the 9th generation international geomagnetic reference field summary the international association of geomagnetism and aeronomy has recently released the 9th generation international geomagnetic reference field the latest version of a standard mathematical description of the earth s main magnetic field used widely in studies of the earth s deep interior its crust and its ionosphere and magnetosphere the coefficients were recently finalized at the xxiii general assembly of the international union of geophysics and geodesy held at sapporo in japan in 2003 july the igrf is the product of a huge collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and from observatories and surveys around the world

variability of the 0 3 ma palaeomagnetic field observed from the boring volcanic field of the pacific northwest the boring volcanic field of the pacific northwest usa composed of more than 80 eruptive units ranging in age from 3200 to 60 ka offers a unique possibility to investigate the variability of the quaternary to late neogene palaeomagnetic field to complement previous work on palaeodirections we conducted 240 absolute palaeointensity api experiments with the joint use of the continuous wilson and stepwise thellier coe double heating protocol along with 620 relative palaeointensity rpi experiments based on the pseudo thellier approach we successfully determined absolute estimates for 12 independent eruptive units as well as relative estimates for 47 out of 132 investigated sites we compare these results with the existing database for the last 3 myr and obtain an estimate of the relative variability in palaeointensity on the order of 40 45 per cent as a proxy for palaeosecular variation api and rpi data suggest a possible asymmetry between normal and reverse polarities

a new towed marine vector magnetometer methods and results from a central pacific cruise summary this paper focuses on new instrumental and methodological aspects of the acquisition processing and interpretation of marine magnetic data between two overhauser sensors towed as a longitudinal gradiometer a new fluxgate vector magnetometer was employed a second independent vector magnetometer system operated simultaneously this equipment was used during research cruise so 180 of r v sonne in the central pacific at about 120 w just south of the equator the survey area on the pacific plate is the mirror image to the currently subducting cocos plate off central america the oceanic crust was formed around 23 ma at the east pacific rise when the farallon plate broke up into the cocos and nazca plates the magnetic seafloor anomalies in the survey area strike approximately north south almost parallel to the main field resulting in very low anomaly amplitudes which had hindered detailed anomaly identification so far a new processing scheme was applied to the data which identifies the weak anomalies in the total field and those in the vertical component that as a consequence of the source body geometry have about doubled amplitude the vertical component constrains 2 d modelling much better than the total field alone processed fluxgate total field data are practically identical to the overhauser reference and even provide a reliable gradient when combined with one overhauser although towed vector magnetometers typically provide no independent estimate of yaw we illustrate that a numerical yaw bandpass filtered magnetic heading can provide reasonable estimates of the horizontal field components these component data open additional analysis tools the strike direction of magnetic lineations can be estimated from single profiles by either magnetic boundary strike ellipses in the space domain or by coherences between vertical and horizontal components in the wavenumber domain auto power spectra of the total field provide an approximate depth to the anomaly source or if in obvious contradiction to the bathymetric depth allow the detection of distortions for example by external temporal geomagnetic variations

geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

fracture apertures from electrical borehole scans three dimensional finite element modeling was performed to investigate the response to fractures of the formation microscanner mark of schlumberger which records high resolution electrical scans of the borehole wall it is found that the equation w carmbrx0l describes over two orders of magnitude of resistivity contrasts between borehole mud and the formation the relationship between fracture width w in mm formation sensitivity rx0 mud resistivity rm and the additional current flow a caused by the presence of the fracture a is the additional current which can be injected into the formation divided by the voltage integrated along a line perpendicular across the fracture trace coefficient c and exponent b are obtained numerically from forward modeling tool standoffs of up to 2 5 mm and fracture dips in the range from 0 to 40 were found to have an insignificant effect on the above relation a three step approach to detect trace and quantify fractures is used potential fractures in formation

