mass balance of east antarctic glaciers and ice shelves from satellite data thevelocityandmassdischarge of ninemajoreast antarcticglaciersnot draining into the ross or filchner ronne ice shelves is investigated using interferometric syntheticapertureradar insar datafromtheeuropeanremote sensingsatellite1and2 ers 1 2 andradarsat 1 theglaciersare david ninnis mertz totten scott denman lambert shiraseandstancomb wills insarisusedtolocatetheirgroundinglinewithpre cision ice velocity is measured with either insar or a speckle tracking technique ice thickness is deduced from prior determined ice shelf elevation assuming hydrostatic equi librium mass fluxes are calculated both at the grounding line and at a flux gate located downstream the grounding line flux is compared to a mass input calculated from snow accumulation to deduce the glacier mass balance the calculation is repeated at the flux gate downstream of the grounding line to estimate the average bottom melt rate of the ice shelf under steady state conditions the main results are 1 grounding lines are found several tens of km upstream of prior identified positions not because of a recent ice sheet retreatbutbecause of the inadequacy of prior determined grounding line positions 2 no gross imbalance between outflow and inflow is detected on the nine glaciersbeing investi gated with anuncertainty of 10 20 prior determined largely positive mass imbalances wereduetoanincorrectlocalizationofthegroundingline 3 highratesofbottommelting 24 7 micea 1 are inferred neargrounding zones where ice reaches the deepestdraft a few glaciers exhibit lower bottom melt rates 4 7 micea 1 bottom melting however appearsto be a major source of mass loss on antarctic ice shelves

joint inversion of crosshole radar and seismic traveltimes acquired at the south oyster bacterial transport site the structural approach to joint inversion entailing common boundaries or gradients offers a flexible and effective way to invert diverse types of surface based and or crosshole geophysical data the cross gradients function has been introduced as a means to construct models in which spatial changes in two distinct physical property models are parallel or antiparallel inversion methods that use such structural constraints also provide estimates of nonlinear and nonunique field scale relationships between model parameters here we jointly invert crosshole radar and seismic traveltimes for structurally similar models using an iterative nonlinear traveltime tomography algorithm application of the inversion scheme to synthetic data demonstrates that it better resolves lithologic boundaries than the individual inversions alone tests of the scheme on gpr and seismic data acquired within a shallow aquifer illustrate that the resultant models have improved correlations with flowmeter data in comparison with models based on individual inversions the highest correlation with the flowmeter data is obtained when the joint inversion is combined with a stochastic regularization operator and the vertical integral scale is estimated from the flowmeter data point spread functions show that the most significant resolution improvements offered by the joint inversion are in the horizontal direction

physics and seismic modeling for monitoring co2 storage we present a new petro elastical and numerical simulation methodology to compute synthetic seismograms for reservoirs subject to co2 sequestration the petro elastical equations model the seismic properties of reservoir rocks saturated with co2 methane oil and brine the gas properties are obtained from the van der waals equation and we take into account the absorption of gas by oil and brine as a function of the in situ pore pressure and temperature the dry rock bulk and shear moduli can be obtained either by calibration from real data or by using rock physics models based on the hertz mindlin and hashin shtrikman theories mesoscopic attenuation due to fluids effects is quantified by using white s model of patchy saturation and the wet rock velocities are calculated with gassmann equations by using an effective fluid modulus to describe the velocities predicted by white s model the simulations are performed with a poro viscoelastic modeling code based on biot s theory where viscoelasticity is described by generalizing the solid fluid coupling modulus to a relaxation function using the pseudo spectral method which allows general material variability a complete and accurate characterization of the reservoir can be obtained a simulation that considers the utsira sand of the north sea illustrates the methodology

chevron ridges and runup deposits in the bahamas from storms late in oxygen isotope substage 5e abstract landward pointing v shaped sand ridges several kilometers long are common along the windward margin of the bahama islands their axes share a northeast southwest trend internally the ridges contain low angle oolitic beds with few erosional truncations commonly interbedded are tabular fenestrae rich beds such as those formed by the sheet flow of water over dry sand defined here as chevron ridges these landforms appear to have originated in the rapid remobilization of bank margin ooid bodies by the action of long period waves from a northeasterly source deposits along adjacent coastlines also preserve evidence of the impact of large waves reworked eolian sand bodies preserve beach fenestrae and hydraulic scour traces up to 40 m on older ridges on cliffed coasts 1000 ton boulders have been thrown well inland recording the impact of large waves amino acid ratios confirm a correlation of the ridges across the archipelago while stratigraphy spacing and cross cutting relationships indicate emplacement as sea level fell rapidly from the substage 5e maximum at or above 6 m

