mass flux and undertow in a surf zone abstract the mass of water carried shoreward by the breaking waves in a surf zone will in a two dimensional situation be compensated by a seaward return flow the undertow it is shown that the undertow is driven by the local difference between radiation stress and the set up pressure gradient which only balance each other in average over the depth turbulent shear stresses are required to maintain a steady situation comparison with measurements confirms the theoretical results

remote sensing of breaking wave phase speeds with application to non linear depth inversions abstract a number of existing models for surface wave phase speeds linear and non linear breaking and non breaking waves are reviewed and tested against phase speed data from a large scale laboratory experiment the results of these tests are utilized in the context of assessing the potential improvement gained by incorporating wave non linearity in phase speed based depth inversions the analysis is focused on the surf zone where depth inversion accuracies are known to degrade significantly the collected data includes very high resolution remote sensing video and surface elevation records from fixed in situ wave gages wave phase speeds are extracted from the remote sensing data using a feature tracking technique and local wave amplitudes are determined from the wave gage records and used for comparisons to non linear phase speed models and for non linear depth inversions a series of five different regular wave conditions with a range of non linearity and dispersion characteristics are analyzed and results show that a composite dispersion relation which includes both non linearity and dispersion effects best matches the observed phase speeds across the domain and hence improves surf zone depth estimation via depth inversions incorporating non linearity into the phase speed model reduces errors to o 10 which is a level previously found for depth inversions with small amplitude waves in intermediate water depths using linear dispersion considering the controlled conditions and extensive ground truth this appears to be a practical limit for phase speed based depth inversions finally a phase speed sensitivity analysis is performed that indicates that typical nearshore sand bars should be resolvable using phase speed depth inversions however increasing wave steepness degrades the sensitivity of this inversion method

mineralogy of three slightly palagonitized basaltic tephra samples from the summit of mauna kea hawaii certain palagonites from hawaii are considered to be among the best analogs for martian fines based upon similar spectral properties for this study three distinctly colored layers were sampled from slightly palagonitized basaltic tephra just below the summit of mauna kea at 4145 m elevation the mineralogy of size fractions of these samples was examined by diffuse reflectance visible and near ir and far ir spectroscopy optical microscopy x ray diffraction mossbauer spectroscopy magnetic analysis electron microprobe analysis empa and transmission and scanning electron microscopy for the 20 1000 m size fraction sample hwmk11 red is essentially completely oxidized and has a hematite ti hematite pigment dispersed throughout the silicate matrix the alteration is present throughout particle volumes and only a trace amount of glass is present no palagonitic rinds were detected in addition to ferric fe ti oxides other phases detected were plagioclase feldspar and a trace of olivine sample hwmk12 black has the lowest proportion of ferric bearing phases and is thus least weathered it consists mostly of unaltered glass with embedded plagioclase and minor amounts of pyroxene olivine and ti magnetite in some grains a thin palagonitic rind is visible indicating some surface alteration the mineralogy for sample hwmk13 yellow is the same as that for hwmk12 except that it has distinct well developed palagonitic rinds consisting of erionite and smectite for all samples the amount of glass and plagioclase decreases and the amount of smectite increases with decreasing particle size for size fractions 20 m for hwmk11 the amount of hematite is essentially constant and mica is present only in the coarse clay sized fraction smectites are low in structural fe for hwmk12 and hwmk13 the zeolite erionite is present along with smectites and nanophase ferric oxides np ox erionite abundance decreases and np ox abundance increases with decreasing particle size the smectite in both black and yellow samples contains some fe3 in octahedral layers there were only two mineral phases containing iron in the fine clay fraction namely smectites and iron oxides for hwmk11 relatively large iron oxide particles 0 1 to 0 4 m were dispersed on clay surfaces for hwmk12 and hwmk13 much finer np ox particles were present in lesser concentrations formation of the zeolite erionite is consistent with the arid climate zone where these samples were collected however transient hydrothermal processes that occurred during the eruption of mauna kea volcano under its permanent ice cap during the pleistocene may have resulted in minerals such as zeolites and smectites which may persist as relicts over a long period of time most of the iron released during weathering of basaltic tephra precipitated as poorly crystalline iron oxides and some of the fe has substituted for the octahedral cations in the structure of authigenic smectites the ti hematite in hwmk11 however is the result of high temperature oxidation of ti magnetite and exsolution from ironbearing silicate phases visible and near ir reflectivity spectra for the 20 m size fraction of hwmk11 is dominated by well crystalline ti hematite corresponding spectra for hwmk12 and hwmk13 whose ferric mineralogy is dominated by np ox particles are more similar to martian bright region spectra

