india madagascar paleo fit based on flexural isostasy of their rifted margins the present study contributes new constraints on and definitions of the reconstructed plate margins of india and madagascar based on flexural isostasy along the western continental margin of india wcmi and the eastern continental margin of madagascar ecmm we have estimated the nature of isostasy and crustal geometry along the two margins and have examined their possible conjugate structure here we utilize elastic thickness te and moho depth data as the primary basis for the correlation of these passive margins we employ the flexure inversion technique that operates in spatial domain in order to estimate the spatial variation of effective elastic thickness gravity inversion and flexure inversion techniques are used to estimate the configuration of the moho crust mantle interface that reveals regional correlations with the elastic thickness variations these results correlate well with the continental and oceanic segments of the indian and african plates the present study has found a linear zone of anomalously low te 1 5 km along the wcmi similar to 1680 km which correlates well with the low te patterns obtained all along the ecmm we suggest that the low te zones along the wcmi and ecmm represent paleo rift inception points of lithosphere thermally and mechanically weakened by the combined effects of the marion hotspot and lithospheric extension due to rifting we have produced an india madagascar paleo fit representing the initial phase of separation based on the te estimates of the rifted conjugate margins which is confirmed by a close fit correlation of moho geometry and bathymetry of the shelf margins the matching of tectonic lineaments lithologies and geochronological belts between india and madagascar provide an additional support for the present plate reconstruction c 2014 international association for gondwana research published by elsevier b v all rights reserved

altimetric gravity anomalies in the norwegian greenland sea preliminary results from the ers 1 35 days repeat mission new fast delivery 35 days repeat ers 1 altimeter data have been used to recover the gravity field in the norwegian greenland sea furthermore the spectral characteristics of the gravity field have been investigated from 18 arcs of 3 days repeat period data the recovered gravity field correlates exclusively with the major geological structures which clearly demonstrates the potential of these new ers 1 altimeter data

intercomparison of recent ocean tide models one of the tremendous achievements of the topex poseidon t p satellite mission is the release of 12 new global ocean tide models during 1994 virtually all of these models are based on the high precision altimetry obtainable from the t p satellite and all of the models are superior to both the cartwright and ray 1990 1991 model as well as to the schwiderski 1980a b model when compared to tide gauges in the present intercomparison only global ocean tide models released during 1994 have been tested as t p continues to operate new ocean tide models will continue to be released and existing ocean models will be updated hence this intercomparison can only present a snapshot of the state of the art within ocean tide modeling however the intercomparison demonstrates the high accuracy and consistency of all these recent ocean tide models from a comparison with a common 104 tide gauge data set compiled by le provost and others unpublished data the general result is that six of the new ocean tide models have rms agreement better than 3 cm the obtainable accuracy with different tide gauge types raises the question about the accuracy of ground truth as ocean tide models become increasingly more accurate the accuracy of the harmonic constants derived from the tide gauge recordings becomes significant generally the rms agreement between models based on 2 years of t p altimetry is significantly better than the agreement between models based on 1 year of t p altimetry for models based on two years of t p altimetry the rms agreement has values around 2 0 1 4 1 0 and 0 7 cm for the m2 s2 k1 and o1 constituents respectively as a preliminary evaluation these values might be taken as a measure of the consistency of ocean tides estimated from the first part of the t p mission which is extremely promising for future ocean tide models derived from t p altimetry using 3 or more years of data this also suggests that further improvement using 3 or more years of data will only be marginal the differences arise when studying the ocean tides on continental shelves surrounding the ocean major differences are seen especially on the patagonian shelf as the continental shelves are critical for tidal dissipation it will be very important to improve tide models on the shelves in future global ocean tide models

sensitivity analysis of the gravity geoid estimation a case study on the azores plateau abstract a numerical investigation into the effects of high resolution heterogeneous data on the estimation of the geoid is presented for the area of the azores plateau gravity data were complemented with high resolution digital terrain models mass density models from geophysical information and the most recent geopotential model from the champ mission ggm02 to derive a high precision gravity model gravity data were reduced from the residual terrain model effects and the ggm02c model and a grid with 1 5 spatial resolution was generated by least squares collocation the gravimetric geoid model was computed by the direct evaluation of stokes integral with a spherical cap radius of 0 8 with gravity data reduced by helmert s second condensation method the geoid model was evaluated over sea by comparison with 6 years of topex poseidon altimeter data and an absolute agreement of 14 cm rms was achieved after removing the bias over land the geoid was compared with a total of 223 gps levelling points corresponding to five different vertical datums locally adjusted solutions were determined for each island with a four parameter model and a maximum rms of 12 cm on pico and a minimum of 2 1 cm on faial were determined as a result of persistent volcanic and tectonic activity on most of the azores islands this geoid residual standard deviation must not be viewed as purely geoid error but containing in addition levelling and gps position errors and vertical displacement the effect on geoid accuracy of the digital terrain model resolution of the spatial density of gravity data and of the mass density was evaluated and two important conclusions were derived first the digital terrain model resolution has a clear effect on the geoid accuracy with a maximum rms of 3 4 cm on s miguel second the mass density model does not affect the accuracy of the geoid this second result indicates that the effect of variable density models on geoid determination may apply only to extensive areas of high terrain and not to smaller topographic units such as single volcanoes the high precision gravity model and gravimetric geoid for azores azgeod07 generated in this study will allow the conversion of old orthometric heights to ellipsoidal heights at precisions useful for the monitoring of vertical deformation the geoid will also have application to investigate ocean circulation modulation and dynamic processes of earth s mantle