a modified archie s law for two conducting phases abstract many types of mixing model are used widely within the earth sciences to determine the electrical properties of porous media consisting of solid and fluid phases of known conductivities volume fractions and distributions i e phase connectivities most models are valid for two or more conducting phases however of the simple models only archie s law includes a variable term the archie cementation exponent m that describes the connectivity of the phases unfortunately archie s law is only valid for one conducting phase distributed within a non conducting phase which makes it inapplicable in instances where the rock matrix has a significant conductivity such as for clay rich rocks and in calculations involving partial melting more complex models exist which account for multiple conducting phases and control over phase conductivity we have adapted the conventional archie s law to produce a simple modified archie s law that can be used with two conducting phases of any conductivity and any volume fraction while retaining the ability to model variable connectivities within those phases that result from variations in their distribution the modified model has two exponents m and p that describe the connectivity of each of the two phases the exponents are related through an equation that depends also on the volume fractions of the two phases the modified and the conventional versions of archie s law have been tested on a granular analogue porous medium with a conducting matrix and a pore space saturated with a range of saline fluids with different salinities and conductivities the new model describes the experimentally determined electrical behaviour of the system extremely well improving greatly on the conventional archie s law

background resistivity model from seismic velocities we developed a methodology to estimate resistivities from seismic velocities we applied known methods including rock physics depth trends structural information and uncertainty analysis the result is the range of background resistivity models that is consistent with the known seismic velocities we successfully tested the methodology with real data from the north sea these 2d or 3d background resistivity models yield a detailed insight into the background resistivity and they are a powerful tool for feasibility studies they could also serve as starting models or constraints in iterative forward modeling of electromagnetic data for the determination of subsurface resistivities

joint inversion of seismic traveltimes and magnetotelluric data with a directed structural constraint we introduce a new structural constraint for joint inversion with an application to regional scale seismic traveltimes and magnetotelluric data we call the constraint directed as it takes into account a priori information on the sign of cross correlation between the gradients of reconstructed parameters with special treatment of singularities arising from vanishing gradients and linearization this constraint demonstrates some properties of an edge preserving stabilizer it provides blocky models with coincident discontinuities we develop an algorithm for 2d pixel based joint inversion including the proposed structural constraint as a penalty term of the objective function additional stabilizing terms are total variation of seismic slowness and levenberg marquardt damping the resulting regularized gauss newton scheme is numerically stable and demonstrates relatively fast convergence both in data misfits and in the structural similarity measure this is shown by a numerical study of the algorithm on a simplified regional model of the earth s crust the considered model has a blocky structure with a positive correlation between p wave velocity and electrical resistivity it represents a faulted basement overlain by sediments embedding an allochthonous salt dome the developed joint inversion improves both velocity and resistivity reconstruction relative to separate inversions in comparison with the cross gradients constraint the considered structural constraint firstly fixes the sign of correlation between the gradients of the parameters thus reducing uncertainty in the model recovery and secondly due to its stabilizing properties it limits the amount of additional regularization which results in sharper reconstructed models

resistivity velocity transforms revisited velocity and density measured in a well are crucial for synthetic seismic generation which is in turn a key to interpreting real seismic amplitude in terms of lithology porosity and fluid because velocity and density curves are sometimes of poor quality or simply absent in older wells it is important to be able to reconstruct these curves from reliable measurements such as resistivity and gamma ray gr a recent example of this approach is by xu et al 2003 where mechanical compaction curves and velocity porosity relations are used to reconstruct a full suite of the needed log data the earliest attempt to reconstruct a sonic curve from resistivity is by faust 1953 where both the velocity and resistivity are empirically related to depth and lithology from these two relations an equation follows that links the sonic velocity to the depth and formation factor where the formation factor is defined as usual as the ratio of the resistivity of water saturated rock to the resistivity of water

