warming of global abyssal and deep southern ocean waters between the 1990s and 2000s contributions to global heat and sea level rise budgets abyssalglobalanddeepsouthern oceantemperature trendsarequantifiedbetweenthe1990sand2000sto assesstheroleofrecentwarmingoftheseregionsin globalheatandsealevelbudgets theauthors1 compute warming rates with uncertainties along 28 full depth high quality hydrographic sections that have been occupied two or more times between 1980 and 2010 2 divide the global ocean into 32 basins defined by the topography and climatological ocean bottom temperatures and then 3 estimate temperature trends in the 24 sampled basins the three southernmost basins show a strong statistically significant abyssal warming trend with that warming signal weakening to the north in the central pacific western atlantic and eastern indian oceans eastern atlantic and western indian ocean basins show statistically insignificant abyssal cooling trends excepting the arctic ocean and nordic seas the rate of abyssal below 4000 m global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0 027 60 009 w m 22 applied over the entire surface of the earth deep 1000 4000 m warming south of the subantarctic front of the antarctic circumpolar current adds 0 068 60 062 w m 22 the abyssal warming produces a 0 053 60 017 mm yr 21 increase in global average sea level and the deep warming south of the subantarctic front adds another 0 093 60 081 mm yr 21 thus warmingin theseregions ventilatedprimarilyby antarcticbottomwater accounts for a statistically significant fraction of the present global energy and sea level budgets

modeling basin scale internal waves in a stratified lake basin scale internal waves provide the driving forces for vertical and horizontal fluxes in a stratified lake below the wind mixed layer thus correct modeling of lake mixing and transport requires accurate modeling of basin scale internal waves examining this capability with a hydrostatic z coordinate three dimensional 3d numerical model at coarse grid resolutions is the focus of this paper it is demonstrated that capturing the correct thermocline forcing with a 3d mixed layer model for surface dynamics results in a good representation of low frequency internal wave dynamics the 3d estuary and lake computer model elcom is applied to modeling lake kinneret israel and is compared with field data under summer stratification conditions to identify and illustrate the spatial structure of the lowest mode basin scale kelvin and poincarewaves that provide the largest two peaks in the internal wave energy spectra the model solves the unsteady reynolds averaged navier stokes equations using a semi implicit method similar to the momentum solution in the trim code with the addition of quadratic euler lagrange dis cretization scalar e g temperature transport using a conservative flux limited approach and elimination of vertical diffusion terms in the governing equations a detailed description is provided of turbulence closure for the vertical reynolds stress terms and vertical turbulent transport using a 3d mixed layer model parameterized on wind and shear energy fluxes instead of the convential eddy viscosity diffusivity assumption this approach gives a good representation of the depth of the mixed layer at coarse vertical grid resolutions that allows the internal waves to be energized correctly at the basin scale wind stresses surface heating and density currents form the driving energy fluxes of a stratified lake the basin scale energy flux from the wind is of particular interest because of its dominant role in setting the thermocline in motion which in the absence of inflows and outflows is the primary energy store for transport and mixing below the wind mixed layer thus modeling the basin scale internal wave behavior is an a priori requirement to modeling and quantifying the flux paths of nutrients in a stratified lake imberger 1994 this paper takes a first step in this direction by analyzing our ability to model basin scale internal waves that are seen in lake kinneret israel energy flux path in a stratified lake energy flux through a stratified lake has a fundamental dependence on forced and free baroclinic motions the wind imparts both momentum and turbulent kinetic energy tke to the water in the sur face layer the tke distributes momentum vertically in the

post processing removal of correlated errors in grace data 1 gravity fields produced by the gravity recovery and climate experiment grace satellite mission require smoothing to reduce the effects of errors present in short wavelength components as the smoothing radius decreases these errors manifest themselves in maps of surface mass variability as long linear features generally oriented north to south i e stripes the presence of stripes implies correlations in the gravity field coefficients here we examine the spectral signature of these correlated errors and present a method to remove them finally we apply the filter to a model of surface mass variability to show that the filter has relatively little degradation of the underlying geophysical signals we seek to recover

lithological control on shear wave velocity anisotropy in core samples from the taiwan chelungpu fault drilling project abstract the present study provides laboratory constrains on the in situ source of shear wave birefringence in siltstone and sandstone lithologies from the taiwan chelungpu fault drilling project tcdp bench top measurements at ambient pressure and temperature are performed across the end faces of vertically drilled samples while the polarization angle of the source and receiver is rotated from 0 to 360 in azimuth shear wave birefringence in siltstone is low 3 5 and controlled by low angle 30 bedding dip the sandstone samples exhibit moderate 15 shear wave anisotropy due to a network of vertical microcracks with normal about the bedding strike direction as related studies infer that the microcracks responsible for shear wave birefringence in sandstone are also open at depth our results suggest that anisotropy in borehole measurements can simply be accounted for by the observed siltstone and sandstone microstructures i e without invoking larger scale objects nor randomly oriented cracks fractures subjected to triaxial stress state

experimental determination of elastic constants of oshima granite barre granite and chelmsford granite employing polyhedral specimens longitudinal and shear wave velocities were measured in various directions of propagation and polarization sound velocities showed orthorhombic elasticity in all of the rocks with the assumption of orthorhombic elasticity the nine stiffness constants of all samples were determined by the sound velocities under atmospheric pressure and kelvin christoffel s equation twenty one stiffness constants of oshima granite determined without assuming any symmetry also showed orthorhombic features directions of the symmetry axes agreed well with the orientation of the preexisting cracks akaike s information criterion showed that the orthorhombic model with nine nonzero elastic stiffnesses was better than the model having 21 nonzero elastic stiffnesses for oshima granite the polyhedrons of two granitic rocks were loaded under hydrostatic pressure all components of the stiffness constants increased with pressure under pressure of more than 120 mpa two granitic rocks were approximately isotropic the results show that oriented microcracks are mainly responsible for the orthorhombic elasticity of the granitic rocks and also indicate that dry oriented cracks can not be a cause for the anisotropic elasticity of granites at depths of more than 6 8 km

velocity anisotropy of upper jurassic organic rich shales norwegian continental shelf abstractthis study investigates the seismic velocity anisotropy of two organic rich shales from the norwegian continental shelf the tested organic rich shale samples were from the upper jurassic draupne and hekkingen formations collected from two wells 16 8 3s and 7125 1 1 drilled in the central north sea and western barents sea respectively the two tested shales are different in organic matter richness and thermal maturation and they have experienced different burial histories the shale core plugs were tested in a triaxial cell under controlled pore pressure seismic velocities vp and vs were measured along different orientations with respect to layering to identify the complete tensor of the rock elastic moduli and to investigate the velocity anisotropy as a function of increasing effective stress the measured velocity values exhibit strong anisotropy for the two tested organic rich shales the anisotropy for both shales is strongest for vs seismic velocities follow an increasing trend as th

