curie point depths in northeast china and their geothermal implications for the songliao basin abstract this work integrates processing and interpretation of the combined geomagnetic anomaly model of ngdc 720 v3 1 to better constrain thermal structures of the northeast china lithosphere which shows intensive extension and active volcanism during the mesozoic and cenozoic numerical tests demonstrate that magnetic anomalies calculated at 20 km altitude can be used for accurate curie depth estimation averaged curie depths using a 3d fractal exponent of 3 0 vary from 13 2 0 to 33 4 1 km with a mean of 22 2 4 km in northeast china with temperature dependent thermal conductivity models constrained by incorporated surface heat flow and curie depths in different geological blocks the thermal lithospheric thicknesses are estimated mostly between 45 and 90 km based on 1d steady state thermal conduction equation beneath the songliao basin the moho temperatures are abnormally high ranging from ca 700 to 1000 c and the mantle contributes about 65 of the total surface heat flow the shallow curie points and thermal lithosphere asthenosphere boundary together with high moho temperatures and mantle heat flow support abnormally high geotherms in the songliao basin originated from hot upper mantle upwelling triggered likely by lithospheric delamination

an experimental study of soil memory and preconsolidation adjacent to an active tectonic structure the meers fault oklahoma usa abstract special consolidation tests were run on undisturbed samples to study the ability of quaternary soils adjacent to the meers fault in southwestern oklahoma to record and remember the maximum effective preconsolidation stresses they experienced during the faulting process the results show that the soils record 60 of the applied total stresses as preconsolidation stresses in 2 s of loading time indicating that these stresses could have been recorded during an earthquake faulting event to record all of the applied total stresses as preconsolidation stresses 100 recording or memory the loading needs to last at least 4 5 min

the influence of volcanological and sedimentological processes on diamond grade distribution in kimberlites examples from the ekati diamond mine nwt canada the distribution of diamonds within individual kimberlite pipes is poorly documented in the public domain due to the proprietary nature of the data the study of the diamond distribution within two pipes fox and koala from the ekati diamond mine nwt canada in conjunction with detailed facies models has shown several distinct relationships of deposit type and grade distribution in both pipes the lithological facies represent grade units which can be distinguished from each other in terms of relative size and abundance of diamonds a positive relationship between olivine grain size and abundance with diamond size and abundance is observed indicating that sorting of fragmental kimberlites influences diamond distribution though surface geological processes do not control the diamond potential of the erupting magma they can be responsible for concentrating diamonds into economically significant proportions a good understanding of the eruption transport and depositional processes responsible for the individual lithological units and the diamond distribution within them is important for successful resource estimation this may lead to recognition of areas suitable for selective mining making a marginal deposit economic

cocorp profiling across the southern oklahoma aulacogen overthrusting of the wichita mountains and compression within the anadarko basin cocorp consortium for continental reflection profiling deep reflection profiles recorded across the wichita mountains and anadarko basin suggest that significant crustal shortening occurred in the final stages of the evolution of the southern oklahoma aulacogen the crystalline rocks of the wichita mountains were thrust in pennsylvanian time northeastward over sedimentary rocks of the anadarko basin along a series of faults with moderate average 30 to 40 and southwesterly dips these faults can be traced possibly as deep as 20 to 24 km listric thrust faults and hanging wall anticlines developed in the sedimentary rocks of the basin these features contrast with conventional interpretations of pennsylvanian structures as the result of predominantly vertical movements along high angle faults and they suggest that pennsylvanian downwarping of the anadarko basin was at least partially due to thrust loading truncations of reflections from cambrian ordovician rocks in the deepest part of the basin suggest normal faulting which would support ideas of an early extensional stage in the aulacogen cycle the distinctive precambrian layering seen on earlier cocorp data recorded south of the wichita mountains cannot be recognized under the anadarko basin and the proterozoic basin containing that layering may have been bounded on its north side by a precambrian fault this inferred fault was probably twice reactivated during formation of the southern oklahoma aulacogen once during late precambrian early cambrian extension and again during pennsylvanian compression the popular view that aulacogens originated from radial rifting of updomed homogeneous continental crust is probably too simplified and a more important constraint on their location and development may be the nature of pre existing lines of weakness

ellipsoid geoid gravity geodesy and geophysics geophysics uses gravity to learn about the density variations of the earth s interior whereas classical geodesy uses gravity to define the geoid this difference in purpose has led to some confusion among geophysicists and this tutorial attempts to clarify two points of the confusion first it is well known now that gravity anomalies after the free air correction are still located at their original positions however the free air reduction was thought historically to relocate gravity from its observation position to the geoid mean sea level such an understanding is a geodetic fiction invalid and unacceptable in geophysics second in gravity corrections and gravity anomalies the elevation has been used routinely the main reason is that before the emergence and widespread use of the global positioning system gps height above the geoid was the only height measurement we could make accurately i e by leveling the gps delivers a measurement of height above the ellipsoid in principle in

single hole imaging using borehole gravity gradiometry abstractwe study the feasibility of imaging density variations away from boreholes using gravity gradient measurements in a single borehole the objective is to develop numerical interpretation tools and to understand the utility and limitations of borehole gravity gradiometry in anticipation of the development of such instruments for the exploration and production of minerals oil and gas we develop an analytic solution for directly locating discrete off hole mass anomalies and apply a generalized inverse approach to image anomalous density distribution in the analytic approach we solve for the distance and direction angles to a point source using the multiple components of the gravity gradient tensor from a set of observations in a single borehole and then apply this approach to the scenarios of prismatic sources in the generalized inverse approach we invert multiple gradient tensor components to construct 3d density contrast distributions around the borehole as few as two independent gravity gr

