an algebraic reconstruction technique for weakly anisotropic velocity laboratory measurements and field experiments indicate that many sedimentary rocks display velocity anisotropy robertson and corrigan 1983 white et al 1983 thomsen 1986 winterstein 1986 gaiser et al 1987 accounting for anisotropy is proving important in several areas including the processing and interpretation of shear wave data lynn and thomsen 1986 bush and crampin 1987 and the integration of vertical seismic profile vsp data and surface seismic data chiu and stewart 1987a

subsurface cavity imaging by crosshole borehole radar measurements travel time tomography uses direct waves of crosshole radar data a great deal of information concerning the media is contained in later arrivals such as reflections and diffractions more reliable results can be obtained by incorporating both direct waves and later arrivals in this paper the combination of travel time tomography and migration is introduced a smoothed velocity model obtained by travel time tomography is used as the basis of migration then a reverse time migration technique is applied to direct wave suppressed crosshole data the result of tomography indicates that there is an abnormal area and the result of migration gives a more accurate position of the abnormal area which is a cavity the real example shows that the cooperation of tomography and migration is an effective technique for subsurface cavity imaging the synthesis of all information including parallel crosshole measurement and forward simulation assists in the interpretation of the results of tomography and migration

the resolving power of cross borehole tomography the data collected in a cross borehole tomography problem is inherently incomplete since the boreholes do not completely surround the media under study the ability of the experiment to resolve structure is therefore limited by poor experimental geometry we use the method of backus and gilbert to investigate the ability of this technique to resolve variations in acoustic velocity and attenuation between the two boreholes both integrals that appear in the backus gilbert formulation can be performed analytically thus expediting the calculations the resolving kernels have significant horizontal width demonstrating that the horizontal position of structures can be only poorly resolved

coupled modeling of hydrogeochemical and electrical resistivity data for exploring the impact of recharge on subsurface contamination 1 the application of geophysical methods in particular electrical resistivity measurements may be useful for monitoring subsurface contamination however interpreting geophysical data without additional data and without considering the associated hydrogeochemical processes is challenging since the geophysical response is sensitive to not only heterogeneity in rock properties but also to the saturation and chemical composition of pore fluids we present an inverse modeling framework that incorporates the simulation of hydrogeochemical processes and time lapse electrical resistivity data and apply it to various borehole and cross borehole data sets collected in 2008 near the s 3 ponds at the u s department of energy s oak ridge integrated field research challenge site where efforts are underway to better understand freshwater recharge and associated contaminant dilution our goal is to show that the coupled hydrogeochemical geophysical modeling framework can be used to 1 develop a model that honors all the available data sets 2 help understand the response of the geophysical data to subsurface properties and processes at the site and 3 allow for the estimation of petrophysical parameters needed for interpreting the geophysical data we present a series of cases involving different data sets and increasingly complex models and find that the approach provides useful information about soil properties recharge related transport processes and the geophysical response spatial heterogeneity of the petrophysical model can be described sufficiently with two layers and its parameters can be estimated concurrently with the hydrogeochemical parameters for successful application of the approach the parameters of interest must be sensitive to the available data and the experimental conditions must be carefully modeled

algebraic reconstruction of a two dimensional velocity inhomogeneity in the high hazles seam of thoresby colliery a high proportion of faces started in mechanized coal mines run into underground faults the faults take many forms from the splitting of a seam through a hidden stress pattern caused by subsidence or folding to a washout or a vertical throw all faults reduce face output a throw of only 1 5 m can lead to a face being abandoned faults of this order cannot be mapped reliably from the surface they may be mapped in an underground seismic survey roadways of a mine may give access to fast refracting horizons above and below a coal seam waveguiding in the plane of the seam if it occurs simplifies migration of wave trains reflected from discrete faults the reduction problem involved in a fault mapping is only two dimensional given guiding whether leaky or not it is possible to map distributed faults of low reflectivity by shooting in transmission across a panel of coal algebraic reconstruction techniques are used here to reduce first break times of flight through a 425 x 950 m rectangular block of coal into the profile of a velocity inhomogeneity input data are derived by static correction from hand picked arrival times the reduction itself is effected using an algorithm which accommodates underground site access restrictions in back projecting first break velocities a truncated cosine is used to weight the relative contributions of rays passing at different distances from any given mapping point the reconstructed velocity field suggests that the coal panel is bisected by a ridge of higher velocity the suspicion of a ridge is reinforced by results of an aberration test based on a standard huygens kirchhoff migration the ridge is found to follow the general line of a system of pillars left in place during the mining of a lower horizon it is concluded that channel waves may be used to map subsidence into old workings underground coal seams apparently share with other sedimentary rocks the property of a pressure sensitive seismic velocity

time lapse seismic tomography of an underground mining zone abstract in this study we determined p wave tomographic images of the yongshaba deposit an underground mining zone in guizhou province china by inverting arrival time data of micro seismic events and blasts recorded by a passive seismic array consisting of 28 sensors during january to april 2014 using an event location technique and a travel time tomography method that can handle complex seismic discontinuities the damping parameter used in the damped least squares method is determined with the help of trade off curve to reveal internal p wave velocity changes of the study area under severe mining activities a time lapse data partition scheme is used to assess the human influence on the underground structure we introduce a parameter to measure the relative velocity changes in different periods the resolution of the tomographic images and the robustness of the obtained features are examined by conducting a series of checkerboard resolution tests and a restoring resolution test our tomographic results obtained from the entire data set reveal a prominent low velocity low v zone and many obvious high velocity high v zones these features match well with the geological setting and the excavation plan carried out in the mine according to in site surveys the low v zone may reflect empty volumes stress releases and rock breaking and cracking caused by mining activities whereas the high v zones are probably the consequences of local stress concentrations caused by regional stress redistribution the time lapse tomographic images may reveal the process of stress concentrations caused by rock breaking due to the continuing excavations in the entire observation period indicating that the mining activities influenced the rock property and caused complex changes of the underground structure

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

stratification of the f 2 layer observed in southeast asia this paper describes the latitudinal variation in f2 stratification balan and bailey 1995 as observed by a number of oblique and vertical ionosondes operating in southeast asia during 1997 stratification of the f2 layer was seen at dip latitudes from 4 s to 18 s on the southern side of the magnetic equator but did not occur at the closest reflection point to the magnetic equator dip latitude 2 3 n the observed transient cusp vertical ionosonde or additional nose oblique ionosonde was defined as an f3 layer or an f1 5 layer depending on whether it occurred above or below the layer which maintained continuity with the normal f2 layer peak within the zone of occurrence the transient layer was commonly seen as an f3 layer at reflection points closest to the magnetic equator but invariably as an f1 5 layer at reflection points farther from the magnetic equator these observations suggest that the distortion in the equatorial electron density profile associated with the phenomenon moved toward the base of the f2 layer as magnetic field lines descended with increasing latitude stratification of the f2 layer commenced at the same local time e g 0845 lt in november 1997 throughout the longitudinal range of coverage and was associated with a rapid rise in f2 layer height following sunrise the stratification ended at times varying from 1300 lt to sunset and was associated with a fall in the height of f2 peak electron density the region of maximum f2 layer stratification lay between the magnetic equator and the peak of the southern equatorial anomaly