structural and tectonic interpretation of geophysical data along the eastern continental margin of india with special reference to the deep water petroliferous basins abstract the study area encompasses the eastern continental margin of india ecmi and the adjoining deep water areas of bay of bengal the region has evolved through multiple phases of tectonic activity and fed by abundant supply of sediments brought by prominent river systems of the indian shield detailed analysis of total field magnetic and satellite derived gravity data along with multi channel seismic reflection sections is carried out to decipher major tectonic features basement structure and the results have been interpreted in terms of basin configuration and play types for different deep water basins along the ecmi interpretation of various image enhanced gravity and magnetic anomaly maps suggest that in general the ene wsw trending faults dominate the structural configuration at the margin these maps also exhibit a clear density transition from the region of attenuated continental crust proto oceanic crust to oceanic crust based on which the continent ocean boundary cob has been demarcated along the margin basement depths estimated from magnetic data indicate that the values range from 1 to 12 km below sea level and deepen towards the bengal fan in the north and reveal horst graben features related to rifting a comparison of basement depths derived from seismic data indicates that in general the basement trends and depths are comparable in cauvery and krishna godavari basins whereas in the mahanadi basin basement structure over the 85 e ridge is clearly revealed in seismic data further eight multichannel seismic sections across different basins of the margin presented here reveal fault pattern rift geometries and depositional trends related to canyon fills and channel levee systems and provide a basic framework for future petroleum in this under explored frontier

accuracy assessment of recent ocean tide models over 20 global ocean tide models have been developed since 1994 primarily as a consequence of analysis of the precise altimetric measurements from topex poseidon and as a result of parallel developments in numerical tidal modeling and data assimilation this paper provides an accuracy assessment of 10 such tide models and discusses their benefits in many fields including geodesy oceanography and geophysics a variety of tests indicate that all these tide models agree within 2 3 cm in the deep ocean and they represent a significant improvement over the classical schwiderski 1980 model by approximately 5 cm rms as a result two tide models were selected for the reprocessing of topex poseidon geophysical data records in late 1995 current ocean tide models allow an improved observation of deep ocean surface dynamic topography using satellite altimetry other significant contributions include theft applications in an improved orbit computation for topex poseidon and other geodetic satellites to yield accurate predictions of earth rotation excitations and improved estimates of ocean loading corrections for geodetic observatories and to allow better separation of astronomical tides from phenomena with meteorological and geophysical origins the largest differences between these tide models occur in shallow waters indicating that the current models are still problematic in these areas future improvement of global tide models is anticipated with additional high quality altimeter data and with advances in numerical techniques to assimilate data into high resolution hydrodynamic models

stacked global satellite gravity profiles gravity field recovery from satellite altimetry provides global marine coverage but lacks the accuracy and resolution needed for many exploration geophysics studies the repeating ground tracks of the ers 1 2 geosat and topex poseidon altimeters offer the possibility of improving the accuracy and resolution of gravity anomalies along widely spaced 40 km spacing tracks however complete ocean coverage is usually needed to convert the sea surface height or along track slope measurements into gravity anomalies here we develop and test a method for constructing stacked gravity profiles by using a published global gravity grid sandwell and smith 1997 v7 2 as a reference model for the slope to gravity anomaly conversion the method is applied to stacks averages of geosat erm up to 62 cycles ers 1 2 up to 43 cycles and topex up to 142 cycles satellite altimeter profiles we assess the accuracies of the ers 1 2 profiles through a comparison with a gravity model of the northern gulf of mexi

new global seamount census from altimetry derived gravity data summary recent revisions to the satellite derived vertical gravity gradient vgg data reveal more detail of the ocean bottom and have allowed us to develop a non linear inversion method to detect seamounts in vgg data we approximate vgg anomalies over seamounts as sums of individual partially overlapping elliptical polynomial functions which allows us to form a non linear inverse problem by fitting the polynomial model to the observations model parameters for a potential seamount include geographical location peak vgg amplitude major and minor axes of the elliptical base and the azimuth of the major axis the non linear inversion is very sensitive to the initial values for the location and amplitude hence they are constrained by the centre and amplitude of the uppermost contours obtained with a 1 eotvos contour interval with these initial conditions from contouring we execute a step wise and fully automated inversion and obtain optimal model estimates for potential seamounts these are statistically evaluated for significance using the akaike information criterion and f tests a logarithmic barrier technique is applied to ensure positivity of all seamount amplitudes after automatic and manual inspections of the model parameters we estimate actual heights and basal ellipses of the inspected potential seamounts directly from the predicted bathymetry grid in this study we find globally 24 643 potential seamounts h 0 1 km that are located away from continental margins 8458 potential seamounts are taller than 1 km although our global estimate is significantly lower than predictions from previous studies a first order reconciliation of the size frequency statistics obtained from those studies reveals that the previous counts are systematically overestimated because of the ambiguity of gravity signals due to small seamounts of h 1 km and the overlap with abyssal hills we estimate the global seamount census to lie in the 40 000 55 000 range the seamount data from this study are accessible from http www soest hawaii edu pt smts