how did the meers fault scarp form paleoearthquake or aseismic creep a soil mechanical perspective abstract studies confirm that the meers fault in southwestern oklahoma has been active in recent times the most recent movement occurred about 1100 y ago in late holocene there is as much as 5 m vertical and possibly appreciably more left lateral strike slip displacements on the fault during faulting the quaternary soils 1 along the fault were folded as well as ruptured in some places almost all of the deformation is accommodated by ductile folding of the soils having this kind of deformation with no record of an earthquake associated with the meers fault during historical times raises the question whether the present scarp was formed seismically by earthquake event s or aseismically by slow deformation aseismic fault creep to determine how the scarp was formed i have developed a multidisciplinary study which involved geological soil mechanical and soil micromorphological techniques geological mapping delineated the deformation stratigraphy and any features that might be associated with the faulting the mapping was also needed to reconstruct the sequence of events that formed the scarp at the study site consolidation tests using the casagrande 1936 method for finding maximum effective stresses were used to determine the states of stresses imposed on the soil deposits when they were first faulted these states of stresses were then compared to the states of stresses needed to slowly deform or shear the soils in triaxial and direct drained shear tests the direction of maximum principal stress was determined by mohr s circle and soil micromorphological analyses the results of soil mechanical analysis show that the faulting of the quaternary soils along the fault had to be sudden or fast which indicates that the scarp was probably created seismically during faulting the soils were anisotropically consolidated or compacted thereby recording in their structure the states of stresses that caused faulting to occur the direction of the maximum principal horizontal stress is between n62 e and n72 e indicating rotation of principal stress axes the technique developed for this study can be used in similar areas where active faults offset quaternary soils with relatively unchanging moisture contents below some depth also for shallow depths this technique might give more reliable young tectonic stress measurements both magnitude and orientation than other techniques such as overcoring hydraulic fracturing and wellbore breakouts because it is used on geologically recent units which unlike lithified rocks have not yet existed through millions of years of deformation

carbonate xenoliths hosted by the mesoproterozoic siddanpalli kimberlite cluster eastern dharwar craton implications for the geodynamic evolution of southern india and its diamond and uranium metallogenesis a number of limestone and metasomatised carbonate xenoliths occur in the 1 090 ma siddanpalli kimberlite cluster raichur kimberlite field eastern dharwar craton southern india these xenoliths are inferred to have been derived from the carbonate horizons of the kurnool palnad and bhima proterozoic basins and provide evidence for a connection between these basins in the geological past a revised mesoproterozoic age is proposed for the bhima and kurnool palnad basins based on this kimberlite association and is in agreement with similar proposals made recently for the chattisgarh and upper vindhyan sediments in central india the observed bhima kurnool interbasinal uplift may have been caused by 1 extension or plume related mafic alkaline magmatism that included the emplacement of the southern indian kimberlites at 1 1 ga 2 mantle plume related doming of the peninsular india during the cretaceous or 3 quaternary differential uplift in this region it is not possible with the currently available geological information to constrain the exact timing of this uplift the deep erosion of primary diamond sources in the raichur kimberlite field in the upper reaches of the krishna river caused by this uplift could be the elusive source of the alluvial diamonds of the krishna valley mesoproterozoic sedimentary basins can host world class unconformity type uranium deposits in light of its inferred mesoproterozoic age a more detailed stratigraphic and metallogenic analysis of the kurnool basin is suggested for uranium exploration

the archaean proterozoic palaeoboundary in the lulea area northern sweden field and isotope geochemical evidence for a sharp terrane boundary abstract extensive sm nd isotope work has been carried out in northern sweden with the intention of studying crustal reactivation and assimilation processes relative to juvenile arc accretion at an archaean cratonic margin previous regional work has shown a gradual change from negative nd t values in northernmost sweden to positive values towards the skellefte sulphide ore district farther south isotopic variation and geophysical data show a break in the character of the crust along a wnw trending zone it is suggested that this zone which passes close to the towns of lulea and jokkmokk represents the transition from the archaean craton in the northeast to proterozoic juvenile crust in the southwest a profile across the eastern part of this transition zone has been studied in detail in the lulea area where archaean rocks recently have been discovered the distribution and character of the archaean rocks have been studied these occur as fragments ranging in size from several km 2 to dm in scale and consist of ca 2 7 ga orthogneisses of granodioritic to dioritic composition and porphyritic granitoids of quartz monzodioritic to granodioritic composition plutonic rocks of ca 1 9 ga age and archaean rocks were analysed for major and trace elements and for sm nd isotopes the calc alkaline ca 1 9 ga granitoids are dominated by granodiorites tonalites quartz diorites and quartz monzodiorites and there is a distinct boundary rather than a transition zone between intrusions with postive nd t values in the southwest and intrusions with negative nd t values in the northeast the locations of the outcropping archaean fragments coincides with this distinct boundary which is interpreted as a terrane boundary separating a ca 1 9 ga juvenile arc terrane in the southwest from the archaean continent in the northeast a possible explanation for this is that the proterozoic juvenile terrane was obducted onto the archaean craton during the final stages of the svecofennian orogeny

ni in chrome pyrope garnets a new geothermometer proton microprobe analyses of the minerals in garnet peridotite xenoliths from kimberlites show that the partitioning of ni between chrome pyrope garnet and olivine is strongly temperature t dependent the range of ni contents in olivines is small relative to that in the analyzed garnets a geothermometer therefore can be derived based only on the ni content of garnet this allows estimation of t for single cr pyrope grains such as the inclusions in diamonds if these can be assumed to have equilibrated with olivine

stratigraphic evidence of holocene faulting in the mid continent the meers fault southwestern oklahoma stratigraphic relations and ten 14c ages show that movement occurred on the meers fault in late holocene time movement on the fault postdates the browns creek alluvium which began to be deposited between 14 000 and 13 000 yr b p and predates the east cache alluvium which was deposited between 800 and 100 yr b p surface warping along the fault led to local stream incision on the upthrown side of the fault and deposition of slopewash and fan alluvium on the down thrown side three 14c ages of charcoal and soil humus buried by fan alluvium indicate that faulting probably occurred between 1400 and 1100 yr b p the soil that formed in the fan alluvium is only slightly more developed than that in the east cache alluvium and the weak development of both soils indicates a geologically recent age that is consistent with the radiocarbon ages obtained for these deposits

