magnetic basement depth inversion in the space domain we present a total field anomaly inversion method to determine both the basement relief and the magnetization direction inclination and declination of a 2d sedimentary basin presuming negligible sediment magnetization our method assumes that the magnetic intensity contrast is constant and known we use a nonspectral approach based on approximating the vertical cross section of the sedimentary basin by a polygon whose uppermost vertices are forced to coincide with the basin outcrop which are presumably known for fixed values of the x coordinates our method estimates the z coordinates of the unknown polygon vertices to obtain the magnetization direction we assume that besides the total field anomaly information about the basement s outcrops at the basin borders and the basement depths at a few points is available to obtain stable depth to basement estimates we impose overall smoothness and positivity constraints on the parameter estimates tests on synthetic data showed that the simultaneous estimation of the irregular basement relief and the magnetization direction yields good estimates for the relief despite the mild instability in the magnetization direction the inversion of aeromagnetic data from the onshore almada basin brazil revealed a shallow eastward dipping basement basin

3d gravity inversion of basement relief a depth dependent density approach we present a 3d gravity inversion technique based on the marquardt algorithm to analyze gravity anomalies attributable to basement interfaces above which the density contrast varies continuously with depth the salient feature of this inversion is that the initial depth of the basement is not a required input the proposed inversion simultaneously estimates the depth of the basement interface and the regional gravity background applicability and efficacy of the inversion is demonstrated with a synthetic model of a density interface we analyze the synthetic gravity anomalies 1 solely because of the structure 2 in the presence of a regional gravity background and 3 in the presence of both random noise and regional gravity background the inverted structure remains more or less the same regardless of whether the regional background is simulated with a second degree polynomial or a bilinear equation the depth of the structure and estimated regional background deviate only modestly from the assumed ones in the presence of random noise and regional background the analyses of two sets of real field data one over the chintalpudi subbasin india and another over the pannonian basin eastern austria yield geologically plausible models with the estimated depths that compare well with drilling data

potential field inversion for a layer with uneven thickness the tyrrhenian sea density model abstract inversion of large scale potential field anomalies aimed at determining density or magnetization is usually made in the fourier domain the commonly adopted geometry is based on a layer of constant thickness characterized by a bottom surface at a fixed distance from the top surface we propose a new method to overcome this limiting geometry by inverting in the usual iterating scheme using top and bottom surfaces of differing but known shapes randomly generated synthetic models will be analyzed and finally performance of this method will be tested on real gravity data describing the isostatic residual anomaly of the southern tyrrhenian sea in italy the final result is a density model that shows the distribution of the oceanic crust in this region which is delimited by known structural elements and appears strongly correlated with the oceanized abyssal basins of vavilov and marsili

interactive gravity inversion we have developed a new approach for estimating the location and geometry of several density anomalies that give rise to a complex interfering gravity field the user interactively defines the assumed outline of the true gravity sources in terms of points and line segments and the method estimates sources closest to the specified outline to achieve a match between the predicted and observed gravity fields each gravity source is assumed to be a homogeneous body with a known density contrast different density contrasts may be assigned to each source tests with synthetic data show that the method can be of use in estimating 1 multiple laterally adjacent and closely situated gravity sources 2 single gravity sources consisting of several homogeneous compartments with different density contrasts and 3 two gravity sources with different density contrasts of the same sign one totally enclosed by the other the method is also applied to three different sets of field data where the gravity sources belong to the same categories established in the tests with synthetic data the method produces solutions consistent with the known geologic attributes of the gravity sources illustrating its potential practicality

