geoforschungszentrum anomaly magnetic map gamma a candidate model for the world digital magnetic anomaly map the world digital magnetic anomaly map wdmam is an ongoing effort toward the mapping of worldwide available aeromagnetic data it is led by a task force of the international association for geomagnetism and aeronomy iaga and aims at distributing a global map in printed and digital forms in this paper we describe in detail our candidate model which has to be evaluated by the iaga task force together with five other candidate maps after discussing the quality of the available data we show a simple but effective method applied to successfully process reduce and merge together individual compilations the near surface data are corrected using global field models and further refined with two dimensional polynomial corrections after the upward continuation to 5 km altitude data are resampled to a 3 minute grid and merged together we then calculate a spherical harmonic model up to degree 199 and analyze the magnetic spectrum of the global map this helps us to confirm that wavelengths larger than 400 km are spurious at a global scale in aeromagnetic compilations therefore we substitute them using a satellite based lithospheric field model mf5 to degree 100 finally our proposed candidate map for wdmam is presented

tectonic history of the north portion of the san andreas fault system california inferred from gravity and magnetic anomalies geologic and geophysical data for the san andreas fault system north of san francisco suggest that the eastern boundary of the pacific plate migrated eastward from its presumed original position at the base of the continental slope to its present position along the san andreas transform fault by means of a series of eastward jumps of the mendocino triple junction these eastward jumps total a distance of about 150 km since 29 ma correlation of right laterally displaced gravity and magnetic anomalies that now have components at san francisco and on the shelf north of point arena indicates that the presently active strand of the san andreas fault north of the san francisco peninsula formed recently at about 5 ma when the triple junction jumped eastward a minimum of 100 km to its present location at the north end of the san andreas fault prior to 5 ma the triple junction was located at the north end of a proposed northwesterly extension of the pilarcitos fault this jump took place at what is now about latitude 38 20 n on the north american plate and may have occurred during part of the time when the relative motion between the north american and pacific plates rotated 20 clockwise resulting in transpression along the earlier transcurrent san andreas fault system the proposed 150 km eastward movement of the triple junction explains the submarine topography near cape mendocino where the continental shelf south of the mendocino fault extends about 130 km farther west than does the shelf directly north of the fault

new way of processing near surface magnetic data the utility of the comprehensive model of the magnetic field in assembling near surface magnetic surveys e g airborne or marine data for regional geologic studies one often has a problem in properly merging different surveys without applying ad hoc leveling methods or warping the long wavelengths of individual data sets a new comprehensive long wavelength and long time span magnetic field model based on satellite and observatory data may at last resolve this problem the model the comprehensive model cm is developed by terry sabaka of raytheon itss nasa and nils olsen of the danish space research institute the present version of the model cm3 incorporates data from magnetic field satellites pogo 1965 1970 magsat 1979 1980 orsted 2000 to present and champ 2001 to present and magnetic observatory data from the early 1960s to 2002

compatibility of high altitude aeromagnetic and satellite altitude magnetic anomalies over canada results from equivalent source distributions derived jointly from high altitude average 4 km aeromagnetic and magsat derived average 400 km magnetic anomalies over canada indicate that long wavelength components 500 2500 km in these fields are extremely compatible with one another with a correlation coefficient of 0 95 the jointly estimated anomaly field at the earth s surface can be used as a long wavelength adjustment surface for regional near surface magnetic anomaly compilations and in assessing the performance of other downward continuation techniques because near surface anomalies are not available over all regions of the world we compare the jointly estimated anomaly field to the results of two different downward continuation techniques the evaluation of anomalies at the earth s surface from spherical harmonic coefficients derived from satellite altitude data and the use of downward continuation methods based on harmonic splines numerical and visual comparisons of these downward conti