earthquake prediction a new physical basis summary subcritical crack growth in the laboratory occurs slowly but progressively in solids subjected to low stresses at low strain rates the cracks tend to grow parallel to the maximum compressive stress so that when this stress is aligned over a large enough region the cracks will also be aligned and possess effective seismic anisotropy it is suggested that such subcritical crack growth produces extensive dilatancy anisotropy eda throughout earthquake preparation zones this process is a possible driving mechanism for earthquake precursors observed at substantial distances from impending focal zones and provides in the shear wave splitting which has been observed in several seismic regions a possible technique for monitoring the build up of stress before earthquakes

inference of mantle viscosity from grace and relative sea level data summary gravity recovery and climate experiment grace satellite observations of secular changes in gravity near hudson bay and geological measurements of relative sea level rsl changes over the last 10 000 yr in the same region are used in a monte carlo inversion to infer mantle viscosity structure the grace secular change in gravity shows a significant positive anomaly over a broad region 3000 km near hudson bay with a maximum of 2 5 gal yr 1 slightly west of hudson bay the pattern of this anomaly is remarkably consistent with that predicted for postglacial rebound using the ice 5g deglaciation history strongly suggesting a postglacial rebound origin for the gravity change we find that the grace and rsl data are insensitive to mantle viscosity below 1800 km depth a conclusion similar to that from previous studies that used only rsl data for a mantle with homogeneous viscosity the grace and rsl data require a viscosity between 1 4 1021 and 2 3 1021 pa s an inversion for two mantle viscosity layers separated at a depth of 670 km shows an ensemble of viscosity structures compatible with the data while the lowest misfit occurs for upper and lower mantle viscosities of 5 3 1020 and 2 3 1021 pa s respectively a weaker upper mantle may be compensated by a stronger lower mantle such that there exist other models that also provide a reasonable fit to the data we find that the grace and rsl data used in this study cannot resolve more than two layers in the upper 1800 km of the mantle

ultrasonic velocity and shear wave splitting behavior of a colton sandstone under a changing triaxial stress ultrasonic experiments on a dry colton sandstone placed in a triaxial pressure machine show that effective stress changes lead to distinct anisotropic velocity changes in compressional waves and shear waves the stress imprint can be recognized from the associated velocity pattern by relating the velocities to the three normal stress directions the ultrasonic velocities indicate that the sensitivity of the different waves to stress predominantly depends on stresses applied in the polarization and propagation directions of the particular wave mode also stress induced changes in shear wave splitting are observed

time variable ice loss in asian high mountains from satellite gravimetry abstract substantial amount of glacial ice is considered to be melting in the asian high mountains gravimetry by grace satellite during 2003 2009 suggests the average ice loss rate in this region of 47 12 gigaton gt yr 1 equivalent to 0 13 0 04 mm yr 1 sea level rise this is twice as fast as the average rate over 40 years before the studied period and agrees with the global tendency of accelerating glacial loss such ice loss rate varies both in time and space mass loss in himalaya is slightly decelerating while those in northwestern glaciers show clear acceleration uncertainty still remains in the groundwater decline in northern india and proportion of almost isostatic e g tectonic uplift and non isostatic e g glacial isostatic adjustment portions in the current uplift rate of the tibetan plateau if gravity increase associated with ongoing glacial isostatic adjustment partially canceled the negative gravity trend the corrected ice loss rate could reach 61 gt yr 1

stress induced seismic azimuthal anisotropy sand shale content and depth trends offshore north west australia abstractseismic azimuthal anisotropy is apparent when p wave velocities vary with source receiver azimuth and downward propagating s waves split into two quasi s waves polarized in orthogonal directions not accounting for these effects can degrade seismic image quality and result in erroneous amplitude analysis and geologic interpretations there are currently no physical models available to describe how azimuthal anisotropy induced by differential horizontal stress varies with sand shale lithology and depth we develop a model that does so in unconsolidated sand shale sequences offshore north west australia our method naturally introduces two new concepts critical anisotropy and anisotropic depth limit critical anisotropy is the maximum amount of azimuthal anisotropy expected to be observed at the shallowest sediment burial depth where the confining pressure and sediment compaction are minimal the anisotropic depth limit is the maximum depth where the stress induced azimuthal anisotropy is ex

improved methods for observing earth s time variable mass distribution with grace using spherical cap mascons we discuss several classes of improvements to gravity solutions from the gravity recovery and climate experiment grace mission these include both improvements in background geophysical models and orbital parameterization leading to the unconstrained spherical harmonic solution jpl rl05 and an alternate jpl rl05m mass concentration mascon solution benefitting from those same improvements but derived in surface spherical cap mascons the mascon basis functions allow for convenient application of a priori information derived from near global geophysical models to prevent striping in the solutions the resulting mass flux solutions are shown to suffer less from leakage errors than harmonic solutions and do not necessitate empirical filters to remove north south stripes lowering the dependence on using scale factors the global mean scale factor decreases by 0 17 to gain accurate mass estimates ocean bottom pressure obp time series derived from the mascon solutions are shown to have greater correlation with in situ data than do spherical harmonic solutions increase in correlation coefficient of 0 08 globally particularly in low latitude regions with small signal power increase in correlation coefficient of 0 35 regionally in addition to reducing the error rms with respect to the in situ data reduction of 0 37 cm globally and as much as 1 cm regionally greenland and antarctica mass balance estimates derived from the mascon solutions agree within formal uncertainties with previously published results computing basin averages for hydrology applications shows general agreement between harmonic and mascon solutions for large basins however mascon solutions typically have greater resolution for smaller spatial regions in particular when studying secular signals