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

higher order gravitational potential gradients for geoscientific applications abstract gravity data have been applied for modelling and interpretation studies in geosciences this contribution reviews currently observable and foreseen gravity data represented by gradients of the gravitational potential functional models linking 3 d mass density distribution functions to potential gradients of up to the third order are formulated using volume integrals of the newtonian type with unitless kernel functions expressed both analytically and using infinite series of associated legendre functions spatial and spectral properties of the kernel functions are analysed and sensitivity of the gradients to particular mass density distributions is studied two particular mass density distribution models are used in numerical experiments a local 3 d mass density model representing shallow mass density variations and a global mass model represented by earth s upper sediments with lateral mass density variations computed values of the gradients demonstrate their different sensitivities to particular mass density distributions which change with an increasing distance of the gradients from gravitating masses third order gradients are particularly useful for studying near subsurface or shallow density structures such as caves caverns salt domes sediment basement morphology continental margins or buried fault systems that could be identified spatially more closely thus higher order gradients would offer an interesting tool for mass density mapping once their observability with the sufficient accuracy and resolution is realized

a new reference model for 3d inversion of airborne magnetic data in hilly terrain a case study from northern sweden abstractthe inherent nonuniqueness in modeling magnetic data can be partly reduced by adding prior information either as mathematical constructs or simply as bounds on magnetization obtained from laboratory measurements if a good prior model can be used as a reference model then the quality of estimated models through an inverse approach can be greatly improved but even though data on magnetic properties of rocks might exist their distribution may often be quite irregular on local and regional scales so that it is difficult to define representative classes of rock types suitable for constraining geophysical models of magnetization we have developed a new way of constructing a reference model that varies only laterally and is confined to the part of the terrain that lies above the lowest topography in the area to obtain this model several estimated 2d magnetization distributions were constructed by data inversion as a function of the iteration number then a suitable 2d model of the magnetization

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

diversity of 1 8 ga potassic granitoids along the edge of the archaean craton in northern scandinavia a result of melt formation at various depths and from various sources the edge of the archaean craton in northern scandinavia had been intensively reworked during the svecofennian orogeny 1 93 1 86 ga ago and was subsequently intruded by potassic granitoids of 1 79 1 80 ga age despite similar or even identical ages and overlapping areas of occurrence these rocks belong to two different groups the edefors and lina granitoids which have contrasting geochemistries and sm nd isotopic characteristics the edefors granitoids range from syenites to granites and are alkali rich and distinctly metaluminous they crystallized from dry magmas this is indicated by the scarcity of pegmatites and aplites the contacts to older rocks are often distinct but gradual transitions to lina type granitoids are common the edefors granitoids have high contents of zr but not of elements such as y ree ta and nb and have low mgmg fe ratios they also frequently have positive eu anomalies even in the quartz rich varieties initial nd values range from 2 1 to 1 4 indicating that the edefors granitoids were formed by the mixing of mantle derived magmas and continental crustal materials the amount of crustal component was probably less than 35 in most cases the lina granitoids are accompanied by abundant pegmatites and aplites ghost structures and remnants of country rock are common true granites predominate but also quartz monzonites occur the content of hfs elements is low and the mgmg fe ratios are higher than in the edefors granitoids initial nd values range from 9 3 to 3 7 reflecting a significant portion of archaean nd in the source materials the lina granitoids are largely the result of remobilisation of continental crust with a small input of juvenile material however the dominant source for these crustally derived granitoids are c 1 9 ga old granitoids these carry a large proportion of archaean nd the most probable environment of the formation of potassic migmatite granitoids such as the lina type is a collision zone between two masses of felsic crust e g arc continent or continent continent but the details of such a collision in the baltic shield remain to evaluated the formation of the edefors granitoids could have been associated with an extensional zone developed due to delamination caused by separation of the down dip oceanic lithosphere from the continental lithosphere

the micro macro diamond relationship a case study from the artemisia kimberlite northern slave craton canada abstract size frequency distributions are the principal tool for predicting the macro diamond grade of new kimberlite discoveries based on micro diamonds i e diamond 0 5 mm recovered from small exploration samples lognormal size frequency distributions as observed for the artemisia kimberlite slave craton canada suggest a common source for micro and macro diamonds recovered from single samples an implication that has never been conclusively tested we analyzed 209 diamonds between 0 2 and 2 mm in size from the artemisia kimberlite for their carbon isotopic compositions and nitrogen characteristics to determine the nature of the micro macro diamond relationship despite overall similarity in the 13c distributions of micro and macro diamonds both are bimodal with peaks in classes 5 0 to 4 5 and 3 5 to 3 0 rare diamonds with 13c between 14 2 and 24 5 of presumed eclogitic origin are restricted to macro diamonds whereas positive values are only observed for micro diamonds in addition a shift in main mode and median value in 13c of about 1 is observed for micro relative to macro diamonds fundamental differences between micro and macro diamonds at artemisia were revealed through the analysis of nitrogen concentrations 68 of micro diamonds are type ii nitrogen free versus 21 of macro diamonds and only 19 of micro diamonds have nitrogen contents 100 atomic ppm versus 43 of macro diamonds similarly the presence of a detectable hydrogen related peak at 3107 cm 1 increases from 40 for micro diamonds to 94 for macro diamonds previous studies on diamond populations from individual deposits have documented that single batches of ascending kimberlite or lamproite magma sample multiple diamond subpopulations formed during distinct growth events in compositionally variable sources and at various depth levels the artemisia data clearly show that even over a fairly narrow size interval spanning the micro to macro diamond transition the specific diamond subpopulations present and their relative proportions may vary significantly with diamond size at artemisia we conclude that the observed lognormal size distribution is not a reflection of an entirely common origin of micro and macro diamonds

