variations in magmatic processes along the east greenland volcanic margin summary seismic velocities and the associated thicknesses of rifted and igneous crust provide key constraints on the rifting history the differentiation between non volcanic and volcanic rifted margins the driving force of magmatism at volcanic margins that is active or passive upwelling and the temperature anomaly in the lithosphere this paper presents two new wide angle seismic transects of the east greenland margin and combines the velocity models with a compilation of 30 wide angle seismic velocity models from several publications along the entire east greenland margin compiled maps show the depth to basement depth to moho crustal thickness and thickness of high velocity lower crust hvlc with velocities above 7 0 km s 1 first we present two new wide angle seismic transects which contribute to the compilation at the northeast greenland margin and over the oceanic crust between shannon island and the greenland fracture zone velocity models produced by ray tracing result in total traveltime rms misfits of 100 120 milliseconds and 2 values of 3 7 and 2 3 for the northern and southern profiles with respect to the data quality and structural complexity 2 d gravity modelling is used to verify the structural and lithologic constraints the northernmost profile awi 20030200 reveals a magma starved break up and a rapidly thinning oceanic crust until magnetic anomaly c21 47 1 ma the southern seismic transect awi 20030300 exhibits a positive velocity anomaly associated with the shannon high and a basin of up to 15 km depth beneath flood basalts between shannon island and the continent ocean boundary break up is associated with minor crustal thickening and a rapidly decreasing thickness of oceanic crust out to anomaly c21 the continental region is proposed to be only sparsely penetrated by volcanism and not underplated by magmatic material at all compared to the vast amount of magmatism further south break up is proposed to have occurred at the seaward boundaries of the continent ocean transition zones at between 50 and 54 ma propagating from north to south based on a joint analysis incorporating transects from the kejser franz joseph fjord and godthab gulf secondly the variation of the hvlc along the east greenland margin from 60 to 77 n and from transects of its conjugate margin shows inverted emplacement of prominent landward and seaward hvlc thickness portions from north to south in a distribution chart the differences in the hvlc distribution are attributed to one or more of the following three models in the first model it is inferred that a transfer zone detachment acts as a barrier to northward magma flow in the second model underplating results in thicker and highly intruded lower crust with several small scale feeder dykes that locally increase the lower crustal velocities in the third model a second magmatic event associated with the separation of the jan mayen microcontinent is considered lithospheric scale inhomogeneities might be responsible for the heterogeneous melt generation the inversion of the hvlc distribution in continental and oceanic domains and differences in its velocities

three dimensional effects causing artifacts in two dimensional cross borehole electrical imaging summary cross borehole electrical resistance tomography ert experiments utilize downhole electrodes typically placed in a borehole filled with material of contrasting resistivity to the host rock the circular geometry of the boreholes is three dimensional and inversion routines are typically two dimensional because of the resistivity contrast artifacts in the form of borehole inversion effects develop in the resistivity images other 3d effects resulting in inversion artifacts are shadow effects caused by use of a 2d code to invert data from a 3d body located outside the image plane in both cases the inversion model misrepresents the spatial change in voltages as a corresponding spatial change in resistivity borehole inversion effects and shadow effects result as the forward solver attempts to resolve the discrepancy in the voltages for numerous electrode pairs into a meaningful resistivity distribution borehole inversion effects are shown to be related to the resistivity contrast between the borehole fill and the host medium and to borehole diameter borehole inversion effects do not materialize with small diameter boreholes e g 0 1 m when the fill resistivity contrast is one order of magnitude or less however a borehole fill resistivity contrast of two orders of magnitude causes artifacts in the form of sheaths near the boreholes and a conductive artifact between the boreholes larger diameter borehole e g 0 2 m induce significant borehole inversion effects with as little as one order of magnitude fill resistivity contrast the general resistivity patterns are similar for the borehole inversion effects however the artifacts are amplified as resistivity contrast and or borehole diameter increase these results are significant because borehole inversion effects may mask a target heterogeneity or an artifact may be confused for an anomaly resulting in improper actions for site characterizations or remediation strategies suggestions of best practices for experimental design to prevent or minimize borehole inversion effects include minimizing borehole diameter minimizing borehole fill resistivity contrast measuring and inputting the resistivity of the borehole fill water into the model and inverting changes in resistivity for time lapse ert data shadow effects are shown to be related directly to the distance of the target heterogeneity out of the image plane our results show that shadow effects become insignificant when the target is between 3 and 5 m outside the 10 m wide image plane because the size of the target and resistivity contrast of the target to the host rock are site specific variables the actual distance at which shadow effects become insignificant will vary from site to site to reduce misinterpretations by shadow effects reduce the dipole length of the four electrode measurements and supplement data from other well pairs and or other methods

changes in sand content of loess deposits along a north south transect of the chinese loess plateau and the implications for desert variations geological records have shown that the deserts east of the helan mountains in northern china were covered by grass during the holocene optimum whereas during marine oxygen isotope stages 2 and 4 distribution of the deserts was almost the same as at present the wide advance retreat cycles of the deserts may have exerted an important control on grain size changes in the loess of the loess plateau by altering the distance between the source and the accumulation zone of the loess this challenges the widely accepted model that winter monsoon winds were the sole factor responsible for spatial and temporal changes in loess texture to observe spatial changes in sedimentological characteristics of loess during the last glacial interglacial cycle the texture of loess was measured along a north south transect of the loess plateau this transect consists of nine loess sections starting at yulin in the transitional region between the loess plateau and the mu us desert and ending at weinan in the southernmost part of the loess plateau southward changes in sand 63 m content along the transect suggest that variations in desert extent have indeed played a significant role in loess grain size distributions particularly in the northern part of the loess plateau it is proposed that sand content 63 m of loess in the loess desert transitional zone may be used as a proxy indicator for proximity to the desert margin

electrical resistivity tomography of vadose water movement cross borehole electrical resistivity tomography ert was used to image the resistivity distribution before and during two infiltration experiments in both cases water was introduced into the vadose zone and the change in resistivity associated with the plume of wetted soil was imaged as a function of time the primary purpose of this work was to study the capabilities and limitations of ert to image underground structure and ground water movement in the vadose zone a secondary goal was to learn specifics of unsaturated flow in a complex geologic setting tomographs of electrical resistivity taken before infiltration image coarser well drained soils sands and gravels as more resistive zones whereas finer grained soils silts and clays which hold more water by capillarity are imaged as more conductive images of changes in resistivity during infiltration show growth of the water infiltration plume with time that is consistent with known geology in the ert images we see the effects of capillary barriers and infer differences between capillary driven flow through fine sediments and gravity driven flow through very permeable sediments images are consistent with numerical flow simulations using hydrological parameter values consistent with soil types inferred from well logs ert can be a useful tool to monitor movement of circuitous moisture fronts in a heterogeneous field setting that would go undetected by borehole measurements

lower crustal high velocity bodies along north atlantic passive margins and their link to caledonian suture zone eclogites and early cenozoic magmatism abstract in this study we use crustal scale ocean bottom seismic models to infer the presence of two types of lower crustal bodies at north atlantic passive margins type i primarily interpreted as early eocene magmatic intrusions and type ii interpreted as caledonian eclogites we discuss how these eclogites might be related to the main caledonian suture zone and other tectonic features in a conjugate north atlantic setting based on the first order approximation that p wave velocities can be related to rock strength the narrower continental margin at the southern more transect may be explained by stronger lower crust there compared with the northern voring transect this difference in strength possibly resulting in a steeper dip in the subducting baltica plate south of the proto jan mayen lineament may explain the asymmetry in extensional style observed across this lineament our interpretation locates the main suture off mid norway close to the more trondelag fault zone on the more margin along the western boundary of the trondelag platform on the voring margin and further northwards beneath the lofoten ridge the lower crustal body type i is about 60 thicker on the greenland side for both transects and its thickness along the northern transect is more than twice that of the southern transect these differences are consistent with sub lithospheric interaction between the icelandic hotspot and the continental rift oceanic accretion system around the time of continental break up

