seismic tomography a window into deep earth abstract the goal of this paper is to provide an overview of the current state of the art in seismic tomography and trace its origins from pioneering work in the early 1970s to its present status as the pre eminent tool for imaging the earth s interior at a variety of scales due to length limitations we cannot hope to cover every aspect of this diverse topic or include mathematical derivations of the underlying principles rather we will provide a largely descriptive coverage of the methodology that is targeted at readers not intimately familiar with the topic the relative merits of local versus global parameterization ray tracing versus wavefront tracking backprojection versus gradient based inversion and synthetic testing versus model covariance are explored a variety of key application areas are also discussed including body wave traveltime tomography surface wave tomography attenuation tomography and ambient noise tomography established and emerging trends many of which are driven by the ongoing rapid increases in available computing power will also be examined including finite frequency tomography full waveform tomography and joint tomography using multiple datasets several practical applications of seismic tomography including body wave traveltime attenuation and surface waveform are presented in order to reinforce prior discussion of theory

tomographic modeling of a cross borehole data set in this paper we describe a methodology for estimating p wave velocities from a cross borehole seismic survey that uses straight ray tomography ray tracing and finite difference wave equation modeling to produce velocity models that fit the first break traveltimes after a starting model is established by straight ray tomography the velocity model is checked by ray tracing and wave equation modeling since the models for each procedure show consistent results and the modeled traveltimes closely match those traveltimes from the actual data we felt our interpretation was confirmed however the fitting of cross well first break traveltimes is only a necessary validity check and is not sufficient to guarantee that the true solution has been found two wells were drilled through the areas that were anomalous on the derived tomogram and check shot velocity surveys were run due primarily to a lateral ambiguity in velocity estimation caused by too few near vertical raypaths the check shot surveys did not agree with the tomogram velocities however subsequently the check shot traveltimes were used to place bounds on velocity in a constrained least squares procedure the combined modeling of uphole and cross well rays produced an optimum velocity model which satisfies all available data

imaging permeability structure within the highly permeable carbonate earth inverse theory and experiment in most oil reservoir rocks the squirt flow characteristic frequency fsq range of 10 100 khz is much less than the biot characteristic frequency f0 range of 1 mhz 1 ghz in contrast carbonate aquifers have very high permeability 10 3000 d and the two characteristic frequencies are reversed f0 from 10 hz to 10 khz and fsq from 1 mhz to 100 mhz the principal objective of this paper is to develop a pilot inverse method for robust imaging of the high permeability structure within carbonate aquifers an analytical approximate model called the super k model is developed the super k model coincides numerically with the combined biot and squirt flow mechanism model when permeability is higher than 100 md and the frequency is lower than 100 khz the super k regime in the super k regime the pore fluid is always relaxed so that the attenuation due to the biot mechanism is roughly four times larger than that of the biot model also empirical equations are developed that relate the stiffness and rigidit

phyllosilicate poor palagonitic dust from mauna kea volcano hawaii a mineralogical analogue for magnetic martian dust the mineralogical and elemental composition of dust size fractions 2 and 5 m of eight samples of phyllosilicate poor palagonitic tephra from the upper slopes of mauna kea volcano hawaii were studied by x ray diffraction xrd x ray fluorescence xrf visible and near ir reflectance spectroscopy mossbauer spectroscopy magnetic properties methods and transmission electron microscopy tem the palagonitic dust samples are spectral analogues of martian bright regions at visible and near ir wavelengths the crystalline phases in the palagonitic dust are in variable proportions plagioclase feldspar ti containing magnetite minor pyroxene and trace hematite no basal reflections resulting from crystalline phyllosilicates were detected in xrd data weak broad xrd peaks corresponding to x ray amorphous phases allophane nanophase ferric oxide possibly ferrihydrite and for two samples hisingerite were detected as oxidative alteration products of the glass residual unaltered glass was also present mossbauer spectroscopy showed that the iron bearing phases are nanophase ferric oxide magnetite titanomagnetite hematite and minor glass and ferrous silicates direct observation by tem showed that the crystalline and x ray amorphous phases observed by xrd and mossbauer are normally present together in composite particles and not normally present as discrete single phase particles ti bearing magnetite occurs predominantly as 5 150 nm particles embedded in noncrystalline matrix material and most likely formed by crystallization from silicate liquids under conditions of rapid cooling during eruption and deposition of glassy tephra and prior to palagonitization of glass rare spheroidal halloysite was observed in the two samples that also had xrd evidence for hisingerite the saturation magnetization js and low field magnetic susceptibility for bulk dust range from 0 19 to 0 68 am2 kg and 3 4 10 6 to 15 5 10 6 m3 kg at 293 k respectively simulation of the mars pathfinder magnet array ma experiment was performed on mauna kea volcano in areas with phyllosilicate poor palagonitic dust and with copies of the pathfinder ma on the basis of the magnetic properties of dust collected by all five ma magnets and the observation that the pathfinder mas collected dust on the four strongest magnets the value for the saturation magnetization of martian dust collected in the ma experiments is revised downward from 4 2 am2 kg to 2 5 1 5 am2 kg the revised value corresponds to 2 7 1 6 wt magnetite if the magnetic mineral is magnetite using js 92 am2 kg for pure magnetite fe3o4 or to 5 0 3 0 to 3 4 2 0 wt maghemite if the magnetic mineral is pure maghemite using js 50 to 74 am2 kg for pure maghemite fe2o3 comparison of the magnetic properties of bulk mauna kea palagonitic dust to those for dust collected by ma magnets shows that the ma magnets extracted culled a subset 25 34 wt of composite magnetic particles from bulk dust the extent of culling of martian dust is not well constrained because the mauna kea palagonitic dust satisfies the essential constraints of the pathfinder magnetic properties experiment composite and magnetic particles capable of being collected by five ma magnets a working hypothesis for the strongly magnetic mineral present in martian dust and soil is magnetite possibly ti bearing formed by rapid crystallization from silicate liquids having volcanic and or impact origins subsequent palagonitization of the glass produces the nanophase ferric oxide phases that dominate the spectral properties of martian bright regions at visible and near ir wavelengths magnetic and phyllosilicate poor palagonitic dust from mauna kea volcano is thus a spectral and magnetic analogue for magnetic martian dust

borehole coupling at sonic frequencies an elastic plane wave incident on a borehole couples through the borehole wall to produce a compressional wave inside the borehole and the effect of this coupling varies with incident angle imaging experiments that include a downhole source and or hydrophones must account for this effect to achieve optimal results in configurations pertinent to vsp surveys and cross well surveys at seismic frequencies a low frequency source can be assumed recently however both cross well and single well imaging experiments have been undertaken at sonic frequencies above 2000 hz where low frequency approximations are no longer valid we have developed new formulas which are valid over all frequencies and incident angles for both shear and compressional incident waves we present explicit formulas to describe this dependence contrary to what might be expected from low frequency approximations we find that at certain angles and for high enough frequencies marked resonances in the coupling terms for both shear an

borehole effects on downhole seismic measurements there are increasing interests in acquiring crosshole and vsp surveys at frequency up to 1 khz or more with the intention to resolve the fine details of structures and lithology between wells bregman et al 1989 harris 1988 tura 1991 however at frequencies on the order 1 khz the existence of the fluid filled borehole has a strong influence on the downhole measurements depending on the frequency and angle of incidence as well as the formation properties the measured displacements on the borehole wall or pressure at the center of borehole may be significantly different from those of the incident wave without taking proper care of this effect any imaging or inversion algorithm which utilizes both the amplitude and phase information of recorded energy will produce erroneous results

inversion of reflection seismic amplitude data for interface geometry summary reflection seismic tomography using only traveltime data may be unable to resolve the ambiguity caused by trade off between reflector position and velocity anomaly the inclusion of amplitude data in the inversion may help to resolve this problem because the amplitudes and traveltimes are sensitive to different features of the model therefore providing us with more accurate information about underground structures and velocity distribution the amplitude of a reflected seismic wave is determined partly by the reflection coefficients and partly by the curvature of the reflector the latter causes the spherical divergence of the seismic rays to be modified at the reflection point focused or defocused and can be represented using a simplified analytical expression we show using geologically relevant synthetic models that the information contained in amplitude versus offset data here excluding traveltime data suffices to constrain accurately the geometry of an arbitrary 2 d reflector separating constant velocity layers the most effective inversion method is a subspace gradient algorithm using a model parametrization in which the interface is described as a discrete fourier series with fixed upper and lower bounds on the wavenumber model parameters are allocated to separate subspaces first on the basis of different physical dimensionality we also found that declaring separate subspaces for those parameters defining short intermediate and long wavelength components of the interface geometry based on the magnitude of singular values of the frechet derivative matrix is very effective in accelerating convergence and obtaining a more accurate solution the inversion is robust with respect to data errors and poor initial estimates

