interpretation of lithofacies of the ashtabula till along the south shore of lake erie northeastern ohio the final advance of the erie lobe into ohio during the port bruce stade of the late wisconsinan deposited the ashtabula till wave erosion and mass wasting along the south shore of lake erie show

shear wave birefringence a new tool for evaluating fractured reservoirs propagation characteristics of shear waves make them particularly well suited to exploration for and definition of fractured reservoirs the department of geophysics at colorado school of mines conducted a three component p and s wave seismic survey in order to determine whether shear wave polarization and splitting birefringence caused by fracture induced azimuthal anisotropy could be measured over a naturally fractured reservoir results indicate that surface seismic recordings of shear waves can be used to calculate azimuthal anisotropy and that seismic observation of azimuthal anisotropy can provide information about the location orientation and intensity of subsurface fractures data obtained from this investigation indicate that measurement of shear wave birefringence is a potentially powerful tool for predicting fracture orientation and permeability trends

application of image cross correlation to the measurement of glacier velocity using satellite image data abstract image to image cross correlation software is applied to pairs of digital satellite images to map the velocity field of moving ice this technique uses small scale glacial surface features such as crevasse scars and snow dunes as markers on the surface of the moving ice displacements of the surface features are mapped by selecting small image areas centered on distinct features or by dividing a large area of densely featured glacial surface into a grid of areas and searching a subsequent image for matching areas using a cross correlation algorithm interpolation of the peak correlation values allows the displacements to be measured to subpixel accuracy resulting in very precise velocity measurements cross correlation is also applied to provide image coregistration in areas devoid of bedrock exposures in such areas subtle large scale topographic undulations in the ice surface related to underlying bedrock structure may be correlated by using large image areas and low pass filtered images both types of applications are demonstrated using ice stream d and ice stream e in west antarctica as test areas a high resolution map of the velocity field of the central portion of ice stream e generated by the displacement measuring technique is presented the use of cross correlation software is a significant improvement over previous manually based photogrammetric methods for velocity measurement and is far more cost effective than in situ methods in remote polar areas

the duration of the active phase on surge type glaciers contrasts between svalbard and other regions many glaciers in svalbard and in other glacierized areas of the world are known to surge however the time series of observations required to assess the duration of fast motion is very restricted data on active phase duration in svalbard come from aerial photographs satellite imagery field surveys and airborne reconnaissance evidence on surge duration is available for eight svalbard ice masses varying from 3 to 1250 km 2 worldwide active phase duration is recorded for less than 50 glaciers few observations are available on high polar ice masses the duration of the active phase is significantly longer for svalbard glaciers than for surge type glaciers in other areas from which data are available in svalbard the active phase may last from 3 to 10 years by contrast a surge duration of 1 2 years is more typical of ice masses in northwest north america iceland and the pamirs ice velocities during the protracted active phase on svalbard glaciers are considerably lower than those for many surge type glaciers in these other regions mass is transferred down glacier more slowly but over a considerably longer period svalbard surge type glaciers do not exhibit the very abrupt termination of the active phase over periods of a few days observed for several alaskan glaciers the duration of the active phase in svalbard is not dependent on parameters related to glacier size the quiescent phase is also relatively long 50 500 years for svalbard ice masses detailed field monitoring of changing basal conditions through the surge cycle is required from surge type glaciers in svalbard in order to explain the significantly longer length of the active phase for glaciers in the archipelago which may also typify other high polar ice masses the finding that surge behaviour in the form of active phase duration shows systematic differences between different regions and their environments has important implications for understanding the processes responsible for glacier surges

satellite image derived velocity field of an antarctic ice stream the surface velocity of a rapidly moving ice stream has been determined to high accuracy and spatial density with the use of sequential satellite imagery variations of ice velocity are spatially related to surface undulations and transverse velocity variations of up to 30 percent occur such large variations negate the concept of plug flow and call into question earlier mass balance calculations for this and other ice streams where sparse velocity data were used the coregistration of images with the use of the topographic undulations of the ice stream and the measurement of feature displacement with cross correlation of image windows provide significant improvements in the use of satellite imagery for ice flow determination

