sand dunes as a major proximal dust source for late pleistocene loess in the negev desert israel grain size analyses of three hilltop primary eolian loess sequences in the negev desert southern israel show a bimodal grain size distribution at 50 60 m and 3 8 m using analyses of mineralogy and osl ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time suggesting an enhancement of a time transgressive proximal dust source compared to a distal saharan fine grain dust the only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into sinai and the negev concurrently with the loess accretion during the late pleistocene as a result of the exposure of the mediterranean shelf we therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea this relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as northern africa china and australia

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

palaeoenvironmental change recorded in the palaeodunefields of the western murray basin south australia new data from single grain osl dating this study is concerned with the reconstruction of the palaeoenvironmental history of southeastern australia for the last 300 ka by establishing a luminescence chronology of dune sand deposition in the western murray basin south australia in the study area vast fields of palaeodunes stabilised by vegetation provide evidence of past environmental change in total 98 samples were collected from dune sand layers at 13 different dune sections the time of their deposition was determined using optically stimulated luminescence dating of single quartz grains accounting for the impact of post depositional mixing by the use of a finite mixture model the oldest depositional phase demonstrates that dune sand layers of great antiquity are preserved in the western murray basin ranging up to at least 380 ka phases of substantial dune sand deposition were identified for the periods 18 38 ka and 63 72 ka older depositional phases also exist but are poorly resolved due to relatively large errors of the luminescence ages aeolian deposition during the last termination and the holocene is relatively limited with a slight clustering of ages at the time of the antarctic cold reversal and from 5 8 ka two modern ages give evidence of very recent dune sand deposition comparison with other palaeoclimate records from the region suggests that phases with high aeolian sedimentation coincide with more arid conditions and breaks in the dune record with more humid phases thus although dune records are often discontinuous and their interpretation in palaeoclimatic terms is not always straightforward the palaeodunes of the western murray basin show a good preservation of phases of aeolian activity and provide useful information for palaeoenvironmental reconstruction

holocene aeolian activity in the southwestern kalahari desert southern africa significance and relationships to late pleistocene dune building events little is known about the timing of dune building episodes in the southwestern kalahari desert previously arid phases when dune activity occurred have been inferred from gaps in chronologies derived from information that attests to former humid periods to redress this optically stimulated luminescence osl dating was applied to sediment samples taken from a range of aeolian landforms in the sw kalahari four periods of dune building are identified in the late pleistocene and holocene holocene aeolian activity at 6 ka and 1 2 ka led to the construction of localised dune forms in contrast to late pleistocene times when the extensive field of linear dunes that dominates the region was emplaced late holocene aridity was however sufficient to allow rapid emplacement of the lunette dune at witpan the record of aeolian activity is evaluated in the context of humid chronologies and an ocean atmosphere model of holocene climate change with good agreement obtained it is concluded that the application of

dimensions of the atlantic mediterranean connection that caused the messinian salinity crisis abstract what kind of gateway is needed to cause a salinity crisis although several reconstructions of possible atlantic mediterranean gateways are proposed for the late miocene so far the gateway that must have existed before the desiccation of the mediterranean during the messinian is unknown this study uses the theory of hydraulic control combined with the effect of bottom friction in order to find out to first order the geometrical dimensions of the connection that existed during the primary lower gypsum stage 5 97 5 61 ma of the messinian salinity crisis 5 97 5 33 ma the connecting strait is assumed to behave in a similar way as existing straits such as the strait of gibraltar or the bosphorus a salinity crisis in an enclosed basin results when its connection to the open ocean is highly restricted a strait needs to be relatively shallow narrow and or long in order to result in exchange fluxes that are of around 25 or less of the exchange at the strait of gibraltar today considering the evaporite deposits together with global sea level variations we estimate the cross section of a strait responsible of the msc to have a minimum depth of 30 45 m and a maximum width of 0 7 2 km for lengths in the range up to 500 km these dimensions are consistent with only a few of the miocene corridors identified the calculations are extended to explore the implications for sedimentary structures on the corridor floor

palaeoclimatological and chronological implications of the vostok core dust record the2 083 m vostok ice core recovered by the soviet antarctic expeditions has provided much information of climatic and environmental interest for a period covering a full glacial inter glacial cycle1 6 here we present and discuss the dust record obtained down to 2 202 m the final depth to which this core was extended in 1986 first we document the fact that major changes in aeolian deposits as recorded in the vostok core appear to be of global significance and confirm the existence of a link between high latitude aeolian deposits and the earth s orbital parameters7 8 second we propose atmospheric dust as a strati graphic marker to compare timing with other records of palaeocli mate and use the magnetic susceptibility profile measured along the rc11 120 indian ocean core9 for this purpose assuming that major dust events correspond to common aeolian inputs this approach indicates that the vostok and marine records were roughly in phase at the previous glacial interglacial transition

elongation and migration of sand dunes two distinct processes are known to act on dynamic dunes the process of migration by erosion on the windward side and deposition on the lee side typical for transverse dunes and the process of elongation typical for linear dunes these two processes are determined by wind direction relative to the dune alignment this article reviews the assertion that linear dunes experience lateral displacement in addition to elongation fieldwork on vegetated linear dunes vlds and gis work on seif dunes indicates no lateral migration for these dunes linear dunes can shift laterally only when a slip face formed on the lee side reaches the plinth of the dune the winds from both sides of the seif dune are never symmetric usually winds from one direction are more dominant and effective the outcome is the formation of peaks and saddles along the dune the strongest winds create a slip face on the lee side of the peak segments of the dune oblique to the dune alignment which reaches the base of the dune and displaces the peak downwind along the dune alignment the internal structure of the seif dune is formed mostly by this dominant wind direction and gives the impression that the dune has shifted laterally on the other hand there are cases in which the wind directions relative to dune alignment fall between those of transverse and seif dunes in such cases both processes act on the dune which subsequently experiences migration as well as elongation

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

late quaternary aeolian and fluvial interactions on the cooper creek fan and the association between linear and source bordering dunes strzelecki desert australia abstract the innamincka dome and associated low gradient fan in the strzelecki desert is the product of cenozoic crustal warping that has aided formation of an extensive array of palaeochannels source bordering transverse dunes and superimposed linear dunes these dunes have impeded the course of cooper creek and provided a repository of evidence for quaternary climate change as well as the interactive processes between transverse and linear dune formation at turra gidgealpa and sites nearby are extensive fluvial and aeolian sand bodies that date from marine isotope stages mis 8 3 and the last glacial maximum lgm and are now surrounded or buried by overbank mud the sandy alluvium was deposited on the downstream slope of the dome by large channels transporting abundant bedload subsequently blown northward to form transverse dunes from what were probably seasonally exposed bars in a palaeo cooper system thermoluminescence tl and optically stimulated luminescence osl ages demonstrate that the base of the dune complex is at least mis 7 in age 250 ka but that it has been subsequently reworked by wind with additional sand blown from the river source bordering dunes formed during a period of enhanced river flow and sand supply from 120 to 100 ka with another short episode of the same at 85 80 ka and from 68 to 53 the lgm was associated with enhanced flows and the supply of dune sediment from 28 to 18 ka pronounced river flow and dune activity occurred in the early to mid holocene but there is no evidence of dunes being supplied from cooper creek since the lgm the dunes forming the oldest basal sand units appear to be largely transverse in form and are aligned roughly parallel to adjacent east west trending palaeochannels linear dunes have formed from and over these and yield basal ages ranging from mis 5 or mis 4 but continuing to accrete and rework through to the holocene the study results in one of the few detailed chronological investigations of the interaction between transverse and linear dunes it is apparent that long distance sand transport has played no significant role in dune formation here for the linear dunes show no significant downwind decline in ages linear dunes appear to have accreted vertically from underlying transverse dunes a wind rift vertical accretion model with only minor lengthwise extension is the dominant mode of linear dune formation in this section of the strzelecki desert the bulk of dune sediment being sourced from adjacent swales since the lgm