hydrogeophysical tracking of three dimensional tracer migration the concept and application of apparent petrophysical relations 1 direct estimation of groundwater solute concentrations from geophysical tomograms has been only moderately successful because 1 reconstructed tomograms are often highly uncertain and subject to inversion artifacts 2 the range of subsurface conditions represented in data sets is incomplete because of the paucity of colocated well or core data and aquifer heterogeneity and 3 geophysical methods exhibit spatially variable sensitivity we show that electrical resistivity tomography ert can be used to estimate groundwater solute concentrations if a relation between concentration and inverted resistivity is used to deal quantitatively with these issues we use numerical simulation of solute transport and electrical current flow to develop these relations which we call apparent petrophysical relations they provide the connection between concentration or local resistivity and inverted resistivity which is measured at the field scale based on ert for media containing ionic solute the apparent petrophysical relations are applied to tomograms of electrical resistivity obtained from field measurements of resistance from cross well ert to create maps of tracer concentration on the basis of synthetic and field cases we demonstrate that tracer mass and concentration estimates obtained using these apparent petrophysical relations are far better than those obtained using direct application of archie s law applied to three dimensional tomograms from ert which gives severe underestimates

bayesian method for hydrogeological site characterization using borehole and geophysical survey data theory and application to the lawrence livermore national laboratory superfund site a stochastic bayesian approach for combining well logs and geophysical surveys for enhancing subsurface characterization is presented the main challenge we face is in creating the bridge to link between ambiguously related geophysical surveys and well data the second challenge is imposed by the disparity between the scale of the geophysical survey and the scale of the well logs our approach is intended to integrate and transform the well log data to a form where it can be updated by the geophysical survey and this tends to be a convoluted process our approach starts with generating images of the lithology conditional to well logs each lithology image is then used as the basis for generating a series of shaliness images conditional to well log data shaliness images are converted to resistivity images using a site specific petrophysical model relating between shaliness resistivity and lithology to create the necessary interface with the cross well resistivity survey the lithology and resistivity images are then updated using cross well electromagnetic resistivity surveys we explored the limits of the approach through synthetic surveys of different resolutions and error levels employing the relationships between the geophysical and hydrological attributes which are weak nonlinear or both the synthetic surveys closely mimic the conditions at the llnl superfund site we show that the proposed stochastic bayesian approach improves hydrogeological site characterization even when using low resolution resistivity surveys

interaction between aggrading geomorphic surfaces and the formation of a late pleistocene paleosol in the palouse loess of eastern washington state abstract variable rates of loess deposition contributed to dramatic regional variation in a soil stratigraphic unit the washtucna soil in the palouse loess deposits in the channeled scabland of eastern washington state throughout most of the channeled scabland the morphology of the washtucna soil is that of a single buried soil but it bifurcates into two well developed and pedologically distinct buried soils in areas immediately downwind of the major source of loessial sediment regional loess stratigraphy confirms that the two well developed soils formed during the same interval of time during which only one soil formed in areas that are distal to loess source areas the variable and perhaps rapid rates of soil formation suggested by the stratigraphy resulted from an interaction between variable rates of loess deposition and the formation of superimposed calcic soils petrocalcic horizons with weak stage iv morphology formed as the zone of carbonate accumulation moved up into former a and cambic horizons that had been profusely burrowed by cicadas the development of cicada burrows in one phase of soil development that were subsequently engulfed by pedogenic carbonate under a rising land surface seems to have greatly accelerated the development of the petrocalcic horizons accelerated rates of formation of the petrocalcic horizons occurred when extrinsic pulses of loess deposition and intrinsic engulfment of burrowed horizons thresholds were exceeded stratigraphic evidence suggests that the soil formation that accompanied the rise in the land surface due to additional loess deposition may have occurred during the late wisconsin glaciation when giant glacial outburst floods in the channeled scabland triggered a new cycle of loess deposition

deposits and soils of the past 130 000 years at the desert loess transition in northern china the desert loess transitional zone in north central china has long been thought sensitive to quaternary climatic change however reconstruction of quaternary climates in this area has been hindered by incompleteness of geological sections here we report the analytical results of two recently found sand loess soil sections both sections have thick eolian deposits from the last interglacial glacial cycle and can be correlated with one another field observations thermoluminescence dating and other laboratory analyses show that the last interglacial period produced three paleosols and two intercalated loess layers loess from the last glacial period is interbedded with three sand horizons that represent desert extension the expansion and contraction of desert in northern china may have been forced by the east asia monsoon

time lapse ert monitoring of an injection withdrawal experiment in a shallow unconfined aquifer toquantifyperformanceof3dtime lapseelectricalresistivity tomography ert a sequential injection withdrawal experiment was designed for monitoring the pump and capture remediation of a conductive solute in an unconfined alluvial aquifer prior information is incorporated into the inversion procedure via regularization with respect to a reference model according to threeprotocols 1independentregularizationinvolvingasingle reference model 2 background regularization involving a referencemodelobtainedviainversionofpreinjectiondata and3 time lapseregularizationinvolvinganevolvingreferencemodel obtained via inversion of data from previous experimental stages emplacementandsequentialwithdrawalofthesoluteisclearly imaged for all protocols time lapse regularization results in greater amounts of model structure while providing significantcomputationalsavings ert estimatedelectricalconductivity is used to predict solute concentration and solute mass in the aquifer at any experimental stage we are able to estimate total solute mass in the aquifer with a maximum accuracy of 60 85 depending on regularization protocol and survey geometry wealsoestimatethewithdrawnsolutemassforeveryexperimentalstagethechangeinmassbetweenexperimentalstages withdrawn mass estimates are more reliable than total mass estimates and do not exhibit systematic underprediction or dependence on regularization protocol withdrawn mass estimates areaccurateforchangesinmassbelow2 4 kgofpotassiumbromide kbr for horizontal and vertical dipole dipole surveys respectively estimating the withdrawn solute mass does not require background subtraction and thus does not require backgrounddata

the crustal structure of central east greenland results from combined land sea seismic refraction experiments summary we present results from the first combined marine land seismic refraction survey in the area of the east greenland caledonides together with gravimetric measurements the seismic and gravimetric models show a consistent picture of the crustal structures in the western area which is part of the caledonian mountains of east greenland crystalline rocks with p wave velocities of about 5 5 km s 1 occur at the surface seismic velocities increase continuously with depth and reach values of 6 6 km s 1 at 12 km the total thickness of the crust as revealed by the seismic measurements reaches high values of up to 48 km in the southwestern part of the region 28 w gravity data which also cover the region west of the seismic lines indicate a possible further increase of the crustal thickness these high values raise questions about whether they represent a caledonide crustal root which would stand in strong contrast to the findings in the caledonian areas of europe or whether the crustal thickening represents a pre caledonian structure and is affine rather to the older regions west of the caledonides and adjacent to the greenland inland ice towards the east crustal thickness decreases rapidly it reaches a minimum of 22 km under the late palaeozoic mesozoic sedimentary basin of jameson land the crustal thinning is the result of the stretching of east greenland which was produced by a general extensional tectonic regime and the collapse of the caledonian mountain chain from devonian time onwards in the area of transition from thick to thin crust the seismic data indicate a layered structure at the moho this region is interpreted as a zone of extensive intrusion or underplating during the rifting in the tertiary