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

seismic tomography in boreholes summary synthetic seismic tomographic data sets for cross hole and hole to surface arrays are computed and inverted inversion imaging is performed through an iterative projection solution to a matrix equation the orientation as well as the position of an anomaly relative to the source and recorder arrays affects both the rate of convergence of the solution and the resolution obtained data density and distribution determine the physical validity of the image obtained at convergence borehole tomography is apparently a viable method for imaging inter hole structure

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

inversion of tracer test data using tomographic constraints 1 we have developed a methodology for inverting tracer test data using zonation information obtained from two dimensional radar tomograms to improve the typically overly smooth hydraulic conductivity fields obtained from conventional inversion of tracer test data the method simultaneously yields two dimensional estimates of hydraulic conductivity as well as petrophysical relationships that relate hydraulic conductivity to radar velocity these relationships can be assumed to be stationary throughout the area of investigation or to vary as a function of zonation using a synthetic three dimensional hydraulic conductivity field we apply the developed inversion methodology and explore the impact of the strength and stationarity of the petrophysical relationship as well as the impact of errors that are often associated with radar data acquisition such as unknown borehole deviation we find that adding radar tomographic data to tracer test data improves hydrogeological site characterization even in the presence of minor radar data errors the results are contingent on the assumption that a relationship between radar velocity and hydraulic conductivity exists therefore the applicability of the proposed method may be limited to field sites where this condition is partially or fully satisfied

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

seismic versus sonic velocities a vertical seismic profiling study vertical seismic profiling vsp techniques provide a method to measure accurately the seismic velocity and lithologic structure near the borehole the analysis of a vsp survey can also provide insight into seismic wave propagation especially when related to sonic measurements but vsp and sonic log velocities or traveltimes are often found to disagree recent field evidence of these differences suggests that the vsp traveltimes are delayed with respect to the integrated sonic times especially in the deep section 3000 ft by about 2 0 ms 1000 ft on the average the vsp has numerous applications in exploration geophysics such as calibrating the sonic log it is thus important to understand why the two measurements differ differences in the geometries source frequencies and instrumental errors of the two surveys are reviewed more detailed analysis of seismic wave propagation in the vsp shows that short path multiples and velocity dispersion can have a significant delaying effect on the seismic tr

additional stratifications in the equatorial f region at dawn and dusk during geomagnetic storms role of electrodynamics 1 the role of electrodynamics in producing additional stratifications in the equatorial f region f 3 layer at dawn and dusk during geomagnetic storms is discussed two cases of f 3 layer at dawn 0600 0730 lt on 5 october 2000 and 8 december 2000 and one case of f 3 layer at dusk 1600 1730 lt on 5 october 2000 are observed for the first time by the digital ionosonde at the equatorial station trivandrum 8 5 n 77 e dip 0 5 n in india the unusual f 3 layers occurred during the geomagnetic storms and are associated with southward turning of interplanetary magnetic field b z suggesting that eastward prompt penetration electric field could be the main cause of the f 3 layers the dawn f 3 layer on 5 october is modeled using the sheffield university plasmasphere ionosphere model by using the e x b drift estimated from the real height variation of the ionospheric peak during the morning period the model qualitatively reproduces the dawn f 3 layer while the existing f 2 layer rapidly drifts upward and forms the f 3 layer and topside ledge a new layer forming at lower heights develops into the normal f 2 layer

target oriented interferometric tomography for gpr data an interferometric form of fermat s principle and traveltime tomography is used to invert ground penetrating radar gpr data for the subsurface velocity distribution the input data consist of gpr traveltimes of reflections from two buried interfaces a reference and b target where the data are excited and recorded by gpr antennas at the surface fermat s interferometric principle is then used to redatum the surface transmitters and receivers to interface a so the associated reflection traveltimes correspond to localized transit times between interfaces a and b the overburden velocity model above interface a is not required the result after tomographic inversion is a high resolution estimate of the velocity between interfaces a and b that does not depend on the velocity model above interface a a motivation for introducing interferometric traveltime tomography is that typical layer stripping approaches will see the slowness error increase with depth as the layers are inverted this suggests that

radar polarimetry analysis applied to single hole fully polarimetric borehole radar a fully polarimetric borehole radar system using four combinations of dipole and slot antennas was developed to acquire fully polarimetric data sets in drilled boreholes first to implement radar polarimetry analysis a processing scheme suitable for analyzing a single hole reflection data set acquired by the system is presented this processing consists of antenna characteristic compensation migration for image reconstruction and time frequency analysis for single frequency data set construction two polarimetric target decomposition methods namely 1 pauli decomposition and 2 eigenvector based decomposition are applied to characterize the scattering problem of the subsurface fractures the pauli decomposition method provided important radar polarimetry information of fractures and the eigenvector based decomposition method made a significant contribution to understanding the scattering mechanisms from different fractures with different properties furthermore information about fracture classification can be obtained by analysis of the h alpha distribution provided by eigenvector based decomposition of local radar image regions the potential of polarimetric target decomposition techniques to fracture characterization is shown which in turn provides valuable information about water permeabilities of fractures in hydrogeological studies

geochemical characterization using geophysical data and markov chain monte carlo methods a case study at the south oyster bacterial transport site in virginia 1 the study demonstrates the use of ground penetrating radar gpr tomographic data for estimating sediment geochemical parameters using data collected at the department of energy south oyster bacterial transport site in virginia by exploiting the site specific mutual dependence of gpr attenuation and extractable fe ii and fe iii concentrations on lithofacies we develop a statistical model in which lithofacies and fe ii and fe iii concentrations at each pixel between the boreholes are considered as random variables the unknown variables are estimated by conditioning to the colocated gpr data and the lithofacies measurements along boreholes using a markov chain monte carlo method cross validation results show that the geophysical data constrained by lithofacies have the potential for providing high resolution multidimensional information on extractable fe ii and fe iii concentrations at the south oyster site

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

closure time in the east qilian ocean and early paleozoic ocean continent configuration in the helan mountains and adjacent regions nw china abstract lithofacies and faunal assemblage affinities of the helan mountains and its adjacent blocks are explored using field investigations and analysis of previous results the tectonic affinity between the alxa block and the north china block is analyzed by means of la icp ms detrital u pb zircon age spectrums the early paleozoic stratigraphic framework is constructed and stratigraphic contact relationships between the study area and its adjacent regions are assessed the ocean continent configuration during the caledonian period is discussed and the closure time in the east of north qilian ocean is determined finally the basin type and its evolutionary process during the early paleozoic are analyzed the carbonate platform facies of the alax block and the abyssal flysch deposition on the margin of the central qilian block established the coexistence of ocean and continent configuration during the cambrian during the early ordovician the stable shallow water platform shelf facies was distributed over all the study area and the biofacies was also unified the east of the north qilian ocean closed at that time the north qilian ocean and the north qinling ocean did not affect the study area but the north china sea was connected intermittently to the research area the east central qilian block the alax block the north china block and the qinling microblock collided together to form a unified megablock which resulted in the formation of a complex foreland depression during the early ordovician the eastern boundary of the basin is the aselang chedao transform fault which lies between the alax block and the north china block the southern boundary of the basin is marked by the guyuan qingtongxia fault which is located between the alax block and the central qilian block the western boundary of the basin is an overlapping boundary toward the alax block during the late ordovician when the yangtze block approached toward the north china block the shangdan ocean began to influence the study area and the turbidite fans were formed because of the large scale transgression thus the basin type is a complicated foreland depression influenced by transgression during the late ordovician