the gravity module assembly used in airborne full tensor gradiometry surveys abstract in airborne gravity gradiometry the gravity module assembly is an optional gravimeter unit that is mounted on the same stabilized platform as the full tensor gradiometer direct measurements of the gravity field are needed from this device to constrain the long wavelengths when gradient data are integrated mathematically to form high resolution gravity fields the gravity module assembly is however capable of providing independent gravity data with a specification approaching that expected from a dedicated airborne gravity system presented here is an error analysis of data from this instrument collected alongside the full tensor gradiometer during an airborne survey by having both gradiometry and gravity datasets comparisons of the information content in these two types of measurement are made

a review of gravity gradiometer survey system data analyses the gravity gradiometer survey system ggss was designed to measure the local and regional gravity field from a ground or airborne moving platform with the first and only airborne field test the ggss was able to recover five arcminute by five arcminute mean gravity anomalies to an accuracy of a few mgal these results were obtained by flying the system with an operational precision of about 10 eotvos ten second average on a grid of orthogonal tracks spaced 5 km apart at an altitude of about 700 m above the terrain despite perpetual navigation problems with the global positioning system and several periods of excessive system noise the results of a performance analysis on 19 out of 128 tracks demonstrated the potential accuracy and efficiency of the ggss as an airborne gravity mapping system the ground tests both road and railway suffering from undue vehicle vibrations and from a lack of ground truth data were correspondingly less successful but they also showed no surprises in the system corrupted by these adverse conditions unfortunately the ggss program has terminated and it is appropriate to reflect on its accomplishments without going into technical details this somewhat historical review summarizes the field tests the data reduction algorithms and the test results which together portray the breadth of expertise the program engendered in the area of gravity gradiometry

geologically constrained gravity inversion for the voisey s bay ovoid deposit constructing a general three dimensional model of the subsurface density distribution by minimum structure or occam style inversion of gravity data has been practical now for several years the usual approach is to seek a model that is simple in the sense of having the least amount of spatial variation while still reproducing the observations hence the description minimum structure this has the advantage of generating models with few if any fictitious features however often the models produced bear only a gross diffuse resemblance to geology it has been recognized since the inception of the minimum structure inversion technique that geological information can be incorporated by seeking a model that is simple in the sense of being as close as possible to a reference model while still fitting the observations this is rarely done often because insufficient geological information is available or because inversion of geophysical data is no longer thought to be useful once a target has been fou

standardization in gravity reduction gravity reduction standards are needed to improve anomaly quality for interpretation and to facilitate the joining together of different data sets to the extent possible data reduction should be quantitative objective and comprehensive leaving ambiguity only to the interpretation process that involves qualitative subjective and geological decisions the term bouguer anomaly describes a field intended to be free of all nongeologic effects not modified by a partial geologic interpretation measured vertical gradients of gravity demonstrate considerable variation but do not suggest as often reported that the normal free air gradient is in error or needs to be locally adjusted such gradients are strongly influenced by terrain and to a lesser extent by the same geologic sources which produce bouguer anomalies a substantial body of existing literature facilitates the comprehensive treatment of terrain effects which may be rigorously implemented with current computer technology although variations in topographic rock density are a major source of bouguer anomalies a constant density appropriate to the area under investigation is normally adopted as a data reduction standard leaving a treatment of the density variations to the interpretation a field example from british columbia illustrates both the variations in vertical gravity gradients which can be encountered and the conclusion that the classical approach to data reduction is practically always suitable to account for the observed effects standard data reduction procedures do not and should not include reduction to datum the interpreter must be aware however that otherwise smooth regional bouguer anomalies caused by regional sources do contain high frequency components in areas of rugged topography

a priori models and inversion of gravity gradient data in hilly terrain abstract the increased popularity of airborne measurements of the gravity gradient tensor for resource studies and geological mapping has resulted in a new awareness of the importance of terrain effects in these measurements the terrain effect often overwhelms that of the underlying crust and it becomes important to formulate a strategy for taking it into account when presenting the data and when inverting the data into density models using newly acquired data from northern sweden we first attempted to estimate a variable terrain density model by inverting the data using a terrain model with a laterally varying density using data weights related to the topography variations we find the best estimate of the lateral variation of the terrain density we translate this model into a full three dimensional model such that all columns have the same vertical centre of mass as estimated from inspecting the radially averaged power spectrum of the area this then defines a reference model for subsequent three dimensional inversion of the gravity gradient tensor dataset we tested this approach first on synthetic data calculated from the measured topography including two density anomalies before we applied it to the measured data the result is a model in which the surface density variations are propagated downwards in a systematic manner now in better agreement with measured densities of rock samples in the area

conforming falcon gravity and the global gravity anomaly gravity derived only from airborne gravity gradient measurements with a normal error distribution will have an error that increases with wavelength it is straightforward in principle to use sparsely sampled regional gravimeter data to provide the long wavelength information thereby conforming the derived gravity to the regional gravity regional surface or airborne gravimeter data are not always available and can be difficult and expensive to collect in many of the areas where an airborne gravity gradiometer survey is flown however the recent release by the danish national space centre of the dnsc08 global gravity anomaly data has provided regional gravity data for the entire earth of adequate quality for this purpose studies over three areas including comparisons with ground marine and airborne gravimetry demonstrate the validity of this approach future improvements in global gravity anomaly data are expected particularly as the product from the recently launched gravity field and steady state ocean circulation explorer goce satellite becomes available and these will lead directly to an improvement in the very wide bandwidth gravity available after conforming gravity derived from gravity gradiometry with the global gravity