internal architecture of a till sheet tiskilwa formation north central illinois usa application of architectural element analysis thick till sheets deposited during the quaternary form significant aquitards in many areas of north america however the detailed sedimentary heterogeneity and architecture and depositional history of till units are not well understood this study utilizes architectural element analysis to delineate the internal sedimentary architecture of the tiskilwa formation exposed at two outcrop sections in north central illinois usa architectural element analysis facilitates systematic delineation of sedimentary architecture based on the nature of facies contacts and change in facies associations delineation of unit geometries and understanding of depositional processes at different scales of resolution making architectural element analysis suitable for the sedimentological analysis and palaeoenvironmental reconstruction of subglacial deposits eleven facies types are identified in this study including sand gravel and diamict facies that record a suite of subglacial depositional processes detailed analysis of facies contacts bounding surface hierarchy and change in facies associations allows the delineation of five architectural elements including coarse grained lens coarse grained sheet mixed zone diamict lens and diamict sheet elements the spatial arrangement and genetic interpretation of elements and their spatial relationship with fifth order bounding surfaces allows the delineation of five larger scale architectural units element associations which can be mapped in the local study area and record at least three stacked successions of meltwater accumulation and till deposition the results of this study can be utilized for architectural analysis of till sheets and provide insight to groundwater flow pathways through till in the study area and elsewhere

finite difference simulations of seismic scattering implications for the propagation of short period seismic waves in the crust and models of crustal heterogeneity synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two dimensional media with random spatial variations in seismic velocity the results of this study provide important insights about the propagation of short period 5 the self similar medium is characterized by a scattering q that is constant with frequency whereas theory predicts that the apparent q in an exponential medium is proportional to frequency these alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal q at frequencies greater than about 1 hz assuming that scattering is responsible for most of the attenuation at these frequencies measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation scattering q 200 in these cases q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission q of the medium the cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium the self similar random medium proposed here for the crust produces waveform variations at high frequencies 15 30 hz similar to those reported for actual small scale seismic arrays with apertures of hundreds of meters

crosswell seismic waveguide phenomenology of reservoir sands shales at offsets 600 m liaohe oil field ne china summary crosswell seismic data recorded at 620 650 m offsets in an oil bearing sand shale reservoir formation at the liaohe oil field northeast china provide robust evidence for waveguide action by low velocity reservoir layers crosswell section velocity models derived from survey well sonic logs and further constrained by observed waveguide seismic wavegroup amplitudes and phases yield plausible evidence for interwell reservoir sand continuity and discontinuity a pair of back to back liaohe crosswell vector seismic surveys were conducted using a source well between two sensor wells at 650 and 620 m offsets along a 200 m thick reservoir formation dipping 7 down to east between depths of 2 5 and 3 km a downhole orbital vibrator generated seismic correlation wavelets with frequency range 50 350 hz and signal noise ratio up to 5 1 over local downhole ambient noise the sensor wells were instrumented with a mobile 12 to 16 level string of clamped vector motion sensor modules at 5 m intervals using 5 m source depth increments crosswell surveys 1 and 2 cover source sensor well intervals above and through the reservoir of respectively 600 m 600 m 13 000 vector traces in 9 common sensor fans and 300 m 560 m 7000 vector traces in 7 common sensor fans survey 1 common sensor gathers show clear consistent high amplitude 20 ms waveletgroup lags behind the first arrival traveltime envelope such arrivals are diagnostic of seismic low velocity waveguides connecting the source and sensor wells observed survey 1 retarded wavegroup depths tally with source and sensor depths in low velocity layers identified in sonic well logs finite difference acoustic model wavefields computed for waveguide acoustic layers constrained by well log sonic velocity data match the observed waveguide traveltime and amplitude systematics model waveforms duplicate the observed m scale and ms scale sensitivity of waveguide spatio temporal energy localization survey 2 crosswell data in contrast provide no comparable evidence for waveguide action despite a sensor well sonic well log similar to that of survey 1 instead acoustic wavefield modelling of survey 2 data clearly favours an interpreted waveguide model with 10 downdip interrupted by a 75 100 m throw down fault near the sensor well the absence of clear waveguide arrivals is adequately explained by dispersal of waveguide energy at the fault discontinuity auxiliary well sonic velocity and lithologic logs confirm the model implied 75 100 m of down throw faulting near the sensor well