age origin and climatic controls on vegetated linear dunes in the northwestern negev desert israel abstract the stabilized northwestern nw negev vegetated linear dunes vld of israel extend over 1300 km 2 and form the eastern end of the northern sinai nw negev erg this study aimed at identifying primary and subsequent dune incursions and episodes of dune elongation by investigating dune geomorphology stratigraphy and optically stimulated luminescence osl dating thirty five dune and interdune exposed and drilled section were studied and sampled for sedimentological analyses and osl dating enabling spatial and temporal elucidation of the nw negev dunefield evolution in a global perspective the nw negev dunefield is relatively young though sporadic sand deposition has occurred during the past 100 ka dunes began to accumulate over large portions of the dunefield area only at 23 ka three main chronostratigraphic units corresponding to three osl age clusters were found throughout most of the dunefield indicating three main dune mobilizations late to post last glacial maximum lgm at 18 11 5 ka late holocene 2 0 8 ka and modern 150 8 years the post lgm phase is the most extensive and it defined the current dunefield boundaries it involved several episodes of dune incursions and damming of drainage systems dune advancement often occurred in rapid pulses and the orientation of vld long axes indicates similar long term wind directions the late holocene episode included partial incursion of new sand reworking of late pleistocene dunes as well as limited redeposition the modern sand movement only reactivated older dunes and did not lengthen vlds this aeolian record fits well with other regional aeolian sections we suggest that sand supply and storage in sinai was initiated by the late pleistocene exposure of the nile delta sands late pleistocene winds substantially stronger than those usually prevailing since the onset of the holocene are suggested to have transported the dune sands across sinai and into the northwestern negev our results demonstrate the sensitivity of vegetated linear dunes located along the northern fringe of the sub tropical desert belt to climate change i e wind and sediment supply

full waveform inversion and the truncated newton method quantitative imaging of complex subsurface structures full waveform inversion fwi is a powerful tool for quantitative seismic imaging from wide azimuth seismic data the method is based on the minimization of the misfit between observed and simulated data this amounts to the resolution of a large scale nonlinear minimization problem the inverse hessian operator plays a crucial role in this reconstruction process accounting accurately for the effect of this operator within the minimization scheme should correct for illumination deficits restore the amplitude of the subsurface parameters and help to remove artifacts generated by energetic multiple reflections conventional preconditioned gradient based minimization methods only roughly approximate the effect of this operator we are interested in this study to another class of minimization methods named as truncated newton methods these methods are based on the computation of the model update through a matrix free conjugate gradient resolution of the newton linear system the aim of this study is to present a feasible implementation of this method for the fwi problem based on a second order adjoint state formulation for the computation of hessian vector products we compare this method with the nonlinear conjugate gradient and the l bfgs method within the context of 2d acoustic frequency fwi for the reconstruction of p wave velocity models two test cases are investigated the first is the synthetic bp 2004 model representative of the gulf of mexico geology with high velocity contrasts associated with the presence of salt structures the second is a 2d real data set from the valhall oil field in north sea these tests emphasize the interesting properties of the truncated newton method regarding conventional optimization methods within the context of fwi

efficient 3 d frequency domain mono parameter full waveform inversion of ocean bottom cable data application to valhall in the visco acoustic vertical transverse isotropic approximation computationally efficient 3 d frequency domain full waveform inversion fwi is applied to ocean bottom cable data from the valhall oil field in the visco acoustic vertical transverse isotropic vti approximation frequency domain seismic modelling is performed with a parallel sparse direct solver on a limited number of computer nodes a multiscale imaging is performed by successive inversions of single frequencies in the 3 5 10 hz frequency band the vertical wave speed is updated during fwi while density quality factor qp and anisotropic thomsen s parameters and are kept fixed to their initial values the final fwi model shows the resolution improvement that was achieved compared to the initial model that was built by reflection traveltime tomography this fwi model shows a glacial channel system at 175 m depth the footprint of drifting icebergs on the palaeo seafloor at 500 m depth a detailed view of a gas cloud at 1 km depth and the base cretaceous reflector at 3 5 km depth the relevance of the fwi model is assessed by frequency domain and time domain seismic modelling and source wavelet estimation the agreement between the modelled and recorded data in the frequency domain is excellent up to 10 hz although amplitudes of modelled wavefields propagating across the gas cloud are overestimated this might highlight the footprint of attenuation whose absorption effects are underestimated by the homogeneous background qp model qp 200 the match between recorded and modelled time domain seismograms suggests that the inversion was not significantly hampered by cycle skipping however late arrivals in the synthetic seismograms computed without attenuation and with a source wavelet estimated from short offset early arrivals arrive 40 ms earlier than the recorded seismograms this might result from dispersion effects related to attenuation the repeatability of the source wavelets inferred from data that are weighted by a linear gain with offset is dramatically improved when they are estimated in the fwi model rather than in the smooth initial model the two source wavelets estimated in the fwi model from data with and without offset gain show a 40 ms time shift which is consistent with the previous analysis of the time domain seismograms the computational efficiency of our frequency domain approach is assessed against a recent time domain fwi case study performed in a similar geological environment this analysis highlights the efficiency of the frequency domain approach to process a large number of sources and receivers with limited computational resources thanks to the efficiency of the substitution step performed by the direct solver this efficiency can be further improved by using a block low rank version of the multifrontal solver and by exploiting the sparsity of the source vectors during the substitution step future work will aim to update attenuation and density at the same time of the vertical wave speed

recovery rates of microbiotic crusts within a dune ecosystem in the negev desert abstract despite the important role played by microbiotic crusts in desert ecosystems data concerning their recovery rates are scarce and are mainly based on estimates that fluctuate between several years to a few hundred years in order to study the recovery rates of microbiotic crusts inhabiting sand dunes in the western negev desert israel annual measurements of chlorophyll protein carbohydrates and moss counts were carried out during 1990 1995 measurements were taken in two pairs of plots 1 5 6 3 m2 established in each north and south facing aspect from which the upper 10 cm surface from one plot of each pair was removed recovery of the crusts was fast with surface removed plots showing a complete recovery of chlorophyll a within 6 7 years of protein within 6 8 years and of carbohydrates within 8 9 years recovery of the mosses was slightly longer at 17 22 years the data are higher than the lower estimates of recovery but much lower than the higher estimates proposed in the literature the data also suggest that upon prohibition of goat and sheep grazing and consequently trampling a relatively rapid stabilization process may take place in the north eastern sinai dune field