modelling the compliance of crustal rock ii response to temporal changes before earthquakes summary there have been several claims that seismic shear waves respond to changes in stress before earthquakes the companion paper develops a stress sensitive model ape for the behaviour of low porosity low permeability crystalline rocks containing pervasive distributions of fluid filled intergranular microcracks and this paper uses ape to model the behaviour before earthquakes modelling with ape shows that the microgeometry and statistics of distributions of such fluid filled microcracks respond almost immediately to changes in stress and that the behaviour can be monitored by analysing seismic shear wave splitting the physical reasons for the coupling between shear wave splitting and differential stress are discussed in this paper we extend the model by using percolation theory to show that large crack densities are limited at the grain scale level by the percolation threshold at which interacting crack clusters lead to pronounced increases in rock matrix permeability in the simplest formulation the modelling is dimensionless and almost entirely constrained without free parameters nevertheless ape modelling of the evolution of fluid saturated rocks under stress reproduces the observed fracture criticality and the narrow range of shear wave azimuthal anisotropy in crustal rocks it also reproduces the behaviour of temporal variations in shear wave splitting observed before and after the 1986 m 6 north palm springs earthquake southern california and several other smaller earthquakes the agreement of ape modelling with a wide range of observations confirms that fluid saturated crystalline rocks are stress sensitive and respond to changes in stress by critical fluid rock interactions at the microscale level this means that the effects of changes in stress and other parameters can be numerically modelled and monitored by appropriate observations of seismic shear waves

closing the sea level rise budget with altimetry argo and grace 1 an analysis of the steric and ocean mass components of sea level shows that the sea level rise budget for the period january 2004 to december 2007 can be closed using corrected and verified jason 1 and envisat altimetry observations of total sea level upper ocean steric sea level from the argo array and ocean mass variations inferred from grace gravity mission observations we find that the sum of steric sea level and the ocean mass component has a trend of 1 5 1 0 mm a over the period in agreement with the total sea level rise observed by either jason 1 2 4 1 1 mm a or envisat 2 7 1 5 mm a within a 95 confidence interval

seismic anisotropy in sedimentary rocks part 1 a single plug laboratory method a single plug method for measuring seismic velocities and transverse isotropy in rocks has been rigorously validated and laboratory tested the method requires only one sample to measure the velocities needed to derive the five independent elastic constants for transversely isotropic materials in this method piezoelectric transducers are fitted to the top bottom and sides of the cylindrical sample laboratory velocity and anisotropy can be measured as functions of pressure temperature fluid saturation and fluid displacement because this method uses a horizontal core plug that has much higher permeability than a vertical core plug it is especially suitable for low permeability shale measurements it reduces the sample preparation and velocity measurement time by more than two thirds

reflection shear wave data collected near the principal axes of azimuthal anisotropy the presence of vertically oriented fractures and or unequal horizontal stresses has created an azimuthally anisotropic earth in which shear wave sh data collected along the principal axes of the anisotropy display time and reflection amplitude anomalies amoco shot two crossing shear wave sh lines that were approximately parallel to the orthogonal principal axes of the azimuthal anisotropy at the tie point these crossing sh lines display a time variant mis tie the tie point also displays reflection coefficient anomalies attributable to azimuthally dependent shear wave velocities field mapping documented a set of fractures striking n69e which are approximately parallel to the line that exhibited greater traveltimes time variant mis ties and reflection coefficient anomalies are two of the seismic responses theoretically expected of an azimuthally anisotropic earth i e one in which the shear wave velocity depends upon the polarization azimuth of the shear wave

comment on ocean mass from grace and glacial isostatic adjustment by d p chambers et al 1 the modern global theory of the glacial isostatic adjustment gia process is a theory that directly addresses the extent to which the geoid of classical geodesy is impacted by this phenomenon because the geoid is by conventional definition the surface of constant potential that overlaps the surface of the sea in the absence of currents and tides we may determine the impact of the gia process upon it only by explicit analysis of the manner in which mass is redistributed among the ocean basins and the level of the sea is thereby influenced although the dominant contribution to gia is that associated with the transfer of mass between the oceans and the continents there is an additional influence due to the variations in earth s rotational state this influence feeds back onto the geoid in the recent paper by chambers et al 2010 several arguments were presented that question earlier attempts to discuss the consequences of this feedback these arguments are interesting and we address them in what follows

grace s spatial aliasing error summary the grace satellite mission provides a near continuous sequence of approximately 30 d gravity field solutions in the form of spherical harmonics sh because sh functions are global while grace measurements are sensitive mainly to variations along the ground track undersampling alias contamination occurs here we investigate how geophysical signals are likely to cause alias error in grace gravity fields we use actual grace orbits and systematically sample several types of time varying signals that might represent either errors in geophysical models such as tide models or unmodelled geophysical signals we show how error in semi diurnal tides like s 2 can alias into long period variations in particular harmonics particularly as a possible error source in the degree 2 order 0 term c 20 of grace fields we also show that aliasing associated with non tidal geophysical model errors is significant at order 15 or multiples of 15 due to the grace ground track spacing in longitude this can be predicted from kaula s resonance formula and might be reduced by suppressing amplitudes of affected harmonics

computations of the viscoelastic response of a 3 d compressible earth to surface loading an application to glacial isostatic adjustment in antarctica and canada s u m m a r y we develop a 3 d finite element model to study the viscoelastic response of a compressible earth to surface loads the effects of centre of mass motion polar wander feedback and selfconsistent ocean loading are implemented to assess the model s accuracy we benchmark the numerical results against a semi analytic solution for spherically symmetric structure we force our model with the ice 5g global ice loading history to study the effects of laterally varying viscosity structure on several glacial isostatic adjustment gia observables including relative sea level rsl measurements incanada and present day time variable gravity and uplift rates in antarctica canadian rsl observations have been used to determine the earth s globally averaged viscosity profile antarcticgps uplift rates have been used to constrainantarcticgia models and gia time variable gravity and uplift signals are error sources for grace and altimeter estimates of present day antarctic ice mass loss and must be modelled and removed from those estimates computinggia results for a 3 d viscosity profile derived from a realistic seismic tomography model and comparing with results computed for 1 d averages of that 3 d profile we conclude that 1 a gia viscosity model based on canadian relative sea level data is more likely to represent a canadian average than a true global average 2 the effects of 3 d viscosity structure on grace estimates of present day antarctic mass loss are probably smaller than the difference between gia models based on different antarctic deglaciation histories and 3 the effects of 3 d viscosity structure on antarctic gps observations of present day uplift rate can be significant and can complicate efforts to use gps observations to constrain 1 d gia models