apparent density mapping using entropic regularization we present a new apparent density mapping method on the horizontal plane that combines the minimization of the first orderentropywiththemaximizationofthezeroth order entropyoftheestimateddensitycontrasts theinterpretation modelconsistsofagridofvertical juxtaposedprismsinboth horizontal directions we assume that the top and the bottom of the gravity sources areflat and horizontal and estimate the prisms densitycontrasts theminimizationofthefirst order entropy favors solutions presenting sharp borders and the maximization of the zeroth order entropy prevents the tendency of the source estimate to become a single prism thus ajudiciouscombinationofbothconstraintsmayleadtosolutions characterized by regions with virtually constant estimated density contrasts separated by sharp discontinuities we apply our method to synthetic data from simulated intrusive bodies in sediments that presentflat and horizontal tops by comparing our results with those obtained with the smoothness constraint we show that both methods produce good and equivalent locations of the sources central positions however the entropic regularization delineates the boundaries of the bodies with greater resolution even in the case of 100 m wide bodies separated by a distance as small as 50 m both the proposed and the global smoothness constraints are applied to real anomalies from the eastern alps and from the matsitama intrusive complex northeastern botswana in the first case the entropic regularization delineates two sources with a horizontal and nearly flat top being consistent with the known geologic information in the second case both constraints produce virtually the same estimate indicating in agreement with results of synthetic tests thatthetopsofthesourcesareneitherflatnorhorizontal

tropical extratropical geopotential height teleconnections during the northern hemisphere winter abstract simultaneous and lagged correlation statistics have been calculated between time series of seasonal height anomalies at selected stations and extratropical grid point anomalies in both hemispheres the tropical stations in two major tropical precipitation zones the indo china maritime continent and africa are well correlated with each other these stations are also correlated with stations in the north pacific and australia but the coefficients are smaller the correlations between height anomalies at any of these stations and northern hemisphere height anomalies show a well defined global pattern depending upon the location of the stations the pattern is either a pacific north american pna a tropical northern hemisphere tnh pattern or a mixed pattern having both elements all three patterns pna tnh and wpo western pacific oscillation have been linked to tropical variations the correlations between height anomalies at these well correlated stations and the southern hemisphere heig

gravity inversion of blocky basement relief using l 0 norm constraint with exponential density contrast variation depicting the basement relief of a sedimentary basin with gravity data is vital to predicting the hydrocarbon potential of a sedimentary basin and guiding exploration work we have developed a gravity inversion method to estimate the depth to a blocky basement of a sedimentary basin the basement rocks are assumed to be homogeneous and have uniform density while the density of the sediment over the basement increases exponentially with depth the density contrast between the sediment and the basement at the surface varies horizontally the decay factor of density contrast is also nonuniform the sediment above the basement is divided into vertically juxtaposed prisms and the depth of the bottom of each prism represents the depth to the basement and is the parameter to be estimated the l0 norm is introduced to limit the gradient of the parameter vector to obtain the model constraint function we then establish the objective function for inversion by combining the gravity data misfit function the known depth constraint function and the model constraint function the inversion is performed by minimizing the objective function using the nonlinear conjugate gradient algorithm the inversion method is evaluated using a 2d and a 3d sedimentary basin model the results show that our proposed method is capable of delineating the blocky basement relief of a sedimentary basin and the result is sharper than that obtained using the l1 norm constraint the method is applied to real data from the western part of the zhu 1 depression in the pearl river mouth basin northern south china sea the solution reveals a strongly faulted basement which is in accordance with the known tectonic information indicating the basin is a fully developed graben

stable inversion of gravity anomalies of sedimentary basins with nonsmooth basement reliefs and arbitrary density contrast variations we present a new stable method for interpreting the basement relief of a sedimentary basin which delineates sharp discontinuities in the basement relief and incorporates any law known a priori for the spatial variation of the density contrast the subsurface region containing the basin is discretized into a grid of juxtaposed elementary prisms whose density contrasts are the parameters to be estimated any vertical line must intersect the basement relief only once and the mass deficiency must be concentrated near the earth s surface subject to the observed gravity anomaly being fitted within the experimental errors in addition upper and lower bounds on the density contrast of each prism are introduced a priori one of the bounds being zero and the method assigns to each elementary prism a density contrast which is close to either bound the basement relief is therefore delineated by the contact between the prisms with null and nonnull estimated density contrasts the latter occupying the upper part