a distribution based parametrization for improved tomographic imaging of solute plumes summary difference geophysical tomography e g radar resistivity and seismic is used increasingly for imaging fluid flow and mass transport associated with natural and engineered hydrologic phenomena including tracer experiments in situ remediation and aquifer storage and recovery tomographic data are collected over time inverted and differenced against a background image to produce snapshots revealing changes to the system these snapshots readily provide qualitative information on the location and morphology of plumes of injected tracer remedial amendment or stored water in principle geometric moments i e total mass centres of mass spread etc calculated from difference tomograms can provide further quantitative insight into the rates of advection dispersion and mass transfer however recent work has shown that moments calculated from tomograms are commonly biased as they are strongly affected by the subjective choice of regularization criteria conventional approaches to regularization tikhonov and parametrization image pixels result in tomograms which are subject to artefacts such as smearing or pixel estimates taking on the sign opposite to that expected for the plume under study here we demonstrate a novel parametrization for imaging plumes associated with hydrologic phenomena capitalizing on the mathematical analogy between moment based descriptors of plumes and the moment based parameters of probability distributions we design an inverse problem that 1 is overdetermined and computationally efficient because the image is described by only a few parameters 2 produces tomograms consistent with expected plume behaviour e g changes of one sign relative to the background image 3 yields parameter estimates that are readily interpreted for plume morphology and offer direct insight into hydrologic processes and 4 requires comparatively few data to achieve reasonable model estimates we demonstrate the approach in a series of numerical examples basedonstraight raydifference attenuationradarmonitoringofthetransportofanionictracer and show that the methodology outlined here is particularly effective when limited data are available

seismic images of eclogites crustal scale extension and moho relief in the eastern grenville province quebec seismic images from a 250 km lithoprobe reflection profile in the interior of the eastern grenville province provide important new constraints on the crustal architecture of this part of the orogen prominent upper crustal reflections can be correlated with exposures of high pressure metamorphic rocks in the manicouagan shear belt providing the first direct evidence for eclogite reflectivity in the grenville province the eclogites are cut by major late grenvillian normal faults that penetrate the deep crust and preserve evidence of extensional collapse of the overthickened orogen north to south crustal thinning indicated by a change in moho reflection time from 16 to 13 s correlates well with regional bouguer gravity trends and is accompanied by a dramatic increase in the reflectivity of the lower crust these features underscore the significance of recently recognized along strike variations in tectonic style within the grenville province and point to the internal complexity that characterizes the root zones of collisional orogens

characterization of mixing and dilution in heterogeneous aquifers by means of local temporal moments breakthrough curves of a conservative tracer in a heterogeneous two dimensional aquifer are analyzed by means of their temporal moments the average velocity and the longitudinal macrodispersion coefficient of the equivalent one dimensional aquifer obtained through cross sectional averaging of concentration can be defined from the first and second central moments of a breakthrough curve integrated over the outflow boundary of the domain on the basis of an integrated breakthrough curve one cannot distinguish between actual solute dilution which involves concentration reduction and variability of arrival times among parts of the plume at different cross sectional positions analyzing the temporal moments of breakthrough curves at a point within the domain gives additional information about the dilution of the tracer from these local first and second central moments an apparent seepage velocity a and an apparent dispersivity of mixing a can be derived for short travel distances a equals the local scale longitudinal dispersivity it increases with the travel distance but much more slowly than the macrodispersivity at the large distance limit a may eventually reach the level of macrodispersivity lenses of high conductivity where groundwater flow converges are identified as regions of preferential enhanced mixing the spatial distribution of these regions causes a high degree of variability of a within a domain indicating a high degree of uncertainty in the quantification of dilution at early stages in an accompanying paper cirpka and kitanidis this issue the results of conservative tracer transport are utilized for the study of mixing controlled reactive transport

electrical characterization of non fickian transport in groundwater and hyporheic systems 1 recent work indicates that processes controlling solute mass transfer between mobile and less mobile domains in porous media may be quantified by combining electrical geophysical methods and electrically conductive tracers whereas direct geochemical measurements of solute preferentially sample the mobile domain electrical geophysical methods are sensitive to changes in bulk electrical conductivity bulk ec and therefore sample ec in both the mobile and immobile domains consequently the conductivity difference between direct geochemical samples and remotely sensed electrical geophysical measurements may provide an indication of mass transfer rates and mobile and immobile porosities in situ here we present 1 an overview of a theoretical framework for determining parameters controlling mass transfer with electrical resistivity in situ 2 a review of a case study estimating mass transfer processes in a pilot scale aquifer storage recovery test and 3 an example application of this method for estimating mass transfer in watershed settings between streams and the hyporheic corridor we demonstrate that numerical simulations of electrical resistivity studies of the stream hyporheic boundary can help constrain volumes and rates of mobile immobile mass transfer we conclude with directions for future research applying electrical geophysics to understand field scale transport in aquifer and fluvial systems subject to rate limited mass transfer

mapping permeability in heterogeneous aquifers using hydrologic and seismic data a new method is presented for identification of the permeability distribution in near surface aquifers in addition to using the usual sparsely sampled pressure and permeability data the method incorporates densely sampled seismic data as obtained from a reflection or tomography survey along with empirical relationships between seismic and hydraulic properties the procedure is to first estimate by hydrologic inversion a pressure field then the velocity permeability pressure relationship is used to map the inverted pressure and measured seismic data to multivalued estimates of the permeability of those the most probable value based on the hydrologic inversion is selected in synthetic case studies the tremendous increase in coverage offered by the seismic data leads to dramatically better results in terms of both accuracy and resolution an appealing feature is the use of relatively easy to acquire pressure data a second is the incorporation of geophysical data which can sample an entire aquifer remotely without the need for an expensive and invasive drilling program

vadose zone flow model parameterisation using cross borehole radar and resistivity imaging cross borehole geoelectrical imaging in particular electrical resistivity tomography ert and transmission radar tomography can provide high resolution images of hydrogeological structures and in some cases detailed assessment of dynamic processes in the subsurface environment through appropriate petrophysical relationships these tools offer data suitable for parameterising and constraining models of groundwater flow this is demonstrated using cross borehole radar and resistivity measurements collected during a controlled vadose zone tracer test performed at a field site in the uk sherwood sandstone both methods show clearly the vertical migration of the tracer over a 200 h monitoring period by comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two and three dimensional ert and cross borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0 4 m d such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site

continent ocean transition and voluminous magmatic underplating derived from p wave velocity modelling of the east greenland continental margin summary deep seismic refraction data were gathered across the entire east greenland rifted margin north of the jan mayen fracture zone between 72 n and 75 n in 2003 investigations of the deep crustal structure of this continental margin provide constraints on the formation of the margin and its structural evolution during and after late cretaceous early tertiary rifting and continental break up we present here the results along two profiles located in the prolongation of the godthab gulf and the kejser franz joseph fjord regional p wave velocity models were derived from forward traveltime modelling of land stations and ocean bottom hydrophone obh recordings for the first time long deep seismic sounding transects off east greenland provide a full insight into the crustal architecture of the transition from continental to oceanic crust a mean result is the identification of voluminous magmatic underplating which is wider and thicker than previously thought p wave velocities of the underplated material range between 7 1 and 7 4 km s 1 and the horizontal extents on the profiles are 225 and 190 km the maximum thickness of the underplated material is 15 16 km furthermore the p wave velocity models reveal a 120 130 km wide continent ocean transition zone cot based on an interpretation of the extent of cretaceous syn rift sediments mixed with basaltic intrusions and the lateral increase of velocities in the crustal layers excess magmatism must have been present during a long term rifting process accompanying the extension of the continental crust and giving rise to the voluminous magmatic underplating a consequence of our interpretation of the seismic refraction data is a likely rift propagation in the greenland sea from north to south additionally a comparison of p wave velocity models of the east greenland margin and voring margin reveals significantly asymmetric crustal architectures the voluminous magmatic underplating and asymmetrical conjugate margins formations are considered as a mirror of complex pre and syn rift processes