crustal seismic imaging from multifold ocean bottom seismometer data by frequency domain full waveform tomography application to the eastern nankai trough 1 in offshore surveys the deep crust is generally investigated by traveltime tomography applied to sparse ocean bottom seismometer data the inferred velocity models are of limited resolution precluding a quantitative analysis of deep tectonic discontinuities if dense arrays of ocean bottom seismometers can be deployed the resulting data sets become amenable to full waveform processing which should lead to a significant improvement in the resolution of structures such acquisition and processing were achieved on the eastern nankai subduction zone full waveform inversion is entirely implemented in the frequency domain enabling efficient finite difference wave modeling and allowing to limit the inversion to a few discrete frequencies of increasing value such a hierarchical procedure defines a multiresolution approach to seismic imaging the data set was recorded by 93 instruments deployed along a 105 km long profile thirteen frequencies ranging from 3 to 15 hz were inverted sequentially wavelengths imaged by the full waveform inversion typically range between 0 5 and 8 km full waveform tomography reveals an intense compression in the upper prism and underlying backstop as evidenced by several thrusts the frontal ones still active corresponding to negative velocity anomalies the subducting paleo zenisu ridge is also reconstructed above which stands the decollement velocities in the upper mantle beneath the ridge are rather low 7 5 km s 1 suggesting partially serpentinized mantle beneath the ridge this paper demonstrates the feasibility of full waveform tomography based on dense ocean bottom seismometer data sets and its ability to quantitatively image the entire crust with a significantly improved resolution compared to what is usually achieved through traveltime tomography

luminescence dating of periods of sand movement from the godollő hills hungary abstract a sand dune intercalated by soil horizons was investigated using luminescence and radiocarbon dating methods to determine the time of aeolian activity and soil formation in the north eastern part of the godoll hills in hungary optically stimulated luminescence osl dating and infrared stimulated luminescence irsl dating of sand sized 100 200 m grains of quartz and feldspar respectively were tested in the present study the luminescence properties of quartz were not suitable for osl dating hence irsl dating of feldspar grains was applied to all samples with subsequent correction for anomalous fading two periods of increased aeolian activity were identified in the sediment succession at tura the sediments of the lower part of the profile accumulated during the end of the late pleniglacial and through the late glacial when climatic variations caused the alternation of sand and soil horizons in the region the sand and soil layers of the upper part of the sediment succession were deposited and formed during the subatlantic phase of the holocene when sand mobility was probably mainly triggered by human activities

multiparameter waveform inversion of a large wide azimuth low frequency land data set in oman abstractseveral 3d seismic acoustic full waveform inversions fwis of offshore data sets have been reported over the last five years a successful updating of the long to intermediate wavelengths of the earth model by fwi requires good quality wide angle long offset low frequency data recent improvements in acquisition make such data sets available on land too we evaluated a 3d application on a data set recorded in north oman the data contain low frequencies down to 1 5 hz long offsets and wide azimuths the application of acoustic fwi on land remains complicated because of the elastic effects notably the strong ground roll and many acquisition and human activity related noises the presence of fast carbonate layers in this region induces velocity inversions difficult to recover from diving or postcritical waves we accounted for anisotropic effects as we include fwi in a classical structural imaging workflow with a dedicated processing of the data and a simultaneous inversion of the nmo veloc

filling the gap osl data expanding 14c chronologies of late quaternary environmental change in the libyan desert several decades of geomorphological and archaeological research in the libyan desert conducted by the cologne projects b o s and acacia have yielded a wealth of radiocarbon data from archaeological sites and over the last decade also 48 osl ages mainly from aeolian deposits this paper focuses on the combination of both data sets in order to obtain a synthesis of late quaternary occupational and environmental history in this region case studies demonstrate that despite a poorer time resolution of osl chronologies compared to 14 c data osl ages can be more consistent with the archaeological context particularly if the dating of charcoals poses problems due to poor quality or re deposition comparison of data sets from the egyptian sand seas and from the wadi howar sudan shows that in both cases osl and 14 c data cover complementary time slices on the regional scale however contradictory intervals of aeolian accumulation are documented which can be explained by the different environmental histories the results accentuate that interpretation of osl data has to be done in the context of the entire environmental systems including the effective geomorphological processes r 2007 elsevier ltd and inqua all rights reserved

a parametric analysis of two dimensional elastic full waveform inversion of teleseismic data for lithospheric imaging the development of dense networks of broad band seismographs makes teleseismic data amenable to full waveform inversion fwi methods for high resolution lithospheric imaging compared to scattered field migration fwi seeks to involve the full seismic wavefield in the inversion we present a parametric analysis of 2 d frequency domain fwi in the framework of lithospheric imaging from teleseismic data to identify the main factors that impact on the quality of the reconstructed compressional p wave and shear s wave speed models compared to controlled source seismology the main adaptation of fwi to teleseismic configuration consists of the implementation with a scattered filed formulation of plane wave sources that impinge on the base of the lithospheric target located below the receiver network at an arbitrary incidence angle seismic modelling is performed with a hp adaptive discontinuous galerkin method on unstructured triangular mesh a quasi newton inversion algorithm provides an approximate accounting for the hessian operator which contributes to reduce the footprint of the coarse acquisition geometry in the imaging a versatile algorithm to compute the gradient of the misfit function with the adjoint state method allows for abstraction between the forward problem operators and the meshes that are during seismic modelling and inversion respectively an approximate correction for obliquity is derived for future application to real teleseismic data under the two dimension approximation comparisons between the characteristic scales involved in exploration geophysics and in teleseismic seismology suggest that the resolution gain provided by full waveform technologies should be of the same order of magnitude for both applications we first show the importance of the surface reflected wavefield to dramatically improve the resolving power of fwi by combining tomography like and migration like imaging through the incorporation of the forward scattered and the backscattered wavefields in the inversion the resolution of fwi is assessed through checkerboard tests and confirms a resolution of the order of the wavelength for both the p and s speeds when the full wavefield is incorporated in the inversion secondly we show that computationally efficient strategies which consist of decimating the number of frequency components involved in the inversion do not apply to teleseismic acquisitions because the scattering angle bandwidth sampled by plane wave sources can be narrow and coarsely sampled compared to that provided by dense profiles of point sources in exploration seismology the waveform inversion is less sensitive to the band of incidence angles spanned by the plane wave sources and to the sampling of this band however the deficit of vertically propagating plane waves hampers the vertical resolution of planar layers aliasing artefacts created by coarse arrays of receivers are illustrated we show how taking into account the hessian in the inversion and the suitable management of frequencies in the inversion help to mitigate these artefacts acceptable reconstructions are shown for both the p and s wave speeds for a receiver spacing of up to 20 km in the 0 1 0 4 hz frequency range building a reliable initial model for fwi is a highly non linear problem in exploration seismology we show how the low frequency content of the teleseismic sources allow us to build accurate p and s wave speed models starting from simple vertical gradient velocity models all of these results are derived using a 2 d realistic synthetic experiment that was performed with noise free data most of conclusions of this parametric study should apply in three dimensions the impact of noise and the footprint of other experimental parameters such as the estimation of the temporal plane wave signature and the estimation of the incidence angle of the impinging plane waves need however to be assessed in the future

locally modified surface winds on linear dunes as derived from directional raingauges the study deals with local airflow patterns induced by 12 16 m high partly vegetated dunes under various prevailing wind conditions detailed empirical data were derived by means of an unconventional use of directional raingauges the utility and accuracy of the method have been previously tested in a combined empirical and numerical study over ridges on a similar scale results are presented on the nature extent and intensity of locally modified patterns of surface flow and on their dependence on wind conditions and slope inclination results may serve to verify or refine existing perceptions or models of the flow affecting sand movement over dunes for example deflected surface wind flow and even stationary vortices were found to form under winds with resultant angles of incidence of only 5 10 relative to the axes of the dunes and on slopes inclined only 12 15 i e lower angles than often assumed in previous studies of dune morphology various effects of the resulting surface flow on the dune ecosystem are also referred to e g the distribution of settling dust and seed dispersal copyright 2002 john wiley sons ltd

