azimuth moveout for 3 d prestack imaging we introduce a new partial prestack migration operator called azimuth moveout amo that rotates the azimuth and modifies the offset of 3 d prestack data followed by partial stacking amo can reduce the computational cost of 3 d prestack imaging we have successfully applied amo to the partial stacking of a 3 d marine data set over a range of offsets and azimuths when amo is included in the partial stacking procedure high frequency steeply dipping energy is better preserved than when conventional partial stacking methodologies are used because the test data set requires 3 d prestack depth migration to handle strong lateral variations in velocity the results of our tests support the applicability of amo to prestack depth imaging problems amo is a partial prestack migration operator defined by chaining a 3 d prestack imaging operator with a 3 d prestack modeling operator the analytical expression for the amo impulse response is derived by chaining constant velocity dmo with its inverse equivalentl

ultrashallow depth imaging of a channel stratigraphy with first arrival traveltime inversion and prestack depth migration a case history from bull creek oklahoma depth imaging in ultrashallow 50 m environments presents twofold challenge 1 coda available for depth migration is very limited and 2 conventional time processing with limited coda generally fails to estimate reliable velocity models for depth migration we studied the combining of first arrival traveltime inversion and prestack depth migration psdm for depth imaging of ultrashallow paleochannel stratigraphy associated with the bull creek drainage system oklahoma restricted by a limited number of geophones 24 we acquired data for inversion and migration through two coincident profiles the first profile for inversion has a wider survey aperture 115 m maximum shot receiver spacing and consequently sparse cmp spacing 2 5 m whereas the second profile for psdm has denser cmp spacing 1 m and consequently a narrower survey aperture 46 m maximum shot receiver spacing we also found that the velocity model from traveltime inversion of the wider aperture data set is more preferable for dep

kirchhoff migration using eikonal equation traveltimes the use of ray shooting followed by interpolation of traveltimes onto a regular grid is a popular and robust method for computing diffraction curves for kirchhoff migration an alternative to this method is to compute the traveltimes by directly solving the eikonal equation on a regular grid without computing raypaths solving the eikonal equation on such a grid simplifies the problem of interpolating times onto the migration grid but this method is not well defined at points where two different branches of the traveltime field meet also computational and data storage issues that are relatively unimportant for performance in two dimensions limit the applicability of both schemes in three dimensions a new implementation of a gridded eikonal equation solver has been designed to address these problems a 2 d version of this algorithm is tested by using it to generate traveltimes to migrate the marmousi synthetic data set using the exact velocity model the results are compared with three other images an f x migration a standard for comparison a kirchhoff migration using ray tracing and a kirchhoff migration using traveltimes generated by a commonly used eikonal equation solver the f x migrated image shows the imaging objective more clearly than any of themore kirchhoff migrations and the authors advance a heuristic reason to explain this fact of the kirchhoff migrations the one using ray tracing produces the best image and the other two are of comparable quality less

tomographic determination of velocity and depth in laterally varying media estimation of reflector depth and seismic velocity from seismic reflection data can be formulated as a general inverse problem the method used to solve this problem is similar to tomographic techniques in medical diagnosis and we refer to it as seismic reflection tomography seismic tomography is formulated as an iterative gauss newton algorithm that produces a velocity depth model which minimizes the difference between traveltimes generated by tracing rays through the model and traveltimes measured from the data the input to the process consists of traveltimes measured from selected events on unstacked seismic data and a first guess velocity depth model usually this first guess model has velocities which are laterally constant and is usually based on nearby well information and or an analysis of the stacked section the final model generated by the tomographic method yields traveltimes from ray tracing which differ from the measured values in recorded data by approximately 5 ms root mean square the i

unified imaging of multichannel seismic data combining traveltime inversion and prestack depth migration imaging 2d multichannel land seismic data can be accomplished effectively by a combination of traveltime inversion and prestack depth migration psdm referred to as unified imaging unified imaging begins by inverting the direct arrival times to estimate a velocity model that is used in static corrections and stacking velocity analysis the interval velocity model from stacking velocities is used for psdm the stacked data and the psdm image are interpreted for common horizons and the corresponding wide aperture reflections are identified in the shot gathers using the interval velocity model the stack interpretations are inverted as zero offset reflections to constrain the corresponding interfaces in depth the interval velocity model remains stationary we define a coefficient of congruence j that measures the discrepancy between horizons from the psdm image andtheir counterparts from the zero offset inversion a value of unity for j implies that the interpreted and inverted horizons are consisten

seismic imaging of the solfatara crater campi flegrei caldera southern italy new evidence of the fluids migration pathways in the shallow structures abstract seismic imaging is used in this work to reconstruct the shallow structure of the solfatara crater a surface marker of deep magmatic activity inside campi flegrei caldera southern italy we analyze the 1d orthogonal seismic arrays deployed in nne ssw directions for 400 m through the solfatara crater during the recent active experiment ricen repeated induced earthquake and noise performed in the framework of the eu project medsuv seismic data have been edited in the pre stack stage by removing the noisy traces low frequency noise and reduce the ground roll phases then a velocity analysis has been carried out starting from the velocity spectrum to obtain a rms velocity model which has been followed by nmo residual statics and dmo corrections we used the post stack kirchhoff migration technique before the extraction of the energy root mean square envelope and sweetness attributes defining the highest amplitude zones the time gain attribute in order to interpret the deep reflectors and the variance attribute to define the faults discontinuities and chaotic zones amplitude versus offset avo analysis has been performed to identify the gas saturated zone using partial angle stacks which is a benchmark to verify the presence of gas the main contribution of this work is to provide a more detailed and improved seismic reflection image of the shallow depth of the solfatara crater the reliability of our velocity model has been assessed through the use of the vp velocity model previously obtained by the non linear bayesian technique this provides a final stack showing that the shallower minor faults and the extension of the major faults represent the main pathways for the uprising fluids we present the visual evidence for the fluids trapped in the shallower part of the crater at depths between 20 and 50 m below the surface of the crater

p wave reflection imaging of submerged soil models using ultrasound an ultrasonic p wave reflection imaging system is used to noninvasively image submerged soil models with embedded anomalies and complex geometric layer contacts the ultrasonic transducers emit compressive waves into water that subsequently transmit into the underlying soil and measurements of the reflections are used to construct the images the properties of the transducers and data acquisition hardware and software are explained fast signal stacking is used to improve signal to noise ratio and provide clearer images transducer directivity is explained as a wave passage effect and transfer functions are derived for square and circular transducers to quantify directivity the transfer functions agree reasonably with measured amplitude data the cause of errors in the imaged position of dipping reflectors is explained and a kirchhoff migration algorithm is implemented to correct these errors a soil model consisting of embedded high and low impedance anomalies dipping soil layer contacts and an u

wavefield tomography using reverse time migration backscattering abstractreverse time migration backscattering contains kinematic information that can be used to constrain velocity models the backscattering results from the correlation between forward scattered and backscattered wavefields from sharp interfaces i e sediment salt interfaces the synchronization between these wavefields depends on the velocity of the sediment section and the correct interpretation of the sharp boundary we have developed an optimization workflow in which the sediment velocity and the sharp boundary are updated iteratively the presence of sharp boundaries in the model lead to high and low wavenumber components in the objective function gradient the high wavenumber components correspond to the correlation of wavefields traveling in opposite directions whereas the low wavenumber components correspond to the correlation of wavefields traveling in the same direction this behavior is similar to reverse time migration in which the high wavenumber components represent the reflectors th

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

understanding the reverse time migration backscattering noise or signal reverse time migration backscattered events are produced by the cross correlation between waves reflected from sharp interfaces e g salt bodies these events along with head waves and diving waves produce the so called reverse time migration artefacts which are visible as low wavenumber energy on migrated images commonly these events are seen as a drawback for the reverse time migration method because they obstruct the image of the geologic structure which is the real objective for the process in this paper we perform numeric and theoretical analysis to understand the reverse time migration backscattering energy in conventional and extended images we show that the reverse time migration backscattering contains a measure of the synchronization and focusing information between the source and receiver wavefields we show that this synchronization and focusing information is sensitive to velocity errors this implies that a correct velocity model produces reverse time migration backscattering with maximum energy therefore before filtering the reverse time migration backscattered energy we should try to obtain a model that maximizes it

systematics of ni and co in olivine from planetary melt systems lunar mare basalts the systematics of co and ni in olivine from six apollo 12 olivine basalts were studied by sims techniques and correlated with major and minor element data obtained with the electron microprobe our results together with previous studies demonstrate that one of these basalts 12009 was extruded as a liquid onto the lunar surface and was parental to five other cumulates 12075 12020 12018 12040 and 12035 the concentrations of ni in zoned olivine phenocrysts behave as expected for a highly compatible element with initial estimated d ni 9 9 on the other hand co concentrations in olivine vary hardly at all and show flat patterns across crystals that retain normal zoning trends for mg fe mn and ni the explanation for this behavior is not that d co nearly equal 1 our estimated d co 4 or that co zoning has been erased by rapid diffusion of co compared to the other elements e g mg and fe that still show normal zoning the explanation for the behavior as originally suggested by kohn et al 1989 is that the increase in d co with crystallization exactly balances the depletion of co in the melt this decoupling of the behavior of ni and co in olivine results in significant increases in co ni with crystallization

