the time averaged geomagnetic field global and regional biases for 0 5 ma summary palaeodirectional data from lava flows and marine sediments provide information about the long term structure and variability in the geomagnetic field we present a detailed analysis of the internal consistency and reliability of global compilations of sediment and lava flow data time averaged field models are constructed for normal and reverse polarity periods for the past 5 ma using the combined data sets nonzonal models are required to satisfy the lava flow data but not those from sediments alone this is in part because the sediment data are much noisier than those from lavas but is also a consequence of the site distributions and the way that inclination data sample the geomagnetic field generated in the earth s core different average field configurations for normal and reverse polarity periods are consistent with the palaeomagnetic directions however the differences are insignificant relative to the uncertainty in the average field models thus previous inferences of non antipodal normal and reverse polarity field geometries will need to be re examined using recently collected high quality palaeomagnetic data our new models indicate that current global sediment and lava flow data sets combined do not permit the unambiguous detection of northern hemisphere flux lobes in the 0 5 ma time averaged field highlighting the need for the collection of additional high latitude palaeomagnetic data anomalous time averaged field structure is seen in the pacific hemisphere centred just south of hawaii the location of the anomaly coincides with heterogeneities in the lower mantle inferred from seismological data the seismic observations can be partly explained by lateral temperature variations however they also suggest the presence of lateral compositional variations and or the presence of partial melt the role of such heterogeneities in influencing the geomagnetic field observed at the earth s surface remains an unresolved issue requiring higher resolution time averaged geomagnetic field models along with the integration of future results from seismology mineral physics and numerical simulations

spatiotemporal gravity variations to look deep into the southern flank of etna volcano 1 a 14 year long microgravity data set october 1994 to september 2007 collected along a 24 km east west trending profile of 19 stations was analyzed to detect underground mass redistributions related to the volcanic activity involving the southern flank of mt etna italy a multiresolution wavelet analysis was applied to separate the volcano related anomalies from the unwanted components the residual image having both spatial extension and temporal duration evidenced two complete gravity increase decrease cycles mainly affecting the central and eastern stations of the profile the first gravity increase early 1995 to the end of 1996 and decrease end of 1996 to late in 1998 cycle reached a maximum amplitude of approximately 90 gal the second gravity increase mid 1999 to mid 2000 and decrease mid 2000 to early 2004 cycle attained an amplitude of about 80 gal after about 5 years of a persistent negative gravity anomaly a new semicycle started at the end of 2006 and continued during the last survey carried out in september 2007 the density changes modeled over time since 1994 using a quadratic programming algorithm are mainly located at a depth of 2 4 km bsl in a region recognized to be a preferential pathway of magma rising and an intermediate zone of magma storage withdrawal the computed positive mass variations of about 105 109 kg were interpreted as magma accumulation while negative mass changes of about 120 109 kg were associated with either magma drainage or opening of new voids by tectonic stresses within a source volume where tensional earthquakes occurred

the time averaged paleomagnetic field we review indications of persistent deviations from the geocentric axial dipole model of the time averaged geomagnetic field and present a zonal harmonic model derived from 185 deep sea sediment piston cores taken from low to middle latitudes to approximately 45 analysis of the paleomagnetic inclination recorded in these cores for the brunhes normal polarity 0 73 ma and matuyama reverse polarity 0 73 2 47 ma chrons after plate motion correction gives well constrained estimates of the dominant long term nondipole contributions the axial quadrupole and axial octupole and shows no significant deviation from axial symmetry the amplitude of the axial quadrupole is found to vary with polarity 2 6 of the geocentric axial dipole for normal 4 6 for reverse while the axial octupole does not show appreciable change 2 9 for normal 2 1 for reverse these estimates of the quadrupole contribution agree well with prior determinations for the plio pleistocene 0 5 ma however the octupole contribution we find is opposite in sign to previous estimates we suggest that a negative octupole is representative of the actual time averaged paleomagnetic field while prior positive octupole estimates probably reflect spurious inclination shallowing the lack of polarity asymmetry in the octupole suggests that this nondipole component may be more closely linked to the main dipole field than is the quadrupole and so supports models of the geodynamo in which dipole and quadrupole families do not interact

thermal core mantle interactions and time averaged paleomagnetic field recent studies of historical geomagnetic secular variation and lower mantle seismic velocity suggest the earth s magnetic field is controlled by lateral variations in mantle temperature in this paper the average expected magnetic field pattern is compared with the time averaged field obtained from paleomagnetic pole positions from the last 5 m y the historical record suggests that the time averaged inclination anomalies are negative far sided in the atlantic region north of 30 s and the west pacific and positive in the south atlantic extreme north and south pacific and east pacific the pole positions give positive inclination anomalies in the south atlantic and extreme north pacific and negative anomalies elsewhere in agreement with the theory except for the east pacific this suggests that the historical record is not long enough to give an accurate picture of long term secular change in the eastern pacific but that elsewhere the time averaged field of paleomagnetism is predicted satisfactorily the preponderance of far sidedness in the paleomagnetic record is a consequence of the present distribution of temperature at the base of the mantle rather than a fundamental property of the geodynamo and it may therefore change on the long time scale of mantle convection in the historical record declinations average to negative values in the atlantic hemisphere and positive values in the pacific which if typical of longer term behavior could explain the preponderance of positive declinations for reversed polarity which are mainly in the atlantic hemisphere

inner core anisotropy anomalies in the time averaged paleomagnetic field and polarity transition paths abstract the diffusion of the dynamo generated magnetic field into the electrically conducting inner core of the earth may provide an explanation for several problematic aspects of long term geomagnetic field behavior we present a simple model which illustrates how an induced magnetization in the inner core which changes on diffusive timescales can provide a biasing field which could produce the observed anomalies in the time averaged field and polarity reversals the earth s inner core exhibits an anisotropy in seismic velocities which can be explained by a preferred orientation of a polycrystalline aggregate of hexagonal close packed hcp iron an elastically anisotropic phase room temperature analogs of hcp iron also exhibit a strong anisotropy of magnetic susceptibility ranging from 15 to 40 anisotropy at inner core conditions the magnetic susceptibility of hcp iron is estimated to be between 10 4 and 10 3 si we speculate here that the anisotropy in magnetic susceptibility in the inner core could produce the observed anomalies in the time averaged paleomagnetic field polarity asymmetry and recurring transitional virtual geomagnetic pole vgp positions

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

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

coupling of the core dynamo and mantle thermal or topographic static features in the earth s magnetic field and fixed sources of secular variation suggest the dynamo is anchored to the lowermost mantle via either thermal or topographic coupling here we show a correspondence with dynamic core topography which is related to mantle temperature and suggest further effects due to topography associated with subducting slabs the two coupling mechanisms may occur on different time scales providing a potential means for discriminating between them

geographical distribution of transitional vgps evidence for non zonal equatorial symmetry during the matuyama brunhes geomagnetic reversal abstract paleomagnetic records of the matuyama brunhes polarity reversal obtained recently from the northern equatorial and southern latitudes of the atlantic sector display a distinct symmetry with respect to the equator the virtual geomagnetic pole vgp paths from the mid latitude sites in the northern and southern hemispheres dsdp site 609 and core v16 58 are nearly coincident tracking northward through the americas the vgp path from the equatorial site odp site 664 tracks northward through eastern asia nearly antipodal to the other two paths modeling results indicate that superimposing an h 1 3 geometry onto a reversing axial dipole explains the sense of equatorial symmetry exhibited by these three records these results are consistent with the bulk of the data available from other records of this polarity transition suggesting that the transitional vgps during this reversal tend to fall along two distinct longitudinal bands the grouping of transitional vgps suggests that there is a strong geographical control over the reversal process an apparent correlation between the longitudinal bands of transitional vgps and the location of the major flux concentrations in the radial component of the historical geomagnetic field at the core mantle boundary 1 suggests that the processes which cause these flux concentrations may have influenced the geometry of the matuyama brunhes transitional field

