in perlitic glass fast supercooling of water will initially lead to brine retention in the ice phase however after some time these brines would be laterally rejected toward fractures furthermore as solidification progresses downward a shrinking ocean would increase brine concentration these brines would eventually escape to the surface via the fracture network finally high pressure crystallization of salts within fractures may provide an efficient mechanism for differential plate separation horizontal movement and formation of new fractures