using motionally induced electric signals to indirectly measure ocean velocity instrumental and theoretical developments abstract the motion of conductive sea water through the earth s magnetic field generates electromagnetic em fields through a process called motional induction direct measurements of oceanic electric fields can be easily converted to water velocities by application of a first order theory this technique has been shown to obtain high quality velocities through instrumental advances and an accumulation of experience during the past decades em instruments have unique operational considerations and observe for instance vertically averaged horizontal velocity from stationary sensors or vertical profiles of horizontal velocity from expendable probes or autonomous profiling floats the first order theory describes the dominant electromagnetic response in which vertically averaged and vertically varying horizontal velocities are proportional to electric fields and electric currents respectively after discussions of the first order theory and deployment practices operational capabilities are shown through recently published projects that describe stream coordinate velocity structure of the antarctic circumpolar current quickly evolving overflow events in the denmark strait and time development of momentum input into the ocean from a hurricane a detailed analysis of the gulf stream at its separation point from the continental slope serves as a case study for interpreting em measurements including the incorporation of geophysical knowledge of the sediment in addition the first order approximation is tested by the many features at this location that contradict the approximation s underlying assumptions sharp horizontal velocity gradients steep topography and thick and inhomogeneous sediments numerical modeling of this location shows that the first order assumption is accurate to a few percent a few cm s 1 in almost all cases the errors in depth varying velocity are 1 are substantiated by the direct observations and can be corrected by iterative methods though errors in the depth uniform velocity are 1 1 or less in almost all regions of the ocean an error similar to the instrumental accuracy of em instruments

lithostratigraphy of the volcanic sequences at hole 917a leg 152 se greenland margin abstract an overall high recovery rate up to 52 and 450 m of continuous logging data of good quality at odp hole 917a leg 152 se greenland margin allow us to refine the petrological descriptions made onboard and to establish a precise lithostratigraphy of the palaeocene volcanic succession changes in the dips of the flow banding between the upper series and the middle and lower series coincide with the transition from continental magmatism to post breakup volcanism established by the geochemistry

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

the relationship between riverine u series disequilibria and erosion rates in a basaltic terrain u series isotopes have been measured in the dissolved phase suspended load and bedload of the main rivers draining basaltic catchments in iceland for the dissolved phase 234u 238u and 238u 230th range between 1 08 and 2 2 and 7 4 and 516 respectively for the suspended load and bedload 234u 238u and 238u 230th range from 0 97 to 1 09 and from 0 93 to 1 05 respectively chemical erosion rates calculated from dissolved major elements range between 13 and 333 t km 2 yr 1 physical erosion rates have also been estimated from existing data and range between 21 and 4864 t km2 yr with an average of 519 t km 2 yr 1 u series disequilibria indicate that weathering in iceland operates at close to steady state conditions a model of continuous weathering indicates a maximum weathering timescale of 10 kyr with an average rate of uranium release into water of 1 6 10 4 yr 1 which is significant when compared to granitic terrains located at similar latitudes and to tropical basaltic terrains all river waters display 234u 238u greater than secular equilibrium consistent with the effects of alpha recoil the same dissolved phase 234u 238u exhibit a negative trend with physical erosion rates explained by the dominant effect of close to congruent chemical weathering of hyaloclastites in the younger basaltic terrains therefore chemical erosion rate and mineral weathering susceptibility play a major role in determining 234u 238u disequilibria in basaltic river waters comparison of global data for river basins in which weathering was recently strongly limited indicates a negative correlation between silicate weathering rates estimated with major elements and the age of weathering estimated with u series disequilibria this strongly suggests a key role of time and soil thickness on the chemical erosion of silicates