crosshole seismic tomography many tomographic interpretations of crosshole seismic traveltimes have approximated the raypaths with straight lines connecting the source and receiver this approximation is valid where the velocity does not vary greatly but in many regions of interest velocity variations of 10 20 percent or more are observed causing significant ray curvature other work has taken this nonlinear effect into account but there do not appear to be many cases of demonstrated success in its application to the crosshole seismic problem we present here an iterative inversion scheme based on two dimensional ray tracing and its successful application to field data the interpretation method iteratively ray traces and then updates the velocity model within each iteration the differences between the data and the current model traveltimes obtained by ray tracing are related to the unknown velocity perturbations through a system of linear equations a damped least squares method solves for the velocity perturbations which updat

minero petrographical features of weathering profiles in calabria southern italy abstract the paper reports interdisciplinary research of weathering profile stages on gneiss with regard to tectonic and landscape evolutions of the western sila grande massif southern italy the outcropping rocks consist of medium to coarse grained biotite garnet and sillimanite gneiss bgs g and medium to coarse grained biotite muscovite migmatitic gneiss m g the bgs g rocks are fractured and weathered with either massive or foliated texture whereas the m g rocks are intensely weathered and fractured with a massive texture and frequent pegmatite veins petrographical and mineralogical variations show that both gneissic rocks bgs g and m g samples underwent weathering processes characterized by a progressive chemical attack on the labile minerals with generation of neoformed minerals and substitution of the original rock fabric the weathering processes produced phyllosilicates and fe oxides neoformed clay minerals and ferruginous products replaced feldspars and biotite during the most advanced weathering stage microfractures and morphological variations occur on the original rock and thereby affect the surrounding landscape processes the weathering profile mineralogy and rock textures viewed in the context of landscape evolution provide useful insights into the widespread slope movement phenomena in the sila grande massif gneiss

anisotropic velocity tomography a case study in a near surface rock mass cross borehole data were acquired in the surface crown pillar of a massive sulfide ore mine the data consist of five two dimensional 2 d cross borehole panels each with approximately 900 source receiver pairs the panels were located within the crown pillar at either side of and within a major subvertical fault zone that intersects the orebody an initial analysis of the data indicates that the bedrock containing the orebody is seismically anisotropic a rigorous analysis of the traveltimes using anisotropic velocity tomography confirms the initial assessment that anisotropy exists within the crown pillar rock mass anisotropic velocity tomography is the generalization of tomographic methods to anisotropic media as in any geophysical problem the data are insufficient to completely resolve the distributions of the rock properties at all scale lengths we use external constraints on the roughness of the final solution to ensure an algebraically well posed problem plots of the data residuals the t

travel time and amplitude analysis in seismic tomography in cross hole tomography straight lines connecting the source and receiver are often used to approximate the true ray paths thus linearizing the inverse problem a recent paper by bregman et al 1989a has shown that this approximation may be very poor in the regions of greatest interest where large velocity gradients cause significant ray curvature the interpretation method presented by bregman et al 1989a iteratively ray traces and updates the velocity model with model perturbations obtained by a damped least squares inversion of the travel time residuals this paper presents a modification of the travel time tomography method so that it may be applied to the inversion of first motion amplitudes for inverse quality factor q 1 after determining the velocity structure using travel time tomography the amplitudes are inverted using a similar scheme no additional ray tracing is required for the amplitude inversions the effect of the velocity structure previously determined through travel time tomography is taken into account so that amplitude variations due to the focusing and defocusing effects of the velocity structure are not interpreted as being due to attenuation structure both the travel time and amplitude tomography methods are applied here to field data from a cross hole experiment in crystalline rock wong et al 1983 the frequency range of the seismograms is 1 6 6 khz allowing resolution of velocity structure on a scale of several meters the resulting velocity image shows good agreement with other geological and geophysical data reversing the model by placing the model boreholes on opposite sides relative to the original reconstruction yields almost identical results indicating that the interpolation scheme used in the forward modeling has not biased the final model synthetic maslov seismograms calculated for the derived velocity model agree well with the waveform data further confirming the validity of the model in addition the amplitude tomography results place absorptive regions in the same location as the most pronounced low velocity features which correlate with fractures in the boreholes highly transmissive regions also correlate well with high velocity regions

multiarrival wavefront tracking and its applications 1 multivalued traveltimes have traditionally not been used in seismic imaging with only a handful of notable exceptions in the field of exploration geophysics for studies at local and regional scales e g local earthquake teleseismic tomography the focus has largely been on first arrivals with numerous ray and grid based schemes developed for their calculation however later arrivals often contribute to the length and shape of a recorded wave train particularly in regions of complex geology these arrivals are likely to contain additional information about seismic structure as their two point path differs from that of the first arrival in particular they are more amenable to sampling regions of lower velocity in this work the wavefront construction principle is used as the basis of a new scheme for computing multivalued traveltimes that arise from smooth variations in both velocity structure and interface geometry the idea is to represent the wavefront as a set of points in reduced phase space and use local ray tracing and interpolation to advance the wavefront in a series of time steps the scheme is robust in the presence of strong velocity heterogeneity and interface curvature with phases comprising multiple reflections refractions and triplications successfully tracked outside the field of exploration seismology wavefront construction techniques are rarely used yet they hold great potential for addressing problems in other areas of seismology this paper demonstrates the viability of the new wavefront construction scheme by applying it to a range of scenarios including multiarrival body and surface wave tomography teleseismic receiver function prediction using gaussian beams and the tracking of global phases such as pcp

porosity permeability shear strength crosswell tomography below an iron foundry crosswell tomography of a sedimentary foundation at an iron foundry was affected by very high background noise nevertheless high resolution velocity images were obtained between wells separated by long distances 120 to 250 m a piezoelectric source in a water filled well used long sequences 4095 cycles of pseudorandom binary codes at high carrier frequencies 1 to 10 khz a 24 channel hydrophone array in another well received the signal beamforming of common source data selected the directions and arrival times of multiple raypaths and tube waves and further enhanced the signal to noise ratio inversion of first arrival times by damped least squares imaged the compressional wave velocities assuming the normal consolidation condition the porosity and shear strength images are predicted from the compressional wave velocity image the direct measurements of porosity and shear strength conducted on the cores and boreholes were used to verify the tomographic predictions the slight differences in the

shear wave velocity structure beneath europe the northeastern atlantic and western asia from waveform inversions including surface wave mode coupling summary waveforms of 449 seismograms have been inverted for s wave velocity structures beneath europe the northeastern atlantic and western asia down to a depth of 670 km recorded waveforms were used in the time window starting at the s wave arrival and ending after the fundamental mode rayleigh wave arrival the inversion method is based on the partitioned waveform inversion nolet 1990 with the difference that synthetic seismograms are calculated taking surface wave mode coupling into account in order to model body waves in laterally heterogeneous media more accurately the partitioning of the inversion procedure makes non linear optimization feasible even for inversions including surface wave mode coupling the non linear inversion of the waveforms resulted in linear constraints on the 3 d velocity structure in a second step these constraints were used in a linear inversion for the 3 d shear wave velocity model beneath europe the northeastern atlantic and western asia the eur sc 95 model is presented which is characterized by a wide range of length scales of the velocity structures in central europe where the ray density is highest small scale structures are recovered such as the presence of high velocities associated with the hellenic subduction zone on the edges of the inversion model where the ray density and therefore also the resolution is poorer we find larger scale features such as the relatively laterally homogeneous high velocity structure beneath the russian platform to a depth of 300 km in this paper we discuss the inversion method data processing parametrization difficulties due to the introduction of surface wave mode coupling spatial resolution of the model and structures in the eur sc 95 model

comparison of labradorite evolution during weathering in basanite and pyroxenite effect of texture on plagioclase alteration summary the behaviour of labradorite plagioclases during weathering was investigated by comparing two arenites the first one developed on a cretaceous pyroxenite at mont saint bruno quebec and the second one on a pliocene basanite from the french massif central the evolution factors climatic conditions mineralogical relationship of the fresh rocks and cristallochemical relationship of the labradorites are the same for the two rocks the decreasing order of vulnerability of the minerals is for the pyroxenite olivine labrador augite and in the basanite olivine augite verre labrador labradorite plagioclases in the pyroxenite are more or less strongly weathered to smectites on the contrary labradorites in the basanite are slightly vulnerable and give little or no clay minerals size and shape of the crystals and a different textural environment granular for the pyroxenites and microcrystalline within a vitreous phase for the basanite influence the resistance of the plagioclases to weathering and modify the classical sequence of vulnerability of these silicates

