limnologic analysis of gusev crater paleolake mars abstract the survey of the hydrogeologic system formed by gusev crater and ma adim vallis aeolis subquadrangle of mars points out evidence for the existence of an ice covered lake in gusev crater a first lake was formed by the drainage of the aquifer in the region surrounding gusev before the entry of ma adim vallis in the crater the existence of a former lake in gusev is deduced from the morphology of the ma adim delta its comparison with terrestrial antarctic analogs argues for the presence of an ice covered lake in gusev at the time that the southern part of the crater s rampart was breached by ma adim first release and for a subice lacustrine construction of the valley s delta our survey shows that ma adim vallis may have entered gusev crater as late as late hesperian early amazonian as part of a second lake episode the relationship between the variation of the gusev lake water level the volume of the lake and the surface of the lake bed is established by our bathymetric model the elevation of the former lake is deduced from the elevation of the mesa like structures in the delta of ma adim vallis furthermore the correlation of the crater frequency of gusev rampart with mars stratigraphic age shows that lakes may have occupied gusev crater over a period of time covering 2 gyrs from the formation of the crater to the last episode of water release from ma adim vallis though it is most likely that the lake was episodical the recurrence of abundant water in gusev crater makes this site a high priority for missions either for martian resource exploration or for the search of life

methodology for dense spatial sampling of multicomponent recording of converted waves in shallow marine environments a widespread use of converted waves for shallow marine applications is hampered by spatial aliasing and field efficiency their short wavelengths require dense spatial sampling which often needs to be achieved by receivers deployed on the seabed we adopted a new methodology where the dense spatial sampling is achieved in the common receiver domain by reducing the shot spacing this is done by shooting one track multiple times and merging the shot lines in an effective manner in a separate processing step this processing step is essential because positioning errors introduced during the field measurement can become significant in the combined line particularly when they exceed the distance between two adjacent shot positions for this processing step a particular shot line is used as a reference line and relative variations in source and receiver positions in the other shot lines are corrected for using crosscorrelation the combined shot line can subsequently be regularized for further processing the methodology is adopted in a field experiment conducted in the danube river in hungary the aim of the seismic experiment was to acquire properly sampled converted wave data using a multicomponent receiver array the dense spatial sampling was achieved by sailing one track 14 times after correcting for the underwater receiver positions using the direct arrival the crosscorrelation step was applied to merge the different shot lines the successfully combined result is regularized into a densely sampled data set free of visible spatial aliasing and suitable for converted wave processing

pre stack full waveform inversion of ultra high frequency marine seismic reflection data the full waveform inversion fwi of seismic reflection data aims to reconstruct a detailed physical properties model of the subsurface fitting both the amplitude and the traveltime of the reflections generated at physical discontinuities in the propagation medium unlike reservoir scale seismic exploration where seismic inversion is a widely adopted remote characterization tool ultrahigh frequency uhf 0 2 4 0 khz multichannel marine reflection seismology is still most often limited to a qualitative interpretation of the reflections architecture here we propose an elastic fwi methodology custom tailored for pre stack uhf marine data in vertically heterogeneous media to obtain a decimetric scale distribution of p impedance density and poisson s ratio within the shallow subseabed sediments we address the deterministic multiparameter inversion in a sequential fashion the complex trace instantaneous phase is first inverted for the p wave velocity to make up for the lack of low frequency in the data and reduce the nonlinearity of the problem this is followed by a short offset p impedance optimization and a further step of full offset range poisson s ratio inversion provided that the seismogram contains wide reflection angles 40 we show that it is possible to invert for density and decompose a posteriori the relative contribution of p wave velocity and density to the p impedance a broad range of synthetic tests is used to prove the potential of the methodology and highlights sensitivity issues specific to uhf seismic an example application to real data is also presented in the real case trace normalization is applied to minimize the systematic error deriving from an inaccurate source wavelet estimation the inverted model for the top 15 m of the subseabed agrees with the local lithological information and core log data thus we can obtain a detailed remote characterization of the shallow sediments using a multichannel sub bottom profiler within a reasonable computing cost and with minimal pre processing this has the potential to reduce the need of extensive geotechnical coring campaigns