new insights on intraplate volcanism in french polynesia from wavelet analysis of grace champ and sea surface data in this paper we discuss the origin of superswell volcanism on the basis of representation and analysis of recent gravity and magnetic satellite data with wavelets in spherical geometry we computed a refined gravity field in the south central pacific based on the grace satellite ggm02s global gravity field and the kms02 altimetric grid and a magnetic anomaly field based on champ data the magnetic anomalies are marked by the magnetic lineation of the seafloor spreading and by a strong anomaly in the tuamotu region which we interpret as evidence for crustal thickening we interpret our gravity field through a continuous wavelet analysis that allows to get a first idea of the internal density distribution we also compute the continuous wavelet analysis of the bathymetric contribution to discriminate between deep and superficial sources according to the gravity signature of the different chains as revealed by our analysis various processes are at the origin of the volcanism in french polynesia as evidence we show a large scale anomaly over the society islands that we interpret as the gravity signature of a deeply anchored mantle plume the gravity signature of the cook austral chain indicates a complex origin which may involve deep processes finally we discuss the particular location of the marquesas chain as suggesting that the origin of the volcanism may interfere with secondary convection rolls or may be controlled by lithospheric weakness due to the regional stress field or else related to the presence of the nearby tuamotu plateau

an effective elastic thickness map of australia from wavelet transforms of gravity and topography using forsyth s method 1 we have developed a wavelet version of forsyth s coherence method for estimating the effective elastic thickness te of the lithosphere from gravity and topography we have previously shown that the fan wavelet is particularly well suited to making localised coherence estimates and here we progress the method by showing how the coherence can be modelled by using the wavelet transforms of gravity and topography to infer the initial loads that flex the plate the effectiveness of the method is demonstrated on synthetic data from a model having a rectangular area of large te embedded in a uniform low te surrounding and a load ratio that increases with wave number the results for the australia region show a core of high te under north and central australia with much lower values to the east and also unexpectedly under the western parts of the yilgarn and pilbara cratons

antarctic marine gravity field from high density satellite altimetry summary closely spaced satellite altimeter profiles 5 km collected during the geosat geodetic mission geosat gm and those planned for the extended ers 1 mission are easily converted to grids of vertical gravity gradient and gravity anomaly as profile spacing decreases it becomes increasingly difficult to perform a crossover adjustment on the original geoid height profiles without introducing large cross track gradients if one is only interested in the horizontal and vertical derivatives of the gravitational potential however adjustment of the profile is unnecessary the long wavelength radial orbit error is suppressed well below the noise level of the altimeter by simply taking the along track derivative of each profile ascending and descending slope profiles are then interpolated onto separate uniform grids these two grids are summed and differenced to form comparable grids of east and north vertical deflection using laplace s equation the vertical gravity gradient is calculated directly from the vertical deflection grids fourier analysis is required to construct gravity anomalies from the two vertical deflection grids these techniques are applied to high density 2 km profile spacing geosat gm profiles in antarctic waters 60 s to 72 s gridding and interpolation are performed using the method of projection onto convex sets where the smoothness criteria corresponds to upward continuation through 4 km of ocean the resultant gravity grids have resolution and accuracy comparable to shipboard gravity profiles after adjustment of a dc shift in the shipboard gravity profiles 5 mgal the rms difference between the ship and satellite gravity is 5 5 mgal many interesting and previously uncharted features are apparent in these new gravity maps including a propagating rift wake and a large leaky transform along the pacific antarctic rise

wavelet approach to improvement of gravity field geoid modeling for japan 1 an improved gravimetric geoid model for japan jgeoid2004 on a grid of 1 1 5 minutes was constructed by the one dimensional fast fourier transform method with egm96 as a foundation model the model geoid heights in the nontidal system refer to the grs80 ellipsoid aligned in the itrf94 epoch 1997 0 newly acquired terrestrial gravity data supplemented the data gaps of the previous model jgeoid2000 a semidiscrete wavelet analysis reconstruction with two dimensional 2 d halo wavelets were developed and successfully applied to a combination of marine gravity data and an altimetric gravity model kms02 the method is used to localize 2 d signal components in the spatio frequency domain and to screen them as a locally adjustable band pass filter compared with 816 gps leveling benchmarks jgeoid2004 showed significant improvement over jgeoid2000 the standard deviation of the differences from the best fit planes is reduced from 15 3 cm to 9 2 cm substantial localized errors which are due to systematic errors of the marine gravity data as well as to data gaps on land and in the inland sea were effectively removed