high resolution aquifer characterization using seismic cross hole tomography an evaluation experiment in a gravel delta we performed field experiments at a well studied aquifer test site to evaluate the geophysical method of seismic cross hole tomography for high resolution aquifer characterization we address the challenge of finding meaningful relationships between seismic velocity and hydraulic conductivity at the field scale for hydraulic conductivity estimation the resolution of seismic cross hole data is limited by inversion ambiguities and diffraction effects which are not accounted for using conventional ray based inversion algorithms for velocity reconstruction we investigate the impact of diffraction effects on seismic velocity inversion and implications for hydraulic modelling our ray based seismic tomograms correlate well with sedimentary cores and hydraulic conductivity logs allowing us to interpret a zone model with distinct geophysical hydraulic zones we use this zone model to constrain seismic inversions using two approaches for forward modelling ray tracing infinite frequency approximation and wavefield modelling at a realistic frequency which accounts for diffraction we show that using the common ray tracing approach seismic velocities in low velocity zones may be significantly overestimated based on the available data we observe a negative linear relationship between logarithmic hydraulic conductivity and seismic velocity this relationship is used to parameterize hydraulic models based on seismic velocity models computer simulations of advective contaminant transport demonstrate that their results are extremely sensitive to an accurate determination of seismic low velocity zones we conclude that seismic tomography is indeed very useful for high resolution aquifer characterization however an inversion approach that accounts for diffraction effects a priori knowledge of the subsurface structure and additional well data should be applied for quantitative interpretations

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

study of traveltime and amplitude time lapse tomography using physical model data in seismic tomography the observed traveltimes or amplitudes of direct waves are inverted to obtain an estimate of seismic velocity or absorption of the section surveyed there has been much recent interest in using cross well traveltime tomography to observe the progress of fluids injected into the reservoir rocks during enhanced oil recovery eor processes if repeated surveys are carried out then eor processes may monitored over a period of time this paper describe the results of simulated time lapse tomography experiment to image the flood zone in an eor process two physical models were made out of epoxy resins to simulate an essentially plane layered sedimentary sequence containing a reservoir layer and simple geological structure the models differed only in the reservoir layer which was uniform in the pre flood model and contained a flood zone of known geometry in the post flood model data sets were acquired from each model using a cross well survey geometry traveltime and amplitude tomographic imaging techniques have been applied to these data in an attempt to locate the extent of the flood zone traveltime tomography locates the flood zone quite accurately amplitude tomography shows the flood zone as a region of higher absorption but does not image itsmore boundaries as precisely this is primarily because of multipathing and diffraction effects which are not accounted for by the ray based techniques for inverting seismic amplitudes less

broad band trajectory mechanics author s vasco dw nihei k abstract 2019 published by oxford university press on behalf of the royal astronomical society we present a trajectory based solution to the elastodynamic equation of motion that is valid across a wide range of seismic frequencies that is the derivation of the solution does not invoke a high frequency assumption or require that the medium have smoothly varying properties the approach adopted from techniques used in quantum dynamics produces a set of coupled ordinary differential equations for the trajectory the slowness vector and the elastic wave amplitude along the ray path the trajectories may be determined by a direct solution of the governing equations or derived as the by product of a numerical wavefield simulation synthetic tests with interfaces and layers containing increasingly narrow transition zones indicate that the conventional high frequency trajectories associated with the eikonal equation bend too sharply into high velocity regions as the wavelength exceeds the transition zone width tests in a velocity model based upon mapped structural surfaces from the geysers geothermal field in california indicate that discrepancies between high frequency and broad band trajectories can exceed several hundred metres at wavelengths of 1 hz an application to a crosswell tomographic imaging experiment demonstrates that the technique provides a basis for the seismic monitoring of fluid flow along narrow features such as fracture zones

time lapse monitoring of fluid induced geophysical property variations within an unstable earthwork using p wave refraction abstracta significant portion of the uk s transportation system relies on a network of geotechnical earthworks cuttings and embankments that were constructed more than 100 years ago whose stability is affected by the change in precipitation patterns experienced over the past few decades the vulnerability of these structures requires a reliable cost and time effective monitoring of their geomechanical condition we have assessed the potential application of p wave refraction for tracking the seasonal variations of seismic properties within an aged clay filled railway embankment located in southwest england seismic data were acquired repeatedly along the crest of the earthwork at regular time intervals for a total period of 16 months p wave first break times were picked from all available recorded traces to obtain a set of hodocrones referenced to the same spatial locations for various dates along the surveyed period of time traveltimes extracted from each acquisition were then compared to trac

topography dependent eikonal traveltime tomography for upper crustal structure beneath an irregular surface seismic modeling of the crust with nonflat topography can be made by first arrival traveltime tomography which faces the challenge of an irregular free surface a feasible way to deal with this problem consists of expanding the physical space by overlapping a low velocity layer above the irregular surface in order to have a flat topography besides using the classical eikonal equation solver for traveltime computation however the undesirable consequences of this method include seismic ray deviations due to the transition from an irregular surface that is the free boundary to an inner discontinuity lying in the expanded computational space an alternative solution called irregular surface flattening which involves the transformation between curvilinear and cartesian coordinate systems has been recently proposed through the formulation of the topography dependent eikonal equation tdee and a new solver for forward modeling of traveltimes based on the solution of this equation we present topography dependent eikonal traveltime tomography hereafter tdett for seismic modeling of the upper crust first arrival traveltimes are calculated using the tdee solver and the raypaths with the minimum traveltime that can be found by following the steepest traveltime gradient from the receiver to the source by solving an algebraic equation system that connects the slowness perturbations with the already determined traveltimes these variables can be obtained making use of the back projection algorithm this working scheme is evaluated through three numerical examples with different topographic complexities that are conducted from synthetic data and a fourth example with somewhat more complicated topography and real data acquired in northeastern tibet the comparison of the results obtained by both methods i e physical space expansion above the irregular surface and irregular surface flattening fully validates the tomography scheme that is proposed to construct seismic velocity models with nonflat topography

a parametric study of borehole influence in resolving seismic velocity in well to well tomograms the data collected in a well to well tomography experiment is inherently incomplete even when augmented by vsp data the nature of the experiment suggests a geometric limitation to the resolution of any central structure a parametric model has now been developed which examines the effect on reconstructed velocity due to the borehole size transducer standoff altered annulus and the degree of velocity attenuation of the altered annulus using a range of host velocities and hole separations it was found that there are significant velocity variations caused by perturbations in borehole size these errors are particularly significant for boreholes with large diameters and small transducer offsets for an altered annulus errors in both the dimensions and the degree of velocity alteration gave significant velocity variation in reconstructed velocity particularly with large boreholes in all cases it is observed that the variation and alteration in reconstructed velocities increased as hole separation is decreased

f3 layer during penetration electric field 1 the occurrence of an additional layer called f3 layer in the equatorial ionosphere at american indian and australian longitudes during the super double geomagnetic storm of 7 11 november 2004 is presented using observations and modeling the observations show the occurrence reoccurrence and quick ascent to the topside ionosphere of unusually strong f3 layer in australian longitude during the first super storm 8 november and in indian longitude during the second super storm 10 november all with large reductions in peak electron density nmax and total electron content gps tec the unusual f3 layers can arise mainly from unusually strong fluctuations in the daytime vertical e b drift as indicated by the observations and modeling in american longitude the strongest upward e b drift or eastward prompt penetration electric field ppef ever recorded at jicamarca produces unusually strong f3 layer in the afternoon hours 1400 1600 lt of ppef with large reductions in nmax and tec the layer also reappears in the following evening 1700 1800 lt owing to an unusually large downward drift at night when the drift is unusually upward and strong the f region splits into two layers