modeling elastic anisotropy resulting from the application of triaxial stress abstractelastic wave velocities in rocks vary with stress due to the presence of discontinuities and microcracks within the rock we analytically derived a model to account for stress dependency of seismic velocities when a rock is subjected to triaxial stresses we first considered a linearly isotropic elastic medium permeated by a distribution of cracks with random orientations the geometry of cracks is not specified instead their behavior is defined by a ratio b of their normal to tangential excess compliances when this isotropic rock is subjected to triaxial stresses cracks tend to close depending on their orientation with respect to the applied stresses for small stresses the model predicts ellipsoidal anisotropy and expresses the ratios of thomsen s parameters in the three orthogonal planes of symmetry as a function of the compliance and poisson s ratios it also establishes relationships between anisotropy parameters and stress ratios deriving the model for larger stresses shows that su

effects of wave rollers and bottom stress on wave setup 1 setup the increase in the mean water level associated with breaking waves observed between the shoreline and about 6 m water depth on an ocean beach is predicted well by a model that includes the effects of wave rollers and the bottom stress owing to the mean flow over the 90 day observational period the measured and modeled setups are correlated squared correlation above 0 59 and agree within about 30 although rollers may affect setup significantly on beaches with large amplitude several meters high sandbars and may be important in predicting the details of the cross shore profile of setup for the data discussed here rollers have only a small effect on the amount of setup conversely bottom stress calculated using eddy viscosity and undertow formulations based on the surface dissipation and assuming that the eddy viscosity is uniform throughout the water column significantly affects setup predictions neglecting bottom stress results in underprediction of the observed setup in all water depths with maximum underprediction near the shoreline where the observed setup is largest

modeling the alongshore current on barred beaches mean alongshore currents observed on two barred beaches are compared with predictions based on the one dimensional time and depth averaged alongshore momentum balance between forcing by breaking waves wind and 10 100 km scale alongshore surface slopes bottom stress and lateral mixing the observations span 500 hours at egmond netherlands and 1000 hours at duck north carolina and include a wide range of conditions with maximum mean currents of 1 4 m s including rollers in the wave forcing results in improved predictions of the observed alongshore current structure by shifting the predicted velocity maxima shoreward and increasing the velocity in the bar trough compared with model predictions without rollers for these data wave forcing balances the bottom stress within the surfzone with the other terms of secondary importance the good agreement between observations and predictions implies that the one dimensional assumption holds for the range of conditions examined despite the presence of small alongshore bathymetric nonuniformities with stronger bathymetric variations the model skill deteriorates particularly in the bar trough consistent with earlier modeling and laboratory studies

hyperspectral reflectance mapping of cinder cones at the summit of mauna kea and implications for equivalent observations on mars 1 atmospherically corrected hyperspectral reflectance data 0 4 to 2 5 m derived from the airborne visible infrared imaging spectrometer aviris validated with field based traverses and laboratory analyses were used to map the distribution of ferric oxide sulfate and phyllosilicate minerals exposed on fresh and altered cones on the summit of mauna kea volcano hawaii spectra from 0 4 to 1 1 m exhibit charge transfer and electronic transition features related to hematite nanophase iron oxide and possibly jarosite whereas spectra from 2 0 to 2 5 m are characterized by cation oh features related to kaolinite montmorillonite and saponite unaltered cones exhibit concentric zoning of iron oxide signatures with crystalline hematite located near the summits and nanophase iron oxide signatures found at the base of cones and on flow surfaces altered cones puu poliahu and puu waiau have exposures of three phyllosilicate and possible jarosite units in some cases there is zoning with a core of saponite surrounded by montmorillonite kaolinite is only found in two exposures on puu poliahu with one exposure coinciding with a possible jarosite unit the relatively small spatial scale associated with alteration zones seen on mauna kea demonstrates the importance of obtaining high spatial resolution hyperspectral observations of mars