gravity gradient and magnetic terrain effects for airborne applications a practical fast fourier transform technique we have implemented a practical fast fourier transform technique for fast and approximate calculation of terrain effects for airborne measurement of the gravity gradient tensor and the total magnetic field the calculations proceed in two steps starting from a digital terrain model dtm we first calculate the fields on a plane surface lying above the highest point of the terrain in the selected area this calculation can be made arbitrarily accurate by including a sufficiently large number of terms in parker s well known fourier transform technique the second step involves a downward continuation of the fields to a draped surface describing the positions of the airborne measurements the inherent instability of downward continuation through the level of the highest terrain is compensated for by low pass filtering the calculated fields on the plane surface prior to downward continuation we use a gaussian filter with cutoff wavenumbers well below the nyquist wavenumber corresponding to a wavelength equal to the distance between flight lines tests on synthetic data as well as on real data from a dtm from northern sweden demonstrated that the method works well and provides a low pass filtered version of the true terrain effect

airborne gravity gradiometry terrain corrections and elevation error terrain corrections for airborne gravity gradiometry data are calculated from a digital elevation model dem grid the relative proximity of the terrain to the gravity gradiometer and the relative magnitude of the density contrast often result in a terrain correction that is larger than the geologic signal of interest in resource exploration residual errors in the terrain correction can lead to errors in data interpretation such errors may emerge from a dem that is too coarsely sampled errors in the density assumed in the calculations elevation errors in the dem or navigation errors in the aircraft position simple mathematical terrains lead to the heuristic proposition that terrain correction errors from elevation errors in the dem are linear in the elevation error but follow an inverse power law in the ground clearance of the aircraft simulations of the effect of elevation error on terrain correction error over four measured dems support this proposition this power law relation may be used in selecting an optimum survey flying height over a known terrain given a desired terrain correction error

soil particle and pore orientations during drained and undrained shear of a cohesive sandy silt clay soil the orientations of particles pores and other constituents of an artificially made cohesive sandy silt clay soil were studied to investigate how they change during drained and undrained shear th

consistency investigation vertical gravity estimation and inversion of airborne gravity gradient data a case study from northern sweden for airborne gravity gradient data it is a challenge to distinguish between high frequency intrinsic and dynamically produced noise caused by the aircraft and small scale effects from shallow dens

constraints in 3d gravity inversion a three dimensional 3d inversion program is developed to interpret gravity data using a selection of constraints this selection includes minimum distance flatness smoothness and compactness constraints which can be combined using a lagrangian formulation a multigrid technique is also implemented to resolve separately large and short gravity wavelengths the subsurface in the survey area is divided into rectangular prismatic blocks and the problem is solved by calculating the model parameters i e the densities of each block weights are given to each block depending on depth a priori information on density and the density range allowed for the region under investigation the present computer code is tested on modelled data for a dipping dike and multiple bodies results combining different constraints and a weight depending on depth are shown for the dipping dike the advantages and behaviour of each method are compared in the 3d reconstruction recovery of geometry depth size and density distribution of the original model is dependent on the set of constraints used from experimentation the best combination of constraints for multiple bodies seems to be flatness and a minimum volume for the multiple bodies the inversion method is tested on real gravity data from the rouyn noranda quebec mining camp the 3d inversion model for the first 10 km is in agreement with the known major lithological contacts at the surface it enables the determination of the geometry of plutons and intrusive rocks at depth

assessing the diamond potential of kimberlites from discovery to evaluation bulk sampling the economic evaluation of diamond bearing kimberlites is usually carried out in four stages expenditure tends to increase by an order of magnitude at each successive stage at the end of each stage the sample results should be critically appraised before deciding to proceed to the next phase in the first stage even before individual kimberlite bodies have been discovered the indicator mineral geochemistry will give a first rough idea of the diamond potential the relative abundance of harzburgitic pyropes subcalcic chrome rich is often directly correlated with the diamond grade in the next stage when the kimberlite body has been discovered a relatively small sample of a few hundred kilograms will be enough to recover sufficient microdiamonds to allow an extrapolation of the size distribution towards the commercial sized diamonds and a rough estimate of their grade if positive the third stage should be a limited bulk sampling programme order of 200 tonnes to determine the commercial sized diamond grade expressed as carats per tonne the aim of the final stage is to obtain a parcel of the order of 1 000 carats to estimate the average commercial value of the diamonds the robustness and reliability of the grade and value estimates can be verified with extreme value analysis and by obtaining the confidence limits with bootstrapping

near surface folding along an active fault seismic or aseismic abstract the meers fault in southwestern oklahoma has been active in recent times the most recent movement occurred about 1100 years ago in the late holocene during the faulting the quaternary age alluvial deposits along the fault were folded as well as ruptured in some places almost all of the deformation is accommodated by ductile folding of these deposits having this type of deformation with no record of an earthquake associated with the meers fault during historical times raises the question whether the present scarp was formed seismically by earthquake event s or aseismically by slow deformation aseismic fault creep triaxial shear tests with various shear rates were run to determine the conditions for brittle ductile and brittle ductile transition type failures relationships between ductility moisture content strain rate shear rate or failure time and confining stress were determined the results show that under the possible field conditions that existed during the faulting the ductile folding of these deposits is possible indicating the meers fault scarp could have been created contemporaneously with earthquake event s