the joint gravity model 3 an improved earth geopotential model complete to spherical harmonic degree and order 70 has been determined by combining the joint gravity model 1 jgm 1 geopotential coefficients and their associated error covariance with new information from slr doris and gps tracking of topex poseidon laser tracking of lageos 1 lageos 2 and stella and additional doris tracking of spot 2 the resulting field jgm 3 which has been adopted for the topex poseidon altimeter data rerelease yields improved orbit accuracies as demonstrated by better fits to withheld tracking data and substantially reduced geographically correlated orbit error methods for analyzing the performance of the gravity field using high precision tracking station positioning were applied geodetic results including station coordinates and earth orientation parameters are significantly improved with the jgm 3 model sea surface topography solutions from topex poseidon altimetry indicate that the ocean geoid has been improved subset solutions performed by withholding either the gps data or the slr doris data were computed to demonstrate the effect of these particular data sets on the gravity model used for topex poseidon orbit determination

east greenland ridge in the north atlantic ocean an integrated geophysical study of a continental sliver in a boundary transform fault setting 1 the combined greenland senja fracture zones gsfz represent a first order plate tectonic feature in the north atlantic ocean the gsfz defines an abrupt change in the character of magnetic anomalies with well defined seafloor spreading anomalies in the greenland and norwegian basins to the south but ambiguous and weak magnetic anomalies in the boreas basin to the north substantial uncertainty exists concerning the plate tectonic evolution of the latter area including the role of the east greenland ridge which is situated along the greenland fracture zone in 2002 a combined ocean bottom seismometer and multichannel seismic mcs survey acquired two intersecting wide angle reflection and coincident mcs profiles across and along the east greenland ridge we present the results of integrated reflection seismic interpretation first arrival tomography 2d kinematic raytracing full wave amplitude modeling and gravity modeling of the intersecting profiles the results show that 1 the greenland basin is characterized by a normal oceanic crustal velocity structure 2 the velocity structure of the east greenland ridge is of overall continental type and 3 a major faulted basin province above highly extended continental crust exists to the ne of the ridge the results further suggest that a zone of extremely thin and faulted continental crust above partially serpentinized mantle peridotite defines the nw edge of the east greenland ridge and the transition to the ne greenland margin

in situ elemental and isotopic analysis of fluorapatite from the taocun magnetite apatite deposit eastern china constraints on fluid metasomatism metasomatic alteration of fluorapatite has been reported in several iron oxide apatite ioa deposits but its effect on elemental and isotopic variations has not been well understood in this study we present integrated elemental u pb sr and o isotopic microanalytical data on fresh and altered domains in fluorapatite from the taocun ioa deposit eastern china to evaluate the timing and nature of the metasomatism and its effects on the ore forming event orebodies of the taocun deposit are spatially associated with a subvolcanic intermediate intrusion which displays zonal alteration patterns with albite in the center and increasing actinolite chlorite epidote and carbonate toward the margin both disseminated and vein type ores are present in the taocun deposit and fluorapatite commonly occurs with magnetite and actinolite in most ores fluorapatite grains from the both types of ores have been variably metasomatized through a coupled dissolution reprecipitation mechanism many trace elements including na cl s si mg sr u th and rees y were variably leached from the fluorapatite grains during this process and the sr and o isotopic signatures of the grains were also modified the altered fluorapatite grains domains have in situ 87 sr 86 sr ratios 0 70829 0 70971 slightly higher than those of the fresh fluorapatite 0 70777 0 70868 and 18 o values 3 0 to 3 4 variably lower than the primary domains 5 3 to 7 5 the sr and o isotopes of the primary fluorapatite are consistent with or slightly higher than those of the ore hosting intrusion implying that the early stage ore forming fluids were magmatic in origin but underwent weak interaction with the country rocks u pb dating of the fresh and altered domains of the fluorapatite yielded indistinguishable ages of 131 ma which are the same as the age of the ore hosting intrusion in combination with fluid inclusion data we propose that the metasomatism of fluorapatite was induced by hydrothermal fluids at a late stage of the ore forming event the shifts to higher 87 sr 86 sr ratios and lower 18 o values in the altered fluorapatite indicate that the alteration was induced by fluids with more radioactive sr and lighter o isotope signatures the metasomatic fluids were likely dominated by meteoric waters that were mixed with the earlier magmatic fluids and interacted with sedimentary rocks our study highlights that elemental and isotopic compositions of fluorapatite can be significantly modified by hydrothermal fluids during ore forming events thus instead of traditional bulk rock analysis in situ microanalysis is important to provide accurate constraints on the magmatic and or hydrothermal evolution of complex ore forming systems