archean and proterozoic crustal evolution evidence from crustal seismology seismic velocity models for archean and proterozoic provinces throughout the world are analyzed the thickness of the crust in archean provinces is generally found to be about 35 km except at collisional boundaries whereas proterozoic crust has a significantly greater thickness of about 45 km and has a substantially thicker high velocity 7 0 km s layer at the base we consider two models that may explain these differences the first model attributes the difference to a change in the composition of the upper mantle the higher temperatures in the archean mantle led to the eruption of komatiitic lavas resulting in an ultradepleted lithosphere unable to produce significant volumes of basaltic melt proterozoic crust developed above fertile mantle and subsequent partial melting resulted in basaltic underplating and crustal inflation in the second model convection in the hot archean mantle is considered to have been too turbulent to sustain stable long lived subduction zones by the proterozoic the mantle had cooled sufficiently for substantial island and continental arcs to be constructed and the high velocity basal layer was formed by basaltic underplating

moho and basement depth in the ne atlantic ocean based on seismic refraction data and receiver functions seismic refraction data and results from receiver functions were used to compile the depth to the basement and moho in the ne atlantic ocean for interpolation between the unevenly spaced data points the kriging technique was used free air gravity data were used as constraints in the kriging process for the basement that way structures with little or no seismic coverage are still presented on the basement map in particular the basins off east greenland the rift basins off nw europe are mapped as a continuous zone with basement depths of between 5 and 15 km maximum basement depths off ne greenland are 8 km but these are probably underestimated plate reconstructions for chron c24 c 54 ma suggest that the poorly known ammassalik basin off se greenland may correlate with the northern termination of the hatton basin at the conjugate margin the most prominent feature on the moho map is the greenland iceland faroe ridge with moho depths 28 km crustal thickness is compiled from the moho and basement depths the oceanic crust displays an increased thickness close to the volcanic margins affected by the iceland plume

the t reflection and the deep crustal structure of the voring margin offshore mid norway seismic reflection data along volcanic passive margins frequently provide imaging of strong and laterally continuous reflections in the middle and lower crust we have completed a detailed 2d seismic interpretation of the deep crustal structure of the voring margin offshore mid norway where high quality seismic data allow the identification of high amplitude reflections locally referred to as the t reflection using a dense seismic grid we have mapped the geometry of the t reflection in order to compare it with filtered bouguer gravity anomalies and seismic refraction data the t reflection is identified between 7 and 10 s sometimes it consists of one single smooth reflection however it is frequently associated with a set of rough multiple reflections displaying discontinuous segments with varying geometries amplitudes and contact relationships the t reflection seems to be connected to deep sill networks and is locally identified at the continuation of basement high structures or terminates over fractures and faults the spatial correlation between the filtered positive bouguer gravity anomalies and the deep dome shaped reflections indicates that the latter represent a high impedance boundary contrast associated with a high density and velocity body in 50 of the outer voring margin the depth of the mapped t reflection is found to correspond to the depth of the top of the lower crustal body lcb which is characterized by high p wave velocities 7 km s we present a tectonic scenario where a large part of the deep crustal structure is composed of preserved upper continental crustal blocks and middle to lower crustal lenses of inherited high grade metamorphic rocks deep intrusions into the faulted crustal blocks are responsible for the rough character of the t reflection whereas intrusions into the ductile lower crust and detachment faults are likely responsible for its smoother character deep magma intrusions can be responsible for regional metamorphic processes leading to an increasing velocity of the lower crust to more than 7 km s the result is a heterogeneous lcb that likely represents a complex mixture of pre to syn breakup mafic and ultramafic rocks cumulates and sills and old metamorphic rocks such as granulites and eclogites an increasing degree of melting towards the breakup axis is responsible for an increasing proportion of cumulates and sill intrusions in the lower crust

regional lithofacies and pedofacies variations along a north to south climatic gradient during the last glacial period in the central loess plateau china abstract five lateral sand loess palaeosol continua occur within the last glacial sediments of the central loess plateau of china along a 500 km north to south climatic gradient the continua shift southward or northward in concert with desert expansion or contraction respectively lateral lithofacies desert sand to loess variations are evident at the north end of the gradient and follow walther s law of the correlation of facies lateral pedofacies loess to palaeosol variations are present near the south end of the gradient where the climate was warmer and wetter the lateral stratigraphic changes from sand to loess or loess to soil are driven by variations in the rate of sedimentation along a climatic gradient vertical stratigraphic profiles at the north end of the gradient reveal alternating sand and loess beds in contrast alternating loess and palaeosols occur within the same stratigraphic interval in the southern loess plateau where dust accretion rates were lower however in high resolution studies of climate change vertical profiles of alternating loess and palaeosols especially weak palaeosols may not reflect regional or global climate change alternating loess and weak palaeosols may reflect local variations in the balance between the rates of dust accretion and pedogenesis local fluctuations in either of these rates could result in the presence of time equivalent loess and palaeosols at high resolutions thus some of the high resolution loess palaeosol alternations may reflect local climatic variation rather than global or hemispherical climate change

fully coupled hydrogeophysical inversion of a laboratory salt tracer experiment monitored by electrical resistivity tomography 1 we perform a salt tracer experiment monitored by time lapse electrical resistivity tomography in a quasi two dimensional sandbox with the aim of determining the hydraulic conductivity distribution in the domain we use sodium chloride as a tracer together with cochineal red for visual monitoring the time series of observed resistance for each electrode configuration is characterized by its temporal moments we invert the mean arrival time of electrical potential perturbations and a few steady state hydraulic head measurements using the fully coupled hydrogeophysical approach recently introduced by pollock and cirpka 2010 this is the first application of the approach to experimental data the results obtained show a reasonable agreement between the estimated hydraulic conductivity field and the pattern of the actual sandbox filling using this estimation a transient simulation is performed to compute the propagation of the salt tracer plume through the sandbox the latter is compared to pictures taken during the experiment these results show an even better agreement indicating that the lenses of different sand types are not entirely homogeneous and some unexpected preferential flow paths are present we conclude that temporal moments of potential perturbations obtained during salt tracer tests provide a good basis for inferring the hydraulic conductivity distribution by fully coupled hydrogeophysical inversion

comparison of proxy records of late pleistocene climate change from a high resolution loess palaeosol sequence in north central china a micromorphologically based pedosedimentary reconstruction of a 40 m loess palaeosol sequence from the western part of the chinese loess plateau provides a sensitive proxy record of changing processes and associated environmental conditions in this region between ca 150 000 and 10 000 yr bp depth functions of more traditional climate proxies such as magnetic susceptibility calcium carbonate content and median grain size support the broad pattern of environmental changes inferred from the micromorphology although the bulk properties sometimes lag behind or are out of phase with each other and do not match all the fluctuations in the micromorphological record the reasons for the disparities are probably complex although they partly reflect differences in response rates and sensitivities of proxies to different climate parameters as well as genuine out of phase changes in strength of monsoonal climate controls this work illustrates the sensitivity of micromorphology in detecting past environmental changes within rapidly aggrading landscapes and emphasises the need to understand more fully the local and regional significance of bulk proxies currently used in global correlations with marine and ice core records copyright 1999 john wiley sons ltd

a salt tracer test monitored with surface ert to detect preferential flow and transport paths in fractured karstified limestones in hard rock aquifers fractured zones constitute adequate drinking water exploitation areas but also potential contamination paths one critical issue in hydrogeological research is to identify characterize and monitor such fractured zones at a representative scale a tracer test monitored with surface electrical resistivity tomography ert could help by delineating such preferential flow paths and estimating dynamic properties of the aquifer however multiple challenges exist including the lower resolution of surface ert compared with crosshole ert the finite time that is needed to complete an entire data acquisition and the strong dilution effects we conducted a natural gradient salt tracer test in fractured limestones to account for the high transport velocity we injected the salt tracer continuously for four hours at a depth of 18 m we monitored its propagation with two parallel ert profiles perpendicular to the groundwater flow direction concerning the data acquisition we always focused

