modelling of magnetic data for scaling geology interpretation of magnetic data can be carried out either in the space or frequency domain the interpretation in the frequency domain is computationally convenient because convolution becomes multiplication the frequency domain approach assumes that the magnetic sources distribution has a random and uncorrelated distribution this approach is modified to include random and fractal distribution of sources on the basis of borehole data the physical properties of the rocks exhibit scaling behaviour which can be defined as p k ak where p k is the power spectrum as a function of wave number k and a and are the constant and scaling exponent respectively a white noise distribution corresponds to 0 the high resolution methods of power spectral estimation e g maximum entropy method and multi taper method produce smooth spectra therefore estimation of scaling exponents is more reliable the values of are found to be related to the lithology and heterogeneities in the crust the modelling of magnetic data for scaling distribution of sources leads to an improved method of interpreting the magnetic data known as the scaling spectral method the method has found applicability in estimating the basement depth curie depth and filtering of magnetic data

wavelet analysis for the regional residual and local separation of potential field anomalies a method based on the discrete wavelet transform was applied to the regional residual separation of potential fields and to the filtering of local anomalies a specific space scale wavelet analysis called multiresolution analysis allowed decomposition of the signal with respect to a vast range of scales different analysing wavelets were applied to anomalies in both synthetic and real cases but the more appropriate basis needed to be chosen by requiring the maximum compactness for the multiresolution analysis moreover since such analysis was found not to be shift invariant the same criterion was applied to choosing the best signal shift application of the technique to both synthetic and real cases produced an optimal space scale representation of the fields and a consistent regional residual separation furthermore the space localization allowed a variety of filtered signals to be obtained each one with a specific scale and local area content fourier and wavelet analyses were both applied to the filtering out of the intense etna anomaly from the aeromagnetic field of sicily the wavelet method was more powerful suppressing only the etna volcano anomaly and leaving the rest of the map practically unchanged

scaling nature of crustal susceptibilities scale invariant or self similar properties have been demonstrated for a wide range of geophysical processes and rock properties evidence from well logs and inferences from aeromagnetic field power spectra suggest that crustal susceptibility also shows this behaviour with a power spectrum proportional to the 4 power of the spatial frequency we examine two large susceptibility measurement data sets and find that they both support the scaling hypothesis

gravity and magnetic investigation on the distribution of volcanic rocks in the qinggelidi area north eastern junggar basin north west china a detailed investigation on the location of magmatic intrusions in the carboniferous strata of the qinggelidi area north eastern junggar basin is presented based on the interpretation of gravity and magnetic data constrained by petrophysical data seismics and surface geology the wavelet multi resolution analysis based on the discrete wavelet transform is adopted to the regional residual separation of gravity and magnetic anomalies a power spectrum analysis is applied to estimate the source depths corresponding to different scales a comparative analysis on the characteristics of local gravity and magnetic anomalies improved our understanding of volcanic rock distribution in the carboniferous strata generally speaking in total 75 anomalies are recognized among which 23 are inferred to be the responses of basalts diabases and andesites with high density and strong magnetization twelve anomalies are assumed to be caused by andesites rhyolites and volcanic breccias with medium low density and high magnetization there are still five anomalies that are believed to be generated by volcanic tuffs with low density and weak magnetization lastly four cross sections in 3d gravity and magnetic modelling are displayed to provide a more thorough image of volcanic rocks in our study area