crustal structure and transform margin development south of svalbard based on ocean bottom seismometer data abstract the barents sea is located in the northwestern corner of the eurasian continent where the crustal terrain was assembled in the caledonian orogeny during late ordovician and silurian times the western barents sea margin developed primarily as a transform margin during the early tertiary in the northwestern part south of svalbard multichannel reflection seismic lines have poor resolution below the permian sequence and the early post orogenic development is not well known here in 1998 an ocean bottom seismometer obs survey was collected southwest to southeast of the svalbard archipelago one profile was shot across the continental transform margin south of svalbard which is presented here p wave modeling of the obs profile indicates a caledonian suture in the continental basement south of svalbard also proposed previously based on a deep seismic reflection line coincident with the obs profile the suture zone is associated with a small crustal root and westward dipping mantle reflectivity and it marks a boundary between two different crystalline basement terrains the western terrain has low 6 2 6 45 km s 1 p wave velocities while the eastern has higher 6 3 6 9 km s 1 velocities gravity modeling agrees with this as an increased density is needed in the eastern block the s wave data predict a quartz rich lithology compatible with felsic gneiss to granite within and west of the suture zone and an intermediate lithological composition to the east a geological model assuming westward dipping caledonian subduction and collision can explain the missing lower crust in the western block by subduction erosion of the lower crust as well as the observed structuring due to the transform margin setting the tectonic thinning of the continental block during opening of the norwegian greenland sea is restricted to the outer 35 km of the continental block and the continent ocean boundary cob can be located to within 5 km in our data distinct from the outer high commonly observed on transform margins the upper part of the continental crust at the margin is dominated by two large rotated down faulted blocks with throws of 2 3 km on each fault apparently formed during the transform margin development analysis of the gravity field shows that these faults probably merge to one single fault to the south of our profile and that the downfaulting dominates the whole margin segment from spitsbergen to bjornoya south of bjornoya the faulting leaves the continental margin to terminate as a graben 75 km south of the island adjacent to the continental margin there is no clear oceanic layer 2 seismic signature however the top basement velocity of 6 55 km s 1 is significantly lower than the high 7 km s 1 velocity reported earlier from expanding spread profiles esps and we interpret the velocity structure of the oceanic crust to be a result of a development induced by the 7 8 km thick sedimentary overburden

elastic thickness structure of the andaman subduction zone implications for convergence of the ninetyeast ridge abstract we use the bouguer coherence morlet isostatic response function technique to compute the spatial variation of effective elastic thickness te of the andaman subduction zone the recovered te map resolves regional scale features that correlate well with known surface structures of the subducting indian plate and the overriding burma plate the major structure on the india plate the ninetyeast ridge ner exhibits a weak mechanical strength which is consistent with the expected signature of an oceanic ridge of hotspot origin however a markedly low strength 0

gsfc00 mean sea surface gravity anomaly and vertical gravity gradient from satellite altimeter data a mean sea surface gsfc00 and its derivatives the altimetry gravity anomaly and vertical gravity gradient fields were computed using sea surface heights of topex ers and geosat satellite altimeter missions provided by the nasa ocean altimeter pathfinder project koblinsky et al 1998 a new estimation method distinct from the gsfc98 mean sea surface computation wang 2000a was explored and used to reduce ocean variability in the mean sea surface heights the gravity anomaly and vertical gravity gradient fields were then computed from the mean sea surface height implied geoid undulations validation of the gsfc00 mean sea surface and gravity anomaly was also performed

simultaneous estimation of the gravity field and sea surface topography from satellite altimeter data by least squares collocation summary the signal content of seasat altimeter data is evaluated with respect to magnitude and wavelength based on this information covariance functions associated with the different signals errors have been determined the covariance function associated with the sea surface heights contains covariances associated with the geoid the stationary sea surface topography and the time varying sea surface topography these three components have been estimated from seasat altimeter data in the faeroe islands region using least squares collocation in the solution error covariances associated with errors in the orbits corrections for instrumental atmospherical and tidal effects and sea state related bias are taken into account the accuracies of the solutions are evaluated by computing error estimates and error correlations a special effort has been made to evaluate the correlations between the estimated geoid and the other signals errors the results show that geoid undulations may be estimated with an accuracy of 0 13 0 16m approximately 50 per cent of the error variance has a long wavelength signature which is mainly correlated with errors in the estimation of the permanent sea surface topography the short wavelength part of the error is mainly correlated with errors due to liquid water in rain and clouds free air gravity anomalies may be estimated with an accuracy of 8 8 11 7 times 10 5 ms 2 this error has a short wavelength signature which is mainly correlated with errors due to liquid water in rain and clouds however a comparison with gravity observations resulted in an agreement of 7 8 times 10 5 ms 2 both the permanent and the time varying sea surface topography may be estimated with accuracies of about 0 21 m