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

long term geometry of the geomagnetic field for the last five million years an updated secular variation database lee 1983 assembled more than two thousand paleomagnetic directional data from lava flows in 65 sampling sites with ages spanning the last 5 million years constable 1992 recently suggested that the virtual geomagnetic poles vgp derived from this data base have been preferentially located within two antipodal bands of longitude we have reanalyzed and updated the lee data base yielding a total of 3179 data from 86 distinct sites neither the total data set nor various subsets of the data unambiguously show any large and clear maxima in the longitude distribution of vgps the shape of the common site longitude distribution is far more striking with a pronounced and robust minimum close to the common site longitude and secondary maxima about 120 o away from it the former first order feature is equivalent to the far sided effect discovered by wilson 1970 and corresponds to a persistent axial quadrupole amounting to about 5 of the axial dipole as previously found by several authors the latter second order feature could correspond to the vgp biasing effect described by egbert 1992 although its observed amplitude appears larger than predicted part of this effect an asymmetry in the maxima may also correspond to wilson s 1971 right handed effect given only a small axial quadrupolar component and the very uneven actual site distribution the expected longitude distribution of vgps can be calculated this is found to be in good agreement with the paleomagnetic observations i e rather flat with a moderate maximum near 120oe this study emphasizes problems related to the unsatisfactory distribution of sites the amplitude and significance of other terms beyond the dominant axial dipole and significant axial quadrupole contribution remain to be assessed

continuous wavelet transform theoretical aspects and application to aeromagnetic data at the huanghua depression dagang oilfield china we use the continuous wavelet transform based on complex morlet wavelets which has been developed to estimate the source distribution of potential fields for magnetic anomalies of adjacent sources they always superimpose upon each other in space and wavenumber making the identification of magnetic sources problematic therefore a scale normalization factor a n is introduced on the wavelet coefficients to improve resolution in the scalogram by theoretical modelling we set up an approximate linear relationship between the pseudo wavenumber and source depth the influences of background field random noise and magnetization inclination on the continuous wavelet transform of magnetic anomalies are also discussed and compared with the short time fourier transform results synthetic examples indicate that the regional trend has little effect on our method while the influence of random noise is mainly imposed on shallower sources with higher wavenumbers the source horizontal position will be affected by the change of magnetization direction whereas the source depth remains unchanged after discussing the performance of our method by showing the results of various synthetic tests we use this method on the aeromagnetic data of the huanghua depression in central china to define the distribution of volcanic rocks the spectrum slices in different scales are used to determine horizontal positions of volcanic rocks and their source depths are estimated from the modulus maxima of complex coefficients which is in good accordance with drilling results

lower mantle structure from scs s differential travel times knowledge of the spectrum of structure in the lower mantle is crucial to our understanding of the dynamical evolution of the earth and in principle can be inferred from the analysis of global seismic data sets the long wavelength compressional velocity structure has usually been constrained through tomographic inver sion of the isc catalogue of p wave travel times1 3 whereas shear velocity has been inferred from waveform modelling of long period shear waves4 6 the models that have been produced are similar in only the largest scale features7 and explain little of the variance of the raw data used in their construction thus there is a legitimate concern that the current generation of global scale models give only a crude approximation to the largest scale structure and that there may be significant aliasing of short wavelength heterogeneity here we use scs s differential travel times to demonstrate that the three dimensional structure of the lower mantle is indeed dominated by continental scale features particularly convincing is the fact that the features are apparent in the raw data and are not the product of a complicated modelling procedure

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

palaeosecular variation over the past 5 myr based on a new generalized database summary a generalized database of global palaeomagnetic data from 3719 lava flows and thin dykes of age 0 5 ma has been constructed for use with a relational database management system the database includes all data whose virtual geomagnetic poles vgp lie within 45 of the spin axis and can be used for studies of palaeosecular variation and for geomagnetic field modelling because many of these data were collected and processed more than 15 20 years ago each result has been characterized according to the demagnetization procedures carried out analysis of these data in terms of the latitude variation of the angular dispersion of vgps palaeosecular variation from lavas strongly suggests that careful data selection is required and that many of the older studies may need to be redone using more modern methods differences between the angular dispersions for separate normal and reverse polarity data sets confirm that many older studies have not been adequately cleaned magnetically therefore the use of the database for geomagnetic field modelling should be carried out with some caution using a vgp cut off angle that varies with latitude the best data set consists of 2636 results that show a smooth increase of vgp angular dispersion with latitude model g for palaeosecular variation which is based on modelling of the antisymmetric dipole and symmetric quadrupole dynamo families provides a good fit to these results

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

mean winds and tidal and planetary wave motions over hawaii during airborne lidar and observations of hawaiian airglow aloha 93 the mean and low frequency wave motions in the mesosphere and lower thermosphere from 70 to 98 km were observed with the mf radar on kauai during the airborne lidar and observations of hawaiian airglow aloha 93 measurement campaign two day mean zonal winds exhibited a transition from a variable structure with altitude at the beginning of october having westward motions near 80 km and eastward motions at upper and lower levels to more uniform eastward winds with altitude at the end of october two day mean meridional motions were equally variable with northward motions at all altitudes on october 1 northward motions above 80 km and southward motions below throughout much of the campaign and largely northward motions at the end of october zonal and meridional winds exhibited significant oscillations at 5 to 30 day periods indicative of planetary wave activity during this interval diurnal tidal amplitudes and phases were likewise variable with maximum and minimum rms amplitudes of 35 and 10 ms 1 approximate phase quadrature with meridional leading zonal amplitude and phase variability on time scales of 5 to 15 days and an overall phase advance during october of 10 h other tidal components and the two day wave had rms amplitudes of 5 to 10 ms 1

application of the continuous wavelet transform of gravity and magnetic data to estimate sub basalt sediment thickness the continuous wavelet transform was recently proposed for the interpretation of gravity and magnetic potential data we utilize the continuous wavelet transform of gravity and magnetic data to address one of the most common issues in exploration geophysics mapping of sub basaltic sedimentary strata we observe that the magnetic response of the basaltic layer is dominant in a three layer case of a basalt sediment basement whereas the gravity signal is dominated by the base of the sediment thus the continuous wavelet transform of the magnetic data is related to the thickness of the basalt and the continuous wavelet transform of the gravity data is related mostly to the bottom of the sediment these observations are demonstrated with a synthetic model and a few field examples derived depths using continuous wavelet transform are in good agreement with known vertical cross sections therefore continuous wavelet transform analysis of both gravity and magnetic data offers a possibility for primary information of sub basaltic sediment thickness which can provide a basis for further detailed modelling

doppler ducting of atmospheric gravity waves atmospheric gravity waves are subject to horizontal ducting in a stably stratified atmosphere that contains levels of wind maximum or minimum quite apart from any superimposed consequences of vertical variation of stability and quite apart from the existence or otherwise of critical levels the process doppler ducting is examined here for two prototype cases an isolated wind maximum and a wind minimum at ground level and for two more realistic model cases a strong tropospheric jet and a nocturnal boundary layer jet the wave structure modal behavior and dispersion curves of all four are very similar it is argued that doppler ducting is available to a part of the gravity wave spectrum in all real circumstances and that it should be considered as a possible candidate whenever observations indicate that some ducting process is operative one particular wave event is discussed in some detail and it is shown that doppler ducting in its simplest form provides a plausible alternative to a more complicated ducting process which involved critical levels and energy leakage previously inferred doppler ducting is available equally to gravity waves in the oceans when background currents vary with depth

