joint inversion of 2d resistivity and seismic travel time data to image saltwater intrusion over karstic areas the simultaneous inversion of multiple geophysical data types has been proven to be a powerful tool to both improve subsurface imaging and help in the interpretation process the main goal of this paper was to develop joint inversion strategies to provide improved resistivity and seismic velocity images for delineating saline water zones in karstic geological formations the cross gradient constraint approach was adopted to jointly invert resistivity and seismic first arrival data the basic idea of this approach is to quantitatively estimate the structural similarity between resistivity and seismic velocity models using the cross product of their gradients and to achieve a unified geological model which satisfies both data sets initially synthetic data were employed to help develop a joint inversion strategy to be used over such complex geological structures the proposed strategy uses a weighting factor for the cross gradient constraints and separate damping factors for the resistivity and seismic data this strategy was applied successfully on field data from the karstic region of stilos crete greece

solutions of the inherent problem of the equivalence in direct current resistivity and electromagnetic methods through global optimization and joint inversion by successive refinement of model space the problem of equivalence in direct current dc resistivity and electromagnetic methods for a thin resistive and conducting layer is well known attempts have been made in the past to resolve this problem through joint inversion however equivalence still remains an unresolved problem in the present study an effort is made to reduce non uniqueness due to equivalence using global optimization and joint inversion by successive refinement of the model space a number of solutions derived for dc resistivity data using very fast simulated annealing global inversion that fits the observations equally well follow the equivalence principle and show a definite trend for a thin conductive layer the quotient between resistivity and thickness is constant while for a resistive one the product between these magnitudes is constant three approaches to obtain very fast simulated annealing solutions are tested in the first one layer resistivities and thicknesses are optimized in a linear domain in the second layer resistivities are optimized in the logarithmic domain and thicknesses in the linear domain lastly both layer resistivities and thicknesses are optimized in the logarithmic domain only model data from the mean models corresponding to very fast simulated annealing solutions obtained for approach three always fit the observations the mean model defined by multiple very fast simulated annealing solutions shows extremely large uncertainty almost 100 in the final solution after inversion of individual dc resistivity or electromagnetic em data sets uncertainty associated with the intermediate resistive and conducting layers after global optimization and joint inversion is still large in order to reduce the large uncertainty associated with the intermediate layer global optimization is performed over several iterations by reducing and redefining the search limits of model parameters according to the uncertainty in the solution the new minimum and maximum limits are obtained from the uncertainty in the previous iteration though the misfit error reduces in the solution after successive refinement of the model space in individual inversion it is observed that the mean model drifts away from the actual model however successive refinement of the model space using global optimization and joint inversion reduces uncertainty to a very low level in 4 5 iterations this approach works very well in resolving the problem of equivalence for resistive as well as for conducting layers the efficacy of the approach has been demonstrated using dc resistivity and em data however it can be applied to any geophysical data to solve the inherent ambiguities in the interpretations

on the applicability of joint inversion of gravity and resistivity data to the study of a tectonic sedimentary basin in northern portugal the chaves basin is a pull apart tectonic depression implanted on granites schists and graywackes and filled with a sedimentary sequence of variable thickness it is a rather complex structure as it includes an intricate network of faults and hydrogeological systems the topography of the basement of the chaves basin still remains unclear as no drill hole has ever intersected the bottom of the sediments and resistivity surveys suffer from severe equivalence issues resulting from the geological setting in this work a joint inversion approach of 1d resistivity and gravity data designed for layered environments is used to combine the consistent spatial distribution of the gravity data with the depth sensitivity of the resistivity data a comparison between the results from the inversion of each data set individually and the results from the joint inversion show that although the joint inversion has more difficulty adjusting to the observed data it provides more realistic and geologically meaningful models than the ones calculated by the inversion of each data set individually this work provides a contribution for a better understanding of the chaves basin while using the opportunity to study further both the advantages and difficulties comprising the application of the method of joint inversion of gravity and resistivity data

two dimensional joint inversion of radiomagnetotelluric and direct current resistivity data an algorithm for the two dimensional 2d joint inversion of radiomagnetotelluric and direct current resistivity data was developed this algorithm can be used for the 2d inversion of apparent resistivity data sets collected by multi electrode direct current resistivity systems for various classical electrode arrays wenner schlumberger dipole diplole pole dipole and radiomagnetotelluric measurements jointly we use a finite difference technique to solve the helmoltz and poisson equations for radiomagnetotelluric and direct current resistivity methods respectively a regularized inversion with a smoothness constrained stabilizer was employed to invert both data sets the radiomagnetotelluric method is not particularly sensitive when attempting to resolve near surface resistivity blocks because it uses a limited range of frequencies on the other hand the direct current resistivity method can resolve these near surface blocks with relatively greater accuracy initially individual and joint inversions of synthetic radiomagnetotelluric and direct current resistivity data were compared and we demonstrated that the joint inversion result based on this synthetic data simulates the real model more accurately than the inversion results of each individual method the developed 2d joint inversion algorithm was also applied on a field data set observed across an active fault located close to the city of kerpen in germany the location and depth of this fault were successfully determined by the 2d joint inversion of the radiomagnetotelluric and direct current resistivity data this inversion result from the field data further validated the synthetic data inversion results

joint inversion of gravity and geoelectrical data for groundwater and structural investigation application to the northwestern part of sinai egypt summary the simulated annealing method was applied to jointly invert gravity and resistivity data to obtain the geometry of the density resistivity interfaces and subsurface electrical resistivity distribution the results obtained from the inversions of synthetic data indicate that the joint inversion significantly improves the solution decreasing the ambiguity of the models the method was applied to gravity and resistivity data carried out in sinai northwestern egypt the results obtained revealed the geometry of the water bearing zone with thickness ranging from 80 to 180 m and of the limestone bedrock interface dipping northwards

a first attempt at monitoring underground gas storage by means of time lapse multichannel transient electromagnetics two successive transient electromagnetic surveys were carried out over an underground gas storage site in france the idea was to monitor changes in the gas bubble from the differences in the data if successful the new methodology could help to reduce the number of monitoring wells and finally reduce costs preliminary 3d modelling indicated that the resistivity changes caused by movements of the gas water contact should be detectable in the electric field transients provided that the signal to noise ratio is at least 100 1 the surveys were performed with the teamex multichannel acquisition system adapted from a seismics system the highly redundant data were analysed by calculating the relative differences in the electric field transients the differences were common midpoint sorted and spatially stacked another approach was the calculation of electric field time derivatives in a log log domain to eliminate static shift effects which are present in the data even though the data quality is excellent from a classical point of view neither of the two approaches reveals changes in the data which might be caused by changes in the gas reservoir in future applications to monitoring transmitters and receivers should be installed permanently and the transmitter input waveform should be monitored continuously to avoid some of the problems encountered here moreover the signal to noise ratio will have to be further increased by at least one order of magnitude

deep schlumberger sounding and the crustal resistivity structure of central australia summary three 200 km schluniberger resistivity soundings have been conducted over the central australian shield using telephone lines to obtain the large electrode spacings these represent the first crustal scale controlled source electrical study to be carried out in this continent a computer controlled data acquisition system was used which allowed precise measurements to be made with only modest emission currents 0 1 0 5 a the three soundings centred on the towns of renner springs wauchope and aileron showed the southern part of the study area the arunta block to be an order of magnitude more resistive than the more northerly section the tennant creek block this difference correlates with the higher heat flow of the tennant creek block a lowering of apparent resistivity at large electrode spacings for one sounding wauchope is taken to indicate the presence of a low resistivity layer in the middle crust at a depth less than 20 km however the effect of the highly conductive overburden characteristic of inland australia combined with the large transverse resistance of the crust prevented the other two soundings from detecting such a layer without support from these two soundings it is impossible to be sure that the lowered resistivity at wauchope is not caused merely by lateral variations in near surface resistivity the data also show that crustal resistivities are much lower than the expected values for dry rock whether or not a low resistivity layer is included in the model this implies a widespread occurrence of free water in the crust with greater amounts occurring at depth if the low resistivity zone exists

cooperative joint inversion of 3d seismic and magnetotelluric data with application in a mineral province abstractthe integration of different geophysical data has the potential to provide more accurate estimate of subsurface rock properties several methodologies and attempts have been developed over the years with the objective of reducing exploration risk we have developed a cooperative joint inversion approach intended to facilitate recovery of acoustic impedance ai using seismic and magnetotelluric mt data in this approach the mt data provided a pathway for iteratively building large scale low frequency information content not directly recoverable from the seismic data themselves the mt data provided complementary information to seismic especially in seismically complex terrains such as overthrust belts subbasalt and subsalt carbonate reefs or for targets below deep cover containing limestone concretionary layers or basalt on the other hand the seismic data provided structural information necessary to derive accurate resistivity models from mt inversion and small scale features during seis

