surface destabilisation by the invasive burrowing engineer mus musculus on a sub antarctic island abstract invasive species are known to have substantial trophic effects on ecosystems and ecosystem processes the invasion of the house mouse mus musculus onto sub antarctic islands has had a devastating effect on plants invertebrates and birds with substantial changes in ecosystem functions less well understood however are the nontrophic geomorphic effects of mice resulting from their burrowing activities we examined the extent of burrow construction by m musculus across an area of about 20 ha on marion island and the effects of burrows on water flow and sediment movement we recorded a density of 0 59 0 48 mean sd burrows m 2 with more burrows at lower altitudes and shallower slopes and twice the density in the solifluction risers 0 86 0 54 m 2 than the intervening terraces or treads 0 40 0 51 m 2 most burrows were dug horizontally into the slope and tended to extend about 20 cm deep before turning a very conservative estimate of sediment removed from burrows from this depth is 2 4 t ha 1 however taking into account more detailed data on burrow morphology based on excavations actual amounts may be closer to 8 4 t ha 1 average soil displacement rate for a single burrow measured over 5 days was 0 18 kg burrow 1 day 1 burrows acted as conduits for water and warmer air stones at burrow entrances were moved eight times farther by water 10 4 cm than those not associated with burrows similarly temperatures adjacent to burrow entrances were 4 1 c higher than sites 10 cm away together our data indicate that mice are having substantial deleterious and geomorphic effects on sub antarctic ecosystems through their burrowing with lower rates of mouse mortality resulting from warmer climates predicted under global climate models we can expect an increase in damage resulting from mouse activity

estimation of rock physics properties from seismic attributes part 2 applications abstractthe estimation of quantitative rock physics properties is of great importance for reservoir characterization and monitoring in co2 storage or enhanced oil recovery as an example we have combined the high resolution results of full waveform inversion fwi methods with rock physics inversion because we consider a generic and dynamic rock physics model our method is applicable to most kinds of rocks for a wide range of frequencies the first step allows determination of viscoelastic effective properties i e quantitative seismic attributes whereas the rock physics inversion estimates rock physics properties porosity solid frame moduli fluid phase properties or saturation this two step workflow is applied to time lapse synthetic and field cases the sensitivity tests that we had previously carried out showed that it can be crucial to use multiparameter inputs to accurately recover fluid saturations and fluid properties however due to the limited data availability and difficulties in get

elastic full waveform inversion of multi component obc seismic data elastic full waveform inversion of seismic reflection data represents a data driven form of analysis leading to quantification of sub surface parameters in depth in previous studies attention has been given to p wave data recorded in the marine environment using either acoustic or elastic inversion schemes in this paper we exploit both p waves and mode converted s waves in the marine environment in the inversion for both p and s wave velocities by using wide angle multi component ocean bottom cable seismic data an elastic waveform inversion scheme operating in the time domain was used allowing accurate modelling of the full wavefield including the elastic amplitude variation with offset response of reflected arrivals and mode converted events a series of one and two dimensional synthetic examples are presented demonstrating the ability to invert for and thereby to quantify both p and s wave velocities for different velocity models in particular for more realistic low velocity models including a typically soft seabed an effective strategy for inversion is proposed to exploit both p and mode converted ps waves whilst p wave events are exploited for inversion for p wave velocity examples show the contribution of both p and ps waves to the successful recovery of s wave velocity

scalar magnetic anomaly maps of earth derived from pogo and magsat data a new pogo scalar magnetic anomaly map at 400 km altitude is presented which consists of spherical harmonics of degree 15 60 on the basis of the common features of this map with two new magsat anomaly maps dawn and dusk two scalar magnetic anomaly maps of the earth are presented using two selection criteria with different levels of stringency these selection criteria suppress the noncrustal components of the original maps by different amounts the more stringent selection criteria seek to eliminate as much contamination as possible at the expense of suppressing some anomaly signal this map is represented by spherical harmonics of degree 15 60 the less stringent selection criteria seek to retain as much crustal signal as possible at the expense of also retaining some contaminating fields this map is represented by spherical harmonics of degree 15 65 the resulting two maps are highly correlated with degree correlation coefficients greater than 0 8

three dimensional seismic full waveform inversion using the finite difference contrast source inversion method we present the extension of the so called finite difference contrast source inversion method for the three dimensional interpretation of full waveform seismic data using the acoustic approximation the finite difference contrast source inversion method does not simulate a full forward problem in its inversion process hence it is computationally more efficient than the standard non linear inversion methods furthermore it allows the use of an inhomogeneous background medium hence this method has a great potential for carrying out time lapse seismic inversion however the price that we have to pay is the storing of the lu decomposition arrays of the impedance matrix of the background medium we show some numerical examples to illustrate the dis advantages of this method