crosswell seismic imaging in a contaminated basalt aquifer multiple seismic crosswell surveys have been acquired and analyzed in a fractured basalt aquifer at idaho national engineering and environmental laboratory most of these surveys used a high frequency 1000 10 000 hz piezoelectric seismic source to obtain p wave velocity tomograms the p wave velocities range from less than 3200 m s to more than 5000 m s additionally a new type of borehole seismic source was deployed as part of the subsurface characterization program at this contaminated groundwater site this source known as an orbital vibrator allows simultaneous acquisition of p and s waves at frequencies of 100 to 400 hz and acquisition over larger distances the velocity tomograms show a relationship to contaminant transport in the groundwater zones of high contaminant concentration are coincident with zones of low velocity and high attenuation and are interpreted to be fracture zones at the boundaries between basalt flows the orbital vibrator data show high vp vs values from 1 8 to 2 8 in

crosshole seismic tomography and borehole logging for engineering site characterization in sikeston mo usa abstract this paper presents a geophysical investigation performed in the median separating the east and west bound lanes of u s highway 60 approximately 15 km west from the town of sikeston mo usa two boreholes drilled at depth of 45 m approximately located 6 m from the wahite ditch bridge in u s highway 60 were used to carry out the geophysical tests the objective of the survey was to obtain the density distribution of soil materials and high resolution compressional and shear wave velocities of the shallow subsurface for computation of elastic engineering properties of the unconsolidated material interposed between the two investigated boreholes the studied site is located in the new madrid seismic zone nmsz one of the major seismic source zones in the eastern united states although no major seismic events have occurred in the new madrid area since the catastrophic earthquakes of 1811 1812 more intensive studies in this area are required to better understand the local soil effects and the liquefaction potential of unconsolidated earth materials on strong ground motion joint interpretation of borehole logs and velocity images obtained by p and s wave traveltime inversions outlined shallow anomalies which were interpreted as caused by variation in relative porosity and compactness of saturated unconsolidated soil materials in the interval between 17 and 19 m of depth a velocity anomaly with distinct characteristics is recognized analysis of traveltimes of p wave energy propagated from common source receiver depth positions at that depth interval delineated a low velocity zone lower than estimated p wave velocity in water in which propagated s wave energy was negligible analysis of porosity logs did not outline any porosity anomaly for that region the anomaly is interpreted as caused by the presence of a gas bearing zone extending for 1 5 m 0 76 m from the top and the bottom of the depth interval through which propagation of shear energy was almost prevented and compressional energy traveled a very low speed relative lower values of shear modulus were computed for the gas bearing zone the same depth interval also exhibited relative lower values of bulk modulus relative higher values of compressibility and relative high porosity however the low velocity anomaly is not caused by relative increased porosity but rather to replacement of water by gas in the pore volumes of this zone the presence of a shallow thin gas bearing zone is interpreted as hazardous in the occurrence of strong motion in the new madrid seismic zone shallow water table as detected by seismic and log measurements in the area increases the risk of liquefaction of the sampled soil under strong ground motions

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

acoustic velocities in heated block of granite subjected to uniaxial stress acoustic velocities have been measured within a 38 cm cubic block of granite isolated from the surrounding rock the block was subjected to uniaxial stresses in the range 0 24 mpa and to heating in the range 14 sup 0 to 98 sup 0 c an increase in temperature from 14 sup 0 to 72 sup 0 c in the unstressed block resulted in an increase in velocities in directions parallel and perpendicular to the applied stress a further increase in temperature to 98 sup 0 c in the unstressed block resulted in a decrease in velocities application of uniaxial stress with the block at a temperature of 98 sup 0 c resulted first in uniform increases in velocity to an applied stress of mpa and then sharp decreases from 10 to 14 mpa followed by uniform increases in velocity to a maximum stress of 24 mpa a reduction in temperature to 16 sup 0 c resulted in a sharp reduction in velocity 25 percent less than originally measured at ambient temperature it is concluded that at temperatures rising to 72 sup 0 c anisotropic thermal expansion of the crystals comprising the granite causes the closure of microcracks present in the unheated rock between 72 sup 0 and 98 supmore 0 c particularly when stress was applied irreversible mechanical changes occurred in the block less

application of diffraction tomography to fracture detection two diffraction tomography techniques are applied to crosshole field data to detect fractures in granitic rock the techniques used are the conventional back propagation method and a new quadratic programming method incorporating constraints in this formulation the born approximation is used for linearization of the inverse problem two dimensional 2 d pseudo spectral finite difference synthetic data are generated to demonstrate the inversion methods and justify use of the born approximation also using 2 d born synthetic data the velocity sensitivity of the inversion algorithm and reduction of fracture generated tube waves and s waves are investigated the inversion methods are applied to field data from the grimsel test site in switzerland the data are collected from a 10 21 5m rectangular area where fractures are known to exist data acquisition with 0 5 m spacing of three component receivers and a piezoelectric source is carried out so as to obtain a nearly complete coverage of the region cros

multiborehole seismic imaging in steam injection heavy oil recovery projects crosshole seismic measurements before and after steam injection were obtained for the purpose of delineating the fluid invaded zone the experiment despite its limited temporal and spatial sampling showed significant changes in seismic signature after steam injection a single chemical explosive seismic source was fired repeatedly at a fixed depth within the source well for various positions of a receiver clamped within the receiver well the seismic records of the before and after steam flood experiments were normalized by using the tube waves important results were obtained from power spectral studies which show significant changes after fluid injection for higher resolution and increased constraints on the determination of the steam invaded zone a more sophisticated cross hole experiment has been designed computer simulation of the proposed experiment has been carried out assuming an asymmetrical shape for the steam zone inversion via a tomographic approach by solution of an overdetermine

applications of algebraic reconstruction techniques to crosshole seismic data tomographic imaging techniques were applied to two crosshole data sets to determine the velocity structures and the reliability and resolution of the algorithms on real data the experiments were carried out at the retsoff salt mine in new york and at the underground radioactive waste study site at the stripa mine facility in sweden the traveltimes at restoff were high quality and were obtained over raypaths of up to 500 m in length the structure was quite complicated with velocity contrasts up to 50 percent the stripa site was in granitic rock with velocity contrasts of only a few percent the dimensions of the experiment were small with maximum ray lengths of just over 10 m the data at this site were collected with very high accuracy source and receiver locations were measured to better than 1 0 mm and traveltimes were read to 0 001 ms a number of algorithms similar to the algebraic reconstruction techniques art used in medical imaging have been applied to the data some modifications of the algorithms such as the application of weighting schemes damping parameters and curved raypaths were performed the resulting velocity fields were compared to the known fields and with each other to determine an optimal method the algorithms were found to be a rapid reliable means of reconstructing the slowness field of real data low velocity zones were recovered with accuracy in location and value it was also found that great care was necessary in application of the techniques to ensure that proper damping parameters are used and the proper number of iterations taken otherwise poor reconstructions will result