visible near infrared and middle infrared spectroscopy of altered basaltic tephras spectral signatures of phyllosilicates sulfates and other aqueous alteration products with application to the mineralogy of the columbia hills of gusev crater mars 1 we studied visible to near infrared vnir 0 35 2 5 m and middle infrared mir 1800 250 cm 1 also called thermal infrared and vibrational spectra of basaltic tephras from mauna kea volcano that were altered under ambient hydrothermal hydrolytic and acid sulfate and dry heat conditions although models of mir spectra of altered tephras generally produce fits whose quality is reduced compared to deconvolutions of primary lithologies they successfully identify major alteration phases cristobalite oxide phyllosilicate and sulfate except in palagonites mir spectra of the 1 in spectra of the 500 1000 m fraction only if phyllosilicates are present although mauna kea palagonitic tephra is considered a vnir analog to martian dust comparison of mir altered tephra spectra 45 m fraction to dust spectra retrieved from mars global surveyor and mars exploration rover instruments do not provide good spectral matches the best mir match is a tephra that has a strong plagioclase feldspar transparency feature and was altered under dry high temperature oxidizing conditions this sample is not a vnir analog and is not a process analog but it emphasizes the mineralogical importance of plagioclase feldspar in martian dust no single tephra is a good spectral analog across the vnir and mir we found no evidence for substantial sulfates or phyllosilicates in mini thermal emission spectrometer mini tes spectra from gusev crater

a decade of tomography over the past 10 years ray based postmigration grid tomography has become the standard model building tool for seismic depth imaging while the basics of the method have remained unchanged since the late 1990s the problems it solves have changed dramatically this evolution has been driven by exploration demands and enabled by computer power there are three main areas of change first standard model resolution has increased from a few thousand meters to a few hundred meters this order of magnitude improvement may be attributed to both high quality complex residual moveout data picked as densely as 25 m to 50 m vertically and horizontally and to a strategy of working down from long wavelength to short wavelength solutions second more and more seismic data sets are being acquired along multiple azimuths for improved illumination and multiple suppression high resolution velocity tomography must solve for all azimuths simultaneously to prevent short wavelength velocity heterogeneity from being mistaken for azimuthal anisotropy third there has been a shift from predominantly isotropic to predominantly anisotropic models both vti and tti with four component data anisotropic grid tomography can be used to build models that tie pz and ps images in depth

transition zone width and implications for modeling surfzone hydrodynamics the surfzone associated with a wave breaking on a plane slope may be subdivided into three regions the transition zone the inner zone and the swash zone the transition zone is the region just shoreward of the point of wave breaking and is characterised by rapid wave decay and also by constant wave setdown and thus constant radiation stress in this paper an empirical expression for the width of this zone is developed from monochromatic wave data two techniques are proposed for the consideration of this phenomenon in the numerical modelling of surfzone hydrodynamics for random waves the implications of a zone of nearly constant radiation stress inside the breakpoint are examined with respect to wave induced current generation both cross shore and longshore and sediment transport prediction comparisons are made to both field and laboratory data from plane and undulating profiles

field observations of wave driven setdown and setup wave driven setdown and setup observed for 3 months on a cross shore transect between the shoreline and 5 m water depth on a barred beach are compared with a theoretical balance between cross shore gradients of the mean water level and the wave radiation stress the observed setdown the depression of the mean water level seaward of the surf zone is predicted well when radiation stress gradients are estimated from the observations using linear theory at each location along the transect the observed setdown also agrees with analytical predictions based on offshore wave observations and the assumption of linear dissipationless normally incident waves shoaling on alongshore homogeneous bathymetry the observed setup the superelevation of the mean water level owing to wave breaking is predicted accurately in the outer and middle surf zone but is increasingly underpredicted as the shoreline is approached similar to previous field studies setup at a fixed cross shore location increases with increasing offshore wave height and is sensitive to tidal fluctuations in the local water depth and to bathymetric changes numerical simulations and the observations suggest that setup near the shoreline depends on the bathymetry of the entire surf zone and increases with decreasing surf zone beach slope defined as the ratio of the surf zone averaged water depth to the surf zone width a new empirical formula for shoreline setup on nonplanar beaches incorporates this dependence

a study of radiation stress and set up in the nearshore region abstract in this paper the variations of radiation stress and mean water level are studied for the two dimensional shoaling and breaking of progressive periodic waves on a plane gently sloping laboratory beach observations of radiation stress and mean water level were made for two initial conditions the observed variations are compared to the variations as calculated by a linear theory james nonlinear theory and a new nonlinear theory based on cokelet s work it is shown that the nonlinear theories are qualitatively and quantitatively superior to the linear theory thus indicating that the effects of finite amplitude are important for the present case

quantification of sand bar morphology a video technique based on wave dissipation a technique is presented to remotely measure the scales and morphology of natural sand bars based on the preferential dissipation of wind waves and swell over the crests of the bar photographic or video images are recorded and statistical uncertainties associated with incident wave height modulations removed by averaging time exposures ground truth testing of the technique was carried out as part of the superduck experiment in october 1986 the time exposures generally provided a good mapping of underlying morphology allowing detection of the bar and determination of cross shore and longshore length scales however during high waves persistent surface foam obscures the relationship of image intensity to local dissipation modeled theoretically by dissipation of a random wave field and an enhancement technique of image differencing must be done to remove the bias errors in the estimate of bar crest distance from the shoreline are generally less than 35 but this value depends on the geometry of the particular bar logistic simplicity and quantitative capabilities make this technique very attractive