deglacial land emergence and lateral upper mantle heterogeneity in the svalbard archipelago i first results for simple load models summary the glacial isostatic adjustment following the removal of the pleistocene ice sheets furnishes basic information on the thickness of the earth s lithosphere and the viscosity of the subjacent mantle paper i is concerned with an elementary interpretation of the post glacial land emergence observed at a restricted set of six locations in the svalbard archipelago the interpretation is based on a three layer incompressible maxwell viscoelastic earth model which is forced by a time dependent load distribution simulating the deglaciation history of the svalbard archipelago and the barents sea in view of inconclusive geomorphological evidence suggesting either total or partial glaciation of the area at glacial maximum two simple load models barents t1 and barents p1 are considered in the first instance a comparison between the calculated and observed values of land emergence suggests increases in lithosphere thickness and asthenosphere viscosity with increasing distance of the location from the continental margin the trends are qualitatively insensitive to the load model load thickness or load cross section used for load model barents t1 with parabolic cross section an initial load thickness of 1 50 km and a relaxed fitting criterion the lateral variations are only weak if a more restrictive fitting criterion is employed the variations become more prominent and suggest increasing values of lithosphere thickness from below 80 km to above 140 km and of asthenosphere viscosity from below 3 1018 pa s to above 2 1019 pa s over a distance of about 300 km in paper ii kaufmann wolf 1995 a high resolution load model and an extended set of land emergence observations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the svalbard archipelago

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

experimental investigation on the creep behavior of an unsaturated clay to better understand the long term deformation of landslides with consideration of the influence of water content variation a series of triaxial creep tests with suction control was conducted on clay specimens taken from one large scale landslide in the three gorges reservoir area in china results indicate that in the double logarithmic coordinates the axial strain increases linearly and the axial strain rate decreases linearly with the elapsed time the axial strain and strain rate increase with increasing deviator stress levels and decreasing matric suction for theoretical analysis based on the simulation of the test results by an empirical creep model developed for saturated soils a linear relationship was established between suction and one of the parameters of the model then a revised model with consideration of suction effects was developed in the revised model a power function was adopted for the description of the strain time relationship and a hyperbolic function was employed for the stress strain relationship verification indicated that the calculated results were in good agreement with the experimental ones

decorrugation and removal of directional trends of magnetic fields by the wavelet transform application to archaeological areas the problem of removing directional trends frequently occurs in the processing of magnetic data and also in the subsequent steps of data interpretation the so called corrugations are typical directional trends occurring in levelled data which may be removed in several ways classical techniques are based on high pass filtering of the data and successively filtering these transformed data with directional cosine filters other linear features are due to real sources such as pipelines in shallow surveys or dike swarms in regional surveys they should nevertheless be considered as noise due to the fact that their effect is strong and tends to hide the field features related to structures of more interest we deal with both kinds of problem presenting the results of a study in an archaeological area of southern italy decorrugation of magnetic field anomalies is performed using a method based on the excellent space frequency localization properties of wavelet bases allowing a very sharp filtering of the field along a selected direction we compare this technique with the classical one in a synthetic case and find that the wavelet decorrugation is simpler and produces low distortion maps besides the field decorrugation the wavelet approach was also shown to be useful in the subsequent enhancement of the measured field in fact we show that the wavelet analysis offers a unique framework where various filtering problems directional isotropic global or local as well may be easily solved as regards the archaeological case strong noisy effects from elongated sources pipelines were successfully removed in a sharp and local way

paleorift structure constrained by gravity and stratigraphic data the statherian arai rift case abstract gravimetric and stratigraphic data were used to investigate the paleoproterozoic arai paleorift a failed statherian continental rift located in the western margin of the sao francisco craton where basement and cover were affected by the neoproterozoic brasiliano orogeny euler deconvolution tilt total horizontal gradient amplitude and upward continuation technics were applied to terrestrial gravimetric data in order to investigate the rift s main faults location direction and depth allowing to identify its main horsts grabens volcanic and plutonic centers we found that rift faults occur to a maximum depth of ca 38 km but major fault throw occurs from 4 to 8 km deep and attenuates from 8 to 12 km probably the brittle ductile transition zone at the time of rifting practically disappearing at 20 km stratigraphic data and basement mapping were used in order to constraint gravimetric results we classify the arai rift as a passive three armed failed rift narrow to divergent type that produced preferably anorogenic rapakivi related magmas most of it still lodged in the crust from surface down to ca 19 km deep and subsidiary mafic magmatism the results indicate the deep occurrence of low density magmas beneath the rift s main axis detected up to 20 km deep correlation to other global statherian rifts show that the sao francisco craton was strongly affected by taphrogenesis during the statherian together with siberia north america and north china cratons finally by comparing our results to recent rifts we found that the ethiopian rift s morphology is quite similar to the arai surrounding the tanzanian craton the cenozoic east africa rift system morphology is compared to the arai espinhaco rift system which surrounds the sao francisco craton the major contribution of this paper is the recognition of arai paleorift surface and subsurface morphology up to now unknown over an area of ca 45 000 km2

