application of vertical radar profiling technique to sendai castle the vertical radar profiling vrp technique is able to explore much deeper than conventional surface ground penetrating radar gpr because it uses boreholes it has been successfully applied at the sendai castle site in japan to investigate the extent of an old stone wall and strata buried by a more recent stone wall the transmitter of a polarimetric radar system was moved within a borehole and the receiver was fixed on the ground surface several meters away from the borehole head cross and copolarization data were measured at a receiver position with a different orientation to the receiver ten data sets were acquired by placing the receiver in five directions the depolarization is strong indicating the subsurface contains a great amount of gravel to get clear and intuitive images of the subsurface we applied data processing techniques including the separation of direct and reflected waves of raw vrp data using f k filtering approach and kirchhoff migration of separated reflected waves by com

postmap migration of crosswell reflection seismic data vertical seismic profiling common depth point vsp cdp mapping is often preferred to crosswell migration when imaging crosswell seismic reflection data the principal advantage of vsp cdp mapping is that it can be configured as a one to one operation between data in the acquisition domain and data in the image domain and therefore does not smear coherent noise such as tube waves guided waves and converted waves as crosswell migration could however unlike crosswell migration vsp cdp mapping cannot collapse diffractions therefore the lateral resolution of reflection events suffers we present a migration algorithm that is applied to the crosswell data after they have been mapped by performing crosswell migration in two distinct steps mapping followed by diffraction stacking noise events can be identified and filtered in the mapped domain without smearing effects commonly associated with conventional crosswell migration operators tests on noise free synthetic crosswell data indicate that the two ste

fogo volcano cape verde islands seismicity derived constraints on the mechanism of the 1995 eruption seismic data recorded in the vicinity of the active vent of the 1995 fogo eruption global volcanism network bulletin 1995 20 3 2 4 is used to constrain the associated stress field and deformation using the frequency content of the seismograms to distinguish between brittle fracture of cold host rock and deformation in the vicinity of the intruding magma a sub vertical dyke with 060 strike is identified as the feeder of the eruption and delineated down to a depth of about 4 km the local stress field during the eruption is estimated from composite focal mechanisms besides the expected 3 direction normal to the dyke a group of focal solutions point to a stress field with nearly dyke parallel 3 which is interpreted as a re adjustment of the edifice following the eruption maybe partially controlled by gravity this effect may have increased the instability of the steep eastern flank of the island since the deformation detected during the magma drainback is compatible with predominantly dip slip motion on east dipping surfaces

borehole seismic surveys for fault delineation in the dutch north sea a significant share of gas production in the dutch sector of the southern north sea basin comes from permian rotliegend fault blocks precise knowledge of the positions of these faults is necessary for efficient exploitation of the reservoir structures and for future field development strategies two areas are presented where the lateral resolution of the surface seismic data was not sufficient to determine positions of major fault block boundaries accurately walkaway borehole seismic profiles were shot over each of these areas with the objective of illuminating the fault boundaries to obtain an image with a higher resolution the images were generated using borehole seismic reflection point mapping and migration techniques large aperture migrations tend to produce unacceptable migration smiles while reflection point mapping is a model dependent process a hybrid approach to these processes was necessary to avoid problems associated with the limited angular illumination permitted by the field acquisiti

reconstruction of reflecting structures from vertical seismic profiles with a moving source when a vertical seismic profile vsp is recorded the illuminated part of a reflector depends upon the shape and position of the reflector itself as well as on the seismic velocities and the positions of sources and receivers a preferable arrangement for the investigation of structures of reflectors is to fix the receiver s at constant depth s in the well and move the source horizontally along a line at the earth s surface usually called a multioffset vsp msp or walkaway vsp as a test of the resolution power of this survey geometry synthetic records were generated from a subsurface model by inverse kirchhoff migration three different methods were applied for the reconstruction wavefront construction leads to the correct shape of the reflectors thus assuring the validity of the modeling method applied reflection point mapping delivered a near similarity to the model but without focusing fault edges kirchhoff migration resulted in a detailed image of the reflectors with fault edges focuse