white rock an eroded martian lacustrine deposit the existence and location of ancient lake sites and sediments have important implications for martian paleoclimate and exobiology white rock an enigmatic crater interior deposit may be the eroded remnant of such a lacustrine deposit stereogrammetric analysis of newly processed viking images allows better determination of the dimensions of white rock 12 5 x 15 km thickness 180 to 540 m volume 40 km 3 reveals differences in erosion patterns that may reflect differences in depositional environment and allows the identification in or on the crater wall of a possible source region of the high albedo white rock material if white rock is the remnant of a once larger deposit then open system circulation may have been required to deliver the required quantity of evaporites

observations on attenuation and shear wave velocity in fine grained marine sediments compressional p wave attenuation shear s wave attenuation and shear s wave velocity measurements compiled for fine grained unconsolidated sediments show trends that do not support empirical relationships hamilton j acoust soc am 68 1313 1340 1980 in acoustics and ocean bottom f a s e specialize conf madrid 1987 commonly used for geoacoustic modeling the exception is compressional wave attenuation data from 10 hz to 500 khz that essentially follow a frequency dependence of f1 2 standard deviations p wave attenuation with depth is difficult if not impossible to predict given the variability in the data examination of several attenuation depth profiles indicates that those of mitchell and focke j acoust soc am 67 1582 1589 1980 may be the best choice for predicting p wave attenuation with depth at the present time the assumption that s wave and p wave attenuations are proportional hamilton j acoust soc am 60 334 338 1976c in acoustics and ocean bottom

comparison of methods to determine q in shallow marine sediments from vertical reflection seismograms four methods for the determination of q in marine sediments are compared two traditional methods i e the risetime and the spectral ratio method and two newly established ones the spectrum modeling and the wavelet modeling method in the latter one q and the reflection time t are determined simultaneously which gives a much better accuracy for t than reading it from the seismogram the risetime and the spectral ratio methods are used for obtaining q directly from the data the principle of the modeling methods is to calculate the effect of absorption and dispersion on a reference wavelet or its spectrum for various values of q and the best fit between the observed and the calculated data leads to the optimum result numerical tests on synthetic data show that a precision of more than 25 for data containing noise or superposed arrivals can hardly be achieved in any case wavelet modeling is the superior method application to data from a vertical reflection profile in the baltic sea yields q in the range of 15 100 for different layers which is to be expected in the sedimentary environment of this area

surficial properties in gale crater mars from mars odyssey themis data abstract we examine the nature of the surface layer in gale crater as determined from high resolution thermal and visible mars odyssey thermal emission imaging system themis data as well as how our conclusions compare to past analyses at themis resolution the thermal surface structure is dominated by local control thus providing us with detailed images that contain thermophysical information as well using these data sets we have created a map of the area defining units based primarily on their geomorphology as determined from the daytime thermal and visible images and then using the nighttime thermal data to interpret the nature of the surface layer within each unit seven units have been defined i partially blanketed knobby plateaus ii crater walls with terrain similar to that on the plateaus on the upper half and exposed rocky surfaces on the lower half iii v three floor units with varying combinations of bedrock and indurated and or particulate deposits vi sand sheets and vii a central mound consisting of indurated and or rocky material forming layers terraces and slides covered by particulate material that tapers in thickness downslope additionally dozens of channels have been observed on the crater walls and central mound the results indicate that aeolian processes have played a major role in shaping much of the present surface layer within gale and may still be active today because of the dramatic size and structure of gale the winds are most likely controlled by the local topography additionally the presence and frequency of channels within gale bolster hypotheses involving aqueous episodes in the history of the crater