3 d modelling and analysis of dst c responses in the north pacific ocean region revisited summary during the last decade a number of one dimensional 1 d conductivity profiles have been constructed for the upper and mid mantle of the north pacific ocean region these profiles differ significantly and from our point of view it is still unclear which profile is the best candidate for the upper and mid mantle conductivity reference model for this region keeping the differences in mind and inspired by recent findings that the ocean effect is a major contributor to the anomalous behaviour of c responses up to the period of 20 days especially at coastal observatories the goal of this paper has been three fold 1 to understand on the basis of systematic model studies using 3 d ocean models which of the published 1 d upper and mid mantle profiles is in best agreement with the available observations 2 to try to reduce the misfit between the observed and modelled responses by using dense grids in modelling by considering 3 d models which include not only an inhomogeneous surface layer but also inhomogeneous deeper structures 3 to derive an alternative 1 d upper and mid mantle section for the north pacific ocean by carefully selecting the data for interpretation and by using 3 d models that are as realistic and detailed as possible in order to perform the simulations using realistic 3 d models on a routine basis a novel 3 d spherical forward solution has been elaborated in this paper the solution combines the modified iterative dissipative method with a conjugate gradient iteration and allows one to compute efficiently the electromagnetic fields in full 3 d spherical models with very high lateral contrasts of conductivity and for very dense grids during the 3 d simulations a systematic shift of observed c responses at honolulu compared with those at other observatories was detected the reason for this shift is still unclear even if a very detailed grid of 0 3 0 3 is used the 3 d simulations using a model of the inhomogeneous surface has no notable ocean effect to c responses at this site an attempt has been made to reduce the misfit between observed and modelled c responses by incorporating a 3 d model with inhomogeneous lithosphere and upper mantle however this has resulted only in a slight change in responses the main conclusion drawn from our 3 d model studies is that there exists a significant disagreement between observed and 3 d modelled c responses if the published 1 d sections with conducting uppermost 400 km are considered as the upper and mid mantle sections our 3 d simulations and reinterpretation of the data also confirm the recent finding that the upper and mid mantle beneath north pacific ocean in the depth range down to 400 km is much more resistive than hitherto assumed

a comprehensive model of the quiet time near earth magnetic field phase 3 summary the near earth magnetic field is caused by sources in the earth s core ionosphere magnetosphere lithosphere and from coupling currents between the ionosphere and the magnetosphere and between hemispheres traditionally the main field low degree internal field and magnetospheric field have been modelled simultaneously with fields from other sources being modelled separately such a scheme however can introduce spurious features especially when the spatial and temporal scales of the fields overlap a new model designated cm3 comprehensive model phase 3 is the third in a series of efforts to coestimate fields from all of these sources this model has been derived from quiet time magsat and pogo satellite and observatory hourly means measurements for the period 1960 1985 it represents a significant advance in the treatment of the aforementioned field sources over previous attempts and includes an accounting for main field influences on the magnetosphere main field and solar activity influences on the ionosphere seasonal influences on the coupling currents a priori characterization of the influence of the ionosphere and the magnetosphere on earth induced fields and an explicit parametrization and estimation of the lithospheric field the result is a model that describes well the 591 432 data with 16 594 parameters implying a data to parameter ratio of 36 which is larger than several popular field models

full waveform tomography for radially anisotropic structure new insights into present and past states of the australasian upper mantle article i nfo we combine spectral element simulations and adjoint techniques in a non linear full seismic waveform tomography for the radially anisotropic structure of the australasian upper mantle our method allows us to explain 30 s waveforms in detail and it yields tomographic images with locally 2 lateral resolution in the course of 19 conjugate gradient iterations the total number of exploitable waveforms increased from 2200 to nearly 3000 the final model amsan 19 thus explains data that were not initially included in the inversion this is strong evidence for the effectiveness of the inversion scheme and the physical consistency of the tomographic model amsan 19 confirms long wavelength heterogeneities found in previous studies and it allows us to draw the following inferences concerning the past and present states of the australian upper mantle and the formation of seismic anisotropy 1 small scale neutral to low velocity patches beneath central australia are likely to be related to localised paleozoic intraplate deformation 2 increasing seismic velocities between the moho and 150 km depth are found beneath parts of proterozoic australia suggesting thermochemical variations related to the formation and fragmentation of a centralian superbasin 3 radial anisotropy above 150 km depth reveals a clear ocean continent dichotomy we find strong vshnvsv beneath the coral and tasman seas the anisotropy is strongest at the top of the inferred asthenospheric flow channel where strain is expected to be largest radial anisotropy beneath the continent is weaker but more variable localised patches with vshbvsv appear in accord with small scale intraplate deformation 4 the ocean continent dichotomy disappears gradually between 150 and 250 km depth where the continental lithospheric mantle and the oceanic asthenosphere pass into the underlying convecting mantle 5 significant anisotropy exists below 250 km depth its character can be explained by sublithospheric small scale convection and a change in the dominant glide system of olivine

zoogeomorphology in the anthropocene abstract the anthropocene embodies the concept of human impacts on the natural environment but disagreements exist as to when to identify its inception starting date in this paper i illustrate that regardless of the proposed starting date of the anthropocene important zoogeomorphic impacts were initiated at each of these proposed starting dates humans have profoundly altered geomorphic pathways through extinctions and the near extirpation of native populations of animal species that strongly influenced hydrology and removal of surface sediment and through the introduction of populations of animals that bring to bear a suite of different geomorphic effects on environmental systems domestication of animals brought its own suite of zoogeomorphic implications introductions of exotic species and the spread of feral species often led to dramatic new geomorphic landscapes because of the absence of natural controls on population expansion in the mountains of the western usa and elsewhere the geomorphic actions of animals are being impacted by human induced climate change climate change in some cases affects the spatial pattern and range of species whereas in other cases it may lead to the extirpation of species with zoogeomorphic impacts