a gabbro to eclogite transition on flemsoy sunnmore western norway the migmatitic gneisses on the nordoyane islands western norway enclose abundant inclusions of coronitic gabbros and different types of country rock eclogites gabbros on flemsoy show a prograde step wise transition to eclogite via a transitional stage in which garnet and orthopyroxene form coronas between igneous olivine and sodic plagioclase relics after igneous plagioclase cumulates eclogitization proceeds by a complex set of continuous and discontinuous reactions opx and spinel form as transient phases but are consumed in various omphacite forming reactions during eclogite recrystallization relict igneous clinopyroxene shows a continuous increase in jd content while garnet becomes less calcic and more homogeneous from the corona stage to recrystallized eclogite the reactions are strongly diffusion controlled and have been enhanced locally by oxidation and the presence of a fluid phase and deformation while low strain areas of the gabbros remained coronitic whole rock chemistry mineral parageneses and calculated p t conditions are similar for the gabbroeclogites and two types of country rock eclogites some of the layered country rock eclogites appear to have been derived from the coronite bodies p estimates are in the order 15 20 kbar while kgarcpxd values suggest maximum t values of 750 60 c for the eclogite metamorphism in the area

and the geophysicist replied which model do you want abstractmarine controlled source electromagnetic csem and magnetotelluric mt soundings were carried out between 1997 and 2003 over the gemini prospect in the gulf of mexico during early development of marine instrumentation the resulting data sets provide a good test bed for examining the effect of the data type and misfit choice on regularized inversion solutions we inverted the data sets individually and jointly for isotropic and anisotropic resistivity at a variety of data misfits we found that multifrequency csem inversions vastly improved structural resolution over single frequency inversions suggesting that variation in skin depth added significant information joint mt and csem inversion appeared to improve resolution over mt only inversions at depths considerably deeper than the csem data can resolve probably by constraining shallow structure in the parts of the model to which the mt data were sensitive the addition of model anisotropy improved data fit but introduced an arbitrary scali

inversion of gravity and magnetic data for the lower surface of a 2 5 dimensional sedimentary basin gravity and magnetic data have been inverted to obtain the continuous lower surface of a 2 5 dimensional sedimentary basin the non linear problem is linearized and a solution is calculated through a recursive process until the predicted data matches the observed data an average model is then calculated and a resolution analysis shows which features are uniquely determined the results of individual inversion indicate that a final solution is initial model dependent but the average models are independent of the initial model except at the margins the average model for the magnetic solutions have uniformly smaller spreads than the gravity solutions the algorithms were applied to data from the sanford basin in north carolina the results indicate that the basin is asymmetrical in shape with a maximum depth of 3 2 km comparing these results with those obtained from a generalized linear inverse gli algorithm indicate that the higher frequency features determined from the gli algorithm are not resolved

joint inversion of seismic refraction and resistivity data using layered models applications to groundwater investigation we developed a method for joint inversion of seismic refraction and resistivity data using sharp boundary models with few layers typically three we demonstrated the usefulness of the approach v

combined application of dc and tem to sea water intrusion mapping a geoelectric survey using a dc resistivity method and a transient electromagnetic induction tem method was carried out from 1986 to 1988 it was used to help map the lateral and vertical distributions of the freshwater salt water interface in the pei kang area on the west coast of taiwan the dc and tem soundings were performed at 79 localities over an area of 240 km2 of quaternary alluvium significant changes in pore water conductivity at some places were detected by these two methods a low resistivity value 1 5 ohm m implies salt water contamination of groundwater the results of spatial distribution of apparent resistivity indicate the salt water affected aquifers are confined to the southwest part of the study area and the affected aquifers are confined to the top of two aquifers a geoelectric model with three to four layers is inferred from the joint inversion of dc and tem data based on a modified archie s law suggested by the authors an empirical relation between pore water resistivity

cooperative inversion of geophysical data geophysical inversion by iterative modeling involves fitting observations by adjusting model parameters both seismic and potential field model responses can be influenced by the adjustment of the parameters of the rock properties the objective of this cooperative in version is to obtain a model which is consistent with all available surface and borehole geophysical data al though inversion of geophysical data is generally non unique and ambiguous we can lessen the ambiguities by inverting all available surface and borehole data this paper illustrates this concept with a case history in which surface seismic data sonic logs surface gravity data and borehole gravity meter bhgm data are ad equately modeled by using least squares inversion and a series offorward modeling steps the traditional analysis of various geophysical data sets has been termed integrated interpretation such analysis has traditionally involved much processing modeling and subjec tive interpretation in order to develop a geologic model which is consistent with various surface and borehole geophysical data a method which automates some of the above pro cedures is least squares inversion this procedure perturbs an initial set of model parameters in order to fit the observed data least squares inversion is described in many papers in cluding those of jackson 1972 wiggins 1972 jupp and vozoff 1975 and lines and treitel 1984 this inversion technique could also be termed automated iterative mod eling in terms of modeling different geophysical data sets there are many possible approaches which allow inversion of a given data set and it is doubtful whether one single recipe will prove suitable for all problems nevertheless by jointly invert ing various types of geophysical observations we may lessen the extent of some of the ambiguities inherent in individual data sets lafehr 1984 gives a germane discussion of several reasons for this type of coordinated geophysical effort in the present study we define cooperative inversion as the esti mation of a subsurface model which is consistent with various independent geophysical data sets in the case discussed in this paper these data sets include surface and borehole observa tions of the seismic and gravity responses in our definition cooperative inversion may include either joint inversion or sequential inversion

geological relationships and u pb zircon and 40 ar 39ar tourmaline geochronology of gneisses and tourmalinites from the nevado filabride complex western sierra nevada spain tectonic implications abstract the nevado filabride complex the lowest complex in the betic hinterland forms a stack of alpine nappes the tectonic units consist of metasedimentary sequences whose ages are not well constrained gneiss bodies included in the sequences have been one of the few sources of geochronological data in this metamorphic complex new radiometric data from u pb zircon dating on gneisses from the western sierra nevada confirm the presence of late carboniferous intrusive rocks in the betic hinterland these results combined with available data from the literature and a detailed structural analysis suggest that the gneisses represent a single late variscan magmatic event evidence for a close genetic relation between gneisses and tourmalinites is provided by field and petrographic observations in conjunction with geochemical data u pb zircon 314 7 304 23 ma and 40 ar 39 ar tourmaline 319 85 5 81 317 85 3 67 ma geochronology a pre late carboniferous age for the basal formation of the nevado filabride sequence can be inferred the gneiss protolith and the graphite schist are considered to be the boron source and the precursor of the tourmalinites respectively superposed tectonic units rather than a continuous palaeozoic sequence is supported by the occurrence of palaeozoic rocks at the top of the nevado filabride complex the nappe tectonics as evidenced from the contractional character of the unit boundaries and the superposition of higher grade on lower grade metamorphic rocks is additionally supported by the superposition of older on younger rocks as revealed from radiometric data

uncertainty reduction through geologically conditioned petrophysical constraints in joint inversion abstractwe have developed a joint geophysical inversion workflow that aims to improve subsurface imaging and decrease uncertainty by integrating petrophysical constraints and geologic data in this framework probabilistic geologic modeling is used as a source of information to condition the petrophysical constraints spatially and to derive starting models the workflow then uses petrophysical measurements to constrain the values retrieved by geophysical joint inversion the different sources of constraints are integrated into a least squares framework to capture and integrate information related to geophysical petrophysical and geologic data this allows us to quantify the posterior state of knowledge and to calculate posterior statistical indicators to test this workflow using geologic field data we have generated a set of geologic models which we used to derive a probabilistic geologic model in this synthetic case study we found that the integration of geologic information and petrophysical con

joint petrophysical and structural inversion of electromagnetic and seismic data based on volume integral equation method a joint petrophysical and structural inversion method for electromagnetic em and seismic data based on the volume integral equation vie is proposed in this paper in the forward em problem only the contrast of conductivity is solved by the electric field integral equation method however in the forward seismic problem both the contrasts of velocity and mass density are solved by the combined field vie method both forward solvers are accelerated by the fast fourier transform in the inversion problem by using the petrophysical equations about the porosity and saturation and applying the chain rule we fuse the em and seismic data and construct the joint petrophysical inversion equations which can be solved by the variational born iteration method then in order to further enhance the reconstructed results of the joint petrophysical inversion we enforce the structural similarity constraint between porosity and water saturation and add the cross gradient function to the joint petrophysical inversion cost function two typical geophysical models based on the remote sensing measurement are used to validate the proposed methods one is the cross well model and the other is the marine surface exploration model the advantage of the joint inversion compared with the separate inversion is evaluated based on the resolution and the data misfits of the reconstructed profiles as well as the antinoise ability