tributaries of west antarctic ice streams revealed by radarsat interferometry interferometric radarsat data are used to map ice motion in the source areas of four west antarctic ice streams the data reveal that tributaries coincident with subglacial valleys provide a spatially extensive transition between slow inland flow and rapid ice stream flow and that adjacent ice streams draw from shared source regions two tributaries flow into the stagnant ice stream c creating an extensive region that is thickening at an average rate of 0 49 meters per year this is one of the largest rates of thickening ever reported in antarctica

flow of glaciar moreno argentina from repeat pass shuttle imaging radar images comparison of the phase correlation method with radar interferometry high resolution radar images of glaciar moreno argentina acquired by the shuttle imaging radar c sir c on 9 and 10 october 1994 at 24 cm wavelength l band are utilized to map the glacier velocity both interferometrically and using the phase correlation method the precision of the interferometric ice velocities is 1 8 cm d 1 6 m a 1 1 the phase correlation method measures ice velocity with a precision of 14 cm d 1 50 m a 1 with image data at a 6 m sample spacing acquired 1 day apart averaged strain rates are measured with a precision of 10 4 d 1 at a 240 m sample spacing with the phase correlation method and 10 5 d 1 with radar interferometry the phase correlation method is less precise than radar interferometry but it performs better in areas of rapid flow is more robust to temporal changes in glacier scattering and measures the glacier velocity in two dimensions with only one image pair using this technique we find that glaciar moreno flows at 400 m a 1 in the terminal valley and 800 m a 1 at the calving front in agreement with velocities recorded a decade ago assuming steady state flow conditions the vertical strain rates measured by sir c are combined with prior data on mass ablation to estimate the glacier thickness and ice discharge the calculated discharge is 0 6 0 2 km3 ice a 1 at 300 m elevation and 1 1 0 2 km3 ice a 1 at the equilibrium line elevation 1150 m which yields a balance accumulation of 6 1m ice a 1

verification of velocity resistivity relationships derived from structural joint inversion with borehole data we present results of three dimensional joint inversion of seismic magnetotelluric and gravity data over a marine salt dome such structures are difficult to image with a single method and our results demonstrate how combining different techniques can yield improved results more importantly we examine the reliability of velocity conductivity relationships derived from structure coupled joint inversion approaches comparison with a seismic reflection section shows that our models match the upper limit of the salt furthermore velocity and resistivity logs from a borehole drilled into the salt dome s flank match within error those recovered by the inversion the good match suggests that the difference in length scale does not have a significant effect in this case this provides a strong incentive to incorporate borehole data into the joint inversion in the future and substantiates approaches that use the relationships derived from joint inversion models for lithological classification

determining the dilation factor in 4d monitoring of compacting reservoirs by rock physics models hydrocarbon depletion and fluid injection cause compaction and stretching of the reservoir and overburden layers 4d prestack seismic data can be used to detect these changes because compaction stretching causes changes in traveltimes and seismic velocities we show that by using two different petro elastic models at varying effective pressures a good approximation is to assume that the fractional changes in layer

joint elastic electrical effective medium models of reservoir sandstones improvements in the joint inversion of seismic and marine controlled source electromagnetic data sets will require better constrained models of the joint elastic electrical properties of reservoir rocks various effective medium models were compared to a novel laboratory data set of elastic velocity and electrical resistivity obtained on 67 reservoir sandstone samples saturated with 35 g l brine at a differential pressure of 8 mpa with mixed results hence we developed a new three phase effective medium model for sandstones with pore filling clay minerals based on the combined self consistent approximation and differential effective medium model we found that using a critical porosity of 0 5 and an aspect ratio of 1 for all three components the proposed model gave accurate model predictions of the observed magnitudes of p wave velocity and electrical resistivity and of the divergent trends of clean and clay rich sandstones at higher porosities using only a few well constrained input parameters the new model offers a practical way to predict in situ porosity and clay content in brine saturated sandstones from co located p wave velocity and electrical resistivity data sets