vertical seismic profiling separation of upgoing and downgoing acoustic waves in a stratified medium one of the essential steps in the processing of a vertical seismic profile is the separation of upgoing and downgoing signals with this perspective in mind seismic data recorded in a borehole are modeled in terms of these waves and a mathematically optimal least squares technique for extracting them is derived the method imposes practically no constraints on the spacing between recording levels and allows almost perfect rejection of a coherent downgoing signal the exact formulation of the one dimensional model requires that acoustic impedance information be included but a reasonable and realistic approximation can neglect impedance we derive frequency wavenumber response plots for the two limiting cases of even and randomly spaced levels and compare these to the response of a conventional velocity filtering technique by a careful study of available logs recording levels can be chosen to optimize geophone coupling rather than insisting on uniform spatial sampling data editing normalization a

provenance studies of esie sculptural soapstone from southwestern nigeria a group of soapstone statues found near the village of esie in southwestern nigeria is one of the largest collections of prehistoric sculpture found in sub saharan africa the statues were found at esie by people of the igbomina sub grouping of the yoruba ethnic group when they settled in the esie area some 300 years ago the origin of the statues remains unknown several areas of soapstone in the nigerian schist belt are considered as potential source areas for the esie statues mineral assemblages textures and compositions of talc cummingtonite and chlorite from some of the statues suggest a source for the statue soapstone from the agbonda area the closest proposed source area to esie however mineralogic data from one of the statues are unlike any of the proposed source areas the result of our study together with earlier studies of stevens hambolu and onabajo provides strong evidence that the soapstone statues were carved from local ultramafic rocks from esie area

a comparison between kirchhoff and grt migration on vsp data1 a modern approach to migration is to perform wavefield extrapolation subject to an imaging condition correct wavefield extrapolation requires that the boundary conditions at the array of geophones satisfy the wave equation a sufficient condition is to perform the survey with a single stationary source contrary to this condition many vsps are conducted in deviated wells where the source is maintained vertically above the down hole geophone at each well station such a survey fails to provide the boundary conditions theoretically necessary for wave equation migration a recently published inversion scheme referred to as acoustic generalized radon transform migration grt migration was developed to handle any configuration of sources and geophones including moving source deviated well vsp surveys grt migration may be viewed as a weighted version of the generalized kirchhoff migration derived in this paper from the exploding reflector model when a vsp survey geometry has been specified grt migration can be expressed in terms of array parameters and compared with the equivalent expression for kirchhoff wave equation migration the differences between the two integrals are significant and their effect is demonstrated on vsp data

adaptation of a triaxial cell for ultrasonic p wave attenuation velocity and acoustic emission measurements adaptation of a triaxial cell for ultrasonic p wave attenuation velocity and acoustic emission measurements j a donald s d butt s iakovlev department of mining and metallurgical engineering dalhousie university 1360 barrington street sexton campus p o box 1000 halifax nova scotia canada b3j 3x4 department of engineering mathematics dalhousie university 1360 barrington street sexton campus p o box 1000 halifax nova scotia canada b3j 3x4

soils in the semi arid area of the el melah lagoon ne tunisia variability associated with a closing evolution abstract soils of the semi arid area of the el melah coastal lagoon ne tunisia with a closing evolution dynamic were studied aiming 1 the chemical and mineralogical characterization of surface and subsurface layers of soil profiles from locations previously submerged and of soils developed on dunes 2 to evaluate the dependence on the environment conditions of the geochemical patterns of the soils and 3 to determine chemical and mineralogical variations with the emersion of the sediments resulting from the decrease in the extent of the area permanently covered by water in the lagoon the compositional results obtained showed significant differences depending on the environment littoral plain old dunes and sandy spit but soils of the different environmental zones studied do not appear to be significantly polluted as far as trace elements are concerned among the elements studied high element sc ratios and variations were found for as sb and zn antimony is more concentrated in coarser samples suggesting its adsorption in fe or mn oxides coating quartz grain surfaces arsenic and zinc may be incorporated into the carbonates structure as well as adsorbed on or coprecipitated with iron oxides zinc may also be significantly incorporated in clay minerals iron was found to be more oxidized in the cultivated soil from the old dune strand and more reduced in the sandy spit where ankerite occurs suggesting the reduction of fe3 in oxide hydroxides by microorganisms and incorporation of fe2 in carbonates ree patterns particularly the hree lree are correlated with carbonates indicating preferential incorporation of the hree in carbonates and of the lree in clay minerals iron oxides high ga contents were found in soils and sediments rich in clay minerals al suggesting its incorporation in clay minerals structure therefore ga may be used as an indicator of the clay minerals proportion in sediments and soils carbonates sulphates besides fe and or mn oxides and clay minerals appear to play an important role on the trace elements distribution