precision analysis of first break times in grid models rectangular grid velocity models and their derivatives are widely used in geophysical inversion techniques specifically seismic tomographic reconstruction techniques whether they be based on raypath methods bregman et al 1989 moser 1991 schneider et al 1992 cao and greenhalgh 1993 zhou 1993 or full wave equation methods vidale 1990 qin and schuster 1993 cao and greenhalgh 1994 for calculating synthetic arrival times involve propagation through a grid model likewise migration of seismic reflection data using asymptotic ray theory or finite difference pseudospectral methods stolt and benson 1986 zhe and greenhalgh 1997 involve assigning traveltimes to upward and downward propagating waves at every grid point in the model the traveltimes in both cases depend on the grid specification however the precision level of such numerical models and their dependence on the model parameters is often unknown in this paper we describe a two dimensional velocity model and derive an err

a comparative study of island seafloor and subseafloor ambient noise levels abstract a study of seafloor and island stations shows that for the frequency band 0 1 to 10 hz the seismic noise levels on islands are comparable to the levels on the seafloor the microseism peak at the seafloor appears to be comparable to the highest levels observed on small islands for this band seafloor stations are realistic alternatives when island sites are not available seven year averages of the ambient noise levels recorded by seismic research observatory sro stations on three islands guam gumo taiwan tato and new zealand9s north island snzo are compared with those recorded by the international deployment of accelerometers ida station on easter island and on and beneath the ocean floor by ocean bottom seismometers obss and the marine seismic system mss deployed in a south pacific dsdp drill hole at 23 8 s 165 5 w adair et al 1986 from 0 3 to 2 hz the sro displacement power levels fall in the range historically observed by the scripps9 obss decreasing at 70 db decade from 1 by 10 6 nm 2 hz at 0 3 hz to 1 nm 2 hz at 2 hz and are 10 to 15 db above mss levels above 2 hz it appears that the same ratios hold the sro power levels decrease at 70 db decade to 1 by 10 3 nm 2 hz at a frequency of 10 hz although this correlation is based on very limited high gain short period data at frequencies below 0 3 hz the sro noise levels peak and decrease to approximately 2 by 10 3 nm 2 hz at 40 mhz the noise levels recorded at easter island are somewhat higher decreasing at 70 db decade from 1 by 10 7 nm 2 hz at 0 2 hz to 1 nm 2 hz at 10 hz and to 1 by 10 5 nm 2 hz at 50 mhz at the microseism peak near 0 2 hz the mss levels are from 15 to 20 db higher than observed by the sro stations and equivalent to those recorded at easter island there appears to be little dependence of the variance in noise level estimates on frequency the upper 95 per cent confidence limit generally lies 10 db above the average noise levels for all island stations all island noise level curves are dominated by the broad double frequency microseism peak centered between 0 15 to 0 2 hz the single frequency peak ranges from absent easter island to discernable guam and new zealand to obvious at taiwan the center frequency of this peak ranges from 0 07 hz at guam and new zealand to 0 1 hz at taiwan we speculate that the increased amplitude and frequency of the single frequency microseism peak is due to the interaction between the shallow continental shelf and surface gravity waves and or the presence of taiwan in a region of limited fetch

elastic wave velocities within oceanic layer 2 from sonic full waveform logs in deep sea drilling project holes 395a 418a and 504b multichannel full waveform acoustic logs were recorded in deep sea drilling project dsdp hole 418a during ocean drilling program odp leg 102 dsdp hole 395a during odp leg 109 and dsdp hole 504b during odp leg 111 to provide nearly continuous measurements of elastic wave velocities as a function of depth within oceanic layer 2 for different spreading rates and crustal ages the velocities depend primarily on the morphology of the basalt massive units have vp above 5 km s vs above 2 8 km s and vp vs below 1 9 their velocities increase with depth as expected from crack closure due to confining stress and are lower where fractures are present vp and vs within pillows are quite variable but in general are lower than in massive units and vp vs is higher velocities within breccias are similar to or lower than those of pillows within a given morphology the elastic properties do not depend on spreading rate within pillows velocity variations depend primarily on the degree of alteration infilling and the mineralogy of the infilling material and secondarily on conditions at emplacement coherent shear arrivals are sometimes not found within shallow pillows and in extreme cases the compressional arrival is also incoherent because of scattering resulting from the similarity between the sonic wavelength and the pillow size this sampling bias in the sonic log is the most likely cause of somewhat higher average sonic than seismic velocities measured within extrusive basalts at shallow depths other causes include the fact that laterally finite massive units may be oversampled by borehole measurements and that voids between pillows and fractures whose size is within an order of magnitude of the sonic wavelength have less effect on sonic than on seismic velocities the crustal section can be separated only roughly into seismic layers on the basis of the sonic velocities changes in velocity with depth within the extrusive section at a single site giving rise to previously defined seismic layers 2a and 2b are due to a change with depth in the properties of the pillows associated with differences in the amount and type of infilling materials rather than to a change with depth in the relative proportion of pillows and massive units because alteration occurs early and its history is different at different depths depth dependent variations in pillow properties are 1 established at young age and 2 persist even in old crust within the intrusive section of dsdp hole 504b velocities are similar to or higher than those measured in saturated minicores at atmospheric pressure and seismic and sonic velocities are approximately equal suggesting that little large scale porosity is present

method of imaging the permeability and fluid content structure within sediment a non destructive method of measuring physical characteristics of a medium such as uncemented sediment sandstone or limestone a pseudo random code is generated and is used to generate a pseudo random acoustic signal this signal is transmitted into the medium to be measured through the use of a transducer such as a piezoelectric element and is received by a plurality of hydrophones the received signal is then processed to obtain an image of its velocity and attenuation a universal geoacoustic model of the medium for a given set of measured data is determined and the model is solved to obtain a pair of permeability porosity results for the medium the one of this pair of permeability porosity results which is correctly indicative of the physical characteristics of the medium is then determined

seismic tomography at a fire flood site a crosshole seismic experiment was conducted to locate and characterize a firefront at an enhanced oil recovery eor pilot project the reservoir engineers involved in the project were interested in finding out why the burnfront apparently had stalled between two wells 51 m apart in a noisy producing environment good quality seismic data were recorded at depths ranging from 710 to 770 m the frequency range of the data 500 to 1500 hz allows resolution of the velocity structure on a scale of several meters the moveout of first arrivals indicates that there are large velocity variations in the study region a high amplitude late arriving channel wave points to the existence of a low velocity channel connecting the boreholes using an iterative nonlinear scheme which incorporates curved ray tracing and least squares inversion in each iteration the first arrival times were inverted to obtain a two dimensional model of the compressional seismic velocity between the boreholes the velocities range from

subsurface imaging using reversed vertical seismic profiling and crosshole tomographic methods a combined reversed vertical seismic profile rvsp crosshole and surface seismic experiment was performed to image the subsurface between two 1000 ft wells separated by 600 ft explosives were used as downhole sources and a 24 channel hydrophone streamer provided the downhole receivers surface shots were 1 3 lb dynamite charges and the surface receivers were vertical geophones rvsp data consisting of 48 offsets ranging from 25 ft to 1200 ft were processed with a ray tracing method to produce an equivalent stacked seismic section the crosshole data were processed with an sirt traveltime transmission tomography algorithm to produce a velocity cross section the stacked rvsp subsurface image and the crosshole tomography velocity cross section both have higher resolution than does the surface seismic image for example the velocity map from tomography exhibits a rapid lateral velocity change that is not resolved by surface seismic however all three methods agree within the limits of their common re

analysis of high frequency acoustic scattering data measured in the shallow waters of the florida strait experiments were conducted in the florida strait region of the united states in july 1995 to investigate the contribution of sediment volume scattering to measured acoustic backscatter levels at frequencies of 7 5 and 15 khz five sites were analyzed for bottom backscattering level in the radial and azimuthal directions sediment geophysical parameters were established by a cross well tomographic measurement and used as inputs for modeling both sediment volume and rough interface scattering models were utilized in analyzing the data comparison of model predictions with measured data showed that for grazing angles at the water sediment interface from the critical angle to approximately 60 degrees volume scattering dominated for angles greater than approximately 60 degrees surface roughness scattering consistently dominated in geographic areas where the interface sound speed ratio exceeded one roughness scattering controled the backscattered level for grazing angles less than the critical angle in