seismic imaging of complex onshore structures by 2d elastic frequency domain full waveform inversion quantitative imaging of the elastic properties of the subsurface at depth is essential for civil engineering applications and oil and gas reservoir characterization a realistic synthetic example provides for an assessment of the potential and limits of 2d elastic full waveform inversionfwiof wide aperture seismic data for recovering high resolution p and s wave velocity models of complex onshore structures fwi of land data is challengingbecauseoftheincreasednonlinearityintroducedbyfreesurface effects such as the propagation of surface waves in the heterogeneous near surface moreover the short wavelengths of the shear wavefield require an accurate s wave velocity starting modeliflowfrequenciesareunavailableinthedata weevaluated different multiscale strategies with the aim of mitigating the nonlinearities massively parallel full waveform inversion was implemented in the frequency domain the numerical optimization relies on a limited memory quasi newton algorithm that outperforms the more classic preconditioned conjugate gradient algorithm the forward problem is based upon a discontinuous galerkin dg method on triangular mesh which allows accuratemodelingoffree surfaceeffects sequentialinversionsofincreasingfrequenciesdefinethemostnaturallevelofhierarchyin multiscale imaging in the case of land data involving surface waves the regularization introduced by hierarchical frequency inversions is not enough for adequate convergence of the inversion a second level of hierarchy implemented with complexvalued frequencies is necessary and provides convergence of the inversion toward acceptable p and s wave velocity models amongthepossiblestrategiesforsamplingfrequenciesintheinversion successive inversions of slightly overlapping frequency groups is the most reliable when compared to the more standard sequential inversion of single frequencies this suggests that simultaneous inversion of multiple frequencies is critical when consideringcomplexwavephenomena

zoogeomorphology and resilience theory abstract zoogeomorphology the study of animals as geomorphic agents has been largely overlooked in the context of resilience theory and biogeomorphic systems in this paper examples are provided of the interactions between external landscape disturbances and zoogeomorphological agents we describe cases in which naturally occurring zoogeomorphological agents occupy a landscape and examine whether those zoogeomorphic agents provide resilience to a landscape or instead serve as a landscape stress capable of inducing a phase state shift several cases are described whereby the presence of exotic introduced zoogeomorphic agents overwhelms a landscape and induce collapse the impact of climate change on species with zoogeomorphological importance is discussed in the context of resilience of a landscape we conclude with a summary diagram illustrating the relationships existing between zoogeomorphic impacts and landscape resilience in the context of our case studies and speculate about the future of the study of zoogeomorphology in the framework of resilience theory

human induced changes in animal populations and distributions and the subsequent effects on fluvial systems abstract humans have profoundly altered hydrological pathways and fluvial systems through their near extirpation of native populations of animal species that strongly influenced hydrology and removal of surface sediment and through the introduction of now feral populations of animals that bring to bear a suite of different geomorphic effects on the fluvial system in the category of effects of extirpation examples are offered through an examination of the geomorphic effects and former spatial extent of beavers bison prairie dogs and grizzly bears beavers entrapped hundreds of billions of cubic meters of sediment in north american stream systems prior to european contact individual bison wallows that numbered in the range of 100 million wallows each displaced up to 23 m 3 of sediment burrowing by prairie dogs displaced more than 5000 kg and possibly up to 67 500 kg of sediment per hectare in the category of feral populations the roles of feral rabbits burros and horses and pigs are highlighted much work remains to adequately quantify the geomorphic effects animals have on fluvial systems but the influence is undeniable

seismic tomography of the southern california crust based on spectral element and adjoint methods we iteratively improve a 3 d tomographic model of the southern california crust using numerical simulations of seismic wave propagation based on a spectral element method sem in combination with an adjoint method the initial 3 d model is provided by the southern california earthquake center the data set comprises three component seismic waveforms i e both body and surface waves filtered over the period range 2 30 s from 143 local earthquakes recorded by a network of 203 stations time windows for measurements are automatically selected by the flexwin algorithm the misfit function in the tomographic inversion is based on frequency dependent multitaper traveltime differences the gradient of the misfit function and related finite frequency sensitivity kernels for each earthquake are computed using an adjoint technique the kernels are combined using a source subspace projection method to compute a model update at each iteration of a gradient based minimization algorithm the inversion involved 16 iterations which required 6800 wavefield simulations the new crustal model m 16 is described in terms of independent shear v s and bulk sound v b wave speed variations it exhibits strong heterogeneity including local changes of 30 per cent with respect to the initial 3 d model the model reveals several features that relate to geological observations such as sedimentary basins exhumed batholiths and contrasting lithologies across faults the quality of the new model is validated by quantifying waveform misfits of full length seismograms from 91 earthquakes that were not used in the tomographic inversion the new model provides more accurate synthetic seismograms that will benefit seismic hazard assessment

elastic full waveform inversion application using multicomponent measurements of seismic data collection abstractrecent computational improvements allowed us to simulate elastic wavefields in a 3d manner and undertake the challenge of executing elastic full waveform inversion efwi the 3d seg eage overthrust synthetic data were used to run the initial tests which included using all three components for the simulation the inversion targeted two regions the channel system and the overthrusted zone which proved the effectiveness of efwi to delineate geology in terms of vp and vs velocity fields for the field data experiment to demonstrate the technologies we elected to use a gulf of mexico ocean bottom cable data set which allowed us to take advantage of relatively large offsets along with the 4c acquisition the input data were minimally processed mostly through noise removal and the initial model was a gaussian smoothed version of grid tomography output which is done by a prestack migrated gather flattening process during ewfi a multiscale approach was followed to ensure convergence and the earl