electromagnetic mode conversion by surface conductivity anomalies applications for conductivity soundings summary a natural source electromagnetic sounding of the earth made near a surface conductivity anomaly will resolve different features of the underlying conductivity structure than a sounding in a more uniform region the surface conductivity anomaly deflects horizontal electric currents induced by an external source into a vertical plane converting transverse electric te mode currents into the transverse tm mode the resulting current distribution involves both vertical current flow and spatial variations with shorter wavelengths than the external field providing increased resolution of resistive layers and of the conductivity structure at shallow depths we exmine the sensitivity of the converted mode response for the vertical gradient sounding vgs method in order to plan electromagnetic soundings in a narrow ocean strait such as the strait of georgia between vancouver island and the canadian mainland an integral equation method is used to model the current system induced by a mode converter consisting of a known conductivity structure such as a body of ocean water it is shown that the depth of penetration of the secondary current distribution produced by the mode converter depends on both the horizontal scale of the feature and the distance from its edge within this depth range the current system is strongly perturbed by the existence of either conductive or resistive layers the sensitivity of the vgs response the ratio of the horizontal magnetic field at the base and surface of the mode converter is examined using forward modelling of layered conductivity structures the response is found to be dependent on both the te and tm current systems for a narrow ocean strait such as the strait of georgia a measurement of the converted mode vgs response along a line of sites on the floor of the strait will provide resolution of conductive and resistive layers in the upper 10 km the appropriate frequency range over which the vgs response should be measured in the strait is 10 2 hz to 10 hz in our investigation of mode conversion we examine both the frequency and time domain response snap shots showing the current system evolving in the earth after a step or impulse illustrate the interaction of the em signals with resistive and conductive layers we show that the time domain response can be used in a geometrical sounding analogous to seismic refraction to determine the conductivity structure finally we examine the limitations on the accuracy of the frequency and time domain vgs response imposed by natural signal levels and instrument sensitivity

joint inversion of gravity and magnetic data for two layer models gravity and magnetic data are inverted jointly in terms of a model consisting of an interface separating two layers having a constant density and magnetization contrast a damped least squares inversion is used to determine the topography of the interface the inversion requires knowledge of the physical property contrasts across the interface and its average depth since the relationship between model parameters and data is weakly nonlinear a constant damped least squares inverse is used during the iterative solution search the effect of this inverse is closely related to a downward continuation of the field to the average interface depth the method is used to map the base of the sept iles mafic intrusion quebec canada and the shape of the central uplift at the chicxulub impact crater yucatan mexico at sept iles the intrusion reaches a thickness of 7 km coincident with the maximum gravity anomaly south of the intrusion center at chicxulub the top of the central uplift is modeled to be 3

2d joint inversion of rmt and ert data versus individual 3d inversion of full tensor rmt data an example from trecate site in italy tensor radiomagnetotelluric rmt and electrical resistivity tomography ert data were acquired along 10 parallel lines to image electrical resistivity of the vadose and the saturated zone in an a

transient electromagnetic responses in seafloor with triaxial anisotropy summary electrical anisotropy of young oceanic crust at mid ocean ridges is detectable by observation of the rate and geometry of the diffusion of electromagnetic fields the anisotropy in electrical properties arises from the presence of conductive seawater in an interconnected network of mostly ridge parallel cracks in this paper we first justify the choice of a triaxial model to represent young oceanic crust with three distinct electrical conductivities in the vertical strike and spreading directions we then present an algorithm to calculate the transient electromagnetic responses generated by an electric dipole source over such a triaxially anisotropic seafloor we show that if the transient passages are measured with three distinct electric dipole dipole configurations it is possible to discern all three unknown conductivities independently of each other

3d joint inversion of geophysical data with gramian constraints a case study from the carrapateena iocg deposit south australia explorers are moving to increase the discovery space by exploring under cover and to greater depths e g subsalt and sub basalt exploration for oil and gas and beneath transported cover for minerals with this shift there becomes an increased reliance on geophysical methods to delineate resources with no recognized geological or geochemical expressions different geophysical fields provide information about different physical properties of the earth multiple geophysical surveys spanning gravity magnetic electromagnetic and seismic methods are often interpreted to infer geology from models of different physical properties in many cases the various geophysical data are complementary making it natural to consider a formal mathematical framework for their joint inversion to a shared earth model there are different approaches to joint inversion the simplest case of joint inversion is where the physical properties are identical between different geophysical methods e g jupp and vozoff 1975 in other cases joint inversion may infer theoretical empirical or statistical correlations between different physical properties e g hoversten et al 2003 2006 in cases where the physical properties are not correlated but nevertheless can be assumed to share a similar structure joint inversions have been formulated as a minimization of the cross gradients between different physical properties e g haber and oldenburg 1997 gallardo and meju 2003 2004 the latter has now been widely adopted by joint inversion practitioners as the de facto standard e g colombo and de stefano 2007 hu et al 2009 jegen et al 2009 de stefano et al 2011

joint inversion of lake floor electrical resistivity tomography and boat towed radio magnetotelluric data illustrated on synthetic data and an application from the aspo hard rock laboratory site sweden joint inversion of lake floor electrical resistivity tomography and boat towed radio magnetotelluric data illustrated on synthetic data and an application from the aspo hard rock laboratory site sweden

joint inversions of three types of electromagnetic data explicitly constrained by seismic observations results from the central okavango delta botswana the okavango delta of northern botswana is one of the world s largest inland deltas or megafans to obtain information on the character of sediments and basement depths audio magnetotelluric amt

cooperative constrained inversion of multiple electromagnetic data sets abstractwe evaluated a method for cooperatively inverting multiple electromagnetic em data sets with bound constraints to produce a consistent 3d resistivity model with improved resolution field data from the antonio gold deposit in peru and synthetic data were used to demonstrate this technique we first separately inverted field airborne time domain em aem controlled source audio frequency magnetotellurics csamt and direct current resistivity measurements each individual inversion recovered a resistor related to gold hosted silica alteration within a relatively conductive background the outline of the resistor in each inversion was in reasonable agreement with the mapped extent of known near surface silica alteration variations between resistor recoveries in each 3d inversion model motivated a subsequent cooperative method in which aem data were inverted sequentially with a combined csamt and dc data set this cooperative approach was first applied to a synthetic inversion over an antonio l

marine controlled source electromagnetic of the scarborough gas field part 3 multicomponent 2d magnetotelluric controlled source electromagnetic inversionsmulticomponent inversion

an objective real time data adaptive technique for efficient model resolution improvement in magnetotelluric studies a scheme is described whereby the error associated with the least well resolved model eigenparameter in a magnetotelluric survey is reduced by focusing data collection on a specific range of frequencies the scheme also gives a quantitative estimate of the statistical error associated with the least well resolved model parameter and thus provides an objective criterion to the operator regarding when to cease data collection at that location the scheme is based on a linearization of the relationship between variations in the model parameters and the changes thereby introduced to the computed response function the matrix of partial derivatives describing this linearization is factored orthogonally by a singular value decomposition the scheme is illustrated by applying it to a synthetic data set also the algorithm has been coded in basic on an hp9845 and employed in the field an example is given of its field operation in a sedimentary basin environment

damped least squares inversion of time domain airborne em data based on singular value decomposition1 airborne electromagnetic aem methods are increasingly being used as tools of geological mapping groundwater exploration and prospecting for coal and lignite in such applications quantitative interpretation is commonly based on the layered earth model a new approach a damped least squares inversion with singular value decomposition is proposed for interpretation of time domain towed bird aem data studies using theoretical and field aem data indicate that inversion techniques are dependable and provide fast converging solutions an analysis has been made of the accuracy of model parameter determination which depends on resistivity and thickness distribution in the common case of conductive overburden upper layer resistivity and thickness are usually well determined although situations exist where their separation becomes difficult in the case of a resistive layer overlying a conductive basement the layer thickness is the best determined parameter in both cases estimates of basement resistivity are the least reliable field data obtained with the chinese made m l aem system in dongling anhui province china were processed using the described inversion algorithm the survey area comprised fluvial cenozoic clays and weathered mesozoic sediments inversion of aem data resulted in accurate depth to bedrock sections and realistic estimates of the resistivities of overburden and bedrock which agree with the results of drilling and resistivity sounding