high resolution quantitative seismic imaging of a strike slip fault with small vertical offset in clay rocks from underground galleries experimental platform of tournemire france imaging tectonic faults with small vertical offsets in argilittes clay rock using geophysical methods is challenging in the context of deep radioactive waste disposals the presence of such faults has to be assessed since they can modify the rock confining properties in the tournemire experimental platform tep france fault zones with small vertical offsets and complex shape have been identified from underground works however 3d high resolution surface seismic methods have shown limitations in this context that led us to consider the detection and characterization of the faults directly from underground works we investigate here the potential of seismic full waveform inversion fwi applied in a transmission configuration to image the clay rock medium in a horizontal plane between galleries and compare it with first arrival traveltime tomography fatt our objective is to characterize seismic velocities of a block of argilittes crossed by a subvertical fault zone with a small vertical offset the specific measurement configuration allows us to neglect the influence of the galleries on the wave propagation and to simplify the problem by considering a 2d isotropic horizontal imaging domain our fwi scheme relies on a robust adaptation of early arrival waveform tomography the results obtained with fatt and fwi are in accordance and both correlate with the geological observations from the gallery walls and boreholes we show that even though various simplifications are done in the inversion scheme and only a part of the data is used fwi allows to get higher resolution images than fatt and is especially less sensitive to the incomplete illumination as it uses also diffracted energy the results provided in this study highlight the complexity of the fault zone showing a complex interaction of the main fault system with a secondary system composed of decimetric fractures associated with the presence of water

tomographic image of the axial low velocity zone at 12 50 n on the east pacific rise the 1982 magma seismic refraction experiment yielded a large set of accurate p wave travel times corrected for bathymetry and anisotropy which sample the structure of the east pacific rise epr at 12 50 n the arrivals were recorded using ocean bottom seismographs at three sites on axis and at 7 km and 16 km east of the axis we invert 2320 travel times for the twodimensional crustal seismic velocity structure across the epr axis assuming that the velocity structure is invariant along strike the travel times provide strong evidence for compressional velocity anisotropy in the upper crust corresponding to 10 faster velocities for propagation parallel to the axis than perpendicular to the axis the travel tunes used for the tomography are corrected for the effects of this azimuthal anisotropy our preferred model contains only the structure clearly required by the data structure which is stable under excessive smoothing and achieves a variance reduction of 81 relative to the laterally homogeneous starting model we resolve a substantial zone beneath the rise axis in which the velocity is reduced by 0 4 to 0 7 km s this low velocity zone lvz is about 7 km wide and extends from a depth of about 1 5 2 0 km down to moho at a depth of 5 5 km the lvz is slightly asymmetric extending 1 km further to the east than to the west of the axis in the shallow 1 0 km depth crust a pattern of velocity variations is imaged in which velocities are high at the spreading axis decrease between 3 km and 7 km east of the axis and then increase again between 10 and 15 km east of the axis we investigate the resolution of the inversion using an impulse response method the lvz and off axis upper crustal variations are well resolved in addition the travel time data indicate that an axial high velocity anomaly less than 2 km wide exists in the upper crust but is not resolved by the inversion the small velocity reductions of the lvz are consistent with hot rock containing only a small quantity of melt these results combined with the multichannel seismic reflection lines and expanded spread profiles from the northern epr suggest that the zone of high melt fraction under the spreading center is confined to a narrow thin lens capping a broad zone of hot plutonic rocks the upper crustal velocity reduction within 1 km of the axis reflects near axial thickening of the extrusive layer and the later reduction probably reflects porosity increases due to near axial tectonism the upper crustal velocity increase beyond 15 km off axis is attributed to porosity decreases associated with hydrothermal alteration

full waveform processing and interpretation of kilohertz cross well seismic data high frequency cross well seismic data from the midale oil field of southeastern saskatchewan are analyzed for direct and reflected energy the goal of the analysis is to produce interpretable sections to assist in enhanced oil recovery activities co2 injection in this field direct arrivals are used for velocity information while reflected arrivals are processed into a reflection image raw field data show a complex assortment of wave types that includes direct compressional and shear waves and reflected shear waves a traveltime inversion technique layer stripping via ray tracing is used to obtain p and s wave interval velocities from the respective direct arrivals the velocities from the cross well inversion and the sonic log are in reasonable agreement the subsurface coverage of the cross well geometry is investigated it covers zones extending from the source well to the receiver well and includes regions above and below the source receiver depths upgoing and downgoing primary reflections

an aem tem study of weathering and diagenesis abert lake oregon i weathering reactions in the volcanics abstract abert lake in south central oregon provides a site suitable for the study of sequential weathering and diagenetic events in this first of two papers transmission electron microscopy was used to characterize the igneous mineralogy subsolidus alteration assemblage and the structural and chemical aspects of silicate weathering reactions that occur in the volcanic rocks basalts basaltic andesites and dacitic rhyolitic extrusive and pyroclastics that outcrop around the lake olivine and pyroxene replacement occurred topotactically whereas feldspar and glass alteration produced randomly oriented smectite in channels and cavities the tetrahedral octahedral and interlayer compositions of the weathering products largely dioctahedral smectites varied with primary mineral composition rock type and as the result of addition of elements released from adjacent reaction sites weathering of the highly evolved fe rich jug mountain complex at the north end of the lake produced a homogeneous smectite assemblage that contrasts with the heterogeneous smectite assemblage replacing the volcanics along the eastern margin of the lake the variability within and between the smectite assemblages highlights the microenvironmental diversity fluctuating redox conditions and variable solution chemistry associated with mineral weathering reactions in the surficial environment late stage exhalative and aqueous alteration of the volcanics redistributed many components and formed a variety of alkali and alkali earth carbonate chloride sulfate and fluoride minerals in vugs and cracks overall substantial mg si na ca and k are released by weathering reactions that include the almost complete destruction of the mg smectite that initially replaced olivine the leaching of these elements from the volcanics provides an important source of these constituents in the lake water the nature of subsequent diagenetic reactions resulting from the interaction between the materials transported to the lake and the solution will be described in part ii banfield et al 1991

reconciliation of crosshole seismic velocities with well information in a layered sedimentary environment in sedimentary environments horizontal fine layering can cause significant complications when analyzing and comparing seismic data with different frequencies and propagation directions at the whitchester test site three boreholes penetrate upper carboniferous cyclical sediments involving interbedded carbonates sandstones and mudstones with seismic velocities ranging from less than 3 0 km s in the mudstones to over 4 5 km s in the carbonates initial crosshole results from two boreholes approximately 200 m deep and 75 m apart showed a poor correlation with the borehole logs recorded in a third intermediate borehole furthermore the tomographic images were inconsistent with the expected geology the objective of this paper is to reconcile the crosshole seismic data with the borehole log information the borehole information must be upscaled to match the resolution of the crosshole experiment however upscaling techniques based on backus averaging lead to the prediction of significant anisotropy of the order of 20 in places with a vertical symmetry axis this anisotropy is a result of a combination of fine layering and the intrinsic mineral anisotropy measured on the core samples although it is the layer induced anisotropy that dominates at the crosshole frequencies of 400 hz this prediction was tested by including anisotropy parameters into the analysis of the crosshole data using anisotropic velocity tomography in the central part of the final anisotropic velocity tomograms where the ray coverage is adequate these crosshole results are consistent with the anisotropy predictions once the anisotropy was properly accounted for the tomographic images are consistent with the layered nature of the geology at the site and they show the location and throw of a known fault in the section we conclude that at this site and at crosshole frequencies seismic layer induced anisotropy plays a significant role and must be accounted for when processing and interpreting crosshole seismic data

crustal structure flexure and subsidence history of the hawaiian islands seismic reflection profile data have been used to estimate the long term 106 years mechanical properties of the oceanic lithosphere underlying the hawaiian islands the data show prominent reflectors associated with the top of the oceanic crust reflector 2 the m discontinuity and the base of the crust reflector 3 the two way travel time to the reflectors has been depth converted using velocity depth functions derived from seismic refraction expanding spread profile data and compared to calculated depths based on simple three dimensional elastic plate models a good fit to the reflector depths was obtained for a model with an effective elastic thickness of the lithosphere te of 40 km the main discrepancies with the refraction data occur beneath oahu and molokai where the predicted depth of the base of the flexed crust is too shallow and beneath the southeast flank of hawaii where it is too deep we attribute the thickened crust beneath oahu to ponding of magma at the base of the crust following the last phases of tholeiitic shield building and the thinned crust beneath the flanks of hawaii to crustal melting beneath the youngest part of the chain the effective te of 40 km is higher than expected for 80 m y oceanic lithosphere possibly due to the effects of subsurface loads that act at or near the base of the flexed crust according to free air gravity anomaly and bathymetry data te does not change significantly along the island chain retaining a similar value for hawaii as it does for oahu we have used this result to estimate the pattern of subsidence and uplift that would be expected along the hawaiian islands because of flexural loading of hawaii the observed depth of the haleakala wave cut terrace northeast of maui can be generally explained by the flexure model the main discrepancies between observed and the predicted depths occur northwest of hawaii where they suggest a somewhat higher value of te possibly due to incomplete adjustment of the lithosphere we suggest that the addition of loads to the end of a volcanic chain generated as a plate moves over a mantle hotspot is accommodated by progressive flexing downstream causing subsidence of preexisting volcanos that lie in the flexural moat and uplift of islands on the flanking bulge the progressive flexure model predicts a characteristic pattern of offlap and onlap in the regions flanking the hawaiian islands that is generally similar to stratigraphic relationships observed along previously published seismic profiles of the moat a progressive flexure model may also apply to the case of a continental plate moving over a mantle hotspot and could explain the observations of 1 a clinoform pattern of stratigraphy in some flood basalt provinces and 2 a seaward dipping reflector sequence at some passive continental margins