identifying mineral prospectivity using seismic and potential field data in the hongniangyu district inner mongolia china abstract since the discovery of several large porphyry mo deposits 0 1 mt mo in the jining region of inner mongolia china during the past decades the area has been receiving wide interest for mining activities however mineral exploration in this area is challenging because most of it is thickly covered by cenozoic sediments geophysical surveys especially the seismic method are becoming increasingly important for investigating deep seated ore controlling structures e g porphyry granites faults and even orebodies supporting the discovery of buried ore deposits recently potential field data and seismic reflection data have been acquired for the hongniangyu area south of jining region in this study we mainly use seismic reflection and potential field data to obtain subsurface geological model in support of mineral exploration targeting gravity and magnetic data were firstly used for spatial analysis of mineral system by mapping the distribution of the faults concealed granites and the sedimentary basin through wavelet analysis tilt angle and euler deconvolution to address the common problem of low signal to noise ratio of seismic reflection data obtained in hard rock terranes we applied a sophisticated workflow including refraction static correction noise filtering surface consistent deconvolution and velocity analysis the obtained post stack migrated seismic profile clearly imaged the geometry of the concealed graben located at the north end of the datong basin and the south east dipping kouquan normal fault controls the depression of the graben and offsets cenozoic sediments by several hectometers up to 500 m joint modeling of seismic gravity and magnetic data further provided evidence of the three buried belts of granites intriguingly one of the concealed granitic belts located in the north of hongniangyu area was found to have both significant chargeability and mo geochemical anomalies indicating a high potential of hosting porphyry type mo ore deposits as expected mo and w mineralized cores were discovered in this target area but limited to only one deep drilling hole the presented results provide the geological framework of hongniangyu district and guidelines for delineating new potential mo mineralization in the jining region

regional and residual gravity anomaly separation using singular spectrum based frequency filtering methods a case study of shallow subsurface modeling from nagpur india we present here the application of a single and multichannel singular spectrum analysis ssa based data filtering algorithm for regional and residual gravity field separation initially the single channel ssa method was tested on synthetic gravity profile data generated using gravity and magnetics modelling system gm sys a gravity modeling software for a sedimentary basin structure corrupted with gaussian white noise and compared with the convnetional fast fourier transform fft based wave number non data adaptive and discrete wavelet transform semi data adaptive filtering approaches the comparative results show that the residual filtering of gravity data using the ssa method produces less minimal artifacts compared to fft based wave number filtering and wavelet filtering methods following the synthetic examples we further employed multichannel ssa based frequency filtering on 2d gridded gravity data from umred nagpur district maharashtra india to separate the residual anomaly for modelling the shallow subsurface structures the modelled depth sections of two mutually perpendicular profiles suggest the presence of alluvium lameta kamthi and barakar formations with varying thicknesses the formations identified from the models show a clear match with the local geology and nearby borehole information we suggest that the single and multichannel ssa based frequency filtering are robust approaches for separating regional and residual components from gravity anomalies

gravity anomaly separation by wiener filtering we introduce a gravity anomaly separation method based on frequency domain wiener filtering gravity anomaly separation can be effected by such wavelength filtering when the gravity response from the geologic feature of interest the signal dominates one region or spectral band of the observed gravity field s power spectrum the wiener filter is preferable to a conventional band pass filter because geologic information from the study area can be incorporated to a greater extent in specifying the filter s transfer function our method differs from previous wiener filtering schemes in that it provides through direct modeling of known geology e g outcrop and borehole data a more objective estimate of the signal power spectrum required for defining the transfer function of the filter we illustrate the technique first with synthetic data and then with a field example from the southern paradox basin the paradox basin example reveals the limitation inherent to all wavelength filtering which results f