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

generalized compact gravity inversion extending the compact gravity inversion technique by incorporating a priori information about the maximum compactness of the anomalous sources along several axes provides versatility thus the method may also incorporate information about limits in the axes lengths or greater concentration of mass along one or more directions the judicious combination of different constraints on the anomalous mass distribution allows the introduction of several kinds of a priori information about the arbitrary shape of the sources this method is particularly applicable to constant linear density sources such as mineralizations along faults and intruded sills dikes and laccoliths in a sedimentary basin the correct source density must be known with a maximum uncertainty of 40 percent otherwise the inversion produces thicker bodies for densities smaller than the true value and vice versa because of the limitations of the inverse gravity problem the proposed technique requires an empirical technique to analyze the sensitivity of solutions to uncertainties in the a priori information the proposed technique is based on a finite number of acceptable solutions presumably representative of the ambiguity region by using standard statistical techniques each parameter is assigned a coefficient measuring its uncertainty the known hematite and magnetite ore body shape in the vicinity of iron mountain mo was reproduced quite well using this inversion technique

reconstruction of geologic bodies in depth associated with a sedimentary basin using gravity and magnetic data summary we present a comprehensive review of the most comm on gravity and magnetic interpretation methods to in depth retrieval of the geometry of two types of geologic bodies associated with a sedimentary basin 1 sedimentary basement relief and 2 salt bodies in reconstructing a basement topography we identify three groups of methods the automatic the spectral and the nonspectral methods the reconstruction of salt bodies geometries from gravity data usually uses the interactive forward modeling but recently gravity inversion methods have been developed to interpret this kind of geological environment

simultaneous 3d depth to basement and density contrast estimates using gravity data and depth control at few points we have developed a gravity inversion method for simultaneouslyestimatingthe3dbasementreliefofasedimentary basin and the parameters defining a presumed parabolic decay of the density contrast with depth in a sedimentary pack assumingpriorknowledgeaboutthebasementdepthatafew points thesedimentarypackisapproximatedbyagridof3d vertical prisms juxtaposed in both horizontal directions of a right handed coordinate system the prisms thicknesses representthedepthstothebasementandaretheparametersto be estimated from the gravity data to estimate the parameters defining the parabolic decay of the density contrast with depthandtoproducestabledepth to basementestimates we imposed smoothness on the basement depths and proximity between estimated and known depths at boreholes we applied our method to synthetic data from a simulated complex 3d basement relief with two sedimentary sections having distinct parabolic laws describing the density contrast variationwithdepth theresultsprovidegoodestimatesofthetrue parameters of the parabolic law of density contrast decay with depth and of the basement relief inverting the gravity data from the onshore and part of the shallow offshore almadabasinonbrazil snortheasterncoastshowsgoodcorrelationwithknownstructuralfeatures

estimating free parameters in 2d inversion example of gravity inversion in a rifted basement abstract we advance a principle directed to assigning numerical values to free parameters usually present in inversion methods it may be formulated as optimum estimates of free parameters in an inversion procedure must lead in tests using synthetic data to solutions whose geometrical expression reflects the main qualitative or semiquantitative geological characteristic of the study area to this end the interpreter should i specify a typical anomalous source geometry which incorporates the most relevant geological information for the study area ii compute the corresponding gravity anomaly and iii invert the anomaly for the source geometry finding the numerical values of the free parameters that lead to a solution closest to the typical source application of the above methodology to synthetic and real data from the basement relief of a rift basin has asserted its efficacy