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

a review of gravity wave saturation processes effects and variability in the middle atmosphere this paper provides a review of our current understanding of the processes responsible for gravity wave saturation as well as the principal effects and variability of saturation in the lower and middle atmosphere we discuss the theoretical and observational evidence for linear and nonlinear saturation processes and examine the consequences of saturation for wave amplitude limits momentum and energy fluxes the diffusion of heat and constituents and the establishment of a near universal vertical wavenumber spectrum recent studies of gravity wave variability are reviewed and are seen to provide insights into the significant causes of wave variability throughout the atmosphere

the time averaged geomagnetic field as recorded by lava flows over the past 5 myr summary a recently compiled lava flow data base spanning the last 5 million years is used to investigate properties of the time averaged geomagnetic field more than 90 per cent of the power in the palaeofield can be accounted for by a geocentric axial dipole however there are significant second order structures in the field declination and inclination anomalies for the new data base indicate that the main second order signal is the far sided effect and there is also evidence for non zonal structure vgp virtual geomagnetic pole latitude distributions indicate that over the last 5 million years normal and reverse polarity morphologies are different and that any changes in the normal polarity field morphology are undetectable given the present data distribution regularized non linear inversions of the palaeomagnetic directions support all these observations we test the hypothesis that zonal models for the time averaged field are adequate to describe the data and find that they are not non zonal models are needed to fit the data to within the required tolerance level normal and reverse polarity field models obtained are significantly different field models obtained for the brunhes epoch data alone are much smoother than those obtained from combining all the normal polarity data simulations indicate that these differences can be explained by the less extensive data distribution for the brunhes epoch the field model for all of the normal polarity data ln1 contains features observed in the historical field maps although the details differ ln1 suggests that although the two northern hemisphere flux lobes observed in the historical field are stationary to a first order approximation they do show changes in position and amplitude a third less pronounced flux lobe is observed in ln1 over central europe the lack of structure in the southern hemisphere is due in part to the paucity of data jackknife estimates of the field models for different subsets of the data suggest that a few sites contribute significant structure to the final field models more conservative estimates of the time averaged field morphology are obtained by removing these sites

3d gravity anomaly separation method taking into account the gravity response of the inhomogeneous mantle abstract in order to ensure that the gravity data processing and inversion are consistent with the actual geology we propose that in integrated geophysical research 3d gravity anomaly separation gas should take into account the gravity response of the inhomogeneous mantle this is an effective method by which the residual gravity anomaly rga may be obtained as well as an important basis for the inversion and interpretation of gravity data aimed at the petroliferous basin structure evolution of continental margin ocean continental transition zone and other widely discussed geological problems we extensively investigate the upper mantle structure in many regions around the world and the results show that the lateral inhomogeneity of the mantle is widespread in many comprehensive studies based on gravity and seismic data the gravity anomaly modeling and separation are typically performed within the crust above the moho which actually relies on an assumption of homogeneous mantle although this assumption simplifies the difficulty of the gravity modeling and separation it ignores gravity anomalies caused by inhomogeneities of the deep mantle the rga along with the inverted density structure and other interpretations involves the risk of deviating from the actual geology on the basis of the 2d forward calculation of several typical interface models we implement the quantitative analysis of the effect that the inhomogeneous mantle has on the bouguer gravity anomaly in case studies of the southeastern united states and the sichuan basin taking the shear wave velocity vs structure of the upper mantle as the constraint condition we calculate the gravity anomaly caused by the inhomogeneous mantle by means of the forward method it is found that the gravity response of the inhomogeneous mantle cannot be neglected therefore we conduct 2 5d joint simulation combining gravity and seismic data in the sichuan basin the fitting results after separating the gravity response of the inhomogeneous mantle are clearly superior to those of the homogeneous mantle hypothesis on the basis of the 3d depth data of several sedimentary strata the moho and the mantle high velocity bodies we implement 3d gas obtain the rga of the basement in the sichuan basin and discuss the geological origin of the dazu high gravity

distribution of the crustal magnetic anomaly and geological structure in xinjiang china based on the high order crustal magnetic field model ngdc 720 v3 we investigate the distribution of crustal magnetic anomaly the decay characteristics of the anomaly and the relationship between the magnetic anomaly and geological structure in xinjiang china topography of the magnetic layer basement is studied through curie isothermal surface using the power spectrum method it is found that south tarim basin junggar basin and turpan hami basin have strong positive magnetic anomaly whereas west kunlun mountain altun mountain tianshan mountain and altai mountain have weak or negative anomaly the magnetic anomaly well reflects the regional tectonic structure i e three alternating mountains intervened by two basins the magnetic anomaly on the ground surface in tarim basin is well corresponding to the mafic dykes the decay of the magnetic anomaly with altitude indicates that xinjiang is a large massif composed of several magnetic blocks with different sizes in different directions the curie surface presents a feature of being shallow under mountains whereas being deep under basins roughly having an anti mirror correspondence with the moho depth

plate motions and the geomagnetic field i quaternary and late tertiary summary we have tested the hypothesis that the apparent increase in the northward offset of the axial dipole i e the ratio g gy with age for the last 25 ma wilson mcelhinny is due to the failure to correct for plate motions spherical harmonic analyses were performed on two types of data palaeomagnetic poles from continents islands and seamounts and magnetic inclinations from deep sea cores after returning the sampling sites to their predrift locations in fixed hotspots coordinates the results show that the quadrupole term g maintained a value of about 0 05 gy throughout the last 35 ma and that the axial octupole had a small value of about 0 02 gy for the last 5 ma sea core inclinations analysed separately gave essentially the same results as continental palaeopoles for the last few million years independent data sets for the past 2 ma and for the period 2 6 ma gave nearly identical solutions showing that the persistence of the axial terms is not a phenomenon of the more densely sampled quaternary field alone nor is it an artifice of predominantly northward motion of the plates returning all 0 5 ma data to a 5 ma reconstruction failed to eliminate the quadrupole the non zonal coefficients for the 0 5 ma field are typically an order of magnitude less than the zonal terms with the exception of h and are probably insignificant suggesting that longitudinal drift is generally effective in averaging out these components the present distribution of data is inadequate to determine coefficients of third and higher degree prior to 5 ma but there is evidence that g may have changed little during the last 35 ma in addition there has been very little relative motion between the palaeomagnetic dipole axis as defined by the first degree terms and the axis of the hotspots reference frame