primitive clay precursors formed on feldspar high resolution transmission electron microscopy of clay formation on k feldspar has revealed the existence of intermediate states between feldspar and crystalline clay products during the earliest weathering stages of k feldspar a primitive clay precursor forms on the feldspar surface that is spotted by ion oxides this reactive iron is incorporated into the primitive clay precursors which have an ultrathin 150 200 a 1 a 0 1 nm circular form and 14 20 a lattice images or long curled fiber forms with varied lattice image spacings the electron diffraction patterns of primitive clay precursors show diffuse rings at 2 65 2 04 and 1 51 a suggesting low crystallinity random orientation and partial inheritance of the original structure edx step scanning analysis showed that the major element concentrations of si al and k tend to decrease from unaltered parts to altered parts of precursors with substantial increase in fe auger depth profiling showed the thickness of the primitive clay layers is

velocity inversion in cross hole seismic tomography bycounter propagation neural network genetic algorithmand evolutionary programming techniques the disadvantages of conventional seismic tomographic ray tracing and inversion by calculus based techniques include the assumption of a single ray path for each source receiver pair the non inclusion of head waves long computation times and the difficulty in finding ray paths in a complicated velocity distribution a ray tracing algorithm is therefore developed using the reciprocity principle and dynamic programming approach this robust forward calculation routine is subsequently used for the cross hole seismic velocity inversion seismic transmission tomography can be considered to be a function approximation problem that is of mapping the traveltime vector to the velocity vector this falls under the purview of pattern classification problems so we propose a forward only counter propagation neural network cpnn technique for the tomographic imaging of the subsurface the limitation of neural networks however lies in the requirement of exhaustive training for its use in routine interpretation since finding the optimal solution sometimes from poor initial models is the ultimate goal global optimization and search techniques such as simulated evolution are also implemented in the cross well traveltime tomography genetic algorithms ga evolution strategies and evolutionary programming ep are the main avenues of research in simulated evolution part of this investigation therefore deals with ga and ep schemes for tomographic applications in the present work on simulated evolution a new genetic operator called region growing mutation is introduced to speed up the search process the potential of the forward only cpnn ga and ep methods is demonstrated in three synthetic examples velocity tomograms of the first model present plausible images of a diagonally orientated velocity contrast bounding two constant velocity areas by both the cpnn and ga schemes but the ep scheme could not image the model completely in the second case while ga and ep schemes generated an accurate velocity distribution of a faulted layer in a homogeneous background the cpnn scheme overestimated the vertical displacement of the fault one can easily identify five voids in a coal seam from the ga constructed tomogram of the third synthetic model but the cpnn and ep schemes could not replicate the model the performances of these methods are subsequently tested in a real field setting at dhandadih colliery raniganj coalfields west bengal india first arrival traveltime inversion by these algorithms from 225 seismic traces revealed a p wave velocity distribution from 1 0 to 2 5 km s 1 a low velocity zone 1 0 km s 1 the position of a suspected gallery in the jambad top coal seam could be successfully delineated by cpnn ga and ep schemes

crosswell traveltime tomography in three dimensions conventional crosswell direct arrival traveltime tomography solves for velocity in a 2 d slice of the subsurface joining two wells many 3 d aspects of real crosswell surveys including well deviations and out of well plane structure are ignored in 2 d models we present a 3 d approach to crosswell tomography that is capable of handling severe well deviations and multiple profile datasets three dimensional pixelized models would be even more seriously underdetermined than the pixelized models that have been used in 2 d tomography we therefore employ a thinly layered vertically discontinuous 3 d velocity model that greatly reduces the number of model parameters the layers are separated by 2 d interfaces represented as 2 d chebyshev polynomials that are determined using a priori structural information and remain fixed in the traveltime inversion the velocity in each layer is also represented as a 2 d chebyshev polynomial unlike pixelized models that provide limited vertical resolution and may be overparameterized horizontally this 3 d model provides vertical resolution comparable to the scale of wireline logs and reduces the degrees of freedom in the horizontal parameterization to the expected in line and out of well plane horizontal resolution available in crosswell traveltime data ray tracing for the nonlinear traveltime inversion is performed in three dimensions the 3 d tomography problem is regularized using penalty constraints with a continuation strategy that allows us to extrapolate the velocity field to a 3 d region containing the 2 d crosswell profile although this velocity field cannot be expected to be accurate throughout the 3 d region it is at least as accurate as 2 d tomograms near the well plane of each 2 d crosswell profile futhermore multiple profile crosswell data can be inverted simultaneously to resolve better the 3 d distribution of velocity near the profiles our velocity parameterization is quite different from pixelized models so resolution properties will be different using wave modeled synthetic data we find that near horizontal raypaths have the largest mismatch between ray traced traveltimes and traveltimes estimated from the data in conventional tomography horizontal raypaths are essential for high vertical resolution with our model however the highest resolution and most accurate inversions are achieved by excluding raypaths that travel nearly parallel to the geologic layering we perform this exclusion in both a static and model based manner we apply our 3 d method to a multiple profile crosswell survey at the cymric oil field in california an area of very steep structural dips and significant well trajectory deviations results of this multiple profile 3 d tomography correlate very well with the independently processed single profile results with the advantage of an improved tie at the common well

weathering of gneiss in calabria southern italy abstract the effects of weathering in a mediterranean climate on the mineralogy and microfabric of paleozoic gneiss of the sila massif calabria southern italy have been studied field observations show highly weathered rock forms a residual soil micromorphological and mineralogical properties of bedrock and saprolite show that the weathering process is characterized by at least two major stages having two distinct rock microfabrics in the first stage the morphological features of the original rock are preserved and weathering is manifested mainly by microfracturing and large portions of the rock remain unaltered the second stage of weathering involves further development of microcracks and progressive chemical attack on the minerals this latter stage occurs along both compositional and microstructural discontinuities with etch pitting of feldspar and neoformation of clay minerals and ferruginous products replacing feldspar biotite and iron bearing garnet the determination of quantitative petrographic indices provides a measure of the various stages of weathering

physical properties of upper oceanic crust ocean drilling program hole 801c and the waning of hydrothermal circulation 1 the hydrologic evolution of oceanic crust from vigorous hydrothermal circulation in young permeable volcanic crust to reduced circulation in old cooler crust causes a corresponding evolution of geophysical properties ocean drilling program odp hole 801c which obtained the world s oldest section of in situ normal oceanic crust provides the opportunity to examine relationships among hydrologic properties porosity permeability fluid flow crustal alteration and geophysical properties at both core plug and downhole log scales within these upper crustal basalts fluid flux in zones with high porosity and associated high permeability fosters alteration particularly hydration consequently porosity is correlated with both permeability and a variety of hydration indicators porosity dependent alteration is also seen at the log scale potassium enrichment is strongly proportional to porosity we extend the crustal alteration patterns observed at hole 801c to a global examination of how physical properties of upper oceanic crust change as a function of age based on global data sets of deep sea drilling project and odp core physical properties and downhole logs increasing crustal age entails macroporosity reduction and large scale velocity increase despite intergranular velocity decrease with little microporosity change the changes in macroporosity and velocity are significant for pillows but minor for flows matrix densities provide the strongest demonstration of systematic age dependent alteration on the basis of observed decreases in matrix density that are proportional to the logarithm of age approximately half of all intergranular scale crustal alteration occurs after the first 10 15 myr apparently crustal alteration continues at a decreasing rate throughout the lifetime of oceanic crust