new results on the resistivity structure of merapi volcano indonesia derived from three dimensional restricted inversion of long offset transient electromagnetic data three long offset transient electromagnetic lotem surveys werecarried out at the active volcano merapi in central java indonesia during the years 1998 2000 and 2001 the measurements focused on the general resistivity structure of the volcanic edifice at depths of 0 5 2 km and the further investigation of a southside anomaly the measurements were insufficient for a full 3d inversion scheme which could enable the imaging of finely discretized resistivity distributions therefore a stable damped least squares joint inversion approach is used to optimize 3d models with a limited number of parameters the mode ls feature the realistic simulation of topography a layered background structure and additional coarse 3d blocks representing conductivity anomalies twenty eight lotem transients comprising both horizontal and vertical components of the magnetic induction time derivative were analyzed in view of the few unknowns we were able to achieve reasonable data fits the inversion results indicate an upwelling conductor below the summit suggesting hydrothermal activity in the central volcanic complex a shallow conductor due to a magma filled chamber at depths down to 1 km below the summit suggested by earlier seismic studies is not indicated by the inversion results in conjunction with an anomalous density model derived from arecent gravity study our inversion results provide information about the southern geological structure resulting from a major sector collapse during the middle merapi period the density model allows to assess a porosity range andthus an estimated vertical salinity profile to explain the high conductivities on a larger scale extending beyond the foothills of merapi

long offset transient em sounding north of the rhine ruhr coal district germany1 during the past two decades electromagnetic methods have been increasingly applied to problems in hydrocarbon exploration it has been shown that em methods achieve satisfactory results which can be supplementary to results of the seismic method we extend the application of the long offset transient electromagnetic sounding lotem to exploration problems in the coal mining industry a survey was conducted north of the rhine ruhr coal district using a grounded dipole source and receivers laid out along several profile lines giving areal coverage the strong noise from cultural as well as natural electromagnetic sources was reduced using prestack data processing techniques resulting in reliable data with a good signal to noise ratio the interpretation is self consistent and matches the well logs and the geological information of the area quite well the high station density permitted the mapping of the top of the carboniferous formation to a depth of between 800 and 1000 m below surface

on the salt water intrusion into the durusu lake istanbul a joint central loop tem and multi electrode ert field survey durusu lake is the biggest and most important freshwater source supplying drinking water to the european side of istanbul in this study electrical resistivity tomography ert and transient electromagnetic tem measurements were applied to detect a possible salt water intrusion into the lake and to delineate the subsurface structure in the north of durusu lake the ert and tem measurements were carried out along six parallel profiles extending from the sea coast to the lake shore on the dune barrier tem data were interpreted using different 1 d inversion methods such as occam marquardt and laterally constrained inversion lci ert data were interpreted using 2 d inversion techniques the inversion results of ert and tem data were shown as resistivity depth sections including topography the sand layer spreading over the basin has a resistivity of 150 400 omega m with a thickness of 5 10 m the sandy layer with clay silt and gravel has a resistivity of 15 100 omega m and a thickness of 10 40 m followed by a clay layer of a resistivity below 10 omega m when the inversion of these data is interpreted along with the hydrogeology of the area it is concluded that the salt water intrusion along the dune barrier is not common and occurs at a particular area where the distance between lake and sea is very close using information from boreholes around the lake it was verified that the common conductive region at depths of 30 m or more consists of clay layers and clay lenses

quasi 2d hybrid joint inversion of seismic and geoelectric data many joint inversion schemes use 1d forward modelling in the integrated interpretation of various geophysical data in extending the joint inversion approach to the investigation of 2d structures the discretization of the model parameters and the appropriate choice of the forward modelling procedure play a very important role in this paper a hybrid seismic geoelectric joint inversion method is proposed for the investigation of 2d near surface geological structures the electric and seismic models are coupled together through the use of common boundaries between the adjacent layers assuming a 2d model composed of homogeneous layers with curved boundaries a fast ray tracing algorithm is used for the calculation of refraction seismic traveltime data in the geoelectric forward modelling a locally 1d approximation is used the boundary surfaces are written in the form of series expansion the inversion algorithms are formulated for the expansion coefficients and the petrophysical parameters as unknowns two versions of the inversion method are proposed in versions a and b interval wise constant functions and chebyshev polynomials are respectively used as basis functions of the series expansion the versions are tested by means of synthetic and in situ measured data the tests show that both methods are stable and accurate

joint inversion of seismic traveltime and frequency domain airborne electromagnetic data for hydrocarbon exploration geophysical joint inversion requires setting of few parameters for the optimum performance of the process however there are yet no known detailed procedures for selecting the various parameters for performing the joint inversion previous works on the joint inversion of em and seismic data have reported parameter applications for both data sets acquired from the same dimensional geometry either both in 2d or in 3d and few on variant geometry but none has discussed the parameter selections for the joint inversion of methods from variant geometry for example a 2d seismic travel and pseudo 2d frequency domain em data with the advantage of affordable computational cost and the sufficient approximation of 1d em model in a horizontally layered sedimentary environment we are able to set optimum joint inversion parameters to perform structurally constrained joint 2d seismic traveltime and pseudo 2d em data for hydrocarbon exploration from the synthetic experiments even in the presence of noise we are a

ree geochemistry of eclogites and associated rocks from sauviat sur vige massif central france abstract representative samples of metagabbros eclogites and a garnet peridotite from the massif de sauviat sur vige west massif central have been analyzed for major and trace elements including ree the lree enriched patterns are distinct from those of modern morb but resemble those of continental or ocean island tholeiites an intraplate tectoning setting is thus inferred geochemical modeling using ree and major element contents suggests that all the rock types might be related genetically by fractional crystallization and in some instances by mixing of cumulates and differentiated liquid as in the case of the garnet peridotite p t estimates from microprobe analyses of coexisting garnet clinopyroxene pairs yield about 820 c and p 15 kb for the eclogite facies metamorphism

disequilibrium in co existing clinopyroxene and garnet from blueschist facies fe rich eclogites voltri group italy clinopyroxenes and garnets from 11 blueschist facies fe rich eclogite samples from the voltri group show a wide range of chemical compositions detailed analyses of single pyroxene and garnet grains show wide and scattered chemical inhomogeneity the kd kd fe2 mg gt fe2 mg cpx ranges from 20 to 87 based on rim analyses only the data obtained indicate that the mineral pairs never attained equilibrium under uniform p t conditions and that the compositions of the metamorphic minerals were influenced mainly by the composition of the pre metamorphic minerals and by topotactical reactions

a survey of current trends in near surface electrical and electromagnetic methods electricalandelectromagnetice emmethodsfornearsurface investigations have undergone rapid improvements over the past few decades besides the traditional applications in groundwater investigations natural resource exploration and geological mapping a number of new applications have appeared these include hazardous waste characterizationstudies precision agricultureapplications archeological surveys and geotechnical investigations the inclusion of microprocessors in survey instruments development ofnewinterpretationalgorithms andeasyaccesstopowerful computers have supported innovation throughout the geophysical community and the e em community is no exception most notable are development of continuous measurement systems that generate large dense data sets efficiently these have contributed significantly to the usefulness of e em methods by allowing measurements over wide areas without sacrificing lateral resolution the availability of theseluxuriantdatasetsinturnspurreddevelopmentofinterpretation algorithms including laterally constrained 1d inversionaswellasinnovative2d and3d inversionmethods taken together these developments can be expected to improve the resolution and usefulness of e em methods and permit them to be applied economically the trend is clearly towarddensesurveyingoverlargerareas followedbyhighly automated post acquisition processing and interpretation to provide improved resolution of the shallow subsurface in a cost effectivemanner

quasi 2d inversion of dcr and tdem data for shallow investigations joint or sequential inversion of direct current resistivity dcr and time domain electromagnetic tdem data commonly are performed for individual soundings assuming layered earth models dcr and tdem have different and complementary sensitivity to resistive and conductive structures making them suitable methods for the application of joint inversion techniques this potential joint inversion of dcr and tdem methods has been used by several authors to reduce the ambiguities of the models calculated from each method separately a new approach for joint inversion of these data sets based on a laterally constrained algorithm was found the method was developed for the interpretation of soundings collected along a line over a 1d or 2d geology the inversion algorithm was tested on two synthetic data sets as well as on field data from saudi arabia the results show that the algorithm is efficient and stable in producing quasi 2d models from dcr and tdem data acquired in relatively complex environments