gravity anomalies derived from seasat geosat ers 1 and topex poseidon altimetry and ship gravity a case study over the reykjanes ridge summary we have employed least squares collocation to derive a gravity field over the reykjanes ridge using seasat geosat erm ers 1 and topex poseidon altimeter data combined with ship gravity to avoid a crossover adjustment to correct for orbital errors we used mean geoid gradients which were obtained by averaging gradients over 60 10 and 36 repeat cycles for geosat erm ers 1 and topex poseidon respectively the average standard deviations for the geosat erm ers 1 and topex poseidon mean gradients are 1 12 3 25 and 2 01 rad respectively the standard deviations of the ship gravity which were assigned based on weightings derived from an analysis of crossing differences range from 6 72 to 20 17 mgal the necessary covariances for the least squares collocation computations were derived using the law of covariance propagation before merging with the altimeter data the ship gravity for each leg was adjusted by removing a quadratic polynomial in time in order to match a satellite only gravity field in a least squares sense the result of the adjustment suggests that most of the ship gravity data collected in the 1960s and the 1970s have average offsets of about 14 mgal which is close to the offset of the potsdam datum the rms difference between the satellite only gravity derived using least squares collocation and the adjusted ship gravity is 7 10 mgal smaller than the rms difference of 12 47 mgal between the satellite only gravity derived by a fourier transform method and the adjusted ship gravity the rms difference between the combined gravity field derived from both altimetry and ship gravity and the adjusted ship gravity is 2 65 mgal suggesting that the former has successfully absorbed the high frequency component of the gravity signal provided by the latter the combined gravity field thus features a regionally uniform medium resolution from altimetry and a locally high resolution from ship gravity the average accuracy estimate given by least squares collocation for the combined gravity is 5 76 mgal the combined gravity field reveals detailed tectonic structures over the reykjanes ridge related to the interaction of the iceland hot spot and sea floor spreading at the ridge

3d density model of the central andes abstract we developed a 3d density model of the continental crust the subducted plate and the upper mantle of the central andes between 20 29 s and 74 61 w through the forward modelling of bouguer anomaly the goal of this contribution is to gain insight on the lithospheric structure integrating the available information geophysical geologic petrologic and geochemical in a single model the geometry of our model is defined and constrained by hypocentre location reflection and refraction on and offshore seismic lines travel time and attenuation tomography receiver function analysis magnetotelluric studies thermal models and balanced structural cross sections the densities allocated to the different bodies are calculated considering petrologic and geochemical data and pressure and temperature conditions the model consists of 31 parallel e w vertical planes where the continental crust comprises distinct bodies which represent the different morphotectonic units of the central andes we include a partial melting zone at midcrustal depths under the altiplano puna low velocity zone and consider the presence of a rheologically strong block beneath the salar de atacama basin according to recent seismic studies contour maps of the depth of the continental moho the thickness of the lower crust and the depth to the bottom of the lithosphere below south america are produced the possible percentage of partial melt in the central andes low velocity zone is estimated the residual anomaly is calculated by subtracting from the bouguer anomaly the gravimetric effect of the modelled subducted slab and of the modelled moho isostatic anomalies are calculated from regional and local isostatic mohos calculated with and without internal loads derived from our gravity model which are then compared to the modelled continental moho this study contributes to a more detailed knowledge of the lithospheric structure of this region of the andes and provides an integrated 3d density model which may be used by the geoscientific community as a tool that can help to understand and interpret the geodynamic features and processes acting along the central andes

determining the optimal bouguer density for a gravity data set implications for the isostatic setting of the mediterranean sea summary we have used free air gravity satellite data from geosat and ers 1 missions to compile a bouguer gravity map of the mediterranean sea the complete bouguer correction has been applied by using the method of parker that acts in the fourier domain and permits the exact evaluation of the gravity contribution from an highly sampled topographic model of the land the density used for the bouguer reduction has been obtained from the gravity data set itself by using two different optimization methods that have given the same optimal result of 2400 kg m 3 we have studied the radial power spectrum of the data choosing the optimal bouguer density from its slope as the one which minimizes the fractal dimension of the resulting gravity map the second approach consists of studying the correlation between topography and bouguer anomaly by spatial cross plots for a significant subset of the data both these approaches are aimed at reducing the short wavelength effects of topography in the gravity map but in the past they have been traditionally used alternatively since they gave different optimization values especially the second method that seems to ignore large wavelength isostatic effects actually we have revisited both the methodologies proposing slight modifications to make their efforts compatible their coincident results confirm their validity of application and give reliability to the recovered value of the bouguer optimal density moreover modifying the second approach allows us to compile a sort of normalized correlation map which we propose in this paper defining the 2 d isostatic setting of the investigated region without introducing any further lithospheric model the final result is a revised bouguer map compiled using a grid with a resolution of 2 min that is useful for large scale geological studies and gives important information about the compensation mechanism of the mediterranean sea in a direct way we have found that the overall region seems to be in a complete isostatic equilibrium apart from the young basins of tyrrhenian sea and aegean sea confirming previous similar results