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

crosshole seismology and seismic imaging in crystalline rocks a borehole to borehole audiofrequency seismic system using piezoelectric transducers as active elements has been developed and used to investigate crystalline rocks in canada high quality seismograms have been recorded for transmitter receiver distances of up to 230 meters it has been found that both travel times and signal amplitudes provide diagnostic information about rock quality two dimensional images of seismic velocity and transparency distributions between two boreholes derived from observed arrival times and amplitudes by simple back projection tomography reflect lithology and geological structure the results indicate the potential usefulness of crosshole seismic imaging as a tool for rock mass characterization

borehole radar applied to the characterization of hydraulically conductive fracture zones in crystalline rock1 this paper discusses the borehole radar system ramac developed within the framework of the international stripa project which can be used in three different measuring modes single hole reflection cross hole reflection and cross hole tomography the reflection modes basically provide geometrical data on features located at some distance from the borehole in addition the strength of the reflections indicate the contrast in electrical properties single hole reflection data are cylindrically symmetrical with respect to the borehole which means that a unique fracture orientation cannot be obtained a method has been devised where absolute orientation of fracture zones is obtained by combining single hole reflection data from adjacent holes similar methods for the analysis of cross hole reflection data have also been developed and found to be efficient the radar operates in the frequency range 20 60 mhz which gives a resolution of 1 3 m in crystalline rock the investigation range obtained in the stripa granite is approximately 100 m in the single hole mode and 200 300 m in the cross hole model variations in the arrival time and amplitude of the direct wave between transmitter and receiver have been used for cross hole tomographic imaging to yield maps of radar velocity and attenuation the cross hole measurement configuration coupled withmore tomographic inversion has less resolution than the reflection methods but provides better quantitative estimates of the values of measured properties the analysis of the radar data has provided a consistent description of the fracture zones at the stripa cross hole site in agreement with both geological and geophysical observations less

stratigraphy and geochronology of permo carboniferous strata in the western north china craton insights into the tectonic evolution of the southern paleo asian ocean abstract the northwestern ordos terrane not in the western north china craton w ncc comprises the northwestern ordos basin in the east and the eastern alxa massif in the west bound by the helanshan tectonic belt htb the key position makes the not crucial for understanding the evolutionary processes of the w ncc and particularly the tectonic relation of the alxa massif with the w ncc in this study petrologic stratigraphic and geochronologic studies were conducted on permo carboniferous successions in the not stratigraphic correlation reveals that carboniferous marine successions display a transgressive sequence with a slight westward deepening facies variation evidenced by the continuous onlap of tidal flat layers toward the east the permian nonmarine strata in the htb and the ordos basin have no substantial facies variation defining an upward regressive sequence from deltaic to fluvial associations while time equivalent units in the eastern alxa massif have been eroded the generally ssw directed paleocurrents suggest that permo carboniferous siliciclastic materials were derived from a highland to the northeast the unified sedimentary system in the not constrains the alxa massif to be part of the w ncc the lower carboniferous sandstone contain zircons with a concentrated age cluster of 1700 2700 ma comparable to archean to paleoproterozoic crystalline basement in the northern w ncc by contrast in addition to zircons of 1700 2700 ma late carboniferous and permian sandstones all contain abundant paleozoic zircons with two age clusters around 300 ma and 420 ma which are similar to age patterns of paleozoic magmatism in the northern w ncc zircon age profile and sandstone modal composition indicate the origin from an andean type continental arc the permo carboniferous tectono sedimentary processes of the not should occur in a marginal basin behind the continental arc along the northern w ncc in response to the southward subduction of solonker ocean southern branch of paleo asian ocean

provenance of ediacaran sinian sediments in the helanshan area north china craton constraints from u pb geochronology and hf isotopes of detrital zircons abstract the tectonic relationship between the alxa block and the north china craton has long been controversial the helanshan area lies at the western margin of the ordos block and to the east of the alxa block and it contains eidacaran zhengmuguan formation and tuerkeng formation the zhengmuguan formation is made up of tillites limestone and dolomine and the tuerkeng formation consists of silty slate a parallel unconformity marks the boundary between the tuerkeng formation and the early cambrian suyukou formation which is composed mainly of phosphatic pebbly sandstone and sandstone u pb dating ages of detrital zircons in the zhengmuguan and suyukou formations reveal two neoproterozoic age peaks of 818 4 ma n 88 and 905 8 ma n 20 neoproterozoic magmatic events have yet been reported in the basement of the ordos block while some neoproterozoic igneous rocks have been found in the basement of the alxa block moreover the two neoproterozoic age peaks correspond well with the ages of neoproterozoic igneous rocks in alxa block the hf isotopic characteristics of a part of neoproterozoic zircons from the ediacaran zhengmuguan formation in the helanshan area ehf t 7 812 to 3 274 tdmc 2211 1578 ma n 10 are similar to those neoproterozoic igneous zircons from the langshan area ehf t 1 105 to 5 928 tdmc 1 75 1 38 ga n 23 and bayinnuoergong area in the alxa block the parental magmas had a long residency time in the crust it seems therefore that alxa block provenance provided neoproterozoic clastics for helanshan area in ediacaran and alxa block had already been a part of the north china craton by the late neoproterozoic even earlier

crossvalidation method for crosswall seismic tomography crosswell seismic tomography is used to determine the variation of elastic wave velocity or attenuation between two boreholes and if possible boreholes and the surface from which they are drilled in a transmission tomographic survey traveltimes or amplitudes are measured for many raypaths between the boreholes and the surface the data are inverted for velocity and attenuation respectively in this paper we only discuss traveltimes but the methods are equally applicable to amplitude inversions

equatorial plasma fountain and its effects over three locations evidence for an additional layer the f 3 layer the equatorial plasma fountain and equatorial anomaly in the ionospheres over jicamarca 77 w trivandrum 77 e and fortaleza 38 w are presented using the sheffield university plasmasphere ionosphere model under magnetically quiet equinoctial conditions at high solar activity the daytime plasma fountain and its effects in the regions outside the fountain lead to the formation of an additional layer the f3 layer at latitudes within about plus or minus 10 of the magnetic equator in each ionosphere the maximum plasma concentration of the f3 layer which occurs at about 550 km altitude becomes greater than that of the f2 layer for a short period of time before noon when the vertical e b drift is large within the f3 layer the plasma temperature decreases by as much as 100 k the ionograms recorded at fortaleza on january 15 1995 provide observational evidence for the development and decay of an f3 layer before noon the neutral wind which causes large north south asymmetries in the plasma fountain in each ionosphere during both daytime and nighttime becomes least effective during the prereversal strengthening of the upward drift during this time the plasma fountain is symmetrical with respect to the magnetic equator and rises to over 1200 km altitude at the equator with accompanying plasma density depletions in the bottomside of the underlying f region the north south asymmetries of the equatorial plasma fountain and equatorial anomaly are more strongly dependent upon the displacement of the geomagnetic and geographic equators jicamarca and trivandrum than on the magnetic declination angle fortaleza

convolutional back projection imaging of physical models with crosshole seismic data1 the development of crosshole seismic tomography as an imaging method for the subsurface has been hampered by the scarcity of real data for boreholes in excess of a few hundred metres depth crosshole seismic data acquisition is still a poorly developed and expensive technology a partial solution to this relative lack of data has been achieved by the use of an ultrasonic seismic modelling system such ultrasonic data obtained in the laboratory from physical models provide a useful test of crosshole imaging software in particular ultrasonic data have been used to test the efficacy of a convolutional back projection algorithm designed for crosshole imaging the algorithm is described and shown to be less susceptible to noise contamination than a simultaneous iterative reconstruction technique sirt algorithm and much more computationally efficient