exploring some issues in acoustic full waveform inversion the least squares error measures the difference between observed and modelled seismic data because it suffers from local minima a good initial velocity model is required to avoid convergence to the wrong model when using a gradient based minimization method if a data set mainly contains reflection events it is difficult to update the velocity model with the least squares error because the minimization method easily ends up in the nearest local minimum without ever reaching the global minimum several authors observed that the model could be updated by diving waves requiring a wide angle or large offset data set this full waveform tomography is limited to a maximum depth here we use a linear velocity model to obtain estimates for the maximum depth in addition we investigate how frequencies should be selected if the seismic data are modelled in the frequency domain in the presence of noise the condition to avoid local minima requires more frequencies than needed for sufficient spectral coverage we also considered acoustic inversion of a synthetic marine data set created by an elastic time domain finite difference code this allowed us to validate the estimates made for the linear velocity model the acoustic approximation leads to a number of problems when using long offset data nevertheless we obtained reasonable results the use of a variable density in the acoustic inversion helped to match the data at the expense of accuracy in the inversion result for the density

rocking the landscape chacma baboons papio ursinus as zoogeomorphic agents abstract animals sculpt landforms by physically altering the substrate many digging and burrowing animals are then considered zoogeomorphic agents while the significance of soil disturbing species is well established geomorphic impacts are rarely quantified for rock transporting species the chacma baboon papio ursinus a widespread and abundant primate throughout most of southern africa south of the zambezi may be a zoogeomorphic agent through its role in rock displacement while foraging we quantified baboon rock movement along belt transects placed across a catena in a semi arid karoo environment in south africa along each transect we the counted the number of moved rocks and recorded their dimensions mass and shape and related this to rock i e mass shape and landscape i e hillslope obstacles that hinder movement features to assess the drivers of the extent of rock transport baboon rock movement was found to be extensive ranging from 26 to 54 615 kg 10 967 2 2300 9 kg of rock material displaced per ha and year the distance of rock movement was influenced by rock size large rocks were displaced further and rock shape flat rocks were moved further followed by angular and rounded rocks furthermore slope influenced rock movement with rocks displaced greater distances on steeper slopes baboon rock movement brought about a loss in potential energy and a change in landscape entropy through the net downward movement of rocks we show that baboons play an important geomorphic role and probably serve as a keystone species as they are the only species in this environment to intentionally move rocks in this way because baboons are considered pests and are widely persecuted their role in zoogeomorphic processes are vulnerable to being lost

implementation of marine seismic source wavefields in finite difference methods using wavefield injection abstractwe have developed a method for implementing source wavefields in finite difference fd schemes for marine seismic modeling migration and inversion by using the wavefield injection technique it is possible to inject arbitrary source wavefields into an fd grid we have assumed that the notional source signatures from each gun in an air gun array and their positions are known the source wavefield is extrapolated to a specified surface below the true source positions using analytical green s functions on this surface the pressure and its vertical derivative are inserted into the fd grid the wavefield propagating from this surface will then propagate downward and appear as if it came from the true source position the source positions do not need to coincide with the fd grid points and the free surface reflection coefficient for the source ghost can be specified i e it can deviate from 1 and it can be frequency dependent these features are possible because of the analytical extrapolatio

the impact of climate change on patterns of zoogeomorphological influence examples from the rocky mountains of the western u s a abstract many animals in the mountains of the western u s a and elsewhere are geomorphically active the spatial pattern and intensity of these impacts associated with activities such as digging for food burrowing for shelter and damming of streams may change as a result of climate change food sources utilized will be affected by processes such as meadow infilling with trees upward advancement of trees and changes in intensity of other geomorphic processes such as avalanching and glacial action and associated meltwater examples are presented here that illustrate the importance of accurate habitat mapping to be able to assess the impact of climate change on geomorphically active animals as well as the importance of knowledge of food sources of these animals as climate change impacts food sources and habitats some geomorphically active animals may become much more limited in the geographic range and intensity of their influence and some may disappear altogether if the habitat disappears

application of multi source waveform inversion to marine streamer data using the global correlation norm conventional multi source waveform inversion using an objective function based on the least square misfit cannot be applied to marine streamer acquisition data because of inconsistent acquisition geometries between observed and modelled data to apply the multi source waveform inversion to marine streamer data we use the global correlation between observed and modelled data as an alternative objective function the new residual seismogram derived from the global correlation norm attenuates modelled data not supported by the configuration of observed data and thus can be applied to multi source waveform inversion of marine streamer data we also show that the global correlation norm is theoretically the same as the least square norm of the normalized wavefield to efficiently calculate the gradient our method employs a back propagation algorithm similar to reverse time migration based on the adjoint state of the wave equation in numerical examples the multi source waveform inversion using the global correlation norm results in better inversion results for marine streamer acquisition data than the conventional approach