vertical seismic profiling depth migration of a salt dome flank vertical seismic profiles vsps can supply information about both velocity and subsurface interface locations properly designed vsps can be used to map steeply dipping interfaces such as salt dome flanks mapping subsurface interfaces with vsp data requires careful survey design appropriate data processing interval velocity estimation and reflector mapping the first of these four ingredients is satisfied in most cases by preacquisition modeling the second is accomplished by careful data processing initial velocity estimates are provided by seismic tomography velocity model refinement is accomplished by a combination of iterative modeling and iterative least squares inversion finally the resultant interval velocities are used in depth migration of the processed vsp these four ingredients have been combined to map a salt dome flank

characterization and imaging of a hydrothermally active near vertical fault zone in crystalline rocks based on hydrophone vsp data abstract a shallow hydrothermally active fault zone embedded in fractured crystalline rocks of the central swiss alps has been drilled and geophysically explored in view of its potential analogies to planned petrothermal reservoirs in the alpine foreland vertical seismic profiling vsp experiments have been performed using a 24 channel borehole hydrophone array with a sensor spacing of 1 m in order to image the fault core and to detect hydraulically open fractures the dense sensor spacing allows for an accurate sampling of the wavefields this in turn enables their separation through standard seismic processing methodologies thus allowing for the generation of seismic body wave vsp profiles and a tube wave corridor stack which maps brittle deformation in the surrounding rock mass multiple offset hydrophone vsp data were acquired with a crooked line survey geometry and processed with 3d methods hereby a laterally changing velocity cube representative of the vertical structural variations associated with the fault zone is generated and utilized for kirchhoff pre stack depth migration psdm imaging the resulting seismic image delineates various vertical structures notably the target fault zone the interpretation of the vsp data is complemented by and corroborated through a suite of geophysical borehole logs which characterize the fine scale petrophysical variations in response to brittle deformation in the fault core and the surrounding damage zones this study exemplifies typical targets of hardrock seismic exploration where the structures are frequently near vertical discontinuous and where acoustic impedance contrasts are commonly associated with deformation as such it illustrates the benefits of using borehole seismic methods in such environments and the use of borehole hydrophone arrays for targeting fractures and shear zones

iron speciation in volcanic topsoils from fogo island cape verde iron oxide nanoparticles and trace elements concentrations abstract iron contents its compounds and forms in topsoils of the volcanic fogo island cape verde were studied by neutron activation analysis mossbauer spectroscopy and x ray diffraction the topsoils were collected from all units of the island in diverse geological formations carbonatite nephelinites limburgite pyroclasts deposits pre historic lavas and historic lavas fine materials from mota gomes volcanic crater the most recent eruption which occurred in 1995 were also sampled the total iron content varies significantly from 1 7 fe2o3 weight in acid sulfate topsoils ph 3 9 up to between 9 9 and 20 6 in the other geological contexts ph 5 9 to 9 3 the most oxidized topsoils from the pre caldera formations are the oldest ones as expected while the reverse is observed for the post caldera topsoils in the latter case fast weathering of the lava outer layers which have a higher glass component may explain this observation after erosion periods of 50 200 years significant amounts of the highly oxidized small particles are removed the inner part of the lava less oxidized is then exposed and more slowly weathered than the former outer layers topsoils from pre caldera formations derived from the more weather resistant inner layers are also strongly altered since they have been exposed for periods of time several orders of magnitude longer than the post caldera ones in topsoils fe2 mainly occurs in pyroxenes phyllosilicates and pure or slightly oxidized magnetite with increasing age the fe2 total fe ratio of the pre caldera topsoils gradually decreases down to 4 indicating that the iron that is still incorporated in the silicates structures is increasingly oxidized maghemite is detected instead of magnetite and hematite appears becoming the main fe containing phase in the oldest materials these results suggest that in a first weathering step fe2 is oxidized within the silicates structure and within magnetite which gradually evolves to maghemite with the eventual decomposition of silicates fe3 is remobilized in hematite as weathering proceeds maghemite is also replaced by hematite goethite was not detected by mossbauer spectroscopy which may be explained by the aridity of the island iron in jarosite was identified by mossbauer spectroscopy in topsoils developed on volcanic conduits the presence of this mineral in alkaline surficial environments may be explained by a hypogene origin and stability over at least a few hundred years in the surficial environments of the semi arid fogo island contents of cr and as that are potentially harmful to health increase with the concentration of nanosized fe oxides this correlation may be related to their high specific surface area