quantitative imaging of complex structures from dense wide aperture seismic data by multiscale traveltime and waveform inversions a case study an integrated multiscale seismic imaging flow is applied to dense onshore wideaperture seismic data recorded in a complex geological setting thrust belt an initial p wave velocity macromodel is first developed by first arrival traveltime tomography this model is used as an initial guess for subsequent full waveform tomography which leads to greatly improved spatial resolution of the p wave velocity model however the application of full waveform tomography to the high frequency part of the source bandwidth is difficult due to the non linearity of this kind of method moreover it is computationally expensive at high frequencies since a finitedifference method is used to model the wave propagation hence full waveform tomography was complemented by asymptotic prestack depth migration to process the full source bandwidth and develop a sharp image of the short wavelengths the final traveltime tomography model and two smoothed versions of the final full waveform tomography model were used as a macromodel for the prestack depth migration in this study wide aperture multifold seismic data are used after specific preprocessing of the data 16 frequency components ranging from 5 4 hz to 20 hz were inverted in cascade by the full waveform tomography algorithm the full waveform tomography successfully imaged sw dipping structures previously identified as highresistivity bodies the relevance of the full waveform tomography models is demonstrated locally by comparison with a coincident vertical seismic profiling vsp log available on the profile the prestack depth migrated images inferred from the traveltime and the smoothed full waveform tomography macromodels are shown to be on the whole consistent with the final full waveform tomography model a more detailed analysis based on common image gather computations and local comparison with the vsp log revealed that the most accurate migrated sections are those obtained from the full waveform tomography macromodels a resolution analysis suggests that the asymptotic prestack depth migration successfully migrated the wideaperture components of the data allowing medium wavelengths in addition to the short wavelengths of the structure to be imaged

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

toward a robust workflow for deep crustal imaging by fwi of obs data the eastern nankai trough revisited crustal scale imaging by the full waveform inversion fwi of long offset seismic data is inherently difficult because the large number of wavelengths propagating through the crust makes the inversion prone to cycle skipping therefore efficient crustal scale fwi requires an accurate starting model and a stable workflow minimizing the nonlinearity of the inversion here we attempt to reprocess a challenging 2d ocean bottom seismometer obs dataset from the eastern nankai trough the starting model is built by first arrival traveltime tomography fat which is fwi assisted for tracking cycle skipping we iteratively refine the picked traveltimes and then reiterate the fat until the traveltime residuals remain below the cycle skipping limit subsequently we apply laplace fourier fwi in which progressive relaxation of time damping is nested within frequency continuation to hierarchically inject more data into the inversion these two multiscale levels are complemented by a layer stripping approach implemented through offset continuation the reliability of the fwi velocity model is assessed by means of source wavelet estimation synthetic seismogram modeling ray tracing modeling dynamic warping and checkerboard tests although the visco acoustic approximation is used for wave modeling the synthetic seismograms reproduce most of the complexity of the data with a high traveltime accuracy the revised fwi scheme produces a high resolution velocity model of the entire crust that can be jointly interpreted with migrated images derived from multichannel seismic data this study opens a new perspective on the design of obs crustal scale experiments amenable to fwi however a further assessment of the optimal obs spacing is required for reliable fwi

late quaternary stratigraphy and paleogeography of the eastern nile delta egypt abstract a petrological study of numerous sediment borings identifies the late pleistocene and holocene lithofacies in the northeastern nile delta of egypt a coarsening upward sequence characterizes the major holocene depocenters located along the northern margin of the present delta stratigraphic correlation of radiocarbon dated sections and mapping of key facies such as delta front mud reveal the locations of four major holocene delta lobes related to former distributary branches of the nile river mendesian pelusiac tanitic and pre modern damietta these lobes formed primarily of marine prodelta and delta front deposits interfinger geographically but radiocarbon dating indicates that their bases are not synchronous lobes developed for the most part since 8000 years b p i e as the rate of eustatic sea level rise began to decrease climatic and sediment discharge fluctuations lateral migrations of distributaries and isostatic subsidence of land are additional factors that affected the temporal and spatial distributions of the lobes paleogeographic maps reveal the changes with time in the distributions of different lobes and deltaic plain environments marsh lagoons and concomitant displacement of the coastline holocene sediment accumulation rates to 500 cm per 1000 years are calculated this is 10 times greater than that on the nile cone and 50 times greater than on the egyptian continental shelf the delta coastal margin in the study area migrated northward by as much as 50 km during the past 5000 years an average progradational rate of up to 10 m per year the general configuration of the present delta developed during the past millennium the major changes recently induced by man in this region coupled with a series of continuing natural phenomena slow rise in sea level coastal erosion subsidence have markedly affected the evolution of the delta petrological study of the nile delta sediments provides baseline reference information to help recognize changes in the recent geological past to help identify those taking place at present and possibly to help predict those likely to occur in this region in the future

late quaternary linear dune accumulation and chronostratigraphy of the southwestern kalahari implications for aeolian palaeoclimatic reconstructions and predictions of future dynamics abstract the linear dunes of the kalahari now largely inactive have long been identified as having potential palaeoenvironmental significance the application of optically stimulated luminescence osl dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region though field methodologies and time consuming multiple aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated in order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records this intensive study presents 71 osl ages from the linear dunes of the southwestern kalahari at witpan south africa sampled with coring equipment at regular and frequent intervals down to bedrock the earliest sand accumulation recorded at witpan is at 104 ka and in spatially discrete locations other evidence of dune activity is recorded at 77 76 57 52 and 35 27 ka although an inherently discontinuous archive the linear dunes of the southwestern kalahari have the potential to record multiple phases of dune construction following the last glacial maximum there is near continuous evidence of dune building with a peak of accumulation recorded from 15 to 9 ka at five individual sites this latter period is generally recognised from other proxy evidence as being unusually arid in this region and such periods of dune activity are likely to be related to intensification of the continental anticyclone during the holocene accumulation has continued at most sites sampled albeit at a lesser intensity this may imply that these dunes are presently not far from thresholds of activation

application of waveform tomography to a crooked line 2d land seismic data set abstractonshore hydrocarbon exploration in the back arc region of japan suffers from seismic imaging challenges seismic data are typically acquired in a difficult environment along a crooked line over a rough surface topography underlain by severe near surface weathering layers the area is geologically complex and prestack depth processing is desirable however the data quality is suboptimal at near offsets and it hinders the migration velocity analysis required for depth processing thus a geologic interpretation needs to rely on time processing results nevertheless some data sets are rich in low frequency components and contain clear refracted and wide angle reflected waves both of which are favorable conditions for the application of waveform tomography we have used one such data set and we determined the applicability of waveform tomography to estimate the p wave velocity distribution to mitigate difficulties in the data we carefully optimized waveform tomography strategies and diligentl

chronology and palaeoenvironmental interpretation of holocene aeolian sands at the inland edge of the sinai negev erg three holocene dune units overlying pleistocene loess were studied in a sand quarry near the limit of inland penetration of the sinai negev erg from the mediterranean coast radiocarbon dating of hearths in these units indicates ages of c 4100 cal bc cal ad 600 900 and cal ad 1700 1950 for the units each of these dates corresponds to a period of relatively dense occupation of the region i e the chalcolithic period the late byzantine early islamic period and the recent period of bedouin settlement activation of the sands at these times is probably due to the grazing and trampling activity of livestock the chalcolithic sands have a high content of fines and appear to have accumulated under relatively moist conditions amino acid epimerization analysis of land snail shells from the dune sands indicates that none of the shells is contemporary with the sands the shells were incorporated during earlier periods of dune movement and subsequently redeposited along with the sands