joint inversion of marine magnetotelluric and gravity data incorporating seismic constraints preliminary results of sub basalt imaging off the faroe shelf breakup of the north atlantic during the early tertiary was accompanied by widespread and massive magmatism resulting in the coverage of large areas of the north atlantic with flood basalts these flood basalts hamper seismic investigations of underlying sequences and thus the understanding of the rifting subsidence and evolution of the margin which in turn increases the risk for hydrocarbon exploration in this paper we present a methodology for the simultaneous joint inversion of diverse geophysical datasets i e free air gravity and magnetotelluric soundings mt using seismic a priori constraints the attraction of the joint inversion approach is that different geophysical measurements are sensitive to different properties of the sub surface so through joint inversion we significantly reduce the null space and produce a single model that fits all datasets within a predefined tolerance using sensitivity analysis of synthetic data we show how each data set contains complementary important information of the supra and sub basalt structure while separate inversions of individual datasets fail to image through the basalt layer our joint inversion approach leads to a much improved sub basalt structure application of the joint inversion algorithm to satellite gravity data and mt data acquired on the flare10 seismic line south west of faroe islands supports the existence of a 1 km to 2 km thick low velocity region that might be indicative of the existence of a sedimentary basin underneath the basalt layer though in this paper we demonstrate the use of joint inversion on a sub basalt target we believe it has wider applicability to other areas where conventional seismic imaging fails

joint inversion of geophysical data summary by jointly inverting several different kinds of geophysical measurements at a site we avoid some of the ambiguity inherent in the individual methods we show how this can be done for the combination of dc resistivity and magnetotelluric measurements on a layered medium by considering a simple 3 layer model the combination resolves the resistivity of the thin resistive second layer even though neither of the two methods can do so alone the method is then applied to field data from a shallow sedimentary basin a blind zone occurs beneath a thick near surface conductive shale by a study of the eigenvalue structure of the model it can be seen that resolution in this zone would be slightly enhanced by higher frequency magnetotelluric data but additional dc data at larger spacing would yield no improvement

a joint inversion algorithm to process geoelectric and surface wave seismic data part ii applications for the exploration of near surface structures seismic and geoelectric methods are often applied usually these two types of method give independently of each other a sufficiently exact model of the geological structure however sometimes the inversion of the seismic or geoelectric data fails these failures can be avoided by combining various methods in one joint inversion which feads to much better parameter estimations of the model than the independent inversions a suitable seismic method for exploring near surface structures is the use of dispersive surface waves the dispersive characteristics of rayleigh and love surface waves depend strongly on the structural and petrophysical seismic velocities features of the near surface underground geoelectric exploration of the structure underground may be carried out with the well known methods of dc resistivity sounding such as the schlumberger the radial dipole and the two electrode arrays the joint inversion algorithm is tested by means of synthetic data it is demonstrated that the geoelectric joint inversion of schlumberger radial dipole and two electrode sounding data yields more reliable results than the single inversion of a single set of these data the same holds for the seismic joint inversion of love and rayleigh group slowness data the best inversion result is achieved by performing a joint inversion of both geoelectric and surface wave data the effect of noise on the accuracy of the solution for both gaussian and non gaussian sparsely distributed large errors is analysed after a comparison between least square lsq and least absolute deviation lad inversion results the lad joint inversion is found to be an accurate and robust method

coronitic reactions and ductile shear zones in eclogitised ophiolite metagabbro western alps north italy abstract the objective of this work is to study the most significant static and syn tectonic transformations which accompanied the eclogite metamorphism 450 50 c 12 15 kbar of an ophiolite metagabbro from the western alps in partly undeformed volumes abundant igneous mineral relics occur and the eclogite metamorphism produced coronitic or incomplete pseudomorphic reactions the disequilibrium or local equilibrium conditions implied by these features suggest that slow diffusion and interface kinetics were the rate limiting factors which prevented a large scale eclogite equilibration the undeformed volumes are bounded by syn eclogite ductile shear zones where the magmatic minerals and textures are obliterated and a new fabric foliation develops the enlargement of equilibrium domains observed in the shear zones indicates that a close approach to eclogite equilibration of these metagabbros was not attained without the catalytic effect of pervasive deformation the bulk rock chemistry also played an important role in determining the kind of eclogite assemblage in particular only sheared gabbros rich in fe can produce bimineralic eclogites

identifying seawater intrusion in coastal areas by means of 1d and quasi 2d joint inversion of tdem and ves data abstract seawater intrusion is an increasingly widespread problem in coastal aquifers caused by climate changes sea level rise extreme phenomena like flooding and droughts and groundwater depletion near to the coastline to evaluate and mitigate the environmental risks of this phenomenon it is necessary to characterize the coastal aquifer and the salt intrusion geophysical methods are the most appropriate tool to address these researches among all geophysical techniques electrical methods are able to detect seawater intrusions due to the high resistivity contrast between saltwater freshwater and geological layers the combination of two or more geophysical methods is recommended and they are more efficient when both data are inverted jointly because the final model encompasses the physical properties measured for each methods in this investigation joint inversion of vertical electric and time domain soundings has been performed to examine seawater intrusion in an area within the ferragudo albufeira aquifer system algarve south of portugal for this purpose two profiles combining electrical resistivity tomography ert and time domain electromagnetic tdem methods were measured and the results were compared with the information obtained from exploration drilling three different inversions have been carried out single inversion of the ert and tdem data 1d joint inversion and quasi 2d joint inversion single inversion results identify seawater intrusion although the sedimentary layers detected in exploration drilling were not well differentiated the models obtained with 1d joint inversion improve the previous inversion due to better detection of sedimentary layer and the seawater intrusion appear to be better defined finally the quasi 2d joint inversion reveals a more realistic shape of the seawater intrusion and it is able to distinguish more sedimentary layers recognised in the exploration drilling this study demonstrates that the quasi 2d joint inversion improves the previous inversions methods making it a powerful tool applicable to different research areas

shear deformation and eclogite formation within granulite facies anorthosites of the bergen arcs western norway the anorthosites of the bergen arcs contain two distinct metamorphic mineral assemblages which are stable under different p t conditions a granulite facies assemblage which equilibrated at t 800 900 c p 10 kbar is defined by the minerals plagioclase al rich diopside cpx i garnet gnt i scapolite orthopyroxene dark brown hornblende this assemblage is linked by corona structures to a primary magmatic mineralogy where coexistence of olivine and plagioclase limits the maximum crystallization pressure of the anorthosites to 8 kbar at 1200 c the anorthosites are transected by a series of fine grained shear zones in which the granulite facies assemblage is replaced by an eclogite mineralogy defined by omphacite cpx ii jd40 50 garnet kyanite epidote clinozoisite phengite quartz amphibole with plagioclase sometimes remaining in the marginal parts mineral compositions indicate equilibration conditions for the eclogite paragenesis of t 700 800 c p 16 19 kbar a series of textural and mineralogical changes which can be observed as the strain increases into the shear zones demonstrates that the eclogite mineralogy is formed at the expense of the granulite facies minerals during the early stages of shear zone development the eclogite mineralogy defines a strong mylonitic fabric which again is truncated by centimetres thick secondary shear zones containing clasts of both granulite and eclogite minerals these latter fine grained ultramylonites may be connected to uplift of this deep seated complex the eclogite shear zones are highly oblique to the granulite structures indicating that the eclogite shear zones formed under a new stress regime rb sr dating shows that the granulite facies assemblage formed in sveconorwegian time or earlier while minerals from shear zones define ages around 400 ma indicating a caledonian formation of the eclogites this work demonstrates the critical role of deformation in triggering metamorphic reactions whether the shear stress also was important in stabilizing the eclogite assemblages is not clear from the available data

delineation of sediments below flood basalts by joint inversion of seismic and magnetotelluric data a one dimensional joint inversion ji scheme considering seismic reflection and refraction and mt data is developed its efficacy to resolve low velocity conducting sediments below high velocity resistive flood basalts is tested for a representative geological model considering noisy incomplete data the ji is found to provide improved results in comparison to those obtained by individual seismic and mt inversions

metagabbro and associated eclogites in the lubrin area nevado filabride complex spain abstract several small bodies of metabasite maximum dimensions of 1000 m x 500 m are included in the metamorphic rocks of the nevado filabride complex in the betic cordilleras almeria region the body of 400 m x 100 m located 200 m due west of the lubrin village contains troctolitic gabbro with well preserved igneous textures and mineral compositions wholly amphibolitized gabbro garnet bearing metagabbro eclogite along with the textural and mineral changes sensible and regular geochemical variations can be observed where the content of mgo decreases from 24 to 11 while that of cao and na2o increases from 7 to 11 and from 2 to 3 respectively in addition the content of some minor elements such as sr y nb zr and sc increases while that of ni and cr decreases from troctolitic gabbro to the eclogite the amphibolitized gabbro shows values scattered around those of the troctolitic gabbro these geochemical variations are ascribed to inherited differences in the pre metamorphic protolith i e a fractionated gabbro which varies from olivine rich to clinopyroxene rich gabbro nevertheless some metasomatism affected the lubrin body without changing the main chemical trends as documented by the significantly different 87sr 86sr ratios of each rock type this points to a metasomatism which involved the introduction of crustal radiogenic strontium the petrographical and mineral chemical features are interpreted to be the result of syn metamorphic fluid circulation possibly combined with deformation by shearing the igneous texture and mineral chemistry have been retained wherever both fluid circulation and shearing were ineffective on the contrary where both events were effective the formation of eclogite occurred later the entire body underwent a retrogressive amphi bolitic stage under greenschist facies conditions which was probably responsible for the formation of the amphibolitized gabbro portion and for the retrogression of the eclogite