the steepbank crosswell seismic project reservoir definition and evaluation of steamflood technology in alberta tar sands two crosswell seismic surveys were conducted at chevron canada s oil sand lease 49 steepbank located about 60 km northeast of fort mcmurray alberta this is the site of the hasdrive commercial pilot project in which steam is circulated through a horizontal well in order to preheat the tar sand prior to conventional steam injection the objective of the crosswell survey was to define the geology and to monitor the movement of the injected steam as part of the hasdrive evaluation the first survey was conducted 25 september 6 october 1991 just prior to steam injection the second was acquired 7 14 january 1992 after 72 days of continuous steam injection

the cause of frequency dependent seismic absorption in crustal rock summary the absorption of 5 to 200 hz seismic wave energy propagating at depth in fracture bearing crystalline basement in southern california is observed to increase as a power law in wave frequency as f0 43 0 1 so that energy absorption per unit frequency q 1 decreases with frequency as f 0 57 and the seismic quality factor q increases with frequency as f0 57 the value of q at 10 hz is 1000 crustal fracture density which elastic scattering and borehole logs show to vary with fracture dimension l as a power law l0 4 cannot easily explain the observed frequency dependence of absorption a likely hypothesis identifies the f0 43 0 1 frequency dependence of seismic absorption with the f1 12 frequency dependence of a thermal diffusion process seismic absorption computed for thermal gradients induced by localized strain concentrations depends on a single free parameter the thermal absorption domain characteristic size d if d 0 2 mm the computed magnitude of absorption agrees with the observed q 1000 at 10 hz thin sections from deep borehole rock samples show that 0 2 mm is the characteristic dimension of microfracture shear fabric and crystalline grains where seismic elastic scattering occurs over a wide range of fracture sizes seismic absorption occurs predominantly at the dimension of microfractures and granularity systematic wide band borehole seismic observation of seismic absorption magnitude and particularly frequency dependence combined with thin section analysis of the rock microfabric can test the hypothesis for a range of crustal rocks the evidence of thermal activity at the scale of microfractures suggests that static stress concentrations possess a free energy that can act to align microfractures thus explaining the shear wave birefringence widely observed in the crust

disturbed state constitutive modeling of two pleistocene tills the disturbed state concept dsc provides a general approach for constitutive modeling of deforming materials here we briefly explain the dsc and present the results of laboratory tests on two regionally significant north american tills along with the results of a numerical simulation to predict the behavior of one of the tills in an idealized physical system laboratory shear tests showed that plastic strain starts almost from the beginning of loading and that failure and resulting motion begin at a critical disturbance when about 85 of the mass has reached the fully adjusted or critical state specimens of both tills exhibited distributed strain deforming into barrel shapes without visible shear planes dsc parameters obtained from shear and creep tests were validated by comparing model predictions against test data used to find the parameters as well as against data from independent tests the dsc parameters from one of the tills were applied in a finite element simulation to predict gravity induced motion for a 5000 m long 100 m thick slab of ice coupled to an underlying 1 5 m thick layer of till set on a 4 incline with pore water pressure in the till at 90 of the load the simulation predicted that in the middle segment of the till layer i e from x 2000 to 3000 m the induced computed shear stress strain and disturbance increase gradually with the applied shear stress induced shear stress peaks at 60 kpa the critical disturbance at which failure occurs is observed after the peak shear stress at an induced shear stress of 23 kpa and shear strain of 0 75 in the till calculated horizontal displacement over the height of the entire till section at the applied shear stress of 65 kpa is 4 5 m we note that the numerical prediction of critical disturbance when the displacement shows a sharp change in rate compares very well with the occurrence of critical disturbance observed in the laboratory triaxial tests when a sharp change in the rate of strain occurs this implies that the failure and concomitant initiation of motion occur near the residual state at large strains in contrast to the mohr coulomb model which predicts failure and motion at very small elastic strain the dsc thus predicts failure and initiation of motion after the till has undergone considerable plastic strain these results suggest that subglacial till may be able to sustain stress in the vicinity of 20 kpa even after the motion begins they also demonstrate the potential of the dsc to model not only local behavior including potential sticky spot mechanisms but also global behavior for soft bedded ice