three dimensional lithospheric structure of the western continental margin of india constrained from gravity modelling implication for tectonic evolution this paper describes a 3 d lithospheric density model of the western continental margin of india wcmi based on forward modelling of gravity data derived from satellite altimetry over the ocean and surface measurements on the indian peninsula the model covers the north eastern arabian sea and the western part of the indian peninsula and incorporates constraints from a wide variety of geophysical and geological information salient features of the density model include 1 the moho depth varying from 13 km below the oceanic crust to 46 km below the continental interior 2 the lithosphere asthenosphere boundary lab located at depths between 70 km in the southwestern corner under oceanic crust and about 165 km below the continental region 3 thickening of the crust under the chagos laccadive and laxmi ridges and 4 a revised definition of the continent ocean boundary the 3 d density structure of the region enables us to propose an evolutionary model of the wcmi that revisits earlier views of passive rifting the first stage of continental scale rifting of madagascar from india at about 90 ma is marked by relatively small amounts of magmatism a second episode of rifting and large scale magmatism was possibly initiated around 70 ma with the opening of the gop rift subsequently at around 68 ma the drifting away of the seychelles and formation of the laxmi ridge was a consequence of the down faulting of the northern margin during this second episode of rifting the northern part of the wcmi witnessed massive volcanism attributed to interaction with the reunion hotspot at around 65 ma subsequent stretching of the transitional crust between about 65 and 62 ma formed the laxmi basin the southward extension of the failed gop rift as the interaction between plume and lithosphere continued the chagos laccadive ridge was emplaced on the edge of the nascent oceanic crust rifted continental margin in the south as the indian plate was moving northwards

fylla bank structure and evolution of a normal to shear rifted margin in the northern labrador sea summary cenozoic seafloor spreading between greenland and north america is generally considered a major right stepping ridge transform ridge system between nw se trending spreading ridge segments in the labrador sea and baffin bay the ridges were linked by n s nne ssw trending transform motions in the davis strait in particular expressed by the 1000 km long ungava fault zone fylla bank part of the southern west greenland continental margin is located in the northernmost labrador sea at the transition between the normal and shear rifting regimes of the labrador sea and davis strait as such the bank may be compared with the demerara plateau part of the french guinea northeast brazil continental margin seismic reflection interpretations presented in this study show that fylla bank is situated above an extensive basin complex herein referred to as fylla structural complex which contains an up to 5 km thick cretaceous cenozoic sedimentary succession above an inferred pre cretaceous basement seismic mapping of basement structures show that the complex is dominated by nnw nw striking rift basins in its southern part and nne striking rift basins in its northern part the rift basins are interpreted to be the result of an initial late early cretaceous rift phase which mainly resulted in the formation of the nnw nw striking structures and a subsequent early campanian rift phase mainly resulting in the formation of large nne striking rotated fault blocks resumed rifting in the early cenozoic deepened the nne striking rift basins the nne oriented structures have previously been interpreted to initiate during the latest cretaceous however this study suggests that they initiated transfer faults already during the late early cretaceous rift phase and possibly correlate with along strike discontinuities in oceanic crust in the labrador sea to define margin segmentation in southern west greenland including the borders of fylla bank a structural kinematic model presented here thus suggests that the cretaceous cenozoic poly phase rifting to some extent was controlled by pre existing crustal fabric combined with an interpreted interplay between normal stresses in the labrador sea and oblique shear stresses in the davis strait this resulted in a very complex structural tectonic evolution and the formation of several distinct structural styles the seismic interpretations are supported by maps of the moho topography and crustal thickness which were compiled from results of pseudo 3 d gravity modelling the maps show minimum crustal thicknesses 11 km and maximum moho uplifts in areas where the nnw nw and nne striking structures interact moreover a strong correlation is found between moho topography crustal attenuation rift enforced thermal uplift and erosion and post rift subsidence in the area this is interpreted to be a result of thermally controlled basin dynamics

dnsc08 mean sea surface and mean dynamic topography models 1 the danish national space center data set dnsc08 mean sea surface mss is a new enhanced mapping of the mean sea surface height of the worlds oceans derived from a combination of 12 years of satellite altimetry from a total of eight different satellites covering the period 1993 2004 it is the first global mss without a polar gap including all of the arctic ocean by including laser altimetry from the icesat mission the mean dynamic topography mdt is the quantity that bridges the geoid and the mean sea surface constraining large scale ocean circulation here we present a new high resolution 1 min global mdt called dnsc08 mdt derived from the slightly smoothed difference between the dnsc08 mss and the egm2008 geoid the derivation and quality control of the new dnsc08 mss and dnsc08 mdt is presented in this paper along with suggestions for time period standardization of the mss and mdt models this way a consistent modeling of the interannual sea level variability is carried out before different mss and mdt models are compared altimetric derived physical mss can be converted into an inverse barometer corrected mss by correcting the altimeter range for the inverse barometer effect of the atmosphere on the sea surface height it is demonstrated that it is important to choose the right version of the mss when comparing with hydrodynamic models and gps measured tide gauges

global marine gravity field from the ers 1 and geosat geodetic mission altimetry satellite altimetry from the geosat and the ers i geodetic missions provide altimeter data with very dense spatial coverage therefore the gravity field may be recovered in great detail as neighboring ground tracks are very closely distributed cross track variations in the sea surface heights are extremely sensitive to sea surface variability to avoid errors in the gravity field caused by such effects sea surface variability needs to be carefully eliminated from the observations initially a careful removal of gross errors and outliers was performed and the tracks were fitted individually to a geoid model and crossover adjusted using bias and tilt subsequently sea surface heights were gridded using local collocation in which residual ocean variability was considered the conversion of the heights into gravity anomalies was carried out using the fast fourier transform fft in this process filtering was done in the spectral domain to avoid the so called orange skin characteristics comparison with marine gravity was finally carried out in three different regions of the earth to evaluate the accuracy of the global marine gravity field from ers 1 and geosat