reverse time migration migration of stacked or zero offset sections is based on deriving the wave amplitude in space from wave field observations at the surface conventionally this calculation has been carried out through a depth extrapolation we examine the alternative of carrying out the migration through a reverse time extrapolation this approach may offer improvements over existing migration methods especially in cases of steeply dipping structures with strong velocity contrasts this migration method is tested using appropriate synthetic data sets

a 160 000 year record of dune development and atmospheric circulation in southern arabia aeolian deposits in the wahiba sands sultanate of oman reveal patterns of atmospheric circulation over the past 160 000 years luminescence dating indicates a correlation of dune activity with periods of low global sea level and decreased monsoon intensity evidence from dune orientation and sedimentary structures shows exclusively northbound transport of sand during times of high latitude glaciation these results are in contrast to the current paleocirculation model that assumes an increase of northwesterly winds because of a southward shift of the intertropical convergence zone our results indicate that the circulation pattern during glacial times was comparable to that of the present

monitoring surface change on a namib linear dune in tackling the apparently intractable problem of linear dune initiation and maintenance there has been a move away from large scale deductive models to smaller scale field studies of individual dunes this paper reports a study of surface change on a large complex linear dune in the namib desert southern africa the dune surface responds to a markedly seasonal wind regime in summer westerly winds erode sand from the west flank of the dune and deposit it on the easterly lee side of the dune crest in winter this pattern is reversed easterly winds erode sand from the east slope and deposit it on the west slope the crest therefore moves back and forth some 15 m each year returning at the end of a year s cycle to its position at the beginning the position of the base of the dune appears to remain fixed even though sand is moving throughout the dune system the dune does extend northward along some resultant of the westerly and easterly winds despite relatively high levels of activity especially at the dune crest there is no evidence of the breakdown of the linear dune form the conclusion must therefore be that linear dunes can be maintained in bimodal wind regimes and are not necessarily related to unidirectional parallel regimes as others have suggested

mapping exposed and buried drainage systems using remote sensing in the negev desert israel abstract this paper examines the use of optical visible and infrared ir data synthetic aperture radar data sar and ground penetrating radar gpr for detection identification and mapping of exposed and buried channels under sands in the western negev israel and northern sinai egypt field observations and shallow geophysical methods corroborated the observations the halutza agur and shunra sand dunes are the continuation of the northern sinai dunes playa type sediments from the late quaternary are found in upper reaches of dry river channels between the dunes of the northwest negev and represent a deterioration of the drainage system caused by shifting sand dunes a dual polarimetric radar sir c image from srl 1 having two frequencies and two polarizations exhibits meaningful differences in reflectance between the buried and abandoned channels and their surroundings the buried continuation of wadi mobra and the larger nahal nizzana channels under the western shunra sand dunes can be observed in l band radar data these channels are not clearly observed either in the landsat thematic mapper tm visible nor in the near infrared nir images the radar wavelengths and polarizations that improve the contrast between the buried river beds and the surrounding sand mantle are in descending order l hv l hh and c hh however in places where the sand mantle is very thick or where channels cut through bedrock the visible and near infrared data from landsat tm are easier to interpret and tend to be more useful for mapping fluvial patterns

quantifying the basal conditions of a mountain glacier using a targeted full waveform inversion bench glacier alaska usa glacier dynamics are inextricably linked to the basal conditions of glaciers seismic reflection methods can image the glacier bed under certain conditions however where a seismically thin layer of material is present at the bed traditional analyses may fail to fully characterize bed properties we use a targeted full waveform inversion algorithm to quantify the basal layer parameters of a mountain glacier thickness d p wave velocity and density we simultaneously invert for the seismic quality factor q of the bulk glacier ice the inversion seeks to minimize the difference between the data and a one dimensional reflectivity algorithm using a gradient based search with starting values initialized from a monte carlo scheme we test the inversion algorithm on four basal layer synthetic data traces with 5 added gaussian noise the inversion retrieved thin layer parameters within 10 of synthetic test parameters with the exception of seismic q for the seismic dataset from bench glacier alaska usa inversion results indicate a thin basal layer of debris rich ice within the study area having mean velocity 4000 700ms 1 density 1900 200kgm 3 and thickness 6 1 5m

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

luminescence dating of sediments using single aliquots new procedures abstract the application of luminescence dating to quaternary sediments has been hampered by the labour intensive procedures involved determination of equivalent doses using single aliquots measured using an automated luminescence reader offers a significant reduction in labour equivalent dose determinations using two single aliquot additive dose methods are compared with equivalent doses measured using standard multiple aliquot methods for a suite of 12 dune sand samples from southwest north island new zealand the single aliquot correction method based upon adjusting the magnitude of the measured luminescence signal is found to give underestimates for those samples whose equivalent dose is greater than 80 gy and whose luminescence response to dose is non linear a second correction method based upon adjusting the value of the total added dose that the sample has received is described this second method gives equivalent dose results similar to those measured using standard multiple aliquot methods over the range from 0 1 to 400 gy

significance of primary hilltop loess in reconstructing dust chronology accretion rates and sources an example from the negev desert israel 1 although high latitude loess sequences have been studied extensively for reconstructing past climates loess in desert margins has been mostly overlooked moreover many low latitude loess studies have focused on secondary reworked sequences for which paleoclimatic inferences are complicated owing to postdepositional processes acting under local control in this respect the spatial distribution of the loess and its different types are crucial in this study we differentiate primary and secondary loess using remote sensing and field criteria we present remote sensing and geographic information system procedures for mapping loess distribution in general and for identifying pristine hilltop loess sequences in particular then we present the mineralogical and textural analyses combined with optically stimulated luminescence ages of one such primary hilltop loess sequence in the negev desert that show that the late pleistocene negev loess started accumulating at 95 ka much earlier than previously proposed 70 ka it was preceded by a previously unknown middle pleistocene period of loess formation at 180 130 ka the ages also suggest that the threshold of dust accretion rate needed for loess formation is 0 02 mm a 1 30 g m 2 a 1 a factor of 2 or more lower than previously thought 0 04 to 1 0 mm a 1 our results also provide insights into causes of late pleistocene loess accretion and its close association with regional dune field activity the methodology for mapping the loess distribution may potentially be generalized to help understanding loess formation in other more remote desert areas

abrasion derived sediments under intensified winds at the latest pleistocene leading edge of the advancing sinai negev erg abstract quaternary desert loess and sandstone loessite relationships in the geological record raise questions regarding causes and mechanisms of silt formation and accretion in the northern sinai negev desert carbonate terrain only sand abrasion in active erg could have produced the large quantities of quartzo feldspathic silts constituting the late quaternary northwestern negev loess in the continuum of source medium to fine sand of dunes to sink silts in loess the very fine sand is unaccounted for in the record this weakens the sand abrasion model of silt formation as a global process here we demonstrate that as predicted by experiments abrasion by advancing dunes generated large quantities of very fine sand 60 110 m deposited within the dune field and in close proximity downwind this very fine sand was generated 13 11 ka possibly synchronous with the younger dryas under gusty sand dust storms in the southeastern mediterranean and specifically in the northern sinai negev erg these very fine sands were washed down slope and filled small basins blocked by the advancing dunes outside these sampling basins it is difficult to identify these sands as a distinct product we conclude that ergs are mega grinders of sand into very fine sand and silt under windy quaternary and ancient aeolian desert environments