multiple level set joint inversion of traveltime and gravity data with application to ore delineation a synthetic study abstractwe have developed a multiple level set method for simultaneous inversion of gravity and seismic traveltime data the method recovers the boundaries between regions with distinct physical properties assumed constant and known creating structurally consistent models of two subsurface properties p wave velocity and density in single level set methods only two rock units can be considered background and inclusion such methods have been applied to examples representing various geophysical scenarios including in the context of joint inversion in multiple level set methods several units can be considered which make them far more applicable to real earth scenarios recently a multiple level set method has been proposed for inversion of magnetic data we extend the multiple level set formulation to joint inversion of gravity and traveltime data improving upon previous work and we investigate applicability of such an inversion method in ore delineation in mineral exploration environments trad

joint inversion of seismic and geoelectric data recorded in an underground coal mine1 until the present time the rock coal rock layer sequence and offsets in coal seams in underground coal mines have been detected with the aid of seismic waves and geoelectric measurements in order to determine the geometrical and petrophysical parameters of the coal seam situation the data recorded using seismic and geoelectric methods have been inverted independently in consequence the inversion of partially inaccurate data resulted in a certain degree of ambiguity this paper presents the first results of a joint inversion scheme to process underground vertical seismic profiling data geolectric resistivity and resistance data the joint inversion algorithm makes use of the damped least squares method and its weighted version to solve the linearized set of equations for the seismic and geolectric unknowns in order to estimate the accuracy and reliability of the derived geometrical and petrophysical layer parameters both a model covariance matrix and a correlation matrix are calculated the weighted least squares algorithm is based on the method of most frequent values mfv the weight factors depend on the difference between measured data and those calculated by an iteration process the joint inversion algorithm is tested by means of synthetic data compared to the damped least squares algorithm the mfv inversion leads to smaller estimation errors as well as lower sensitivities due to the choice of the initial model it is shown that compared to an independent inversion the correlation between the model parameters is definitely reduced while the accuracy of the parameter estimation is appreciably increased by the joint inversion process thus the ambiguity is significantly reduced finally the joint inversion algorithm the mfv method is applied to underground field data the model parameters can be derived with a sufficient degree of accuracy even in the case of noisy data

long offset transient electromagnetic lotem depth soundings applied to crustal studies in the black forest and swabian alb federal republic of germany the long offset transient electromagnetics lotem sounding method is a valuable complementary technique for deep seismic exploration as applied to earth crustal investigations during 1986 two lotem surveys were conducted to augment completed seismic investigations for crustal studies in southern west germany east of the rhine graben our studies were motivated by the geoscientific activities within the framework of the german continental deep drilling ktb project the survey objectives were 1 to determine the applicability of the lotem method to crustal geophysics 2 to investigate the correlation of resistivity anomalies with velocity anomalies and 3 to confirm the method and interpretation in an area of known geology with existing geophysical data the black forest and the urach geothermal area survey results exhibit conductive features in the upper 10 km of the crust which were not previously defined by other geophysical data importantly the results demonstrate a very strong correlation

2d joint inversion of geophysical data using petrophysical clustering and facies deformation geologic expertise and petrophysical relationships can be brought together to provide prior information while inverting multiple geophysical data sets the merging of such information can result in more realistic solution in the distribution of the model parameters we have evaluated the geophysical inverse problem in terms of gaussian random fields with mean functions controlled by petrophysical relationships and covariance functions controlled by a prior geologic cross section including the definition of spatial boundaries for the geologic facies the petrophysical relationship problem is formulated as a regression problem upon each facies the inversion of the geophysical data is performed in a bayesian framework we have developed the usefulness of this strategy using a first synthetic case for which we have performed a joint inversion of gravity and galvanometric resistivity data with the stations located at the ground surface the joint inversion was used to recover the density and resistivity distributions of the subsurface in a second step we considered the possibility that the facies boundaries were deformable and their shapes were inverted as well we used the level set approach to perform such deformation preserving a priori topological properties of the facies throughout the inversion with the help of a priori facies petrophysical relationships and the topological characteristics of each facies we made a posteriori inference about multiple geophysical tomograms based on their corresponding geophysical data misfits we have applied this method to a second synthetic case showing that we can recover the heterogeneities inside the facies the mean values for the petrophysical properties and to some extent the facies boundaries using the 2d joint inversion of gravity and galvanometric resistivity data

delineation of shallow subsurface structure by azimuthal resistivity sounding and joint inversion of ves tem data case study near lake qaroun el fayoum egypt an azimuthal resistivity survey was conducted at the transition zone between the desert area and the cultivated land near lake qaroun egypt this area has been affected by an east west trending fault system as indicated from the surface geology apparent resistivity values were plotted along azimuth on a polar diagram resistivity anomalies for most of the ab 2 values with long axes strike in a direction parallel to the contact between the desert and cultivated lands indicate the presence of electrical macro anisotropy mainly due to the faulting effect at this area vertical electrical soundings ves and transient electromagnetic tem measurements were conducted at eight stations along a line that crosses the boundary between the desert and cultivated land joint inversion of ves tem data was successfully used for identification of the subsurface lithostratigraphic succession and demonstrated the effect of the fault zone on the investigated subsurface medium apparent anisotropy coefficients at all current electrode spacings were calculated plotted against ab 2 values and compared with the geoelectrical cross section the effect of the fault zone was detected at ab 2 spacings equal to 100 m and extended downward and is largely related to the depth of the fault as indicated in the constructed cross section

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

examples of resolution improvement in geoelectrical soundings applied to groundwater investigations1 one simulation and two field examples from new jersey illustrate resolution improvement in geoelectrical soundings applied to groundwater exploration layered earth parameter resolution is derived from data obtained with the commonly used methods of resistivity induced polarization ip and transient electromagnetic tem soundings resolution improvement is achieved by simultaneous inversion of two or more data sets and by constraining parameters of the inverse problem a quantitative analysis showing the contribution of ip data to the resolution of geo electric sections is presented simultaneous inversion of simple ip data with conventional resistivity and resistivity tem data sets resulted in improved parameter resolution ip data improved resolution in three ways 1 by decoupling correlated layered earth parameters 2 by adding information to a geological interpretation about a second physical property namely chargeability and 3 by increasing the electrical information available

improved hydrogeophysical characterization using joint inversion of cross hole electrical resistance and ground penetrating radar traveltime data appropriate regularizations of geophysical inverse problems and joint inversion of different data types improve geophysical models and increase their usefulness in hydrogeological studies we have developed an efficient method to calculate stochastic regularization operators for given geostatistical models the method which combines circulant embedding and the diagonalization theorem of circulant matrices is applicable for stationary geostatistical models when the grid discretization in each spatial direction is uniform in the volume of interest we also used a structural approach to jointly invert cross hole electrical resistance and ground penetrating radar traveltime data in three dimensions the two models are coupled by assuming at all points that the cross product of the gradients of the two models is zero no petrophysical relationship between electrical conductivity and relative permittivity is assumed but is instead obtained as a by product of the inversion the approach has been applied to data collected in a u k sandstone aquifer in order to improve characterization of the vadose zone hydrostratigraphy by analyzing scatterplots of electrical conductivity versus relative permittivity together with petrophysical models a zonation could be obtained with corresponding estimates of the electrical formation factor the water content and the effective grain radius of the sediments the approach provides greater insight into the hydrogeological characteristics of the subsurface than by using conventional geophysical inversion methods