hydrophone vsp surveys in hard rock abstractseismic imaging in hard rock environments is gaining wider acceptance as an exploration technique and as a mine planning tool to date 13 successful case studies have been acquired in australia the images generated from hard rock targets exhibit large levels of complexity and their interpretations remain an active area of study to assist the imaging and better understand the source of the reflections observed vertical seismic profiling vsp can be employed this technique is not readily applied to hard rock environments because cost and operational issues often prove prohibitive we propose the use of hydrophone arrays as a cost effective solution to vsp acquisition we highlight the key challenges in using these receivers and propose solutions to overcome them by careful acquisition methodologies and refined signal processing techniques the tube waves that have up to now compromised the use of hydrophones for vsp acquisition can be effectively mitigated we show that the data acquired with

chemical characterization of some potsherd pavements from parts of yorubaland in southwestern nigeria several samples of potsherd pavement were recovered during excavation and archaeological reconnaissance of six sites along the trade and migration route of the yoruba of southwestern nigeria a significant feature of these pavements is the similarity to ife in design which consists of a herringbone design with a ritual pot embedded in their middle microscopic analysis of samples shows the presence of high proportions of non plastic grains mainly quartz micas minor plagioclases and traces of ferruginous grains tourmaline and amphibole interpreted as being produced by low temperature firing major trace and rare earth elements composition of 21 samples of sherds was determined using inductively coupled plasma icp ms technique the chemistry of the potsherd samples is generally similar to regolith derived from granitic rocks which are abundant in the area principal component analysis pca was used to reduce the number of variables and model based cluster analysis was used to find clusters in the pca scores model based clustering found one major cluster in the data set which corresponds to the local weathered granitic pegmatitic raw materials near the sites our work shows that the technology for the manufacture of these pavements might have originated from ile ife but the production was geologically controlled

offset source vsp surveys and their image reconstruction zero offset source vsp surveys provide information about the subsurface only within the fresnel zone centered at the well offsetting the source location moves the reflection zones away from the well thus providing lateral cover conventional processing of this type of data gives rise to a distorted image of the subsurface using a simple ray tracing scheme this image may be reconstructed into the more familiar coordinate system of the surface seismic section this simple data independent mapping is based on the assumption of horizontal layering and requires a vertical velocity profile the technique of placing the source away from the borehole was first applied to the single offset source vsp survey however data from any survey geometry such as deviated well with rig source walkaway vsp etc can be mapped to the coordinate system defined by the appropriate seismic section to obtain the best results from this type of survey the target area must be defined and simple modeling techniques used to optimize the source location s these pre survey modeling methods may also be used to anticipate and hence avoid a number of problem areas which experience has highlighted the data from any vsp survey is the result of a realizable experiment and as such obeys the wave equation this implies that the wave equation may be used to migrate the data to its true subsurface location theoretically such a process is more secure than ray tracing techniques although its practice presents many difficulties

clay mineral assemblages in weathered basalt profiles from central and southern portugal climatic significance abstract mineralogical and chemical changes during weathering of basalts from central and southern portugal were studied both regions have a temperate mediterranean type climate the algarve being more arid the areas concerned are the lisbon 72 ma and the runa volcanic complexes 100 70 ma and rio maior 160 130 ma in central portugal and budens 170 180 ma in the south the basalts are generally rich in olivine phenocrysts clay minerals are in general well crystallised and comprise smectites associated with 1 1 minerals principally halloysite illite and palygorskite kaolin minerals prevail in topographic highs whilst smectites predominate in lower areas smectites were analysed from the