elastic full waveform inversion of multicomponent ocean bottom cable seismic data application to alba field u k north sea elastic full waveform inversion of multichannel seismic data represents a data driven form of analysis leading to direct quantification of the subsurface elastic parameters in the depth domain previous studies have focused on marine streamer data using acoustic or elastic inversion schemes for the inversion of p wave data in this paper p and s wave velocities are inverted for using wide angle multicomponent ocean bottom cable obc seismic data inversion is undertaken using a two dimensional elastic algorithm operating in the time domain which allows accurate modeling and inversion of the full elastic wavefield including p and mode converted ps waves and their respective amplitude variation with offset avo responses results are presented from the application of this technique to an obc seismic data set from the alba field north sea after building an initial velocity model and extracting a seismic wavelet the data are inverted instages in the first stage the intermediate wavelength p wave v

resolution of direction of oceanic magnetic lineations by the sixth generation lithospheric magnetic field model from champ satellite magnetic measurements the champ satellite continues to provide highly accurate magnetic field measurements from decreasing orbital altitudes 350 km at solar minimum conditions using the latest 4 years 2004 2007 of readings from the champ fluxgate magnetometer including an improved scalar data product we have estimated the lithospheric magnetic field to spherical harmonic degree 120 corresponding to 333 km wavelength resolution the data were found to be sensitive to crustal field variations up to degree 150 down to 266 km wavelength but a clean separation of the lithospheric signal from ionospheric and magnetospheric noise sources was achieved only to degree 120 this new mf6 model is the first satellite based magnetic model to resolve the direction of oceanic magnetic lineations revealing the age structure of oceanic crust

multiscale imaging of complex structures from multifold wide aperture seismic data by frequency domain full waveform tomography application to a thrust belt summary an application of full waveform tomography to dense onshore wide aperture seismic data recorded in a complex geological setting thrust belt is presented the waveform modelling and tomography are implemented in the frequency domain the modelling part is solved with a finite difference method applied to the visco acoustic wave equation the inversion is based on a local gradient method only the p wave velocity is involved in the inversion the inversion is applied iteratively to discrete frequency components by proceeding from low to high frequencies this defines a multiscale imaging in the sense that high wavenumbers are progressively incorporated in images the linearized waveform tomography requires an accurate starting velocity model that has been developed by first arrival traveltime tomography after specific pre processing of the data 16 frequency components ranging between 5 4 and 20 hz were inverted ten iterations were computed per frequency component leading to 160 tomographic models the waveform tomography has successfully imaged southwest dipping structures previously identified from other geophysical data as being associated with high resistivity bodies the relevance of the tomographic images is locally demonstrated by comparison of a velocity depth function extracted from the waveform tomography models with a coincident vertical seismic profiling vsp log available on the profile moreover comparison between observed and synthetic seismograms computed in the starting traveltime and waveform tomography models demonstrates unambiguously that the waveform tomography successfully predicts for wide angle reflections from southwest dipping geological structures this study demonstrates that the combination of first arrival traveltime and frequency domain full waveform tomographies applied to dense wide aperture seismic data is a promising approach to quantitative imaging of complex geological structures indeed wide aperture acquisition geometries offer the opportunity to develop an accurate background velocity model for the subsequent waveform tomography this is critical because the building of the macromodel remains an open question when only near vertical reflection data are considered

an overview of depth imaging in exploration geophysics prestack depth migration is the most glamorous step of seismic processing because it transforms mere data into an image and that image is considered to be an accurate structuraldescriptionoftheearth thus ourexpectationsofitsaccuracy robustness and reliability are high amazingly seismic migration usually delivers the past few decades have seen migration move from its heuristic roots to mathematically sound techniques that using relatively few assumptions render accurate pictures of the interior of the earth interestingly theearthandthesubjectswewanttoimageinside itarevariedenoughthat sofar nosinglemigrationtechnique has dominated practical application all techniques continually improve and borrow from each other so one technique mayneverdominate despitetheprogressinstructuralimaging wehavenotreachedthepointwhereseismicimagesprovide quantitatively accurate descriptions of rocks and fluids nor have we attained the goal of using migration as part of a purelycomputationalprocesstodeterminesubsurfacevelocity in areas where images have the highest quality we might be nearing those goals collectively called inversion where data are more challenging the goals seem elusive we describe the progress made in depth migration to the present and the most significant barriers to attaining its inversion goalsinthefuture wealsoconjectureonprogresslikelytobe made in the years ahead and on challenges that migration mightnotbeabletomeet

on data independent multicomponent interpolators and the use of priors for optimal reconstruction and 3d up down separation of pressure wavefields in marine acquisition the interference between the upgoing and downgoing wavefields introduces a receiver ghost which reduces the effective bandwidth of the seismic wavefield a two component streamer provides means for removing the receiver ghost by measuring pressure and vertical particle velocity however due to nonuniform and relatively sparse sampling in the crossline direction the seismic data are usually severely aliased in the crossline direction and the deghosting may not be feasible in a true 3d sense a true multicomponent streamer measures all components of the particle motion wavefield in addition to the pressure wavefield this enables solving the 3d deghosting and crossline reconstruction problems simultaneously without making assumptions on the wavefield or the subsurface we havedeveloped two data independent algorithms suited for multicomponent acquisition the first algorithm reconstructs the total pressure wavefield in the crossline direction by using the pressure and the crossline