changes in p wave velocity during operation of a hot dry rock geothermal system p wave arrival times have been picked on seismograms recorded during two dual well seismic experiments separated in time by one year that were carried out in the los alamos scientific laboratory hot dry rock geothermal energy reservoir average in situ p wave velocity is computed from arrival times measured along segments of the borehole velocity decreases as temperature drops owing to heat extraction from the reservoir the velocity changes linearly with the change in temperature at a rate of 1 07 km s 100 c the linear decrease in velocity leads to the important conclusion that p wave velocity can be used as an effective measure of change in in situ temperature during operation of the geothermal system the change in velocity is attributed to an increase in the microcrack porosity which is a result of the heat extraction from the rock

features of additional stratification in ionospheric f2 layer observed for half a solar cycle over indian low latitudes 1 the features of the additional stratification in the ionospheric f2 layer often referred to as the f3 layer observed over an indian low latitude station waltair 17 7 n 83 3 e magnetic latitude mag lat 8 2 n during the period 1997 2003 are presented along with the data from two other indian stations the observations grossly confirm those reported earlier in the occurrence and seasonal variability of the f3 layer from an analysis of half a solar cycle ionosonde data 1997 2003 it is observed that the layer appeared more frequently during the summer solstice months of low solar activity period and persisted for longer durations during this season compared with equinox and winter solstice the best stratification is seen between 10 12 hours ist the occurrence of the f3 layer does not seem to depend on magnetic activity but the percentage of occurrence decreased with increasing solar activity the solar activity dependence over waltair confirms the model predictions of balan et al 1998 that the layer becomes less distinct and less frequent as solar activity increases the ionosonde data for the same period 1997 2003 from an equatorial station trivandrum 8 4 n 76 9 e mag lat 0 47 n and another low latitude station shar 14 n 80 e mag lat 6 8 n are also analyzed with a view to examine the effect of the equatorial plasma dynamics on the occurrence of such events

joint cross well and single well seismic studies of co2 injection in an oil reservoir a series of time lapse seismic cross well and single well experiments were conducted in a diatomite reservoir to monitor the injection of co2 into a hydrofracture zone based on p and s wave data a high frequency piezo electric p wave source and an orbital vibrator s wave source were used to generate waves that were recorded by hydrophones as well as 3 component geophones during the first phase the set of seismic experiments was conducted after the injection of water into the hydrofractured zone the set of seismic experiments was repeated after a time period of seven months during which co2 was injected into the hydrofractured zone the questions to be answered ranged from the detectability of the geological structure in the diatomic reservoir to the detectability of co2 within the hydrofracture furthermore it was intended to determine which experiment cross well or single well is best suited to resolve these features during the pre injection experiment the p wave velocities exhibited relatively low values between 1700 and 1900 m s which decreased to 1600 1800 m s during the post injection phase 5 the analysis of the pre injection s wave data revealed slow s wave velocities between 600 and 800 m s while the post injection data revealed velocities between 500 and 700 m s 6 these velocity estimates produced high poisson s ratios between 0 36 and 0 46 for this highly porous 50 material differencing post and pre injection data revealed an increase in poisson s ratio of up to 5 both velocity and poisson s ratio estimates indicate the dissolution of co2 in the liquid phase of the reservoir accompanied by an increase in pore pressure the single well data supported the findings of the cross well experiments p and s wave velocities as well as poisson s ratios were comparable to the estimates of the cross well data the cross well experiment did not detect the presence of the hydrofracture but appeared to be sensitive to overall changes in the reservoir and possibly the presence of a fault in contrast the single well reflection data revealed an arrival that could indicate the presence of the hydrofracture between the source and receiver wells while it did not detect the presence of the fault possibly due to out of plane reflections

early paleozoic paleomagnetic poles from the western part of the north china block and their implications abstract we collected 917 oriented drill core samples 124 sites from 22 units spanning the early cambrian to middle ordovician formations of the north china block ncb to construct an apparent polar wander path apwp of the early paleozoic for the ncb sampling areas are located in the helanshan tongchuan hancheng and yuncheng luliang regions along the margin of the ordos basin characteristic remanent magnetizations for five periods between the cambrian and ordovician are isolated from 281 samples by careful demagnetization directions cluster around northwesterly direction with upward shallow inclination and its antipode after tilt correction reliability of these five directions is ascertained through positive fold and reversal tests the five cambrian and ordovician paleopoles plot in the present atlantic ocean which is consistent with previously reported paleomagnetic poles a newly constructed apwp between the cambrian and ordovician indicates that the ncb was located in the southern hemisphere around 15 s during cambro ordovician time motion of the ncb between the early and middle cambrian comprised a counterclockwise rotation of 22 3 7 0 and a northward latitudinal displacement of 7 2 6 8 combining the paleobiogeographic and paleoclimatic data with the paleomagnetic implies that the ncb was probably located in east gondwana in the early cambrian and may have separated from gondwana in post early cambrian time the ncb is also inferred to have been located close to siberia and north america during the middle ordovician

observations of daytime f2 layer stratification under the southern crest of the equatorial ionization anomaly region 1 ionospheric vertical sounding observations are being carried out at sao jose dos campos 23 2 s 45 9 w dip latitude 17 6 s brazil under the southern crest of the equatorial ionization anomaly eia since august 2000 in this paper we present and discuss the observations of daytime f2 layer stratification near the crest of eia for the first time under magnetically quiet high solar activity conditions three examples and a year of statistics are presented the f2 layer stratification and f3 layer were observed between 10 40 and 11 45 ut on 31 december 2000 between 13 30 and 14 30 ut on 1 january 2001 and between 13 15 and 15 15 ut on 11 february 2001 the statistics during september 2000 to august 2001 shows that the f3 layer occurs only for 66 days 18 occurrence and it occurs only during september february spring summer with maximum occurrence in september october and longest duration in february the f2 layer stratification seems to be associated with gravity waves gws which have periods of about 30 60 min downward phase velocities of about 60 140 m s and vertical wavelengths of about 200 500 km the presence of powerful gravity waves in a vertically extended f layer seems to stratify the f2 layer and produce the f3 layer because the stratifications are observed during geomagnetically quiet periods the source of the gravity waves are most likely to be associated with local tropospheric disturbances and not with high latitude disturbances