full waveform inversion and distance separated simultaneous sweeping a study with a land seismic data set abstract dense wide aperture and broad frequency band acquisition improves seismic imaging and potentially allows the use of full waveform inversion for velocity model building the cost of dense acquisitions however limits its applicability blended or simultaneous shooting could lead to a good compromise between cost and dense acquisition although the cross talk between simultaneous sweeps may reduce imaging capabilities onshore a compromise is achieved with distance separated simultaneous sweeping acquisition because the shots are easily separated when the processing focuses on pre critical reflected events full waveform inversion for velocity model building however relies on post critical reflected refracted and diving events these events can interfere in a distance separated simultaneous sweeping acquisition by using a single vibrator single receiver data set recorded in inner mongolia china a distance separated simultaneous sweeping data set is created to study the robustness of full waveform inversion in this acquisition context this data set is well suited for full waveform inversion since it contains frequencies down to 1 5 hz and offsets up to 25 km full waveform inversion after a crude deblending of the distance separated simultaneous sweeping data set leads to a result very similar to the one obtained from the single vibrator single receiver data set the inversion of the blended data set gives a slightly less good result because of the cross talk but it is still quite satisfactory

holocene evolution of the northeastern corner of the nile delta abstract the constructive phase of the modern nile delta as manifested in a 48 m section drilled east of the suez canal commenced in very early holocene times sands rich in marine fauna were deposited in the littoral zone and the shoreline was more than 20 km landward of its present day position subsequently clays and silts were dumped from the nile distributaries and the marine faunal spectrum became very limited and brackish later in early and middle holocene times the sediments deposited were rich in freshwater delta plain diatoms and pollen and in allochthonous fern spores from the tropics indicating proximity of a distributary mouth the middle part of the section 22 5 17 5 m is very poor in faunal and floral remains pollen grains from sabkha vegetation are abundant the environment which seems lagoonal and slightly hypersaline is related to the sea regression in middle holocene times euryhaline pelecypods dating from about 3000 yr b p are abundant around the 8 m depth upward there is an increase in pollen grains from sabkhas the section is poor in diatoms and those present are mostly euryhaline and lagoonal allochthonous spores derived from the nearby pelusiac branch are abundant between 3000 and 2000 yr b p the constructive phase of the modern delta terminated and winnowed sands began accreting in front of the delta plain

evaluating the use of dune sediments as a proxy for palaeo aridity a southern african case study abstract the dominance of dryland environments in the southern hemisphere makes the study of these regions of critical importance for the development of regional hemispheric and global models of environmental change unfortunately the wetting and drying cycles associated with semi hyperarid climates are not conducive to the preservation of traditional organic proxy data sources the last decade however has seen the development of a number of alternative archives including the application of luminescence dating techniques to dunes and other aeolian deposits in continental situations the existence of relict dune fields has long been thought to be evidence of drier conditions during the pleistocene and direct ages from these features have been interpreted almost exclusively as indicating phases of aridity however an increasing number of ages from a broader range of environments are calling into question the assumption that aeolian activity can be simply equated with aridity presented here is a comparison of dune ages that have been obtained from across southern africa with a range of proxies from both terrestrial and marine records taken as a whole three primary phases of activity can be identified at 60 40 35 20 and 17 4 ka the frequent discordance with other terrestrial records indicating coeval increases in humidity and the close correlation of these phases with wind strength proxies suggest that aridity is unlikely to be the sole or even primary forcing mechanism for aeolian activity in the region and the palaeoclimatic significance of these sedimentary archives needs to be reassessed

understanding linear dune chronologies insights from a simple accumulation model abstract dunefields are today often found in regions where environmental conditions are no longer conducive to widespread aeolian transport and deposition and are thus seen as potential archives of palaeoenvironmental information some dune types are more suitable for this purpose than others and linear dunes used here synonymously with longitudinal dunes have been most frequently employed they are commonly found in dryland and dryland marginal regions and they are apparently less migratory than some other dune forms thereby offering the potential for longer environmental histories most recent studies have employed optical osl dating surveys which directly date the emplacement of dune sands to attempt to produce a representative history of aeolian accumulation at a dunefield scale yet such studies have not always given due consideration to the geomorphology of linear dune accumulation although linear dunes do not rework their sand as readily as say barchans dunes it is clear that sand deposited during an aeolian event is likely to have been removed from elsewhere on the dunefield s surface for this reason all dune archives must be assumed to be discontinuous over long timescales the effect of sediment redistribution on dune preservation and thus palaeoenvironmental interpretation is difficult to observe and poorly understood we present a simplified probabilistic model to replicate deposition erosion of sand at a linear dune crest thus simulating the type of profile sampled in many field studies in order to produce a local accumulation history the modelled sand flux incorporates various feedbacks and the simulations are run with varying boundary conditions in which the simulated surface is assumed to be in equilibrium over the multi millennial timescales of the model s duration periodic instabilities in the landscape are generally well recorded by the modelled dune accumulation history particularly when the events involve the system as a whole briefly functioning out of an equilibrium state i e the probabilities of deposition and reworking are not equal however under forcing conditions where the probabilities are unchanged throughout the duration of the model run the results can show apparent structure within the data when sample sizes are low although at large sample sizes the preservation potential decays with burial age according to a power law the model confirms the importance of rigorous sampling strategies for such studies but also suggests that if such precautions are taken the reworking inherent to linear dune aeolian systems does not preclude their use as a quaternary palaeoenvironmental archive of environmental change

age and dynamics of linear dunes in the namib desert bristow c s duller g a t lancaster n 2007 age and dynamics of linear dunes in the namib desert geology 35 6 555 558 sponsorship american chemical society

two dimensional velocity models from wide angle seismic data by wavefield inversion summary modern wide angle surveys are often multi fold and multi channel with densely sampled source and receiver spacings such closely spaced data are potentially amenable to multi channel techniques involving wavefield propagation methods such as those commonly used in reflection data processing however the wide angle configuration requires techniques capable of handling very general wave types including those not commonly used in reflection seismology this is a situation analogous to that faced in cross borehole seismics where similar wave types are also recorded in a real cross borehole example we compare pre stack migration traveltime tomography and wavefield inversion we find that wavefield inversion produces images that are quantitative in velocity as are the tomograms but are of significantly higher resolution the wavefield inversion results have a resolution comparable to that of the qualitative pre stack migration images we seek to extend this novel development to the larger scale problem of crustal imaging an essential element of the approach we adopt is its formulation entirely within the temporal frequency domain this has three principal advantages 1 we can choose to decimate the data by selecting only a limited number of frequency components to invert thus making inversion of data from large numbers of source positions feasible 2 we can mitigate the notorious non linearity of the seismic inverse problem by progressing from low frequency components in the data to high frequency components and 3 we can include in the model any arbitrary frequency dependence of inelastic attenuation factors q and indeed solve for the spatial distribution of q an initial synthetic test with an anomaly located within the middle crust yields a velocity image with the correct structural features of the anomaly and the correct magnitude of velocity anomaly this is related to the fact that the reconstruction is obtained from forward scattered waves under these conditions the method thus behaves much like tomography a second test with a deeper more extensive anomaly yields an image with the correct velocity polarity and the correct location but with a deficiency in low and high wavenumbers in this case this is because the reconstruction is obtained from backscattered waves under these conditions the method behaves not like tomography but like migration a more extensive test based on a large wide angle survey in south eastern california and western arizona demonstrates a real potential for high resolution imaging of crustal structures although our results are limited by the acoustic approximation and by the relatively low frequencies that we can model today the images are sufficiently encouraging to warrant future research the problem of local minima in the objective function is the most significant practical problem with our method but we propose that appropriate layer stripping methods can handle this problem