the myth of the pacific dipole window the angular dispersion of virtual geomagnetic poles vgp from lava flows is often cited as having been anomalously low in the pacific during the brunhes epoch because the dispersion from hawaiian lavas is said to be much lower than measured elsewhere this led to the concept of the pacific dipole window or pacific non dipole low because lavas tend to be erupted in bursts of activity many of the hawaiian data are serially correlated and thus cannot necessarily be treated as independent observations geochronological controls as are available for hawaii have been used in a previous analysis to thin the data to try to avoid repeated sampling of the same geomagnetic field unfortunately in that analysis the angular dispersion of vgps was calculated about the mean vgp instead of about the spin axis and thus underestimated the dispersion we have therefore reanalyzed the relevant data using the following criteria 1 only those lavas with 95 10 have been considered 2 a latitude dependent cut off angle is used to eliminate those vectors that are not part of the normal secular variation 3 we have developed a statistical method to rationalise those flows that have repeatedly sampled the same geomagnetic field vector because suitable geochronological controls are rarely available application of this new method to the hawaiian data shows excellent agreement with the results from using geochronological controls where possible we have therefore included this method in our overall analysis as expected the resulting global data are compatible with a fisher distribution about the spin axis brunhes age data from hawaii n 96 independent measurements give a vgp angular dispersion about the spin axis of sf 12 4 and for the pacific region as a whole sf 12 5 n 190 between latitudes 15 and 30 north or south these values are the same as sf 12 4 n 160 calculated for the rest of the world in the same latitude range this clearly demonstrates that the hypothesis of the pacific dipole window may confidently be rejected

crustal configuration of the northwest himalaya based on modeling of gravity data the gravity response and crustal shortening in the himalayan belt are modeled in detail for the first time in the nw himalaya the bouguer gravity anomaly along a 450 km long projected transect from the sub himalaya in the south to the karakoram fault in the north across the indus tsangpo suture zone is modeled using spectral analysis wavelet transform and forward modeling the spectral analysis suggests three layer interfaces in the lithosphere at 68 34 and 11 km depths corresponding to the moho the conrad discontinuity and the himalayan decollement thrust respectively the coherence admittance and cross spectra suggest crustal shortening because of convergence compensated by lithospheric folding at 536 and 178 km wavelength at the moho and the upper crustal level an average effective elastic thickness of around 31 km is calculated using the coherence method the gravity data are modeled to demarcate intracrustal to subcrustal regional thrust fault zones the geometrical constraints of these faults are obtained in the space scale domain using the wavelet transform showing good correlation with the major tectonic boundaries the crustal configuration along the transect shows how the moho depth increases from 45 to 80 km towards the north with the locus of flexure of the indian crust beneath the higher himalayan zone the combination of forward modeling and wavelet analysis gives insight into the subsurface extent and geometry of regional structures across the nw himalaya

whole mantle p wave travel time tomography abstract a method of tomographic inversion to obtain three dimensional velocity perturbations in the earth s whole mantle has been developed and applied to more than two million p wave arrival time data reported by international seismology center isc the model is parameterized with 32 768 blocks the divisions in latitude longitude and radius are 32 64 and 16 respectively horizontal cell size is 5 6 5 6 the layer thicknesses vary with depth 29 km just below the surface and 334 km just above the core mantle boundary starting from a spherically symmetric earth model we obtained a three dimensional model using the following iterative procedures first we relocated all the events second we backprojected the residual into the whole mantle third we refined the spherically symmetric earth model the solutions have been converged in five iterations we adopted the following techniques in the backprojection procedure the first order smoothness was introduced as a damping which makes the solution independent of the starting model and its apparent fluctuation minimal the basic equations for delay times and smoothness are solved using the conjugate gradient method an iterative method which guarantees the convergence of solution into the exact least squares solution the weight on the smoothness i e the damping factor was objectively determined by a simplified cross validation technique the final solution was obtained as an average of the ten solutions each of which was derived from one tenth of the total data set the reliability of the solution is examined in two ways 1 mapping the resolution given by the reconstruction of checkerboard patterns and 2 mapping the variance given from the gaussian noise input this is the first result which delineates the whole mantle structure with its reliability mapping the longest wavelength anomalies of the lower mantle are similar to those of previous studies by dziewonski 1984 and hager and clayton 1989 however the shorter wavelength patterns have many discrepancies the fast anomalies of the uppermost mantle beneath the shield and the slow anomalies beneath the active tectonic regions are clearly seen we also revealed the l 2 pattern at the transition zone reported by the previous surface wave and free oscillation studies the most striking feature is that of the fast anomalies lying along the extension of the large subducting plate up to depths of about 1000 km or more the resolving powers in these regions are generally good

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

robust inversion of iasp91 travel time residuals for mantle p and s velocity structure earthquake mislocations and station corrections using both p and s arrival time information 41 108 events in the international seismological centre isc catalog for the years 1964 to 1987 are relocated relative to the iasp91 velocity model the mean absolute horizontal relocation is 7 7 km and the mean absolute depth relocation is 9 1 km the mean absolute origin time shift is 1 2 s the relocation procedure increased the p residual standard deviation slightly from 2 3 s to 2 5 s while decreasing the s residual standard deviation from 6 8 s to 6 1 s when plotted as bottoming point averages the resulting iasp91 p and s arrival time residuals show coherent patterns as a function of geographic location an iterative lp residual norm minimization algorithm is used to estimate the set of p and s velocity variations as well as the earthquake relocation and seismographic station parameters which best explain the travel time residuals the procedure is robust in that extremely large travel time residuals which are common in the isc data do not unduly influence the velocity estimates both the p and s models of lateral heterogeneity contain prominent circum pacific low velocities 1 to 2 perturbations underlying the back arc basins between 35 and 200 km depth this ring of negative deviations continues into the depth interval 200 400 km the continental cratons are underlain by high velocity anomalies with maximum amplitudes of 2 iceland and the azores are underlain by low velocity mantle material that extends down to at least 400 km the benioff zones are only intermittently imaged as 1 2 high velocity regions in the uppermost 400 km they are best resolved in the p velocity variations both the p and s velocity models contain a circum pacific ring beneath the benioff zones of 1 2 positive velocity deviations in the depth range 660 870 km coherent high velocity features are seen below south america borneo tonga fiji the marianas and the northern kuriles the anomalies beneath south america and borneo extend into the 870 1070 km depth range below depths of 1270 km for p variations and 1070 km for s variations the amplitude of the heterogeneity has decreased significantly it is only in the lowermost mantle 2670 km to the core mantle boundary that the level of p heterogeneity rises significantly above the estimated noise level in this depth range a partial ring around the pacific basin is observed although this

wavelet correlation filter for wide angle seismic data a new filtering technique for single fold wide angle reflection refraction seismic data is presented the technique is based on the wavelet decomposition of a set of adjacent traces followed by coherence analysis the filtering procedure consists of three steps in the first a wavelet decomposition of traces into different detail levels is performed in the second the coherence attributes for each level are evaluated by calculating cross correlation functions of detail portions contained in a space time moving window finally the filtered traces are obtained as a weighted reconstruction of the trace details each weight is obtained from the coherence attributes distribution estimated in a proper interval a sequence of tests is then conducted in order to select possible optimum or unsuitable wavelet bases the efficiency of the filter proposed was assessed by calculating some properly designed parameters in order to compare it with other standard de noising techniques the proposed method produced a clear signal enhancement in high density wide angle seismic data thus proving that it is a useful processing tool for a reliable correlation of seismic phases

weighted averages of magnetization from magnetic field measurements a fast interpretation tool 1 magnetic anomalies may be interpreted in terms of weighted averages of magnetization wam by a simple transformation the wam transformation consists of dividing at each measurement point the experimental magnetic field by a normalizing field computed from a source volume with a homogeneous unit magnetization the transformation yields a straightforward link among source and field position vectors a main wam outcome is that sources at different depths appear well discriminated due to the symmetry of the problem the higher the considered field altitude the deeper the sources outlined by the transformation this is shown for single and multi source synthetic cases as well as for real data we analyze the real case of mt vulture volcano southern italy where the related anomaly strongly interferes with that from deep intrusive sources the volcanic edifice is well identified the deep source is estimated at about 9 km depth in agreement with other results