numerical simulation of first order backscattered p and s waves for time lapse seismic imaging in heterogeneous reservoirs summary first order elastic wave scattering theory validated in general features by deep borehole seismic coda wave observations is used to numerically simulate time lapse borehole seismic data aimed at monitoring oil water substitution in heterogeneous hydrocarbon reservoirs a first order perturbation solution of the vector wave equation leads to p p and s s backscattered displacement vector motion expressed as the angular summation of the second radial derivative of p and s wave velocity and density fluctuations over expanding spherical wave fronts of radii t 2 and t 2 p and s wave velocity and density spatial heterogeneity is modelled as long range correlated random fluctuations consistent with the power law scaling character of crustal rock physical properties measured by borehole logs the spectra of model scattering displacement seismograms for a power law scaling volumetric noise distribution duplicate the frequency enrichment observed in the spectra of broadband earthquake coda waves recorded in a deep well modelling of time lapse scattering in power law scaling permeability structures suggests that a stable borehole seismic source can locate oil water substitution in reservoir volumes tens of metres on a side at distances of up to a few hundred metres from an observation well using currently available borehole seismic technology time lapse tracking of oil water substitution and the monitoring of reservoir stress conditions can lead to spatially well constrained reservoir models despite large scale large amplitude correlated random heterogeneity

digital comparison of high resolution sojuzkarta kfa 1000 imagery of ice masses with landsat and spot data russian satellite imagery of the polar regions has recently become available to western scientists through sojuzkarta the kfa 1000 photographic camera is of particular interest to glaciologists due to its high resolution a nominal 5 m digitized photographic products from this instrument are compared with digital data from landsat and spot series satellites for a partly glacierized area of northwest spitsbergen comparison of kfa 1000 data with detailed maps of man made structures at the settlement of ny alesund demonstrates that the resolution of the photographic imagery is about 3 m but scanner resolution limited our digital data to about 6 m significantly less detail can be resolved on landsat tm imagery and landsat mss data fail to resolve any of the structures kfa 1000 data are compared with landsat tm and mss images and spot hrv multispectral imagery for several tidewater glaciers in spitsbergen kfa 1000 imagery is of a significantly higher geometric resolution than the other sensors allowing the clear identification of individual crevasses and other ice surface features kfa 1000 scenes from 1985 and 1988 are used to measure ice marginal fluctuations for several northwest spitsbergen glaciers and the onset of a surge can also be identified this imagery has a 60 overlap between scenes and the heighting accuracy of the stereoscopic data is calculated at 45 m radiometric analysis of kfa 1000 data is restricted to relative brightness values since no absolute calibration is available the photographic products appear speckled and the range and standard deviation of normalized pixel brightness values over snow is greater than for equivalent landsat tm data the very high spatial resolution of the kfa 1000 camera is its principal attraction for glaciologists