on mertz and ninnis glaciers east antarctica two large glacier tongues which extend substantially across the coastline of king george v land in east antarctica have been studied by remote sensing synthetic aperture radar jers 1 the tongue of mertz glacier is in a state of advance while the ninnis glacier tongue is retreating some more specific points are the distinctive surface structure and the form of the glacier tongues indicates that they are floating while the tongue of ninnis glacier has lost about two thirds of its area since 1913 the mertz glacier tongue has advanced substantially and has about doubled its areal extent over the same time period the annual movement of the tongue of mertz glacier was determined as about 1 2 km this is close to the value of the advance of the tip of the tongue since 1963 which was determined as 0 9 km year 1

seismically regularized controlled source electromagnetic inversion marine controlled source electromagnetic csem data can be highly sensitive to the presence of resistive hydrocarbon bearing layers in the subsurface yet due to the relatively poor depth resolution of csem data and the smoothness constraints imposed by electromagnetic em inversion methods the resulting resistivity models are often highly smoothed out typically underestimating the reservoir resistivity and overestimating its thickness conversely seismic full waveform inversion fwi can accurately recover the depths of seismic velocity changes yet is relatively insensitive the presence of hydrocarbons in spite of their low depth resolution csem data have been shown to be highly sensitive to the resistivity thickness product of buried resistive layers suggesting that if the thickness of a target layer can be constrained a priori very accurate resistivity estimates may be obtained we developed a method for leveraging the high depth resolution of fwi into a standard csem inversion algorithm so

contribution to the glaciology of northern greenland from satellite radar interferometry interferometric synthetic aperture radar insar data from the ers 1 and ers 2 satellites are used to measure the surface velocity topography and grounding line position of the major outlet glaciers in the northern sector of the greenland ice sheet the mass output of the glaciers at and above the grounding line is determined and compared with the mass input we find that the grounding line output is approximately in balance with the input except for the three largest glaciers for which the mass loss is 4 3 km3 ice year 1 or 11 8 of the mass input along the coast we detect a systematic retreat of the grounding lines between 1992 and 1996 with insar which implies that the outlet glaciers are thinning the inferred coastal thinning is too large to be explained by a few warm summers glacier thinning must be of dynamic origin that is caused by spatial and temporal changes in ice velocity iceberg production from the glaciers is uncharacteristically low it accounts for only 8 of the ice discharge to the ocean about 55 of the ice is lost through basal melting 5 8 m ice year 1 on average from the underside of the floating glacier tongues that are in contact with warm ocean waters mass losses are highest in the first 10 km of floating ice where ice reaches the greatest depths and basal melting is 3 times larger than on average only a small increase in basal melting would suffice to disintegrate the floating glacier tongues copyright 2001 by the american geophysical union

cross property relations between electrical conductivity and the seismic velocity of rocks cross property relations are useful when some rock properties can be measured more easily than other properties relations between electrical conductivity and seismic velocity stiffness moduli and density can be obtained by expressing the porosity in terms of those properties there are many possible ways to combine the constitutive equations to obtain a relation each one representing a given type of rock the relations depend on the assumptions to obtain the constitutive equations in the electromagnetic case the equations involve archie s law and its modifications for a conducting frame the hashin shtrikman hs bounds and the self similar and complex refraction index method crim models in the elastic case the stress strain relations are mainly based on the time average equation the hs bounds and the gassmann equation also expressions for dry rocks and for anisotropic media using backus averaging are analyzed the relations are applied to a shale saturated with brineoverburden and to a sandstone saturated with oilreservoir tests with sections of a north sea well log show that the best fit is given by the relation between the gassmann velocity and the crim selfsimilar and archie models for the conductivity