seafloor instabilities and sediment deformation processes the need for integrated multi disciplinary investigations abstract in this paper we present the current practice of investigations of seafloor instabilities and deformation processes based on extensive research conducted over the last years which sets the scene for future research activities in this field the mapping of the continental margins and coastal areas with ever increasing resolution systematically reveals evidence of instabilities and deformation processes both active and palaeo features in order to properly assess the hazards and risks related to these features an integrated and multi disciplinary approach is essential but challenging such an approach consists of combining field data geophysics geology sedimentology geochemistry and geotechnical data with numerical simulations constrained by results from laboratory data as such it is of paramount importance to build a common knowledge base and understanding that unify these disciplines into more complete and conceptual models constrained by all the data we review the status of this integrated approach adapted to palaeo landslides e g storegga ana vesteralen and recent deformations finneidfjord nice gulf of guinea allowing to identify gaps in our knowledge at these sites by reviewing these case studies one can conclude that each case remains highly site specific in which both the regional and local geological tectonic settings have a distinct effect of the type of instability or deformation taking place or that can take place our knowledge on the actual triggers remains poorly constrained and there is even ambiguity for historic landslides e g finneidfjord also our knowledge of the preconditioning factors is incomplete there is a general lack of geotechnical data both in situ and from laboratory and therefore modelling the dynamics e g rheology of the instabilities relies on a number of assumptions rather than facts in addition excess pore pressure and its evolution is one of the key parameters driving instabilities despite this fact in situ excess pore pressure is rarely measured or monitored much work remains to be done to relate and integrate geotechnical data with geophysics e g through inversion and rock physical models in order to obtain additional quantitative information from the sub surface but also with respect to partial saturation free gas hydrate and pore pressure behaviour or lithologies it is of critical importance to be able to identify the different processes which can lead to hazardous situations which include establishing recurrence intervals timing and frequencies through event recognition and age control and magnitudes so that proper mitigation measures can be developed in this perspective the smaller scale instabilities deserve much attention as there are many instances where such features had far reaching consequences for society e g nice finneidfjord in that perspective human interferences e g exploitation drilling blasting loading must be one of the factors that should be taken into consideration

scattering attenuation in randomly layered structures with finite lateral extent a hybrid q model since the pioneering work of o doherty and anstey 1971 much research has been devoted to understand the effect of stratigraphic filtering of seismic waves i e the problem of multiple scattering in 1d random structures e g burridge et al 1993 shapiro and hubral 1999 for many subsurface structures such as sedimentary basins the assumption of layering is reasonable as a first approximation however real geostructures do not show perfect layering but exhibit a finite lateral extent in their elastic properties this becomes particularly important when studying overburden effects in reflection seismology where amplitude information is used in subsequent data analysis for example malme et al 2003 showed that the amplitude variation with offset avo response for a vertical seismic profile vsp experiment over a north sea field is significantly distorted by nonlayered overburden inhomogeneities they demonstrated by seismic forward modeling that pointlike diffractors and large scale gas filled sand bodies can be responsible for strong amplitude fluctuations in this short note we study the transmission behavior of seismic primaries when the finite lateral extent of the inhomogeneities is accounted for physically speaking we intend to quantify the combined effects of scattering attenuation due to thin layering and random diffractions and refractions it is important to understand that our approach describes scattering attenuation of seismic primaries and not attenuation of the mean field ensemble averaged wavefield as presented in earlier works e g lerche 1986 we use the model of an anisotropic 3d random medium anisotropy in this context means that the randomly distributed inhomogeneities have three different characteristic length scales and are characterized by a spatially anisotropic correlation function we also assume that the medium is lossless so that no intrinsic wave attenuation occurs a sketch of such a structure is shown in figure 1 resembling a realization of a 2d