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

reconstructing the gravity gradient anomaly field from surveys with wide line spacing using equivalent source processing an error analysis when anomalous gravity gradient signals provide a large signal to noise ratio airborne and marine surveys can be considered with wide line spacing in these cases spatial resolution and sampling requirements become the limiting factors for specifying the line spacing rather than anomaly detectability this situation is analysed by generating known signals from a geological model and then sub sampling them using a simulated airborne gravity gradient survey with a line spacing much wider than the characteristic anomaly size the data are processed using an equivalent source inversion which is used subsequently to predict and grid the field in between the survey lines by means of forward calculations spatial and spectral error analysis is used to quantify the accuracy and resolution of the processed data and the advantages of acquiring multiple gravity gradient components are demonstrated with measurements of the full tensor along survey lines spaced at 4 4 km it is shown that the vertical gravity gradient can be reconstructed accurately over a bandwidth of 2 km with spatial root mean square errors less than 30 a real airborne full tensor gravity gradient survey is presented to confirm the synthetic analysis in a practical situation

gravity gradiometer survey errors gradiometer system noise sampling effects downward continuation and limited data extent are the important contributors to moving base gravity gradiometer survey error we apply a two dimensional frequency domain approach in simulations of several sets of airborne survey conditions to assess the significance of the first two sources a special error allocation technique is used to account for the downward continuation and limited extent effects these two sources cannot be modeled adequately as measurement noise in a linear error estimation algorithm for a typical characterization of the earth s gravity field our modeling indicates that limited data extent generally contributes about one half of the total error variance associated with recovery of the gravity disturbance vector at the earth s surface gradiometer system noise typically contributes about one third however sampling effects are also very important and are controlled through the survey track spacing a 5 km track spacing provides a re

comment on known and suggested quaternary faulting in the midcontinent united states by russell l wheeler and anthony crone abstract studying previously published and other publicly available geologic evidence of quaternary faulting in the midcontinent united states wheeler and crone eng geol 62 2001 51 judged that the 30 km northwest extension of the meers fault in southwestern oklahoma suggested by cetin cetin h 1992 the northwest extension of the meers fault in southwestern oklahoma proc 28th symp eng geology and geotechnical eng university of idaho boise id pp 43 58 is not of quaternary age and claimed that holocene surface rupture has been limited to the previously reported 26 37 km section of the fault to the southeast surface rupture length is one of the most commonly used parameters to infer magnitudes of paleoearthquakes and thus potential future earthquakes in seismic hazard studies as a result underestimating fault dimensions may lead to serious errors in earthquake hazard evaluation evidence for the northwestward extension include displaced terrace deposits of pleistocene age displaced buried and or overthickened soil horizons fault related colluvium deposits colluvial wedges found near and only on the downthrown side of the fault active oil seepage near the fault deflection of stream alignments and the land use pattern along the fault the assessment of the northwestward extension of the meers fault by wheeler and crone thus appears to be mistaken

style and timing of holocene surface faulting on the meers fault southwestern oklahoma abstract stratigraphic relations and radiocarbon ages of deposits exposed in several trenches and excavations help to establish the timing sense of slip and style of the deformations that resulted from late holocene surface faulting on the meers fault in southwestern oklahoma the eastern half of the scarp is formed on relatively ductile permian hennessey shale and quaternary alluvium whereas the western half is formed on well lithified relatively brittle permian post oak conglomerate in the slick hills

structural controls of holocene reactivation of the meers fault southwestern oklahoma from magnetic studies holocene reactivation of the aseismic meers fault in southwestern oklahoma illustrates the limitation of using the historical seismic record for identifying hazardous faults in the central united states the 26 to 37 km long fault scarp is one of the few known scamps recording holocene movement in the central and eastern united states two documented late holocene slip events each with about 2 5 m of net slip and estimated m s ranging from 6 to 7 identify the meers fault as a potentially hazardous fault during carboniferous and early permian tectonism the meers fault displaced rocks of sharply contrasting magnetic properties analysis of aeromagnetic data and twelve ground magnetic profiles provides a detailed look at the fault within the magnetic basement because subsequent reactivation has been minor and of an opposite sense the pronounced magnetic anomaly associated with the meers fault reflects paleozoic structures in the magnetic basement the location of the holocene fault scarp corresponds to the strong horizontal magnetic gradient caused by paleozoic offset of magnetic basement indicating that the paleozoic fault controlled holocene displacement two features apparent in both sets of magnetic data are splays of the meers fault northwest of the holocene scarp and dikelike bodies immediately south of the fault magnetic susceptibility measurements and rock magnetic data from unoriented core penetrating a dikelike body were incorporated into models of the ground magnetic profiles in most cases secondary faults mapped or visible on low sun angle photographs correspond to faults modeled from magnetic data this correlation shows that preexisting structures probably controlled secondary faulting however secondary faults at the southeastern end of the 26 km long continuous fault scarp previously interpreted from low sun angle photography are not apparent in the magnetic data of importance to seismic hazard evaluation the magnetic models show that the northwestern splays probably begin at the northwestern end of the reactivated segment and may indicate a persistent rupture propagation barrier to the west in addition the models show the dip of the meers fault to be nearly vertical to about 0 5 km depth this dip is consistent with the nearly straight fault trace results of trenching studies interpretation of shallow seismicreflection data and regional gravity and aeromagnetic models in the present day strike slip regional stress field the observed up to the north holocene displacement suggests that either the fault continues to dip steeply at depth or the regional stress field is approaching a normal faulting stress regime if the former is true the scarcity of near vertical faults with similar orientation within the area of the southern oklahoma aulacogen implies that few are likely candidates for reactivation

comparing gravity and gravity gradient surveys noise levels in marine and airborne full tensor gravity gradiometer surveys together with conventional land marine and airborne gravity surveys are estimated and analysed in gridded form resulting in relations that detail how these different survey systems can be compared analytically after defining survey parameters including line spacing speed and instrument bandwidth the relations estimate the noise levels that result on either grids of gravity gz or gravity gradient gzz as a function of the spatial filtering often applied during geological interpretation such comparisons are believed to be a useful preliminary guide for survey selection and planning

apparent density mapping and 3d gravity inversion in the eastern alps1 power spectrum analysis of the bouger gravity values in the eastern alps suggests that the gravity field may be separated into long and short wavelength components the long wavelength component is assumed to be caused by alpine crustal thickening this long wavelength component was subjected to a gravimetric single density interface inversion procedure giving a gravimetric mohorovicic model which is generally in good agreement with moho depths derived by refraction and reflection seismology the residual high frequency gravity component correlates well with the main surface geological units in the eastern alps apparent density mapping by applying an inverse density deconvolution filter to the short wavelength gravity component gives density values for the upper crust which correspond well with averaged density values from rock samples