identifying the effects of petrologic processes in a closed basaltic system using trace element concentrations in olivines and glasses implications for comparative planetology we use trace element concentrations in olivines and glasses from a closed basaltic system to identify the effects of petrologic processes on the trace element record of that system the closed basaltic system in question is the makaopuhi lava lake mll which is closed with respect to magma mixing detailed studies of this lava lake have provided important information about system variables and petrologic processes that have been measured and observed at the lake these previous studies show that olivine crystallized from the lava lake at all stages of the lake s evolution which means that olivine and residual glasses contain a record of the lake s petrologic history we use this information in conjunction with variations in trace element concentrations in olivines and glasses to show that mineral crystallization gravitational settling convective flow filter pressing and mineral melt interface kinetics have characteristic effects on the trace element record of a closed basaltic system these results are pertinent to the field of comparative planetology because they can be used to evaluate petrologic information in small samples from other planetary bodies where information about system variables and or petrologic processes is limited

fast 3d target oriented reverse time datuming imaging of subsalt sediments is a challenge for traditional migration methods such as kirchhoff and one way waveequation migration consequently the more accurate twowaymethodofreverse timemigrationrtmispreferredfor subsalt imaging but its use can be limited by high computation cost to overcome this problem a 3d target oriented reverse time datuming rtd method is presented which can generate redatumed data economically in target areas beneath complex structures such as salt domes the redatumed datainthetargetareathencanbemigratedinexpensivelyusing a traditional migration method if the target area is much smaller than the acquisition area computation costs are reduced significantly by the use of a novel bottom up strategy to calculate the extrapolated green s functions target orientedrtdistestedon2dand3dseg eagesyntheticdata sets and a 3d field data set from the gulf of mexico results show that target oriented rtd combined with standard migration can image sediments beneath complex structures accurately with much less calculation effort than full volume rtm the requirement is that the area over the target zone is smallerthanthatoftheacquisitionsurvey

true amplitude frequency wavenumber constant offset migration low s n ratios interfering diffractions and dip related problems e g reflector point dispersal dip dependent nmo and reflection angle make reliable amplitude versus offset avo analysis a difficult task prestack time migration pstm collapses diffractions increases the s n ratio and reduces dip related problems therefore pstm is usually required before offset dependent information can be extracted from seismic data and pstm is mandatory before comparing real seismic data with 1 d earth model synthetic data we present a 2 d frequency wavenumber common offset prestack time migration algorithm to treat the amplitudes correctly a 3 d to 2 d transform of the data is required before doing the migration this is done by correcting the data for out of plane geometrical spreading migration artifacts are attenuated exploiting the fact that the maximum dip to be migrated decreases with increasing traveltime and offset the final processing steps before further processing are 2 d geometrical spre

frequency selective design of the kirchhoff migration operator1 integral migration techniques perform a sum over an aperture of input traces to obtain output at a single point the length of the aperture is limited by a spatial nyquist criterion which typically prohibits imaging very steep dips at very high frequencies without generating severe migration artifacts migration operator aliasing for time domain kirchhoff migration this can be a fatal shortcoming the standard way to address this problem is to interpolate traces spatially before migration this reduces the trace spacing thereby increasing the frequency content which can be migrated without aliasing at steep dips an alternative remedy to the operator aliasing problem is to modify the phase response of the kirchhoff migration operator this operator is frequency selective across the migration aperture it passes all temporal frequencies of the input traces in the innermost portion of the aperture referring to the shallow dips and gradually cuts out the higher frequencies as it approaches the outer portion of the aperture thus while all frequencies of the input data contribute to the shallow dip portion of the migrated image only the permissible low frequencies of the input data contribute to imaging the steepest dips using a simple realization of a frequency selective kirchhoff migration operator this technique is illustrated on a synthetic data set involving greater than vertical dips

velocity anisotropy of shales and depth estimation in the north sea basin it is known that in the north sea basin the depths to major reflectors as determined from surface seismic data are often larger than the well log depths from a study of data sets which tie 21 wells i found a strong correlation between the occurrence of the depth error and the presence of shales in the subsurface assuming that the error is caused by elliptical velocity anisotropy in shales i measured the anisotropy from a comparison of the well log sonic data and the interval velocity profile obtained from the surface seismic data and also from a comparison of the seismic depth and the well log depth it was found that the two methods of measurements agree with each other and also agree qualitatively with the previous laboratory measurements of anisotropy in shale samples the results strongly suggest that the depth anomaly in the north sea basin is caused by the velocity anisotropy of shales a simple method to correct the seismic depth is given

numerical methods for the migration of constant offset sections in homogeneous and horizontally layered media this paper describes schemes for the frequency domain migration of constant offset sections in homogeneous and horizontally layered media their main advantage is that individual constant offset sections can be processed in isolation the basis for these schemes is a generalization of the following plane wave analysis of migration for the zero offset case migration can be viewed in the time domain as a process whereby the plane waves echoed from a source to a geophone by a reflecting point are shifted in time to a common intersection the shift applicable to each plane wave can be derived from the knowledge of the diffraction curve for the reflecting point in a neighborhood of the geophone abscissa this time shift in turn determines the phase shift applicable in the frequency domain to the associated fourier component of the seismic section the central part of our methods is the construction of those elements of the diffraction curve pertinent to the shifts from the velocity map of the time section th

evaluating the relationship between the carbon and sulfur cycles in the later cambrian ocean an example from the port au port group western newfoundland canada abstract we present a high resolution 34 s sulfate and pyrite and 13 c carbonate record from the middle upper cambrian port au port group a mixed carbonate siliciclastic succession exposed in western newfoundland canada the results illustrate systematic 34 s sulfate shifts of 15 over relatively short stratigraphic intervals 10 m likely 34 s sulfate pyrite ca 23 and a generally positive coupling between changes in 13 c carbonate and 34 s sulfate together these results indicate that middle to late cambrian sulfate concentrations were low and that the sulfate reservoir was more sensitive to change than it was in either terminal neoproterozoic or cenozoic oceans however a simple carbon c and sulfur s isotope box model of the late cambrian ocean illustrates that low sulfate concentrations alone fail to account for the 15 34 s sulfate shifts recognized in port au port strata such large shifts can be generated only if fluctuating oceanic redox is invoked marine anoxia forces reduced c s burial and elevated 34 s driving larger 34 s changes per mole of organic carbon buried the conclusion that later cambrian oceans featured both low sulfate levels and widespread subsurface anoxia supports hypotheses that link fluctuating marine redox conditions in the delayed recovery of skeletal animals and metazoan reefs from late early cambrian extinction

true amplitude seismic migration a comparison of three approaches knowledge of elastic parameter compressional and shear velocities and density contrasts within the earth can yield knowledge of lithology changes elastic parameter contrasts manifest themselves on seismic records as angle dependent reflectivity interpretation of angle dependent reflectivity or amplitude variation with offset avo on unmigrated records is often hindered by the effects of common depth point smear incorrectly specified geometrical spreading loss source receiver directivity as well as other factors it is possible to correct some of these problems by analyzing common reflection point gathers after prestack migration provided that the migration is capable of undoing all the amplitude distortions of wave propagation between the sources and the receivers a migration method capable of undoing such distortions and thus producing angle dependent reflection coefficients at analysis points in a lossless isotropic elastic earth is called a true amplitude migration the principles of tr

stratigraphy and environmental conditions of the terminal neoproterozoic cambrian period in oman evidence from sulphur isotopes terminal neoproterozoic and cambrian evaporite rocks worldwide record a marked sulphur isotope excursion to very heavy 34 s isotopes that reflect a period of significant burial of reduced sulphur new 34 s data from anhydrite and pyrite of the ara group in oman extend this record to arabia depositional history of the ara group spans c 8 ma across the terminal neoproterozoic cambrian boundary therefore these rocks provide a detailed record of sulphur isotopic evolution in this important time interval ara group sulphur isotope values include a mean 34 s anhydrite of 39 4 2 6 1 range 32 4 46 4 n 61 and a mean 34 s pyrite of 1 4 7 3 1 range 10 8 to 11 4 n 12 the isotope signatures were not altered significantly during diagenesis and are representative of the isotopic composition of parent waters in the basin marine bromine concentrations in halite and marine fossils in associated carbonate rocks indicate that these waters had a marine origin bacterial sulphate reduction was the dominant process leading to the segregation between isotopically heavy sulphur incorporated in evaporite rocks and isotopically light sulphur buried in pyrite and organic matter strong sulphate reduction operated in a hypersaline and partly anoxic basin these environmental conditions were also conducive to the preservation of organic material and make the ara group a prolific hydrocarbon province significant variation of the observed values is attributed to the inherent variability of bacterial sulphate reduction including partially closed system behaviour disproportionation processes limited diagenesis and possibly secular variation of sulphur isotopes within the basin ara group 34 s anhydrite values overlap with data from other terminal neoproterozoic to cambrian basins but the mean 34 s anhydrite is highest in oman this observation cannot be attributed solely to the specific anoxic conditions and strong bacterial sulphate reduction in oman because such conditions were widespread in most evaporite basins of the terminal neoproterozoic cambrian periods instead slight age differences between these basins can introduce a bias in the sulphur isotope curve excellent preservation of ara group deposits and in particular the precise age constraints make the ara group representative for the seawater sulphur isotopic composition at the terminal neoproterozoic cambrian boundary as a result of the inherent variability of bacterial sulphate reduction 34 s values at the lower end of the spectrum should be most representative for the global signal based on results of this study the global signal is estimated to be approximately 35 40