an ellipsoidal harmonic representation of earth s lithospheric magnetic field to degree and order 720 1 while high degree models of the earth s gravity potential have been inferred from measurements for more than a decade corresponding geomagnetic models are difficult to produce the primary challenge lies in the estimation of the magnetic potential which is not completely determined by available field intensity measurements and cannot be computed by direct integration described here is the methodology behind the third generation of the national geophysical data center s degree 720 magnetic model key issues are 1 the ellipsoidal harmonic representation of the magnetic potential 2 the reduction of ambiguities by a suitable penalty function and 3 the use of an iterative method to estimate the model coefficients the ngdc 720 model provides the lithospheric magnetic field vector at any desired location and altitude close to and above the earth s surface anticipated uses are in geological and tectonic studies of the lithosphere as a local correction for magnetic navigation and heading systems and the calibration of ground marine airborne and spaceborne magnetometers the ngdc 720 model is available at http geomag org models ngdc720 html and for long term archive at http earthref org cgi bin er cgi s erda cgi n 989

the beaver meadow complex revisited the role of beavers in post glacial floodplain development we evaluate the validity of the beaver meadow complex hypothesis used to explain the deposition of extensive fine sediment in broad low gradient valleys previous work establishes that beaver damming forms wet meadows with multi thread channels and enhanced sediment storage but the long term geomorphic effects of beaver are unclear we focus on two low gradient broad valleys beaver meadows and moraine park in rocky mountain national park colorado usa both valleys experienced a dramatic decrease in beaver population in the past century and provide an ideal setting for determining whether contemporary geomorphic conditions and sedimentation are within the historical range of variability of valley bottom processes we examine the geomorphic significance of beaver pond sediment by determining the rates and types of sedimentation since the middle holocene and the role of beaver in driving floodplain evolution through increased channel complexity and fine sediment deposition sediment analyses from cores and cutbanks indicate that 33 50 of the alluvial sediment in beaver meadows is ponded and 28 40 was deposited in channel in moraine park 32 41 is ponded sediment and 40 52 was deposited in channel radiocarbon ages spanning 4300 years indicate long term aggradation rates of 0 05 cm yr 1 the observed highly variable short term rates indicate temporal heterogeneity in aggradation which in turn reflects spatial heterogeneity in processes at any point in time channel complexity increases directly downstream of beaver dams the increased complexity forms a positive feedback for beaver induced sedimentation the multi thread channel increases potential channel length for further damming which increases the potential area occupied by beaver ponds and the volume of fine sediment trapped channel complexity decreased significantly as surveyed beaver population decreased beaver meadows and moraine park represent settings where beaver substantially influence post glacial floodplain aggradation these findings underscore the importance of understanding the historical range of variability of valley bottom processes and implications for environmental restoration copyright 2011 john wiley sons ltd

magnetic field gradients from the st 5 constellation improving magnetic and thermal models of the lithosphere received 20 august 2007 revised 17 october 2007 accepted 6 november 2007 published 25 december 2007 1 we report the development of a new technique magnetic gradiometry for satellite based remote sensing of the lithosphere the measurements reported here represent the first systematic measurements of lithospheric magnetic field gradients and were collected from a spinning spacecraft the three satellite st 5 mission collected vector magnetic field observations at 300 800 km altitudes over mid and high northern latitudes in 2006 away from the auroral oval and over the continents the gradients of the low altitude 400 km total anomaly field are dominated by lithospheric magnetic fields using a seismic starting model and magnetic field observations from st 5 and other recent satellite missions we demonstrate how these techniques can be used to improve our knowledge of the processes involved in the thickened crust of the colorado plateau and the sierra madre occidental citation purucker m t sabaka g le j a slavin r j strangeway and c busby 2007 magnetic field gradients from the st 5 constellation improving magnetic and thermal models of the lithosphere geophys res lett 34 l24306 doi 10 1029 2007gl031739

the human impact in geomorphology 50 years of change abstract concern with the human impact in geomorphology has a long history what is new is that since 1969 a number of developments have taken place that have led to an increasing realisation of its importance these developments are in four main areas i intellectual and policy related ii technological developments that alter geomorphological processes iii demographic trends and iv the proliferation of techniques for the study of landform and process change there has been a realisation of the role of humans in landscape transformation in ancient times the human impact has developed through time but particularly notable are the potential early effects of fire extinctions and deforestation on geomorphological processes the spread of european agriculture particularly in the nineteenth century transformed erosion and sedimentation rates in many parts of the world notwithstanding the importance of some of these changes in prehistoric and historic times recent researches have demonstrated that humans have become an increasingly important agent of geomorphological change during the period of the great acceleration of the past five or six decades the interest in global warming that has developed since the early 1980s has created considerable interest in its consequences for a range of geomorphological phenomena it is also becoming apparent that anthropogenic geomorphological change is having an impact on the earth system as a whole finally geomorphologists have taken an increasing interest in how they can make an impact in the field of landscape conservation

anisotropic 3d full waveform inversion abstractwe have developed and implemented a robust and practical scheme for anisotropic 3d acoustic full waveform inversion fwi we demonstrate this scheme on a field data set applying it to a 4c ocean bottom survey over the tommeliten alpha field in the north sea this shallow water data set provides good azimuthal coverage to offsets of 7 km with reduced coverage to a maximum offset of about 11 km the reservoir lies at the crest of a high velocity antiformal chalk section overlain by about 3000 m of clastics within which a low velocity gas cloud produces a seismic obscured area we inverted only the hydrophone data and we retained free surface multiples and ghosts within the field data we invert in six narrow frequency bands in the range 3 to 6 5 hz at each iteration we selected only a subset of sources using a different subset at each iteration this strategy is more efficient than inverting all the data every iteration our starting velocity model was obtained using standard psdm model bui