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

tidal motion ice velocity and melt rate of petermann gletscher greenland measured from radar interferometry over a floating glacier ice tongue or an ice shelf the glacier motion measured by a single repeat pass radar interferogram is difficult to analyze because the long term steady motion of the ice is intermixed with its cyclic downward motion induced by tidal forcing multiple interferograms and a quadruple difference technique are necessary to separate the tidal signal from the long term steady motion of the ice an example of application of this technique is given here using ers 1 radar images of petermann gletscher a major outlet glacier of northern greenland tidal displacements are measured with 5 mm statistical noise the long term ice velocity is measured with a precision of 1 m a 1 the inferred tidal displacements agree well with model predictions from a fixed elastic beam with an elastic damping factor of 0 47 0 01 km 1 the hinge line is mapped with a precision of 20 80 m combining the interferometric ice velocities with ice thickness data the glacier ice discharge is calculated at and below the hinge line at the hinge line the ice flux is 12 1 1 km3 a 1 at the ice front calf ice production is only 0 59 km3 a 1 meaning that 95 of the ice that crosses the grounding line melts before it reaches the calving front assuming steady state conditions the melt rate of the glacier tongue averages 12 1 m a 1 with peak values exceeding 20 m a 1 near the hinge line this high melt rate cannot be accommodated by surface ablation alone only about 2 3 m a 1 and is attributed to pronounced basal melting of the ice tongue basal melting often assumed to be negligible in greenland is the dominant process of mass release from the floating section of petermann gletscher

joint inversion of rock properties from sonic resistivity and density well log measurements well log data are processed in order to derive subsurface physical parameters namely rock porosity fluid saturations and permeability this step involves the selection and inversion of experimental constitutive equations which are the link between the rock parameters and geophysical measurements in this paper we investigate the rock parameter observability and the reliability of well log data processing we present a visual analysis of the constitutive equations and of the inverse problem conditioning when using independently or jointly log data from different domains the existence of a common set of rock properties cross properties that influence different measurements makes it possible to reduce the ambiguities of the interpretation we select a test case in a reservoir scenario and we explore how to determine rock porosity and fluid saturation from sonic conductivity and density logs we propose a bayesian joint inversion procedure which is able to control the conditioning problems to efficiently take into account input data and model uncertainty and to provide a confidence interval for the solution the inversion procedure is validated on a real well log data set

determination of effective grain geometry for electrical modeling of sedimentary rocks accurate electrical modeling of sedimentary rocks is crucial for the interpretation of electrical survey data and must take into account the geometric information of the rock grains we have developed an incremental model for the multiphase electrical conductivity of sedimentary rocks on the theoretical basis of differential effective medium models the developed incremental model was first validated on clean and clay rich sandstones and then applied to simulate the conductivity offive digitally created rock samples with different spectra of grain aspect ratios the conductivity is calculated as a function of water conductivity at full water saturation and an effective grain aspect ratio for a two phase medium is determined to reproduce the electrical behavior of the digital rocks it was found that the effectivegrain aspect ratio can either be determined analytically or estimated from the aspect ratio spectrum a link between the obtained effective grain aspect ratio and the cementation coefficient widely used in petrophysics has been established the cementation coefficient increases with the decrease of the grain aspect ratio increasing the z axis depolarization factor and grain conductivity and the increase of sample porosity it showed that the cementation coefficient can be interpreted as a measure of the connectivity of pores as well as the conductivity of the grains our results gave us new insights into the physical meanings of the grain aspect ratio and cementation coefficient which could be used to facilitate the electrical modeling or interpretation of reservoir rocks

high resolution velocity modeling by seismic airborne tem joint inversion a new perspective for near surface characterization we discuss the use of helicopter borne transient electromagnetic htem for a high resolution spatial and vertical characterization of the near surface in a structure controlled wadi in central saudi arabia in this area seismic data quality is poor and seismic imaging suffers from a combination of scattering effects due to swarms of faults reaching the surface and large velocity variations occurring along subvertical boundaries between the wadi sediment infill and the surrounding carbonate plateaus htem was selected from a suite of nonseismic methods for multiparameter velocity model building to enhance the velocity estimation for the wadi and surrounding areas htem data were modeled by performing spatially constrained 1d resistivity inversion to obtain a high resolution image of the near surface with sensitivity to a depth of 400 500 m from the surface sharp boundaries of the wadi and fine vertical layering obtained from the htem inversion provide detailed information about the parameter vari