sulfur isotopic trends and pathways of iron sulfide formation in upper holocene sediments of the anoxic black sea down core trends for extents of iron sulfidation in upper holocene microlaminated deposits of the black sea abyssal plain imply that most of the pyrite in these sediments is formed in the sulfidic water column and or very close to the sediment water interface sulfur isotopic data for pyrite within microlaminated muds from two localities in the deep basin show striking uniformity between sites and down core with a mean 34scdt value of 37 2 0 9 1 n 18 these isotopic trends support the hypothesis of early pyrite formation isotopic compositions of pyrite sulfur in the microlaminated bottom sediments are similar to those reported for particulate reduced sulfur collected in middepth sediment traps and to 34s values for water column dissolved sulfide within a narrow zone immediately below the o2 h2s interface these three sulfur reservoirs are distinctly different from the isotopic composition of ambient dissolved sulfide of the deep water column 175 m with 34s values for the deep dissolved sulfide reservoir being consistently lower by 2 to 4 these isotopic relationships suggest that iron sulfidation is occurring dominantly within a narrow shallow region at the top of the sulfidic water mass isotopic data from a fine grained turbidite collected in the deep basin and from rapidly accumulating iron monosulfide rich muds on the anoxic upper slope are enriched in34s relative to the microlaminated deposits the enrichments on the basin margin reflect a large component of iron sulfide formed during rapid burial a broad suite of geochemical data including sulfur isotopic results are consistent with an upper slope sediment source for the ubiquitous muddy turbidites of the deep basin the collective effects of reworking transport and redeposition result in a complete conversion of avs to pyrite with little additional iron sulfidation this conclusion is supported by a detailed isotopic mass balance the present isotopic study also highlights fundamental differences in the reactivities of the iron reservoirs distributed throughout the anoxic basin sediments of the upper slope and the genetically linked turbidites of the deep basin show similar extents of iron sulfidation that are significantly lower than those of the microlaminated deposits of the deep basin floor suggesting dramatically shorter timescales of iron reactivity for the microlaminated sediments of the deep basin importantly isotopic patterns from the modern black sea should assist greatly in the recognition and interpretation of ancient anoxia in the stratigraphic record

anisotropy signature in reverse time migration extended images reverse time migration can accurately image complex geologic structures in anisotropicmedia extended images at selected locations in the earth i e at commonimage point gathers carry rich information to characterize the angle dependent illumination and to provide measurements for migration velocity analysis however characterizing the anisotropy influence on such extended images is a challenge extended common image point gathers are cheap to evaluate since they sample the image at sparse locations indicated by the presence of strong reflectors such gathers are also sensitive to velocity error that manifests itself through moveout as a function of space and time lags furthermore inaccurate anisotropy leaves a distinctive signature in common image point gathers which can be used to evaluate anisotropy through techniques similar to the ones used in conventional wavefield tomography it specifically admits a v shaped residual moveout with the slope of the v flanks depending on the anisotropic parameter regardless of the complexity of the velocity model it reflects the fourth order nature of the anisotropy influence on moveout as it manifests itself in this distinct signature in extended images after handling the velocity properly in the imaging process synthetic and real data observations support this assertion

depth migration of imaged time sections none of the leading approaches to the migration of seismic sections the kirchhoff summation method the finite difference method or the frequency domain method readily migrates seismic reflections to their proper positions when overburden velocities vary laterally for inhomogeneous media the diffraction curve for a localized buried scatterer is no longer hyperbolic and its apex is displaced laterally from the position directly above the scatterer hubral observed that the kirchhoff summation method images seismic data at emergent image ray locations rather than at the desired positions vertically above scatterers in addition distortions in diffraction shapes lead to incorrect imaging i e incomplete diffraction collapse and hence to further displacement errors for dipping reflections the finite difference method has been believed to continue waves downward correctly through inhomogeneous media in conventional implementations however both the finite difference method and frequency domain a

three dimensional radar imaging of structures and craters in the martian polar caps abstract over the last decade observations acquired by the shallow radar sharad sounder on individual passes of the mars reconnaissance orbiter have revealed the internal structure of the martian polar caps and provided new insights into the formation of the icy layers within and their relationship to climate however a complete picture of the cap interiors has been hampered by interfering reflections from off nadir surface features and signal losses associated with sloping structures and scattering foss et al the leading edge 36 43 57 2017 https doi org 10 1190 tle36010043 1 addressed these limitations by assembling three dimensional data volumes of sharad observations from thousands of orbital passes over each polar region and applying geometric corrections simultaneously the radar volumes provide unprecedented views of subsurface features readily imaging structures previously inferred from time intensive manual analysis of single orbit data e g trough bounding surfaces a buried chasma and a basal unit in the north massive carbon dioxide ice deposits and discontinuous layered sequences in the south our new mapping of the carbon dioxide deposits yields a volume of 16 500 km 3 11 larger than the prior estimate in addition the radar volumes newly reveal other structures including what appear to be buried impact craters with no surface expression our first assessment of 21 apparent craters at the base of the north polar layered deposits suggests a hesperian age for the substrate consistent with that of the surrounding plains as determined from statistics of surface cratering rates planned mapping of similar features throughout both polar volumes may provide new constraints on the age of the icy layered deposits the radar volumes also provide new topographic data between the highest latitudes observed by the mars orbiter laser altimeter and those observed by sharad in general mapping of features in these radar volumes is placing new constraints on the nature and evolution of the polar deposits and associated climate changes

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

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

three dimensional 3 d seismic imaging of conduits and radial faults associated with hydrothermal vent complexes voring basin offshore norway abstract here we document a suite of radial faults associated with hydrothermal vent complexes in the voring basin offshore norway these complexes have pyramid shaped cylindrical and conical shaped conduits with a dome or eye shaped morphology at their summit intruding on paleogene sedimentary rocks hydrothermal vents are intimate with the tips of magmatic sills that were emplaced at depths ranging between 1800 and 5800 ms two way travel time twtt at shallower depths of 1800 to 3000 ms twtt and intermediate depths of 3000 to 5000 ms twwt magmatic sills regularly intersect the lower parts of the vent conduits which are characterized here as pipes an important parameter that is used to characterize the morphology of a hydrothermal vent conduit is the width of the conduit which is defined as the longest axis marking the extent of the vents conduit within the surrounding host rock strata our findings reveal that radial faults are commonly associated with the summits of hydrothermal vents implying the existence of local stress fields around the vents where the maximum compressive stress is radial and minimum stress is circumferential which overrides the regional stress field and indicate variable stress regimes as opposed to tectonic faults importantly circumferential stretching due to catastrophic plumbing of hydrothermal fluids differential compaction and intensive fracturing enabled the polygonal faults to realign in a radial pattern resulting in the formation of radial faults at the vent summit as a corollary of this work we hypothesize that pyramid shaped hydrothermal conduits are possibly markers of protracted sill emplacement in sedimentary basins

dip moveout by fourier transform the conventional normal moveout nmo and common midpoint cmp stacking process enhances reflections having a particular moveout velocity while attenuating events such as multiple reflections having different moveout velocities unfortunately this process also acts as a dip filter applied to the cmp stack in other words nmo and stacking enhances reflections having a particular slope in the cmp stack while attenuating reflections having different slopes nmo and stacking like any dip filter degrades lateral resolution fortunately this dip filtering action can be suppressed by applying in addition to nmo a prestack process known variously as devilish prestack partial migration and dip moveout as the latter term implies this process is a dip dependent moveout correction that enables reflections from both horizontal and dipping reflectors to be stacked with the same nmo velocity stated another way nmo velocities estimated from dip moveout corrected seismograms are independent of the dips o