electromagnetic evidence for an ancient avalanche caldera rim on the south flank of mount merapi indonesia abstract long offset transient electromagnetic lotem data and vibrotem data from the south flank of mount merapi on java island indonesia are interpreted with one dimensional 1d inversions as well as two dimensional 2d forward modelling one dimensional joint inversions of several components of the electromagnetic field with occam s method reduce the number of equivalent models which were derived from inversions of single components and fit the data to a similar misfit the 1d results together with results from other geophysical measurements serve as the basic model for further 2d forward modelling the final model depicts a layering that follows the topography of the strato volcano in the depth range of 500 m to 1000 m the resistivity of the layers decreases rapidly downwards into a good conductor with resistivities below 10 m the deepest layer has a resistivity of 0 4 m which is quantitatively explained with a combination of saline fluids and hydrothermally altered minerals furthermore the final model supports a hypothesis from the interpretation of central loop tem transient electromagnetic data that there is a fault structure below the southern flank approximately 7 3 km south of the summit to the north of the fault the top of the good conductor is lowered from a depth of 500 m to 1000 m we propose that the fault structure coincides with an ancient avalanche caldera rim

alternating joint inversion of controlled source electromagnetic and seismic data using the joint total variation constraint an alternating joint inversion method for controlled source electromagnetic csem and seismic data is developed the structural constraint is used for correlating and constraining the electromagnetic em resistivity and seismic velocity parameters during the inversion the structural coupling used is the joint total variation jtv constraint which is incorporated into the objective function of the individual em or seismic inversion to enforce the structural similarity between the resistivity and velocity in this paper the conventional cross gradient constraint is not preferred as it can only be used for enforcing structural similarity for 2 d or 3 d case since it is always zero for 1 d joint inversion the jtv constraint can be applied for 1 d joint inversion as well as for the 2 d 3 d case which is of a broader interest the improved gauss newton gn is used for minimizing the objective function and for reconstructing the subsurface resistivity and velocity the alternating joint inversion algorithm is applied for integrating land csem data with cross well seismic data for subsurface reservoir evaluation and water oil identification numerical examples show that the developed joint inversion can improve the inversion results significantly over those from the separate em or seismic inversion

a time domain electromagnetic survey of the tag hydrothermal mound a conductivity survey of the tag mound was made using innovative transient electric dipole dipole instrumentation the receiver was deployed on the sulfide mound 30 m south of the central black smoker while the submersible alvin carried the transmitter on a survey path around the receiver at a radius of approximately 70 m conductivity measurements of the seafloor between the transmitter and receiver were made at 5 minute intervals the survey lasted 4 hours measurements made at 12 sites are initially interpreted in terms of an apparent conductivity of a uniform seafloor a more complex model in which the seafloor has two layers is then used apparent conductivities range from 1 4 to 15 9 s m generally higher than that of seawater the results suggest possible focusing of hydrothermal convection in the northern quadrant of the mound adjacent zones of anhydrite accumulation and fluid convection in the north eastern quadrant heterogeneity and layering in the kremlin zone and unexpected spatial variability in the western quadrant the data from several sites show evidence of distortion attributed to 3 d anomalies

joint inversion of gravity magnetic and petrophysical data a case study from a gabbro intrusion in boden sweden we have studied a gabbro intrusion in northern sweden using 3d inversion of airborne magnetic data ground based gravity data and petrophysical measurements on outcrop samples gabbro intrusions are of interest because they are potential hosts of cu ni and platinum group element mineralization we developed a joint inversion algorithm and applied it to both potential field data sets to obtain spatial distributions of density and magnetic susceptibility the distributions were coupled through a nonrigidly enforced parameter relationship determined from the petrophysical samples we managed the problem of balancing the influence of the two data sets by a novel adaptive reweighting scheme that enforced the discrepancy principle for each data set independently we demonstrated in tests with synthetic data that neither individual nor joint inversions gave reliable estimates for the depth extension of the intrusive body the near surface details or any complex geometrical features however the joint inversion improved the image of the interface between the intrusion and the surrounding rocks and revealed that the density and susceptibility models satisfied the observed petrophysical relationship which in turn caused the structures in the models to align the geometry of the intrusion was an intrinsic result of the inversion based on the two distinct petrophysical trends for the gabbro and the surrounding rocks the inferred shape was simple and concise and was therefore a useful and testable hypothesis about the subsurface geology that was in agreement with both potential field data sets and the petrophysical information

joint inversion of seismic and electric data applied to 2d media abstractmethods based on the seismic p wave seismic surface wave and apparent resistivity are commonly used in the solution of several near surface problems however the solution nonuniqueness and the intrinsic limitations of these methods can cause inconsistency in the final results dispersion curves of surface waves p wave traveltimes and apparent resistivity data were jointly inverted to obtain internally consistent and more reliable final model of p and s wave velocities and resistivity a collection of 1d layered models was obtained by a deterministic joint inversion algorithm based on the laterally constrained inversion scheme the three data sets were jointly inverted imposing the same structure and poisson s ratio was introduced as a physical link between p and s wave velocities to better constrain the inversion no physical link was imposed between the resistivity and the seismic velocities the inversion algorithm was tested on synthetic data and then applied to a field case where bench

joint interpretation of gravity and magnetic data over axial symmetric bodies with application to the darnley bay anomaly nwt canada a method is presented for determining bounds of the properties of axial symmetric bodies from a finite number of gravity and magnetic observations based on parker s theory of ideal bodies bounds on the density contrast and the intensity of magnetization are calculated as a function of depth to the top of the anomalous source restricting the range of smallest possible solutions to fit the data the model studied is approximated by an array of vertical annuli cylinders each of uniform density and magnetization linear programming algorithms based on the ideal body theory were used to calculate the distribution of these parameters within the body simultaneous inversion of gravity and magnetic data is performed assuming a constant ratio between the density contrast and the intensity of magnetization and that a common body is responsible for both observed fields the parameter kappa absolute value of j delta rho provides information about the rock type of the structure interpretation of gravity and aeromagnetic data from darnley bay nwt canada indicated the presence of a shallow ultrabasic intrusion

pulled array continuous electrical sounding with an additional inductive source an experimental design study electrical and electromagnetic profiling methods are used extensively in environmental geophysical investigations for many different purposes the pulled array continuous electrical sounding paces method where a tail of electrodes is towed behind a small vehicle while continuously and simultaneously measuring several electrode configurations has been used extensively for mapping the vulnerability of aquifers in denmark measurements are taken every 1 m and 10 15 km of profile can be achieved in one day this paper presents a theoretical study of the resolution capabilities of paces measurements as they are now performed and an experimental design study for including an inductive source in the measuring equipment the joint interpretation of the galvanic data set of ordinary paces measurements with inductive data from a horizontal magnetic dipole source will enhance the resolution capabilities of the data set significantly the study is carried out as an analysis of the uncertainty of the model parameters of one dimensional three layer models using the estimation error variances of the inversion problem the results indicate that the addition of only two frequency data from a magnetic dipole source will substantially improve the resolution of the subsurface resistivity structure the improvement is model dependent but reduction in the relative error of model parameters by an order of magnitude is observed

inversion of long offset tem soundings near the borehole munsterland 1 germany and comparison with mt measurements summary data from a long offset transient electromagnetic lotem survey in northwest germany around the borehole munsterland 1 are interpreted using 1 d inversion special emphasis is given to the fact that the best fitting model is not necessarily the most realistic one we therefore investigate different inversion algorithms in order to obtain a more geologically meaningful result the 1 d inversion results using a second order marquardt algorithm show a three layer structure with a conductor embedded between two more resistive layers this is in good agreement with the known lithology and the well logs profile inversion uses the result from one site as the starting model for the next the application of the technique yields a smoother section than the individual inversions and corresponds more closely to the presumably layered structure in the area if desired using a parameter weighting scheme makes it possible to force consistency at the cost of a larger misfit yielding a smooth section even in a part of the area where the data are influenced by a 3 d anomaly occam inversion is a smoothness constrained technique which is independent of the starting model the result of the occam inversion shows the same features as the marquardt inversion including effects which are attributed to 3 d distortions in the data joint inversions of the lotem data were carried out with magnetotelluric data from the same area in that case the lotem electric field is recognized as crucial for the resolution of the resistive layer in the section

on reducing ambiguity in the interpretation of transient electromagnetic sounding data1 an attempt to resolve non uniqueness in the interpretation of transient electromagnetic tem sounding data using measured data alone is made it is shown in the various examples studied that sufficiently early time measurements can be the determining factor in reducing the ambiguity caused by model equivalence the early delay times thus play a dual role in transient soundings they are responsible for resolving shallow structures and they may eliminate the ambiguity in the interpretation of geoelectric parameters of deeper targets this is illustrated by the results of a follow up tem survey at the dead sea coast of israel where the use of supplementary early time measurements allowed non uniqueness in the determination of the depth to fresh saline groundwater interface to be resolved