3d geophysical inversions of the north east amer belt and their relationship to the geologic structure the amer lake area is located within the churchill structural province in the kivalliq region of nunavut approximately 160 km north west of baker lake two distinct geophysical geological entities are structurally intercalated an archean mixed granitoid gneiss metasedimentary metavolcanic basement and the unconformably overlying paleoproterozoic amer group metasediments from east of amer lake stretching toward the south west these two entities form the amer fold and thrust belt at the north east end of this belt high resolution aeromagnetic data define a distinctive oval shape that has been interpreted as a south west trending doubly plunging synform the outcrop within the interior of this structure is sparse resulting in limited structural data and speculative geological interpretations with multiple geometries possible the high resolution aeromagnetic data compiled through an industry government consortium and newly acquired detailed gravity profiles were modelled to provide constraints on the geometry of this synform we document a geophysical geological feedback process whereby the available geological and geophysical data were used to derive constraints on inversion models for the synform starting with available limited litho structural data the presence of a double plunging synform was directly inferred from the aeromagnetic data segments of the aeromagnetic data have 2d morphology and so can be modelled using a simple parametric 2d dipping slab inversion approach models of profiles extracted from the aeromagnetic data were used to provide preliminary dip and magnetic susceptibility constraints for the three lakes mudstone with iron formation and the five mile lake basalt landsat imagery outlined the spatial limits of the stratigraphically underlying non magnetic ayagaq quartzite incorporating these outputs as bounds in the input reference model for a ubc gif 3d magnetic inversion helped to accentuate the geological structure in the output mesh an enhanced inversion that incorporates both geological and geophysical constraints the validity of the resulting inversion model was tested by computing 2d forward models of the gravity profile data the inversion model generated by this study emphasizes the importance of integrating information from as many knowledge sources as one can find more trust can be placed on forward and inversion models where there is agreement among all data sets and a coherency of structural style

applying laterally varying density corrections to ground gravity and airborne gravity gradiometry data a case study from the bathurst mining camp the influence of topography on gravity and gravity gradiometry measurements is profound and should be minimized prior to geological interpretation the standard way of minimizing these effects is through the computation of a terrain correction terrain corrections require two inputs topography and density often geology and topography are inextricably intertwined topography is caused by a change in geology in geologic environments where there is a structural and or stratigraphic control on the near surface mass distribution using a single density value in the corrections leads to removal of the topographic effect of rocks having the chosen density any remaining gravity signal that correlates with topography is providing geological information if the objective is to produce a gravity map with minimal topographic signal then a regionally variable density correction is a means of compensating for this effect in this paper we demonstrate how to apply a spatially variable density correction using g

characterization of heterogeneous near surface materials by joint 2d inversion of dc resistivity and seismic data 1 we have developed a robust 2d joint inversion scheme incorporating the new concept of cross gradients of electrical resistivity and seismic velocity as constraints so as to investigate more precisely the resistivity velocity relationships in complex near surface environments the results of joint inversion of dc resistivity and seismic traveltime data from collocated experiments suggest that one can distinguish between different types or facies of unconsolidated and consolidated materials refining a previously proposed resistivity velocity interrelationship derived from separate inversions of the respective data sets a consistent interpretive structural model can be obtained from the joint inversion models

the geological and tectonic evolution of the precambrian of northern sweden a case for basement reactivation abstract this study is the result of a regional mapping programme of the precambrian to the extreme north of sweden by the geological survey of sweden in the years 1976 1981 it takes into account most of the geological geochemical and geophysical data concerning the region a brief description and revision of the stratigraphy is given in the light of recent mapping results and radiometric age determinations an attempt is made to trace the main petrogenetic trends of the volcanic and the plutonic rock series in order to determine which geotectonic model can best be inferred for the region following the archaean consolidation phase two major tectonic episodes have been recognized 1 a tensional episode characterized by incipient rifting which resulted in the extrusion of basic magma and in the deposition of predominantly quartzitic sediments and 2 a complex episode of reactivation of older structures and formations corresponding to the peak of the svecokarelian orogeny and to later consolidation this tectonic evolution is interpreted here as a phase of basement reactivation and shows much resemblance to ensialic mobile belts described in other parts of the world a characteristic feature of the aeromagnetic gravimetric and landsat maps is the profusion of circular and arcuate structures of variable magnitude and distinctiveness the possibility that some of these are due to the process of sequential inheritance of early impact scars is discussed

shallow seismic reflection profile of the meers fault comanche county oklahoma this is the publisher s version also available electronically from http onlinelibrary wiley com

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

gravity and magnetic expression of the san leandro gabbro with implications for the geometry and evolution of the hayward fault zone northern california the hayward fault one of the most hazardous faults in northern california trends north northwest and extends for about 90 km along the eastern san francisco bay region at numerous locations along its length distinct and elongate gravity and magnetic anomalies correlate with mapped mafic and ultramafic rocks the most prominent of these anomalies reflects the 16 km long san leandro gabbroic block inversion of magnetic and gravity data constrained with physical property measurements is used to define the subsurface extent of the san leandro gabbro body and to speculate on its origin and relationship to the hayward fault zone modeling indicates that the san leandro gabbro body is about 3 km wide dips about 75 80 northeast and extends to a depth of at least 6 km one of the most striking results of the modeling which was performed independently of seismicity data is that accurately relocated seismicity is concentrated along the western edge or stratigraphically lower bounding surface of the san leandro gabbro the western boundary of the san leandro gabbro block is the base of an incomplete ophiolite sequence and represented at one time a low angle roof thrust related to the tectonic wedging of the franciscan complex after repeated episodes of extension and attenuation the roof thrust of this tectonic wedge was rotated to near vertical and in places the strike slip hayward fault probably reactivated or preferentially followed this preexisting feature because earthquakes concentrate near the edge of the san leandro gabbro but tend to avoid its interior we qualitatively explore mechanical models to explain how this massive igneous block may influence the distribution of stress the microseismicity cluster along the western flank of the san leandro gabbro leads us to suggest that this stressed volume may be the site of future moderate to large earthquakes improved understanding of the three dimensional geometry and physical properties along the hayward fault will provide additional constraints on seismic hazard probability earthquake modeling and fault interactions that are applicable to other major strike slip faults around the world manuscript received 11 january 2002