tes and themis study of proposed paleolake basins within the aeolis quadrangle of mars 1 several studies have described photogeologic evidence for paleolacustrine basins on mars mostly within impact craters if these basins contained persistent standing water subsequently lost through evaporation they may have contained deposits of evaporite minerals if still present and sufficiently exposed these evaporites would be detectable in orbital thermal infrared spectra using data from mars orbiter thermal emission imaging system mo themis and mars global surveyor thermal emission spectrometer mgs tes we examined proposed paleolake basins within aeolis quadrangle including gusev and gale craters gusev crater is dominated by units with a spectrally intermediate to thick layer of dust mantling the surface tes linear deconvolutions of the low albedo deposits which have a thinner dust mantling include surface type 1 basalt materials when sulfates are included in the end member library otherwise the linear deconvolution uses surface type 2 andesite or weathered basalt themis surface emissivity spectra for the low albedo deposits do not display sufficient contrast to distinguish between surface types gale crater is relatively dust free except for the mound variably covered in a spectrally intermediate to thick layer of dust tes linear deconvolutions of crater floor and less dusty portion of the mound are consistent with a mixture of surface types 1 and 2 themis surface emissivity spectra are consistent with surface type 1 or a mixture of surface types 1 and 2 for the crater floor and surface dust for the mound these results do not discriminate between several previously suggested origins fluvial lacustrine aeolian or volcanic deposition for the mound layers we find no spectral evidence for evaporite deposits that might substantiate paleolakes existed in these craters

at sea measurements of sound penetration into sediments using a buried vertical synthetic array at sea measurements were conducted to understand the propagation of sound into sediments these investigations used a new buried vertical synthetic array system developed and built at the naval research laboratory the design of this at sea system is based on a system developed for laboratory experiments that utilized a two dimensional synthetic array technique j acoust soc am 107 2000 for the measurements reported here the hydrophone was water jetted into the sediment to a depth of 2 m once buried the hydrophone was mounted to a vertical robotics stage that pulled the hydrophone up in 1 cm increments a spherical source positioned 50 cm above the interface was used to ensonify the sediment the ensonification angle was varied by changing the horizontal distance of the source from the insertion point in this manner several measurements were made with ensonification angles above and below the critical angle in addition the enhancement of sound penetration due to interface roughness was investigated this new system along with the results of the measurements will be discussed work supported by onr

scattering versus intrinsic attenuation in the vadose zone a vsp experiment abstractwe studied scattering versus intrinsic attenuation estimates in the vadose zone from a shallow vsp experiment conducted in the lawrence livermore national laboratory llnl facility using permanent downhole geophones and a vertical impact source we estimated effective attenuation of the downgoing transmitted p wave we compared theoretical scattering attenuation estimates and finite difference synthetics to the measured field q values 1 q being a measure of attenuation using a selected range of impedance profiles of variance typical for a sedimentary basin our estimates of qscattering are in the order of 20 85 given the short propagation pathlengths involved 30 m we show that attenuation due to lateral heterogeneity is not significant we analyzed additional distorting factors including near field presence local impedance effects and interference from reflections originating beneath receivers and found that they may significantly impact attenuation measurement in near surface studi

measurements of acoustic wave velocities and attenuation in marine sediments propagation and attenuation of acoustic waves in fluid saturated sediments have been studied theoretically and experimentally in situ acoustic transmission tests in saturated beach sand show that compressional waves are dispersive within a certain frequency band where the intrinsic attenuation is maximum this indicates that low frequency wave velocities in marine sediments are at least 5 to 10 less than the velocities obtained from high frequency measurements and viscous damping due to the relative motion between solid skeleton and fluid is the main damping mechanism in the frequency range of 1 30 khz the agreement between the experimental results and biot s theory enables the remote determination of porosity and permeability of marine sediments by using measured compressional and shear wave characteristics approximate relations are used to determine the porosity and permeability of the marine sediments using the measured acoustic wave velocities and attenuation

comment on the article morphodynamic classification of sandy beaches in low energetic marine environment by gomez pujol l orfila a canellas b alvarez ellacuria a mendez f j medina r and tintore j marine geology 242 pp 235 246 2007 abstract in a recent study gomez pujol et al gomez pujol l orfila a canellas b alvarez ellacuria a mendez f j medina r tintore j 2007 morphodynamic classification of sandy beaches in low energetic marine environment mar geol 242 pp 235 246 used the wright and short beach classification scheme fed with hindcasted wave and sediment settling velocity data to classify the morphodynamic states of a group of low energy mediterranean beaches mallorca spain here we use morphodynamic data obtained from an argus video station and a morphodynamic model to assess the validity of this type of model for predicting beach states under typical mediterranean wave conditions the results show that values alone do not provide a realistic prediction of beach states statistics and that the intensity of the forcing represented by the wave energy level and the duration of the events must also be taken into account