non linear stochastic inversion of gravity data via quantum behaved particle swarm optimisation application to eurasia arabia collision zone zagros iran potential field data such as geoid and gravity anomalies are globally available and offer valuable information about the earth s lithosphere especially in areas where seismic data coverage is sparse for instance non linear inversion of bouguer anomalies could be used to estimate the crustal structures including variations of the crustal density and of the depth of the crust mantle boundary i e moho however due to non linearity of this inverse problem classical inversion methods would fail whenever there is no reliable initial model swarm intelligence algorithms such as particle swarm optimization pso are a promising alternative to classical inversion methods because the quality of their solutions does not depend on the initial model they do not use the derivatives of the objective function hence allowing the use of l1 norm and finally they are global search methods meaning the problem could be non convex in this paper quantum behaved particle swarm qpso a probabilistic swarm intelligence like algorithm is used to solve the non linear gravity inverse problem the method is first successfully tested on a realistic synthetic crustal model with a linear vertical density gradient and lateral density and depth variations at the base of crust in the presence of white gaussian noise then it is applied to the eigen 6c4 a combined global gravity model to estimate the depth to the base of the crust and the mean density contrast between the crust and the upper mantle lithosphere in the eurasia arabia continental collision zone along a 400 km profile crossing the zagros mountains iran the results agree well with previously published works including both seismic and potential field studies this article is protected by copyright all rights reserved

gravity inversion of 2d basement relief using entropic regularization we have developed a gravity interpretation method for estimating the discontinuous basement relief of a sedimentary basin the density contrast between the basement and the sediments is assumed to be known and it could be either constant or vary monotonically with depth the interpretation model consists of a set of vertical juxtaposed prisms whose thicknesses are the parameters to be estimated we used the entropic regularization that combines the minimization of the first order entropy measure with the maximization of the zeroth order entropy measure of the solution vector we validated the method by applying it to synthetic data produced by a simulated basin bordered by high angle step faults we obtained a good definition of the relief particularly of the discontinuities we also applied the method to a profile across the buyuk menderes valley in west turkey and obtained a solution exhibiting a gravity fault with large slip on the northern border of the valley when applied to the interpretation of a discontinuous basement relief the method has a better performance than the global smoothness method it is comparable to the weighted smoothness method but it does not require the a priori knowledge about the maximum basin depth

magnetic basement gravity guided magnetic source depth analysis and interpretation we present a new integrated approach to the interpretation of magnetic basement that is based on recognition of characteristic patterns in distributions and alignments of magnetic source depth solutions above and below the surface of magnetic basement this approach integrates a quantitative analysis of depth solutions obtained by 2d werner deconvolution of the magnetic data with a qualitative evaluation of the bouguer gravity anomalies the crystalline metamorphic basement and sedimentary cover have different origins tectonic histories lithologies and magnetic properties these differences result in different geometries of magnetic sources associated with faults fracture zones igneous intrusions erosional truncations subcrop edges and other structural discontinuities properly tuned 2d werner deconvolution is able to resolve the intra sedimentary and intra basement magnetic source geometries into distinctly different distributions and alignments of calculated depth solutions an empirical set of criteria basement indicators was developed for identification and correlation of the basement surface the ambiguity of basement correlation with limited or non existent well control which is common for onshore frontier and offshore explorations can be reduced by incorporating the bouguer gravity data into the process of correlation

gravity inversion of basement relief and estimation of density contrast variation with depth we present a method to estimate the basement relief as well as the density contrast at the surface and the hyperbolic decaying factor of the density contrast with depth assuming that the gravity anomaly and the depth to the basement at a few points are known in both cases the interpretation model is a set of vertical rectangular 2d prisms whose thicknesses are parameters to be estimated and that represent the depth to the interface separating sediments and basement the solutions to both problems are stable because of the incorporation of additional prior information about the smoothness of the estimated relief and the depth to the basement at a few locations presumably provided by boreholes the method was tested with synthetic gravity anomalies produced by simulated sedimentary basins with smooth relief providing not only well resolved estimated relief but also good estimates for the density contrasts at the surface and for the decaying factors of the density contrast with depth the method was ap

determination of crustal interface topography from potential fields we present a method for determination of the topography of an interface separating two uniformly but differently magnetized media the technique is developed within the framework of discrete linear inverse theory and exploits the quasi linearity of the problem to derive a simple efficient algorithm suitable for use on large gridded data sets variation of auxiliary parameters allows a suite of acceptable models to be produced rapidly these parameters can be appraised in light of available geologic and geophysical evidence because very large matrices are involved when large amounts of data are interpreted approximate resolution measures requiring no matrix inversion provide useful information concerning averages of the constructed topography