quantitative imaging of solute transport in an unsaturated and undisturbed soil monolith with 3 d ert and tdr electrical resistivity tomography ert has proved to be a valuable tool for imaging solute transport processes in the subsurface however a quantitative interpretation of corresponding ert results is constrained by a number of factors one such factor is the nonuniqueness of the ert inverse problem if no additional constraints are imposed in the vadose zone further problems arise from the general ambiguity of the imaged bulk electrical conductivity in terms of water content and solute concentration in this study we address these issues in detail for a solute tracer experiment conducted in an undisturbed unsaturated soil monolith where the tracer transport was monitored by means of 3 d smoothness constrained ert and time domain reflectometry tdr measurements the experimental design allowed the determination of solute tracer concentrations directly from imaged bulk electrical conductivity independent tdr data and effluent tracer concentrations provided a ground truth for the ert derived apparent convection dispersion equation transport parameters the apparent transport velocity calculated from the ert results was consistent with that based on tdr data and the sampled effluent independent of the degree of smoothness imposed in the ert inversion on the other hand the apparent dispersivity calculated from the ert results was larger than that estimated from tdr data but smaller than that estimated from the sampled effluent with the magnitude of deviations dependent on the degree of smoothing importantly no mass balance problems were observed in the ert results we believe that this is largely a consequence of the uniform application of the tracer as a front and of the configuration of the electrode array with respect to the main transport direction in conclusion the study demonstrates that ert can yield unprecedented quantitative information about local and column scale solute transport characteristics in natural soils

hydrogeophysical investigations of the former s 3 ponds contaminant plumes oak ridge integrated field research challenge site tennessee abstractat the oak ridge integrated field research challenge site near oak ridge tennessee contaminants from the former s 3 ponds have infiltrated the shallow saprolite for over 60 years two and three dimensional dc resistivity tomography is used to characterize the number and location of the main contaminant plumes which include high concentration of nitrate these contaminant plumes have typically an electrical resistivity in the range 2 20 ohm m while the background saprolite resistivity is in the range 60 120 ohm m so the difference of resistivity can be easily mapped using dc resistivity tomography to locate the contaminant pathways we develop a relationship to derive the in situ nitrate concentrations from the 3d resistivity tomograms accounting for the effect of surface conductivity the footprint of the contamination upon the resistivity is found to be much stronger than the local variations associated with changes in the porosity and the clay content with this method we identified a tot

insights from the jan mayen system in the norwegian greenland sea ii architecture of a microcontinent summary we study the formation and evolution of the jan mayen microcontinent jmmc in the framework of conjugate margin evolution in the norwegian greenland sea the jmmc structural map and crustal architecture have been constrained by seismic mapping and potential field modelling supplemented by published seismic refraction transects the sedimentary and basement geometries have been further studied together with their conjugate to refine our knowledge on the less explored microcontinent structurally the jmmc main ridge is characterized by a platform and or terrace architecture flanked by sag type basins similar to those described on the mid norwegian conjugate margin while its southern part is marked by windows exposing crustal and or mantle material that was exhumed during higher degrees of extension the eastern side of the jmmc broke up in a magma rich fashion while the western side is magma poor the limited amount of magma involved in the jmmc formation suggests that changes in far field forces were the driving mechanism to initiate the isolation process and that a mantle plume had a lesser influence but might have helped the final mid ocean ridge establishment between the western jan mayen and greenland margin

monitoring snowmelt induced unsaturated flow and transport using electrical resistivity tomography the flow and transport of a non reactive tracer and melt water was monitored in a heterogeneous coarse sandy unsaturated zone in southeastern norway during the snowmelt of 2001 electrical resistivity tomography ert as well as conventional suction cup techniques was employed a frozen solution of nabr in water was supplied as a line source on the ground surface above two parallel vertical profiles monitored by the two measurement systems prior to the onset of snowmelt the two monitored vertical profiles were separated by approximately 1 m the results were analysed by visual comparison of images and by the use of spatial moments analysis the two measurement approaches showed that the system was affected by the presence of preferential flow paths during the early stages of the snowmelt perhaps due to ice near the surface but the major part of the plume moves uniformly later in the snow melting period after most of the tracer plume has reached the depth monitored by both systems i e below 0 4 m depth there is a good consistency between the two datasets spatial moment calculations on the basis of ert cannot be used to describe the movement of tracer alone as the resistivity is affected by changes in both saturation levels and tracer concentration nevertheless ert appears to be an appropriate method to characterise regions of localised high infiltration in this type of soil the method therefore constitutes a possible alternative and supplement to suction cups in a monitoring system

leaching surfaces to characterize transport in a heterogeneous aquifer comparison between flux concentrations resident concentrations and flux concentrations estimated from temporal moment analysis 1 for subsurface solute transport flux concentrations are key while usually resident concentrations are measured flux concentrations are frequently estimated from resident concentrations by temporal moment analysis we tested this approach by simulating transport of an injected tracer during steady flow in an aquifer with a heterogeneous saturated hydraulic conductivity we constructed grid cell scale breakthrough curves btcs from flux concentrations and approximated btcs from resident concentrations and estimated flux concentrations we assembled these btcs into spatiotemporal leaching surfaces at various aquifer cross sections for subsequent analysis resident concentrations were unsuitable to assess solute movement in the aquifer temporal moment analysis worked well when the entire aquifer cross section was considered but performed poorer at the grid cell scale because it approximates the local velocity by the trajectory average the leaching surfaces served as valuable tools to demonstrate and quantify the limitations of temporal moment analysis

imaging and characterisation of subsurface solute transport using electrical resistivity tomography ert and equivalent transport models abstract we assess the usefulness of electrical resistivity tomography ert in imaging and characterising subsurface solute transport in heterogeneous unconfined aquifers a field tracer experiment was conducted at the krauthausen test site germany the spatial and temporal evolution of the injected nabr solute plume was monitored in a 2d ert image plane located downstream of the injection well for 90 days since ert maps changes in bulk electrical conductivity the reconstructed images at selected time intervals are first converted to solute concentration maps by postulating a linear relation the concentration maps are then analysed using an equivalent convection dispersion model cdm which conceptualises the aquifer as a homogeneous medium with a uniform mean flow velocity as demonstrated by associated synthetic model studies ert resolution in terms of recovered equivalent dispersivities is limited due to spatial smoothing inherent to the imaging algorithm since for heterogeneous media local concentrations within the plume deviate from those predicted by the equivalent cdm we also interpret the ert derived pixel breakthrough curves in terms of an equivalent stream tube model stm the stm represents transport in the aquifer by a set of 1d convection dispersion processes allowing the degree of mixing and the heterogeneity of transport within the plume to be quantified we believe that the observed tracer plume is satisfactorily described by the equivalent cdm probably because the tracer plume was small relative to the heterogeneity scale of the aquifer even though application of the stm revealed some deviation from the ideal homogeneous case the equivalent dispersivity in the stm matches the longitudinal dispersivity of the cdm closely consistent with predominantly homogeneous mixing however the stm analysis illustrates how ert results can be used to quantify the variability of parameters relevant to flow and transport in heterogeneous aquifers