deep borehole log evidence for fractal distribution of fractures in crystalline rock summary sonic velocity and electrical resistivity logs run to a depth of 3 5 km in crystalline rock near the san andreas fault at cajon pass in southern california correlate over scale lengths both small sub metre and large tens to hundreds of metres no such correlations are seen with the more lithologically sensitive natural gamma intensity log the correlation between the sonic velocity and electrical resistivity logs suggests that a non lithologic property of the crystalline rock controls fluctuations in situ fracture intensity is a logical candidate for the controlling rock property the fluctuations of the individual sonic velocity and electrical resistivity logs are examined with the hurst rescaled range parameter over borehole log intervals 1 5 m l 1500 m for log fluctuations arising from a scale invariant physical process the hurst rescaled range scales with data interval as lh 0 h 1 a purely random sequence of in situ fractures produces a scaling exponent h 0 50 fluctuations in the cajon pass sonic velocity and electrical resistivity logs yield h 0 70 evidence that in situ fracture sets tend to occur in clusters rather than at purely random intervals the tendency for fracture clustering over log intervals 1 5 m l 1500 m suggests that fracture formation is a fractal process independent of length scale in which larger fracture intervals form from clustering of numerous smaller fracture intervals seismic reflectivity derived from the borehole sonic velocity log is also scale independent over the range of data intervals 1 5m l 1500 m with a hurst exponent h 0 21 if we associate fracture clustering with crustal fault formation the cajon pass borehole sonic velocity and electrical resistivity logs predict that crustal faults scale fractally with fractal dimension d 2 30 the equivalent b value for earthquake size distribution is b d 2 1 15 on this hypothesis observed b values 1 15 indicate a tendency for earthquakes to cluster on existing weak faults a scale independent mechanics for crystalline rock fracture formation in which larger scale fractures form as clusters of smaller scale fractures provides a mechanical link between the small pervasive stress aligned flaws cracks and microfractures which can impart anisotropy to crystalline rock and the larger scale fractures associated with finite strain and faulting thus in crustal regions of active but low strain fracture anisotropy is observed to be aligned with the inferred maximum principal stress while in actively faulted crust fracture anisotropy is observed to be more nearly fault parallel as if the fractures are aligned by the finite strain faulting process

a millennium of variable ice flow recorded by the ross ice shelf antarctica an enhanced composite advanced very high resolution radiometer avhrr image is used to map flow stripes and rifts across the ross ice shelf antarctica the patterns of these flow related features reveal a history of discharge variations from the ice streams feeding the eastern part of the shelf the most profound variations are visible in the track of rifts downstream of crary ice rise flow stripe bends to the west of this ice rise and adjacent to steershead ice rise and changes in the northern margin of ice stream b the track of rifts downstream of crary ice rise indicates that the ice rise has existed for at least 700 years the character of this track changes about 350 km downstream indicating a rearrangement of flow patterns about 550 years ago the large bulge in the flow stripes to the west of crary ice rise is shown in detail with bent flow stripes extending for several hundred kilometers along flow this feature formed from the south possibly due to a change in the discharge of ice stream a the avhrr image documents a complex history associated with the shutdown of ice stream c with changes in the margins of ice stream c and the northern margin of ice stream b and the grounding of steershead ice rise with an associated bending and truncation of flow stripes landsat imagery shows a region that appears to be actively extending just downstream of the ice rise as the shelf continues to respond to recent changes in ice stream discharge we present a four stage flow history which accounts for the features preserved in the ice shelf

acoustic tomography for monitoring enhanced oil recovery in 1984 professor amos nur of stanford university presented a paper at the seg annual international meeting in which he reported results from work carried out by his group to measure compressional and shear wave velocities as well as attenuation in samples of heavy oil sands from several reservoirs although the explanation for the observed effect was not clear the results suggested that acoustic velocities and attenuation in sands saturated with heavy oils are strongly dependent on the degree of heating of the sample to many who heard that presentation it was apparent that these observations might provide the basis for applying geophysical technology to the problem of monitoring the progression of flood fronts in thermal enhanced oil recovery eor projects in heavy oil reservoirs since that time a number of important projects have been carried out to test the theory and to attempt to verify the results predicted by the laboratory experiments it is reasonable to say that results to date have b