long term and seasonal caspian sea level change from satellite gravity and altimeter measurements we examine recent caspian sea level change by using both satellite radar altimetry and satellite gravity data the altimetry record for 2002 2015 shows a declining level at a rate that is approximately 20 times greater than the rate of global sea level rise seasonal fluctuations are also much larger than in the world oceans with a clearly defined geographic region and dominant signal magnitude variations in the sea level and associated mass changes provide an excellent way to compare various approaches for processing satellite gravity data an altimeter time series derived from several successive satellite missions is compared with mass measurements inferred from gravity recovery and climate experiment grace data in the form of both spherical harmonic sh and mass concentration mascon solutions after correcting for spatial leakage in grace sh estimates by constrained forward modeling and accounting for steric and terrestrial water processes grace and altimeter observations are in complete agreement at seasonal and longer time scales including linear trends this demonstrates that removal of spatial leakage error in grace sh estimates is both possible and critical to improving their accuracy and spatial resolution excellent agreement between grace and altimeter estimates also provides confirmation of steric caspian sea level change estimates grace mascon estimates both the jet propulsion laboratory jpl coastline resolution improvement version 2 solution and the center for space research csr regularized are also affected by leakage error after leakage corrections both jpl and csr mascon solutions also agree well with altimeter observations however accurate quantification of leakage bias in grace mascon solutions is a more challenging problem

space geodesy constrains ice age terminal deglaciation the global ice 6g_c vm5a model a new model of the last deglaciation event of the late quaternary ice age is here described and denoted as ice 6g c vm5a it differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available global positioning system gps measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal additional space geodetic constraints have also been applied to specify the reference frame within which the gps data are described the focus of the paper is upon the three main regions of last glacial maximum ice cover namely north america northwestern europe eurasia and antarctica although greenland and the british isles will also be included if peripherally in the discussion in each of the three major regions the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the gravity recovery and climate experiment satellites as an independent means of verifying the improvement of the model achieved by applying the gps constraints several aspects of the global characteristics of this new model are also discussed including the nature of relative sea level history predictions at far field locations in particular the caribbean island of barbados from which especially high quality records of postglacial sea level change are available but which records were not employed in the development of the model although ice 6g c vm5a is a significant improvement insofar as the most recently available gps observations are concerned comparison of model predictions with such far field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration

mass transport between a semienclosed basin and the ocean maracaibo system 1 field data and three dimensional numerical estuary and lake computer model simulations are used to investigate exchange between lake maracaibo and the gulf of venezuela this exchange occurs along a dredged shipping lane 100 km long and 14 m deep it is driven by a density difference between the lake and gulf and modulated at tidal and subtidal timescales by water level fluctuations in the gulf propagating to the lake at tidal frequencies exchange is modulated by barotropic forcing and nonlinear baroclinic response leading to a severance of high salinity bottom water into seaward and landward segments bottom water in the landward segment is moved lakeward along the shipping lane where it is mixed vertically and flushed out subtidal water level fluctuations in the gulf force barotropic currents along the shipping lane dominating variability of volume and salt flux at timescales of 1 4 weeks the barotropic component of simulated salt flux decreases from the gulf to the lake as depth averaged salinity decreases while simulated baroclinic exchange is only 20 of that predicted by quasi steady two layer hydraulic theory these reductions in salt flux are due to intense mixing that occurs throughout the shipping lane

measurements of time variable gravity show mass loss in antarctica using measurements of time variable gravity from the gravity recovery and climate experiment satellites we determined mass variations of the antarctic ice sheet during 2002 2005 we found that the mass of the ice sheet decreased significantly at a rate of 152 80 cubic kilometers of ice per year which is equivalent to 0 4 0 2 millimeters of global sea level rise per year most of this mass loss came from the west antarctic ice sheet

patagonia icefield melting observed by gravity recovery and climate experiment grace 1 using recently released reprocessed gravity solutions from the gravity recovery and climate experiment grace we estimate the ice loss rate for the patagonia icefield pif of south america for the period april 2002 through december 2006 after postglacial rebound and hydrological effects are corrected the estimated rate is 27 9 11 km 3 year equivalent to an average loss of 1 6 m year ice thickness change if evenly distributed over the entire pif area the estimated contribution to global sea level rise is 0 078 0 031 mm year this is an independent confirmation of relatively large melting rate estimates from earlier studies employing topographic and cartographic data

tidal and subtidal water volume exchange in an estuarine system abstract estuarine water movements occur over a broad range of time scales in this study moored current meter data were used to investigate water volume exchange in the tidal passes of lake pontchartrain louisiana on the tidal and subtidal time scales a calibration technique employing cross channel measurements of water velocity was used to calibrate the moored current meters thus allowing for calculation of volume flow over a 35 day period the local diurnal tide accounted for 50 of the total volume exchange the rest being due to subtidal events frontal passage this subtidal exchange occurs primarily as large scale events characterized by volume fluxes up to six times greater than the normal tidal prism neglecting this subtidal component in the determination of the volume fluxes for a system such as lake pontchartrain could result in substantial underestimation by as much as 50 of these volume and their corresponding material fluxes

elastic anisotropy of shales accompanying the resource potential of gas shales is a new interest in understanding the physical and petrophysical properties of shales shale by geochemical or stratigraphic measures is arguably the most common lithology encountered in sedimentary basins despite this shales remain little studied while engineers and explorationists focused on conventional reservoirs geophysicists did this knowing full well that often a reflection coefficient from a reservoir was controlled by the shale properties of the cap rock we compensated for this ignorance by arguing that shales are deposited in deepwater environments in which lateral and vertical changes are slow and therefore inconsequential we further compounded this ignorance by assuming that the shales were isotropic an example of the consequences of this ignorance was clearly documented by margesson and sondergeld 1999 engineers share culpability for this ignorance too since most of the drilling problems occur in shales and most of the lithologies d

stress in the earth s crust the link between crustal fluids and extensive dilatancy anisotropy observations of seismic shear wave splitting birefringence along almost all raypaths in the earth9s crust have led to the recognition that the fluid filled cracks microcracks and pores known to pervade most rocks in the crust have been preferentially aligned by the prevailing stress field this phenomenon is known as extensive dilatancy anisotropy or eda and the fluid filled microstructures as eda cracks because the seismic effects can be modelled by distributions of parallel cracks the effects of these stress aligned eda cracks have been observed in many different areas and they appear ubiquitous in the upper 10 to 20 km of the crust many details of the crack geometry and the current stress field can be readily determined from records of the shear waves which have propagated through these aligned cracks in separate studies geochemists have confirmed the presence of microscopic fluid filled cavities in almost all geological material these are referred to as fluid inclusions and provide unequivocal evidence of crustal fluid circulation often along stress controlled fractures different stress episodes can be recognized in many rock samples and studies of fluid inclusions can be used to interpret the palaeo stress history of a rock where the in situ morphology of these inclusions is related to the current regional stress field this paper discusses the relationship between the fluid inclusions of the geochemical literature and eda cracks and concludes that the former may be regarded as one of the constituent inclusion types of extensive dilatancy anisotropy