tectonic evolution of the northeastern south china sea from seismic interpretation 1 we interpret a grid of 2 d seismic reflection profiles to resolve the tectonic evolution of the northeastern south china sea scs identifying two significant postbreakup events t1 and t2 which occurred before the end of the scs opening in the absence of the drilling data in the deep basin we date these two events using the identification of the magnetic anomalies the age of major unconformities at ocean drilling program site 1148 drilled on the northeastern scs margin and the age of basalt samples in the deep scs the tectonic phase t1 is a slight tensional tectonic event which occurred in the deep scs south of the luzon ryukyu transform plate boundary lrtpb it is characterized by oceanic tilted blocks and fan shaped deposits which developed 8 10 myr after the onset of scs seafloor spreading 37 8 ma it corresponds to the first ene wsw to e w change in spreading direction which occurred around chron c10 28 7 ma event t2 is a magmatic phase observed in the deep scs south of the lrtpb it is characterized by the uplift of former spreading features caused by an early miocene 22 ma magmatic phase which is also recorded in north and south central taiwan

vertically averaged velocities in the north atlantic current from field trials of a lagrangian electric field float abstract a subsurface lagrangian float that utilizes motional induction to calculate vertically averaged velocities was tested in the north atlantic current nac taking advantage of existing cruises and infrastructure the electric field float eff is a rafos float with horizontal electrodes that measures its own velocity by rafos tracking and calculates vertically averaged velocities when merged with the electrode system the observations showed depth averaged velocities that were fast in the core of the nac 0 6 0 9 m s 1 and moderate in adjacent recirculations and eddies 0 3 0 4 m s 1 a float at 850 dbar moved at close to the depth averaged velocity while shallower floats followed surface intensified flow on top of the depth averaged motion integral time scales of depth averaged velocity 1 3 1 6 0 4 d are slightly shorter than time scales of float velocity 1 6 2 0 0 3 d while integral length scales of depth averaged water velocity 35 10 km for u 18 6 km for v are slightly shorter than length scales of float motion 53 12 km for u 28 6 km for v velocity spectra of depth averaged velocity show significant variance at inertial periods quantitative and qualitative validation with multiple independent data sets confirms the accuracy of the instrument and sampling strategy in the nac advancing the limited observational knowledge of depth averaged circulation in subpolar regions

relocating and orientating cores by the integration of electrical and optical images a case study from ocean drilling program hole 735b while the dip of structural features on recovered rotary drilled core can be accurately measured the azimuth of such features in a geographical reference frame is not known scribing techniques and analysis of magnetic signatures have been used in attempts to solve this problem but scribing has so far failed in deep sea drilling operations and magnetic signatures cannot always be easily resolved here we demonstrate a method for core reorientation and accurate location within a borehole using a comparison between borehole electrical images and whole core digital images odp hole 735b penetrates a 1500 m section of lower oceanic crustal gabbroic rocks with an average core recovery of 86 6 the absence of orientated core pieces severely restricts the interpretation of these data in this study the entire outer surface of individual core pieces was scanned using the dmt digital colour corescan system structural features on these unrolled digital images are correlated with images of the same features on formation microscanner logs obtained during the wireline logging programme using this approach it is possible to reorientate and accurately locate core pieces within the drilled section

multi decadal ingredients of the secular variation of the geomagnetic field insights from long time series of observatory data abstract the temporal evolution of the geomagnetic field is shown on data from 24 observatories with 100 150 years long time series of annual means to be composed of several ingredients which we call the steady the 80 year the 22 year and the 11 year variations the latter is the result of incomplete averaging out in the annual mean of external effects and shows a characteristic 11 year solar cycle related evolution with an amplitude of 10 40 nt in h and z and within 0 05 in d the other three characterize the main field while the steady variation carries the largest part of the main field and is smoothly increasing or decreasing in time the 80 year variation shows changes with amplitudes amounting to several hundred nt in the intensity components h and z and of 0 2 0 7 in declination the 22 year variation changes with much smaller amplitudes of 20 60 nt in h and somewhat larger in z 20 100 nt and of about 0 05 0 15 in d the analysis of the first time derivative of declination for the 24 study observatories showed that the 80 year variation dominated the secular variation in the last 100 years and that the 22 year variation has gotten its importance in defining the time evolution of the first time derivative of declination jerks included since 1960 the external contribution is decisive though in establishing the very short time scale characterizing jerks and to some extent also the amplitude and timing of the jerk the analysis of 400 years long declination time series from three european locations london munich rome resulted in tracing back of the 80 year variation to the 15th century and showed that what we called steady variation based on 150 years of observatory data proves to be only a part of a larger timescale variation when 400 years of data are available according to our results the term jerk loses its presently accepted meaning of sudden change in the temporal evolution of secular variation a more complex concept in describing the secular variation of the main field namely the superposition of several quasi periodic effects corresponding to specific core processes at various time scales should be used instead