the crustal structure of central east greenland i from the caledonian orogen to the tertiary igneous province summary we present a regional crustal model of the east greenland fjord region between 69 n and 74 nw hich spans the caledonian fold belt and the adjoining devonian and mesozoic basins the model is a compilation of existing seismic models that were partly reinterpreted and newly derived results from different modelling approaches remodelling of 33 stations on three deep seismic lines in the southern area yielded consistent p wave velocity models for the entire fjord region seismic velocities between 5 5 km s 1 near the surface and 6 9 km s 1 in the lower crust are typical for regions of palaeozoic age moho depths up to 48 km in the seismic models suggest the existence of a crustal root beneath the caledonian orogen shear wave modelling of 51 stations on six refraction seismic profiles resulted in s wave velocities between 3 2 km s 1 in the upper crust 4 0 km s 1 at the crust mantle boundary and 4 2 km s 1 in the partial magmatic underplating of the lower crust in the northern area calculation of poisson s ratio portrays a fairly homogeneous crust with only slight variations in poisson s ratio of 0 26 0 30 for the uppermost crystalline crust and 0 22 0 24 for the middle crust these values cannot be linked to lithological variations because they are either small scale or span several tectonic provinces finite difference modelling and amplitude analysis confirm models without magmatic underplating in the lower crust of the southern hall bredning scoresby sund area

late quaternary dust flow on the chinese loess plateau abstract the dust flux of over 25 g cm2 103yr was reached in the central part of the chinese loess plateau during the last glacial maximum this is more than three times higher than during the last interglacial and early glacial time the grain size of the pleniglacial dust reached a peak shortly after 20 000 years ago and testifies to the occurrence of strong winds and frequent dust storms

a tracer test in a shallow heterogeneous aquifer monitored via time lapse surface electrical resistivity tomography we illustrate a case study of a saline tracer test in a shallow highly heterogeneous aquifer monitored by means of surface time lapse ert the test was aimed at identifying the system s hydraulic properties some of the expected limitations of the method particularly caused by the strong decrease in ert resolution with depth and the consequent problems with mass balance and moment calculation could be partly balanced by the use of direct measurements of groundwater electrical conductivity and tracer concentration at one selected location the vast heterogeneity of the system ranging in lithology from clay to gravel at a scale of meters to tens of meters reflects itself in the tracer migration and distribution over time the tracer is trapped in the low permeability regions and from these it is slowly released over time high resolution surface ert proves effective at picturing this system behavior over time the extreme heterogeneity is also a challenge in the attempt to translate bulk electrical

potential of electrical resistivity tomography to infer aquifer transport characteristics from tracer studies a synthetic case study 1 with time lapse electrical resistivity tomography ert transport processes in the subsurface can be imaged and monitored the information content of obtained spatiotemporal data sets opens new ways to characterize subsurface spatial variability difficulties regarding a quantitative interpretation of the imaged transport may arise from the fact that data inversion used in ert is generally underdetermined and that ert data acquisition is often limited to two dimensional 2 d image planes to address this problem we conducted a numerical tracer experiment in a synthetic heterogeneous aquifer with preset variability and spatial correlation of the hydraulic conductivity and monitored the tracer breakthrough in a 2 d image plane perpendicular to the mean flow direction using time lapse ert the tracer breakthrough patterns in the image plane were interpreted using equivalent transport models an equivalent convection dispersion equation to characterize the spatially averaged breakthrough and a stream tube model to characterize local breakthrough curves equivalent parameters derived from simulated and from ert inverted concentrations showed a good agreement which demonstrates the potential of ert to characterize subsurface transport using first order approximate solutions of stochastic flow and transport equations equivalent model parameters and their spatial variability were interpreted in terms of the local scale dispersion and the spatial variability of the hydraulic conductivity the spatial correlations of the stream tube velocity and of the hydraulic conductivity were found to be closely related consequently the hydraulic conductivity spatial correlation may be inferred from stream tube velocity distributions which can be observed with sufficiently high spatial resolution using ert

assessment of local hydraulic properties from electrical resistivity tomography monitoring of a three dimensional synthetic tracer test experiment 1 in recent years geophysical methods have become increasingly popular for hydrological applications time lapse electrical resistivity tomography ert represents a potentially powerful tool for subsurface solute transport characterization since a full picture of the spatiotemporal evolution of the process can be obtained however the quantitative interpretation of tracer tests is difficult because of the uncertainty related to the geoelectrical inversion the constitutive models linking geophysical and hydrological quantities and the a priori unknown heterogeneous properties of natural formations here an approach based on the lagrangian formulation of transport and the ensemble kalman filter enkf data assimilation technique is applied to assess the spatial distribution of hydraulic conductivity k by incorporating time lapse cross hole ert data electrical data consist of three dimensional cross hole ert images generated for a synthetic tracer test in a heterogeneous aquifer under the assumption that the solute spreads as a passive tracer for high peclet numbers the spatial moments of the evolving plume are dominated by the spatial distribution of the hydraulic conductivity the assimilation of the electrical conductivity 4d images allows updating of the hydrological state as well as the spatial distribution of k thus delineation of the tracer plume and estimation of the local aquifer heterogeneity can be achieved at the same time by means of this interpretation of time lapse electrical images from tracer tests we assess the impact on the performance of the hydrological inversion of i the uncertainty inherently affecting ert inversions in terms of tracer concentration and ii the choice of the prior statistics of k our findings show that realistic ert images can be integrated into a hydrological model even within an uncoupled inverse modeling framework the reconstruction of the hydraulic conductivity spatial distribution is satisfactory in the portion of the domain directly covered by the passage of the tracer aside from the issues commonly affecting inverse models the proposed approach is subject to the problem of the filter inbreeding and the retrieval performance is sensitive to the choice of k prior geostatistical parameters

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

time lapse mise a la masse measurements and modelling for tracer test monitoring in a shallow aquifer abstract the main goal of this study is to evaluate the reliability of the mise a la masse malm technique associated with saline tracer tests for the characterization of groundwater flow direction and velocity the experimental site is located in the upper part of the alento river alluvial plain campania region southern italy in this paper we present the hydrogeological setting the experimental setup and the relevant field results subsequently we compare those data against the simulated results obtained with a 3d resistivity model of the test area coupled with a model describing the advection dispersion equation for continuous tracer injection in particular we calculate a series of 3d forward solutions starting from a reference model all derived from electrical tomography results but taking into consideration different values of mean flow velocity and directions each electrical resistivity 3d model is used to produce synthetic voltage maps for malm surveys finally the synthetic malm voltage maps are compared with the ones measured in the field in order to assess the information content of the malm dataset with respect to the groundwater field characteristics the results demonstrate that the information content of the malm data is sufficient to define important characteristics of the aquifer geometry and properties this work shows how a combination of three dimensional time lapse modeling of flow tracer transport and electrical current can substantially contribute towards a quantitative interpretation of malm measurements during a saline tracer test this approach can thus revive the use of malm as a practical low cost field technique for tracer test monitoring and aquifer hydrodynamic characterization

thermoluminescence chronology of sand profiles in the mu us desert china abstract thermoluminescence tl is used to calculate the ages of two sand loess profiles in the marginal zone of the mu us desert china alternating units of dune sand and loess with palaeosols in the two profiles imply episodes of dune formation separated by periods of loess accumulation and pedogenesis our results indicate that there are three layers of dune sand intercalated in sediments of the last full glacial cycle suggesting the occurrence of three arid episodes during this time the first arid episode within this period occurred between

a shallow geothermal experiment in a sandy aquifer monitored using electric resistivity tomography groundwater resources are increasingly used around the world for geothermal exploitation systems to monitor such systems and to estimate their governing parameters we rely mainly on borehole observations of the temperature field at a few locations bulk electric resistivity variations can bring important information on temperature changes in aquifers we have used surface electric resistivity tomography to monitor spatially temperature variations in a sandy aquifer during a thermal injection test heated water 48 c was injected for 70 hours at the rate of 87 l h in a 10 5 c aquifer temperature changes derived from time lapse electric images were in agreement with laboratory water electric conductivity temperature measurements in parallel a coupled hydrogeologic saturated flow and heat transport model was calibrated on geophysical data for the conceptual model and on hydrogeologic and temperature data for the parameters the resistivity images showed an upper flow of heated water along the well above the injection screens and led to a new conceptualization of the hydrogeologic source term the comparison between the temperature models derived from resistivity images and from the simulations was satisfactory quantitatively resistivity changes allowed estimating temperature changes within the aquifer and qualitatively the heated plume evolution was successfully monitored this work demonstrates the ability of electric resistivity tomography to study heat and storage experiments in shallow aquifers these results could potentially lead to a number of practical applications such as the monitoring or the design of shallow geothermal systems