the pole tide and its effect on grace time variable gravity measurements implications for estimates of surface mass variations gravity recovery and climate experiment grace provides monthly solutions for the earth s gravity field in the form of spherical harmonic coefficients these can be used to infer changes in mass at the earth s surface the pole tide the response of the earth and oceans to polar motion causes gravity signals dominated by harmonics of degree 2 order 1 if the pole tide is not removed from grace data it affects the coefficients of those harmonics c21 s21 and introduces errors when using those coefficients to determine surface mass variations the pole tide is partially removed by grace processing centers before solving for the gravity field but long period pole tide signals are not usually included in the grace pole tide correction and so those signals are still present in the grace coefficients we discuss this issue from the standpoint of somebody who uses the grace gravity fields to infer changes in surface mass we arrive at a recommendation for an optimal grace pole tide correction we describe how to modify the c21 s21 coefficients provided by the processing centers so that they conform with our recommendation we discuss the size of the pole tide contributions to c21 s21 compared to those of the direct load induced contributions as an example we show how an incompletely removed pole tide can impact grace results for the trend in ocean mass we consider the impact of mantle anelasticity on long period pole tide corrections and conclude that it is unlikely to affect those corrections by more than 20

anisotropic elastic moduli of carbonates and evaporites from the weyburn midale reservoir and seal rocks assuming vertical transverse isotropy vti symmetry the elastic anisotropy as a function of confining pressure of four carbonates and one evaporite from the williston sedimentary basin in saskatchewan canada is investigated using the ultrasonic pulse transmission method ultrasonic p and s wave velocities are obtained from cylindrical plugs cut from a main sample along horizontal vertical and 45 orientations with respect to the sample s presumed vertical axis of symmetry the elastic constants were then calculated from the measured velocities and densities anisotropy was quantified by estimating thomsen parameters thomsen 1986 from elastic constants the results show that the samples are at the best weakly anisotropic the presence of microcracks and pores as well as the heterogeneity of the samples play an important role in defining the p and s wave velocities the weak anisotropy found in these samples suggests that intrinsic properties of these rocks negligibly contribute to the anisotropy observed at the seismic scale

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

velocity anisotropy and attenuation of shale in under and overpressured conditions the seismic velocity and attenuation of fully saturated shales were measured for the first time under overpressured conditions using the ultrasonic reflection technique shale cores from naturally overpressured horizons in the north sea were tested in the laboratory at confining and pore pressures relevant to in situ conditions a single frequency tone burst pulse wave was used to determine the seismic wave velocities and quality factors of the shale samples with errors less than 0 3 and 0 1 db cm respectively at a frequency of 0 75 mhz sample length changes with varying confining and pore pressure were measured and the pore pressure equilibration time was monitored for each sample the anisotropy of the seismic attributes vp vs qp and qs was determined over a range of differential pressures from 5 to 60 mpa with respect to the predominant foliation the ultrasonic velocity data followed a transversely isotropic pattern depending on the direction of wave propagation with respect to the laminations the poisson s ratio was found to rise by 5 as the shale material progressed from a normally pressured to an overpressured state the quality factor q characteristics were interpreted in terms of pore geometry and connectivity as well as the directional permeability of the transversely isotropic shale material the results were converted to bulk and shear loss modulus defects and a positive bulk loss was observed for waves propagating perpendicular to the lamination plane even above differential pressures of 20 mpa this indicates different levels of biot flow and squirt flow attenuation mechanisms acting within the shale structure depending on the wave propagation and vibration directions

shear wave velocity anisotropy in sedimentary rocks a laboratory study a systematic laboratory study of shear wave velocity anisotropy in sedimentary rocks has been carried out as a function of both hydrostatic and uniaxial stress the presence of shear wave velocity anisotropy in sedimentary rocks was confirmed by transmitting a polarized shear wave in a rock sample and receiving a signal on an orthogonally polarized receiver the magnitude of the observed velocity anisotropy is dependent upon the magnitude and nature of the applied stress and the lithology of the rock sample shales exhibit significant velocity anisotropy independent of both uniaxial and hydrostatic stress which suggests the presence of preferentially aligned minerals sandstones also exhibit significant velocity anisotropy but the anisotropy is strongly dependent upon the stress hydrostatic stress was found to diminish the velocity anisotropy and uniaxial stress was found to enhance it this implies the presence of preferentially oriented cracks limestones exhibit weak velocity anisotropy these laboratory observations may be helpful in in situ identification of lithology

texture development in naturally compacted and experimentally deformed silty clay sediments from the nankai trench and forearc japan the petrophysical properties of fine grained marine sediments to a large extent depend on the microstructure and crystallographic preferred orientations cpos in this contribution we show that rietveld based synchrotron texture analysis is a new and valuable tool to quantify textures of water saturated fine grained phyllosilicate rich sediments and assess the effects of compaction and tectonic deformation we studied the cpo of compositionally almost homogeneous silty clay drillcore samples from the nankai accretionary prism slope and the incoming philippine sea plate offshore sw japan basal planes of phyllosilicates show bedding parallel alignment increasing with drillhole depth thus reflecting progressive burial and compaction in some samples calcite and albite display a cpo due to crystallographically controlled non isometric grain shapes or nannofossil tests consolidated undrained experimental deformation of a suite of thirteen samples from the prism slope shows that the cpos of phyllosilicate and calcite basal planes develop normal to the experimental shortening axis there is at least a qualitative relation between cpo intensity and strain magnitude scanning electron micrographs show concurrent evolution of preferred orientations of micropores and detrital illite flakes normal to axial shortening this indicates that the microfabrics are sensitive strain gauges and contribute to anisotropic physical properties along with the cpo

shear wave splitting and earthquake forecasting seismic shear wave splitting sws monitors the low level deformation of fluid saturated microcracked rock we report evidence of systematic sws changes recorded above small earthquakes monitoring the accumulation of stress before earthquakes that allows the time and magnitude of impending large earthquakes to be stress forecast the effects have been seen with hindsight before some 15 earthquakes ranging in magnitude from an m1 7 seismic swarm event in iceland to the ms7 7 chi chi earthquake in taiwan including a successfully stress forecast of a m5 0 earthquake in sw iceland characteristic increases in sws time delays are observed before large earthquakes which abruptly change to deceases shortly before the earthquake occurs there is a linear relationship between magnitudes and logarithms of durations of both increases and decreases in sws time delays before large impending earthquakes however suitably persistent swarms of small earthquakes are too scarce for routine stress forecasting reliable forecasting requires controlled source cross hole seismics between neighbouring boreholes in stress monitoring sites sms it would be possible to stress forecast damaging earthquakes worldwide by a global network of sms in real time