making ends meet in gondwana retracing the transforms of the indian ocean and reconnecting continental shear zones interpretation of the detailed patterns of ocean floor transforms revealed by satellite altimetry enables the creation of the indian ocean to be described quantitatively as four consecutive plate tectonic regimes separated at 200 136 89 and 43 ma each regime is reversed in turn by keeping transform termini coincident and colinear until conjugate points on the margins of pre existing plates regain their pre regime integrity progressive elimination of the indian ocean demonstrable as a smooth computer animation http www kartoweb itc nl gondwana leads to a refined re assembly of the continental fragments of central gondwana that is substantiated by new geological data a sequence of euler interval poles that describes the dispersal of the gondwana fragments time calibrated against available magnetic anomaly data is given the model requires a mid cretaceous position for india s southern tip about 1000 km south of madagascar prior to india s rapid northward migration

downward continuation of magsat lithospheric anomalies to the earth s surface summary the assumed lithospheric component of magsat data is downward continued to the earth s surface over continental sized areas using the depleted basis method with a regularizing constraint parker shure 1982 to make the problem numerically tractable and stable respectively the depleted basis is arranged to have a high density of points over the area of interest lower elsewhere all three components at satellite altitudes are used in the inversion for three orthogonal components at the earth s surface edge effects are seen if the depleted basis changes rapidly from a high to low spatial density which are eliminated by inserting a region of intermediate density basis points the downward continued field fits the data to within their probable uncertainties regularizing the solution produces a much smoother solution for very little increase in misfit some of the anomalies in the downward continued field over africa correlate with known tectonic features although the relationship between magnetic highs or lows and basins or cratons is not clear cut this magsat derived downward continued field can be used to control the longer wavelength component of the crustal magnetic field that is not defined by aeromagnetic surveys the method is illustrated on an aeromagnetic compilation of about 30 surveys from south africa however there is a mismatch in amplitudes between the aeromagnetic data and downward continued magsat data

subsurface imaging of the harrat lunayyir 2007 2009 earthquake swarm zone western saudi arabia using potential field methods abstract the harrat lunayyir hl 2007 2009 earthquake swarm has attracted much scientific interest mainly due to its occurrence within the large igneous province lip of saudi arabia qualitative interpretation of aeromagnetic anomalies is suggestive of linear dike like anomalies striking nw se across the earthquake swarm zone esz residual bouguer anomaly data for hl range between 4 3 and 1 5 mgal and show a 20 km wide gravity low flanked by lateral gravity highs the axial zone of low gravity corresponds to the esz cluster employing a three dimensional 3d inversion of the residual gravity field with a one dimensional 1d p wave velocity model as a proxy for background density variations with depth we imaged a mid to upper crustal low density zone 10 km depth we interpret this zone as the source area of ascending magma that intruded into the upper crust underlying the hl during the 2009 seismic crisis the inversion also highlights lower than average density rocks beneath the western parts of the hl whereas its eastern part is composed of rocks of higher density the 3d magnetic inversions lead us to infer magmatic intrusion of lower magnetic susceptibility at this locality extending vertically from 1 57 km altitude above sea level to its bottom edge at 10 8 km depth below sea level based on these results the 2007 2009 esz is likely associated with rift related extension associated with the red sea spreading where a trans crustal magmatic plumbing system extends to depths of about 10 km beneath the centre of hl

earth s lithospheric magnetic field determined to spherical harmonic degree 90 from champ satellite measurements summary the champ magnetic field mission is providing highly reliable measurements from which the global lithospheric magnetic field can be determined in unprecedented resolution and accuracy using almost 5 yr of data we derive our fourth generation lithospheric field model termed mf4 which is expanded to spherical harmonic degree and order 90 after subtracting from the full magnetic field observations predicted fields from an internal field model up to degree 15 an external field model up to degree two and the predicted magnetic field signatures for the eight dominant ocean tidal constituents we fit and remove remaining external fields and polar electrojet signatures in a track by track scheme from a subset of least disturbed tracks we estimate the mf4 model by least squares damping ill determined coefficients by regularization the resulting mf4 model provides a good representation of the lithospheric field down to an altitude of about 50 km at lower latitudes with reduced accuracy in the polar regions crustal features come out significantly sharper than in previous models in particular bands of magnetic anomalies along subduction zones become visible by satellite for the first time