the antarctic ice sheet during the last glacial interglacial cycle a three dimensional experiment a complete 3 d thermo mechanical ice sheet model for the entire antarctic ice sheet including an ice shelf grounding line dynamics and isostatic bedadjustment is employed to simulate the response of the ice sheet during the last glacial interglacial cycle with respect to changing environmental conditions to do this the vostok temperature signal is used to force changes in surface temperature and accumulation rate and sea level prescribed by a piecewise linearsawtooth function model calculations started at 160 kyears bp in line with glacial geological evidence the most pronounced fluctuations are found in thewest antarctic ice sheet and appear to be essentially controlled by changes in eustatic sea level grounding occurs more readily in the weddell sea than in theross sea and due to the long time scales involved the ice sheet does not reach its full glacial extent until 16 kyears bp the concomitant disintegration of thewest antarctic ice sheet is triggered by a rise in sea level and takes around 6000 years to complete the ice sheet then halts close to the present state and nocollapse takes place this holocene deglaciation appears to have added 6 8 million km3 of ice to the world oceans corresponding with an antarcticcontribution to world wide sea level of 12 15 m

the calabrian arc and the ionian sea in the dynamic evolution of the central mediterranean in the central mediterranean area it is possible to recognize three main realms the tyrrhenian sea the pelagian block and the ionian block these domains are limited by important fracture zones that are easily recognizable on land and offshore these fracture zones can be grouped into four main trends 1 the nw se trend which is characterized by dextral horizontal movements 2 the ne sw trend which is generally characterized by sinistral lateral horizontal movements 3 the e w trend which also shows dextral shear movements and 4 the n s trend which is characterized by normal faults only the tyrrhenian sea realm is characterized by a thinned crust of oceanic type and is connected to the apenninic chain by means of listric faults from a geophysical point of view the area shows a high heat flow which follows the main structural trends and positive gravimetric anomalies which are compatible with seismic refraction data and can be explained by the proposed model the pelagian block shows a continental crust about 20 km thick which progressively increases beneath the sicilian chain here an abrupt interruption with the tyrrhenian block takes place in the pelagian realm rifting processes developed according to the nw se and n s trend the n s trend characterizes the westernmost zone of the realm where volcanic processes and a relatively high heat flow can also be observed the ionian block is characterized by the following a thinned crust 17 20 km which increases 40 km towards the southern calabrian chain a thick sedimentary sequence high positive bouguer anomalies 300 mgal and very low heat flow 50 mw m 2 geophysical and structural analyses allowed us to evaluate the post tortonian evolution of the whole area under consideration this evolution resulted in continental crust formation according to a rigid plastic deformation model according to our model the ionian block can be considered as a domain characterized by a thinned continental crust and affected by intrusive material derived from the upper mantle furthermore this domain of probably jurassic age can be considered as a pelagic basin bordered by the pelagian block to the west and by the apulian block to the east northeast this basin according to its position with respect to the apenninic and sicilian chains has not been affected by tectogenesis and still represents a site of continuous sedimentation from a kinematic point of view the ionian realm can be linked with the pelagian block shifting towards the east northeast whereas it is limited towards the north by an e w fracture zone which regulates the opening of the tyrrhenian sea and the counterclockwise rotation of the apenninic chain according to the proposed model the opening of the tyrrhenian sea can be considered as a megaextension fracture which developed parallel to the maximum principal stress direction and evolved as a triangular shaped structural feature in preparing the model the authors have taken into account a large set of data collected both on land and offshore