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

reconstructing the primary reflections in seismic data by marchenko redatuming and convolutional interferometry state of the art methods to image the earth s subsurface using active source seismic reflection data involve reverse time migration this and other standard seismic processing methods such as velocity analysis provide best results only when all waves in the data set are primaries waves reflected only once a variety of methods are therefore deployed as processing to predict and remove multiples waves reflected several times however accurate removal of those predicted multiples from the recorded data using adaptive subtraction techniques proves challenging even in cases in which they can be predicted with reasonable accuracy we present a new alternative strategy to construct a parallel data set consisting only of primaries which is calculated directly from recorded data this obviates the need for multiple prediction and removal methods primaries are constructed by using convolutional interferometry to combine the first arriving events of upgoing and direct wave downgoing green s functions to virtual receivers in the subsurface the required upgoing wavefields to virtual receivers are constructed by marchenko redatuming crucially this is possible without detailed models of the earth s subsurface reflectivity structure similar to the most migration techniques the method only requires surface reflection data and estimates of direct nonreflected arrivals between the virtual subsurface sources and the acquisition surface we evaluate the method on a stratified synclinal model it is shown to be particularly robust against errors in the reference velocity model used and to improve the migrated images substantially

a three dimensional perspective on two dimensional dip moveout prestack migration in a constant velocity medium spreads an impulse on any trace over an ellipsoidal surface with foci at the source and receiver positions for that trace the same ellipsoid can be obtained by migrating a family of zero offset traces placed along the line segment from the source to the receiver the spheres generated by migrating the zero offset impulses are arranged to be tangent to the ellipsoid the resulting nonstandard moveout equation is equivalent to two consecutive moveouts the first requiring no knowledge of velocity and the second being standard normal moveout nmo the first of these is referred to as dip moveout dmo because this dmo nmo algorithm converts any trace to an equivalent set of zero offset traces it can be applied to any ensemble of traces no matter what the variations in azimuth and offset may be in particular this three dimensional perspective on dmo can be used with multifold inline data then it becomes clear that velocity independent dmo operates on rad

a neogene seawater sulfur isotope age curve from calcareous pelagic microfossils abstract until now our knowledge of the sulfur isotopic composition of seawater through geologic time has depended on stable isotopic analysis of sulfate from evaporites owing to the sporadic occurrence of evaporites through time the secular sulfur isotope age curve contains many gaps with little or no data in order to fill in some of these gaps particularly the neogene we have analyzed the sulfur isotopic composition of carbonate associated sulfate in carbonate tests of planktonic foraminifera other investigators have shown that sulfate may occur in biogenic calcites either lattice bound as micro fluid inclusions in adsorbed phases or as protein polysaccharides whatever the origin the sulfur isotopic composition of this sulfate appears to be representative of that of the water in which the organism lived as shown by results on recent calcareous foraminifera and macrofossils using this approach for study of miocene to recent pelagic marine sediments supplemented by new data for miocene marine evaporites from the gulf of suez we have found that the 34 s of seawater has decreased about 2 5 over the past 25 m y and that most of the decrease has occurred over the past 5 m y parallelling a decrease in the 13 c of dissolved oceanic bicarbonate from the same interval sedimentary redox models based on isotope records suggest that organic carbon and sulfide burial have both decreased over the past 5 m y alternatively an increase in weathering rates over the past 5 m y would not require a decrease in organic carbon or sulfide burial as long as the isotopic effect of the increased river input exceeds the isotopic effect of the burial of the reduced species in either case the net result would be a decrease in atmospheric p o 2

determination of planetary basalt parentage a simple technique using the electron microprobe many basaltic meteorites are being discovered in old and new meteorite suites including those from cold deserts e g antarctica and hot desert environments it is important to establish the specific planetary body source proven techniques for establishing planetary parentage include stable isotopic signatures especially oxygen certain elemental ratios in bulk samples and certain elemental ratios in specific minerals some of these techniques are expensive require considerable sample preparation and are adversely affected by weathering processes on the parent body or on earth we have been seeking key major and minor elemental ratios in pyroxene olivine and feldspar that can be measured by the electron microprobe on standard thin sections these ratios may be preserved in unweathered portions of mineral grains and thus see through weathering processes in addition if the sample is too small to provide a representative bulk composition it may still have key information recorded in individual minerals we have found that some of the most useful chemical parameters are fe mn atomic in olivine or pyroxene and the percent anorthite an in plagioclase solid solutions a plot of fe mn in pyroxene and or olivine verses an defines compositional fields that are significantly different for earth mars moon 4 vesta and the angrite parent body this method may be especially powerful when combined with oxygen isotope data

isotope fractionation by sulfate reducing natural populations and the isotopic composition of sulfide in marine sediments isotope fractionations during sulfate reduction by natural bacterial populations were measured in seven different marine sediments and compared with the isotopic composition of solid phase sulfides in the same sediments the measured fractionations during sulfate reduction could explain only between 41 and 85 of the 34s depletion in the sedimentary sulfides this result directly demonstrates that the depletion of 34s in solid sulfides is an expression of the combined activity of sulfate reducing organisms with additional fractionations accumulated during the oxidative part of the sulfur cycle the only known process to significantly augment the fractionations created during sulfate reduction is the microbial disproportionation of the intermediate sulfur compounds elemental sulfur thiosulfate and sulfite in a simple model we show how important each of these disproportionation processes could be in generating the isotopic composition of sedimentary sulfides the sulfate reduction rates in the sediments studied varied by a factor of 1000 and did not correlate with the fractionation during sulfate reduction by contrast a correlation was observed between sulfate reduction rate and the extent of 34s depletion into sedimentary sulfides the most 34s depleted sulfides found in sediments supporting the lowest rates of sulfate reduction thus the fractionations imposed during the disproportionating processes are better expressed in sediments with low sulfate reduction rates the direct phototrophic oxidation of sulfide to sulfate with minimal fractionation may have been important in the sediments that had a high sulfate reduction rate

split step fourier migration the split step fourier method is developed and applied to migrating stacked seismic data in two and three dimensions this migration method which is implemented in both the frequency wavenumber and frequency space domains takes into account laterally varying velocity by defining a reference slowness reciprocal of velocity as the mean slowness in the migration interval and a perturbation term that is spatially varying the mean slowness defines a reference vertical wavenumber which is used in the frequency wavenumber domain to downward continue the data across a depth interval as in constant velocity phase shift migration the perturbation term is used to define a source contribution that is taken into account by the application of a second phase shift in the frequency space domain since the method does not include the effects of second and higher order spatial derivatives of the slowness field the method theoretically is accurate only when there are no rapid lateral slowness variations combined wi

gaussian beam migration just as synthetic seismic data can be created by expressing the wave field radiating from a seismic source as a set of gaussian beams recorded data can be downward continued by expressing the recorded wave field as a set of gaussian beams emerging at the earth s surface in both cases the gaussian beam description of the seismic wave propagation can be advantageous when there are lateral variations in the seismic velocities gaussian beam downward continuation enables wave equation calculation of seismic propagation while it retains the interpretive raypath description of this propagation this paper describes a zero offset depth migration method that employs gaussian beam downward continuation of the recorded wave field the gaussian beam migration method has advantages for imaging complex structures like finite difference migration it is especially compatible with lateral variations in velocity but gaussian beam migration can image steeply dipping reflectors and will not produce unwanted reflectio

imaging salt with turning seismic waves turning seismic waves which first travel downward and then upward before and after reflection have been recorded in a 3 d seismic survey conducted over an overhanging salt dome careful processing of these turning waves enables the imaging of the underside of the salt dome and of intrusions of salt into vertical faults radiating from the dome when seismic wave velocity increases with depth waves that initially travel downward are reflected and may turn so as to travel upward before reflection a simple geometrical argument suggests that these turning waves are likely to exhibit abnormal moveout in com mon midpoint cmp gathers in that reflection time decreases with increasing source receiver offset this abnormal moveout and the attenuation of turning waves by most migration methods suggest that conventional seismic processing does not properly image turning waves the most important step in imaging turning waves assuming that they have been recorded is the migration process simple and inexpensive modifications to the conventional phase shift migration method enable turning waves to be imaged for little additional computational cost the examples provided in this paper suggest that these and other such modifications to conventional processing should be used routinely when imaging salt domes

seismic imaging of the naga thrust using multiscale waveform inversion this case study images the structural features related to the naga thrust fault northeast india using a combination of multiscale waveform inversion and prestack depth migration psdm the waveform model and the psdm image complement each other the former provides a physical property map p wave velocity model and the latter provides a structural image the velocity model encompassing the starting model for waveform inversion is constructed using joint inversion of first and reflected traveltimes the 4 8 hz data are inverted consecutively in 1 hz bandwidths to yield the final waveform model which in turn is used for psdm the psdm image and the waveform model are consistent with the lithological interpretation of an inline exploratory well when interpreted jointly the psdm image and the waveform model reveal the presence of a conjugate fault system in the naga thrust and fold belt