a note on the three dimensional shear stress distribution in a surf zone the three dimensional time mean shear stress distribution in a surf zone is analyzed thereby determining the vertical distribution of the driving forces due to wave breaking it is found that on a uniform coast the longshore current can be described as driven by a surface shear stress equal to the cross shore gradient in the shear component of the radiation stress the near surface shear stress is found to be in the direction of wave propagation having a magnitude determined by the dissipation of wave energy it can be determined as the shear force acting on the waves from the surface rollers of spilling breakers or broken waves

estimating surfzone wave transformation and wave setup from remote sensing data abstract the spatial distribution of wave roller dissipation is derived from optical remote sensing observations in a laboratory setting and is used to estimate wave transformation and radiation stress forcing through the surfzone the methodology relies on direct measurements of the size of individual wave breaking rollers in an irregular wave field via remote sensing the wave roller measurements are used to calculate the roller energy roller dissipation and the roller component of the radiation stress these hydrodynamic quantities then serve as input into the wave energy flux and cross shore momentum balances in order to derive the wave height transformation and mean water level profiles the accuracy of the methodology is shown to be very good through comparison with in situ data in addition the mean water level profile reproduces the transition zone lag and maximum water level at the most shoreward measuring point overall it is demonstrated that the methodology can be successfully applied to irregular waves and can be used to estimate both wave transformation and radiation stress forcing through the surf zone

sensitivity of elastic wave velocities to stress changes in sandstones the drilling of wells and production of hydrocarbons lead to changes in the stresses acting on the reservoir and surrounding rocks and these changes in stress may lead to problems such as wellbore instability sanding loss of permeability reservoir compaction casing deformation surface subsidence etc elastic wave velocities in sandstones are sensitive to changes in stress due to the presence of grain boundaries and microcracks within the rock this paper shows how changes in elastic wave velocities can be used to monitor the changes in stress that occur and a method for predicting the velocity changes due to a given change in stress is illustrated using the example of a borehole drilled into a sandstone reservoir

diagenetic k feldspar pseudomorphs in the triassic buntsandstein sandstones of the iberian range spain early diagenetic k feldspar in the triassic buntsandstein of the iberian range spain occurs as pseudomorphs after detrital k feldspar or 99 untwinned commonly heavily clouded by vacuoles and tiny inclusions dark luminescing and are composed of numerous fine euhedral crystals of k feldspar the latter property suggests that the pseudomorphs form via dissolution of detrital k feldspar and plagioclase and precipitation of authigenic k feldspar x ray diffraction analysis shows that the authigenic k feldspar is intermediate microcline

a laboratory study of longshore currents over barred and non barred beaches abstract a detailed description is given of the results of laboratory experiments on wave driven longshore currents on both barred and non barred beaches the objective is to examine the cross shore distribution of the longshore current velocities for purely wave driven currents with emphasis on the position of maximum current velocity with respect to areas where wave energy is dissipated unidirectional obliquely incident waves both regular and random were used the measurements were performed in a large wave basin with a pump recirculation system to create spatially homogeneous longshore currents the experiments yielded information on wave transformation set up of the mean water level and the cross shore distribution of wave driven longshore current velocity a number of cases are presented and compared with each other the measurements show that in the case of purely wave driven longshore currents the maximum current velocities occur close to areas where wave breaking is most intense the effect of mixing bottom friction and wave rollers on the longshore current velocity profile are examined in more detail with help of numerical modelling existing model equations based on the assumption of alongshore uniformity are used the results for the mean longshore current profile on a barred beach are in close agreement with the measurements