comparison of airborne and marine magnetic data in donegal basin ireland exploration of ireland s donegal basin in the last 10 years concentrated on structural plays within the triassic sherwood sandstone and culminated in the corrib gas discovery in 1998 despite this economic success the structural history and hence petroleum geology of the basin remained poorly understood due in large measure to igneous intrusives and salt which degrade seismic data quality these problems caused operators to consider alternative methods and given the success of potential fields in adjacent areas faroes irish sea new gravity and magnetic surveys were undertaken in 1999 before 1999 the only speculative magnetic data set over donegal basin was a 5 km grid of various vintages compiled by the geological survey of canada this was useful for identifying regional structural trends but little else as exploration intensified in 1999 a 2d seismic survey was acquired along with marine gravity and magnetics data the new data enabled better structural definition within the basin but still left many unanswered questions about the detailed character and extent of igneous intrusions to address this a high resolution aeromagnetic hram survey was flown in late 1999 the dense data coverage and high sampling rate provided much greater detail than previous surveys table 1 view this table table 1 comparison of acquisition parameters for various surveys acquired in the donegal basin this paper discusses the advantages and disadvantages of the various data types acquired in donegal basin each has an optimum application determined by technical objectives and budget but to choose the most appropriate it is important to understand the limitations that each has the underlying aim of this paper is to help explorationists make better informed decisions when planning acquisition of potential fields data the 2d marine gravity and magnetics data acquired in conjunction with the 1999 seismic survey had line orientations that were north south and east west respectively and line spacing

drained creep of undisturbed cohesive marine sediments long term drained triaxial creep and direct simple shear creep tests were conducted on undisturbed marine specimens from the gulf of mexico and the north central pacific results indicated that time dependent deformations can be represented by a power law equation and the creep strain rate can be represented by an equation similar to that suggested earlier by other researchers however it was found that the m parameter suggested by these scientists was not a constant but dependent on stress level and sediment plasticity ageing effects were evidenced in triaxial specimens by the increase of shear strength with both test duration and stress level the results provided a guide for the development of mathematical stress strain time relationships that will be developed in a separate paper key words drained triaxial creep simple shear creep stress strain time behavior

multiscale derivative analysis a new tool to enhance detection of gravity source boundaries at various scales 1 potential fields generally require to be analyzed by different scales owning to sources of different depth and extent fourier or wavelet filtering not always yield an optimal separation of those different source effects often introducing some amount of distortion we propose therefore a new method the multiscale derivative analysis mda based on the enhanced horizontal derivative ehd of the field which does not imply any separation of the effects but simply enhances those related to a given scale such process based on a weighted sum of increasing order derivatives of the field converges quickly toward the actual boundaries of the sources mda applied to gravity data of the of thyrrenian sea italia yields 3 maps of structural lineaments each one characterized by a different scale known partially known or relatively new structures are described in the maps allowing a rapid analysis of all the gravity related structural lineaments of this region

middle proterozoic compressional orogen in northwestern canada evidence from seismic reflection profiling drill holes potential field measurements and regional geology shows that an east verging proterozoic thin skinned thrust and fold belt is situated beneath the interior platform of northwestern canada balanced cross sections and associated palinspastic reconstructions provide constraints on the extent of the shortening in the thrust belt and suggest that at least 50 90 km of compression can be accounted for although the proterozoic stratigraphy in the subsurface is not well known the cross sections are constrained essentially by seismic reflection geometry shortening occurred on subhorizontal detachment s that lie above the autochthonous hudsonian basement seismic reflection data from the area west of the major thin skinned thrust structures show that the proterozoic strata there can be traced for up to 100 km and are characterized by broad open folds with wavelengths of 10 km or more uniform potential field anomalies and subhorizontal seismic reflections further indicate that there are no major crustal boundaries such as sutures in the area between the thrust belt and the campbell uplift near inuvik northwest territories that were associated with the thrusting the detachment s that carried the folded and thrust faulted allochthons must therefore extend for a considerable distance to the northwest of the thrust belt new deep crustal seismic reflection data from the campbell uplift however show evidence for crustalpenetrating proterozoic structures that dip northwestward and that were probably reactivated during late paleozoic compression and mesozoic extension taken together the various data thus indicate that the area from great bear lake to the campbell uplift about 400 km is underlain by a mid proterozoic decollement above which the compressional deformation took place and that the deformation extended to the north side of the present campbell uplift where steeply north dipping structures indicate that the underlying autochthonous basement is characterized by a ramp structure that was probably associated with the southern edge of a proterozoic basin