concurrent oh imager and sodium temperature wind lidar observation of localized ripples over northern colorado 1 on 3 and 5 september 2002 the oh all sky imager at platteville colorado 40 2 n 104 7 w observed small scale wavelike patterns known as ripples with horizontal wavelengths of 9 km and 7 km and lifetimes of 9 min and 15 min respectively the colorado state university sodium lidar at nearby fort collins colorado 40 6 n 105 w also made concurrent observations of temperature and zonal and meridional winds which allowed us to determine the nature of the ripples observed our observations suggest that the 3 september ripple was induced by a convective instability located at 87 5 km and the 5 september ripple was induced by a dynamic instability at 88 5 km the ripples clearly advected as packets with the background wind lidar measurements also allowed us to relate the directions of wind shear to the phase front alignments of both the ripples and the nearby short period atmospheric gravity waves these spatial relationships provided a meaningful comparison with previously observed ripples as well as with current theoretical models using the 16 hour continuous lidar data set for each case we deduced that long period waves created an unusually large temperature perturbation at the ripple times on 3 september and an unusually large wind shear perturbation on 5 september these perturbations prepared the background atmosphere to be near the verge of local instability but as revealed again by lidar observation it was the superposition of smaller scale perturbations at the time of the ripples that helped to actually reach the conditions required for instability and generation of the ripples

global and local multiscale analysis of magnetic susceptibility data geophysical well logs often show a complex behavior which seems to suggest a multifractal nature multifractals are highly intermittent signals with distinct active bursts and passive regions which cannot be satisfactorily characterized in terms of just second order statistics they need a higher order statistical analysis in contrast with monofractals which have a homogeneous scaling multifractals may include singularities of many types here we describe how a multiscale analysis can be used to describe the magnetic susceptibility data scaling properties for a deep well ktb germany down to about 9000 m a multiscale analysis describes the local and global singular behavior of measures or distributions in a statistical fashion the global analysis allows the estimation of the global repartition of the various holder exponents as such it leads to the definition of a spectrum d called the singularity spectrum the local analysis is related to the possibility of estimating the lipschitz regularity locally i e at each point of the support of a multifractal signal the application of both approaches to the ktb magnetic susceptibility data shows a meaningful correlation between the sequence of holder exponents vs depth and the lithological units the holder exponents reach the highest values for gneiss units intermediate ones for amphibolite units and the lowest values for variegated units faults are found to correspond to changes for h also when they are of intra lithological type

modelling potential field sources in the gelibolu peninsula western turkey using a markov random field approach in this study a markov random field mrf approach is used to locate source boundary positions which are difficult to identify from bouguer gravity and magnetic maps as a generalized form of markov chains the mrf approach is an unsupervised statistical model based algorithm and is applied to the analysis of images particularly in the detection of visual patterns or textures here we present a dynamic programming based on the mrf approach for boundary detection of noisy and super positioned potential anomalies which are produced by various geological structures in the mrf method gravity and magnetic maps are considered as two dimensional 2 d images with a matrix composed of n1 n2 pixels each pixel value of the matrix is optimized in real time with no a priori processing by using two parameter sets average steering vector and quantization level m they carry information about the correlation of neighboring pixels and the locality of their connections we have chosen mrf as a processing approach for geophysical data since it is an unsupervised efficient model for image enhancement border detection and separation of 2 d potential anomalies the main benefit of mrf is that an average steering vector and a quantization level are enough in evaluation of the potential anomaly maps we have compared the mrf method to noise implemented synthetic potential field anomalies after satisfactory results were found the method has been applied to gravity and magnetic anomaly maps of gelibolu peninsula in western turkey here we have observed anafartalar thrust fault and another parallel fault northwest of anafartalar thrust fault we have modeled a geological structure including a lateral fault which results in a higher susceptibility and anomaly amplitude increment we have shown that the mrf method is effective to detect the broad scale geological structures in the gelibolu peninsula and thus to delineate the complex tectonic structure of gelibolu peninsula

statistical characteristics of gravity waves observed by an all sky imager at darwin australia 1 an all sky airglow imager with a cooled charge coupled device camera in place at darwin 12 4 s 131 0 e australia since october 2001 has been used to obtain two dimensional gravity wave images in the mesopause region using airglow images of the oi 557 7 nm emission altitude 96 km and oh band 720 910 nm 86 km emissions obtained for october 2001 to august 2002 we investigated the wavelengths phase velocities and propagation directions of gravity waves wave occurrence in oh images 60 90 is higher than in oi images 30 70 for all seasons the waves have wavelengths of less than 90 km peak 30 50 km and phase velocities of less than 90 m s peak 30 60 m s most of the waves propagate in the meridional direction and the directionality strongly depends on the season in winter waves propagate both poleward and equatorward while in summer almost all waves propagate poleward an examination of airglow imaging statistics at adelaide 35 s 138 e australia obtained by walterscheid et al 1999 leads us to conclude that this clear directionality is caused by the location of the wave sources and by the wave ducting processes that is poleward waves in summer come from an equatorial convective source through a thermal duct structure the effect of wind filtering on the waves is also discussed for zonal wave propagation

tomographic inversions for mantle p wave velocity structure based on the minimization of l 2 and l 1 norms of international seismological centre travel time residuals we use international seismological centre isc p arrival data 1964 1987 and iterative algorithms which minimize the l1 and l2 residual norms to solve simultaneously for three dimensional p velocity variations in earth s mantle source mislocations and station corrections we find that the maximum velocity perturbations produced by the l1 minimization approximately 4 in our final model are relatively insensitive to smoothing and damping constraints therefore using an l1 norm criterion allows us to keep the bias introduced to the inversion to a minimum among the well resolved features contained in both the l1 and the l2 velocity models are a fast anomaly in the lower mantle beneath the tonga new hebrides subduction zone to a depth of 1670 km and another fast anomaly beneath the japanese island arc and eastern asia continuity between these anomalies and shallower fast anomalies is not clear a fast anomaly extending from 670 km to 2070 km depth appears beneath eastern north america the caribbean and north central south america a broad fast anomaly appears beneath eastern asia just above the core mantle boundary as well as several slow anomalies under the pacific basin of comparable size both models contain a circum pacific ring of 2 lower velocities in the depth range 0 200 km associated with back arc basins high velocities over 2 associated with the continental shields tend to disappear below 400 km though a significant region of high velocity remains beneath the siberian platform in the 400 to 670 km depth interval

depth determinations of shallow hydrothermal systems by self potential and multi scale wavelet tomography in hydrothermal studies the depth of the hydrothermal system is always required but rarely known via traditional geophysical exploration techniques while previous studies have shown that continuous wavelet transform algorithms applied to self potential data can theoretically determine the depth of the hydrothermal fluids this study uses multi scale wavelet tomography with multiple wavelets field measurements and geophysical models to accurately determine this depth on stromboli waita and masaya volcanoes multi scale wavelet tomography of field measurements gives reproducible depth results supported by independent geophysical measurements and models and accurately locates the main water flow paths at shallow depths unlike other traditional geophysical methods multi scale wavelet tomography using self potential data is a low cost tool to rapidly determine depths of the shallowest hydrothermal structures this approach has the potential to significantly enhance our ability to locate geothermal systems and monitor active volcanoes