petrophysical implications of source rock microfracturing abstract hydrocarbon generation induced microfracturing in source rocks is important affecting both primary migration of hydrocarbons and unconventional shale plays in this study petrographic observations rock eval and total organic carbon content toc data and log derived physical properties were analyzed in order to evaluate eventual petrophysical implications of microfracturing induced by hydrocarbon generation petrographically evidences of microfracturing both normal and parallel to bedding have been found horizontal microfractures typically cross cut each other at an angle between 30 and 90 horizontal microfractures are readily imaged compared to vertical microfractures vertical microfractures were clearly observed only in rare cases in samples with a high degree of microfracturing in the case of moderate microfracturing the vertical component of microfractures may be too small to be detectable using conventional microscopy techniques longer vertical components of the microfractures may be facilitated by higher toc and particularly dense laminated organic matter fabric as well as higher thermal maturity levels clay minerals particularly smectites are also playing a role in reducing permeability and thereby increasing the local pressure generated by hydrocarbon generation eventually resulting in microfracturing log derived petrophysical properties particularly p wave velocity vp and formation resistivity can give information on microfracturing potential even though the techniques can t resolve the microfractures directly vp has been postulated to be sensitive to organic matter quantity and fabric whereas formation resistivity is largely governed by fluid content and clay minerals a reverse trend of increasing resistivity with decreasing vp was found and is linked to higher hydrocarbon saturation and toc and or dense laminated fabric of organic matter favoring microfractures the implications of the log derived petrophysical results are in agreement with the direct petrographic observations formation resistivities in the source rocks however are lower than those observed in non clay dominated hydrocarbon saturated intervals this indicate that low permeable organic rich source rocks with a high clay content particularly smectites may facilitate formation of the hydrocarbon filled vertical microfractures even at relatively low thermal maturities

sensitivity analysis from single well ert simulations to image co2 migrations along wellbores co2 plume imaging is a required step in co2 geological storage for both performance assessment and risk management purposes this work has been performed in the frame of the co2care project and its aim is to develop tools and methodologies to monitor co2 migration and verify the long term well integrity after site abandonment the timely detection of an anomaly is essential to perform a suitable remediation for this purpose downhole tools are permanently installed but it is important to check the resolution and efficiency of the adopted techniques in particular this study investigates the possibility of using electrical resistivity tomography ert to image co2 migrations around observation boreholes through a sensitivity study

antarctic elevation change from 1992 to 1996 satellite radar altimeter measurements show that the average elevation of the antarctic ice sheet interior fell by 0 9 0 5 centimeters per year from 1992 to 1996 if the variability of snowfall observed in antarctic ice cores is allowed for the mass imbalance of the interior this century is only 0 06 0 08 of the mean mass accumulation rate

greenland ice sheet high elevation balance and peripheral thinning aircraft laser altimeter surveys over northern greenland in 1994 and 1999 have been coupled with previously reported data from southern greenland to analyze the recent mass balance of the greenland ice sheet above 2000 meters elevation the ice sheet is in balance on average but has some regions of local thickening or thinning thinning predominates at lower elevations with rates exceeding 1 meter per year close to the coast interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet sufficient to raise sea level by 0 13 millimeter per year approximately 7 of the observed rise

evidence for rapid retreat and mass loss of thwaites glacier west antarctica thwaites glacier the second largest ice stream in west antarctica drains an area of 166 500 2000 km2 which accumulates 55 5 gt a 1 or 60 6 km3 ice a 1 into the amundsen sea unrestrained by an ice shelf using interferometric synthetic aperture radar insar data collected by the european remote sensing satellites ers 1 and 2 in 1996 an output flux of 71 7 gt a 1 or 77 8 km3 ice a 1 is estimated at the grounding line where ice thickness is deduced from hydrostatic equilibrium a similar flux 70 7 gt a 1 or 76 8 km3 ice a 1 is obtained at a gate located 20 km upstream where ice thickness was measured in 1978 by ice sounding radar total accumulation in between the two gates is 1 6 gt a 1 or 1 8 km3 ice a 1 ice discharge therefore exceeds mass accumulation by 30 15 and thwaites glacier must be thinning and retreating at present the insar data show that the glacier floating ice tongue exerts no back pressure on the inland ice calves into tabular icebergs along a significant fraction of its grounding line and has a grounding line thickness which exceeds a prior calculated limit for stability glacier thinning is confirmed at the coast by the detection of a 1 4 0 2 km retreat of its grounding line between 1992 and 1996 with insar which implies 3 2 0 6 m ice a 1 thinning at the glacier center and less near the sides these results complement the decimeter scale annual surface lowering observed with satellite radar altimetry several hundred km inland of the grounding line the magnitude of ice thinning estimated at the coast however rules out temporal changes in accumulation as the explanation for surface lowering ice thinning must be due to changes in ice flow