glacial isostasy and the interplay between upper and lower mantle lateral viscosity heterogeneities from the analysis of sea level data near the centre of the former fennoscandian ice sheet and the theoretical predictions of vertically and laterally stratified earth models we explore the extent to which lateral viscosity variations could have influenced the estimate of long term mantle viscosity we follow a finite element scheme in cylindrical symmetry focusing on the effects of lateral viscosity contrasts of different magnitudes and wavelengths sea levels are consistent with long wavelength lateral viscosity contrasts of at most 2 orders of magnitude short wavelength variations comparable with the lateral extension of the surface load should be ruled out differences in the average viscosities inferred from laterally stratified and uniform mantle models may be as high as 1 order of magnitude if we allow for different lateral viscosity patterns in the upper and lower mantle we find that sea levels are consistent with short wavelength variations in the upper mantle of around 2 orders of magnitude coupled with smoother lateral viscosity contrasts in the lower mantle

modeling the growth and decay of the antarctic peninsula ice sheet a model of the growth and decay of the antarctic peninsula ice sheet during the last glacial interglacial cycle is used to identify the main controls on ice sheet behavior using as input glaciological assumptions derived by w f budd and i n smith 1982 annals of glaciology 3 4249 bedrock topography isostatic compensation and mass balance relationships the model is driven by sea level change over the last 40 000 yr in association with assumed changes in the rate of melting beneath ice shelves an ice sheet dome over 3 5 km thick grows on the offshore shelf and straits west of the antarctic peninsula and reaches a maximum at 18 000 yr b p collapse begins at 14 000 yr b p but becomes rapid and continuous after 10 000 yr b p the present stable ice cover is achieved at 6500 yr b p ice growth and decay are characterized by thresholds which separate periods of steady state from periods of rapid transition the thresholds usually relate to topography tests show that ice sheet behavior is most sensitive to sea level change basal marine melting and accumulation and is less sensitive to isostasy spatial variation in accumulation calving rates and ice flow parameterization tests of the model against field evidence show good agreement in places as well as discrepancies which require further work o

a geochemical and geophysical investigation of the hydrothermal complex of masaya volcano nicaragua abstract masaya volcano nicaragua is a persistently active volcano characterized by continuous passive degassing for more than 150 years through the open vent of santiago crater this study applies self potential soil co 2 and ground temperature measurements to highlight the existence of uprising fluids associated to diffuse degassing structures throughout the volcano the diffuse degassing areas are organized in a semi circular pattern and coincide with several visible and inferred surface volcanic structures cones fissure vents and likely consist of a network of buried faults and dykes that respectively channel uprising flow and act as barrier to gravitational groundwater flow water depths have been estimated by multi scale wavelet tomography of the self potential data using wavelets from the poisson kernel family compared to previous water flow models our water depth estimates are shallower and mimic the topography typically less than 150 m below the surface between 2006 and 2010 the depths of rising fluids along the survey profiles remained stable suggesting that hydrothermal activity is in a steady state this stable activity correlates well with the consistency of the volcanic activity expressed at the surface by the continuously passive degassing when compared to previous structural models of the caldera floor it appears that the diffuse degassing structures have an important effect on the path that shallow groundwater follows to reach the laguna de masaya in the eastern part of the caldera the hydrogeological system is therefore more complex than previously published models and our new structural model implies that the flow of shallow groundwater must bypass the intrusions to reach the laguna de masaya furthermore these diffuse degassing structures show clear evidence of activity and must be connected to a shallow magmatic or hydrothermal reservoir beneath the caldera as such the heat budget for masaya must be significantly larger than previously estimated