a time dependent model of the earth s magnetic field and its secular variation for the period 1980 2000 1 this study presents an investigation and description of the secular variation of the earth s magnetic field between 1980 and 2000 a time dependent model c3fm continuous covariant constrained endpoints field model of the main field and its secular variation between 1980 and 2000 is developed with gauss coefficients expanded in time on a basis of cubic b splines this model is constrained to fit field models from high quality vector measurements of magsat in 1980 and orsted in 2000 and to fit both magnetic observatory and repeat station secular variation estimates for the period in between these secular variation estimates first time derivatives are derived from observatories monthly or annual means and repeat station data in order to reduce the contributions of crustal noise annual and semiannual variation on average the model input consists secular variation estimates of the x y and z components at 130 locations per month treatment of covariance between the different components allows a higher temporal sensitivity of the model due to the exclusion of some external field variation the model is computed up to degree and order 15 the model is a useful extension of the hitherto existing time dependent description of the secular variation gufm which describes the secular variation until 1990 it reveals a short term secular variation on subdecadal timescale and has a higher spatial resolution than previously resolved the model is also valuable to test the frozen flux hypothesis and to link features of the radial field at the core mantle boundary to the geodynamo

can core surface flow models be used to improve the forecast of the earth s main magnetic field 1 geomagnetic main field models used for navigation are updated every 5 years and contain a forecast of the geomagnetic secular variation for the upcoming epoch forecasting secular variation is a difficult task the change of the main magnetic field is thought to be principally due to advection of the field by flow at the surface of the outer core on short timescales and when large length scales are considered with accurate secular variation sv and secular acceleration sa models now available from new satellite missions inverting for the flow and advecting it forward could lead to a more accurate prediction of the main field however this scheme faces two significant challenges the first arises from the truncation of the observable main field at spherical harmonic degree 13 this can however be handled if the true core flow is large scale and has a rapidly decaying energy spectrum the second is that even at a given single epoch the instantaneous sv and sa cannot simultaneously be explained by a steady flow nevertheless we find that it may be feasible to use flow models for an improved temporal extrapolation of the main field a medium term 10 years hindcast of the field using a steady flow model outperforms the usual extrapolation using the presently observed sv and sa on the other hand our accelerated toroidal flow model which explains a larger portion of the observed average sa over the 2000 2005 period fails to improve both the short term and medium term hindcasts of the field this somewhat paradoxical result is related to the occurrence of so called geomagnetic jerks the still poorly known dynamical nature of which remains the main obstacle to improved geomagnetic field forecasts

tectonics of the southern tip of the parece vela basin philippine sea plate we report new geophysical and petrological data collected at the southern tip of the parece vela basin in the philippine sea the parece vela basin which was formed as a backarc basin behind proto mariana arc trench system from late oligocene to middle miocene provides us a good opportunity to study the nature of successive backarc basin formations in the philippine sea and the relationship between are and backarc magmatisms regional bathymetric map derived from satellite altimetry shows that the southern tip of the basin now located just west of the yap arc trench system has unique morphological and tectonic features which include 1 the absence of spreading center or its trace 2 shallow average depth and 3 enigmatic curved structures our newly collected high resolution bathymetric data reveal that the spreading fabric similar to the central parece vela basin exists to the north of 9 degrees 20 n thus it appears that the present day yap arc and backarc region represent the western half of the seafloor that was produced by the early e w and the following ne sw spreading in the northern and central parece vela basin and that the eastern counterpart now lies west of the west mariana ridge unlike the northern parece vela basin there appears to be no evidence for a systematic propagation of spreading center in the southern part instead two rift segments one which extends from the central parece vela basin and the other which lies within the western remnant arc kyushu palau ridge overlap at the southern tip of the basin producing a complex seafloor that includes curvilinear deeps and deformed topographic highs c 2007 elsevier b v all rights reserved