jasper seamount structure seafloor seismic refraction tomography the velocity structure of jasper seamount was modeled using one and three dimensional inversions of p wave travel times the results represent the first detailed seismic images of a submerged intraplate volcano two seismic refraction experiments were completed on jasper seamount incorporating ocean bottom seismometers and navigated seafloor shots the p wave travel times were first used to compute a one dimensional velocity profile which served as a starting model for a three dimensional tomographic inversion the seamount p velocities are significantly slower than those observed in typical oceanic crust at equivalent subbasement depths this suggests that jasper seamount is constructed predominantly of extrusive lavas with high average porosity the velocity models confirm morphological predictions jasper seamount is a shield volcano with rift zone development high seismic velocities were detected beneath the large radial ridges while low velocities characterize the shallow summit and flanks comparisons between p velocity models of jasper seamount and the island of hawaii reveal that these two shield volcanoes are not structurally proportional jasper seamount is far smaller than hawaii yet both volcanoes exhibit an outer extrusive layer of similar thickness this suggests that seamount size influences the intrusive extrusive proportions density equilibrium between melt and country rock may explain this behavior

ground penetrating radar tomography for soil moisture heterogeneity many ground penetrating radar gpr studies incorporate tomographic methods that use straight raypaths for direct model reconstruction which is unrealistic for media with gradually changing petrophysics ray bending algorithms can sometimes lead to unreliable resolution especially at interfaces of abrupt dielectric changes we present an improved gpr tomography technique based on a combination of seismic tomographic methods and a finite difference solution of the eikonal equation our inversion algorithm uses velocity gradient zones and bending rays that represent realistic geology in the subsurface we tested the technique on theoretical and experimental models with anomalous bodies of varying saturations and velocity and applied it to data from a gpr field experiment that analyzed the root zones of trees synthetic results showed that the resolution of our technique is better than that of published methods especially for local anomalies with sharp velocity contacts our laboratory experiments consisted of four objects buried in sand with various water saturations the gpr tomogram could map the objects and determine their degree of saturation the velocities are compatible with those of the complex refraction index method their relationship to the water content fits a previously published empirical equation our original field experiment around a poplar tree could map the heterogeneous subsurface and distinguish a central low velocity beneath the tree from the peripheral negative anomaly of a refill this zone reflects the whole root zone and is caused by its bulk water content of both the organic root network and its surrounding soils

crosshole seismic imaging for sulfide orebody delineation near sudbury ontario canada crosshole seismic instrumentation based on a piezoelectric source and hydrophone detectors were used to gather seismograms between boreholes at the mcconnell orebody near sudbury ontario high frequency seismograms were recorded across rock sections 50 to 100 m wide containing a continuous zone of massive sulfide ore first arrival traveltimes obtained from a detailed scan were used to create a p wave velocity tomogram that clearly delineated the ore zone refraction ray tracing on a discrete layer model confirmed the main features of the tomogram the survey demonstrated that it is possible to conduct cost effective high resolution crosshole seismic surveys to delineate ore bodies on a scale useful for planning mining operations

effect of alteration formation absorption and standoff on the response of the thermal neutron porosity log in gabbros and basalts examples from deep sea drilling project ocean drilling program sites this study focuses on the effects of hydrous alteration minerals formation absorption and standoff on the response of the thermal neutron porosity log in the basaltic and gabbroic rocks logged at sites 395 418 504 642 and 735 during the ocean drilling program the concentration of hydrogen present in the rocks in the form of free water pore space and bound water hydrous minerals is the primary factor controlling the neutron elastic scattering process while the presence of other elements such as chlorine gadolinium boron lithium and samarium in the fluids and in the rock matrix can largely affect the thermal diffusion phase these neutron absorbers cause an increase of the capture cross section and in turn of the apparent thermal porosity further perturbations occur when the recording conditions depart from those under which the tool has been calibrated a large and irregular hole diameter and a lack of eccentralization both produce erroneous porosity readings the effect of hydrous alteration minerals on the thermal neutron porosity log has been estimated from 922 core oxide measurements using an analysis program that calculates the slowing down length and converts it into apparent porosity the results show that the computed apparent porosity ranges from less than 1 in fresh basalts and gabbros to about 30 in highly altered units depending on the alteration mineral assemblage natural gamma ray capture cross section or hydrogen logs have been used to continuously predict the effect of bound hydrogen at each site corrected porosities generally show excellent agreement with core data for massive units whereas they are higher for pillow basalts and fractured zones the discrepancy is interpreted as the result of 1 difference in the volume of rock investigated core specimens do not sample large vugs and fractures and 2 frequent variations in the hole size and lack of tool contact with the borehole wall standoff not completely accounted for in the corrections high capture cross section values measured on selected basalt samples seem to be associated with more altered basalts suggesting a larger concentration of strong neutron absorbers in secondary minerals the concentrations of elements with large capture cross section measured at three of the five sites studied yield a maximum increase of 1 in the apparent neutron porosity this is too low to explain the porosity values some greater than 7 observed in some of the fresh and unfractured massive units a 1 to 2 inch standoff due to the lack of eccentralization of the tool string used in the ocean drilling program is considered the most probable cause of such discrepancy this interpretation is confirmed by the neutron porosity values recorded at site 735 where the nuclear string was for the first time fully eccentralized and only a correction for borehole size and the presence of hydrous minerals has been applied

physical properties of 110 ma oceanic crust at site osn 1 implications for emplacement of a borehole seismometer an extensive suite of downhole geophysical logs was acquired through a 70 m thick section of basalt drilled by the ocean drilling program odp into 110 ma oceanic crust 225 km sw of hawaii these data include standard sonic electrical and nuclear logs as well as electrical and acoustic images of the wellbore and enable a vertically continuous characterization of the physical properties of shallow old oceanic crust fracture porosity and alteration increase with depth in this hole and consid ered together with results obtained elsewhere in both young and old 5 to 110 ma crust suggest that physical proper ties gradients in the uppermost few hundred meters of oceanic basement are controlled by crustal morphology and alteration and are ubiquitously variable as this hole was drilled primarily for pilot experiments at the first site of the ocean seismic network evaluation of the log data demon strates the importance of careful in situ data collection in order to emplace a broadband monitoring device below the seafloor for long term seismic measurements

seismic waveform inversion in the frequency domain part 2 fault delineation in sediments using crosshole data a crosshole experiment was carried out in a layered sedimentary environment in which a normal fault is known to cut through the section initial traveltime inversions produced stable but low resolution images from which the fault could be only vaguely inferred to image the fault wavefield inversion was used to produce a velocity model consistent with the detailed phase and amplitude of the data at a number of frequencies our wavefield inversion scheme uses a classical descent type algorithm for decreasing the data misfit by iteratively computing the gradient of this misfit by repeated forward and backward propagations our propagator is a full wave equation frequency domain acoustic finite difference method the use of the frequency space domain yields computational advantages for multisource data and allows an easy incorporation of viscous effects by running wavefield inversion on the field data a quantitative velocity image was produced that yielded a significantly improved image of the fault when compared with the original traveltime inversions because the original field data were noisy and contained a high degree of multiple scattering from the layering of the sediments the transmitted arrivals were selectively windowed to enhance the image the sediments at the site were strongly attenuating we therefore used a viscoacoustic model during the modeling and the inversion that correctly simulated the observed decrease in amplitude with increasing frequency and source receiver offset furthermore since the traveltime inversion indicated a high degree of anisotropy at the site a fixed homogeneous level of anisotropy was used during the inversion tests at varying levels of anisotropy confirmed the improvement in image quality and in data fit when anisotropy was incorporated the final image was verified by examining the distribution of the residuals in the frequency domain by comparing time domain modeled wavefields with the observed data and by direct comparison with borehole logs

multiscale geophysical characterization of an unstable rock mass abstract hazard mitigation from rockfalls and landslides is a priority in densely populated areas a proper characterization of the inner structure of the rock mass is key to the comprehension of the mechanisms enhancing the slope instabilities to this aim multi scale geophysical methods can provide a novel and valuable tool for a high resolution imaging of the internal structure of the rock mass and unique constraints on the physical state of the medium we present here a cross hole seismic tomography survey coupled with laboratory ultrasonic velocity measurements and physical properties determination on rock samples to characterize the damaged and potentially unstable granitic cliff of madonna del sasso nw italy results allowed to obtain i a lithological interpretation of the velocity field obtained at the site ii a systematic correlation of the measured velocities with physical properties density and porosity and macroscopic features of the granite weathering and anisotropy of the cliff the multi scale approach adopted within this study revealed to be crucial for the imaging at depth of the main fractures affecting the cliff site scale seismic tests and for the understanding of the variations in the seismic velocity between altered and intact rock laboratory scale tests similar approaches can be potentially used in further microseismic monitoring studies