the geomagnetic power spectrum summary combining champ satellite magnetic measurements with aeromagnetic and marine magnetic data the global geomagnetic field has now been modelled to spherical harmonic degree 720 an important tool in field modelling is the geomagnetic power spectrum it allows the comparison of field models estimated from different data sets and can be used to identify noise levels and systematic errors a correctly defined geomagnetic power spectrum is flat white for an uncorrelated field such as the earth s crustal magnetic field at long wavelengths it can be inferred from global spherical harmonic models as well as from regional grids marine and aeromagnetic grids usually represent the anomaly of the total intensity of the magnetic field appropriate corrections have to be applied in estimating the geomagnetic power spectrum from such data the comparison of global and regional spectra using a consistently defined azimuthally averaged geomagnetic power spectrum facilitates quality control in field modelling and should provide new insights in magnetic anomaly interpretation

a combined study of macroseismic data and focal mechanisms applied to the west bohemian earthquake czechoslovakia the main shock of the west bohemian earthquake swarm czechoslovakia magnitudem 4 5 depthh 10 km exhibits an irregular areal distribution of macroseismic intensities 6 to 7 msk 64 four lobes of the 6 isoseismal are found and the maximum observed intensity is located at a distance of 8 km from the instrumentally determined epicentre this distribution can be explained by the energy flux of the directs wave generated by a circular source the hypocentral location and focal mechanism of which are taken from independent instrumental studies the theoretical intensity which is assumed to be logarithmically proportional to the integrated squared ground motion velocity i e i const log v2 t dt fits the observed intensity with an overall root mean square error less than 0 5 it is important that the present intensity data can also be equally well explained by the isotropic source the fit was attained by means of a horizontally layered model though large fault zones and an extended sedimentary basin suggest a significant lateral heterogeneity of the epicentral region the results encourage a broader application of the simple modelling technique used

magnetic anomaly map for northern western and eastern europe all of the available data describing the earth s magnetic field in northern western and eastern europe c 3 106 data points are compiled and presented at a scale of 1 20 400 000 the compilation meets two requirements i that the total field intensity anomalies reflect a survey acquired at an altitude of 3000 m above m s l and during the same epoch 1980 0 and ii that the anomalies are residuals after subtracting the common reference field dgrf1980 as the data span many epochs geomagnetic data recorded at observatories and repeat stations were used to determine the best model for estimating the secular variation in all data up to 1980 this yielded magnetic anomalies with wavelengths up to the order of 2000 km the precision of the resultant anomalies amplitudes about 1700 nt to 8000 nt differ between 10 nt in central europe and 20 nt in the outer parts of the compilation the resultant anomaly map contains a wealth of information to geoscientists studying global tectonic processes and the deep crustal composition of major continental crusts it clearly shows the different anomaly patterns between the palaeozoic and precambrian crusts of central and eastern europe these anomalies are interpreted as lateral changes of magnetization in a horizontal plate a comparison between the low level compilation and maps derived from the magsat satellite at about 360 km altitude allows the description of the two different crust types in europe

approximating edges of source bodies from magnetic or gravity anomalies cordell and grauch 1982 1985 discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks the final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes we attempt to automate their final step our method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources the method applies to both local surveys and to continent wide compilations of magnetic and gravity data e g zietz 1982 simpson et al 1983a kane et al 1982

fifth generation lithospheric magnetic field model from champ satellite measurements 1 six years of low orbit champ satellite magnetic measurements have provided an exceptionally high quality data resource for lithospheric magnetic field modeling and interpretation here we describe the fifth generation satellite only magnetic field model mf5 the model extends to spherical harmonic degree 100 as a result of careful data selection extensive corrections filtering and line leveling the model has low noise levels even if evaluated at the earth s surface the model is particularly suited for inferring large scale structure and composition of the lithosphere it is also meant to serve as the long wavelength part of continental and global scale marine and aeromagnetic anomaly maps