forward modeling for marine sediment characterization using chirp sonars this paper investigates the forward modeling of chirp sonar data for the quantitative characterization of marine subbottom sediment between 1 and 10 khz the forward modeling based on a transfer function approach included impacts of layering or impedance mismatch attenuation roughness and transitional layers i e continuous impedance variations the presented approach provided the best compromise between the number of available geoacoustic parameters from chirp sonar data and the subbottom modeling accuracy the forward model was tested on deep sea chirp sonar data acquired at a central frequency of 3 5 khz comparisons between synthetic and experimental seismograms showed good agreement for the first 15 m of buried layers performance of the inversion using this forward model was also examined through sensitivity analysis the results suggested that estimations of layer thickness impedance and transitional layer thickness were robust whereas roughness and attenuation estimations were subject to wavelength and layer thickness conditions

mars white rock feature lacks evidence of an aqueous origin results from mars global surveyor the white rock feature on mars has long been viewed as a type example for a martian playa largely because of its apparent high albedo along with its location in a topographic basin a crater data from the mars global surveyor thermal emission spectrometer tes demonstrate that white rock is not anomalously bright relative to other martian bright regions reducing the significance of its albedo and weakening the analogy to terrestrial playas its thermal inertia value indicates that it is not mantled by a layer of loose dust nor is it bedrock the thermal infrared spectrum of white rock shows no obvious features of carbonates or sulfates and is in fact spectrally flat images from the mars orbiter camera show that the white rock massifs are consolidated enough to retain slopes and allow the passage of saltating grains over their surfaces material appears to be shed from the massifs and is concentrated at the crests of nearby bedforms one explanation for these observations is that white rock is an eroded accumulation of compacted or weakly cemented aeolian sediment

pancam multispectral imaging results from the spirit rover at gusev crater panoramic camera images at gusev crater reveal a rock strewn surface interspersed with high to moderate albedo fine grained deposits occurring in part as drifts or in small circular swales or hollows optically thick coatings of fine grained ferric iron rich dust dominate most bright soil and rock surfaces spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine atmospheric observations show a steady decline in dust opacity during the mission and astronomical observations captured solar transits by the martian moons phobos and deimos as well as a view of earth from the martian surface

3d seismic imaging of buried younger dryas mass movement flows lake windermere uk abstract windermere is a glacially overdeepened lake located in the southeastern lake district uk using the three dimensional 3d chirp subbottom profiler we image mass movement deposits related to the younger dryas yd within a decimetre resolution 3d seismic volume documenting their internal structure and interaction with preexisting deposits in unprecedented detail three distinct flow events are identified and mapped throughout the 3d survey area package structures and seismic attributes classify them as a small total volume of c 1500 m 3 debris flow containing deformed translated blocks a large inferred total volume of c 500 000 m 3 homogeneous fine grained mass flow deposit and a debris flow inferred total volume of c 60 000 m 3 containing small c 8 0 2 0 m deformed translated blocks geomorphological mapping of their distribution and interaction with preexisting sediments permit the reconstruction of a depositional history for the stratigraphic units identified in the seismic volume

velocity dispersion in water saturated granular sediment recent experiments in the gulf of mexico have yielded a wealth of information on the environmental conditions and geoacoustic response of a uniform sand stratum immediately beneath the seafloor a comparison of p wave velocities measured at low 125 hz and high 11 50 khz frequencies in this layer indicates that there is a significant amount of velocity dispersion that occurs in the interval between these extremes this narrow band dispersion which is not consistent with the often used assumption of a nearly constant q model is in accordance with the predictions of the biot theory it results from viscous damping in the fluid as it moves relative to the skeletal frame other recent field data that support this conclusion are presented