paleomagnetic tomography of the core mantle boundary abstract analysis of updated global paleomagnetic data indicates that over the last 5 million years the normal and reverse polarity states are discernibly different this difference which can be characterized by a higher ratio of the axial quadrupole to dipole field for the reverse polarity relative to the normal polarity is attributed to lateral variations in temperature or composition at or near the core mantle boundary although several mechanisms are considered thermal electric effects associated with core mantle topography and or with chemical variations in d the seismic layer approximately 150 km thick at the base of the mantle are judged to be the most likely sources of the observed polarity asymmetry this asymmetry should not necessarily be expected to give rise to systematic trends in polarity transitions

separation and interpretation of gravity field data based on two dimensional normal space scale transform nsst2d algorithm a case study of kauring airborne gravity test site western australia the gravity field signal observed on the surface of the earth is the superposition of the gravitational effects produced mainly by the mass sources at different locations and depths from the surface down to the underground reliable geophysical interpretation of gravity anomalies is highly dependent on the validity of the data processing methods and the rationality of the calculated results this paper proposes a novel potential field separation method based on two dimensional normal space scale transform nsst2d algorithm to implement the residual regional field separation compared with the two dimensional discrete wavelet transform dwt2d method often appeared in the previous potential field separation studies the nsst2d algorithm can keep the shape of the separated field from distortion by normalizing the conventional two dimensional wavelet transform kernels based on gravity field of synthetic models the separated residual regional fields respectively derived from dwt2d with five different wavelet bases and those from nsst2d are compared the experimental results verify the effectiveness and superiority of the proposed nsst2d algorithm finally the nsst2d algorithm is also applied to the separation of the complete bouguer gravity anomaly in the kauring airborne gravity test site western australia the results show that the characteristics of the separated field from the corresponding mass sources with different depths maintain relatively good consistency with the feature of the three dimensional inversion density contrast distribution

on convection in the earth s core driven by lateral temperature variations in the lower mantle summary lateral variations in heat flux or temperature in the lowermost mantle associated with mantle convection will drive fluid flow in the liquid core the effect is modelled by a rotating spherical shell with uniform lower boundary temperature and a laterally varying upper surface temperature and the solutions found by numerical calculation some for a density stratified fluid the problem depends upon two dimensionless numbers a horizontal rayleigh number and a stratification parameter the calculations are restricted to surface temperatures which are symmetric about the equator and steady solutions are found induced toroidal flows near the surface are closely linked with the applied temperature profile through the thermal wind equation and coriolis forces make the convection penetrate into the shell stratification acts mainly to suppress radial flow but the surface toroidal flow is relatively unaffected the results illustrate the powerful influence exerted by the surface temperature but are difficult to apply directly to the earth s core because molecular values of the thermal diffusivity entail a very long time scale assuming a turbulent thermal diffusivity equal to the magnetic diffusivity gives a more realistic time scale and it is possible to recover for specific simple imposed temperature profiles flows similar to those found in the earth s core from inversion of geomagnetic secular change

integrated analysis on gravity and magnetic fields of the hailar basin ne china implications for basement structure and deep tectonics the hailar basin is one of the typical basins among the ne china basin groups which is situated in the east of east asia orogene between the siberia plate and the north china plate based on the detailed analysis of magnetic gravity petrophysical geothermal and seismological data we separate the gravity and magnetic anomalies gma into four orders using wavelet multi scale decomposition wmd the apparent depths of causative sources were then assessed by power spectrum analysis psa of each order low order wavelet detail anomalies were used to study the basin s basement structure such as major faults the basement lithology uplifts and depressions high order ones were used for the inversion of moho and curie discontinuities using the parker method the results show that the moho uplifting area of the hailar basin is located at the ne part of the basin the curie uplifting area is at the nw part and neither of them is consistent with the basin s sedimentary center this indicates that the hailar basin may differ in basin building pattern from other middle and eastern basins of the basin groups and the hailar basin might be of a passive type when the pacific plate was subducting to ne china the frontier of the plate lying on the mantle transition zone didn t pass through the great khingan mountains region so there is not an obvious magma upwelling or lithospheric extension in the hailar basin area finally based on the seismological data and results of wmd a probable 2d crust model is derived from an across basin profile using the 2d forward modeling of the bouguer gravity anomaly the results agree with those from seismic inversion suggesting wmd is suitable for identifying major crustal density interfaces

absence of preferred longitude sectors for poles from volcanic records of geomagnetic reversals according to a recent compilation of sedimentary records from the past 12 myr the reversing geomagnetic field displays a marked long term longitudinal organization which seems to be correlated with the thermal structure of the lower mantle1 however the crucial palaeomagnetic observation that intermediate virtual geomagnetic poles are preferentially confined to longitudes over the americas or antipodal to this sector2 3 might be an artefact caused by distortion and smoothing of the geomagnetic signal by sediments4 6 here we present a compilation of 400 intermediate poles from 121 volcanic records of excursions and reversals less than 16 myr old sampled at various longitudes and latitudes which does not confirm previous inferences1 and reinforces doubts4 6 about the ability of sediments to properly record a rapidly varying field in contrast to virtual poles from excursions those from reversals are uniformly distributed in longitude which indicates that the reversing field is statistically axisymmetrical thus we conclude that there is no evidence for control of transitional fields by the temperature distribution in the lowermost mantle

inclination anomalies from indian ocean sediments and the possibility of a standing nondipole field we report magnetic inclinations measured in deep sea sediments of the equatorial indian ocean which record the behavior of a nondipole component of the time averaged geomagnetic field during the plio pleistocene 0 5 ma the magnitude of the nondipole effect recorded in these sediments appears to depend on polarity state with inclinations showing departures from geocentric axial dipole directions which are small 2 o during normal polarity and larger 5 o during reverse polarity times the overall nondipole effect observed here is consistent with prior spherical harmonic estimates of the paleomagnetic field the polarity bias found agrees in both sense and magnitude with earlier reports of polarity asymmetry in the low degree zonal harmonic fields the presence of this asymmetry supports previous suggestions of the existence of a standing component of the nondipole field which does not invert during reversals of the main field we explore whether the standing field so indicated may have influenced paleomagnetic directions recorded during polarity transitions at other equatorial sites

the time averaged paleomagnetic field 0 5 ma persistent departures from the geocentric axial dipole field model of the time averaged paleomagnetic field over the past 5 myr have been analyzed using oceanic data from deep sea cores and continental data from igneous rocks and sediments the data set comprises the equivalent of 9490 spot readings of the field 5831 normal and 3659 reverse from 930 groups of data variations in declination anomalies between groups of data strongly suggest the existence of second order tectonic effects small rotations that make it difficult if not impossible to identify any nonzonal terms that might exist inclination anomalies have therefore been modeled in terms of low degree zonal harmonics the calculated inclination anomalies within 10 latitude bands are widely scattered for both oceanic and continental data and do not appear to have been drawn from distributions with common means we attribute this large scatter to previously undetected or uncorrected second order tectonic effects in the continental data or in the oceanic data to small departures from the vertical in deep sea cores if it is assumed that these effects are random between groups of data and without a systematic bias they can be averaged out to a large extent if there are sufficient numbers of groups within each latitude band this method also has the major advantage that it maximizes time averaging of the field when this is done an acceptable fit to the inclination anomaly data is found using a zonal harmonic model although the point estimates for the reverse polarity zonal quadrupole term are consistently larger than those for the normal polarity zonal quadrupole term the difference is not significant and is likely due to contamination effects this finding is true for a combination of all the data or for separate combinations of continental igneous rocks and ocean sediments this conclusion differs from all previous analyses the major differences occur in model estimates of the zonal octupole term the estimates varying widely depending on the particular data combination we show that false octupole terms can be introduced by several factors including inclination errors in sediments and lavas the use of unit vectors in the analyses and incomplete magnetic cleaning particularly of reversely magnetized rocks thus we cannot impute a geomagnetic significance to the estimates of a zonal octupole term we suggest that the best estimates for the zonal quadrupole g2 g20 g10 are obtained from the combined brunhes age igneous rocks and oceanic normal data 0 033 0 019 and for the combined matuyama age igneous rocks and oceanic reverse data 0 042 0 022 when these two sets are combined the overall best estimate of g2 is 0 038 0 012