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

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

two dimensional full wavefield inversion of wide aperture marine seismic streamer data summary a 2 d full wavefield inversion method is presented for the processing of wide aperture data the diversity of information contained within such datasets may be handled in a complete manner by first matching the traveltimes of the main events and then progressing to waveform fitting of the data through explicit full wavefield modelling our wavefield inversion scheme is based upon a finite difference solution of the 2 d elastic wave equation in the time distance domain the strength of adopting such an approach is the ability to generate all possible wave types within a given 2 d model multiples converted waves etc and thus to simulate and accurately model complex seismic wavefields the aim of the inversion is to find the 2 d p wave velocity model that minimizes the least squared difference between the observed and synthetic data across the full range of offsets following extensive testing on synthetic data the wavefield inversion scheme has been applied to wide aperture real marine seismic streamer datasets we present results from the synthetic testing and the wavefield inversion of wide aperture real data out to 12 km offset that was recorded on a single streamer even though current computational restrictions allow only a small subsection of the data to be analysed these examples demonstrate the potential value of wide aperture 2 d full wavefield inversion

characteristics of beaver ponds on deltas in a mountain environment many beaver ponds in the rocky mountains that have been described in the literature are in channel ponds that are relatively small and short lived this paper describes floodplain beaver ponds on low gradient deltas in glacial finger lakes in glacier national park montana these ponds are distinctly larger probably fed by hyporheic flow and stable and long lived ponds examined were with one exception 44 years old glacial discharge is present in each valley where beaver ponds occupy low gradient deltas and this discharge likely sustains pond water level over the course of the summer as glaciers recede and disappear deltaic beaver ponds dependent on hyporheic flow may be negatively affected copyright 2012 john wiley sons ltd

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

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

elephants and extinct relatives as earth movers and ecosystem engineers abstract modern african elephants affect habitats and ecosystems in significant ways they push over trees to feed on upper branches and often peel large sections of bark to eat these destructive habits sometimes transform woody vegetation into grasslands systems of elephant trails may be used and re used for centuries and create incised features that extend for many kilometers on migration routes elephants digging in search of water or mineral sediments may remove several cubic meters of sediments in each excavation wallowing elephants may remove up to a cubic meter of pond sediments each time they visit water sources accumulations of elephant dung on frequented land surfaces may be over 2 kg per square meter elephant trampling digging and dust bathing may reverse stratigraphy at archeological localities this paper summarizes these types of effects on biotic geomorphic and paleontological features in modern day landscapes and also describes several fossil sites that indicate extinct proboscideans had very similar effects such as major sediment disturbances

rapidly changing flows in the earth s core variations in the earth s magnetic field over a span of a few months can be resolved despite the potential filtering effects of the electrically conducting mantle and are indicative of rapid flow in the earth s outer core

geomorphic changes upstream of beaver dams in bridge creek an incised stream channel in the interior columbia river basin eastern oregon channel incision is a widespread phenomenon throughout the dry interior columbia river basin and other semi arid regions of the world which degrades stream habitat by fundamentally altering natural ecological geomorphological and hydrological processes we examined the extent of localized aggradation behind beaver dams on an incised stream in the interior columbia river basin to assess the potential for using beaver castor canadensis dams to restore such channels and the effect of the aggradation on riparian habitat we estimated aggradation rates behind 13 beaver dams between 1 and 6 years old on bridge creek a tributary to the john day river in eastern oregon vertical aggradation rates are initially rapid as high as 0 47 m yr 1 as the entrenched channel fills then level off to 0 075 m yr 1 by year six as the sediment begins accumulating on adjacent terraces we found that a 0 5 m elevation contour above the stream channel approximately coincided with the extent of new riparian vegetation establishment therefore we compared the area surrounding reaches upstream of beaver dams that were within 0 5 m elevation of the stream channel with adjacent reaches where no dams existed we found that there was five times more area within 0 5 m elevation of the channel upstream of beaver dams presumably because sediment accumulation had aggraded the channel our results suggest that restoration strategies that encourage the recolonization of streams by beaver can rapidly expand riparian habitat along incised streams copyright 2007 john wiley sons ltd

dual sensor streamer technology used in sleipner co2 injection monitoring co2 has been injected into the saline aquifer utsira fm at the sleipner field since 1996 in order to monitor the movement of the co2 in the sub surface the seventh seismic monitor survey was acquired in 2010 with dual sensor streamers which enabled optimal towing depths compared to previous surveys we here report both on the time lapse observations and on the improved resolution compared to the conventional streamer surveys this study shows that the co2 is still contained in the subsurface with no indications of leakage the time lapse repeatability of the dual sensor streamer data versus conventional data is sufficient for interpreting the timelapse effects of the co2 at sleipner and the higher resolution of the 2010 survey has enabled a refinement of the interpretation of nine co2 saturated layers with improved thickness estimates of the layers in particular we have estimated the thickness of the uppermost co2 layer based on an analysis of amplitude strength together with time separation of top and base of this layer and found the maximum thickness to be 11 m this refined interpretation gives a good base line for future time lapse surveys at the sleipner co2 injection site