integrated prestack depth migration of vertical seismic profile and surface seismic data from the rocky mountain foothills of southern alberta canada we have developed an anisotropic prestack depth migration code that can migrate either vertical seismic profile vsp or surface seismic data we use this migration code in a new method for integrated vsp and surface seismic depth imaging instead of splicing the vsp image into the section derived from surface seismic data we use the same migration algorithm and a single velocity model to migrate both data sets to a common output grid we then scale and sum the two images to yield one integrated depth migrated section after testing this method on synthetic surface seismic and vsp data we applied it to field data from a 2d surface seismic line and a multioffset vsp from the rocky mountain foothills of southern alberta canada our results show that the resulting integrated image exhibits significant improvement over that obtained from a the migration of either data set alone or b the conventional splicing approach the integrated image uses the broader frequency bandwidth of the vsp data to provide

geochemical fingerprints in topsoils of the volcanic brava island cape verde abstract topsoils developed on different lithologies of all the geological units of the volcanic brava island cape verde archipelago were studied by neutron activation analysis and mossbauer spectroscopy sampling was performed according to the recommendations of the igcp 259 international geochemical mapping significant chemical contents variations were found even within the same volcano stratigraphic unit inherited from the parent rock composition under the semi arid climate of the island the chemical heterogeneity of topsoils within the same geological unit particularly in the upper unit was evidenced by a multivariate statistical analysis some differences found can be related with the geographical location underlying basement high contents of mn co ga ba la ce nd sm eu tb ta w th and u were observed in soils related to carbonatites and phonolites ree and w can be used to trace outcrops of extrusive carbonatites in general iron is strongly oxidized occurring in the silicates structure as well as in hematite oxidized magnetite and maghemite the global iron oxidation degree the fraction of fe 3 in silicates and the fraction of nanosized oxides which are higher in topsoils of the older units may be an indicator of weathering degree as br and sb contents were also found to increase with weathering topsoils developed on extrusive carbonatites are clearly distinguished due to the absence of fe 2 in the silicate phases and the remarkable predominance of low oxidized magnetite

imaging the aquistore reservoir after 36 kilotonnes of co2 injection using distributed acoustic sensing abstractaquistore is a geologic co2 storage project that is using a deep saline formation as a storage reservoir from april 2015 to february 2016 approximately 36 kilotonnes of co2 were injected into the reservoir at a depth of 3130 3350 m we have developed an analysis of distributed acoustic sensing das 3d vertical seismic profiling data acquired in february 2016 marking the first seismic survey since injection began the vsp data were processed in parallel with baseline preinjection data from a november 2013 survey with the objective of detecting and characterizing the subsurface co2 plume and evaluating the repeatability of das in a reservoir monitoring project a single processing sequence was devised that 1 accurately imaged the reservoir for the baseline and monitor data and 2 attained adequate repeatability to observe time lapse differences related to the presence of co2 repeatability was somewhat compromised by the less advanced noise cancellation methodology of the das system used for

reverse time migration of offset vertical seismic profiling data using the excitation time imaging condition to apply reverse time migration to prestack finite offset data from variable velocity media the standard time zero imaging condition must be generalized because each point in the image space has a different image time or times this generalization is the excitation time imaging condition in which each point is imaged at the one way traveltime from the source to that point reverse time migration with the excitation time imaging condition consists of three elements 1 computation of the imaging condition 2 extrapolation of the recorder wave field and 3 application of the imaging condition computation of the imaging condition for each point in the image is done by ray tracing from the source point this is equivalent to extrapolation of the source wave field through the medium extrapolation of the recorded wave field is done by an acoustic finite difference algorithm imaging is performed at each step of the finite difference extrapolation by extracting from the propagating wave field the