ice shelf dynamics near the front of the filchner ronne ice shelf antarctica revealed by sar interferometry fifteen synthetic aperture radar sar images of the ronne ice shelf also referred to as the filchner ronne ice shelf antarctica obtained by the european remote sensing satellites ers 1 and 2 are used to study ice shelf dynamics near two ends of the iceberg calving front interferograms constructed from these sar images are used to resolve the ice shelf displacement along several directions in response to both ocean tide and long term creep flow tidal motion is separated from creep flow using differential interferometry i e two or more interferograms in which fringe patterns common to all are predominantly associated with creep flow creep flow velocities thus determined compare well with prior ice shelf velocity surveys using these data we studied the influence of large scale rifts ice rises and coastal separation on the ice shelf flow many of the large rifts that appear to form the boundaries where tabular icebergs may eventually detach from the ice shelf are filled with a melange of sea ice ice shelf debris and wind blown snow the interferograms show that this melange tends to deform coherently in response to the ice shelf flow and has sufficient strength to trap large tabular ice shelf fragments for several decades before the fragments eventually become icebergs in many instances the motion of the tabular fragments is a rigid body rotation about a vertical axis that is driven by velocity shear within the melange the mechanical role of the rift filling melange may be to bind tabular ice shelf fragments to the main ice shelf before they calve this suggests two possible mechanisms by which climate could influence tabular iceberg calving first spatial gradients in oceanic and atmospheric temperature may determine where the melange melts and thus the location of the iceberg calving margin second melting or weakening of ice melange as a consequence of climate change could trigger a sudden or widespread release of tabular icebergs and lead to rapid ice shelf disintegration

an electromagnetic modelling tool for the detection of hydrocarbons in the subsoil electromagnetic geophysical methods such as ground penetrating radar gpr have proved to be optimal tools for detecting and mapping near surface contaminants gpr has the capability of mapping the location of hydrocarbon pools on the basis of contrasts in the effective permittivity and conductivity of the subsoil at radar frequencies 50 mhz to 1 ghz hydrocarbons have a relative permittivity ranging from 2 to 30 compared with a permittivity for water of 80 moreover their conductivity ranges from zero to 10 ms m against values of 200 ms m and more for salt water these differences indicate that water hydrocarbon interfaces in a porous medium are electromagnetically visible in order to quantify the hydrocarbon saturation we developed a model for the electromagnetic properties of a subsoil composed of sand and clay silt and partially saturated with air water and hydrocarbon a self similar theory is used for the sandy component and a transversely isotropic constitutive equation for the shaly component which is assumed to possess a laminated structure the model is first verified with experimental data and then used to obtain the properties of soils partially saturated with methanol and aviation gasoline finally a gpr forward modelling method computes the radargrams of a typical hydrocarbon spill illustrating the sensitivity of the technique to the type of pore fluid the model and the simulation algorithm provide an interpretation methodology to distinguish different pore fluids and to quantify their degree of saturation

a new approach for deriving pseudovelocity logs from resistivity logs1 this paper describes a method of generating pseudovelocity logs using measurements of electrical resistivity a theoretical relation between electrical resistivity and transit time which is applicable to a wide range of lithologies has been developed the application of this relation using a method which defines lithoresistivity zones as lithological intervals related to the same formation and showing small resistivity variations has been tested in the reconcavo sedimentary basin in bahia brazil a comparison of derived pseudovelocity logs with actual sonic logs for five wells shows the validity of the present approach

joint elastic electrical properties of reservoir sandstones and their relationships with petrophysical parameters we measured in the laboratory ultrasonic compressional and shear wave velocity and attenuation 0 7 1 0 mhz and low frequency 2 hz electrical resistivity on 63 sandstone samples with a wide range of petrophysical properties to study the influence of reservoir porosity permeability and clay content on the joint elastic electrical properties of reservoir sandstones p and s wave velocities were found to be linearly correlated with apparent electrical formation factor on a semi logarithmic scale for both clean and clay rich sandstones p and s wave attenuations showed a bell shaped correlation partial for s waves with apparent electrical formation factor the joint elastic electrical properties provide a way to discriminate between sandstones with similar porosities but with different clay contents the laboratory results can be used to estimate sandstone reservoir permeability from seismic velocity and apparent formation factor obtained from co located seismic and controlled source electromagnetic surveys