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

the impact of migration on avo amplitude variation with offset avo analysis is often limited to areas where multidimensional propagation effects such as reflector dip and diffractions from faults can be ignored migration inversion provides a framework for extending the use of seismic amplitudes to areas where structural or stratigraphic effects are important in this procedure sources and receivers are downward continued into the earth using uncollapsed prestack migration instead of stacking the data as in normal migration the prestack migrated data are used in avo analysis or other inversion techniques to infer local earth properties the prestack migration can take many forms in particular prestack time migration of common angle sections provides a convenient tool for improving the lateral resolution and spatial positioning of avo anomalies in this approach a plane wave decomposition is first applied in the offset direction separating the wavefield into different propagating angles the data are then gathered into common angle sections and migrated one angle at a time the common angle migrations have a simple form and are shown to adequately preserve amplitude as a function of angle normal avo analysis is then applied to the prestack migrated data examples using seismic lines from the gulf of mexico show how migration improves avo analysis in the first set of examples migration is shown to improve imaging of subtle spatial variations in bright spots subsequent avo analysis reveals dim spots associated with dry hole locations that were not resolvable using traditional processing techniques including both conventional avo and poststack migration a second set of examples shows improvements in avo response after migration is used to reduce interference from coherent noise and diffractions a final example shows the impact of migration on the spatial location of dipping avo anomalies in all cases migration improves both the signal to noise ratio and spatial resolution of avo anomalies

petrogenetic linkages among martian basalts implications based on trace element chemistry of olivine the shergottites exhibit a range of major and trace element compositions crystallization ages and initial sr nd hf and pb isotopic compositions to constrain the physical mechanisms by which shergottites obtain their compositional characteristics we examined the major and trace element record preserved in olivine in the more primitive shergottites based on such characteristics as the mg v zoning calculated dni co the olivine in y 980459 are most likely phenocrysts many of these same characteristics indicate that the olivines in other shergottites are not in equilibrium with the adjacent melt however in most cases they are not xenocrystic but additions of olivine from the same basaltic system elephant moraine eet a79001 may be an exception with the olivine data suggesting that it is xenocrystic in this case the olivine crystallized from a reduced and lreedepleted melt and was incorporated into an oxidized and enriched basalt vanadium and cao in olivine appear to record the appearance of spinel and pyroxene on the liquidus of most of the shergottites most of the olivine shergottites represent basalts produced by melting of reduced iw to iw 1 depleted mantle sources olivine data indicate that many of the primary melts derived from this source had similar ni co and mn shergottites such as northwest africa nwa 1110 1068 and perhaps roberts massif rbt 04261 that appear to be derived from more enriched sources have distinctly different olivine in the case of nwa 1110 1068 the olivine data suggests that the enriched component was added to system prior to olivine crystallization

ediacaran growth of the marine sulfate reservoir abstract the sulfur isotope record as preserved in sedimentary sulfate and sulfide minerals reflects the progressive oxidation of earth s surface environment the latest proterozoic to early paleozoic marine sulfur isotope record is distinguished by unusually high 34 s values in marine sulfates and sulfides geological considerations and sulfur isotopic data indicate that the 34 s enrichment of the marine sulfate reservoir was the result of a rapid increase in the net fractionation between sedimentary sulfate and pyrite 34 s without a compensatory decline in the fractional burial rate of pyrite f pyr a simple one box model in which 34 s is linked non linearly to marine so 4 is used to explore the response in sedimentary sulfur isotope records 34 s sulf and 34 s pyr to an increasing marine sulfate reservoir the model results when compared with a compilation of existing 34 s sulf and 34 s pyr data suggest that the marine sulfate reservoir grew rapidly to roughly phanerozoic levels in the middle ediacaran period before the gaskiers glaciation and prior to the onset of the shuram wonoka negative 13 c anomaly it is further hypothesized that p o 2 levels rose prior to the onset of this extreme perturbation to the global carbon cycle permitting the oxidation of a previously euxinic deep ocean and appearance of the first ediacaran fauna by ca 575 ma despite the enormous demand on oxidants implied by this large magnitude and long duration carbon isotope anomaly

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

image domain wavefield tomography with extended common image point gathers waveform inversion is a velocity model building technique based on full waveforms as the input and seismic wavefields as the information carrier conventional waveform inversion is implemented in the data domain however similar techniques referred to as image domain wavefield tomography can be formulated in the image domain and use a seismic image as the input and seismic wavefields as the information carrier the objective function for the image domain approach is designed to optimize the coherency of reflections in extended common image gathers the function applies a penalty operator to the gathers thus highlighting image inaccuracies arising from the velocity model error minimizing the objective function optimizes the model and improves the image quality the gradient of the objective function is computed using the adjoint state method in a way similar to that in the analogous data domain implementation we propose an image domain velocity model building method using extended common image point space and time lag gathers constructed sparsely at reflections in the image the gathers are effective in reconstructing the velocity model in complex geologic environments and can be used as an economical replacement for conventional common image gathers in wave equation tomography a test on the marmousi model illustrates successful updating of the velocity model using commonimage point gathers and resulting improved image quality

neoproterozoic sulfur isotope variation in australia and global implications abstract seven sulfur isotope stages are apparent in australian neoproterozoic sections 1 from 840 ma to the sturtian glaciation 700 ma 34ssulfate varied little 19 to 17 5 and 34ssulfide ranged from 20 to 23 2 the sturtian glaciation was followed by 3 a rise in 34ssulfide to an average of 30 seen also in china namibia and canada and in 34ssulfate at least to 26 and possibly to 45 the sharp rise in 34s of all sulfur fractions sulfate sulfide and organic leads us to speculate that sulfide depleted in 34s was deposited on the abyssal plain and that residual sulfate enriched in 34s remained beneath a stagnant ice covered ocean during the sturtian glaciation and was brought to the shallow continental margin during the post glacial transgression 4 34ssulfide and 34ssulfate fall from 640 to 607 ma 34ssulfate down to 17 probably from oxygen excess through massive organic carbon burial which causes weathering of sulfide depleted in 34s continental sulfide and previously deposited sulfide on the abyssal plain 5 the oxic environment of the marinoan 605 595 ma glaciation minimises sulfate reduction unlike the sturtian so that 34ssulfate is unvarying 6 the post glacial environment has sulfide depleted in 34s average 34ssulfide

seismic imaging of complex geometry forward modeling of sandstone intrusions abstract sandstone intrusions form large bedding discordant sandstones that intruded into finer grained less permeable host strata they form naturally sand propped hydraulic fractures that constitute a connected network of permeable conduits through which fluids escape to the earth s surface saucer shaped sandstone intrusions are among the largest volume intrusions and are commonly resolved on seismic data outcrop analogues of seismically resolved saucers shaped intrusions reveal that many attendant intrusions in particular dikes are undetected in seismic data seismic forward modeling of a detailed outcrop description of a saucer shaped intrusion demonstrates that intrusions steeper than 45 are undetected and that up to 40 of the entire volume of sandstone intrusions is not seismically imaged wedge geometry associated with discordant contacts between different lithologies causes constructive and destructive amplitude interference creating imaging artefacts of sandstone thickness and geometry comparison of the outcrop seismic models with 3d seismic data from volund oilfield demonstrate both the similarity of the saucer shaped intrusions and the distribution and quantity of dikes that may be undetected ca 78 using subsurface data lack of detection of dikes has direct implications on the valuation of upward migration of fluids and an overestimation of seal capacity this therefore has major implications when using seismic data to evaluate waste sequestration or to execute hydrocarbon or groundwater exploration and production

imaging complex geologic structure with single arrival kirchhoff prestack depth migration we compare various forms of single arrival kirchhoff prestack depth migration to a full waveform finite difference migration image using synthetic seismic data generated from the structurally complex 2 d marmousi velocity model first arrival traveltime kirchhoff migration produces severe artifacts and image contamination in regions of the depth model where significant reflection energy propagates as late or multiple arrivals in the total reflection wavefield kirchhoff migrations using maximum energy arrival traveltime trajectories significantly improve the image in the complex zone of the marmousi model but are not as coherent as the finite difference migration image by carefully incorporating continuous phase estimates with the associated maximum energy arrival traveltimes we obtain single arrival kirchhoff images that are similar in quality to the finite difference migration image furthermore maximum energy green s function traveltime and phase values calculated within the seismic frequency ban

vertical cable as a subsalt imaging tool the vertical cable is a patented method for acquiring and processing prestack 3 d marine seismic data that is based on technology developed by the us navy for antisubmarine warfare the engineering requirements for a vertical cable are quite different than for a horizontal towed cable because the vertical cable and hydrophone array must retain electrical and mechanical integrity under high hydrostatic pressure at depth

prestack depth migration of primary and surface related multiple reflections part i imaging surface related multiples i e all seismic waves reflected at the free surface at least once often severely contaminate seismic recordings because conventional imaging techniques require input data that consist of primary reflections only significant processing effort is commonly dedicated to attenuating multiples prior to migration on the other hand surface related multiples provide additional illumination of the subsurface and therefore should not be considered as noise we present a prestack depth migration method that allows primary and multiple reflections to be imaged simultaneously depth imaging using primary and multiple reflections dipmr involves decomposing the datainto upgoing and downgoing wave constituents followed by downward extrapolation artifacts generated by interference of upgoing and downgoing events not associated with the same subsurface reflection points crosstalk are attenuated by using a 2d deconvolution imaging condition in contrast to existing methods dipmr doe