rock as a critical point system and the inherent implausibility of reliable earthquake prediction summary the statistical mechanics of critical point thermodynamic systems provide a powerful conceptual tool with which to examine the plausibility of reliable earthquake prediction the issue turns on how rock is heterogeneous if the correlation range of a spatially fluctuating rock property is bounded by a characteristic length then the spatial average of that property over dimensions greater than may be regarded as defining an effective continuum value for that property ideas about earthquake preparation in rock with an effective continuum mechanical strength can plausibly focus on failure that is initiated at small anomalous zones and grows to instability with access to a continuous volume of strain energy the dimensions and temporal evolution of the growing anomaly can then be expected to relate to the size location and timing of the impending seismic event borehole log evidence indicates however that rock heterogeneity correlation lengths are unbounded and hence that the effective continuum approximation for rock must be applied with discretion an infinite correlation length indicates a statistical mechanical critical point system in which the correlation length is related to a singularity in a physical property in thermodynamic critical systems the singularity occurs at the critical system temperature tc 1 t tc in rock the singularity occurs at the critical percolation probability pc 1 p pc statistical physics descriptions of critical point spatial correlations are based on nearest neighbour inter actions at every scale length nearest neighbour interactions at one scale say that of large failure structures the loci of large earthquakes involve minimal coupling to structures at other scales in particular small scale failure structures the loci of small earthquakes the mechanics of nearest neighbour interactions plausibly form a fundamental constraint on the role of small scale failure or related nucleating activity as a prelude to large scale failure in light of 1 the evidence against rock being an effective medium notionally supporting localized precursory activity that reliably grows to large scale mechanical failure and 2 the history of failure to identify reliable precursors to major earthquakes the onus should now be on advocates of earthquake prediction schemes to evaluate their claims for precursory activity in terms of rock as a critical point system

the dynamics of ice sheet outlets a comparison of data from aircraft altimetry landsat imagery and radia echo sounding has shown characteristic surface topographies associated with sheet and stream flow the transition between the two is abrupt and occurs at a step in the subglacial topography this marks the onset of basal sliding and high velocities caused by subglacial water it results in crevassed amphitheatre like basins round the head of outlet glaciers it is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase this abrupt transition appears to be topographically controlled since basal temperatures are at the pressure melting point well inland of the change in regime the marie byrd land ice streams exhibit qualitative differences from other ice sheet outlets however the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice the repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion this is concentrated towards the heads of outlet glaciers up stream of the region where significant basal decoupling occurs this may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls

ice marginal sedimentation and processes of diamicton deposition in large proglacial lakes lake erie ontario canada detailed studies of coastal cliff exposures through two end moraines form the basis for a model of ice marginal sedimentation in large ice contact glacier fed lakes the input to the ice marginal environment directly from the glacier included subglacial till and subaquatic flow tills the subaquatic flow till thinly bedded diamicton was deposited in an apron up to 1 km wide along the ice margin an upward gradient of pore water pressure immediately beyond the ice margin causing heaving and dilation of the sediments initiated debris flows of glacially derived debris subaquatic flow tills most of the stratified sediments in the ice marginal zone entered the lake by way of a large proglacial stream sedimentation was dominated by quasi or near continuous density underflows that resulted in the deposition of a sequence of thick rhythmites the glacier in the lake erie basin most likely behaved like an ice stream with its movement controlled predominantly by a deforming bed of glacial debris separa

digital mapping in polar regions from landsat photographic products a case study landsat photographic products on the space oblique mercator som projection are used to construct a map of nordaustlandet svalbard of known accuracy the map includes ice divides accurately enlarged landsat images were digitized combined digitizer and operator errors were 64 m at the enlargement scale fifteen ground control points fixed the two scenes rms errors in control point identification were 123 m geographical coordinates were extracted by i converting digitizer coordinates to som cartesian coordinates and 2 transforming these coordinates to latitude and longitude this map production method is applicable to any imagery of known projection the digitally stored map may be plotted on a variety of map projections and scales two problems in image interpretation were i shadows obscuring detail on nne facing coasts and 2 summer snow cover obscuring parts of the terrestrial ice cap margins the map is similar to an east coast map produced from landsat computer compatible tapes differences between the landsat map and a 1 50 000 scale