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

crustal magnetic anomaly and curie surface beneath tarim basin china and its adjacent area based on the geomagnetic field model ngdc 720 v3 national geophysical data center the distribution of crustal magnetic anomalies and the curie surface beneath tarim basin china and its adjacent area were investigated the results show that the spatial distribution of the magnetic anomalies in tarim basin coincides with the regional tectonic structure i e a basin sandwiched between mountain ranges shallow parts of the curie surface are located in uplifted zones of the basin and correspond well to high values of heat flow in contrast deep parts of the curie surface having low values of heat flow are distributed along the depression zones of the basin the curie point depth is consistent with the measured heat flow value with a correlation coefficient of 0 65

determination of horizontal and vertical structure of an unusual pattern of short period gravity waves imaged during aloha 93 an all sky ccd imager has been used to measure the properties of short period gravity waves present over the hawaiian islands during the aloha 93 campaign observations of emissions from four different altitudes provided a capability to describe the vertical as well as the horizontal structure of the wave field on several occasions during this campaign an unusual morphology wave pattern was detected that consisted of a group of small scale waves oriented in the same direction these were most noticeable in the oi 557 7 nm emission altitude 96 km and were usually observed in association with a larger scale gravity wave this paper presents a preliminary analysis of data recorded on the night of 22 october during which both types of waves were prominent the small scale waves exhibited highly coherent phase structures at each emission altitude consistent with a ducted wave motion the spatial intensity and phase modulation of this display is indicative of interference between two waves with similar characteristics and slightly different propagation directions the larger scale wave motion was observed to propagate perpendicular to the small scale waves and showed evidence of phase progression with altitude implying upward energy propagation these data have been interpreted in the context of simultaneous wind measurements from an mf radar

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

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

localized cultural denoising of high resolution aeromagnetic data we show how a denoising technique based on the wavelet transform can be used to deal with localized noise related to dc electrified railway lines this method which performs localized and sharp filtering of cultural noise was applied to high resolution aeromagnetic data acquired in the phlegrean volcanic area southern italy in 1999 and 2001 the helicopter borne survey was aimed at giving new detailed insights into the distribution of the magnetization of the area and therefore into the volcanological characteristics of the region the surveyed area is characterized by the presence of towns buildings and dc electrified railway lines whose magnetic effects influenced the measurements and were responsible for some of the measured anomalies this cultural noise has therefore to be minimized as much as possible in order to allow the data to be interpreted accurately due to the excellent space scale localization properties of the discrete wavelet transform the cultural disturbance was removed very precisely leaving the field in the adjacent areas unchanged

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

multispectral tomographic imaging of the midlatitude aurora the cedar optical tomographic imaging facility cotif consists of a midlatitude chain of meridional imaging spectrographs whose slit apertures subtend a common volume in the ionosphere the facility provides a set of simultaneous multispectral brightness measurements that are used in a two dimensional tomographic reconstruction horizontal versus vertical of auroral and airglow features in the midlatitude subauroral ionosphere a tomographic inversion method is summarized which regularizes the vertical field aligned dimension using a nonlinear low dimensional basis expansion three experimental results are presented for atomic oxygen 557 7 and 630 0 nm emissions at midlatitude time sequences of the reconstructed emission fields illustrate the variability in o i excitation patterns in both the diffuse aurora and sar arcs the results are interpreted with respect to outstanding issues associated with midlatitude aurora extracted vertical profiles are compared with published experimental and theoretical results

persistent patterns in the geomagnetic field over the past 2 5 myr historical geomagnetic measurements covering the past 400 years reveal a symmetrical pattern of four relatively stationary flux concentrations lobes at the surface of the liquid core and regions of rapid change extending from the atlantic to the indian ocean1 palaeomagnetic data define a time average over several thousand years2 which might reflect the stationary parts of the present field but unfortunately the historical record is too short to provide a satisfactory average3 here we model palaeomagnetic directions from the past 2 5 myr using the same methods as for modern data4 and find the two northern lobes in the same position as today over arctic canada and siberia in southern regions by contrast the field appears to have been smoothed out as might be expected from the current rapid secular variation1 we propose that the present geomagnetic field morphology and pattern of secular variation have persisted for several million years as would occur if the solid mantle controls flow at the top of the core

palaeomagnetic constraints on the geometry of the geomagnetic field during reversals palaeomagnetic records of the path of the pole during reversals of the earth s magnetic field provide a test of the hypothesis that dipolar or low order axisymmetric components of the field dominate during reversals multiple records of reversals during the past 12 myr show no simple or consistent geographical pattern although a more robust analysis of the transitional field awaits a greater number of well distributed sampling sites the present data are not inconsistent with the simplest models in which a field reminiscent of the non dipole component of the present day field becomes dominant

the secular variation of earth s magnetic field models of the magnetic field at the core mantle boundary at selected epochs from 1715 0 to 1980 0 reveal novel features in the field at the core these suggest that the flow of core fluid is coupled to the mantle and that magnetic diffusion is significant

lateral temperature variations at the core mantle boundary deduced from the magnetic field recent studies of the secular variation of the earth s magnetic field over periods of a few centuries have suggested that the pattern of fluid motion near the surface of earth s outer core may be strongly influenced by lateral temperature variations in the lowermost mantle in this paper we introduce a self consistent method for finding the temperature variations near the core surface by assuming that the dynamical balance there is geostrophic and that lateral density variations there are thermal in origin the calculation is accomplished by using the radial and horizontal components of the magnetic field at the core mantle boundary to calculate the fluid flow and its radial derivative near the core surface which are related to the pattern of lateral temperature variations by the thermal wind equation as expected these lateral temperature variations are very small we find some agreement between this pattern and the pattern of topography of the core mantle boundary but are unable to answer conclusively to what extent core surface motions are controlled by the mantle rather than being determined by processes in the core