magnetic anomaly map of the world merging satellite airborne marine and ground based magnetic data sets abstract we report here a simple but practical method to combine systematically the magnetic surveys of disparate specifications from marine ground aeromagnetic and satellite platforms that aims to be helpful in the framework of the world digital magnetic anomaly map project because the satellite coverage and data quality is more uniform than near surface surveys it is adopted as the base map for wavelengths larger than 400 km and up to spherical harmonic degree inclusive of 16 2500 km after checking that satellite models and large aeromagnetic wavelengths are not consistent we filter out wavelengths longer than 400 km in aeromagnetic compilations existing regional grids and when available individual surveys are merged to give a more uniform spatial variation of the magnetic anomalies the effects of merging the grids are examined by plotting profiles and difference maps of the overlapping regions a preliminary global map is obtained after combining the magnetic anomaly map with the downward continued champ satellite derived magnetic anomaly map forthcoming availability of new datasets as well as improvements in the procedure will help to produce increasingly reliable maps

vertical sediment distribution so far various calculation models for the vertical distribution of suspended sediment concentration have been produced by several investigators from different theories the limitations of all these models imply that it is possible to find a more reasonable model for which each previous model can be included as special case the formulation of a reasonable general model is the purpose of this paper

new aeromagnetic data reveal large strike slip faults in the northern willamette valley oregon high resolution aeromagnetic data from the northern willamette valley oregon reveal large northwest striking faults buried beneath quaternary basin sediments several faults known from geologic mapping are well defined by the data and appear to extend far beyond their mapped surface traces the mount angel fault the likely source of the richter magnitude m l 5 6 earthquake in 1993 is at least 55 km long and may be connected in the subsurface with the gales creek fault 25 km farther northwest northeast of the mount angel fault a 60 km long northwest striking anomaly may represent a previously unrecognized dextral slip fault beneath the towns of canby and molalla vertical offsets along the mount angel fault increase with depth indicating a long history of movement for the fault dominantly northwest trending relatively straight faults consistent stepover geometries offset magnetic anomalies and earthquake focal mechanisms suggest that these faults collectively accommodate significant dextral slip the 1993 earthquake may have occurred on a left stepping restraining bend along the mount angel gales creek fault zone

a global lithospheric magnetic field model with reduced noise level in the polar regions 1 due to persistent ionospheric current systems at high latitudes satellite magnetic measurements have high noise levels in the polar regions consequently small scale lithospheric features are much more difficult to resolve there than at lower latitudes using linear combinations of spherical harmonics sh we define localized functions which are band limited to a given maximum degree thus a model s sh resolution can be varied over the globe we produce a lithospheric field model from champ satellite data which resolves features to sh degree 90 at low latitudes but only to sh degree 60 in the polar regions the new model can be downward continued from satellite altitude to the earth s surface without generating spurious high latitude anomalies citation lesur v and s maus 2006 a global lithospheric magnetic field model with reduced noise level in the polar regions geophys res lett 33 l13304

extending comprehensive models of the earth s magnetic field with orsted and champ data summary a new model of the quiet time near earth magnetic field has been derived using a comprehensive approach which includes not only pogo and magsat satellite data but also data from the orsted and champ satellites the resulting model shows great improvement over its predecessors in terms of completeness of sources time span and noise reduction in parameters with its well separated fields and extended time domain of 1960 to mid 2002 the model is able to detect the known sequence of geomagnetic jerks within this frame and gives evidence for an event of interest around 1997 because all sources are coestimated in a comprehensive approach intriguing north south features typically filtered out with other methods are being discovered in the lithospheric representation of the model such as the s atlantic spreading ridge and andean subduction zone lineations in addition this lithospheric field exhibits significantly less noise than previous models as a result of improved data selection the f region currents through which the satellites pass are now treated as lying within meridional planes as opposed to being purely radial results are consistent with those found previously for magsat but an analysis at orsted altitude shows exciting evidence that the meridional currents associated with the equatorial electrojet likely close beneath the satellite besides the model a new analysis technique has been developed to infer the portion of a model parameter state resolved by a particular data subset this has proven very useful in diagnosing the cause of peculiar artefacts in the magsat vector data which seem to suggest the presence of a small misalignment bias in the vector magnetometer