dynamic extraction of sediment attenuation from subbottom acoustic data reliable and accurate measurements of acoustic attenuation enable correlations between the acoustic responses and properties of sediments to be attempted this paper proposes a dynamic modeling technique which allows for a direct assessment of attenuation from changes in the signal spectral shape caused by absorption losses in the sediment using the frequencies corresponding to the signal spectral maximum and a point 3 db below the maximum attenuation data can be dynamically extracted laboratory experiments on three types of sand were conducted to validate the proposed method although the concept can be applied using any broadband sound source a parametric array source was used in the study because of its broad bandwidth and definable wave shape a comprehensive discussion on the different sets of data collected is given with an emphasis on the attenuation coefficient k and the exponent n of frequency the results of the study demonstrate close agreement when compared with the accepted literature values

estimating quality factor and mean grain size of sediments from high resolution marine seismic data seismic quality factor has the potential to characterize sediment properties but seldom is used by the industry for offshore siteinvestigationsbecauseofpracticaldifficultieswithreflection seismology e g restricted bandwidth and because of uncertaintiesinrock physicsmodels aspectral ratioanalysisofhighresolution marine seismic data can determine a quality factor to within a 95 confidence of 10 within the uppermost 30 m of unconsolidated marine sediments our spectral ratio technique doesnotrequireassumptionsonhowattenuationscaleswithfrequency emphasis is placed on interpretation of spectral signatures before applying an iteratively reweighted robust leastsquaresregressiontosubduetheeffectsofnoiseandlocalheterogeneities when determining the quality factor of a sediment package we combined data from boomer and chirp sources to examine attenuation over four octaves of frequency 0 5 8 0 khz and to demonstrate that expanding the frequency range improves the precision and accuracy of quality factor fits we obtain frequency independent quality factors with 95 confidence intervals of 13512 10 and 1076 5 for silty clays with mean grain sizes of 7 7 and 6 9 phi respectively and 63 10 7 for a modern sand deposit with mean grain size 2 5 phi from the solent u k sediments with higher quality factorsrequiremoreindependentobservationstoachieveadesirable 95 confidence we required only 45 traces over sands and 1250 traces over the lowest attenuating silty clays by constructing an empirical model of quality factor against mean grain size from published sediment studies the mean grain sizes of our solent sediments can be located and we find that quality factor can beusedtodistinguishbetweencoarsegrain dominatedandclaydominatedsediments

the mola topographic signature at the crustal dichotomy boundary zone on mars mola data collected during the aerobraking hiatus provide good longitudinal sampling of the crustal dichotomy boundary zone in eastern mars and reveal a significant topographic signature associated with the transition from cratered highlands to lowland plains total relief between the two major units is always 2 5 km and sometimes 6 km median elevation differences are about 4 km regional slopes are very low 0 02 in both cratered terrain south and in lowland plains north of the boundary within the transition zone where cratered terrain changes to detached plateaus mesas and knobby terrain slopes are 50 100 times steeper and over a few hundred kilometers average about 1 the topographic signature of the boundary zone is best described as a 2 4 km step function between two nearly flat surfaces similar in slope and amplitude to some terrestrial passive margins this supports previous conclusions of a significant difference in crustal properties thickness composition or both between the lowland plains and cratered terrain and suggests this difference occurs over a relatively short distance of a few to several hundred kilometers

decimetric resolution stochastic inversion of shallow marine seismic reflection data dedicated strategy and application to a geohazard case study characterisation of the top 10 50 m of the subseabed is key for landslide hazard assessment offshore structure engineering design and underground gas storage monitoring in this paper we present a methodology for the stochastic inversion of ultra high frequency uhf 0 2 4 0 khz pre stack seismic reflection waveforms designed to obtain a decimetric resolution re mote elastic characterisation of the shallow sediments with minimal pre processing and lit tle a priori information we use a genetic algorithm in which the space of possible solutions is sampled by explicitly decoupling the short and long wavelengths of the p wave velocity model this approach combined with an objective function robust to cycle skipping outperforms a conventional model parametrisation when the ground truth is offset from the centre of the search domain the robust p wave velocity model is used to precondition the width of the search range of the multi parameter elastic inversion thereby improving the efficiency in high dimensional parametrizations multiple independent runs provide a set of independent results from which the reproducibility of the solution can be estimated in a real dataset acquired in finneidfjord norway we also demonstrate the sensitivity of uhf seismic inversion to shallow subseabed anomalies that play a role in submarine slope stability thus the methodology has the potential to become an important practical tool for marine ground model building in spatially heterogeneous areas reducing the reliance on expensive and time consuming coring campaigns for geohazard mitigation in marine areas