ocean mass from grace and glacial isostatic adjustment 1 we examine geoid rates and ocean mass corrections from two published global glacial isostatic adjustment gia models both of which have been used in previous studies to estimate ocean mass trends from gravity recovery and climate experiment grace satellite gravity data these two models are different implementations of the same ice loading history and use similar mantle viscosity profiles the model results are compared with each other and with geoid rates determined from grace during august 2002 to november 2009 when averaged over the global ocean the two models have rates that differ by nearly 1 mm yr 1 of ocean mass with the first model giving a correction closer to 2 mm yr 1 and the second closer to 1 mm yr 1 by comparing the two models we have discovered that 50 of the difference is caused by a global land ocean mean in the first model while it is appropriate to include this mean when subtracting gia effects from measurements of sea level change measured by tide gauges or satellite altimetry the mean should not be included when subtracting gia effects from ocean mass variations derived from satellite gravity data when this mean is removed the ocean mass corrections from the two models still disagree by 0 4 mm yr 1 we trace the residual difference to the fact that the first model also has large trends over the ocean related to large rates in its predicted degree 2 order 1 geoid coefficients such oceanic trends are not observed by grace nor are they predicted by the second model and they are shown to be inconsistent with the polar wander rates predicted by the first model itself if these two problems are corrected we find that the two model predictions agree at the 3 level on the basis of this analysis we conclude that the ocean mass correction for grace is closer to 1 mm yr 1 than 2 mm yr 1 although significant uncertainties remain

seismic anisotropy of shales the seismic properties and preferred clay mineral orientation of a suite of shales are investigated using laboratory velocity measurements as a function of confining pressure x ray diffraction techniques and electron microprobe backscatter bse imaging the velocity measurements indicate that these shales are transversely isotropic with the main symmetry axis perpendicular to bedding anisotropy at elevated pressures caused mainly by preferred orientation of clays illite parallel to bedding ranges from 20 vp and 19 vs for a sample of new albany shale to 30 vp and 35 vs for a sample of chattanooga shale the degree of clay mineral alignment in the shales is constrained by orientation indices produced using simple x ray diffraction techniques a strong positive correlation is found between the degree of preferred orientation as expressed in the orientation indices and seismic anisotropy bse images of the shale fabrics confirm in a qualitative manner the results of the x ray study to investigate wave propagation in the shales elastic constants of each sample are calculated and used to produce phase and group wave velocity surfaces which describe variation in velocity as a function of angle to the bedding normal the calculated velocity surfaces constrained by independent velocity measurements display a lack of shear wave splitting at near normal incidence in even the most anisotropic shales for the highly anisotropic chattanooga shales group velocity surfaces differ significantly from corresponding phase velocity surfaces

closure of the budget of global sea level rise over the grace era the importance and magnitudes of the required corrections for global glacial isostatic adjustment abstract the budget of global sea level rise includes contributions from several distinct factors including thermosteric effects the wasting of small ice sheets and glaciers and the loss of mass by the great polar ice sheets and by the continents due to desiccation since the former contribution may be estimated on the basis of both hydrographic survey data and more recently using argo float data the second may be estimated on the basis of mass balance measurements on existing ice fields and the latter on the basis of modern grace based time dependent gravity field measurements the inputs to the globally averaged rate of sea level rise may be directly constrained since grace also provides a measurement of the rate at which mass is being added to the oceans we are now in a position to ask whether this rate of mass addition to the oceans matches the rate at which mass is being removed from the continents as demonstrated herein the mass component of the budget of global sea level is closed within the observational errors when the mass derived contribution is added to the thermosteric contribution it is furthermore shown that the inference of the net rate of global sea level rise by the altimetric satellites topex poseidon and jason 1 is also reconcilable over the grace era it is noted those individual terms in the budget especially the contribution from small ice sheets and glaciers remains insufficiently accurate it is demonstrated that the lingering influence of the late quaternary ice age upon sea level is profound and that closure of the budget requires an accurate model of its impact

sill processes related to deep water renewal in a fjord observations of the gravitational circulation over the sill at the entrance to puget sound indicate a fortnightly modulation of the two layer flow with a corresponding variation in stratification gravitational circulation and stratification reach a maximum during neap tides and a minimum during spring tides the modulation appears to be a function of the turbulence generation by tidal flow over the sill which varies as a function of tidal amplitude the enhanced gravitational circulation during neap tides augments the flux of dense water across the sill region and episodes of bottom water renewal in puget sound result intrusions of dense water in the main basin of the sound show a fortnightly periodicity with a phase lag appropriate for the propagation of an internal bore from the sill region commencing at the neap tide observations indicate that the intrusions take the form of gravity currents propagating at approximately 20 cm s 1 down the main basin the detailed dynamics of the turbulent mixing processes that modulate the onset of inflow were not resolved in this study but the integrated effect of tidal mixing on the low frequency circulation is clearly demonstrated

estimating geocenter variations from a combination of grace and ocean model output 1 in this study we estimate a time series of geocenter anomalies from a combination of data from the gravityrecoveryandclimateexperiment grace satellitemissionandthe outputfromoceanmodels amatrixequationisderivedrelating totalgeocentervariations to the grace coefficients of degrees two and higher and to the oceanic component of the degree one coefficients we estimate the oceanic component from two state of the art ocean models results are compared to independent estimates of geocenter derived from other satellite data such as satellite laser ranging and gps finally we compute degree one coefficients that are consistent with the processing applied to the grace level 2 gravity field coefficients the estimated degree one coefficients can be used to improve estimates of mass variability from grace which alone cannot provide them directly

the deepwater exchange cycle in indian arm british columbia abstract a silled fjord on the british columbia coast indian arm was used to study the exchange processes controlling deepwater exchange in fjords bottom water renewal took place during the winter of 1984 85 hydraulic control of the exchange is exerted over the long sill which restricts access to the fjord the maximum density at the sill occurs during neap tides no distinct peaks in the velocity at the sill are observed during periods of inflow reduced vertical mixing over the long sill during periods of neap tides sets the timing of the bottom water exchange during each inflow over the 1984 85 winter about 20 of the water in the fjord was replaced these exchanges occurred over periods of 5 10 days between the exchange years diffusion of the water in the basin is important in conditioning the water for the next exchange event the vertical diffusion coefficient k t was determined from an analysis of the salinity data and was found to be related to the buoyancy frequency n by the relationship k v n 1 6