fine scale thermohaline ocean structure retrieved with 2 d prestack full waveform inversion of multichannel seismic data application to the gulf of cadiz sw iberia this work demonstrates the feasibility of 2d time domain adjoint state acoustic full waveform inversion fwi to retrieve high resolution models of ocean physical parameters such as sound speed temperature and salinity the proposed method is first described and then applied to pre stack multi channel seismic mcs data acquired in the gulf of cadiz sw iberia in 2007 in the framework of the geophysical oceanography project the inversion strategy flow includes specifically designed data pre conditioning for acoustic noise reduction followed by the inversion of sound speed in the shotgather domain we show that the final sound speed model has a horizontal resolution of 70m which is two orders of magnitude better than that of the initial model constructed with coincident expendable bathy thermograph xbt data and close to the theoretical resolution of o temperature t and salinity s are retrieved with the same lateral resolution as sound speed by combining the inverted sound speed model with the thermodynamic equation of seawater and a local depth dependent t s relation derived from regional conductivity temperature depth ctd measurements of the national oceanic and atmospheric administration noaa database the comparison of the inverted t and s models with xbt and ctd casts deployed simultaneously to the mcs acquisition shows that the thermohaline contrasts are resolved with an accuracy of 0 18oc for temperature and 0 08 psu for salinity the combination of oceanographic and mcs data into a common pseudo automatic inversion scheme allows to quantitatively resolve submeso scale features that ought to be incorporated into larger scale ocean models of oceans structure and circulation this article is protected by copyright all rights reserved

investigating the use of 3 d full waveform inversion to characterize the host rock at a geological disposal site the u k government has a policy to dispose of higher activity radioactive waste in a geological disposal facility gdf which will have multiple protective barriers to keep the waste isolated and to ensure no harmful quantities of radioactivity are able to reach the surface currently no specific gdf site in the united kingdom has been chosen but once it has the site is likely to be investigated using seismic methods in this study we explore whether 3 d full waveform inversion fwi of seismic data can be used to map changes in physical properties caused by the construction of the site specifically tunnel induced fracturing we have built a synthetic model for a gdf located in granite at 1000 m depth below the surface since granite is one of the candidate host rocks due to its high strength and low permeability and the gdf could be located at such a depth we use an effective medium model to predict changes in p wave velocity associated with tunnel induced fracturing within the spatial limits of an excavated disturbed zone edz modelled here as an increase in fracture density around the tunnel we then generate synthetic seismic data using a number of different experimental geometries to investigate how they affect the performance of fwi in recovering subsurface p wave velocity structure we find that the location and velocity of the edz are recovered well especially when data recorded on tunnel receivers are included in the inversion our findings show that 3 d fwi could be a useful tool for characterizing the subsurface and changes in fracture properties caused during construction and make a suite of suggestions on how to proceed once a potential gdf site has been identified and the geological setting is known

acquisition and processing of simultaneous vibroseis data numerous methods have been developed in the past three decades to speed up vibroseis acquisition this paper gives an overview of the most promising ones and proposes a classification of them into three categories simultaneous shooting cascaded sweeps and slip sweep the principles upon which these methods are based the processing techniques developed to separate the simultaneously acquired data and their main features are also discussed finally some criteria for the selection of the most suitable methods for the acquisition and the separation stages are proposed

frequency domain waveform modelling and inversion for coupled media using a symmetric impedance matrix to simulate the seismic signals that are obtained in a marine environment a coupled system of both acoustic and elastic wave equations is solved the acoustic wave equation for the fluid region simulates the pressure field while minimizing the number of degrees of freedom of the impedance matrix and the elastic wave equation for the solid region simulates several elastic events such as shear waves and surface waves moreover by combining this coupled approach with the waveform inversion technique the elastic properties of the earth can be inverted using the pressure data obtained from the acoustic region however in contrast to the pure acoustic and elastic cases the complex impedance matrix for the coupled media does not have a symmetric form because of the boundary continuity condition at the interface between the acoustic and elastic elements in this study we propose a manipulation scheme that makes the complex impedance matrix for acoustic elastic coupled media to take a symmetric form using the proposed symmetric matrix forward and backward wavefields are identical to those generated by the conventional approach thus we do not lose any accuracy in the waveform inversion results however to solve the modified symmetric matrix ldlt factorization is used instead of lu factorization for a matrix of the same size this method can mitigate issues related to severe memory insufficiency and long computation times particularly for large scale problems

the use of low frequencies in a full waveform inversion and impedance inversion land seismic case study velocity model building and impedance inversion generally suffer from a lack of intermediate wavenumber content in seismic data intermediate wavenumbers may be retrieved directly from seismic data sets if enough low frequencies are recorded over the past years improvements in acquisition have allowed us to obtain seismic data with a broader frequency spectrum to illustrate the benefits of broadband acquisition notably the recording of low frequencies we discuss the inversion of land seismic data acquired in inner mongolia china this data set contains frequencies from 1 5 80 hz we show that the velocity estimate based on an acoustic fullwaveform inversion approach is superior to one obtained from reflection traveltime inversion because after full waveform inversion the background velocity conforms to geology we also illustrate the added value of low frequencies in an impedance estimate

microbiotic crusts as biomarkers for surface stability and wetness duration in the negev desert microbiotic crusts play an important role in arid and semi arid regions yet very little information exists regarding the factors that impact their development in an attempt to assess the main factors that may determine their growth measurements of the amount of fines silt and clay rain moisture content wetness duration and wind erosion and deposition were carried out along a 12 station transect within a partially crusted dune field in the western negev desert and compared to the crust cover and chlorophyll content surface stability was the only variable that exhibited significant relationship with crust cover while daylight wetness duration exhibited strong positive relationship r2 0 92 0 99 with the crust s chlorophyll content the data point out that microbiotic crusts may serve as a useful biomarker for surface stability while wetness duration and wind will control crust cover and the crust chlorophyll content in semi stable habitats with absolute annual change in sand level of 2 3 mm stable habitats absolute change 1 mm will be controlled primarily by moisture while habitats with low surface stability absolute change of tens and hundreds of millimeters will be primarily controlled by wind furthermore owing to the strong positive relationship between daylight wetness duration and the crust s chlorophyll content the crust may serve as a useful biomarker for the quantification of surface wetness duration copyright 2009 john wiley sons ltd