improved extraction of hydrologic information from geophysical data through coupled hydrogeophysical inversion 1 there is increasing interest in the use of multiple measurement types including indirect geophysical methods to constrain hydrologic interpretations to date most examples integrating geophysical measurements in hydrology have followed a three step uncoupled inverse approach this approach begins with independent geophysical inversion to infer the spatial and or temporal distribution of a geophysical property e g electrical conductivity the geophysical property is then converted to a hydrologic property e g water content through a petrophysical relation the inferred hydrologic property is then used either independently or together with direct hydrologic observations to constrain a hydrologic inversion we present an alternative approach coupled inversion which relies on direct coupling of hydrologic models and geophysical models during inversion we compare the abilities of coupled and uncoupled inversion using a synthetic example where surface based electrical conductivity surveys are used to monitor one dimensional infiltration and redistribution through this illustrative example we show that the coupled approach can provide significant reductions in uncertainty for hydrologic properties and associated predictions if the underlying model is a faithful representation of the hydrologic processes however if the hydrologic model exhibits structural errors the coupled inversion may not improve the hydrologic interpretation despite this limitation our results support the use of coupled hydrogeophysical inversion both for the direct benefits of reduced errors during inversion and because of the secondary benefits that accrue because of the extensive communication and sharing of data necessary to produce a coupled model which will likely lead to more thoughtful use of geophysical data in hydrologic studies

the crustal structure of central east greenland ii from the precambrian shield to the recent mid oceanic ridges we present a 3 d crustal model of the east greenland fjord region between 69 n and 74 n the model covers the precambrian shield and the caledonian orogenic belt the adjoining devonian and mesozoic basins the continent ocean transition and the cenozoic oceanic areas as far as the kolbeinsey and the mohns mid oceanic ridges existing seismic models of the crustal structure are extrapolated into adjacent areas using 3 d gravity modelling for this purpose we compile a new regional scale bouguer anomaly map the precambrian shield west of the caledonian orogen approximately west of 32 w shows a mean thickness of 35 km with only small scale undulations this thickness is at the lower limit of the global range in shield thickness the caledonian orogen exhibits a pronounced mountain root with overall crustal thicknesses up to 51 km beside the urals the east greenland caledonides are one of the two palaeozoic mountain belts where a crustal root has preserved to the present day continuation of the crustal model to the east beyond the continent ocean transition yielded thicknesses of the crystalline oceanic crust from 9 km near the kolbeinsey ridge to 3 km west of the mohns ridge differences in the thermal structures of the old continental and the young oceanic lithosphere are responsible for the low density mantle beneath the oceanic crust which is also demonstrated by 3 d gravity modelling

coupled hydrogeophysical inversion using time lapse magnetic resonance sounding and time lapse gravity data for hydraulic aquifer testing will it work in practice 1 temporal changes in water content can be directly related to the time lapse signals retrieved using magnetic resonance sounding tl mrs and relative gravimetry tl rg previous studies suggest that tl rg measurements can potentially provide accurate estimates of aquifer characteristics in an aquifer pumping test experiment when used in a coupled hydrogeophysical inversion approach however these studies considered highly idealized conditions the aim of this paper is twofold first we investigate three major issues which likely limit the practical utility of tl rg for pumping test monitoring partially penetrating pumping wells in anisotropic aquifers delayed drainage effects and typical data errors for tl rg second we introduce tl mrs in a similar coupled hydrogeophysical inversion framework and compare the performance of tl mrs and tl rg for pumping test monitoring for this purpose we consider a virtual pumping test for which we generate synthetic drawdown tl mrs and tl rg observations and subsequently determine the aquifer parameters in an inverse parameter estimation approach the inclusion of tl rg and tl mrs data did slightly improve parameter estimates for the specific yield and hydraulic conductivity when considering a fully penetrating well and minimal data error using more conservative tl rg and tl mrs data error estimates according our own field experience strongly limited the informative value of the tl rg data tl mrs data was less affected by this for a partially penetrating well under anisotropic conditions parameter uncertainty could be reduced more effectively compared to a fully penetrating well delayed drainage effects did not limit the ability of the tl mrs and tl rg data to reduce parameter uncertainty significantly the incorporation of representative measurement error correlation in the tl rg data did not affect its informative value a local sensitivity analysis showed that observations were most sensitive to the pumping rate and the thickness specific yield and hydraulic conductivity of the aquifer the inclusion of tl mrs data proved to be more effective to constrain the aquifer parameters compared with tl rg the inclusion of both tl rg and tl mrs had limited added value compared to tl mrs only we conclude that this particular application of coupled hydrogeophysical inversion has limited potential for tl rg while tl mrs appears to be a more promising method

the mechanics and geological implications of dust transport and deposition in deserts with particular reference to loess formation and dune sand diagenesis in the northern negev israel

fully coupled hydrogeophysical inversion of synthetic salt tracer experiments 1 we present a method for the determination of hydraulic conductivity from monitoring of salt tracer tests by electrical resistivity tomography ert to ensure that the underlying principles of flow transport and geoelectrics are obeyed in the inversion we perform a fully coupled hydrogeophysical analysis using temporal moments of electrical potential perturbations in the predictive mode we use moment generating equations with corresponding adjoint equations for the evaluation of sensitivities for inversion we apply the quasi linear geostatistical inversion approach the method is tested in a synthetic case study mimicking a laboratory scale quasi two dimensional sandbox in which 48 electrodes and 8 piezometers are used the hydraulic conductivity field is estimated from the mean arrival times of electrical potential perturbations and hydraulic heads the estimated hydraulic conductivity field reproduces most features with however a loss of variability even though only the temporal moments of the electrical signals are used for inversion the transient behavior is satisfactorily recovered also the spatial patterns of concentration arrival times in the true and estimated cases are in good agreement so that the propagation of the tracer plume can be followed fairly accurately we test the effects of large measurement errors and erroneous prior information on the performance of the inversion while prior statistical parameters are of minor importance in detecting the major pattern of hydraulic conductivity a large measurement error could have an important impact on the solution also the choice of electrode configurations appears to be important in particular strictly surface based geoelectrical surveys do not seem to be very suitable for identifying spatial patterns of hydraulic conductivity by ert monitoring of salt tracer tests within aquifers

geoelectric characterization of the hydraulic conductivity field and its spatial structure at variable scales this paper describes how to begin with extensive geoelectric measurements of an aquifer along with a few hydraulic measurements and end with an estimate of the aquifer s hydraulic conductivity field and spectrum at variable scales it is based on a preponderance of theoretical and empirical evidence indicating that electrical and hydraulic eh conductivities of aquifers are linearly correlated on a bilogarithmic scale the steps required for a geoelectric characterization are scaling up calibration and spectrum estimation scaling up estimates electrical conductivity at variable scales from the apparent resistivity measurement calibration equilibrates coincident equal scale eh conductivities using the theoretical eh conductivity correlation combined scaling up and calibration provide a variable scale expression for the hydraulic conductivity field in terms of a geoelectric measurement from this expression the hydraulic conductivity field spectrum is calculated these steps are applied to borehole data collected at the department of energy central nevada testing area and the u s geological survey cape cod site in each case a statistically significant eh conductivity correlation is observed the paper ends by conjecturing that a horizontal exploitation of the eh conductivity correlation offers for the first time an inexpensive means of characterizing the hydraulic conductivity field at a high resolution and over a large area