seismic anisotropy caused by rock fabric summary as part of an experiment to investigate the influence of cracks produced by tectonic stress on the observed in situ anisotropic properties of crustal rocks at kent cliffs new york the contribution of rock fabric anisotropy was studied using laboratory core sample ultrasonic measurements measured velocities of intact unfractured specimens corrected to lithostatic pressure allow the effect of rock fabric anisotropy to be evaluated computed phase velocity surfaces and wave surfaces show varying degrees of anisotropy at different depths these surfaces predict various anisotropic phenomena such as s wave splitting and anomalous amplitudes and polarizations some predictions can be applied to the case of a general transversely isotropic medium including negligible p wave in contrast to large s wave polarization anomalies generation of cusps in the wave surface by strong anisotropy and the importance of the elastic stiffness coefficient c1133 to the strength of anisotropy computed ray velocities in the borehole axis direction are compared with acoustic logging results the comparison shows reasonable consistency s wave splitting caused by rock fabric for zero offset vertical seismic profiling vsp is also predicted these results can be used to separate the anisotropy caused by cracks and fractures from the overall observed in situ seismic anisotropy

simultaneous estimation of global present day water transport and glacial isostatic adjustment global water transport between oceans and continents during the transition from glacial to interglacial times has been enormous the viscoelastic solid earth has been responding to this unloading of large ice masses with a rise of the land masses in a process termed glacial isostatic adjustment in addition significant changes in the land ocean water distribution occur at present as both present day changes in the ice water thickness and glacial isostatic adjustment affect space geodetic measurements it is difficult to untangle the relative contributions of these two processes here we combine gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure to simultaneously estimate present day water transport and glacial isostatic adjustment we determine their separate contributions to movements in the geocentre which occur in response to changes in the earth s mass distribution with uncertainties below 0 1 mm yr 1 according to our estimates mass losses between 2002 and 2008 in greenland alaska yukon and west antarctica are 104 23 101 23 and 64 32 gt yr 1 respectively our estimates of glacial isostatic adjustment indicate a large geocentre velocity of 0 72 0 06 mm yr 1 in the polar direction we conclude that a significant revision of the present estimates of glacial isostatic adjustments and land ocean water exchange is required present day changes in the thickness of ice sheets and glacial isostatic adjustment both affect space geodetic measurements a combination of gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure allows the simultaneous estimation of present day water transport and glacial isostatic adjustment

tidal dynamics in a coupled ocean lake system abstract barotropic tides were studied in the lake maracaibo system venezuela the system consists of two larger water bodies the gulf of venezuela and lake maracaibo connected by the strait of maracaibo and tablazo bay the dominant semi diurnal tide resonates in the gulf and co oscillates roughly 180 out of phase in the lake the narrow strait and shallow bay regulate their dynamical interaction two and three dimensional finite element models are used in conjunction with a fresh analysis of tidal data at seven stations several of which lie in the strait and bay a coupled model of the whole system is necessary to properly interpret these data which show the influence of small scale near field effects superimposed on the larger scale dynamics of the gulf and lake the detailed geometry at the connections with the gulf and the lake also plays a significant role in the local response in the strait and bay co tidal charts are presented for nine major astronomical and shallow water tidal constituents found in the data the velocity structure derived under simple eddy viscosity assumptions is shown to be highly dynamic a characteristic phase lead is found in velocities at depth and near the shore where vertical shear dominates over inertia in the force balance

processing modelling and predicting time lapse effects of overpressured fluid injection in a fractured reservoir summary time lapse seismology is important for monitoring subsurface pressure changes and fluid movements in producing hydrocarbon reservoirs we analyse two 4 d 3c onshore surveys from vacuum field new mexico usa where the reservoir of interest is a fractured dolomite in phase vi a time lapse survey was acquired before and after a pilot tertiary recovery programme of overpressured co2 injection which altered the fluid composition and the pore fluid pressure phase vii was a similar time lapse survey in the same location but with a different lowerpressure injection regime applying a processing sequence to the phase vi data preserving normal incidence shearwave anisotropy time delays and polarization and maximizing repeatability interval time analysis of the reservoir interval shows a significant 10 per cent change in shear wave velocity anisotropy and 3 per cent decrease in the p wave interval velocities a 1 d model incorporating both saturation and pressure changes is matched to the data the saturation changes have little effect on the seismic velocities there are two main causes of the time lapse changes any change in pore fluid pressures modifies crack aspect ratios additionally when there are overpressures as there are in phase vi there is a 90 change in maximum impedance directions and the leading faster split shear wave instead of being parallel to the crack face as it is for low pore fluid pressures becomes orthogonal to the crack face the anisotropic poro elasticity ape model of the evolution of microcracked rock calculates the evolution of cracked rock to changing conditions ape modelling shows that at high overburden pressures only nearly vertical cracks to which normal incidence p waves are less sensitive than s waves remain open as the pore fluid pressure increases ape modelling matches the observed time lapse effects almost exactly demonstrating that shear wave anisotropy is a highly sensitive diagnostic of pore fluid pressure changes in fractured reservoirs in this comparatively limited analysis ape modelling of fluid injection at known pressure correctly predicted the changes in seismic response particularly the shear wave splitting induced by the high pressure co2 injection in the phase vii survey ape modelling also successfully predicted the response to the lower pressure injection using the same phase vi model of the cracked reservoir the underlying reason for this remarkable predictability of fluid saturated reservoir rocks is the critical nature and high crack density of the fluid saturated cracks and microcracks in the reservoir rock which makes cracked reservoirs critical systems

contribution of ice sheet and mountain glacier melt to recent sea level rise altimeter data suggest that sea level rose by about 2 4 mm per year from 2005 to 2011 but estimates of the relative contributions of ocean warming and increased ocean mass are equivocal an analysis of ocean temperature and satellite gravity data suggests that the delivery of meltwater from ice sheets and mountain glaciers contributed 75 of the observed sea level rise

experimental mechanical compaction of clay mineral aggregates changes in physical properties of mudstones during burial dry and brine saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory experiments were conducted by increasing vertical effective stress up to 50 mpa to study the changes in physical properties of mudstones during burial the results suggest that the physical properties porosity density acoustic velocity etc of mudstones vary greatly with increasing effective stress clay mineralogy and fluid content kaolinite aggregates are much more compressible than those composed of smectite brine saturated clay mixtures are much more compressible than dry clay mixtures brine may soften and lubricate the clay matrix compared to dry clays resulting in higher compressibility in the brine saturated state the lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays the extremely fine grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse grained kaolinite at 20 mpa effective stress corresponding to about 2 km burial depth with hydrostatic pore pressure brine saturated pure kaolinite compacted to 20 porosity while pure smectite retained 41 porosity brinesaturated clay mixtures show higher vp and lower vs than dry clay mixtures a pronounced difference in vs was observed among the brinesaturated clay mixtures the lowest vs as a function of vertical effective stress was found for pure smectite for a given porosity value smectitic clays have higher velocities and elastic moduli than the kaolinitic clays the vp vs ratio is significantly higher in smectite than in kaolinite aggregates treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties which are strongly affected by the clay mineralogy grain size the amount of other minerals present and fluid content our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth o 2k m 801c above depths where significant chemical compaction takes place r 2007 elsevier ltd all rights reserved