the gradient tensor of potential field anomalies some implications on data collection and data processing of maps the full gradient tensor is presently not measured routinely onboard airplanes or on land this paper describes some improvements that can be made in strategies of data collection and in processing of potential field maps if such tensor measurements were available we suggest that in addition to producing for example standard total field anomaly maps the invariants of the tensor be mapped strikes of magnetic or gravimetric structures may be determined from minimizing the power in the first row and column of the tensor invariants can be looked upon as nonlinear filters enhancing sources with big volumes their lateral resolution is superior to that of the field proper and for a given resolution the flight altitude and separation between flight lines can be increased compared with the standard mode of operation in airborne surveys the distance between flight lines is normally much larger than the height above the ground this may introduce severe aliasing effects in the direction perpendicular to the

geologic and geotechnical effects of an impact caused by an airplane crash abstract a turkish airlines thy boeing 737 400 plane crashed into alluvial soils creating an approximately 13 m deep and 30 m wide crater near the village of adatepe ceyhan in southern turkey effects of the impact on the soils in and around the crater were investigated from both the geological and soil mechanics point of view the results show that the impact caused severe deformations in the soils in and around the crater the soils deformed similar to metamorphic rocks seen at many terrestrial hypervelocity impact craters around the world and became overconsolidated up to a distance of about 10 m from the crater wall as a result of the impact also the crash was recorded as a 2 7 magnitude earthquake by a nearby microtremor seismograph which provided both the location epicenter and time of the crash which was not known immediately after the crash

settlement and slaking problems in the world s fourth largest rock fill dam the ataturk dam in turkey abstract the ataturk dam is the fourth largest clay cored rock fill dam in the world located in southeastern turkey it is the centrepiece of a project called the southeastern anatolian project gap the construction of the dam was finished in the short time of 3 years and 8 months in august 1990 as the reservoir level started to rise settlement problems started to occur along the crest reaching considerable levels by may 1992 and the weathered vesicular basalt used in the rock fill section of the dam started to slake seriously the elevation of the crest has fallen down to such an extent that now the upper part of the dam is being reconstructed to the original height of 549 m in order to maintain the 7 m freeboard and keep the dam operational the settlement and slaking problems of the dam were investigated both in the field and the laboratory using soil and rock mechanical techniques standard proctor tests were run to determine the optimum moisture content at which the highest dry density best compaction is obtained during compaction of the impervious clay core consolidation tests were performed on undisturbed compacted clay core samples to determine if the field compaction of the clay core was done to the standards determined in the laboratory unconfined compression tests were run on the two different sound aphanitic and weathered vesicular basalts used in the rock fill section of the dam to determine their unconfined compressive strengths slake durability tests were run on the same basalts to determine their durability under wetting and drying cycles petrographic and x ray analysis were done so as to study the mineralogical contents of the two basalts and in turn to determine the cause of rapid slaking of the vesicular textured weathered basalt the consolidation test results show that the field compaction of the impervious clay core of the dam was not done to the standards determined through the proctor tests in the laboratory the unconfined compressive strength of the sound aphanitic basalt is more than ten times greater than the weathered vesicular basalt and while the former has extremely high durability the latter only has medium durability because of nontronite iron montmorillonite and secondary calcite amygdules filling the vesicles the weathered vesicular basalt used in the rock fill section is slaking badly causing additional settlement and landslides both in the clay core which is already settling and the rock fill section of the dam with the continuing slaking the present reconstruction of the crest up to the theoretically intended height of 549 m to maintain the 7 m freeboard and keep the dam operational seems only to be a temporary solution

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

interpretation of magnetic and gravity gradient tensor data using normalized source strength a case study from mcfaulds lake northern ontario canada in this paper we present a case study on the use of the normalized source strength nss for interpretation of magnetic and gravity gradient tensors data this application arises in exploration of nickel copper and platinum group element ni cu pge deposits in the mcfaulds lake area northern ontario canada in this study we have used the normalized source strength function derived from recent high resolution aeromagnetic and gravity gradiometry data for locating geological bodies in our algorithm we use maxima of the normalized source strength for estimating the horizontal location of the causative body then we estimate depth to the source and structural index at that point using the ratio between the normalized source strength and its vertical derivative calculated at two levels the measurement level and a height h above the measurement level to discriminate more reliable solutions from spurious ones we reject solutions with unreasonable estimated structural indices this method uses an upward continuation filter which reduces the effect of high frequency noise in the magnetic case the advantage is that in general the normalized magnetic source strength is relatively insensitive to magnetization direction thus it provides more reliable information than standard techniques when geologic bodies carry remanent magnetization for dipping gravity sources the calculated normalized source strength yields a reliable estimate of the source location by peaking right above the top surface application of the method on aeromagnetic and gravity gradient tensor data sets from mcfaulds lake area indicates that most of the gravity and magnetic sources are located just beneath a 20 m thick on average overburden and delineated magnetic and gravity sources which can be probably approximated by geological contacts and thin dikes come up to the overburden

performance of airborne gravity gradiometers airborne gravity gradiometry agg is becoming a widely accepted tool in exploration it provides rapid acquisition of accurate gravity data at high spatial resolution with complete coverage over large areas the data are of significant value to explorers for a wide range of commodities throughout the world with the advent of airborne gravity gradiometer technology it is now possible to collect high resolution gravity with all the attendant advantages