emag2 a 2 arc min resolution earth magnetic anomaly grid compiled from satellite airborne and marine magnetic measurements 1 a global earth magnetic anomaly grid emag2 has been compiled from satellite ship and airborne magnetic measurements emag2 is a significant update of our previous candidate grid for the world digital magnetic anomaly map the resolution has been improved from 3 arc min to 2 arc min and the altitude has been reduced from 5 km to 4 km above the geoid additional grid and track line data have been included both over land and the oceans wherever available the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation based on an oceanic crustal age model the longest wavelengths 330 km were replaced with the latest champ satellite magnetic field model mf6 emag2 is available at http geomag org models emag2 and for permanent archive at http earthref org cgi bin er cgi s erda cgi n 970

magmatic activities on the southwest indian ridge between 35 e and 40 e the closest segment to the marion hotspot 1 we conducted geophysical surveys including bathymetry gravity and magnetism within a first order segment of the southwest indian ridge swir between the prince edward and eric simpson fracture zones fzs latitude 35 40 e segment pe in the vicinity of the marion hotspot segment pe includes four orthogonally spreading second order segments pe 1 pe 2 pe 3 and pe 4 and a long oblique axial valley ntd 1 segments pe 1 pe 2 and pe 4 are magmatic whereas segment pe 3 and ntd 1 are characterized by low magmatic activity segment pe 3 is a nascent segment and ntd 1 contains three tiny magmatic sections each low magmatic interval along the axis of segment pe lies between two magmatic segments this segmentation pattern is similar to the swir between the gallieni and melville fzs therefore a strong melt focusing process can be expected different characteristics of second order magmatic segments suggest that the magmatic activity in each segment varies among each other as well as that of the other segments of swir continuous seafloor morphology and isochrons over off axis areas of segment pe 1 and ntd 1 suggest that pe 1 shortened after the c2an chron the v shaped bathymetric structure between segment pe 1 and ntd 1 suggests that the melt supply center has migrated westward this westward melt migration would have reduced magmatic activity at ntd 1 after c2an ridge obliquity may also have reduced magmatic activity geophysical characteristics of second order segments suggest that magmatic activity of segment pe is mainly controlled by a strong melt focusing process and a comparatively low contribution of melt supply from marion hotspot

geomagnetic secular variation of bransfield strait western antarctica from analysis of marine crossover data summary tracking the secular variation of the geomagnetic field in the past is severely limited in some cases by factors relating to the remoteness of the sites this is maximal in the antarctic where the remote location and severe climate lead to logistic limitations that make it difficult to keep a continuous record of magnetic field variations from the magnetic information available from historical marine expeditions it is possible to infer this time varying component from the comparison of readings at crossovers this study focuses on this technique discusses the impact of the different error sources and proposes a simple mathematical procedure to infer average secular variation rates the result is validated by comparing it with local data from the arctowski and livingston magnetic observatories sited in the area additionally using a high quality data set from a local area in the neighbourhood of deception island we have detected a systematic distribution in its secular variation this dichotomy has been interpreted in terms of a volcano magnetic signal this fact and the nature of its principal mechanisms are analysed and discussed