video observations and model predictions of depth induced wave dissipation time averaged video observations of the nearshore zone show the process of wave breaking as one or more white alongshore bands of high intensity corresponding to the preferential location of breaking wave dissipation on one or more sandbars across a known depth profile similar bands of dissipation can be predicted with existing wave transformation models based on the wave energy balance this opens up possibilities for estimating bathymetry from video observations by processing observed intensities into a model predicted proxy of wave dissipation and the inverse modeling of this dissipation proxy into depth the objectives of this paper are 1 to present a technique for processing time averaged cross shore image intensity profiles into profiles that solely contain the contribution due to wave breaking and 2 to empirically determine which modeled wave dissipation proxy relates best to the cross shore shape of the obtained breaking induced intensity the processing technique involves the removal of background illumination and noise and most importantly a correction for white foam that after being generated in the breaking process remains floating at the water surface this foam thus contributes to high image intensities but is not predicted by wave transformation models based on video and bathymetric data collected at the double barred beach at egmond aan zee the netherlands and a standard wave transformation model containing the wave and roller energy balances we find that the modeled cross shore distribution of the dissipation of the energy of the surface roller the white aerated mass of water at the breaking wave front matches the observed cross shore shape of breaking induced intensity well other hypothesized dissipation proxies result in a larger 10 m seaward bias in the locations of maximum breaking induced intensity and model predicted dissipation or do not predict the cross shore change in the area below the breaking induced intensity bands correctly

estimating wave energy dissipation in the surf zone using thermal infrared imagery thermal infrared ir imagery is used to quantify the high spatial and temporal variability of dissipation due to wave breaking in the surf zone the foam produced in an actively breaking crest or wave roller has a distinct signature in ir imagery a retrieval algorithm is developed to detect breaking waves and extract wave roller length using measurements taken during the surf zone optics 2010 experiment at duck nc the remotely derived roller length and an in situ estimate of wave slope are used to estimate dissipation due to wave breaking by means of the wave resolving model by duncan 1981 the wave energy dissipation rate estimates show a pattern of increased breaking during low tide over a sand bar consistent with in situ turbulent kinetic energy dissipation rate estimates from fixed and drifting instruments over the bar when integrated over the surf zone width these dissipation rate estimates account for 40 69 of the incoming wave energy flux the duncan 1981 estimates agree with those from a dissipation parameterization by janssen and battjes 2007 a wave energy dissipation model commonly applied within nearshore circulation models

video based depth inversion techniques a method comparison with synthetic cases abstract applications of video based depth inversion in the near shore coastal environment are growing in numbers video based capabilities in nearshore monitoring are improving and coastal monitoring programs are expanding due to greater availability and reduced costs video derived beach state indicators such as beach width bar position and wave and current parameters are supplemented by accurate depth estimations through inversion video based depth inversion knows two main approaches a spectral and temporal method of celerity estimation the two methods have so far never been compared as video systems are often tailored for the chosen celerity estimation method here a spectral and temporal method are compared using controlled synthetic datasets obtained using the serre1d boussinesq model to estimate celerity and invert depth the assessment is carried out on a set of wave boundary conditions with over linear and barred bottom profile both methods invert depth with a similar accuracy for the most realistic jonswap cases an evident correlation is found between wave skewness non linearity and depth estimation error linked to the limits of the linear dispersion relation a residual sensing error is linked to method based parameters and a changing wave shape as incident waves propagate inshore the inversion error can be reduced significantly including a wave height dependent non linear correction importantly a method based error is introduced for the temporal method to increase the suitability for data assimilation likewise the spectral method has its own existing depth error estimation to feed into the kalman filter however these method based error estimates show very weakly or no relation to the observed error between estimated cross shore profile and bottom profile used for the model input

energy dissipation in the inner surf zone new insights from lidar based roller geometry measurements the spatial and temporal variation of energy dissipation rates in breaking waves controls the mean circulation of the surf zone as this circulation plays an important role in the morphodynamics of beaches it is vital to develop better understanding of the energy dissipation processes in breaking and broken waves in this paper we present the first direct field measurements of roller geometry extracted from a lidar data set of broken waves to obtain new insights into wave energy dissipation in the inner surf zone we use a roller model to show that most existing roller area formulations in the literature lead to considerable overestimation of the wave energy dissipation which is found to be close to but smaller than the energy dissipation in a hydraulic jump of the same height the role of the roller density is also investigated and we propose that it should be incorporated into modified roller area formulations until better knowledge of the roller area and its link with the mean roller density is acquired finally using previously published results from deepwater wave breaking studies we propose a scaling law for energy dissipation in the inner surf zone which achieves satisfactory results at both the time averaged and wave by wave scales

hydrothermal precipitation of sanidine adularia having full al si structural disorder and specular hematite at maunakea volcano hawai i and at gale crater mars