pyroxene as a recorder of cumulate formational processes in asteroids moon mars earth reading the record with the ion microprobe igneous cumulate rocks provide an important record of planetary magmatism but there are pitfalls in their interpretation cumulus minerals may react with the trapped melt and other cumulus phases during sub solidus reactions thus losing a direct record of their igneous history one of the best approaches for estimating the melt compositions parental to the cumulates is to analyze the cores of cumulus phases for elements with slow diffusion rates e g ree in pyroxene because these most reliably retain a record of the mineralmelt partitioning we have conducted sims studies of pyroxenes from a variety of planetary cumulates including lunar norites martian orthopyroxenites asteroidal orthopyroxenites diogenites asteroidal pyroxene plagioclase cumulates cumulate eucrites and terrestrial orthopyroxenites and norites stillwater complex montana we emphasized the ree la ce nd sm eu dy er yb along with sr y and zr in these investigations our studies yielded the several conclusions i lunar mg suite norites crystallized from highly evolved kreepy melts that were emplaced into the lunar anorthositic crust one viable model suggests remobilization of kreep lithologies that formed late in the crystallization of the lunar magma ocean 2 orthopyroxenites from asteroid 4 vesta diogenites likely formed as cumulates from melts derived from depleted mantle which had previously experienced eucritic basalt removal the calculated parental melts show a limited range of major element compositions but an exceedingly large range of trace element variation that is difficult to explain by any simple crystallization or melting models 3 the diogenites of 4 vesta are cumulates from melts derived from many depleted mantle reservoirs that either formed numerous orthopyroxene plutons later mixed by impact brecciation or commingled by magma mixing to form a limited number of differentiated plutons we base this conclusion on a comparative investigation of a well studied terrestrial orthopyroxenite sequence bronzitite zone of the stillwater complex an important lesson to be learned from these studies in comparative planetology is that if simple petrogenetic models do not work for well studied terrestrial occurrences there is little reason to believe that they will work for planetary environments where we have little geologic control on sampling

slowness driven gaussian beam prestack depth migration for low fold seismic data subsurface images based on low fold seismic reflection data or data with geometry acquisition limitations such as obtained from ocean bottom seismography obs are often corrupted by migration swing artifacts incorporating prestack instantaneous slowness information into the imaging condition can significantly reduce these migration swing artifacts and improve image quality especially for areas with poor illumination we combine the horizontal surface slowness information of observed seismic data with gaussian beam depth migration to implement a new slowness driven gaussian beam prestack depth migration whereby fresnel weighting is combined naturally with beam summation the prestack instantaneous slowness information is extracted from the original obs or shot gathers using local slant stacks and is combined with a local semblance analysis during migration we propagate the seismic energy downward knowing its instantaneous slowness information at each image location the beam summation is localized in a resolution dependent fresnel zone the instantaneous slowness information controls the beam summation synthetic and real data examples confirm that slowness driven gaussian beam migration can suppress most noise from inadequate stacking and give a clearer migration result

upper permian zechstein supergroup carbonate evaporite platform palaeomorphology in the uk southern north sea abstract seismic interpretation geological mapping and depth conversion of the zechstein supergroup z2 cycle using high quality well calibrated three dimensional 3 d seismic has revealed the complex palaeomorphology of a deeply buried ancient carbonate shelf margin on the southwestern margin of the southern permian basin the new mapping shows that the margin comprises a series of corrugated embayments and promontories which extend up to 5 km 3 mi into the basin and locally have a palaeobathymetric relief of 200 m 650 ft well calibration across the margin demonstrates a strongly bipartite lateral thickness distribution between a high velocity anhydrite dominated shelf and a lower velocity halite dominated basin strong lateral and vertical velocity variations in the upper permian zechstein supergroup are known to have major impacts upon seismic imaging and depth conversion in the spb the resulting uncertainty remains one of the major challenges when interpreting and assessing the prospectivity of the underlying upper permian rotliegend group leman sandstone formation reservoirs in the uk southern north sea an understanding of the zechstein shelf edge s 3 d physiography and its velocity variation has implications for the delineation of traps containing the prospective reservoirs that lie below recognition of the complexity and effects of this shelf margin contributed to the recent juliet discovery whose position outside of the presently defined rotliegend group play fairway suggests that prospectivity is more extensive along the basin margin than previously thought as such the work provides a means by which to identify and delineate new structures and extend the life of this mature yet prolific gas province

sulfur cycling in the aftermath of a 635 ma snowball glaciation evidence for a syn glacial sulfidic deep ocean we have analyzed 34 s sulfate and pyrite 18 ocarbonate and 13 ccarbonate and major and trace elemental concentrations including extractable fe and mn phases in four sections of the maieberg formation the cap carbonate sequence to the marinoan glaciation in northern namibia 34 ssulfate profiles and other geochemical characteristics in the basal transgressive cap dolostone keilberg member are nearly identical in all sections and indicate deposition from a water mass with very low sulfate concentrations in the overlying interval that consists of rhythmites deposited during the transgressive high stand large geochemical disparities occur between sections that we interpret to have been deposited in open ocean versus restricted settings in the former a large negative shift in 34 ssulfate of 20 above the cap dolostone accompanies a change in mineralogy from dolomite to limestone a sharp decrease in 18 o and 13 c and a positive spike in fe and mn concentrations in the latter dolomite persists above the cap dolostone 34 ssulfate increases abruptly 18 o and 13 c are invariant and a spike in mn and fe concentrations is present but subtle these contrasting geochemical signatures in coeval sections can be explained by strong lateral chemical gradients that developed as cold euxinic deep water and a cap of warm oxic brackish water flooded the continental shelf during the post glacial transgression the geochemical di e rences between open ocean and restricted sections diminishes upsection presumably recording the gradual mixing and homogenization of the waters along the otavi platform

seismic interpretation of sill complexes in sedimentary basins implications for the sub sill imaging problem application of 3d seismic reflection data to igneous systems in sedimentary basins has led to a revolution in the understanding of mafic sill complexes however there is considerable uncertainty on how geometries and architecture of sill complexes within the subsurface actually relates to geometries in seismic reflection data to provide constraints on how sill complexes in seismic data should be interpreted we present synthetic seismograms generated from a seismic scale 22 0 25 km outcrop in east greenland constrained by abundant field data this study highlights how overlying igneous rocks adversely affect imaging of underlying intrusions and rocks by decreasing seismic amplitude frequency and making steeply dipping features near impossible to image furthermore seismic modelling in this study shows that because of the high impedance contrast between siliciclastic host rock and dolerites very thin 1 5 m intrusions should in principle be imaged in reflection seismic data at 3 km depth however comparison with actual seismic data with well data shows significant amounts of unimaged sill intrusions and this is likely due to limited seismic resolution overburden complexity inadequate velocity models and interference between reflections from closely spaced sills and sill splays significant improvements to sill imaging and interpretation could be made by better predicting occurrence and geometry of sill intrusions and including these in velocity models supplementary material a scaled version of the input panel fig 5d used for seismic modelling a1 and very high resolution versions of subfigures in figure 11 a2 3 are available at https doi org 10 6084 m9 figshare 5607160

the effects of migration velocity errors on traveltime accuracy in prestack kirchhoff time migration and the image of ps converted waves we analyze prestack ps migration images and their focusing sensitivity to errors in the computed ps traveltimes the key analysis tool is a formula that defines ps traveltimes errors as explicit functions of velocity model errors the most important factors in this formula are the ps velocity and the p to s velocity ratio analysis shows that the error in ps traveltime for shallow events is usually larger than that for deep events for a given error in the velocity model also the ps traveltime is affected more severely by errors in the ps velocity model than in the p to s velocity ratio the effect of traveltime errors increases with dip angle of reflectors numerical analysis shows that for a fixed scatterpoint the effect of the ps wave velocity error is several times larger than the effect of the error in the p to s velocity ratio examples from field data show that the ps wave velocity must be estimated accurately with errors less than 1 in order perfectly flatten the events in common image point cip gathers in contrast an error in the ps velocity ratio of up to several percent is allowed this suggests that for acceptable ps wave migration only the ps velocity model and a rough estimate of the p to s velocity ratio is needed this finding is useful for processing ps wave data because it is difficult and time consuming to estimate the velocity ratio accurately from the real data this finding is also useful for our understanding of ps wave behavior and for ps wave imaging

early cambrian seawater chemistry from fluid inclusions in halite from siberian evaporites abstract thirty nine samples of lower cambrian marine sedimentary halite with zoned primary fluid inclusions were analyzed using the umca method introduced by petrichenko 1973 petrichenko o i 1973 metody doslidzhennya u mineralakh galogennykh porid naukova dumka kyiv 91 pp in order to determine the contents of k mg 2 so 4 2 and ca 2 ions and to interpret the composition of parent seawater the analyzed samples were from the giant salt basin of eastern siberia where five major phases of salt deposition can be distinguished in the late vendian danilovo and early cambrian usolye belsk angara and litvintsevo basins our samples are all from early cambrian basins although the largest data set comes from the angara basin the results indicate that early cambrian parent seawater was similar in all studied basins and was characterized by lower mg 2 and so 4 2 and higher ca 2 concentrations relative to modern seawater the concentration of k in early cambrian seawater was similar to that of modern seawater accordingly the seawater in the entire early cambrian was ca 2 rich and so 4 2 poor the change of composition of seawater from so 4 2 rich ca 2 poor in the latest neoproterozoic to ca 2 rich so 4 2 poor recorded throughout the early cambrian probably occurred within a relatively short time span during the earliest cambrian nemakit daldynian time and caused a rise in ca 2 concentrations in the shelf seas leading to the onset of biocalcification and then the cambrian explosion

what can crystal size distributions and olivine compositions tell us about magma solidification processes inside kilauea iki lava lake hawaii abstract lava lakes offer the opportunity to investigate magma solidification and can be considered as a proxy for small magma chambers here we present olivine compositions and crystal size distributions csds from scoria and drill core samples from kilauea iki lava lake which formed during the 1959 eruption of kilauea volcano hawaii three chemically distinct olivine populations were distinguished in the basis of their forsterite fo content 1 a high fo population fo86 90 2 an intermediate fo population fo78 82 and 3 a minor low fo population fo74 78 populations 1 and 2 both have deformed and undeformed crystals the third population may be the result of rejuvenation olivine in the lower 60 m of lake has a less fo rich composition and more crystals are deformed the csd analysis yields estimates of the average olivine residence time 1 60 years the shape of the olivine csds is fairly uniform with respect to depth curved csds are considered to be evidence of hybrid populations partly or totally involving crystal or magma mixing the turndown at the smallest sizes of most foundered crust and lake csds may be the result of coarsening making this process active both before and after eruption our csd modelling does not support significant crystal settling and overall convection in the lava lake although small advective currents are known to have occurred the olivine vertical stratification cannot be an original feature which is consistent with supposed strong stirring of the lake magma due to intense activity over the 17 eruptive phases it is also possible that independent basal feeding of the lake during the eruption may be needed to explain fully features of the chemical and mineralogical stratification

seismic characterization of hydrates in faulted fine grained sediments of krishna godavari basin unified imaging 1 a combination of diffusion and advection in fine grained sediments can create a patchy bottom simulating reflector bsr which has little to no apparent correlation with the overlying hydrate distribution using 2d seismic data from faulted clay rich sediments in the krishna godavari kg basin we show both the hydrate distribution and the bsr structure are fault controlled our demonstration hinges upon a kinematically accurate p wave velocity vp model which is estimated using a composite traveltime inversion depth migration method in an iterative manner the flexibility of the method allows simultaneous usage of traveltimes from multiple discontinuous reflectors the application begins with a simple vp model from time processing which is reflective of a diffusive continuous hydrate and free gas bearing system the application converges in three iterations yielding a final vpmodel which is suggestive of a patchy distribution of hydrates and free gas possibly developing through a combined diffusive advective system the depth image corresponding to the final vp model can be interpreted for faults that suggest ongoing tectonism the bsr appears to be truncated at active faults zones both the final vp model and the corresponding depth image can be reconciled with the hydrate distribution and bsr depth at logging coring sites located 250 m away from the line by projecting the sites along the strike direction of the regional faults

2 d traveltime and waveform inversion for improved seismic imaging naga thrust and fold belt india summary exploration along the naga thrust and fold belt in the assam province of northeast india encounters geological as well as logistic challenges drilling for hydrocarbons traditionally guided by surface manifestations of the naga thrust fault faces additional challenges in the northeast where the thrust fault gradually deepens leaving subtle surface expressions in such an area multichannel 2 d seismic data were collected along a line perpendicular to the trend of the thrust belt the data have a moderate signal to noise ratio and suffer from ground roll and other acquisition related noise in addition to data quality the complex geology of the thrust belt limits the ability of conventional seismic processing to yield a reliable velocity model which in turn leads to poor subsurface image in this paper we demonstrate the application of traveltime and waveform inversion as supplements to conventional seismic imaging and interpretation processes both traveltime and waveform inversion utilize the first arrivals that are typically discarded during conventional seismic processing as a first step a smooth velocity model with long wavelength characteristics of the subsurface is estimated through inversion of the first arrival traveltimes this velocity model is then used to obtain a kirchhoff pre stack depthmigrated image which in turn is used for the interpretation of the fault waveform inversion is applied to the central part of the seismic line to a depth of 1 km where the quality of the migrated image is poor waveform inversion is performed in the frequency domain over a series of iterations proceeding from low to high frequency 11 19 hz using the velocity model from traveltime inversion as the starting model in the end the pre stack depth migrated image and the waveform inversion model are jointly interpreted this study demonstrates that a combination of traveltime and waveform inversion with kirchhoff pre stack depth migration is a promising approach for the interpretation of geological structures in a thrust belt

wide azimuth angle gathers for wave equation migration extended common image point cip gathers contain all of the necessary information for decomposition of reflectivity as a function of the reflection and azimuth angles at selected locations in the subsurface this decomposition operates after the imaging condition applied to wavefields reconstructed by any type of wide azimuth migration method e g using downward continuation or time reversal the reflection and azimuth angles are derived from the extended images using analytic relations between the space lag and time lag extensions the transformation amounts to a linear radon transform applied to the cips obtained after applying the extended imaging condition if information about the reflector dip is available at the cip locations then only two components of the space lag vectors are required thus reducing computational cost and increasing the affordability of the method applications of this method include the study of subsurface illumination in areas of complex geology where ray based methods are

pyrite and organic matter in phanerozoic normal marine shales data have been obtained from our own chemical analyses and from the literature for the concentrations of organic carbon c and pyrite sulfur s in over 600 samples of cambrian to recent normal marine shales normal marine refers to deposition in oxygenated bottom water as evidenced by the presence of benthic fossils and or indicators of bioturbation all samples were selected to minimize 1 1 loss of c and or s due to weathering at the outcrop by emphasizing the use of drill core material 2 2 analytical errors and non diagenetic effects by avoiding sediments low in c or s content such as sandstones 3 3 fe limitation of pyrite formation by avoiding limestones cherts and euxinic shales 4 4 metamorphic loss of c relative to s by avoiding rocks obviously subjected to even low grade metamorphism our results indicate that 1 there is generally a good positive linear correlation between organic c and pyrite s for normal marine shales of all ages and 2 the mean cs ratio for normal marine shales has varied over time devonian to tertiary shales exhibit mean cs weight ratios 1 8 0 5 somewhat lower than quaternary sediments meancs 2 8 this we believe is due to preferential c loss relative to s during biogenic methanogenesis plus diagenetic heating distinctly lower mean c s values for the cambrian and ordovician 0 5 0 1 cannot be explained solely in terms of diagenetic c loss and instead must represent low original ratios the low original ratios we suggest were due mainly to the absence of bacterially refractory organic matter added to the marine environment by rivers at that time because the major source of such material vascular land plants had not yet evolved this along with a possibly lower degree of bioturbation contributed to enhanced pyrite formation and preservation and thus lower early paleozoic cs ratios

manual seismic reflection tomography prestack depth migration needs a good velocity model to produce a good image in fact finding the velocity model is one of the goals of prestack depth migration migration velocity analysis uses information produced by the migration to update the current velocity model for use in the next migration iteration several techniques are currently used to estimate migration velocities ranging from trial and error to automatic methods like reflection tomography here we present a method that combines aspects of some of the more accurate methods into an interactive procedure for viewing the effects of residual normal moveout corrections on migrated common reflection point crp gathers the residual corrections are performed by computing traveltimes along raypaths through both the current velocity model and the velocity model plus suggested model perturbations the differences between those sets of traveltimes are related to differences in depth allowing the user to preview the approximate effects of a veloci

green s function implementation of common offset wave equation migration common offset migration is extremely important in the context of migration velocity analysis mva since it generates geologically interpretable migrated images however only a wave equation based migration handles multipathing of energy in contrast to the popular kirchhoff migration with first arrival traveltimes we have combined the superior treatment of multipathing of energy by wave equation based migration with the advantages of the common offset domain for mva by implementing wave equation migration algorithms via the use of finite difference green s functions with this technique we are able to apply wave equation migration in measurement configurations that are usually considered to be of the realm of kirchhoff migration in particular wave equation migration of common offset sections becomes feasible the application of our wave equation common offset migration algorithm to the marmousi data set confirms the large increase in interpretability of individual migrated sections for about twice

diffraction imaging of sub vertical fractures and karst with full resolution 3d ground penetrating radar abstract vertical fractures with openings of less than one centimetre and irregular karst cause abundant diffractions in ground penetrating radar gpr records gpr data acquired with half wavelength trace spacing are uninterpretable as they are dominated by spatially undersampled scattered energy to evaluate the potential of high density 3d gpr diffraction imaging a 200 mhz survey with less than a quarter wavelength grid spacing 0 05 m 0 1 m was acquired at a fractured and karstified limestone quarry near the village of cassis in southern france after 3d migration processing diffraction apices line up in sub vertical fracture planes and cluster in locations of karstic dissolution features the majority of karst is developed at intersections of two or more fractures and is limited in depth by a stratigraphic boundary such high resolution 3d gpr imaging offers an unprecedented internal view of a complex fractured carbonate reservoir model analogue as seismic and gpr wave kinematics are similar improvements in the imaging of steep fractures and irregular voids at the resolution limit can also be expected from high density seismic diffraction imaging

image registration guided wavefield tomography for shear wave velocity model building multicomponent acquisitions offer the opportunity to form elastic migration images and to estimate elastic parameters of the subsurface compared with better constrained p wave velocity inversions it is more difficult to estimate the s wave velocity due to strong nonlinearities introduced by converted s waves we have developed an iterative s wave velocity inversion method guided by image registration given an accurate p wave velocity and a simple initial s wave model we form p p and p s images using elastic reverse time migration we use image registration to find the shifts between the p s and p p images the s wave velocity model could be updated iteratively by minimizing the differences between the original and the fractionally warped p s images a simple layered model and a modified marmousi model are used to demonstrate the viability of the new method in both examples high quality p s images as well as smooth s wave velocity models are inverted efficiently with a homogeneous s wave initial model

high resolution integrated geophysical investigation at the lancaster gold mine krugersdorp south africa an integrated geophysical approach using seismics and geoelectrical techniques was employed to investigate the architecture of historic narrow reef workings and a proposed open pit mine at lancaster gold mine near krugersdorp south africa the mining activities in the area were mainly carried out within the kimberley reef package in the upper central rand group of the witwatersrand supergroup which hosts several gold bearing conglomerates locally known as reefs the reefs are generally thin 2 m thick and dip between 28 and 32 south the low velocity weathered layer introduces significant static shifts in the reflection seismic data moreover environmental noise from drilling and trucking and the prominent bedrock overburden contact that produces various wave conversions p s conversion caused undesirable noise that contaminates the shot gathers as high amplitude source generated and monochromatic noise the noise was removed from the shot gathers using frequency and velocity filtering techniques the final depth migrated sections are characterised by high resolution images of the subsurface from 10 to 150 m depth which are constrained by the borehole information the reflection seismic data delineate the interfaces between different rock layers and the stopes the refraction and resistivity tomograms on the other hand provide more detailed images of the top 20 50 m of the subsurface and depict the approximate shallow geometry of fluid migration paths mined out areas and bedrock overburden boundaries the integrated results indicate that the study area is characterised by a weathered surface layer with variable low p wave velocity 400 1200 m s and resistivity 150 800 m the deeper layer reveals an increase in resistivity and velocity and it s characterized by discontinuities weak zones cavities or water bearing zones due to the mining activities the combined borehole and geophysical data provide valuable information regarding the physical characteristics of the subsurface and can be helpful for future risk management decisions environmental and engineering studies in the area

migration by extrapolation of time dependent boundary values migration of an observed zero offset wavefield can be performed as the solution of a boundary value problem in which the data are extrapolated backward in time this concept is implemented through a finite difference solution of the two dimensional acoustic wave equation all depths are imaged simultaneously at time 0 the imaging condition and all dips right up to vertical are correctly migrated numerical examples illustrate this technique in both constant and variable velocity media

comparison between reprocessed seismic profiles seismologic and geologic data a case study of the colfiorito earthquake area seismic reflection data are used to reconstruct the subsurface geologic structures below the umbria marche region in italy a highly seismogenic area with a recent history of seismic activity the 1997 1998 colfiorito sequence we reprocess three vibroseis seismic profiles acquired in the early 1980s for hydrocarbon exploration whose stacked sections were optimized for relatively deep oil targets on the reprocessed seismic profile closest to the epicentral area we construct the main reflectors to a depth of about 4 s two way time and compare this interpretation with the available hypocenters of the 1997 earthquakes the improvements in visualizing the shallow and deep reflections provide a better correlation between the reflectors and the observed surface structures as well as a better delineation of the basement rock geometry we find that part of the colfiorito sequence is localized around some of the reflectors in the reflection profile which we interpret as related to the active normal faults

interpretation validation on vertically exaggerated reflection seismic sections abstract reflection seismic data is usually displayed with a vertical exaggeration factor in the range 2 6 irrespective of whether it is time or depth domain data this vertical exaggeration gives certain advantages to stratigraphic and structural interpretation and is sometimes a prerequisite to view long wavelength structures however vertical exaggeration distorts geological structures affecting dip curvature line length cross sectional area volume and angular relationships reflection seismic can be assigned a vertical exaggeration heterogeneity factor based on the extremes of seismic velocities in the absence of appreciable poorly compacted units and bathymetry and generally on depth domain data vertical exaggeration is relatively homogeneous analytical solutions are derived to quantify the distortion of angular relationships curvature and bed thickness under homogeneous vertical exaggeration modelled extensional and compressional geometries give acceptable area balance restorations using vertical shear under homogeneous vertical exaggeration these vertically exaggerated restorations are neither admissible nor viable because the deformed and restored state sections are unrealistic given low heterogeneity of vertical exaggeration and relatively simple structure that typifies many extensional geometries and some thrust geometries aspect ratios of 1 1 are not definitively required for section validation by restoration

seismic migration problems and solutions historically seismic migration has been the practice science technology and craft of collapsing diffraction events on unmigrated records to points thereby moving migrating reflection events to their proper locations creating a true image of structures within the earth over the years the scope of migration has broadened what began as a structural imaging tool is evolving into a tool for velocity estimation and attribute analysis making detailed use of the amplitude and phase information in the migrated image with its expanded scope migration has moved from the final step of the seismic acquisition and processing flow to a more central one with links to both the processes preceding and following it in this paper we describe the mechanics of migration the algorithms as well as some of the problems related to it such as algorithmic accuracy and efficiency and velocity estimation we also describe its relationship with other processes such as seismic modeling our approach is tutorial we avoid presenting the finest details of either the migration algorithms themselves or the problems to which migration is applied rather we focus on presenting the problems themselves in the hope that most geophysicists will be able to gain an appreciation of where this imaging method fits in the larger problem of searching for hydrocarbons

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

seismic imaging in the krafla high temperature geothermal field ne iceland using zero and far offset vertical seismic profiling vsp data abstract among geothermal exploration methods active surface seismic methods have played only a minor role to date especially in high temperature volcanic systems reflection seismic data often reveal poor delineation of volcanic features due to the internal heterogeneity of volcanic sequences to enhance the vertical resolution one possibility is the application of downhole seismic methods like vertical seismic profiling vsp a test experiment was carried out in the krafla high temperature geothermal field ne iceland to assess the ability of vsp to image subsurface structures such as fractures zones of high permeability magmatic bodies and zones of supercritical fluids and steam logging in such hostile environments is technical challenging in many aspects but mainly due to the high temperature impact on the downhole electronic components of the measuring equipment this requires a thorough pre examination and implementation of the measurement especially to avoid delays and tool failures this paper presents results of zero and far offset vsp data from the k 18 borehole from within the krafla caldera which reveal good correlation with the surrounding lithology the raw three component seismic data display a good signal to noise ratio and dominant signal frequencies between 20 and 40 hz down to c 2200 m depth for air gun and explosive sources respectively a zero offset source comparison was also conducted to assess the use of different impulsive sources for future vsp surveys in similar settings by applying a standard vsp processing we identified stratigraphic boundaries between lavas hyaloclastites and intrusions which are in good agreement with existing well data for the zero offset vsp both p and s wave velocity models were calculated and a depth converted corridor stack was determined in addition multicomponent kirchhoff depth migration and fresnel volume migration were tested around the borehole the 3d results are promising but the specific shape and lateral extent of the reflectors could not be determined due to the restriction to only two sources and the insufficient spatial coverage aperture our study demonstrates that vertical seismic profiles can clearly detect variations in the subsurface volcanic stratigraphy in high temperature geothermal fields a more detailed reservoir characterization can be achieved by further data integration enhanced survey design including more source positions and improved processing and imaging techniques such as full waveform inversion

a global carbon isotope excursion spice during the late cambrian relation to trilobite extinctions organic matter burial and sea level abstract the steptoean positive carbon isotope excursion spice marks a global oceanographic event that confirms intercontinental correlations between different biogeographic realms based on agnostids and other blue water trilobites the spice excursion is documented from sections in laurentia kazakhstan china and australia where it begins with the mass extinction at the base of the pterocephaliid biomere steptoean stage in laurentia and at coeval extinction horizons in gondwana and perigondwana terranes the peak of spice 5 coincided with a time of maximum regression in laurentia spice is similar in this regard to excursions that coincide with glacio eustatic falls such as in the late ordovician a plausible scenario involves the transformation of ocean circulation between two states which led to enhanced coastal upwelling and benthic extinctions the lack of evidence for glaciation indicates that the coeval sea level fall sauk ii sauk iii event resulted from tectonic or hydrologic changes that remain poorly understood at this time

prestack migration deconvolution prestack migration in the time and depth domains is the premier tool for seismic imaging of complex structures unfortunately an undersampled acquisition geometry a limited recording aperture and strong velocity contrasts lead to uneven illumination of the subsurface this results in blurring the migrated image sometimes referred to as acquisition footprint noise in the migrated image to remedy this blurring partially we introduce prestack migration deconvolution md the md filter is a layered medium approximation to the inverse hessian matrix that is applied locally to the migrated section both synthetic and field data results show noticeable improvements in reducing migration artifacts and increasing lateral spatial resolution by more than 10 the computational expense for constructing the md filter is related to the md operator length its cost is about the same as that for migration but opportunities exist for significantly reducing this cost results suggest that md should be applied to migrated sections to optimize image quality

improving the resolution of impedance inversion in karst systems by incorporating diffraction information a case study of tarim basin chinaimpedance inversion with diffraction