concept of effective density key to gravity depth determinations for sedimentary basins the gravity anomaly observed over a layered sedimentary basin is close to that calculated over a basin with the same configuration and depth but filled by homogeneous sediments with density equal to the effective weighted average density of the real layered basin therefore it is possible to calculate the effective density contrast of a basin from the residual gravity anomaly over it if the depth of the basin is known at least at one point assuming a mathematical function for density depth dependence an expression for the gravity depth dependence using the infinite slab bouguer formula can be developed this expression makes it possible to calculate the depth of a basin or an isopach map from gravity data an exponential function and a new hyperbolic density depth function and their gravity depth functions are analyzed and implemented for determining the depths of basins from gravity data for the san jacinto graben california and the tucson basin southern arizona the hyperbolic functions are m

total variation regularization for depth to basement estimate part 1 mathematical details and applications we have developed an inversion approach that estimates the basement relief of a fault bounded sedimentary basin the sedimentary pack is approximated by a grid of 3d or 2d vertical prisms juxtaposed in the horizontal directions of a right handed coordinate system the prisms thicknesses represent the depths to the basement and are the parameters to be estimated from the gravity data to obtain depth to basement estimates we introduce the total variation tv regularization as a stabilizing function this approach lets us estimate a nonsmooth basement relief because it does not penalize sharp features of the solution we have deduced a compact matrix form of the gradient vector and the hessian matrix of the approximation to the tv function that allows a regularized gauss newton minimization approach because the hessian matrix of the approximation to the tv function is ill conditioned we have modified this hessian matrix to improve its condition and to accelerate the convergence of the gauss newton algorithm tests conducted with synthetic data show that the inversion method can delineate discontinuous basements presenting large slips or sequences of small slip step faults tests on field data from the almada basin brazil and from the san jacinto graben california u s a confirm the potential of the method in detecting and locating in depth normal faults in the basement relief of a sedimentary basin

a seismic refraction and reflection study across the central san jacinto basin southern california the san jacinto basin is a northwest trending pull apart basin in the san jacinto fault zone of the san andreas fault system in southern california about 24 km long and 2 to 4 km wide the basin sits on a graben bounded by two strands of the san jacinto fault zone the claremont fault on the northeast and the casa loma fault on the southwest we present a case study of shallow structure less than 1 km in the central basin a 2 75 km refraction line running from the northeast to southwest across the regional structural trend reveals a groundwater barrier offset i another line bent southward and continued for 1 65 km shows a crystalline basement offset offset iii near an inferred trace of the casa loma fault although a basement refractor was not observed along the 2 75 km line a mismatch between the estimate of its minimum depth and the basement depth determined for the 1 65 km line suggests that an offset in the basement greater than 260 m exists around the junction of the two refraction lin

combined modeling and smooth inversion of gravity data from a faulted basement relief abstractwe have combined modeling and gravity inversion to estimate an overall smooth but locally discontinuous basement relief of a sedimentary basin through an initial global smoothness solution the method indicates fault positions that may be accepted or modified then the interpreter specifies the fault dip and a tentative fault slip so the fault plane is fixed on the estimated relief the segments of the current interpreted relief that are not accepted faults are estimated through smoothness inversion and the response of the current estimated relief is computed the slip of the fault being incorporated in the estimated relief is then modified interactively until the solution presents no side lobes about the fault extremes the process is repeated for all faults the iteration stops when the tentative solution becomes compatible with the geologic knowledge of the area and produces an acceptable data fit the method was applied to data produced by a simulated graben defined by step faults dipping