comparison of five least squares inversion techniques in resistivity sounding a brief history of the development of the inverse problem in resistivity sounding is presented with the development of the equations governing the least squares inverse five algorithms for finding the minimum of the least square problem are described and their speed of convergence is compared on data from two planar earth models of the five algorithms studied the ridge regression algorithm required the fewest numbers of forward problem evaluations to reach a desired minimum solution space statistics including 1 parameter standard errors 2 parameter correlation coefficients 3 model parameter eigenvectors and 4 data eigenvectors are discussed the type of weighting applied to the data affects these statistical parameters weighting the data by taking log 10 of the observed and calculated values is comparable to weighting by the inverse of a constant data error the most reliable parameter standard errors are obtained by weighting by the inverse of observed data errors all other solution statistics such as dataparameter eigenvector pairs have more physical significance when inverse data error weighting is used

incorporation of topography into two dimensional resistivity inversion direct current resistivity data acquired on rough terrain can be interpreted by using an appropriate inversion technique after a topographic correction in order to avoid the influence of a possibly incomplete topographic correction an improved two dimensional resistivity inversion algorithm has been developed to estimate the subsurface resistivity distribution in the presence of topography in this paper fully discretized modeling is based on the finite element method and the iterative inversion scheme is derived from the second order marquardt damped least squares method the algorithm has been tested on both synthetic and field resistivity data with topography incorporated explicitly into the inversion model both theoretical and field studies indicate that the technique is computationally efficient and provides an improved geologic interpretation for complex subsurface structures a four electrode configuration is used in the algorithm so that the inversion can represent most field measurements

a geophysical study of the taupo volcanic zone new zealand the taupo volcanic zone is a region of intense volcanic activity from which over 16 000 km3 of lavas and pyroclastics have been erupted since the late pliocene analysis of gravity and magnetic anomalies over the zone has revealed the presence of five major centers each associated with an approximately circular negative gravity anomaly and a positive pseudogravity anomaly these centers are interpreted as collapse features resulting from large scale withdrawal of magma from the upper crust four of the depressions occur beneath recognized volcanic centers or calderas the fifth kapenga is inferred to underlie an extinct hidden volcanic center three dimensional models of the thicknesses of low density and magnetized rocks in the taupo volcanic zone have been determined by inversion of gravity and magnetic anomalies beneath three of the centers the thicknesses of low density and magnetized rocks are approximately equal 2 3 km that is the collapse structures are infilled by magnetized volcanics however there is a significant discrepancy between the thicknesses of the gravity 5 km and magnetic models 1 5 km in the region of the okataina volcanic centre it is therefore suggested that a significant volume of low density nonmagnetic rock possibly acidic magma underlies okataina

statistical evaluation of mt and amt methods applied to a basalt covered area in southeastern anatolia turkey ilkisik o m and jones a g 1984 statistical evaluation of mt and amt methods applied to a basalt covered area in southeastern anatolia turkey geophysical prospecting 32 706 724 the efficacy of the magnetotelluric and audiomagnetotelluric mt amt methods for detailing the structure of a hypothetical geological section is investigated by using the singu lar value decomposition svd technique the section is representative of southeastern turkey which is mostly covered by basalt and is a prime area for oil exploration one of the geological units the germav shale at a depth of 600 m is a problem layer for electromagnetic surveys because of its very low resistivity on average 3 om and highly variable thickness across the area 200 900 m in the mt frequency range 0 0004 40 hz its total conductance or since its resistivity is known from resistivity log information its thickness is the best resolved model parameter the total depth to the germav shale and the resistivity of the cambrian precambrian basement are the marginally resolved parameters in the amt frequency range 4 10000 hz the resistivity of the surface basalt layer strongly affects the resolution of the other less important model parameters which are the total depth to the germav shale and the total conductance of the germav shale the errors in the measure ments determine the number of model parameters resolvable and are also important for interpretation of the geological model parameters to within a desired accuracy it is shown that statistical evaluation of the mt and or amt interpretations by using an svd factorization of the sensitivity matrix can be helpful to define the importance of some particular stage of the interpretation and also provides a priori knowledge to plan a pro posed survey arrangements of mt and amt observations together with some schlumber ger resistivity soundings on a large grid will certainly provide three dimensional detailed information of the deep geoelectric structure of the area

joint inversion of long offset and central loop transient electromagnetic data application to a mud volcano exploration in perekishkul azerbaijan mud volcanism is commonly observed in azerbaijan and the surrounding south caspian basin this natural phenomenon is very similar to magmatic volcanoes but differs in one considerable aspect magmatic volcanoes are generally the result of ascending molten rock within the earth s crust whereas mud volcanoes are characterised by expelling mixtures of water mud and gas the majority of mud volcanoes have been observed on ocean floors or in deep sedimentary basins such as those found in azerbaijan furthermore their occurrences in azerbaijan are generally closely associated with hydrocarbon reservoirs and are therefore of immense economic and geological interest the broadside long offset transient electromagnetic method and the central loop transient electromagnetic method were applied to study the inner structure of such mud volcanoes and to determine the depth of a resistive geological formation that is predicted to contain the majority of the hydrocarbon reservoirs in the survey area one dimensional joint inversion of central loop and long offset transient electromagnetic data was performed using the inversion schemes of occam and marquardt by using the joint inversion models a subsurface resistivity structure ranging from the surface to a depth of approximately 7 km was determined along a profile running perpendicular to the assumed strike direction lateral resistivity variations could only be determined in the shallow depth range using the transient electromagnetic data an attempt to resolve further two dimensional threedimensional resistivity structures representing possible mud migration paths at large depths using the long offset transient electromagnetic data failed moreover the joint inversion models led to ambiguous results regarding the depth and resistivity of the hydrocarbon target formation due to poor resolution at great depths 5 km thus 1d 2d modelling studies were subsequently performed to investigate the influence of the resistive terminating half space on the measured long offset transient electromagnetic data the 1d joint inversion models were utilised as starting models for both the 1d and 2d modelling studies the results tend to show that a resistive terminating half space implying the presence of the target formation is the favourable geological setting furthermore the 2d modelling study aimed to fit all measured long offset transient

integration of diverse physical property models subsurface zonation and petrophysical parameter estimation based on fuzzy c means cluster analyses inversions of an individual geophysical data set can be highly nonunique and it is generally difficult to determine petrophysical parameters from geophysical data we show that both issues can be addressed by adopting a statistical multiparameter approach that requires the acquisition processing and separate inversion of two or more types of geophysical data to combine information contained in the physical property models that result from inverting the individual data sets and to estimate the spatial distribution of petrophysical parameters in regions where they are known at only a few locations we demonstrate the potential of the fuzzy c means fcm clustering technique after testing this new approach on synthetic data we apply it to limited crosshole georadar crosshole seismic gamma log and slug test data acquired within a shallow alluvial aquifer the derived multiparameter model effectively outlines the major sedimentary units observed in numerous boreholes and provides plausible estimates

joint inversion of seismic traveltimes and gravity data on unstructured grids with application to mineral exploration seismic methods continue to receive interest for use in mineral exploration due to the much higher resolution potential of seismic data compared to the techniques traditionally used namely gravity magnetics resistivity and electromagnetics however the complicated geology often encountered in hard rock exploration can make data processing and interpretation difficult inverting seismic data jointly with a complementary data set can help overcome these difficulties and facilitate the construction of a common earth model we considered the joint inversion of seismic first arrival traveltimes and gravity data to recover causative slowness and density distributions our joint inversion algorithm differs from previous work by 1 incorporating a large suite of measures for coupling the two physical property models 2 slowly increasing the effect of the coupling to help avoid potential convergence issues and 3 automatically adjusting two tikhonov tradeoff parameters to achieve a desired fit to both d

integrating long offset transient electromagnetics lotem with seismics in an exploration environment1 the applications of electromagnetics have increased in the past two decades because of an improved understanding of the methods improved service availability and the increased focus of exploration in the more complex reservoir characterization issues for electromagnetic methods surface applications for hydrocarbon exploration and production are still a special case while applications in borehole and airborne research and for engineering and environmental objectives are routine in the past electromagnetic techniques in particular deep transient electromagnetics made up a completely different discipline in geophysics although many of the principles are similar to the seismic one with an understanding of the specific problems related to data processing initially and then acquisition the inclusion of principles learned from seismics happened almost naturally initially the data processing was very similar to seismic full waveform processing the hardware was also changed to include multichannel acquisition systems and the field procedures became very similar to seismic surveying as a consequence the integration and synergism of the interpretation process is becoming almost automatic the long offset transient electromagnetic lotem technique will be summarized from the viewpoint of its similarity to seismics the complete concept of the method will also be reviewed an interpretation case history that integrates seismic and lotem from a hydrocarbon area in china clearly demonstrates the limitations and benefits of the method