direct elastic properties to resistivity transforms abstractnumerous publications have dealt with estimations of resistivity from elastic parameters and vice versa attempts have been made in the cross property relationship of elastic and electric properties in particular velocity to resistivity using different parameters such as porosity and water saturation these types of transforms are currently used to predict background seismic velocities and resistivities or even start models for seismic or controlled source electromagnetic csem inversions however they are not reliable predictors because they depict the regional elastic or electric variations with limited accuracy we present a novel approach for the development of models capable of estimating the regional subsurface resistivity based on information from regional wells and seismic inversions we apply multivariate nonlinear regression on data derived from regional wells and seismic inversions and subsequently produced an estimation of subsurface horizontal resistivity that could be either us

zonation for 3d aquifer characterization based on joint inversions of multimethod crosshole geophysical data predictive groundwater modeling requires accurate information about aquifer characteristics geophysical imaging is a powerful tool for delineating aquifer properties at an appropriate scale and resolution but it suffers from problems of ambiguity one way to overcome such limitations is to adopt a simultaneous multitechnique inversion strategy we have developed a methodology for aquifer characterization based on structural joint inversion of multiple geophysical data sets followed by clustering to form zones and subsequent inversion for zonal parameters joint inversions based on cross gradient structural constraints require less restrictive assumptions than say applying predefined petrophysical relationships and generally yield superior results this approach has for the first time been applied to three geophysical data types in three dimensions a classification scheme using maximum likelihood estimation is used to determine theparameters of a gaussian mixture model that defines zonal geometries

permeability prediction from micp and nmr data using an electrokinetic approach theaccuratemodelingofoil gas andwaterreservoirsdependsfundamentallyuponaccesstoreliablerockpermeabilitiesthatcannotbeobtaineddirectlyfromdownholelogs instead a range of empirical models are usually employed we propose a new model that has been derived analytically from electrokinetic theory and is equally valid for all lithologies the predictions of the new model and four other common models kozeny carman berg swanson and van baaren have been compared using measurements carried out on fusedandunfusedglassbeadpacksaswellason91rocksamples representing 11 lithologies and three coring directions the new model provides the best predictions for the glass beadpacksaswellforallthelithologies thecruxofthenew modelistohaveagoodknowledgeoftherelevantmeangrain diameter forexample frommicpdata hence wehavealso predictedthepermeabilitiesof21northseawellcoresusing all five models and five different measures of relevant grain size these data show that the best predictions are provided by the use of the new model with the geometric mean grain size wehavealsoappliedthenewmodeltothepredictionof permeability from nmr data of a 500 m thick sand shale succession in the north sea by inverting the t2 spectrum to provide a value for the geometric mean grain size the new model shows a good match to all 348 core measurements fromthesuccession performingbetterthanthesdr timurcoates hscm andkozeny carmanpredictions

velocity conductivity relationships for mantle mineral assemblages in archean cratonic lithosphere based on a review of laboratory data and hashin shtrikman extremal bounds article i nfo can mineral physics and mixing theories explain field observations of seismic velocity and electrical conductivity and is there an advantage to combining seismological and electromagnetic techniques these two questions are at the heart of this paper using phenomenologically derived state equations for individual minerals coupled with multi phase hashin shtrikman extremal bound theory we derive the likely shear and compressional velocities and electrical conductivity at three depths 100 km 150 km and 200 km beneath the central part of the slave craton and beneath the kimberley region of the kaapvaal craton based on known petrologically observed mineral abundances and magnesium numbers combined with estimates of temperatures and pressures we demonstrate that there are measurable differences between the physical properties of the two lithospheres for the upper depths primarily due to the different ambient temperature but that differences in velocity are negligibly small at 200 km we also show that there is an advantage to combining seismic and electromagnetic data given that conductivity is exponentially dependent on temperature whereas the shear and bulk moduli have only a linear dependence in cratonic lithospheric rocks focussing on a known discontinuity between harzburgite dominated and lherzolitic mantle in the slave craton at a