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

identification of sources of potential fields with the continuous wavelet transform complex wavelets and application to aeromagnetic profiles in french guiana a continuous wavelet technique has been recently introduced to analyze potential fields data first we summarize the theory which primarily consists of interpreting potential fields via the properties of the upward continued derivative field using complex wavelets to analyze magnetic data gives an inverse scheme to find the depth and homogeneity degree of local homogeneous sources and the inclination of their magnetization vector this is analytically applied on several local and extended synthetic magnetic sources the application to other potential fields is also discussed then profiles crossing dikes and faults are extracted from the recent high resolution aeromagnetic survey of french guiana and analyzed using complex one dimensional wavelets maps of estimated depth to sources and their magnetization inclination and homogeneity degree are proposed for a region between cayenne and kourou

lateral variations in mantle velocity structure and discontinuities determined from p pp s ss and ss sds travel time residuals on the basis of p pp s ss arrival times and ss s410s ss s660s differential times we construct models of mantle p and s velocity structure and boundary topography of the 410 km and 660 km discontinuities events from the catalog of the international seismological centre isc are relocated relative to the international association of seismology and physics of the earth s interior 1991 iasp91 velocity model using both p and s arrival times the arrival times are corrected for ellipticity and the pp and ss residuals are corrected for the topography at the bounce point the cap averaged pp p and ss s differential time residuals plotted at the pp and ss surface reflection points form broad coherent patterns the geographic distribution of the cap averaged residuals agrees quite well with pp p and ss s differential time residuals derived from long period global digital seismograph network gdsn data a robust lp inversion scheme is used to infer global mantle structure synthetic tests indicate that for regions well sampled by ss s410s and ss s660s differential times the velocity estimates are not seriously contaminated by the topography of the 410 and 660 km discontinuities however estimates of boundary deflections may be influenced by extensive p and s velocity variations of 3 or greater we find the 410 km discontinuity to be depressed by as much as 24 km beneath north america conversely the discontinuity is deflected upward underneath eurasia in some regions the topography of the 660 km discontinuity is quite distinct from that of the 410 km discontinuity but the two appear to be positively correlated a series of depressions are found at several intersections of the 660 km discontinuity with known subduction zones the elevated topography in the 410 km discontinuity beneath europe is underlain by a trough in the 660 km discontinuity a number of subduction zones are characterized by a thinning of the transition zone negative p and s velocity anomalies underlying back arc basins and tectonically active continental regions encircle the pacific where they are resolved the stable continental cratons are systematically positive velocity features that extend below 200 km with the inclusion of pp and ss travel time residuals we are better able to constrain midmantle structure most notably in the depth range 35 660 km beneath the northwest pacific we observe high p velocity where they are resolved mid ocean ridges are most clearly imaged as low velocity features in the s model the northern portion of the mid atlantic ridge is underlain by negative s velocity anomalies in the pacific the east pacific rise is an extensive low s velocity anomaly

moho topography of the tibetan plateau using multi scale gravity analysis and its tectonic implications abstract determining the moho topography of the tibetan plateau is crucial to understand the tectonic development over the past decades seismic explorations have obtained profound results about the moho topography except in regions where seismic station coverage is poor especially in the central and western tibetan plateau in comparison gravity data have the advantage of global homogeneous coverage which can thus be used to determine the moho structure beneath the entire tibetan plateau in this paper a novel approach the multi scale gravity analysis method is developed to extract the gravity signals originated from the moho undulations and to determine the moho topography beneath the whole tibetan plateau the inverted moho topography for the tibetan plateau is consistent with that derived from the previous works in addition a rich geophysical structure and tectonic development can be revealed from the inverted moho topography 1 the moho depth in the west is deeper than that in the east and the deepest moho which is approximately 77 km is located beneath the western qiangtang block 2 there is an obvious moho offset of approximately 5 km beneath the yarlung zangbo suture at the juncture between the himalayan and lhasa blocks 3 the moho fold and low density channel flow the directions of which are in agreement with the results of surface movement velocities estimated from global positioning system can be observed from the moho topography

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

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

observational evidence of wave ducting and evanescence in the mesosphere a collaborative radar and imaging study of gravity waves over the hawaiian islands was performed during october 1993 as part of the airborne lidar and observations of hawaiian airglow 1993 coupling and dynamics of regions equatorial aloha 93 cadre campaign to investigate the propagation characteristics of short period 1 hour waves at nightglow altitudes the horizontal wavelengths and apparent phase speeds of quasi monochromatic wave events were measured in four separate nightglow emissions using data obtained by a high resolution ccd imager this information was correlated with simultaneous mf radar wind measurements over the same height interval 80 100 km to infer intrinsic wave parameters in each case correlating the two data sets allowed the determination of the local vertical wavenumber for each event in particular whether it be real indicative of freely propagating waves or imaginary indicative of ducted or evanescent waves the results of this study indicate a preponderance of ducted or evanescent waves at 80 100 km during the time of the observations with up to 75 of the events recorded exhibiting ducted or evanescent behavior also noted was a tendency for ducted behavior to be more prevalent among waves with shorter horizontal wavelengths in agreement with doppler ducting theory these results suggest that ducted waves are relatively common in the upper mesosphere and lower thermosphere region at least over the mid pacific ocean as small scale waves which are ducted have the potential to travel much longer horizontal distances than freely propagating waves the frequency of their occurrence should be taken into account in efforts to quantify gravity wave effects at these altitudes

geomagnetic secular variation we analyse over 175000 magnetic observations from an interval spanning 1695 1980 to produce a sequence of maps of the magnetic field at the core mantle boundary we find that even the earlier data enable us to determine reliable maps we produce these maps at approximately 60 year intervals through the eighteenth and nineteenth centuries and at 10 year intervals in the twentieth century this span of maps is long enough to render straightforward the distinction between static and drifting features in the field we observe that some features show no sign whatsoever of drift over the entire 285 year time interval although others drift westwards in particular we observe that the secular variation is very low beneath the pacific ocean but beneath southern africa and the south atlantic ocean we observe rapid secular variation we interpret the morphology of the static field in terms of a simple model of the dynamo and conjecture that interactions between the core and the mantle are an important element of the process as part of the static field we identify four main concentrations of flux two in each hemisphere at high latitudes these features largely account for the earth s axial dipole moment we find unequivocal evidence that magnetic flux has not remained frozen over the time span of our models much of the diffusive behaviour that we identify is associated with the formation of a pair of flux spots a core spot beneath southern africa early in this century nevertheless we are able to construct maps that satisfy a set of necessary conditions for frozen flux and use these maps to construct maps of the core surface fluid flow based on the steady flow hypothesis although we find no strong evidence against the steady flow hypothesis we do find some grounds on which to doubt the validity of the flow maps

medium frequency radar studies of gravity wave seasonal variations over hawaii 22 n 160 w 1 using simple numerical filters estimates of wind variances with period bands of 0 1 to 1 hour and 1 to 5 hours have been derived from data taken with the medium frequency radar on the island of kauai hawaii 22 n 160 w the observations cover altitudes of 70 to 90 km and extend over the years 1990 2000 the results show seasonal and interannual variations of the wind variances which can be attributed to atmospheric gravity waves the mean zonal wind has mainly an annual variation below an altitude of 83 km and a semiannual variation above the gravity waves have maximum intensity at the solstices below 83 km but at higher altitudes the times of the maxima shift to the equinoxes numerical simulations suggest this behavior results from the dependence of gravity wave generation and propagation on the background wind and temperature

a new regional residual separation for magnetic data sets using susceptibility from frequency domain electromagnetic data abstractregional residual separation is a fundamental processing step required before interpreting any magnetic anomaly data numerous methods have been devised to separate deep seated long wavelength regional anomalies from the near surface high frequency residual content such methods range in complexity from simple wavelength filtering to full 3d inversions but most procedures rely on the assumption that all long wavelength anomalies are associated with deep source bodies an incorrect assumption in some geologic environments we evaluated a new method for determining the contributions of near surface magnetic sources using frequency domain helicopter borne electromagnetic hfem data we inverted the in phase and quadrature components of the hfem data to produce an estimate of the spatial variation of magnetic susceptibility using this susceptibility information along with known topography and original survey flight path data we calculated a magnetic intensity grid by forward modeling there ar