importance of the regelation process to certain properties of basal tills deposited by the laurentide ice sheet in iowa and illinois u s a

power law scaling behavior of crustal density and gravity 1 the scale invariant nature of crustal heterogeneity has been established through direct measurements of rock properties and inferences from geophysical observations we examine the behavior of crustal density variations over length scales from centimeters to hundreds of kilometers using well logs surface rock samples and observed gravity data the three data types support a simple model of an isotropic scaling crust with density characterized by a power law spectral behavior

the surface topography of large ice masses from landsat imagery les images de landsat mss de l antarctique et du svalbard ont ete comparees a des mesures altimetriques effectuees a partir d avion

three dimensional seismic monitoring of an enhanced oil recovery process seismic reflection data were used to monitor the progress of an in situ combustion enhanced oil recovery process three sets of three dimensional 3 d data were collected during a one year period in order to map the extent and directions of propagation in time acquisition and processing parameters were identical for each survey so that direct one to one comparison of traces could be made seismic attributes were calculated for each common depth point data set and in a unique application of seismic reflection data the preburn attributes were subtracted from the midburn and postburn attributes the resulting difference volumes of 3 d seismic data showed anomalies which were the basis for the interpretation shown in this case study profiles and horizon slices from the data sets clearly show the initiation and development of a bright spot in the reflection from the top of the reservoir and a dim spot in the reflection from a limestone below it interpretation of these anomalies is supported by informa

physical model for the downhole orbital vibrator dov i acoustic and borehole seismic radiation summary the downhole orbital vibrator dov applies the vibroseis principle to borehole seismic sourcing accelerations by an internal rotating eccentric mass excite cylindrical pressure waves converted at the wellbore to seismic waves essentially within 20 30 of the plane normal to the borehole dov pressure waves in open water are quantitatively described by a rotating point force radiating acoustic waves with displacement amplitude u r 1 2 u0 r1 r where r1 2 dov watera2l 2 1 mm is the dov effective size for dov radius a 5 cm length l 1 m and acoustic radiation wavelength 10 m and u0 1 m and x are respectively the frequency independent dov displacement amplitude and the direction cosine of the observer relative to the instantaneous point force axis in the plane of the rotating point force crosswell seismic radiation amplitude spectrum and angular dependence are quantitatively described by acoustic wave diffraction at a slit with dov axial cross section 2al followed by conversion to seismic waves at the wellbore seismic wave displacement amplitudes u r u0 r2 r scale with effective radius r2 2al 1 cm the frequency dependence of r2 is observed as linear frequency enhancement of the seismic wavelet spectrum relative to the source wavelet spectrum dov borehole p and s wave production peaks strongly in the plane of dov rotation with converted s waves both parallel to and transverse to the borehole axis the small effective source sizes r1 1 mm and r2 1 cm at operational frequencies 50 350 hz imply that dov motion in a borehole is dynamically decoupled from the borehole wall dynamic decoupling allows dov borehole seismic correlation wavelets to be quantitatively modelled in terms of a stable kinematic relation between source and sensor motion acoustic and seismic data rule out dipole source action associated with claims for shear traction and primary s wave radiation from boreholes the stable linear kinetics of dov acoustic action in borehole fluids produces i useful crosswell seismic signals at offsets to 650 800 m ii negligible tube waves and iii stable seismic wavelets suited to in situ time lapse seismic imaging of fluid migration fronts in crustal reservoirs

antarctica measuring glacier velocity from satellite images many landsat images of antarctica show distinctive flow and crevasse features in the floating part of ice streams and outlet glaciers immediately below their grounding zones some of the features which move with the glacier or ice stream remain visible over many years and thus allow time lapse measurements of ice velocities measurements taken from landsat images of features on byrd glacier agree well with detailed ground and aerial observations the satellite image technique thus offers a rapid and cost effective method of obtaining average velocities to a first order of accuracy of many ice streams and outlet glaciers near their termini