third generation of the potsdam magnetic model of the earth pomme the potsdam magnetic model of the earth pomme is a geomagnetic field model providing an estimate of the earth s core crustal magnetospheric and induced magnetic fields the internal field is represented to spherical harmonic sh degree 90 while the secular variation and acceleration are given to sh degree 16 static and time varying magnetospheric fields are parameterized in geocentric solar magnetospheric gsm and solar magnetic sm coordinates and include disturbance storm time dst index and interplanetary magnetic field imf by dependent contributions the model was estimated from five years of champ satellite magnetic data all measurements were corrected for ocean tidal induction and night side ionospheric f region currents the model is validated using an independent model from a combined data set of orsted and sac c satellite measurements for the core field to sh degree 13 the root mean square rms vector difference between the two models at the center of the model period is smaller than 4 nt at the earth s surface the rms uncertainty increases to about 100 nt for the predicted field in 2010 as inferred from the difference between the two models

national geophysical data center candidate for the world digital magnetic anomaly map marine and airborne magnetic anomaly data have been collected for more than half a century providing global coverage of the earth furthermore the german champ satellite is providing increasingly accurate information on large scale magnetic anomalies the world digital magnetic anomaly map project is an international effort to integrate all available near surface and satellite magnetic anomaly data into a global map database teams of researchers were invited to produce candidate maps using a common pool of data sets here we present the national geophysical data center ngdc candidate to produce a homogeneous map the near surface data were first line leveled and then merged by least squares collocation long wavelengths were found to agree surprisingly well with independent satellite information this validates our final processing step of merging the short wavelength part of the near surface data with long wavelength satellite magnetic anomalies

the satellite along track analysis in planetary magnetism summary many physical characteristics of planets such as their topography magnetic and gravitational fields are routinely detected and measured by spacecrafts at satellite altitudes even if little is known about the measured signal it is possible to separate the large scale components from other contributions by a spectral analysis carried out along the spacecraft orbit this procedure which dates back to the early age of the satellite era is routinely applied with spherical harmonics analysis for the study of large scale planetary magnetic fields particularly those that vary rapidly in time in this paper we review the approximations of this procedure for investigating internal and external magnetic fields of planets we show that the magnetic field analyses along the orbits are limited by a finite frequency resolution that is known to introduce a spectral leakage this leakage may lead to artificial spatio temporal variations of the magnetic field such as an apparent internal field secular variation an asymmetry of the magnetospheric field and a regional distortion of the lithospheric field structures we quantify the errors for the earth s lithospheric field and display its distribution in the spatial and the spectral domains we also discuss these limits for the moon and mars lithospheric magnetic fields our analytical results illustrate the pros and cons of the orbit by orbit analyses and should allow us to avoid the pitfall of geophysical overinterpretation of some artificial magnetic field variations

aeromagnetic evidence for a volcanic caldera complex beneath the divide of the west antarctic ice sheet a 1995 96 aeromagnetic survey over part of the sinuous ridge sr beneath the west antarctic ice sheet wais divide shows a 70 km diameter circular pattern of 400 1200 nt anomalies suggesting one of the largest volcanic caldera complexes on earth radar ice sounding ris shows the northern part of this pattern overlies the sr and extends south over the bentley subglacial trench bst modeled sources of all but one the caldera anomalies are at the base of 1 2 km thick ice and their volcanic edifices have been glacially removed the exception is a 700 m high 15 km wide volcano producing an 800 nt anomaly over the bst intrusion of this volcano beneath 3 km of ice probably resulted in pillow basalt rather than easily removed hyaloclastite erupted beneath thinner ice the background area 300 to 500 nt surrounding the caldera is possibly caused by a shallow curie isotherm we suggest uplift of the sr forced the advance of the wais