a historical declination curve for munich from different data sources abstract long series of geomagnetic field changes are important for studying processes in the earth s core we have compiled 635 historical declination values for southern germany and surrounding areas indirect estimations including the oldest ones from back in the 15th century come from 185 sundials and compasses with declination information and 15 historical maps measurements carried out by monks in the time interval 1668 1854 amount to 122 annual mean values and data related to the orientation of mine shafts contributes by 313 annual values for several locations all these data can be useful to improve historical geomagnetic field models previously compiled german church orientations however are shown to be no reliable sources of the past declination the compiled new declination curve for munich shows general agreement with previously published curves for london and paris and allows to detect geomagnetic jerks with a temporal uncertainty of 10 years more or less regular impulses on a decadal time scale ranging from 30 to 60 years are identified for most of the time interval 1400 2000 but the century from about 1760 to 1860 seems to be devoid of sudden secular variation changes

magnetic structure of an oceanic core complex at the southernmost central indian ridge analysis of shipboard and deep sea three component magnetometer data 1 we investigated the magnetic structure of an oceanic core complex occ at the southernmost central indian ridge cir near 25 s on the basis of newly collected magnetic and bathymetric data and submersible dives the occ is located off axis on the western flank of the cir and is characterized by typical megamullion morphology with flow line parallel corrugations the occ is similar in size to those found along the mid atlantic ridge mar but the cir occ formed in an estimated 0 8 ma which is slightly shorter than the average time for the formation of occs along the mar the magnetization intensity over the cir occ is quite weak compared to that over adjacent seafloor of the same age mostly gabbroic rocks were recovered from outcrops during submersible dives fault rocks were also recovered from the corrugated surface suggesting that the occ surface represents the plane of a detachment fault although the magnetization intensity is rather low we were able to identify the brunhes matuyama boundary and the jaramillo and olduvai subchrons on and around the occ using vector magnetic analysis over the occ the jaramillo subchron which cannot be recognized from magnetic data acquired at the sea surface was identified using data from a magnetometer attached to a submersible the locus of this subchron is consistent with that observed over the seafloor adjacent to the occ combining the results of magnetic survey and rock sampling we would like to point out the possibility that the gabbroic rocks constituted the occ and preserved seafloor spreading history although there are several interpretations of the low magnetization

ergodicity of the recent geomagnetic field the geomagnetic field is a fundamental property of our planet its study would allow us to understand those processes of earth s interior which act in its outer core and produce the main field knowledge of whether the field is ergodic i e whether time averages correspond to phase space averages is an important question since if this were true it would point out a strong spatio temporal coupling amongst the components of the dynamical system behind the present geomagnetic field generation another consequence would be that many computations usually undertaken with many difficulties in the phase space can be made in the conventional time domain we analyse the temporal behaviour of the deviation between predictive and definitive geomagnetic global models for successive intervals from 1965 to 2010 finding a similar exponential growth with time also going back in time at around 1600 and 1900 by using the gufm1 model confirms the same findings this result corroborates previous chaotic analyses made in a reconstructed phase space from geomagnetic observatory time series confirming the chaotic character of the recent geomagnetic field with no reliable prediction after around 6 years from definitive values and disclosing the potentiality of estimating important entropic quantities of the field by time averages although more tests will be necessary some of our analyses confirm the efforts to improve the representation of the geomagnetic field with more detailed secular variation and acceleration

architecture of the volcanic layer from the costa rica rift constraints from core log integration 1 an understanding of the architecture of the ocean crust s volcanic layer is critical since this records the variations in volcanic activity during formation and subsequently controls the movement of hydrothermal fluids through this layer unfortunately core recovery in the majority of ocean drilling program odp deep sea drilling program basement holes is generally low and biased toward more massive lithologies consequently the identification and estimation of lithological diversity within the volcanic layer is only possible through the integration of core and wire line logging results wire line logging provides nearly continuous records of both physical and chemical properties of the borehole wall which can be used to identify the various volcanic sedimentary lithologies which then can be calibrated in regions of enhanced core recovery using this approach the architecture of the volcanics from odp hole 896a has been reconstructed this new model illustrates a hiatus in volcanism marked by a thick breccia horizon which probably marks the transition from axis to off axis volcanism

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined