joint inversion of 2d resistivity and seismic travel time data to image saltwater intrusion over karstic areas the simultaneous inversion of multiple geophysical data types has been proven to be a powerful tool to both improve subsurface imaging and help in the interpretation process the main goal of this paper was to develop joint inversion strategies to provide improved resistivity and seismic velocity images for delineating saline water zones in karstic geological formations the cross gradient constraint approach was adopted to jointly invert resistivity and seismic first arrival data the basic idea of this approach is to quantitatively estimate the structural similarity between resistivity and seismic velocity models using the cross product of their gradients and to achieve a unified geological model which satisfies both data sets initially synthetic data were employed to help develop a joint inversion strategy to be used over such complex geological structures the proposed strategy uses a weighting factor for the cross gradient constraints and separate damping factors for the resistivity and seismic data this strategy was applied successfully on field data from the karstic region of stilos crete greece

seismic detection of a subglacial lake near the south pole antarctica 1 seismic reflection data are analyzed to verify radar identification of a subglaical lake near the geographic south pole the seismic amplitude variation with offset avo technique is applied to confirm the presence of extensive free water and seismic imaging of the subsurface constrains lake depth and deeper subglacial structure in the region this lake is at least 4 2 km wide and likely as much as 10 km in diameter is up to 32 10 m deep and occupies a basin of thick sedimentary strata these results imply that extensive water storage is occurring in the south pole region the proximity of this lake to the amundsen scott south pole station makes research drilling to sample the lake and underlying sediments feasible and supportable

de glauconiarum origine the glauconitic facies is widespread on present day continental shelves from 50 s to 65 n and at water depths between 50 and 500 m and is in particularly great abundance on the upper slope and outer shelf between 200 and 300 m it is also common in many ancient rocks of post late precambrian age it occurs as sand to pebble sized essentially green particles granular facies but also as a surface coating on particles and hardgrounds and as a diffuse impregnation film and diffuse facies we suggest the replacement of the term glauconite which has been interchangeably used to designate a morphological form and a specific mineral by glaucony facies and glauconitic smectite and glauconitic mica as end members of the glauconitic mineral family the widely accepted model of burst and hower for glauconitization requires a degraded micaceous 2 1 layer lattice structure parent clay mineral however detailed analysis of numerous samples of recent glaucony reveals that such a parent substrate is exceptional the model therefore requires modification generally the parent material is carbonate particles argillaceous kaolinitic faecal pellets infillings of foraminiferal tests various mineral grains and rock fragments that pass gradually into the commonly occurring green grains we show that the process of glauconitization is achieved by de novo authigenic growth of automorphous crystallites in the pores of the substrate accompanied by progressive alteration and replacement of the substrate it is this two fold evolution that causes the verdissement of granular substrates macrofossils and hardgrounds the authigenic mineral is an iron rich and potassium poor glauconitic smectite while new smectites are growing into the remaining pore space the earlier smectites are modified by incorporation of potassium producing decreasingly expandable minerals with a non expandable glauconitic mica as the end member this mineralogical diversity of the glauconitic mineral family explains the highly variable physical and chemical properties of glaucony four categories nascent little evolved evolved and highly evolved glaucony are distinguished glauconitization appears to be controlled by a delicate balance between degree of physical confinement of a particle and the amount of ionic exchange between the micro environment and ambient open marine sea water the optimum conditions for glauconitization are those of semi confinement as a result the interior of a grain is more glauconitized than its less confined periphery similarly for identical substrate types large grains 500 m provide more favourable substrates for glauconitization than lesser confined small grains on a larger scale the formation of glaucony is governed by the availability of iron and potassium and the balance between detrital influx and winnowing low accumulation rates expose grains to the open marine environment for sufficiently long times 105 106 years for highly evolved glaucony

building 3d shear wave velocity models using surface waves testing the tarcento basin case history the paper reports on the use of surface wave testing for the construction of a three dimensional 3d shear wave velocity model of an alluvial basin the town of tarcento italy is located in a region with a high level of seismic hazard and was strongly affected by the two friuli earthquakes in 1976 the seismic surveys were performed with surface wave multistation methods using a combination of active source and passive source experimental setup experimental data were collected at 16 sites and inversion of the data is based on an innovative procedure for spatially constrained inversion with a single objective function in which a priori information is included the method provides an improvement in the robustness of the solution mitigating solution nonuniqueness available borehole logs at different locations are integrated into the data set in terms of a priori bedrock information three independent cross hole tests are used for a posteriori comparison of the inverted one dimensional 1d profiles three dimensional interpolation of the obtained profiles leads to a shear wave velocity model that is internally consistent and complies with a priori information cross hole results and suitable boundary profiles the model is intended for numerical simulations of the seismic response of the basin online material figure showing the a priori bedrock surface

direct reservoir parameter estimation using joint inversion of marine seismic ava and csem data a new joint inversion algorithm to directly estimate reservoir parameters is described this algorithm combines seismic amplitude versus angle ava and marine controlled source electromagnetic csem data the rock properties model needed to link the geophysical parameters to the reservoir parameters is described errors in the rock properties model parameters measured in percent introduce errors of comparable size in the joint inversion reservoir parameter estimates tests of the concept on synthetic one dimensional models demonstrate improved fluid saturation and porosity estimates for joint ava csem data inversion compared to ava or csem inversion alone comparing inversions of ava csem and joint ava csem data over the north sea troll field at a location with well control shows that the joint inversion produces estimated gas saturation oil saturation and porosity that is closest as measured by the rms difference l1 norm of the difference and net over the interval to the logged values whereas csem inversion provides the closest estimates of water saturation

friction of drill bits under martian pressure 1 frictional behavior was investigated for two materials that are good candidates for mars drill bits diamond impregnated segments and polycrystalline diamond compacts pdc the bits were sliding against dry sandstone and basalt rocks under both earth and mars atmospheric pressures and also at temperatures ranging from subzero to over 400 c it was found that the friction coefficient dropped from approximately 0 16 to 0 1 as the pressure was lowered from the earth s pressure to mars pressure at room temperature this is thought to be a result of the loss of weakly bound water on the sliding surfaces holding the pressure at 5 torr and increasing the temperature to approximately 200 c caused a sudden increase in the friction coefficient by approximately 50 this is attributed to the loss of surface oxides if no indication of the bit temperature is available an increase in drilling torque could be misinterpreted as being caused by an increase in auger torque due to accumulation of cuttings rather than being the result of a loss of oxide layers due to elevated bit temperatures an increase in rotational speed to allow for clearing of cuttings would then cause greater frictional heating and would increase the drilling torque further therefore it would be advisable to monitor the bit temperature or if that is not possible to include pauses in drilling to allow the heat to dissipate higher friction would also accelerate the wear of the drill bit and in turn reduce the depth of the hole

joint inversion of seismic refraction and resistivity data using layered models applications to groundwater investigation we developed a method for joint inversion of seismic refraction and resistivity data using sharp boundary models with few layers typically three we demonstrated the usefulness of the approach v

cooperative inversion of geophysical data geophysical inversion by iterative modeling involves fitting observations by adjusting model parameters both seismic and potential field model responses can be influenced by the adjustment of the parameters of the rock properties the objective of this cooperative in version is to obtain a model which is consistent with all available surface and borehole geophysical data al though inversion of geophysical data is generally non unique and ambiguous we can lessen the ambiguities by inverting all available surface and borehole data this paper illustrates this concept with a case history in which surface seismic data sonic logs surface gravity data and borehole gravity meter bhgm data are ad equately modeled by using least squares inversion and a series offorward modeling steps the traditional analysis of various geophysical data sets has been termed integrated interpretation such analysis has traditionally involved much processing modeling and subjec tive interpretation in order to develop a geologic model which is consistent with various surface and borehole geophysical data a method which automates some of the above pro cedures is least squares inversion this procedure perturbs an initial set of model parameters in order to fit the observed data least squares inversion is described in many papers in cluding those of jackson 1972 wiggins 1972 jupp and vozoff 1975 and lines and treitel 1984 this inversion technique could also be termed automated iterative mod eling in terms of modeling different geophysical data sets there are many possible approaches which allow inversion of a given data set and it is doubtful whether one single recipe will prove suitable for all problems nevertheless by jointly invert ing various types of geophysical observations we may lessen the extent of some of the ambiguities inherent in individual data sets lafehr 1984 gives a germane discussion of several reasons for this type of coordinated geophysical effort in the present study we define cooperative inversion as the esti mation of a subsurface model which is consistent with various independent geophysical data sets in the case discussed in this paper these data sets include surface and borehole observa tions of the seismic and gravity responses in our definition cooperative inversion may include either joint inversion or sequential inversion

imaging permafrost velocity structure using high resolution 3d seismic tomography a 3d seismic survey mallik 3d covering 126 km2 in the mackenzie delta area of canada s north was conducted by industry in 2002 numerous lakes and marine inundation create a complex near surface structure in the permafrost terrain much of the near subsurface remains frozen but significant melt zones exist particularly from perennially unfrozen water bodies this results in an irregular distribution of permafrost ice creating a complex pattern of low and high frequency near surface velocity variations which induce significant traveltime distortions in surface seismic data a high resolution 3d traveltime tomography study was employed to map the permafrost velocity structure utilizing first arrival traveltimes picked from 3d seismic shot records approximately 900 000 traveltime picks from 3167 shots were used in the inversion tomographic inversion of the first arrival traveltimes resulted in a smooth velocity model for the upper 200 m of the subsurface ray coverage in the model is excellent down to

surface wave analysis for identifying unfrozen zones in subglacial sediments abstractto reveal the extent of freezing in subglacial sediments we estimated s wave velocity along a glacier using surface wave analysis because the s wave velocity varies significantly with the degree of freezing of the pore fluid in the sediments this information is useful for identifying unfrozen zones within subglacial sediments which again is important for glacier dynamics we used active source multichannel seismic data originally acquired for reflection analysis along a glacier at spitsbergen in the norwegian arctic and proposed an effective approach of multichannel analysis of surface waves masw in a glacier environment common midpoint crosscorrelation gathers were used for the masw to improve lateral resolution because the glacier bed has a rough topology we used multimode analysis with a genetic algorithm inversion to estimate the s wave velocity due to the potential existence of a low velocity layer beneath the glacier ice and the observation of higher modes in the dispersion curves i

seismic quality factors across a bottom simulating reflector in the makran accretionary prism arabian sea the hydrate bearing sediments above the bottom simulating reflector bsr are associated with low attenuation or high quality factor q whereas underlying gas bearing sediments exhibit high attenuation hence estimation of q can be important for qualifying whether a bsr is related to gas hydrates and free gas this property is also useful for identifying gas hydrates where detection of bsr is dubious here we calculate the interval q for three submarine sedimentary layers bounded by seafloor bsr one reflector above and another reflector below the bsr at three locations with moderate strong and no bsr along a seismic line in the makran accretionary prism arabian sea for studying attenuation q 1 characteristics of sediments interval q for hydrate bearing sediments layer b above the bsr are estimated as 191 11 223 12 and 117 5 whereas interval q for the underlying gas bearing sediments layer c are calculated as 112 7 107 8 and 124 11 at moderate strong and no bsr locations respectively the large variation in q is observed at strong bsr thus q can be used for ascertaining whether the observed bsr is due to gas hydrates and for identifying gas hydrates at places where detection of bsr is rather doubtful interval q of 98 4 108 5 and 102 5 respectively at moderate strong and no bsr locations for the layer immediately beneath the seafloor layer a show almost uniform attenuation

joint inversion of gravity and magnetic data for two layer models gravity and magnetic data are inverted jointly in terms of a model consisting of an interface separating two layers having a constant density and magnetization contrast a damped least squares inversion is used to determine the topography of the interface the inversion requires knowledge of the physical property contrasts across the interface and its average depth since the relationship between model parameters and data is weakly nonlinear a constant damped least squares inverse is used during the iterative solution search the effect of this inverse is closely related to a downward continuation of the field to the average interface depth the method is used to map the base of the sept iles mafic intrusion quebec canada and the shape of the central uplift at the chicxulub impact crater yucatan mexico at sept iles the intrusion reaches a thickness of 7 km coincident with the maximum gravity anomaly south of the intrusion center at chicxulub the top of the central uplift is modeled to be 3

sedimentation across the central california oxygen minimum zone an alternative coastal upwelling sequence abstract distribution abundance and diversity of terrigenous authigenous and biogenous material provide evidence of the effect of bottom currents and oxygen minimum zone omz on continental slope sedimentation offshore central california box core samples and bottom photographs collected across the oxygen minimum zone of the coastal upwelling system were analyzed for lithologic and biologic trends three major omz facies are identified along the upper and lower edges of the omz and one at its core the upper boundary 525 m of the central california omz 80 of total forams with cassidulina the dominant benthic foraminifer with increasing water depth decreasing current speed and dissolved oxygen content toward the core of the omz 750 m grain size glauconite carbonate toc and foraminiferal fragments all decrease as the abundance of mica and detrital silicates increase the greatest number of genera of benthic foraminifera occurs at the core of the omz where their rel tive concentration is at a minimum and bolivina is the dominant genus no heavily calcified macrofauna were found at the core of the omz however near surface sediments are highly bioturbated as the lower boundary 1 025 m of the omz is approached grain size and abundance of detrital silicates continue to decrease as glauconite disappears concomitantly the relative abundance of mica carbonate toc siliceous microfauna benthic foraminifers and foram fragments increase the benthic foraminifer population consists largely 40 of globobulimina and praeglobobulimina the lower edge of the omz is highlighted by a distinct peak of fecal pellets 25 of sand size material lithofacies and biofacies associated with the omz are controlled by an interplay of oceanic circulation dissolved oxygen concentrations and possibly by increased biological activity within the omz edge environment and slight changes in the slope gradient recognition of key lithofacies and biofacies trends may prove to be powerful paleoenvironmental paleoceanographic indicators and may be useful in identifying ancient zones of upwelling analogous to the modern central california system where phosphorites organic rich shales and or chert are absent

parameter estimation and fault detection by three component seismic and geoelectrical surveys in a coal mine three component seismic and geoelectrical in mine surveys were carried out in lyukobanya colliery near miskolc hungary to determine the in situ petrophysical parameter distributions and to detect inhomogeneities in the coal seam the seismic measurements comprise an underground vertical seismic profile using body waves and an in seam seismic amplitude depth distribution and transmission survey using channel waves the geoelectrical measurements are based on the drift and seam sounding method interval traveltime amplitude multiple filter and polarization analysis methods are applied to the seismic data they lead to a five layer model for the strata including the coal seam the coal seam and two underlying beds act as a seismic waveguide the layer sequence supports the propagation of both normal and leaky mode channel waves of the love and rayleigh type a calculation of the total reflected energy for each interface using knott s energy coefficients shows that the velocity ranges of high reflection energy and of normal and leaky mode wavegroups coincide the excitation of wavegroups strongly depends on the seismic source a simultaneous inversion of a geoelectrical drift and seam sounding survey prevents misinterpretations of the seismic data by clearly identifying the low velocity coal seam as a high resistivity bed calculations of dispersion and sounding curves improve the resolution of the slowness and resistivity in each layer both diminished amplitudes and distortions in the polarization of transmission seismo grams and decreasing resistivities in a geoelectrical pseudosection of the coal seam are related to an inhomogeneity a calculation of synthetic seismograms for love and rayleigh channel waves with the finite difference and the alekseev mikhailenko method agrees well with the field data for the main features i e particular arrivals in the wave train wavegroups velocities and symmetries or asymmetries this in mine experiment demonstrates that the simultaneous acquisition processing and interpretation of seismic and geoelectrical data improve the lithological interpretation of petrophysical parameter distributions coal seam inhomogeneities can also be detected more reliably by the two independent surveys than by one alone

compositional variation within some glauconites and illites and implications for their stability and origins textural mineralogical and chemical data are presented for glauconites and illites from the lower cretaceous glauconitic sand formation alberta canada single crystal analyses by scanning transmission electron microscopy stem indicate that both glauconite 29 analyses and illite 44 analyses correspond very closely to ideal dioctahedral structures al dominates the octahedral sheet in illite very extensive a1 for feiii substitution was also found in some of the glauconites much more than previously recorded the dioctahedral mica structure is clearly very stable and flexible with respect to a1 for feiii substitution iron poor glauconites were found associated with pyrite we believe that glauconites tend to lose iron progressively during burial diagenesis especially where pore water iron activities are low high hs activity and low eh it seems probable that a1 for si tetrahedral substitution also takes place during diagenesis with consequent loss of swelling properties this is the same trend which is responsible for conversion of smectite to illite glauconite forms only where sediments reside for lengthy periods at the interface between oxidizing and reducing environments where fe3 is transiently available in solution related marine and terrestrial nontronites also form only in similar interface environments

laboratory drilling under martian conditions yields unexpected results 1 current plans to drill boreholes in the surface of mars suppose that diamond drill bits will be used on drilling equipment developing drilling power of 100 w or less such drilling produces very fine cuttings at martian ambient pressure it has been shown that quite small gas flows are capable of clearing these cuttings from the hole for example the release of 1 l of gas compressed to 50 torr is capable of removing 25 g of cuttings from a borehole 50 mm in diameter and at least 250 mm deep generating such volumes of gas by compressing the martian atmosphere would not be difficult alternatively the required volume of gas could be provided by the sublimation of ice trapped in the pore spaces of soil or rock in the martian surface once heated by the friction of the drill bit the ice transforms into vapor and blows the cuttings out of the hole since the cuttings are in effect freeze dried they do not choke the drill bit or hole with the result that the drilling efficiency is much greater than under terrestrial pressures and temperatures

the effect of the extent of freezing on seismic velocities in unconsolidated permafrost we develop a model to relate velocities of seismic waves in unconsolidated permafrost is idealized as an assemblage of spherical quartz grains imbedded in a matrix composed of spherical water inclusions in ice the theory of kuster and toksoz based on wave scattering considerations is used to determine the effective elastic moduli and hence the wave speeds the hasin shtrikman theoretical bounds on the elastic moduli of heterogeneous materials and considerations establish the plausibility of the model the model predicts vp and vs to be decreasing functions of both the porosity and the water to ice ratio and the ratio vp vs to be an increasing function of these two parameters the theory is then applied to laboratory measurements of shear and compressional wave velocities in 23 permafrost samples from different sites in the beaufort sea mackenzie river valley and canadian arctic islands although no direct measurements were made of the extents of freezing in these samples the data are consistent w

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

uniaxial compressive strengths of rocks drilled at gale crater mars measuring the physical properties of geological materials is important for understanding geologic history yet there has never been an instrument with the purpose of measuring mechanical properties of rocks sent to another planet the mars science laboratory msl rover employs the powder acquisition drill system pads which provides direct mechanical interaction with martian outcrops while the objective of the drill system is not to make scientific measurements the drill s performance is directly influenced by the mechanical properties of the rocks it drills into we have developed a methodology that uses the drill to indicate the uniaxial compressive strengths of rocks through comparison with performance of an identically assembled drill system in terrestrial samples of comparable sedimentary class during this investigation we utilize engineering data collected on mars to calculate the percussive energy needed to maintain a prescribed rate of penetration and correlate that to rock strength

early diagenetic phosphate cements in the albian condensed glauconitic limestone of the tatra mountains western carpathians early diagenetic phosphate cements are described from the albian condensed glauconitic limestone of the tatra mountains western carpathians with regard to their macro and micromorphology distribution classification and genesis the cements occur within stratigraphically condensed semi pelagic foramini feral glauconitic layers and are associated with mature hardgrounds within the tatra albian limestone phosphate cement fabrics consist of crypto to microcrystalline carbonate fluorapatite and they occur as i rim envelopes ii infillings of intraparticle porosity iii rim cement iv multiple rim cement v palisade fabric and vi cluster cement micromorphological variability of the cement fabrics results from varying texture of the cemented sediment the nature of original porosity as well as from presence of associated microbial fabrics the microbial fabrics are interpreted as fossilized coccoid cyanobacteria phosphate cementation developed under peculiar early diagenetic conditions within semi closed microenvironments rich in organic matter in the marine phreatic environment the cementation contributed to the formation of phosphatic fossils and hardgrounds the accretion of the cements was due to concentration of biologically uptaken phosphorus near the sediment water interface enrichment of pore fluids with respect to phosphate and its precipitation within restricted microenvironments phosphate cementation post dated seafloor formation of pelletal glauconite but predated partial decomposition of organic matter as well as dissolution or neomorphism of aragonite and high mg calcite phosphate cementation occurred on a carbonate platform following the submersion of urgonian reefal build ups episodes of phosphate cementation were repeated during the sedimentation of the tatra albian limestone as a response to rapid relative sea level rises and increased influence of nutrient rich tethyan waters

investigation of diamond impregnated drill bit wear while drilling under earth and mars conditions 1 experiments conducted on a dry and a water saturated rock under martian and earth atmospheric pressures revealed two different wear behaviors in diamond impregnated drill bits when the rock was saturated drilling under martian pressure caused the water in contact with the rotating bit to vaporize since the volumetric expansion of the liquid water or ice as it turned into a vapor was 170 000 the continuous flow of water vapor cleared the cuttings out of the hole thus the bit matrix was always exposed to abrasive wear by the rock cuttings and was continually wearing down and exposing new diamonds to the rock when the rock was dry an accumulation of rock cuttings protected the matrix from abrasive wear since fresh diamonds were not exposed in a timely manner the rate of penetration dropped both rock conditions namely dry or water saturated may exist on mars this adds to the complexity of the drill bit design as ideally a bit should penetrate the rock irrespective of whether it is dry or water saturated the fail safe bit would have a very soft matrix to always produce some rock penetration at the expense of potential excessive bit wear and shallower than anticipated hole depth

joint inversion of geophysical data summary by jointly inverting several different kinds of geophysical measurements at a site we avoid some of the ambiguity inherent in the individual methods we show how this can be done for the combination of dc resistivity and magnetotelluric measurements on a layered medium by considering a simple 3 layer model the combination resolves the resistivity of the thin resistive second layer even though neither of the two methods can do so alone the method is then applied to field data from a shallow sedimentary basin a blind zone occurs beneath a thick near surface conductive shale by a study of the eigenvalue structure of the model it can be seen that resolution in this zone would be slightly enhanced by higher frequency magnetotelluric data but additional dc data at larger spacing would yield no improvement

lateglacial and holocene isotopic and environmental history of northern coastal alaska results from a buried ice wedge system at barrow barrow the northernmost point in alaska is one of the most intensively studied areas in the arctic however paleoenvironmental evidence is limited for northern alaska for the lateglacial holocene transition for a regional paleoenvironmental reconstruction we investigated a permafrost ice wedge tunnel near barrow alaska the studied site was first excavated in the early 1960s and intercepts a buried ice wedge system at 3e6 m depth below the surface a multi methodological approach was applied to this buried ice wedge system and the enclosing sediments which in their combination give new insight into the late quaternary environmental and climate history results of geochronological sedimentological cryolithological paleoecological isotope geochemical and microbiological studies reflect different stages of mid to late wisconsin mw to lw allerod ad younger dryas yd preboreal pb and late holocene paleoenvironmental evolution the lwage of the site is indicated by ams dates in the surrounding sediments of 21 7 kyr bp at the lateral contact of the ice wedge system as well as 39 5 kyr bp below the ice wedge system it is only recently that in this region stable isotope techniques have been employed i e to characterize different types of ground ice the stable isotope record oxygen 18o hydrogen d of two intersecting ice wedges suggests different phases of the northern alaskan climate history from ad to pb with radiocarbon dates from 12 4 to 9 9 kyr bp ranging from 14 8 to 10 6 kyr cal bp stable isotope geochemistry of ice wedges reveals winter temperature variations of the lateglacial holocene transition including a prominent yd cold period clearly separated from the warmer ad and pb phases yd is only weakly developed in summer temperature indicators such as pollen for the northern alaska area and by consequence the yd cold stadial was here especially related to the winter season this highlights that the combination of winter and summer indicators comprehensively describes the seasonality of climate relevant processes in discrete time intervals the stable isotope record for the barrow buried ice wedge system documents for the first time winter climate change at the lateglacial holocene transition continuously and at relatively high likely centennial resolution

a joint inversion algorithm to process geoelectric and surface wave seismic data part ii applications for the exploration of near surface structures seismic and geoelectric methods are often applied usually these two types of method give independently of each other a sufficiently exact model of the geological structure however sometimes the inversion of the seismic or geoelectric data fails these failures can be avoided by combining various methods in one joint inversion which feads to much better parameter estimations of the model than the independent inversions a suitable seismic method for exploring near surface structures is the use of dispersive surface waves the dispersive characteristics of rayleigh and love surface waves depend strongly on the structural and petrophysical seismic velocities features of the near surface underground geoelectric exploration of the structure underground may be carried out with the well known methods of dc resistivity sounding such as the schlumberger the radial dipole and the two electrode arrays the joint inversion algorithm is tested by means of synthetic data it is demonstrated that the geoelectric joint inversion of schlumberger radial dipole and two electrode sounding data yields more reliable results than the single inversion of a single set of these data the same holds for the seismic joint inversion of love and rayleigh group slowness data the best inversion result is achieved by performing a joint inversion of both geoelectric and surface wave data the effect of noise on the accuracy of the solution for both gaussian and non gaussian sparsely distributed large errors is analysed after a comparison between least square lsq and least absolute deviation lad inversion results the lad joint inversion is found to be an accurate and robust method

exploring nonlinearity and nonuniqueness in surface wave inversion for near surface velocity estimation with the rapid increase in prospecting for unconventional oil and gas a large part of which remains on land the demand for land seismic data processing has increased substantially and is expected to further increase in the future it is known that land seismic data are often of much poorer quality than marine seismic data this is to a large extent caused by the presence of unconsolidated rock in the near surface with often complex velocity structure which is absent in many marine settings such near surface variations cause the wavefield to scatter or even lose its coherence as it propagates this makes it difficult to accurately image the deeper lying targets in land seismic data

delineation of sediments below flood basalts by joint inversion of seismic and magnetotelluric data a one dimensional joint inversion ji scheme considering seismic reflection and refraction and mt data is developed its efficacy to resolve low velocity conducting sediments below high velocity resistive flood basalts is tested for a representative geological model considering noisy incomplete data the ji is found to provide improved results in comparison to those obtained by individual seismic and mt inversions

rock abrasion tool mars exploration rover mission 1 the rock abrasion tool rat is an integral part of the athena science payload serving primarily as the geologist s rock hammer the rat will expose fresh surfaces of martian rocks to other instruments on the payload the rat also brushes dust and debris from an excavated hole or unaltered rocks to accomplish these tasks autonomously the rat a sophisticated 3 axis precision controlled device was designed data products derived from rat telemetry enable the rat to also act as an important rock physical properties science instrument the returned rat grinding and penetration rate data will be inverted and compared to a rock library on the earth the design is also very compact and lightweight the rat is contained within a cylinder 128 mm long and 85 mm in diameter and has a mass of 687 g

seismic reflection and ground penetrating radar imaging of a shallow aquifer in 1995 and 1996 researchers associated with the us air force s phillips and armstrong laboratories took part in an extensive geophysical site characterization of the groundwater remediation field laboratory located at dover air force base dover delaware this field experiment offered an opportunity to compare shallow reflection profiling using seismic compressional sources and low frequency ground penetrating radar to image a shallow unconfined aquifer the main target within the aquifer was the sand clay interface defining the top of the underlying aquitard at 10 to 14 m depth although the water table in a well near the site was 8 m deep cone penetration geotechnical data taken across the field do not reveal a distinct water table instead cone penetration tests show a gradual change in electrical properties that we interpret as a thick zone of partial saturation comparing the seismic and radar data and using the geotechnical data as ground truth we have associated the deepest coherent event in

dispersion calculations for sh and p sv waves in multilayered coal seams recent work by rader schott dresen and ruter has provided a means of calculating dispersion and amplitude distribution curves for sh channel waves in multilayered media an alternative calculation procedure is presented and the p sv wave type is also included numerical results are given for a coal seam containing a band of dirt of either higher or lower seismic velocities than the coal itself

effect of lateral heterogeneity in the soil column on shear wave velocity estimation by rayleigh wave inversion we conducted elastic wavefield modeling of shot gathers using soil column models with vertical and lateral velocity variations to study the dispersive behavior of rayleigh waves and the effect of lateral heterogeneity on the accuracy of rayleigh wave inversion for shear wave velocity estimation we also conducted a field experiment over an alluvial valley with soil column that thins out in the direction orthogonal to the valley axis from the model and field experiments we found that the dispersion characteristics of rayleigh waves are greatly influenced by the geometry of and lateral heterogeneities within the soil column nevertheless estimation of shear wave velocities within a soil column with lateral heterogeneity by rayleigh wave inversion is sufficiently robust and accurate for geotechnical applications

joint inversion of seismic and geoelectric data recorded in an underground coal mine1 until the present time the rock coal rock layer sequence and offsets in coal seams in underground coal mines have been detected with the aid of seismic waves and geoelectric measurements in order to determine the geometrical and petrophysical parameters of the coal seam situation the data recorded using seismic and geoelectric methods have been inverted independently in consequence the inversion of partially inaccurate data resulted in a certain degree of ambiguity this paper presents the first results of a joint inversion scheme to process underground vertical seismic profiling data geolectric resistivity and resistance data the joint inversion algorithm makes use of the damped least squares method and its weighted version to solve the linearized set of equations for the seismic and geolectric unknowns in order to estimate the accuracy and reliability of the derived geometrical and petrophysical layer parameters both a model covariance matrix and a correlation matrix are calculated the weighted least squares algorithm is based on the method of most frequent values mfv the weight factors depend on the difference between measured data and those calculated by an iteration process the joint inversion algorithm is tested by means of synthetic data compared to the damped least squares algorithm the mfv inversion leads to smaller estimation errors as well as lower sensitivities due to the choice of the initial model it is shown that compared to an independent inversion the correlation between the model parameters is definitely reduced while the accuracy of the parameter estimation is appreciably increased by the joint inversion process thus the ambiguity is significantly reduced finally the joint inversion algorithm the mfv method is applied to underground field data the model parameters can be derived with a sufficient degree of accuracy even in the case of noisy data

joint inversion of gravity and traveltime data using a level set based structural parameterization abstractwe have developed a new level set based structural parameterization for joint inversion of gravity and traveltime data so that density contrast and seismic slowness are simultaneously recovered in the inverse problem because density contrast and slowness are different model parameters of the same survey domain we assume that they are similar in structure in terms of how each property changes and where the interface is located so that we are able to use a level set function to parameterize the common interface shared by these two model parameters the level set parameterization makes it easy to maintain the structural similarity between the two geophysical properties the inversion of gravity and traveltime data is carried out by minimizing a joint data fitting function with respect to density contrast slowness as well as the level set function an adjoint state method is used to compute the traveltime gradient efficiently we have tested our algorithm on various synthetic examples including

surface and guided wave inversion for near surface modeling in land and shallow marine seismic data in several domains of applied geophysics surface and guided waves are considered as a source of information for characterizing the near surface which in a marine environment includes the seabed by contrast in exploration seismic surveys these waves have traditionally been regarded as coherent noise that should be filtered out as soon as possible the authors consider that surface and guided waves are not noise but a signal that can be lifted from the seismic record and exploited for a variety of well established geophysical solutions surface and guided waves constitute a large part of the recorded energy and with proper acquisition analysis and inversion they can be used to characterize the near surface with surprisingly high resolution in this role they can provide valuable information for tasks such as perturbation correction adjustment for near surface traveltime distortions they can also be used for velocity and geological modeling in this article the authors discuss a workflow for the a

surviving the limits to life at the surface of mars the harshness of the environment at its surface severely limits the survival of unprotected terrestrial organisms on mars however the martian geologic record is consistent with an earlier history with much different climatic conditions more conducive to life followed by an extended climate change which led to the currently inhospitable state such a transition is ideal for evolutionary adaptation to new conditions because it provides both the forcing function and the extensive time for progressive specializations it is shown that against each of the current limits to life organics deprivation restricted amounts and physical forms of h2o limited availability of other key nutrients ionizing radiation insult and strongly oxidizing chemical species there are plausible countermeasure solutions most but not all of these mechanisms already exist as known examples in terrestrial biota a combination of these adaptations could conceivably allow highly tailored organisms either active or dormant to survive at or very near the surface of mars even in carefully preserved regolith samples returned to earth microorganisms could be difficult to detect without specific biochemical probes and or purposeful biological amplification by selective enhancement of the supply of nutrients optimized incubation parameters and highly sensitive detection of metabolic activity

characterization of heterogeneous near surface materials by joint 2d inversion of dc resistivity and seismic data 1 we have developed a robust 2d joint inversion scheme incorporating the new concept of cross gradients of electrical resistivity and seismic velocity as constraints so as to investigate more precisely the resistivity velocity relationships in complex near surface environments the results of joint inversion of dc resistivity and seismic traveltime data from collocated experiments suggest that one can distinguish between different types or facies of unconsolidated and consolidated materials refining a previously proposed resistivity velocity interrelationship derived from separate inversions of the respective data sets a consistent interpretive structural model can be obtained from the joint inversion models

multimodal layered transdimensional inversion of seismic dispersion curves with depth constraints multi multimodal layered transdimensional inversion is a markov chain monte carlo implementation of bayesian inversion for the probability distribution of shear wave velocity vs as a function of depth based on multichannel analysis of surface wave methods it requires as data i a rayleigh wave dispersion curve and ii additional layer depth constraints the latter we show significantly improve resolution compared to conventional unconstrained inversions such depth constraints may be drawn from any source e g boreholes complementary geophysical data provided they also represent a seismic interface we apply multi to a norwegian glacier midtdalsbreen in which ground penetrating radar was used to constrain internal layers of snow ice and subglacial sediments with transitions at 2 and 25 5 m and whose vs is assumed to be in the range 500 1 700 1 700 1 950 and 200 2 800 m s respectively synthetic modeling demonstrates that multi recovers the true model of vs variation with depth significantly compared to inversions without depth constraints in this synthetic case multi not only reduces by about a factor of 10 the error between the true and the best fitting model but also reduces by a factor of 2 the vertically averaged spread of the distribution of vs based on the 95 credible intervals we further show that using frequencies above about 100 hz lead to unconverged solutions due to mode ambiguities associated with fine spatial structures for our acquired data on midtdalsbreen we use 14 100 hz data for which multi produces a large scale converged inversion

full waveform inversion of sh and love wave data in near surface prospecting we develop a two dimensional full waveform inversion approach for the simultaneous determination of s wave velocity and density models from sh and love wave data we illustrate the advantages of the sh love full waveform inversion with a simple synthetic example and demonstrate the method s applicability to a near surface dataset recorded in the village c achtice in northwestern slovakia goal of the survey was to map remains of historical building foundations in a highly heterogeneous subsurface the seismic survey comprises two parallel sh profiles with maximum offsets of 24 m and covers a frequency range from 5 hz to 80 hz with high signal to noise ratio well suited for full waveform inversion using the wiechert herglotz method we determined a one dimensional gradient velocity model as a starting model for full waveform inversion the two dimensional waveform inversion approach uses the global correlation norm as objective function in combination with a sequential inversion of low pass filtered field data this mitigates the non linearity of the multiparameter inverse problem test computations show that the influence of visco elastic effects on the waveform inversion result is rather small further tests using a monoparameter shear modulus inversion reveal that the inversion of the density model has no significant impact on the final data fit the final full waveform inversion s wave velocity and density models show a prominent low velocity weathering layer below this layer the subsurface is highly heterogeneous minimum anomaly sizes correspond to approximately half of the dominant love wavelength the results demonstrate the ability of two dimensional sh waveform inversion to image shallow small scale soil structure however they do not show any evidence of foundation walls

guided waves in near surface seismic surveys much of the earth s surface is covered by a thin blanket of unconsolidated sediments or weathered bedrock boundaries within or at the base of this surficial layer e g watertable bedrock surface transition to unweathered rock are commonly associated with a strong seismic contrast layers contained between the surface and shallowest boundaries may be efficient waveguides and as such associated with significant source generated seismic noise whereas rayleigh waves groundroll can be described in terms of normal modes we demonstrate that the faster shingled guided waves can be explained in terms of leaking modes due to the relatively high poisson s ratios in the shallow subsurface guided waves are composed dominantly of multiply reflected p waves we compare our results with those obtained using a conventional acoustic waveguide approximation and discuss methods for extracting information from guided waves for geotechnical and environmental applications

joint inversion of seismic and electric data applied to 2d media abstractmethods based on the seismic p wave seismic surface wave and apparent resistivity are commonly used in the solution of several near surface problems however the solution nonuniqueness and the intrinsic limitations of these methods can cause inconsistency in the final results dispersion curves of surface waves p wave traveltimes and apparent resistivity data were jointly inverted to obtain internally consistent and more reliable final model of p and s wave velocities and resistivity a collection of 1d layered models was obtained by a deterministic joint inversion algorithm based on the laterally constrained inversion scheme the three data sets were jointly inverted imposing the same structure and poisson s ratio was introduced as a physical link between p and s wave velocities to better constrain the inversion no physical link was imposed between the resistivity and the seismic velocities the inversion algorithm was tested on synthetic data and then applied to a field case where bench

subglacial sediment distribution from constrained seismic inversion using multi software examples from midtdalsbreen norway fast ice flow is associated with the deformation of subglacial sediment seismic shear velocities vs increase with the rigidity of material and hence can be used to distinguish soft sediment from hard bedrock substrates depth profiles of vs can be obtained from inversions of rayleigh wave dispersion curves from passive or active sources but these can be highly ambiguous and lack depth sensitivity our novel bayesian transdimensional algorithm multi circumvents these issues by adding independent depth constraints to the inversion also allowing comprehensive uncertainty analysis we apply multi to the inversion of a rayleigh wave dataset acquired using active source multichannel analysis of surface waves techniques to characterise sediment distribution beneath the frontal margin of midtdalsbreen an outlet of norway s hardangerjokulen ice cap ice thickness 0 20 m is constrained using co located gpr data outputs from multi suggest that partly frozen sediment vs 500 1000 m s 1 overlying bedrock vs 2000 2500 m s 1 is present in patches with a thickness of 4 m although this approaches the resolvable limit of our rayleigh wave frequencies 14 100 hz uncertainties immediately beneath the glacier bed are 280 m s 1 implying that multi cannot only distinguish bedrock and sediment substrates but does so with an accuracy sufficient for resolving variations in sediment properties

full wavefield inversion of surface waves for mapping embedded low velocity zones in permafrost abstractsurface waves are advantageous for mapping seismic structures of permafrost in which irregular velocity gradients are common and thus the effectiveness of refraction methods are limited nevertheless the complex velocity structures that are common in permafrost environments often yield unusual dispersion spectra in which higher order and leaky modes are dominant such unusual dispersion spectra were prevalent in the multichannel surface wave data acquired from our permafrost study site at barrow alaska owing to the difficulties in picking and identifying dispersion curves from these dispersion spectra conventional surface wave inversion methods become problematic to apply to overcome these difficulties we adopted a full wavefield method to invert for velocity models that can best fit the dispersion spectra instead of the dispersion curves the inferred velocity models were consistent with collocated electric resistivity results and with subsequent confirmation cores which indicated the re

correlating environmental changes during early albian oceanic anoxic event 1b using benthic foraminiferal paleoecology abstract the nature and consequences of mid cretaceous oceanic anoxic events oaes are the subject of ongoing debate and recent studies have shown that different scenarios are needed to explain each of these events nevertheless similarities between the different oaes can be observed here we have reconstructed paleoenvironmental changes during the early albian oae 1b using benthic foraminiferal distributions and lithologies in three sections from different basins and paleowater depths eutrophic conditions as indicated by the presence of infaunal as well as opportunistic genera such as gyroidinoides pseudobolivina pleurostomella and bolivinitids prevailed before and during the oae and led to dysoxic to anoxic conditions dysoxia was most intense in the bathyal sections but also occurred in the outer shelf where more heterogeneous patterns of foraminiferal distributions are believed to reflect fluctuations of the upper boundary of an oxygen minimum zone a change from eutrophic to mesotrophic conditions caused the termination of oae 1b and opportunistic benthic foraminifera e g pseudobolivina pleurostomella were the first to subsequently repopulate the bathyal sea floor repopulation occurred rapidly in the shallow settings and gradually in the deeper sites where a normal diverse pre event fauna was established a few tens of thousands of years after oae 1b

glaucony from the eocene of the isle of wight southern uk implications for basin analysis and sequence stratigraphic interpretation the lower middle eocene sequence of the hampshire basin which includes an alternation of sands silts and clays interpreted as fluvial to open marine deposits is exposed at two locations on the western alum bay and eastern whitecliff bay margin of the isle of wight glaucony is encountered throughout the study units sand clay alternations of lagoonal origin and estuarine channel fill sands include less than 10 of predominantly poorly evolved allochthonous glaucony shelf silts and sands generally comprise more than 20 of evolved mostly autochthonous glaucony vertical changes in maturity of glaucony confirm the trend predicted by recent models indicating an overall upward increase in the transgressive systems tracts and decrease in the highstand systems tracts with maximum values in coincidence with the condensed sections where a remarkable peak in glaucony concentration is invariably recorded comparison of glaucony characteristics at different sites of depositional sequences shows a slight increase in maturity and abundance from the proximal to the distal areas this lateral tendency is interpreted to reflect more suitable conditions for glauconitization in open marine environments than in shallow waters despite documented intrasequential variability of glaucony characteristics glaucony assemblages from distinct depositional sequences may be generally identified on the basis of more pronounced differences in maturity consequently glaucony attributes can be used as an index for characterization of third order sedimentary cycles

comparison of five least squares inversion techniques in resistivity sounding a brief history of the development of the inverse problem in resistivity sounding is presented with the development of the equations governing the least squares inverse five algorithms for finding the minimum of the least square problem are described and their speed of convergence is compared on data from two planar earth models of the five algorithms studied the ridge regression algorithm required the fewest numbers of forward problem evaluations to reach a desired minimum solution space statistics including 1 parameter standard errors 2 parameter correlation coefficients 3 model parameter eigenvectors and 4 data eigenvectors are discussed the type of weighting applied to the data affects these statistical parameters weighting the data by taking log 10 of the observed and calculated values is comparable to weighting by the inverse of a constant data error the most reliable parameter standard errors are obtained by weighting by the inverse of observed data errors all other solution statistics such as dataparameter eigenvector pairs have more physical significance when inverse data error weighting is used

transition zone reflections and permafrost analysis the usual study of seismic reflections is limited to those from sharply defined contrasts in acoustic impedance for reflections resulting from transition zones in which acoustic impedance is continuously variable such as the zones encountered in permafrost the frequency selective nature of attenuation and phase distortion leads to a number of characteristics which may be used in the sense of pattern recognition to identify such reflections an rms velocity analysis procedure can be used to estimate depths and velocity gradients associated with transition zones some simple approximations allow us to avoid solving a system of nonlinear equations in many cases of interest and the result is a practical technique which can be applied to many transition zone reflections at reasonable computational cost

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history