the tuscarora au ag district eocene volcanic hosted epithermal deposits in the carlin gold region nevada the tuscarora mining district contains the oldest and the only productive eocene epithermal deposits in nevada the district is a particularly clear example of association of low sulfidation deposits with igneous activity and structure and it is unusual in that it consists of two adjoining but physically and chemically distinct types of low sulfidation deposits moreover tuscarora deposits are of interest because they formed contemporaneously with nearby giant carlin type gold deposits the tuscarora deposits formed within the 39 9 to 39 3 ma tuscarora volcanic field along and just outside the southeastern margin of the caldera like mount blitzen volcanic center both deposit types formed at 39 3 ma contemporaneous with the only major intrusive activity in the volcanic field no deposits are known to have formed during any of the intense volcanic phases of the field intrusions were the apparent heat source and structures related to the mount blitzen center were conduits for hydrothermal circulation the ore forming fluids interacted dominantly with eocene igneous rocks the two deposit types occur in a northern silver rich zone that is characterized by relatively high ag au ratios 110 150 narrow alteration zones and quartz and carbonate veins developed mostly in intrusive dacite and in a southern gold rich zone that is typified by relatively low ag au ratios 4 14 more widespread alteration and quartz fissure and stockwork veins commonly developed in tuffaceous sedimentary rocks the deposit types have similar fluid inclusion and pb and s isotope characteristics but different geochemical signatures quartz veins from both zones have similar thermal and paragenetic histories and contain fluid inclusions that indicate that fluids cooled from between 260 and 230 c to less than 200 c fluid boiling may have contributed to precious metal deposition veins in both zones have relatively high as and sb and low bi te and w the silver zone has high ca pb mn zn cd tl and se the gold zone has high hg and mo a few samples from an area of overlap between the two zones share chemical characteristics of both deposit types the deposit types could represent a single zoned or evolving system in which hydrothermal fluids rose along structures within the silver zone preferentially deposited ag and base metals and then spread into the gold zone alternatively the deposit types could represent two distinct but temporally indistinguishable hydrothermal cells that only narrowly overlapped spatially as noted in previous studies the hydrothermal fluids that generated the tuscarora and other epithermal deposits could have evolved from carlin type fluids by boiling and mixing with meteoric water if so the tuscarora deposit may represent epithermal conditions above carlin type deposits and carlin type deposits may lie beneath the district

observation of shear wave splitting in the multicomponent node data from atlantis field gulf of mexico in 2005 a multicomponent ocean bottom node data set was collected by bp and bhp billiton in the atlantis field in the gulf ofmexico our results are based on data from a few sparse nodes with millions of shots that were analysed as common receiver azimuthal gathers a first order look at p wave arrivals on a common receiver gather at a constant offset reveals variation of p wave arrival time as a function of azimuth indicating the presence of azimuthal anisotropy at the top few layers this prompted us to investigate shear arrivals on the horizontal component data after preliminary processing including a static correction the data were optimally rotated to radial r and transverse t components the r component shows azimuthal variation of traveltime indicating variation of velocity with azimuth the corresponding t component shows azimuthal variation of amplitude and phase polarity reversal the observed shear wave s wave splitting previously observed azimuthal p wave velocity variation and azimuthal p wave amplitude variation all indicate the occurrence of anisotropy in the shallow just below the seafloor subsea sediment in the area from the radial component azimuthal gather we analysed the pp and ps wave amplitude variation for the first few layers and determined corresponding anisotropy parameter and vp vs values since fracture at this depth is not likely to occur we attribute the observed azimuthal anisotropy to the presence of microcracks and grain boundary orientation due to stress the evidence of anisotropy is ubiquitous in this data set and thus it argues strongly in favour of considering anisotropy in depth imaging for obtaining realistic subsurface images at the least

field observations of wave setup wave setup is assumed to be a balance between the cross shore convergence of the onshore flux of momentum wave radiation stress sxx in the surfzone and a cross shore pressure gradient oceanic observations between the 2 and 8 m isobaths near duck north carolina provide a test of the wave setup balance without assuming that wave height in the surfzone is proportional to water depth analysis of data from a cross shore array of 11 pressure gauges and 10 sonar altimeters deployed during the fall of 1994 indicates the wave setup balance holds to at least the accuracy of the pressure measurements a few centimeters the correlation between the two terms in the setup balance is 0 93 and the linear regression slope is 1 05 0 19 accurate estimates of the cross shore pressure gradient require density measurements to adjust pressure measurements taken at different depths to the same level the assumption that pressure and bathymetry are linear between the 2 and 8 m isobaths or the more common assumption that the height of normally incident shallow water waves is proportional to the water depth introduces errors of up to 6 cm for the conditions considered here given this assumption 3 5 years of data from pressure gauges in 2 and 8 m of water indicate that the wave setup balance is valid for a wide range of conditions correlation 0 71 and regression slope 0 98 0 08