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

seismic tomographic imaging of a buried concrete target1 this paper describes a field evaluation of an algebraic reconstruction technique for the tomographic imaging of sub surface velocity anomalies the authors describe the construction of a three dimensional concrete model and the acquisition and processing of seismic traveltime data through the model image reconstructions of the data sets using an algebraic reconstruction technique and incorporating prior knowledge are presented and these are compared with the actual model reconstructions show that it is essential that accurate data are obtained as we demonstrate that relatively small errors in the traveltime data can seriously degrade the reconstruction the authors also show that raypath effects are very important limiting factors to the analysis

physical properties of shale at temperature and pressure deformational properties p wave and s wave velocities and electrical resistivity were measured for three north sea malm shales in the laboratory under pressures to 800 bars and temperatures to 100 c these data were used to evaluate how factors such as mineralogy microstructure compaction and pore fluid conductivity affect a shale s seismic and electrical responses deformation in the shales is dominated by inelastic processes which cause time dependent changes in velocity resistivity and pore pressure overall shales are less sensitive to pressure changes as compared to sandstones of similar porosity however changes in temperature result in large changes in physical properties as compared to sandstones or shaly sands p wave and s wave velocities may decrease by as much as 10 percent over the temperature range studied and calculated activation energies for surface conduction are nearly twice those observed in shaly sands these comparisons emphasize fundamental differences in fabric among the

physical mechanism and statistics of occurrence of an additional layer in the equatorial ionosphere a physical mechanism and the location and latitudinal extent of an additional layer called the f3 layer that exists in the equatorial ionosphere are presented a statistical analysis of the occurrence of the layer recorded at the equatorial station fortaleza 4 s 38 w dip 9 s in brazil is also presented the f3 layer forms during the morning noon period in that equatorial region where the combined effect of the upward e b drift and neutral wind provides a vertically upward plasma drift velocity at altitudes near and above the f2 peak this velocity causes the f2 peak to drift upward and form the f3 layer while the normal f2 layer develops at lower altitudes through the usual photochemical and dynamical effects of the equatorial region the peak electron density of the f3 layer can exceed that of the f2 layer the f3 layer is predicted to be distinct on the summer side of the geomagnetic equator during periods of low solar activity and to become less distinct as the solar activity increases ionograms recorded at fortaleza in 1995 show the existence of an f3 layer on 49 of the days with the occurrence being most frequent 75 and distinct in summer as expected during summer the layer occurs earlier and lasts longer compared to the other seasons on the average the layer occurs at around 0930 lt and lasts for about 3 hours the altitude of the layer is also high in summer with the mean peak virtual height being about 570 km however the critical frequency of the layer f0f3 exceeds that of the f2 layer f0f2 by the largest amounts in winter and equinox f0f3 exceeds f0f2 by a yearly average of about 1 3 mhz

early paleozoic to devonian multiple accretionary model for the qilian shan nw china abstract the qilian shan located in the northern tibetan plateau of nw china has an excellent record of early to middle paleozoic subduction accretion that resulted from convergence between the alax and qaidam blocks but there is no consensus about its detailed tectonic history this paper summarizes its tectonic divisions and discusses its tectonic evolution from the cambrian to devonian the belt has the following tectonic divisions in the far north the southern passive margin of the alax block is juxtaposed against an early cambrian to ordovician marianan type intra oceanic arc north qilian the north qilian arc is separated from a japanese type arc central qilian to the south by a high pressure metamorphic belt composed mostly of ophiolitic slices and oceanic crusts the central qilian is bounded to the south by a wide melange zone south qilian consisting of ophiolitic slices and continental margin sequences farther to the south lies the oulongbuluk microcontinent that is separated from the qaidam block and farther south by an ultrahigh pressure metamorphic belt tectonostratigraphic analysis together with geochemical geochronological and geophysical data indicates a complex evolution by subduction accretion processes from the cambrian to the devonian before final amalgamation and docking to the northern alax block this model solves the long lasting discussion on the polarity of subduction in paleozoic time this multiple subduction accretion history sheds light on the continuity of paleozoic sutures along the qilian shan and the nature of the altyn tagh fault and thus contributes to an improved understanding of the tectonic architecture of central asia

inversion strategy in crosshole radar tomography using information of data subsets detecting discrete anomalies such as cavities or tunnels is an important application of crosshole radar tomography however crosshole tomographic inversion results are frequently ambiguous showing smearing effects and inversion artifacts these ambiguities lead to uncertainties in interpretation hence the size and position of anomalies can only be interpreted with limited accuracy and reliability we present an inversion strategy for investigating discrete anomalies with crosshole radar tomography in addition to the full traveltime data set we use subsets of specified ray angle intervals for tomographic inversion by analyzing inversion results from different ray angle intervals a more accurate interpretation of anomalies is possible the second step of our strategy is to develop a good inhomogeneous starting model from joint interpretation of the inversion results from different subsets the third step is to invert the full data set using this new starting model and to evaluate the inversion results by analyzing the distributions of mean square traveltime residuals with respect to the ray angles we use a synthetic model with two discrete anomalies located roughly at the same depth to demonstrate and evaluate our approach this inversion strategy is also applied to a field data set collected to investigate karst cavities in limestone from the inversion results of both examples we show that horizontal smearing of anomalies can be reduced by eliminating near horizontal rays a good starting model can be obtained based on the joint interpretation of the inversion results of the different subsets it leads to a high resolution final image of the full data set

applications of seismic travel time tomography summary this paper describes the application of tomography to seismic travel time inversion there are various implementations of travel time tomography in reflection tomography sources and receivers are on the surface of the earth and the principal seismic events are reflections from subsurface velocity discontinuities in transmission tomography sources and or receivers may be buried beneath the surface and the events correspond to direct or unreflected arrivals this is the analogue of medical tomography there are also cases in which both direct as well as reflected arrivals are important such as in vertical seismic profiling the latter is a direct application of the first two but is not discussed in any detail here it is also shown how the iterative use of travel time tomography and depth migration can produce much enhanced subsurface images examples of both transmission tomography and reflection tomography combined with depth migration illustrate the methods

surface to tunnel seismic tomography studies at yucca mountain nevada 1 a surface to tunnel seismic survey was conducted to estimate fracture intensity and distribution in the proposed nuclear waste repository area at yucca mountain nevada a 5 km long source line and a 3 km long receiver line were located on top of yucca mountain ridge and inside the exploratory study facility esf tunnel respectively numerical modeling showed that the first arrival p waves are mainly propagated in the repository horizon at depth therefore two dimensional travel time inversions were performed after the actual source locations on the ridge were projected onto the layer of interest at depth static corrections were applied to absorb the scatter in the new source locations and to correct for variations in source and receiver coupling and travel time shifts zero offset amplitude variations of the first arrivals across the receiver line inside the tunnel showed strong correlation with the fracture density determined by measurements along the tunnel wall wave guidance by subhorizontal fractures is suggested as a possible source for this phenomenon tomographic inversion of the travel time data revealed a low velocity zone in the south central area of the repository horizon conversion of the velocity tomography results to fracture density tomograms showed good correlation with fracture intensity mapped along tunnel walls the fractured zone extends over a large area in the southern region of the potential repository in particular southwest of the intensely fractured zone encountered in the esf tunnel the rock in the northern section of the repository appears more competent compared to the highly fractured areas in the south

observations of ionospheric f layer quadruple stratification near equatorial region this paper presents and discusses the occurrence of f layer quadruple stratification stf 1 stf 2 stf 3 and stf 4 during southern hemisphere winter season june july and august 2002 and high solar activity condition which was observed at palmas 10 3 s 48 3 w dip latitude 5 5 s near equatorial region brazilian sector this is the first time that the formation of f layer quadruple stratification stf 1 stf 2 stf 3 and stf 4 has been reported in the south american sector the stf 4 has a short lifetime compared with triple stratification f3 layer and it is antecedent and followed by triple f3 layer stratification

a study of methods for tomographic velocity estimation in the presence of low velocity zones this paper deals with the problem of seismic velocity estimation from first arrival traveltimes in a two dimensional 2 d cross hole geometry where explosions are detonated in one borehole while recordings are made in another borehole and on the surface standard tomographic procedures are based on decomposition of the cross hole area into a number of cells and a simplifying assumption of straight raypaths in the presence of significant low velocity zones the resulting images may be contaminated different ways of performing tomographic inversion are tested on a number of synthetic examples images obtained by direct unrestricted least squares inversion are often seriously distorted however methods using more cells and some kind of damping often give more satisfactory results because the risk of distorted images is always present in inversion procedures comparison with synthetic data forward modeling is a valuable tool in the interpretation process with a reasonably good initial solution impro