drunkard s wash unit coalbed methane production from ferron coals in east central utah the drunkard s wash project produces dry coalbed methane gas from coals within the ferron sandstone member of the mancos shale the project covers 120 000 acres on the western flank of the san rafael uplift in east central utah gas was first produced into the sales line in january 1993 the field is being developed on 160 acre spacing with 73 wells currently producing 32 2 mmcfd for an average of 437 mcfd well thirty three of those wells have been producing for 32 months and now average 637 mcfd well most of the wells show a classic coalbed methane negative decline curve with increasing gas rates as the reservoir pressure declines due to production of water daily water production is 14 500 bpd for an average of 199 bwpd well total coal thickness ranges from 7 ft to 48 ft with an average of 24 ft the coals occur in 3 to 6 seams at depths of 1350 to 2450 ft the coal rank is high volatile a b bituminous we can not yet see a correlation between total coal thickness and current production all wells are cased and hydraulically stimulated and most require pumping units to handle the large volumes of water however 22 wells domore not require pumps and flow unassisted to the surface the structure consists of monoclinal westward dip a thin tonstein layer in the bottom coal seam serves as an excellent datum for mapping enhanced production is encountered along a southwest plunging nose that probably formed additional fracture permeability within the coals northeast trending reverse faults with small displacement appear to compartmentalize the reservoir the ferron coals were deposited in a river dominated deltaic system that prograded to the east and southeast during turonian coniacian upper cretaceous time the ferron sandstone member represents an eastward thinning elastic wedge that was deposited during regression of the western interior cretaceous seaway less

effective elastic thickness along the conjugate passive margins of india madagascar and antarctica a re evaluation using the hermite multitaper bouguer coherence application abstract gondwana correlation studies had rationally positioned the western continental margin of india wcmi against the eastern continental margin of madagascar ecmm and the eastern continental margin of india ecmi against the eastern antarctica continental margin eacm this contribution computes the effective elastic thickness te of the lithospheres of these once conjugated continental margins using the multitaper bouguer coherence method the results reveal significantly low strength values te 2 km in the central segment of the wcmi that correlate with consistently low te values 2 3 km obtained throughout the entire marginal length of the ecmm this result is consistent with the previous te estimates of these margins and confirms the idea that the low te segments in the central part of the wcmi and along the ecmm represents paleo rift inception points of the lithospheric margins that was thermally and mechanically weakened by the combined action of the marion hotspot and lithospheric extension during the rifting the uniformly low te value 2 km along the eacm indicates a mechanically weak lithospheric margin probably due to considerable stretching of the lithosphere considering the fact that this margin remained almost stationary throughout its rift history in contrast the ecmi has comparatively high te variations 5 11 km that lack any correlation with the regional tectonic setting using gravity forward and inversion applications we find a leading order of influence of sediment load on the flexural properties of this marginal lithosphere the study concludes that the thick pile of the bengal fan sediments in the ecmi masks and has erased the signal of the original load induced topography and its gravity effect has biased the long wavelength part of the observed gravity signal the hence uncorrelated flat topography and deep lithospheric flexure together contribute a bias in the flexure modeling which likely accounts a relatively high te estimate

the geoid edin2000 and mean sea surface topography around the british isles summary this paper describes a new rationale for computing a gravimetric geoid and reports that the resulting geoid model edin2000 is now good enough to resolve previously contradictory estimates for mean sea surface topography msst around great britain for at least 30 yr it has been known that msst derived from tide gauges levelling and oceanography were mutually inconsistent and differed by an order of magnitude when combined with an altimetric mean sea surface edin2000 is also able to map realistic msst over the northwest european shelf and identify and quantify mean currents flowing in the deep ocean parallel to the shelf edge when compared with 11 gps referenced tide gauges on the british mainland our estimate of msst has a standard deviation of only 0 03 m and its variation with latitude is not significantly different from zero for these sites long distance levelling errors are larger than geoid errors we identify a systematic jump by 0 24 0 05 m in the levelled transfer of ordnance datum newlyn affecting all sites in great britain to the north of latitude 53 n even after this correction the variability of levelling remains larger than that of the geoid and gps implying a more complex structure to the levelling error than a simple step away from coasts we find that the best way to validate marine gravity data is their ability to predict msst with low local variability when combined with altimetric mean sea level there is a large reduction in msst variability when marine gravity data are subjected to an anti aliased adjustment of the mismatch where ship tracks cross we also report two msst model comparisons from a shelf seas and a deep ocean model both of high resolution there is quantitative and qualitative agreement between our geoid derived msst and the model predictions indicating significant improvements compared with earlier geoid models we also show that with the improved accuracy of geoid based msst it will become necessary to validate models and observations at matching epochs