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

localizing co2 at sleipner seismic images versus p wave velocities from waveform inversion abstractthe presence of injected co2 in the utsira sand at the sleipner site norway is associated with a high negative p wave velocity anomaly that is a low postinjection velocity and a strong seismic response time lapse seismic imaging of co2 injection at sleipner is thus a viable monitoring tool of the injected co2 the work flow usually involves conventional seismic processing including stacking and results in seismic images multiple reflections interference effects such as tuning and the velocity pushdown effect due to co2 injection render these seismic images ambiguous in terms of the localization and the quantification of the co2 in the utsira sand nonetheless seismic images often form the basis for analyses that aim to quantify the injected co2 we employed elastic 2d full waveform inversion to invert prestack seismic sleipner data from preinjection 1994 and postinjection 1999 and compared the resulting postinjection p wave velocity model with the corresponding seismic image we fou

the gradient tensor of potential field anomalies some implications on data collection and data processing of maps the full gradient tensor is presently not measured routinely onboard airplanes or on land this paper describes some improvements that can be made in strategies of data collection and in processing of potential field maps if such tensor measurements were available we suggest that in addition to producing for example standard total field anomaly maps the invariants of the tensor be mapped strikes of magnetic or gravimetric structures may be determined from minimizing the power in the first row and column of the tensor invariants can be looked upon as nonlinear filters enhancing sources with big volumes their lateral resolution is superior to that of the field proper and for a given resolution the flight altitude and separation between flight lines can be increased compared with the standard mode of operation in airborne surveys the distance between flight lines is normally much larger than the height above the ground this may introduce severe aliasing effects in the direction perpendicular to the

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

3d prestack plane wave full waveform inversion prestack depth migration has been used for decades to derive velocity distributions in depth numerous tools and methodologies have been developed to reach this goal exploration in geologically more complex areas exceeds the abilities of existing methods new data acquisition and data processing methods are required to answer these new challenges effectively the recently introduced wide azimuth data acquisition method offers better illumination and noise attenuation as well as an opportunity to more accurately determine velocities for imaging one of the most advanced tools for depth imaging is full waveform inversion prestack seismic full waveform inversion is very challenging because of the nonlinearity and nonuniqueness of the solution combined with multiple iterations of forward modeling and residual wavefield back propagation the method is computer intensive especially for 3d projects we studied a time domain plane wave implementation of 3d waveform inversion we found that plane wave gathers

the geomorphic influences of beaver dams and failures of beaver dams abstract uncounted millions of beaver ponds and dams existed in north america prior to european contact and colonization these ponds acted as sediment traps that contained tens to hundreds of billions of cubic meters of sediment that would otherwise have passed through the fluvial system removal of beavers by overtrapping in the 16th 19th centuries severely reduced their number and the number of ponds and dams dam removal altered the fluvial landscape of north america inducing sediment evacuation and entrenchment in concert with widespread reduction in the wetlands environments partial recovery of beaver populations in the 20th century has allowed reoccupation of the entirety of the pre contact range but at densities of only one tenth the numbers nevertheless modern beaver ponds also trap large volumes of sediment in the high hundred millions to low billions of cubic meters range failure of beaver dams is a more common phenomenon than often assumed in the literature during the past 20 years numerous cases of dam failure have been documented that resulted in outburst floods these floods have been responsible for 13 deaths and numerous injuries including significant impacts on railway lines

enhanced zoogeomorphological processes in north africa in thehuman impacted landscapes of the anthropocene abstract new zoogeomorphological features discovered in dryland landscapes of northern africa reflect human animal agency since prehistory and attest to complex networked activities over great distances we discuss the role of zoogeomorphology in shaping earth s surface since the beginning of the anthropocene the timeframe when natural processes shifted and landscape evolution became more human dominated we focus on contexts in arid and semiarid lands of northern africa which are metastable sensitive ecosystems that are prone to modifications triggered by climatic and anthropogenically forced factors studying the geoarchaeological record in context of landscape impact and animal procurement by people throughout antiquity is important for reconstructing domestication and husbandry of cattle sheep and goats in this region among the features we recognize in association with transhumance pastoralism and herding are trails trackways footholds animal daybeds stables animal dwellings rockshelters game blinds and monuments to name a few related activities with landscape scale impacts include herding transport corralling and browsing of cattle bos sp goats and sheep ovicaprines as well as pasturage activities like cropping fire setting and manuring these activities were disturbances that affected surface processes like erosion and dust mobilization as well as reduced vegetation and ecosystems productivity in dryland africa and especially in the sahara intensive herding led to the alteration of the pristine aspects of bare rock surfaces and of the stone desert pavement i e the hamada many regions preserved evidence of middle late holocene animal daybeds trampled areas and barren tracks and trails we suggest that human and herd animal activities affected geomorphic surfaces that affected slope stability intensified erosion and dust mobilization and enhanced dust export from the african continent offshore we reinterpret the increased dust emission from north africa during the mid holocene at the end of the african humid period as has been interpreted from ocean cores aridification of the green sahara followed the insolation forced monsoonal maximum and was exacerbated by human animal activities across the sahara and the sahel we argue that the spread of human activities and intensive husbandry of cattle and caprines goat and sheep in this region significantly influenced the geomorphic stability ecosystem and landscape sustainability in a comparable manner of overuse observed in present day arid and marginal environments where pastoral overgrazing pressure increases erosion processes and enhances dust mobilization we suggest that human animal activities have amplified dust generation from the north african continental interior since 7 ka bp this evidence of prehistoric human impacts on surface processes in north africa supports arguments for an early beginning of the anthropocene