wave driven setup and alongshore flows observed onshore of a submarine canyon 1 the effect of alongshore variations in the incident wavefield on wave driven setup and on alongshore flows in the surfzone is investigated using observations collected onshore of a submarine canyon wave heights and radiation stresses at the outer edge of the surfzone water depth 2 5 m varied by up to a factor of 4 and 16 respectively over a 450 m alongshore distance resulting in setup variations as large as 0 1 m along the shoreline water depth 0 3 m even with this strong alongshore variability wave driven setup was dominated by the cross shore gradient of the wave radiation stress and setup observed in the surfzone is predicted well by a one dimensional cross shore momentum balance both cross shore radiation stress gradients and alongshore setup gradients contributed to the alongshore flows observed in the inner surfzone when alongshore gradients in offshore wave heights were large and a simplified alongshore momentum balance suggests that the large o 1 kg s2 m observed setup induced pressure gradients can drive strong o 1 m s alongshore currents

setup and swash on a natural beach wave setup and swash statistics were calculated from 154 runup time series measured on a moderately steep beach under incident waves varying from 0 4 to 4 0 m significant wave height when scaled by the incident wave height setup swash height and total runup the sum of setup and half the swash height were found to vary linearly with the surf zone similarity parameter 0 h0 l0 1 2 the foreshore slope appeared the appropriate value for the calculation of 0 although the setup data showed some influence of an offshore bar at low tide for low irribaren numbers the swash height in the incident frequency band becomes saturated while for high irribaren numbers no such signs of saturations were seen thus the infragravity band appears to become dominant in the swash below some value of 0 for these data that value is approximately 1 75 although there is considerable scatter associated with that estimate

enhanced crystal fabric analysis of a lava flow sample by neutron texture diffraction a case study from the castello d ischia dome 1 the crystal fabric of a lava has been analyzed for the first time by neutron texture diffraction in this study we quantitatively investigate the crystallographic preferred orientation of feldspars in the castello d ischia ischia island italy trachytic exogenous dome the crystallographic preferred orientation was measured with the monochromatic neutron texture diffractometer sv7 at the forschungszentrum julich in germany and a rietveld refinement was applied to the sum diffraction pattern the complementary thin section analysis showed that the three dimensional crystal shape and the corresponding shape preferred orientation are in agreement with the quantitative orientation distributions of the neutron texture data the 0k0 crystallographic planes of the feldspars are roughly parallel to the local flow bands whereas the other corresponding pole figures show that a pivotal rotation of the anorthoclase and sanidine crystals was active during the emplacement of this lava dome in combination with scanning electron microscopy investigations electron probe microanalysis xrf and x ray diffraction the rietveld refinement of the neutron diffraction data indicates a slow cooling dynamic on the order of several months during their crystallization under subaerial conditions results attained here demonstrate that neutron texture diffraction is a powerful tool that can be applied to lava flows

in situ identification of high vertical stress areas in an underground coal mine panel using seismic refraction tomography abstract because high stress anomalies can induce dynamic failures in the underground panels of coal mines the identification of high stress areas is critically important for mining safety we have identified areas of high vertical stress of an in situ longwall panel with seismic refraction tomography and interpreted our results using rock physics models constrained by core measurements since p and s velocities in rocks are stress sensitive mapping of them can provide useful information to identify areas of potential high stress we have inverted p and s velocities of main roof of an in situ panel with refraction tomography and converted them into vertical stress estimates using a calibration function from core measurements those estimates are classified into three groups high medium and low respectively identified zones of high vertical stress show qualitative agreement with monitored in panel microseismic data zones derived from p waves give a more plausible assessment than s waves we also discuss the link between high vertical stress areas and in panel faults because of the impact of the regional stress field and previously mined out voids the existing fault zone affects the redistribution of vertical stress in the underground panel

investigation of borehole cross dipole flexural dispersion crossover through numerical modeling crossover of the dispersion of flexural waves recorded in borehole cross dipole measurements is interpreted as an indicator of stress induced anisotropy around a circular borehole in formations that are isotropic in the absence of stresses we have investigated different factors that influence flexural wave dispersion through numerical modeling we determined that for a circular borehole surrounded by an isotropic formation that is subjected to an anisotropic stress field the dipole flexural dispersion crossover is detectable only when the formation is very compliant this might happen only in the shallow subsurface or in zones having high pore pressure however we found that dipole dispersion crossover can also result from the combined effect of formation intrinsic anisotropy and borehole elongation we found that a small elongation on the wellbore and very weak intrinsic anisotropy can result in a resolvable crossover in flexural dispersion that might be erroneously interpreted as borehole stress induced anisotropy a thorough and correct interpretation of flexural dispersion crossover thus has to take into account the effects of stress induced and intrinsic anisotropy and borehole cross sectional geometry