separation of potential field data using 3 d principal component analysis and textural analysis summary potential field data represent the superposition of effects of all surface and underground sources a reliable interpretation of different gravity or magnetic anomalies greatly depends on a reasonable separation between regional field and local anomalies we present here a novel separation method based on a 3 d principal component analysis pca and textural analysis the pca used to decompose the potential field data into a linear superposition of eigenimages is performed not only on anomaly values but also on textural features so as to fully use the spatial distribution characteristics of the data and make the separated regional field comprehensively account for the major variations of the data in order to reduce subjectivity and inaccuracy we propose a texture based criterion in separation result selection which measures the highlighted differences between the two kinds of anomaly by textural statistics and select the first several eigenimages corresponding to the most important variability as the region field when the differences reach maximum the method is tested with two synthetic models and two real data examples from the huanghua area located in hebei province china our tests suggest that the method provides a better separation of regional and local anomalies than does the polynomial fitting technique the separated regional fields and local anomalies of the gravity and magnetic data coincide well with the geological structure of the huanghua area

deglacial land emergence and lateral upper mantle heterogeneity in the svalbard archipelago ii extended results for high resolution load models summary in paper i breuer wolf 1995 a preliminary interpretation of the postglacial land emergence observed at a restricted set of six locations in the svalbard archipelago was given the study was based on a simple model of the barents sea ice sheet and suggested increases in lithosphere thickness and asthenosphere viscosity with increasing distance from the continental margin in the present paper the newly developed high resolution load model barents 2 and land uplift observations from an extended set of 25 locations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the northern barents sea a comparison of the calculated and observed uplift values shows that the lithosphere thickness is not well resolved by the observations although values above 110 km are most common for this parameter in contrast to this there are indications of a lateral variation of asthenosphere viscosity whereas values in the range 10 8 1020 pa s are inferred for locations close to the continental margin 1020 102 pa s are suggested further away from the margin a study of the sensitivity of the values found for lithosphere thickness and asthenosphere viscosity to modifications of load model barents 2 shows that such modifications can be largely accommodated by appropriate changes in lithosphere thickness whereas the suggested lateral variation of asthenosphere viscosity is essentially unaffected an estimate of the influence of the fennoscandian ice sheet leads to the conclusion that its neglect results in an underestimation of the thickness of the barents sea ice sheet by about 10 per cent

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

model based separation filtering of magnetic data separating the fields produced by sources at different depths is a common requirement in the interpretation of potential field data approaches to this problem are generally data or model based data based methods require clear linear segments in the logarithmic power spectrum of the data corresponding to different components of the field various types of filters can then be designed to carry out the separation when the logarithmic power spectrum shows no identifiable linear spectral segments other approaches are necessary we outline a model based method that does not depend on power spectral information but requires independent estimates of the average depths of the source distributions e g from seismic interpretations an ensemble of models using fractal source distributions is computed based on these known values and filter parameters are determined that produce the closest fit in a least squares sense to the theoretical fields that each source distribution generates this approach is used to separate basement effects from intrasedimentary sources in magnetic data collected over the colville hills northwest territories canada seismic data interpretation places crystalline basement at 10 km depth and an intrasedimentary basaltic layer at 2 km our approach results in an optimal separation filter with a cutoff wavelength of 12 km that appears to provide an effective separation of the two source effects

a comparison of different ways of dealing with isostasy examples from modelling the antarctic ice sheet during the last glacial cycle the bedrock isostatic response exerts a strong control on ice sheet dynamics and is therefore always taken into account in ice sheet models this paperreviews the various methods normally used in the ice sheet modeling community to deal with the bedrock response and compares these with a moresophisticated full earth model each of these bedrock treatments five in total are coupled with a three dimensional thermomechanical ice sheet model underthe same forcing conditions to simulate the antarctic ice sheet during the last glacial cycle the outputs of the simulations are compared on the basis of thetime dependent behavior for the total ice volume and the mean bedrock elevation during the cycle and of the present rate of uplift over antarctica thiscomparison confirms the necessity of accounting for the elastic bending of the lithosphere in order to yield realistic bedrock patterns it furthermoredemonstrates the deficiencies inherent to the diffusion equation in modeling the complex deformation within the mantle nevertheless when characteristicparameters are varied within their range of uncertainty differences within one single method are often of the same order as those between the variousmethods this overview finally tries to point out the main advantages and drawbacks of each of these methods and to determine which one is mostappropriate depending on the specific modeling requirements