gravity data as a tool for detecting faults in depth enhancement of subtle almada s basement faults brazil we demonstrate the potential of gravity data to detect and to locate in depth subtle normal faults in the basement relief of a sedimentary basin this demonstration is accomplished by inverting the gravity data with the constraint that the estimated basement relief presents local abrupt faults and is smooth elsewhere we inverted the gravity data from the onshore almada basin in northeastern brazil and we mapped several normal faults whose locations and plane geometries were already known from seismic imaging the inversion methoddelineatedwellboththediscontinuitieswithsmallor largeslipsandasequenceofstepfaults usingsyntheticdata weperformedasystematicsearchofnormalfaultslipsversus fault displacement depths to map the fault detectable region inthisspace thismappinghelpstoassesstheabilityofgravityinversiontodetectnormalfaults mappingshowsthatnormalfaultswithsmall0 5 km mediumabout1 km and large about 2 km vertical slips can be detected if the maximummidpointdepthsofthefaultplanesaresmallerthan1 8 3 8 and6 8 km respectively

seismic anisotropy of the archean crust in the minnesota river valley superior province the minnesota river valley mrv subprovince is a well exposed example of late archean lithosphere its high grade gneisses display a subhorizontal layering most likely extending down to the crust mantle boundary the strong linear fabric of the gneisses results from high temperature plastic flow during collage related contraction seismic anisotropies measured up to 1 gpa in the laboratory and seismic anisotropies calculated through forward modeling indicate vp 5 6 and vs 3 the mrv crust exhibits a strong macroscopic layering and foliation and relatively strong seismic anisotropies at the hand specimen scale yet the horizontal attitude of these structures precludes any substantial contribution of the mrv crust to shear wave splitting for vertically propagating shear waves such as sks the origin of the regionally low seismic anisotropy must lie in the upper mantle a horizontally layered mantle underneath the united states interior could provide an explanation for the observed low sws

fast nonlinear gravity inversion in spherical coordinates with application to the south american moho estimating the relief of the moho from gravity data is a computationally intensive non linear inverse problem what is more the modeling must take the earths curvature into account when the study area is of regional scale or greater we present a regularized non linear gravity inversion method that has a low computational footprint and employs a spherical earth approximation to achieve this we combine the highly efficient botts method with smoothness regularization and a discretization of the anomalous moho into tesseroids spherical prisms the computational efficiency of our method is attained by harnessing the fact that all matrices involved are sparse the inversion results are controlled by three hyper parameters the regularization parameter the anomalous moho density contrast and the reference moho depth we estimate the regularization parameter using the method of hold out cross validation additionally we estimate the density contrast and the reference depth using knowledge of the moho depth at certain points we apply the proposed method to estimate the moho depth for the south american continent using satellite gravity data and seismological data the final moho model is in accordance with previous gravity derived models and seismological data the misfit to the gravity and seismological data is worse in the andes and best in oceanic areas central brazil and patagonia and along the atlantic coast similarly to previous results the model suggests a thinner crust of 30 35 km under the andean foreland basins discrepancies with the seismological data are greatest in the guyana shield the central solimoes and amazonas basins the parana basin and the borborema province these differences suggest the existence of crustal or mantle density anomalies that were unaccounted for during gravity data processing

an analysis of daily maximum wind speed in northwestern europe using generalized linear models abstract the basic climatological pattern and recent trends in daily maximum wind speed dmws for the region 47 5 65 n and 12 5 w 22 5 e are studied using gamma distributions within a generalized linear model between 1958 and 1998 dmws has increased over the ocean in winter but weakened over continental europe in summer large scale circulation changes such as those of the north atlantic oscillation nao and arctic oscillation ao account for the strengthening wind over the ocean global warming may have impacted the regional wind climate in particular southern hemisphere temperature exhibits a significant effect on the distinct oceanic and continental trends in dmws it is suggested that the steady warming of the southern hemisphere during the last few decades may have forced the north atlantic storm track to shift in such a way that storms are enhanced toward the northwestern oceanic area but weakened throughout most of the european continent