depth imaging of offset vertical seismic profile data1 amundsen l arntsen b and mittet r 1993 depth imaging of offset vertical seismic profile data geophysical prospecting 41 1009 1031 depth migration consists of two different steps wavefield extrapolation and imaging the wave propagation is firmly founded on a mathematical frame work and is simulated by solving different types of wave equations dependent on the physical model under investigation in contrast the imaging part of migration is usually based on ad hoc principles rather than on a physical model with an associated mathematical expression the imaging is usually performed using the u d concept of claerbout 1971 which states that reflectors exist at points in the subsurface where the first arrival of the downgoing wave is time coincident with the upgoing wave inversion can as with migration be divided into the two steps of wavefield extrapolation and imaging in contrast to the imaging principle in migration imaging in inversion follows from the mathematical formulation of the problem the image with respect to the bulk modulus or velocity perturbations is proportional to the correlation between the time derivatives of a forward propagated field and a backward propagated residual field lailly 1984 tarantola 1984 we assume a physical model in which the wave propagation is governed by the 2d acoustic wave equation the wave equation is solved numerically using an efficient finitedifference scheme making simulations in realistically sized models feasible the two imaging concepts of migration and inversion are tested and compared in depth imaging from a synthetic offset vertical seismic profile section in order to test the velocity sensitivity of the algorithms two erroneous input velocity models are tested we find that the algorithm founded on inverse theory is less sensitive to velocity errors than depth migration using the more ad hoc u d imaging principle

rare earth and other trace and major elemental distribution in a pedogenic calcrete profile slimene ne tunisia a calcrete profile developed on the top of a calcareous consolidated dune located in a coastal area of ne tunisia semi arid climate was studied with the aim to investigate the behavior of the chemical elements rare earth elements ree and other trace and major elements during the processes associated with calcrete formation particularly dissolution and precipitation of carbonates in the vadose zone the profile shows a vertical sequence with clear zonations from the surface downwards a reddish soil at the land surface a nodular horizon a laminar structured level and the consolidated old dune chemical and mineralogical analyses of samples from all levels were performed by neutron activation analysis and x ray diffraction bulk samples and 2 m fraction detailed studies of iron speciation and iron minerals were done by mossbauer spectroscopy microfauna mineralogical and chemical variations in the slimene weathering profile point to a long term aerial exposure of the old dune in a semi arid carbonated environment leading to the development of a pedogenic calcrete profile the mineralogical variations with depth indicate carbonate dissolution at the surface and downward leaching of calcium secondary carbonates overgrow primary ones and precipitate as coating or concretions below minerals found in the upper levels correspond to original materials of the old dune and also weathering phases and atmospheric inputs phyllosilicates decrease while calcite and k feldspars increase with depth kaolinite was the only clay mineral found in the old dune illite and chlorite were also found in all samples with calcrete authigenic smectite formation occurs above the laminar structured calcrete due to restricted drainage conditions the most significant chemical variations associated with the calcrete formation are i enrichment of co u br and ree in calcrete ii depletion of middle ree in the upper levels particularly eu and enrichment of middle ree and heavy ree in calcrete and iii hf zr cr th cs ta ga rb and k appear to be retained in the upper levels where calcite has been dissolved here iron is more reduced fe3 occurs in iron oxides goethite and hematite and clay minerals the ratio goethite hematite appears to increase down the profile and fe2 is mainly present in clay minerals

migration of mixed mode vsp wavefields1 two dimensional vsp surveys are often conducted to provide structural illumination of the subsurface away from the borehole the illumination is achieved through offsetting the source with respect to the downhole geophone this inevitably gives rise to mode conversions in both downgoing and upgoing wavefields migration of mixed mode wavefields is complex because the velocity profile used for wavefield extrapolation is valid only for a particular propagation mode the other mode always propagates at a different velocity it is therefore advisable to separate the wave types p wave and sv wave prior to migration this may be achieved through wavemode filtering a multichannel process which exploits the relation between propagation velocity slowness of events at the recording array and particle motion the necessary information about particle motion is available only if the vsp data are acquired with a three component downhole geophone assembly the wavemode filter partitions wave types at the recording array it provides no information about the various changes of propagation mode experienced by the energy as it travels from source to geophone for the purpose of migration the intermediate modes of propagation must be deduced much of the energy arriving at the receivers is p wave which has followed the p wave velocity profile from the source it can therefore be imaged by conventional kirchhoff migration as an example of sv wave imaging a common mode code is p wave from source to reflector and sv wave from reflector to geophone migration of such data calls for back propagation of the geophone array wavefield at sv wave velocity to the point in the subsurface where it is time coincident with the forward propagated downwave at p wave velocity