potential field modeling of a proterozoic half graben near blackwater lake northwest territories canada and its implications for the fort simpson magnetic anomaly a wedge of proterozoic strata in the blackwater lake area of the northwest territories canada is preserved below the sub cambrian unconformity in a half graben associated with a large normal fault reflection seismic data define the shape of the wedge but neither it nor drilling information is adequate for identifying the strata preserved within the half graben although these data permit either tweed lake assemblage density d 2730 2780 kg m3 or mackenzie shaler assemblage d 2580 kg m3 as the half graben fill gravity and to a lesser extent magnetic modeling show tweed lake assemblage 1270 ma to be the more likely candidate inclusion of any appreciable amount of mackenzie shaler assemblage in the half graben produces too low a gravity response and is therefore rejected the character of the fort simpson magnetic anomaly fsa differs north and south of the liard line n61 north of the line and south of great bear lake the fsa consists of a collection of strong short wavelength featu

characterization of geological boundaries using 1 d wavelet transform on gravity data theory and application to the himalayas we investigate the use of the continuous wavelet transform for gravity inversion the wavelet transform operator has recently been introduced in the domain of potential fields both as a filtering and a source analysis tool here we develop an inverse scheme in the wavelet domain designed to recover the geometric characteristics of density heterogeneities described by simple shaped sources the 1 d analyzing wavelet we use associates the upward continuation operator and linear combinations of derivatives of any order in the gravity case we first demonstrate how to localize causative sources using simple geometric constructions both the upper part of the source and the whole source can be studied when considering low or high altitudes respectively the homogeneity degree of the source is deduced without prior information and allows us to infer its shape introducing complex wavelets we derive analytically the scaling behavior of the wavelet coefficients for the dyke and the step sources the modulus term is used in an inversion procedure to recover the thickness of the source the phase term provides its dip this analysis is performed on gravity data we measured along a profile across the himalayas in nepal good agreement of our results with well documented thrusting structures demonstrates the applicability of the method to real data also deeper less constrained structures are characterized

the intracratonic paleoproterozoic forward orogeny and implications for regional correlations northwest territories canada reflection seismic data from the colville hills and anderson plain document an intracratonic compressional event herein named the forward orogeny which affected strata considered equivalent to the 1663 ma hornby bay group outcropping on coppermine homocline forward orogeny structures were peneplaned and unconformably overlain by strata considered equivalent to the 1267 ma dismal lakes group a comparable tectonic history is recorded in the exposed rocks of coppermine homocline to the east structural orientations indicate a general northwest southeast direction of maximum compression during an early phase and a more west east direction in a later phase regional sequence a of g m young and co workers is subdivided into preorogenic sequence a1 hornby bay and equivalents and postorogenic sequences a2 dismal lakes and equivalents and a3 coppermine river group and equivalents the forward orogeny dated as approximately 1663 ma the age of the syntectonic kaertok formation on coppermine homocline

on the quantitative interpretation of magnetic anomalies by pseudo gravimetric integration poisson s theorem relates linearly the derivative of the gravity potential taken along the total magnetization vector direction and the magnetic potential due to a common isolated source with constant density and magnetization distributions from that theorem two very useful functional transformations for magnetic anomalies were formulated by baranov that is the pseudo gravimetric integration and the reduction to the pole in this paper it is shown that the first transformation is in some sense more useful than the reduction to the pole and further that its utilization presents noticeable advantages as regards the interpretation of magnetic anomalies in fact the pseudo gravimetric integration in contrast to the reduction to the pole also provides a smoothing of the anomaly map and in particular reduces the degree of non linearity existing in the mathematical relationship between the data and the source depth in order to show this last property of the transformation spectral expansion inversions by 21 2d structures were performed on both magnetic and pseudo gravimetric synthetic anomalies and the respective speed and precision were compared the tests clearly indicate that very accurate estimates of the geometric parameters of the known source can be more easily and rapidly calculated by the transformed anomalies furthermore due to its smoothing property the method seems particularly useful when data are noisy tests on real anomalies confirm these results