gravity inversion of basement relief using approximate equality constraints on depths we present a gravity interpretation method for estimating the relief of an arbitrary interface separating two homogeneous media the upper medium is discretized into rectangular juxtaposed prisms whose thicknesses represent the depths to the interface and are the parameters to be estimated from the gravity anomaly the density contrast of each prism is assumed to be constant and known to stabilize the inversion we introduce two kinds of constraints on the depths the first one requires proximity between the observed and computed depths at isolated points such as those obtained from boreholes absolute equality constraint the second one requires that groups of depths approximately follow an established linear relationship among the depths relative equality constraint both kinds of constraints are imposed in the least squares sense we illustrate the method performance by applying it to a synthetic anomaly produced by a simulated basement relief consisting of four narrow and adjacent structural lows

interactive 2d magnetic inversion a tool for aiding forward modeling and testing geologic hypotheses we present a method for inverting magnetic data with interfering anomalies produced by multiple complex 2d magnetic sources having arbitrary shapes and known magnetization vectors our method is stable and can recover a complex 2d magnetization distribution leading to a reliable delineation of sectionally homogeneous sources with complex shapes our method although similar to interactive forward modeling is unique in that it automatically fits the observations and only requires that the interpreter know the outlines of the sources expressed by simple geometric elements such as points and line segments each geometric element operatesasaskeletaloutlineofaparticularhomogeneoussection of the magnetic source to be reconstructed also the interpreter can define the geometric elements interactively without worrying about data fitting because data are fit automatically the examples with synthetic data illustrate the good performance of the method in mapping the complex geometryofmagneticsources thesolutionsensitivitytouncertaintiesintheaprioriinformationshowsthattoproducegoodresults the uncertainty on the magnetization intensity of each homogeneous extent of the source should be smaller than 40 awrongmagnetizationvectordirectioncanbedetected easily because it often leads to poor data fitting and to estimated sources with abrupt borders the method is also applied to two sets of real data from the northwest ore body at iron mountain mine missouri and the hatton rockall basininthenortheastatlanticocean theestimatedmagnetization distribution in all tests demonstrates a good correlation of estimated magnetic sources with corresponding known geologicfeatures

3d gravity inversion through an adaptive learning procedure we have developed a gravity inversion method to estimate a 3d density contrast distribution producing strongly interfering gravity anomalies the interpretation model consists of a grid of 3d vertical juxtaposed prisms in the horizontal and vertical directions iteratively our approach estimates the 3d density contrast distribution that fits the observed anomaly within the measurement errors and favors compact gravity sources closest to prespecified geometric elements such as axes and points this method retrieves the geometry of multiple gravity sources whose density contrasts positive and negative values are prescribed by the interpreter through the geometric element at the first iteration we set an initial interpretation model and specify the first guess geometric elements and their target density contrasts each geometric element operates as the first guess skeletal outline of the entire homogeneous gravity source or any of its homogeneous parts to be reconstructed from the second iteration on our method automatically redefines a new set of geometric elements the associated target density contrasts and a new interpretation model whose number of prisms increases with the iteration the iteration stops when the geometries of the estimated sources are invariant along successive iterations tests on synthetic data from geometrically complex bodies and on field data collected over a mafic ultramafic body and a volcanogenic sedimentary sequence located in the tocantins province brazil confirmed the potential of our method in producing a sharp image of multiple and adjacent bodies

gravity inversion of basement relief constrained by the knowledge of depth at isolated points we present an interpretation method for the gravity anomaly of an arbitrary interface separating two homogeneous media it consists essentially of a downward continuation of the observed anomaly and the division of the continued anomaly by a scale factor involving the density contrast between the media the knowledge of the interface depth at isolated points is used to estimate the depth d1 of the shallowest point of the interface the density contrast between the two media and the coefficients c1 and c2 of a first order polynomial representing a linear trend to be removed from data the solutions are stabilized by introducing a damping parameter in the computation of the downward continued anomaly by the equivalent layer method different from other interface mapping methods using gravity data the proposed method 1 takes into account the presence of an undesirable linear trend in data 2 requires just intervals for both rather than the knowledge of its true value and coefficients c1 and c2