accounting for velocity anisotropy in seismic traveltime tomography a case study from the investigation of the foundations of a byzantine monumental building we estimate velocity anisotropy factors from seismic traveltime tomographic data and apply a correction for anisotropy in the inversion procedure to test possible improvements on the traveltime fit and the quality of the resulting tomographic images we applied the anisotropy correction on a traveltime data set obtained from the investigation of the foundation structure of a monumental building a byzantine church from the 11th century ad in athens greece vertical transverse isotropy is represented by one axis of symmetry and one anisotropy magnitude for the entire tomographic inversion grid we choose the vertical direction for the symmetry axis by analysing the available data set and taking into account information on the character of the foundations of the church from the literature and past excavations the anisotropy magnitude is determined by testing a series of values of anisotropy and examining their effect on the tomographic inversion results the best traveltime fit and image quality are obtained with an anisotropy value vmax vmin of 1 6 restricted to the high velocity structures in the subsurface we believe that this anisotropy value which is significantly higher than the usual values reported for near surface geological material is related to the fabric of the church foundations due to the shape of the individual stone blocks and the layout of the stonework inversion results obtained with the correction for anisotropy indicate that both the traveltime fit and the image quality are improved providing an enhanced reconstruction of the velocity field especially for the high velocity features based on this enhanced and more reliable reconstruction of velocity distribution an improved image of the subsurface material character was made possible in particular the pattern and state of the church foundations and possible weak ground material areas were revealed more clearly this improved subsurface knowledge may assist in a better design of restoration measures for monumental buildings such as byzantine churches

geotomographic imaging in the study of mining induced seismicity geotomographic imaging is a technique which allows seismic waves to be used to gain information about the internal structure of rock masses in a way conceptually similar to medical cat scanning traditional approaches to the study of mining induced seismic phenomena have concentrated on using passive monitoring methods this paper gives an overview of the developments in the acquisition processing and interpretation of geotomographic data and outlines how images can be used in conjunction with passive techniques to study mining induced seismicity

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

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

multiple phases of deformation in the southern helanshan tectonic belt northern china abstract the southern helanshan tectonic belt shtb is surrounded by the alxa massif the ordos basin and the tibetan plateau and its phanerozoic structures records crucial phanerozoic deformation characteristics for studying the multi phased intracontinental deformation processes among these neighboring units combined with regional geology our structural analysis reveals that the shtb has experienced five phases of shortening deformation during the phanerozoic the first phase d1 is represented by e w trending overturned folds in the cambrian and ordovician strata these folds resulted from two episodes of n s shortening during the late cambrian early ordovician and late ordovician early devonian respectively which were attributed to the closure of the qilian ocean the second phase d2 is characterized by e w trending open folds involving the upper devonian strata which was the products of n s shortening caused by the assembly of the qilian ocean and the north china craton ncc at the end of devonian the third phase d3 is indicated by some wnw trending jura type folds in the carboniferous strata formed by nne ssw shortening during the late triassic early jurassic related to the collision between the ncc and the south china block the fourth phase d4 is inferred by nne trending shortening structures in the jurassic and its underlying strata generated by wnw ese shortening in the late jurassic echoing the paleo pacific subduction the fifth stage d5 is characterized by the ne sw shortening in the late miocene leading to the formation of many nw se striking thrust faults in the miocene and its underlying strata because the outward expansion of the tibetan plateau

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

crustal heterogeneity in south australia earthquake evidence summary lateral velocity variations in the south australian crust have been mapped using the relatively new technique of seismic tomography the input data comprised p1 travel times from 1340 local earthquakes recorded on the south australian seismic network during the period 1978 1983 to reduce errors in the earthquake locations focal depths and origin times we used an averaging technique of dividing the area under consideration into a series of overlapping cylindrical cells all earthquakes and seismic stations were assigned to the centre of the nearest cell travel times between all centres were computed by averaging over all relevant cell pairs after first scaling all travel times by a factor equal to the distance between cell centres divided by the actual ray path length only ray paths appropriate to the p1 phase were considered starting with a first guess model based on the number of ray intersections with each cell the travel times were computed along all ray paths and compared with the observed averaged values the errors and residuals were back projected for each ray over all the chords along the ray and the average cell slowness adjusted in an iterative sense until the computed and observed travel times agreed within a specified error tolerance the areas with poor raypath coverage lack of earthquakes and or stations could not be imaged the area covered lies mostly within the adelaide geosyncline where there is believed to be a thick cover of proterozoic sediments the velocity image is of the upper 20 km of the crust so no direct correlation between the surface geology and the crustal velocity is to be expected results indicate a significant variation in crustal velocity from 5 9 to 6 5 km s 1 the velocities correlate remarkably with time terms computed in a separate study of moho refracted arrivals pn low time terms correspond to high crustal velocity and high time terms reflect anomalously low crustal velocity the residual component of the time terms can be explained in terms of variations in depth to the moho throughout the geosyncline of the order of 10 km the prominent features of the tomographic velocity map are a n s trending velocity low over the spencer gulf graben and a ridge of high velocity beneath the flinders ranges the velocity low can be associated with a region of low gravity aligned parallel to the torrens hinge zone which marks the western boundary of the geosyncline the northern end of the high velocity ridge coincides with a region of positive bouguer gravity teleseismic residuals from both earthquakes and nuclear explosions show a similar trend to the pn time terms and indicate lateral variability in crustal thickness and velocity a component of the residual must be attributed to mantle velocity inhomogeneity which extends to depths of 300 km

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

the fracture criticality of crustal rocks summary the shear wave splitting observed along almost all shear wave ray paths in the earth s crust is interpreted as the effects of stress aligned fluid filled cracks microcracks and preferentially oriented pore space once away from the free surface where open joints and fractures may lead to strong anisotropy of 10 per cent or greater intact ostensibly unfractured crustal rock exhibits a limited range of shear wave splitting from about 1 5 to 4 5 per cent differential shear wave velocity anisotropy interpreting this velocity anisotropy as normalized crack densities a factor of less than two in crack radius covers the range from the minimum 1 5 per cent anisotropy observed in intact rock to the 10 per cent observed in heavily cracked almost disaggregated near surface rocks this narrow range of crack dimensions and the pronounced effect on rock cohesion suggests that there is a state of fracture criticality at some level of anisotropy between 4 5 and 10 per cent marking the boundary between essentially intact and heavily fractured rock when the level of fracture criticality is exceeded cracking is so severe that there is a breakdown in shear strength the likelihood of progressive fracturing and the dispersal of pore fluids through enhanced permeability the range of normalized crack dimensions below fracture criticality is so small in intact rock that any modification to the crack geometry by even minor changes of conditions or minor deformation particularly in the presence of high pore fluid pressures may change rock from being essentially intact below fracture criticality to heavily fractured above fracture criticality this recognition of the essential compliance of most crustal rocks and its effect on shear wave splitting has implications for monitoring changes in any conditions affecting the rock mass these include monitoring changes in reservoir evolution during hydrocarbon production and enhanced oil recovery and in monitoring changes before and after earthquakes amongst others