time lapse imaging of saline tracer transport in fractured rock using difference attenuation radar tomography 1 accurate characterization of fractured rock aquifer heterogeneity remains one of the most challenging and important problems in groundwater hydrology we demonstrate a promising strategy to identify preferential flow paths in fractured rock using a combination of geophysical monitoring and conventional hydrogeologic tests cross well differenceattenuation ground penetrating radar was used to monitor saline tracer migration in an experiment at the u s geological survey fractured rock hydrology research site in grafton county new hampshire radar data sets were collected every 10 min in three adjoining planes for 5 hours during each of 12 tracer tests an innovative inversion method accounts for data acquisition times and temporal changes in attenuation during data collection the inverse algorithm minimizes a combination of two functions the first is the sum of weighted squared data residuals second is a measure of solution complexity based on an a priori space time covariance function subject to constraints that limit radarattenuation changes to regions of the tomograms traversed by high difference attenuation ray paths the time series of tomograms indicate relative tracer concentrations and tracer arrival times in the image planes from these we infer the presence and location of a preferential flow path within a previously identified zone of transmissive fractures these results provide new insights into solute channeling and the nature of aquifer heterogeneity at the site index terms 0910 exploration geophysics data processing 0915 exploration geophysics downhole methods 1829 hydrology groundwater hydrology 1832 hydrology groundwater transport 1894 hydrology instruments and techniques keywords radar tomography fractured rock ground penetrating radar geophysics hydrogeophysics

measurements of attenuation from vertical seismic profiles values of attenuation have been extracted from five detailed velocity surveys significant amounts of attenuation are observed in all five wells measured values of attenuation vary by a factor of 10 ranging from less than 0 1 to 0 9 db wavelength correlation of attenuation with lithology is good considering the resolution limits of the surveys one of the surveys was performed in west texas and the other four were carried out in the gulf coast area the total number of recording depths in each survey varied from 31 to 208 with downhole recordings taken every 10 or 20 ft over key stratigraphic zones in all five surveys a monitor geophone was placed near the well to check for source consistency our procedure for measuring attenuation involved constructing the spectral ratio between each downhole pulse and one particular reference pulse a value of cumulative attenuation ca was then extracted from each spectral ratio and plotted as a function of geophone depth this method allowed us to use many m

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

nonlinear traveltime inversion scheme for crosshole seismic tomography in tilted transversely isotropic media crosshole seismic tomography often is applied to image the velocity structure of an interwell medium if the rocks are anisotropic the tomographic technique must be adapted to the complex situation otherwise it leads to a false interpretation we propose a nonlinear kinematic inversion method for crosshole seismic tomography in composite transversely isotropic media with known dipping symmetry axes this method is based on a new version of the first order traveltime perturbation equation it directly uses the derivative of the phase velocity rather than the eigenvectors of the body wave modes to overcome the singularity problem for application to the two quasi shear waves we applied an iterative nonlinear solver incorporating our kinematic ray tracing scheme and directly compute the jacobian matrix in an arbitrary reference medium this reconstructs the five elastic moduli or thomsen parameters from the first arrival traveltimes of the three seismic body waves qp qsv qsh in strongly and weakly anisotropic media we conducted three synthetic experiments that involve determining anisotropic parameters for a homogeneous rock reconstructing a fault embedded in a strongly anisotropic background and imaging a complicated four layer model containing a small channel and a buried dipping interface we compared results of our nonlinear inversion method with isotropic tomography and the traditional linear anisotropic inversion scheme which showed the capability and superiority of the new scheme for crosshole tomographic imaging

combining wave equation imaging with traveltime tomography to form high resolution images from crosshole data traveltime tomography is an appropriate method for estimating seismic velocity structure from arrival times however tomography fails to resolve discontinuities in the velocities wave equation techniques provide images using the full wave field that complement the results of traveltime tomography we use the velocity estimates from tomography as a reference model for a numerical propagation of the time reversed data these backpropagated wave fields are used to provide images of the discontinuities in the velocity field the combined use of traveltime tomography and wave equation imaging is particularly suitable for forming high resolution geologic images from multiple source multiple receiver data acquired in borehole to borehole seismic surveying in the context of crosshole imaging an effective implementation of wave equation imaging is obtained by transforming the data and the algorithms into the frequency domain this transformation allows the use of efficient frequency domain numerical propagat

pilot experiment for the acquisition of marine sediment properties via small scale tomography system a 3 d high resolution crosswell acoustic tomography system was designed and tested in a shallow water environment this system makes use of a damped least squared inversion technique and is used to construct compressional wave velocity images from measured travel time data use of singular value decomposition allowed checks of the linear inversion confirming the validity of the modeled environment it is shown that when the ratio of width to depth of the cross section is about unity or smaller and the domain has not been overparametrized the inverted image model has sufficiently good figures of merit in resolution and variance to visualize small variations in the magnitude compressional velocity field

borehole transmission tomography for velocity plus statics the accuracy of velocity tomograms reconstructed from borehole transmission traveltime data is highly sensitive to traveltime statics we present a least squares tomography algorithm that includes a traveltime static term the algorithm solves for both the velocity field and the traveltime statics simultaneously this enables us to separate traveltime signal from traveltime noise reducing the tomographic velocity artifacts caused by the statics the incorporation of a priori constraints on the poorly determined spectral components of the velocity field further improves accuracy by reducing velocity artifacts as a result of uneven ray coverage application of the algorithm to numerical crosswell data results in velocity and statics estimates that are accurate to within 1 percent application of the algorithm to exxon s friendswood tomography data results in velocity and statics estimates that correlate with independent data

removal of scattered guided waves from seismic data near surface scattered waves form a major source of coherent noise in seismic land data most current methods for removing these waves do not attenuate them adequately if they come from other than the inline direction we present a wave theory based method for removing scattered guided waves by a prediction and removal algorithm we assume that the near surface consists of a laterally varying medium in which heterogeneities are embedded that act as scatterers we first estimate the dispersive and laterally varying phase slowness field by applying a phase based tomography algorithm on the direct groundroll wave subsequently the near surface heterogeneities are imaged using a least squares criterium finally the scattered guided waves are modeled and subtracted adaptively from the seismic data we have applied this method to seismic land data and found that near surface scattering effects are attenuated

inference of multi gaussian relative permittivity fields by probabilistic inversion of crosshole ground penetrating radar data abstractin contrast to deterministic inversion probabilistic bayesian inversion provides an ensemble of solutions that can be used to quantify model uncertainty we have developed a probabilistic inversion approach that uses crosshole first arrival traveltimes to estimate an underlying geostatistical model the subsurface structure and the standard deviation of the data error simultaneously the subsurface is assumed to be represented by a multi gaussian field which allows us to reduce the dimensionality of the problem significantly compared with previous applications in hydrogeology novelties of this study include an improvement of the dimensionality reduction algorithm to avoid streaking artifacts it is the first application to geophysics and the first application to field data the results of a synthetic example show that the model domain enclosed by one borehole pair is generally too small to provide reliable estimates of geostatistical variables a real data example based on two borehole pairs

estimation of field scale soil hydraulic and dielectric parameters through joint inversion of gpr and hydrological data 1 a method is described for the joint use of time lapse ground penetrating radar gpr travel times and hydrological data to estimate field scale soil hydraulic parameters we build upon previous work to take advantage of a wide range of cross borehole gpr data acquisition configurations and to accommodate uncertainty in the petrophysical function which relates soil porosity and water saturation to the effective dielectric constant we first test the inversion methodology using synthetic examples of water injection in the vadose zone realistic errors in the petrophysical function result in substantial errors in soil hydraulic parameter estimates but such errors are minimized through simultaneous estimation of petrophysical parameters in some cases the use of a simplified gpr simulator causes systematic errors in calculated travel times simultaneous estimation of a single correction parameter sufficiently reduces the impact of these errors we also apply the method to the u s department of energy doe hanford site in washington where time lapse gpr and neutron probe np data sets were collected during an infiltration experiment we find that inclusion of gpr data in the inversion procedure allows for improved predictions of water content compared to predictions made using np data alone these examples demonstrate that the complimentary information contained in geophysical and hydrological data can be successfully extracted in a joint inversion approach moreover since the generation of tomograms is not required the amount of gpr data required for analyses is relatively low and difficulties inherent to tomography methods are alleviated finally the approach provides a means to capture the properties and system state of heterogeneous soil both of which are crucial for assessing and predicting subsurface flow and contaminant transport