tides of the caribbean sea analysis of tidal characteristics from 45 gauge locations indicates that the caribbean sea has a microtidal range for the most part between 10 and 20 cm the tide is primarily either mixed semidiurnal or mixed diurnal but a substantial section from puerto rico to venezuela experiences diurnal tides empirical charts of six component tides m sub 2 s sub 2 n sub 2 k sub 1 o sub 1 and p sub 1 show local detail of phase and amplitude each of the semidiurnal component tides is characterized by anticlockwise rotating amphidromes centered in the eastern caribbean there is evidence of strong radiational forcing of the s sub 2 tide in the south western caribbean the diurnal component tides are largely uniform in both phase and amplitude for most of the western and central caribbean however the diurnal phases increase rapidly towards the northwest and the yucatan channel

shear wave reflectivity anisotropies poisson s ratios and densities of a southern appalachian paleozoic sedimentary sequence abstract the physical properties of a sequence of paleozoic sedimentary rocks have been examined in detail with an emphasis on laboratory measurements of density shear wave velocity shear wave splitting and vp vs ratios seismic properties of 147 cores from 49 rock samples collected from the thorn hill sedimentary sequence of eastern tennessee are examined in terms of implications for future seismic studies in the southern appalachians the shear wave velocities of these rocks are strongly influenced by the relatively high shear wave velocity of quartz shear wave velocity anisotropy is present in most of the lithologic groups it is highest in the shales while being almost insignificant in the dolostones the related phenomenon of shear wave splitting occurs to some degree in all of the lithologies studied and at high pressures originates from mineral orientation splitting due to preferred mineral orientation is most prominent in the shales but also is significant in some of the carbonates compressional to shear velocity vp vs ratios of approximately 1 82 dolostones and 1 95 limestones effectively characterize the carbonates while other lithologies display wider ranges of vp vs primarily due to the influence of accessory minerals such as quartz densities of the sample suite range from 2 34 g cm3 shale to 2 86 g cm3 dolostone using average data for each lithologic group to calculate normal incidence reflection coefficients significant differences in the shear and compressional reflectivity of hypothetical interfaces are found normal incidence shear and compressional wave synthetic seismograms approximating the subsurface reflectivity of the entire thorn hill section indicate that three zones of high amplitude reflections would be seen on reflection records obtained over this 3327 m thick sequence overall the shear and compressional synthetics are similar in appearance differences are seen at some interfaces in the mississippian devonian interval which are more reflective to shear waves and in the ordovician martinsburg formation which appears more reflective to compressional waves

seismic source theory in stratified anisotropic media we extend seismic source theory to general anisotropic media for the numerical evaluation of spectral amplitudes of point sources in multilayered anisotropic crustal models first we obtain an explicit representation of the spectral elastodynamic green s tensor in general homogeneous anisotropic media as a sum of three integrals over the corresponding three slowness surfaces the multidimensional stationary phase principle is then applied to derive an asymptotic approximation at the far field in the case of azimuthally isotropic media we offer an alternative representation of the green s tensor and its ensuing displacements fields in the form of an exact hankel transform over the horizontal wave number variable the total field is specified here in terms of two potentials an sh potential and a mixed quasi transverse quasi longitudinal potential both of which assume the role of two scalar green s functions the availability of the green s tensor in analytical form enables one to obtain readily numerical solutions for a wide selection of media and sources it is shown that the radiation field of an explosion has the following new features 1 quasi transverse waves are created with four and eight lobe patterns 2 quasi longitudinal waves are generated for the collatitudinal displacement with four lobe patterns 3 the energy ratio sv p may reach the value of 20 for more than 50 of the azimuths in crustal structures such as tuff and shales and 4 radiation patterns for vertical shear waves are created which are indistinguishable from corresponding waves produced by earthquake faults our formalism allows us to establish a haskell type matrix algorithm for a multilayered azimuthally isotropic half space which enables us to calculate body waves and surface waves in real earth crustal models

3d modeling of fracture induced shear wave splitting in the southern california basin splitting of shear waves generated by local earthquakes in the southern california basin and their polarization changes during propagation through layers with different orientations of anisotropy are investigated from multicomponent seismograms and their hodograms synthetic data for earthquakes in the southern california basin illustrate the effects on polarization caused by dry vertical microcracks with a crack density of 0 04 at the source and receiver locations hodograms for observed and synthetic data show that the polarization at the receiver depends only on the orientation of the anisotropy within two wavelengths of the receiver which qualitatively explains the frequency dependence of anisotropy in previous studies seismograms are simulated for a model with a range of station azimuths and distances if the anisotropy producing crack orientations do not change between the source and a receiver and the source motion is parallel to the cracks there is no shear wave splitting splitting occurs when the anisotropy orientation at the receiver or between the source and receiver is different from the source orientation

constraining hydrological and cryospheric mass flux in southeastern alaska using space based gravity measurements 1 watersheds draining into the gulf of alaska goa experience large seasonal and inter annual variations of water in the form of rain snow and ice but accurate constraints on these variations have been difficult to obtain over larger geographic regions water variations can be inferred directly from the gravity recovery and climate experiment grace data however because goa variations occur over such a small region the inferred average value of water flux increases as the applied smoothing of the grace data decreases we use this observed scaling together with scaling results obtained from forward models to infer a seasonal amplitude of 115 20 km3 of water and an average contribution to sea level rise over the two years of data of 0 31 0 09 mm yr these results suggest that accelerated melting that began in the late 1990s as inferred from altimetry continues unabated

subtidal water level variations in lake pontchartrain louisiana lake pontchartrain louisiana has two major tidal passes connecting it to the mississippi sound and thence to the gulf of mexico the subtidal variability in this system and its relation to wind forcing over a 7 month period were examined the coherence of water level fluctuations in the lake and passes with those of the sound was high at all time scales and the water level in all data sets responded to the east west wind at time scales shorter than 15 days since the local coastline is approximately in the east west direction the results suggest a coupled coastal ocean lake response a linear friction model was developed and it accounted for most of the observed features