full waveform tomography for lithospheric imaging results from a blind test in a realistic crustal model summary a comprehensive validation of 2 d frequency domain acoustic wave equation tomography was undertaken in a blind test using third party realistic elastic wave equation data the synthetic 2 d wide angle seismic data were provided prior to a recent workshop on the methods of controlled source seismology the true model was not revealed to the authors until after the presentation of our waveform tomography results the original model was specified on a detailed grid with variable p wave velocity s wave velocity density and viscoelastic q factor structure designed to simulate a section of continental crust 250 km long and 40 km deep synthetic vertical and horizontal component data were available for 51 shot locations spaced every 5 km recorded at 2779 receivers spaced every 90 m evenly spread along the surface of the model the data contained energy from 0 2 to 15 hz waveform tomography a combination of traveltime tomography and 2 d waveform inversion of the early arrivals of the seismic waveforms was used to recover crustal p velocity structure from the vertical component data using data from 51 sources 1390 receivers and frequencies between 0 8 and 7 0 hz the waveform tomography result contained apparent structure at wavelength scale resolution that was not evident on the traveltime tomography result the predicted acoustic waveforms in the final result matched the original elastic data to a high degree of accuracy during the workshop the exact model was revealed over much of the model the waveform tomography results provided a good correspondence with the true model from large to intermediate wavelength scales with a resolution limit on the order of 1 km a significant near surface low velocity zone invisible to traveltime methods was correctly recovered the results also provided a high resolution image of the complex structure of the entire crust and the depth and nature of the crust mantle transition some inaccuracies were observed near the edges of the images due to the limited ray coverage inherent to the footprint of the survey geometry several aspects of the waveform tomography strategy were critical to the success of the acoustic method with realistic synthetic viscoelastic data i the accuracy of the starting model from traveltime tomography ii implementation in the frequency domain iii the use of complex valued frequencies to effect time damping of the data residuals iv the selection of a suitable subset of data and data frequencies v progressive inversion of low to high frequency components of the data vi initial pre inversion matching of the amplitudes between observed and modelled data and vii sufficient preconditioning of both the data and the update images combined these strategies were effectively equivalent to a multiscale approach that mitigated the non linearity of the seismic inverse problem during the inversion we carried out repeated forward modelling to ensure our modelled waveforms matched the observed data as closely as possible in both frequency and time domains the synthetic data set used in this paper provides a benchmark for future testing of modelling inversion and imaging algorithms for wide angle lithospheric imaging

evidence of active dune sand on the great plains in the 19th century from accounts of early explorers eolian sand is extensive over the great plains of north america but is at present mostly stabilized by vegetation accounts published by early explorers however indicate that at least parts of dune fields in nebraska colorado kansas new mexico and texas were active in the 19th century based on an index of dune mobility and a regional tree ring record the probable causes for these periods of greater eolian activity are droughts accompanied by higher temperatures which greatly lowered the precipitation to evapotranspiration ratio and diminished the cover of stabilizing vegetation in addition observations by several explorers and previous historical studies indicate that rivers upwind of great plains dune fields had shallow braided sandy channels as well as intermittent flow in the 19th century wide braided sandy rivers that were frequently dry would have increased sand supplies to active dune fields we conclude that dune fields in the great plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high with or without greenhouse warming

the eastern mediterranean paleoclimate as a reflection of regional events soreq cave israel the climate of the eastern mediterranean region of the last 60 ky was determined by a high resolution study of the oxygen and carbon isotopic composition 1500 measurement pairs of speleothems from the soreq cave israel with chronology provided by 53 precise 230 th 234 u tims ages the high precision of the speleothem tims ages permits us to determine the timing of regional climatic events in the eastern mediterranean region and to see if they correlate with global events during the period from 60 to 17 ky the 18 o and 13 c values were generally 2 2 5 higher than during the period from 17 ky to present this is consistent with the climatic transition from glacial to interglacial within the 60 to 17 ky period the soreq cave stable isotope profile includes four cold peaks at 46 35 25 and 19 ky and 2 warm peaks at 54 and 36 ky in addition the period 17 ky has two more cold peaks at 16 5 and from 13 2 to 11 4 ky the ages of four of the six cold peaks correlate well with the ages of three heinrich events h1 h2 h5 and with the age of the younger dryas however the other two heinrich events are not reflected in the soreq cave record several other isotope peaks which appear during the last 7 ky are contemporaneous with regional climatic events in the middle east and north africa in addition to the drop in 18 o and 13 c observed between the last glacial and the holocene sharp simultaneous drops in 234 u 238 u 0 ratios sr concentrations and in 87 sr 86 sr are also observed suggesting that the latter are climate related these variations are interpreted in terms of major changes in the temperature the mean annual rainfall and its isotopic composition the isotopic composition of the mediterranean vapor source the soil moisture conditions and in the mixing proportions of sources with different 87 sr 86 sr ratios sea spray dust particles and dolomitic host rock

on acoustic waveform tomography of wide angle obs data strategies for pre conditioning and inversion we successfully apply the acoustic laplace fourier waveform tomography method to delineate p wave velocity structures of the mega splay fault system in the central part of the seismogenic nankai subduction zone offshore japan using densely sampled wide angle ocean bottom seismograph obs data originally acquired in 2004 our success is due to new and carefully designed data preconditioning and inversion strategies to mitigate i the well known non linearity of waveform inversion ii the challenges arising from crustal scale survey designs e g undersampling of the obss and iii modelling errors due to the use of the acoustic assumption we identify a sixfold set of key components that together lead to the success of the high resolution waveform tomography image i availability of low frequency components starting at 2 25 hz reducing the non linearity and access to large offset data up to 55 km increasing the depth of illumination and the recovery of low wavenumber components ii a highly accurate traveltime tomography result with an rms error of approximately 60 ms that further mitigates the non linearity iii a hierarchical inversion approach in which phase spectra are inverted first to reduce artefacts from the acoustic assumption and amplitude information is only incorporated in the final stages iv a laplace fourier domain approach that facilitates a multiscale approach to mitigate non linearity by restricting the inversion to the low frequency components and early arrivals first and sequentially including higher frequencies and later arrivals v a pre conditioning strategy for eliminating undesirable high wavenumber components from the the gradient vi a strategy for source estimation that reduce the influence of the instrumental design in the obs case study used for illustration purposes laplace fourier waveform tomography retrieves velocity anomalies as small as 700 m horizontally and 350 m vertically above the top of the philippine sea plate the resulting velocity structures include low velocity zones and thrust structures which have not been previously identified clearly the velocity models are validated by scrutiny of synthetic and observed waveforms by evaluating the coherency of source estimates and by comparison with 3 d pre stack migrated presdm images chequerboard tests and point scatter tests demonstrate both the reliability and the limitations of the acoustic implementation

linear dune accumulation chronologies from the southwest kalahari namibia challenges of reconstructing late quaternary palaeoenvironments from aeolian landforms abstract the linear dunes of the southern kalahari dunefield constitute one of the major palaeoenvironmental proxies in the region the application of optically stimulated luminescence osl dating since the1990s and advancements in the depth of sampling using augering equipment over the past few years have permitted the reconstruction of linear dune accumulation chronostratigraphies for entire dune profiles from base to crest these methods are applied to four dunes in the mariental stampriet region of the southern kalahari dunefield sampled at predominantly 0 5 m intervals individual dunes record multiple phases of dune construction but with only a few phases recorded consistently between two or more of the dunes results from the 48 osl ages produced here extend the aeolian accumulation record for the southern kalahari dunefield through the last three glacial interglacial cycles with two ages from the early part of mis6 a synthesis of all existing luminescence ages for the southern kalahari reveals that the dunefield has been partially active throughout much of the past 120 ka there are no clear clusters of ages within osl age errors this is in contrast to previous syntheses of ages for this region in addition these new data from mariental stampriet dunes show that clusters in grouped dune osl ages can be spuriously produced as a function of reducing the sampling frequency with depth within the dunes from 0 5 to 1 mintervals this has significant implications for previous conclusions regarding discrete phases of aeolian accumulation based on sampling at 1 m intervals and less vertically intensive sampling techniques the total luminescence data set of 136 ages for the southern kalahari implies that this dunefield has been close to the threshold of reactivation throughout much of the late quaternary