experimental na k exchange between alkali feldspar and an nacl kcl salt melt chemically induced fracturing and element partitioning the exchange of na and k between alkali feldspar and a nacl kcl salt melt has been investigated experimentally run conditions were at ambient pressure and 850 c as well as 1 000 c cation exchange occurred by interdiffusion of na and k on the feldspar sub lattice while the si al framework remained unaffected due to the compositional dependence of the lattice parameters compositional heterogeneities resulting from na k interdiffusion induced coherency stress and associated fracturing depending on the sense of chemical shift different crack patterns developed for the geometrically most regular case that developed when potassic alkali feldspar was shifted toward more sodium rich compositions a prominent set of cracks corresponding to tension cracks opened perpendicular to the direction of maximum tensile stress and did not follow any of the feldspar cleavage planes the critical stress needed to initiate fracturing in a general direction of the feldspar lattice was estimated at 0 35 gpa fracturing provided fast pathways for penetration of salt melt or vapor into grain interiors enhancing overall cation exchange the na k partitioning between feldspar and the salt melt attained equilibrium values in the exchanged portions of the grains allowing for extraction of the alkali feldspar mixing properties

effects of borehole stress concentration on elastic wave velocities in sandstones the stress redistribution that occurs in the vicinity of a borehole may lead to damage or failure of the rock if the vertical stress is a principal stress the principal stresses at the wall of a vertical well are the hoop radial and vertical stresses the hoop stress varies with position around the wellbore and takes its maximum compressive value at the azimuth of the far field minimum horizontal stress this may lead to compressive failure at this azimuth if the compressive strength of the rock is exceeded recent developments in sonic logging allow the variation in elastic wave velocities with radius and azimuth around a borehole to be characterized since elastic wave velocities in sandstones are sensitive to changes in stress owing to the presence of stress sensitive grain boundaries within the rock this allows the changes in stress to be monitored an expansion of the elastic compliance of the grain boundaries to first order in stress shows that a radially polarized vertically propagating shear wave is more sensitive to radial stress than to hoop stress close to the wellbore however large changes in stress occur and any nonlinearity in the variation in compliance of the grain boundaries as a function of stress becomes important this nonlinearity increases the sensitivity to the wellbore pressure and can cause significant reductions in the velocity of compressional and shear waves in the vicinity of the wellbore

remote sensing of wave roller lengths in the laboratory 1 the optical intensity signals from surf zone waves in a laboratory flume are analyzed using several different phase averaging techniques and a methodology is developed for estimating wave roller lengths and local wave dissipation the intensity signals i e phase averaged intensity profiles of individual breaking waves are compared with the wave profiles measured by in situ wave gauges and the optical signal of the wave roller is shown to ramp up from the toe of the wave roller on the front face of the wave to a maximum intensity at the wave crest the remote sensing observations capture the growth equilibrium and decay phases of the roller as it propagates over a fixed bed arranged in a bar trough morphology next for the regular wave conditions considered here the local maxima of the phase averaged intensities are shown to better indicate the initial onset of wave breaking and the occurrence of wave breaking in the bar trough as compared to the more commonly used time averaged mean intensity in addition the phase averaged profiles are used to measure the size of the roller and these measurements are compared to previous observations of smaller scale rollers in equilibrium the observed roller lengths are shown to agree with predictions from a wave roller model and to provide a new physical link between the remotely sensed signal and roller dissipation finally as an example application of these new data a simple wave height inversion model is presented that allows an estimation of surf zone wave heights from the remotely sensed roller lengths

video imaged surf zone wave and roller structures and flow fields 1 the measurement of mean water levels roller geometries and phase ensemble averaged velocity and turbulence intensity fields under spilling and plunging waves breaking in a two dimensional laboratory surf zone is presented the velocities were measured using digital correlation image velocimetry while water levels and roller geometries were determined through gray scale filtering of video images the phase ensemble averaged horizontal and vertical components of velocity and turbulence intensities are measured throughout the entire flow domain including the wave roller area by utilizing the aerated areas as part of the flow structure the time averaged horizontal velocities undertow turbulence intensities and turbulent kinetic energies are determined by averaging across the wave phase turbulence magnitudes are found to compare favorably with existing laser doppler anemometry measurements below the wave trough level where such measurements have generally been confined because of aeration contamination effects the significantly higher velocity and turbulence intensity magnitudes measured above the trough level in the present experiments highlight the novel nature of the present investigation for describing flow regimes in the surf zone