a geostatistical framework for incorporating seismic tomography auxiliary data into hydraulic conductivity estimation abstract a geostatistical approach is presented for the inclusion of seismic tomography data and sonic log data into the estimation of hydraulic conductivity the procedure accounts for the errors in seismic tomography inversion and for the correlation of such errors the proposed methodology consists of two steps 1 the cross variogram inference is carried out using only the data at the wellbore both hydraulic and seismic 2 a co kriging procedure takes the cross well data into account to interpolate between boreholes no postulated a priori relationship is needed in order to illustrate the methodology a synthetic data set is generated on the basis of evidence from published case studies and simplified physical considerations the numerical experiments show that the choice of the excitation frequency is critical a trade off exists between the need for a high resolution survey asking for higher frequencies and the need for a good correlation between hydraulic conductivity and seismic properties asking for frequencies below the squirt frequency of the medium in the simulation using seismic data with the best excitation frequency 1 khz in this case the mean squared error of the hydraulic conductivity estimate is two thirds lower than using hydraulic data alone it is important to note also that only a part of the interwell region is adequately sampled by the tomographic experiment such a region can be readily identified by calculating the energy of the quasi null space through singular value decomposition of the tomographic matrix in planning this type of experiments it is necessary to carefully verify case by case whether the adopted range of high frequencies does not prevent the seismic energy from propagating effectively from sources to receivers

micromorphology and chemical weathering of a k rich trachyandesite and an associated sedimentary cover parkes se australia abstract the micromorphology composition and sequential formation of weathering products of a k rich trachyandesite and an associated sedimentary cover at parkes se australia are described this has been achieved using a combination of mineralogical optical x ray microdiffraction and sem edxa microanalysis and chemical x ray fluorescence techniques the weathering profiles have developed in a low altitude relatively flat landscape setting the following processes are dominant a weathering of primary minerals notably feldspars and micas to transient poorly crystalline oxyhydroxide patches smectite and ultimately kaolinite b weathering of sediments in a zone of intense solution activity and redox reactions resulting in development of mottles and ferruginous nodules and c greater thickness up to 350 cm and compositional differences between the soil over weathered sediments and in situ weathered bedrock the dominant profile microsystems evolved under a past humid climate later modified by the prevailing semi arid to arid conditions

hydrogeological characterization of the south oyster bacterial transport site using geophysical data a multidisciplinary research team has conducted a field scale bacterial transport study within an uncontaminated sandy pleistocene aquifer near oyster virginia the overall goal of the project was to evaluate the importance of heterogeneities in controlling the field scale transport of bacteria that are injected into the ground for remediation purposes geochemical hydrological geological and geophysical data were collected to characterize the site prior to conducting chemical and bacterial injection experiments in this paper we focus on results of a hydrogeological characterization effort using geophysical data collected across a range of spatial scales the geophysical data employed include surface ground penetrating radar radar cross hole tomography seismic cross hole tomography cone penetrometer and borehole electromagnetic flowmeter these data were used to interpret the subregional and local stratigraphy to provide high resolution hydraulic conductivity estimates and to provide information about the log conductivity spatial correlation function the information from geophysical data was used to guide and assist the field operations and to constrain the numerical bacterial transport model although more field work of this nature is necessary to validate the usefulness and cost effectiveness of including geophysical data in the characterization effort qualitative and quantitative comparisons between tomographically obtained flow and transport parameter estimates with hydraulic well bore and bromide breakthrough measurements suggest that geophysical data can provide valuable high resolution information this information traditionally only partially obtainable by performing extensive and intrusive well bore sampling may help to reduce the ambiguity associated with hydrogeological heterogeneity that is often encountered when interpreting field scale bacterial transport data

spatial correlation structure estimation using geophysical and hydrogeological data the large spatial variability of hydraulic properties in natural geologic systems over a wide range of scales and the difficulty of collecting representative and sufficient hydraulic property measurements using conventional sampling techniques render estimation of spatial correlation parameters difficult further compounding the estimation problem is the observation that the integral scale estimate is a function of the measurement support scale to mitigate these problems we investigate the use of tomographic geophysical data in combination with hydrogeological data in the spatial correlation estimation procedure two synthetic case studies were investigated where the scale of the geophysical measurements were varied relative to the scale of the hydrogeological properties the spatial correlation structure parameter estimation procedure was performed in the spectral domain where analysis of data having different support scales and spatial sampling windows was facilitated comparison of the spatial correlation structure parameters estimated from measured data with those of the synthetic aquifers revealed which type of data tomographic hydrogeological or a combination of both was most effective for recovering spatial correlation statistics under different sampling heterogeneity conditions these synthetic case studies suggest that collection of a few tomographic profiles and interpretation of these profiles together with limited well bore data can yield correlation structure information that is otherwise obtainable only from extensive hydrological sampling

seismic characterization of a highly stressed rock mass using tomographic imaging and induced seismicity a seismic tomography study was carried out at falconbridge s lockerby mine sudbury canada in april 1989 the objective was to determine the integrity of a rock mass at 1 km depth and to investigate the correlation between induced seismicity and p wave velocity structure the tomographic image showed two distinct and significant p wave velocity anomalies a low velocity zone at the source region of a mn 2 3 mining induced tremor recorded in 1985 and a high velocity zone at the source region of a mn 2 6 mining induced tremor recorded in 1988 analysis of mining induced microseismicity showed that the high velocity zone was the focus for seismic activity prior to and after the 1988 tremor in contrast to the low velocity zone which remained aseismic for the same period the seismic anomalies were diamond drilled following the tomographic imaging to verify the physical characteristics of the zones the seismically active high velocity zone showed severe core disking indicative of a highly stressed strong rock while the low velocity zone was characterized by extensive fracturing and failed rock the results showed that the 1985 tremor and rock burst sequence resulted in a major failure of the rock mass in the source region of the event and stress was redistributed and concentrated in the source region of the 1988 tremor the 1988 event and rock burst sequence did not result in failure of the source region which therefore remains a seismically active high velocity zone with a potential for significant seismic energy release and further rock bursting the study has highlighted a correlation between p wave velocity structure and induced seismicity which can be used to characterize highly stressed rock masses in underground mines

multi scale tomography for crustal p and s velocities in southern california seismic tomography is a viable tool in building depth velocity models in the presence of strong lateral velocity variations in this study 3 d p and s velocity models for the crust of southern california are constrained using more than 1 000 000 p wave first arrivals and 130 000 s wave arrivals from local earthquakes to cope with the uneven distribution of raypaths a multi scale tomography is applied with overlapping model cells of different sizes within the 300 480 39 km3 model volume the smallest cell size is 10 10 3 km3 during the iterations of velocity updating earthquake hypocenters are determined using both p and s arrivals and full 3 d ray tracing is implemented except near the edges and in the lower crust the resultant models are robust according to various tests on the effects of reference models resolution and signal to noise ratio the tomographic velocities at shallow depths correlate very well with the regional geology of southern california in the upper crust the p wave and s wave models exhibit slow velocities in major sedimentary basins and fast velocities in areas of crystalline rocks mid crustal low velocity zones are present under the coso range san gabriel mountains and a large portion of the mojave desert p and s velocity patterns maintain their similarity in the lower crust though the models are less reliable there

crosshole seismic waveform tomography i strategy for real data application summary the frequency domain version of waveform tomography enables the use of distinct frequency components to adequately reconstruct the subsurface velocity field and thereby dramatically reduces the input data quantity required for the inversion process it makes waveform tomography a computationally tractable problem for production uses but its applicability to real seismic data particularly in the petroleum exploration and development scale needs to be examined as real data are often band limited with missing low frequencies a good starting model is necessary for waveform tomography to fill in the gap of low frequencies before the inversion of available frequencies in the inversion stage a group of frequencies should be used simultaneously at each iteration to suppress the effect of data noise in the frequency domain meanwhile a smoothness constraint on the model must be used in the inversion to cope the effect of data noise the effect of non linearity of the problem and the effect of strong sensitivities of short wavelength model variations in this paper we use frequency domain waveform tomography to provide quantitative velocity images of a crosshole target between boreholes 300 m apart due to the complexity of the local geology the velocity variations were extreme between 3000 and 5500 m s 1 making the inversion problem highly non linear nevertheless the waveform tomography results correlate well with borehole logs and provide realistic geological information that can be tracked between the boreholes with confidence

resolution of slowness and reflectors in crosswell tomography with transmission and reflection traveltimes we sometimes encounter situations in seismic imaging in which knowing the position of key reflectors between wells would be very useful in many crosswell data sets both transmission and reflection traveltimes for selected reflectors can be picked we investigated the possibility that transmission plus reflection crosswell traveltime tomography can determine the position of these reflectors with a high level of accuracy thereby providing an independent way of verifying and perhaps improving the position of these reflectors obtained from crosswell reflection imaging we studied the effect of combining reflection traveltimes for selected reflectors with transmission traveltimes on the resolution of the interwell slowness field and depth determination of selected reflectors we found that theoretically the position of reflectors is determined uniquely from transmission and reflection traveltimes in a linearized continuum formulation ofcrosswell tomography we also computed diagonal elements of the resol