surficial geologic surveys of gale crater and melas chasma mars integration of remote sensing data abstract remote sensing observations of gale crater and melas chasma are synthesized to better understand the present surface layer in these two scientifically interesting regions data sets analyzed include geologic maps mars orbiter laser altimeter mola elevation thermal emission spectrometer tes albedo tes thermal inertia mola residual pulse width tes rock abundance and viking and mars orbiter camera images using these data sets we constrain the properties of and processes acting on the present surface and create self consistent models for the surface layer surface properties within gale crater are variable and complex and interpreting the surface layer is not straightforward observations indicate that aeolian processes have shaped some of the intracrater surface but other areas do not comply with this model and have counterintuitive surface characteristics in contrast aeolian activity appears to have played a large role in shaping the present day physical structure of all surfaces in melas chasma and is reflected in the remote sensing data sets here we summarize our analysis and discuss the surface attributes as determined from these data sets

dynamic poroelasticity a unified model with the squirt and the biot mechanisms the velocities and attenuation of seismic and acoustic waves in rocks with fluids are affected by the two most important modes of fluid solid interaction 1 the biot mechanism where the fluid is forced to participate in the solid s motion by viscous friction and inertial coupling and 2 the squirt flow mechanism where the fluid is squeezed out of thin pores deformed by a passing wave traditionally both modes have been modeled separately with the biot mechanism treated in a macroscopic framework and the squirt flow examined at the individual pore level we offer a model which treats both mechanisms as coupled processes and relates p velocity and attenuation to macroscopic parameters the biot poroelastic constants porosity permeability fluid com pressibility and viscosity and a newly introduced microscale parameter a characteristic squirt flow length the latter is referred to as a fundamental rock property that can be determined experimentally we show that the squirt flow mechanism dominates the biot mechanism and is responsible for measured large velocity dispersion and attenuation values the model directly relates p velocity and attenuation to measurable rock and fluid properties therefore it allows one to realistically interpret velocity dispersion and or attenuation in terms of fluid properties changes e g viscosity during thermal enhanced oil recovery eor or to link seismic measurements to reservoir properties as an example of the latter transformation we relate permeability to attenuation and achieve good qualitative correlation with experimental data

the accuracy of estimating q from seismic data a major aim of seismic interpretation is the inference of petrophysical properties of reservoir rocks because the inversion from seismic to petrophysical characteristics is far from unique this task requires a range of seismic parameters prominent among which are seismic velocity impedance and poisson s ratio the inclusion of seismic absorption in this list could add desirable complementary information for example absorption may be more sensitive to clay content than seismic velocity klimento and mccann 1990 however seismic absorption is difficult to measure particularly over depth intervals as short as most reservoir intervals

effects of the near field on shallow seismic studies seismic studies in the near surface typically involve path lengths that are on the order of a wavelength however most investigators extrapolate seismic imaging and parameter extraction techniques to the near surface without incorporating the near field in their processing approach for such short path lengths we find that the near field is strongly present in the recorded waveforms which consequently biases seismic parameter estimation such as q measurement to suppress the near field effects we examined the challenges of near field removal and the issues involving the accurate modeling of the near field using the mathematical expression for a source monopole which describes an elastic impact source typically used in shallow seismic studies we modeled the near and far field terms of the waveform with distance in a homogeneous elastic medium for thiscase we found that the near field can be suppressed through frequen cy domain or polarization filtering however in heterogeneous media the near