imaging and characterization of solute transport during two tracer tests in a shallow aquifer using electrical resistivity tomography and multilevel groundwater samplers 1 the relevance of aquifer heterogeneity for flow and transport is recognized broadly however its characterization is hampered by the inaccessibility of the subsurface time lapse electrical resistivity tomography ert offers the possibility of imaging noninvasively subsurface transport we present results of two tracer tests that were carried out successively in a shallow aquifer at the krauthausen test site germany the breakthroughs of an electrically conductive and a resistive tracer were monitored with ert and local multilevel groundwater samplers mls along two cross sections perpendicular to the mean flow direction sinking of the conductive salt tracer due to density effects was observed with ert we applied a stream tube model to characterize the spatially variable transport ert derived stream tube parameters showed similar patterns for the two tracer experiments reflecting the effect of aquifer heterogeneity on transport mls data did not show similar spatial patterns which indicates that these measurements may be prone to subtle changes of the flow field in the small sampling volume and mixing within screened wells between 50 and 10 of the tracer was recovered in the ert derived breakthrough curves compared with transport simulations in a homogeneous aquifer ert derived time integrated changes in electrical conductivity were locally larger but focused in a smaller area mls data indicated that in this area ert did not underestimate the tracer recovery the relatively low tracer recovery was attributed to undetected tracer breakthrough in regions with low ert sensitivity and in regions where the length of the tracer plume and the electrical conductivity contrast were small

insights from the jan mayen system in the norwegian greenland sea i mapping of a microcontinent summary in this contribution we present a model of microcontinent architecture within a system that involves a complex rifted margin setting and different phases of deformation and continental breakup our case study is the jan mayen microcontinent jmmc located in the central part of the norwegian greenland sea we have revised its basement and sedimentary geometries using modern and vintage seismic reflection profiles and updated potential field data the northern part of the jmmc consists of a 10 15 km thick continental crust body flanked by two major sedimentary basins we propose that the microcontinent is divided into six distinct segments characterized by different basement and sedimentary architectures the shallow stratigraphy is well imaged and has been detailed three distinct sedimentary units have been defined together with pronounced reflectors ja red jo and f related to erosional magmatic thermal or uplift events the continent ocean boundary has been revised together with the mapping of the distinct volcanic events that characterize the evolution of the microcontinent a companion paper aims to further detail the interpretation of the jmmc structure presented here by constraining the conjugated mid norwegian and mid east greenland structures

crustal composition of the more margin and compilation of a conjugate atlantic margin transect highlights the basement at the mid norwegian more margin is dominantly felsic in composition a lower crustal body is interpreted as a mixture of continental blocks and eclogite the thickness of the outer lower crustal body is twice as thick on the east greenland margin the thinning during this first phase of post caledonian extension was highest for proto norway abstract the inner part of the volcanic passive more margin mid norway expresses an unusual abrupt thinning from high onshore topography with a thick crust to an offshore basin with thin crystalline crust previous p wave modeling of wide angle seismic data revealed the presence of a high velocity 7 7 8 0 km s body in the lower crust in this transitional region these velocities are too high to be readily interpreted as early cenozoic intrusions a model often invoked to explain lower crustal high velocity bodies in the region we present a vp vs model derived from the modeling of wide angle seismic data acquired by use of ocean bottom seismograph horizontal components the modeling suggests dominantly felsic composition of the crust an average vp vs value for the lower crustal body is modeled at 1 77 which is compatible with a mixture of continental blocks and caledonian eclogites the results are compiled with earlier results into a transect extending from onshore norway to onshore greenland back stripping of the transect to early cenozoic indicates asymmetric conjugate magmatism related to the continental break up further back stripping to the time when most of the caledonian mountain range had collapsed indicates that the thinning during the first phase of extension was about 25 higher for proto norway than proto greenland

time lapse electrical resistivity imaging of solute transport in a karst conduit the use of electrical resistivity surveys to locate karst conduits has shown mixed success however time lapse electrical resistivity imaging combined with salt injection improves conduit detection and can yield valuable insight into solute transport behaviour we present a proof of concept above a known karst conduit in the kentucky horse park lexington kentucky a salt tracer solution was injected into a karst window over a 45 min interval and repeat resistivity surveys were collected every 20 min along a 125 m transect near a monitoring well approximately 750m downgradient from the injection site in situ fluid conductivity measurements in the well peaked at approximately 25 of the initial value about 3 h after salt injection time lapse electrical resistivity inversions show two broad zones at the approximate conduit depth where resistivity decreased and then recovered in general agreement with in situ measurements combined salt injection and electrical resistivity imaging are a promising tool for locating karst conduits the method is also useful for gaining insight into conduit geometry and could be expanded to include multiple electrical resistivity transects

imaging of a fluid injection process using geophysical data a didactic example author s commer m pride sr vasco dw finsterle s kowalsky mb abstract the authors in many subsurface industrial applications fluids are injected into or withdrawn from a geologic formation it is of practical interest to quantify precisely where when and by how much the injected fluid alters the state of the subsurface routine geophysical monitoring of such processes attempts to image the way that geophysical properties such as seismic velocities or electrical conductivity change through time and space and to then make qualitative inferences as to where the injected fluid has migrated the more rigorous formulation of the time lapse geophysical inverse problem forecasts how the subsurface evolves during the course of a fluid injection application using time lapse geophysical signals as the data to be matched the model unknowns to be estimated are the multiphysics forward modeling parameters controlling the fluid injection process properly reproducing the geophysical signature of the flow process subsequent simulations can predict the fluid migration and alteration in the subsurface the dynamic nature of fluid injection processes renders imaging problems more complex than conventional geophysical imaging for static targets this work intents to clarify the related hydrogeophysical parameter estimation concepts

variations in loess and palaeosol properties as indicators of palaeoclimatic gradients across the loess plateau of north china abstract new data are presented on micromorphology magnetic susceptibility and particle size characteristics of three soil sediment units at four locations along a wnw ese transect across the loess plateau of north china differences and spatial trends are used to assess the sensitivity of such data as proxies of regional palaeoclimatic gradients the steepest climatic gradient suggested by the magnetic susceptibility for the s1 palaeosol is at the eastern humid end of the traverse micromorphology and particle size analysis show that the loess units in the east are richer in clay than the best developed palaeosols in the semi arid west and that particle size in the west appears to provide a more sensitive record of climatically driven changes than magnetic susceptibility the use of surface and near surface soils as a datum for inferring palaeoprecipitation values is reviewed in the light of recent evidence of substantial degradation of such soils micromorphological and particle size analysis of closely spaced samples from loess palaeosol sequences is a sensitive addition to magnetic susceptibility stratigraphy and correlation

spatial correlation structure estimation using geophysical and hydrogeological data the large spatial variability of hydraulic properties in natural geologic systems over a wide range of scales and the difficulty of collecting representative and sufficient hydraulic property measurements using conventional sampling techniques render estimation of spatial correlation parameters difficult further compounding the estimation problem is the observation that the integral scale estimate is a function of the measurement support scale to mitigate these problems we investigate the use of tomographic geophysical data in combination with hydrogeological data in the spatial correlation estimation procedure two synthetic case studies were investigated where the scale of the geophysical measurements were varied relative to the scale of the hydrogeological properties the spatial correlation structure parameter estimation procedure was performed in the spectral domain where analysis of data having different support scales and spatial sampling windows was facilitated comparison of the spatial correlation structure parameters estimated from measured data with those of the synthetic aquifers revealed which type of data tomographic hydrogeological or a combination of both was most effective for recovering spatial correlation statistics under different sampling heterogeneity conditions these synthetic case studies suggest that collection of a few tomographic profiles and interpretation of these profiles together with limited well bore data can yield correlation structure information that is otherwise obtainable only from extensive hydrological sampling

estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography in situ and laboratory experiments have shown that electrical resistivity tomography ert is an effective tool to image transient phenomena in soils however its application in quantifying soil h