seismic imaging of reflectors in the sg4 borehole middle urals russia the upper crust in the middle urals is known to be highly reflective however it is not clear whether the observed reflections originate from lithological boundaries or from fault zones the sg4 borehole located in the tagil synform of the middle urals drilled to 5354 m as of august 1995 presents one opportunity to study the source of this reflectivity the hole has penetrated several different lithologies as well as numerous tectonic or fracture zones the upper 5070 m consist of island arc rocks which have presumably been thrust on top of basalts to allow correlations between available surface seismic studies and the borehole observations vertical and offset seismic profile data were acquired in the borehole over the interval 520 m to 3940 m two shot points were used a near offset one at 135 m from the wellhead and a far offset one at 1845 m from the wellhead after processing the borehole seismic data show numerous reflecting horizons many reflections correlate with major fracture zones while others have no clear correlation with fracture zones nor lithological contrasts the interval between approximately 4450 m and 5100 m which is imaged below the bottom of the survey shows a layered reflective pattern that correlates with the lower part of a flysch unit which ends at 5070 m the basalts below appear to be relatively transparent a prominent east dipping reflector on a w e cdp line about 700 m north of the wellhead is not clearly imaged on the borehole seismic however in a pilot hole which deviates a few hundred metres in the northerly direction from the main hole a marked low velocity zone is observed at the corresponding depth for this reflector indicating its source to be from a fault zone that the fault zone is not clearly observed on the borehole seismic data is attributed to 3d effects

vertical seismic profile migration using the kirchhoff integral wave equation migration can form an accurate image of the subsurface from suitable vsp data the image s extent and resolution are determined by the receiver array dimensions and the source location s experiments with synthetic and real data show that the region of reliable image extent is defined by the specular zone of illumination migration is achieved through wave field extrapolation subject to an imaging procedure wave field extrapolation is based upon the scalar wave equation and for vsp data is conveniently handled by the kirchhoff integral the migration of vsp data calls for imaging very close to the borehole as well as imaging in the far field this dual requirement is met by retaining the near field term of the integral the complete integral solution is readily controlled by various weighting devices and processing strategies whose worth is demonstrated on real and synthetic data

metal partitioning in sediments and mineralogical controls on the acid mine drainage in ribeira da agua forte aljustrel iberian pyrite belt southern portugal abstract this work focuses on the geochemical processes taking place in the acid drainage in the ribeira da agua forte located in the aljustrel mining area in the iberian pyrite belt the approach involved water and stream sediment geochemical analyses as well as other techniques such as sequential extraction mossbauer spectroscopy and x ray diffraction ribeira da agua forte is a stream that drains the area of the old mine dumps of the aljustrel mine which have for decades been a source of acid waters this stream flows to the north for a little over than 10 km but mixes with a reduced organic rich high ph waste water from the municipal waste water pools of the village this water input produces two different results in the chemistry of the stream depending upon the season i in the winter season effective water mixing takes place and the flux of acid water from the mine dumps is continuous resulting in the immediate precipitation of the fe from the acid waters ii during the summer season acid drainage is interrupted and only the waste water feeds the stream resulting in the reductive dissolution of fe hydroxides and hydroxysulfates in the stream sediments releasing significant quantities of metals into solution throughout the year water ph stays invariably within 4 0 4 5 for several meters downstream of this mixing zone even when the source waters come from the waste water pools which have a ph around 8 4 the coupled interplay of dissolution and precipitation of the secondary minerals hydroxides and sulfates keeps the system ph between 3 9 and 4 5 all along the stream in particular evidence suggests that schwertmannite may be precipitating and later decomposing into fe hydroxides to sustain the stream water ph at those levels while fe content decreases by 50 from solution the most important trace metals are only slightly attenuated before the solution mixes with the ribeira do roxo stream waters concentrations of as are the only ones effectively reduced along the flow path partitioning of cu zn and pb in the contaminated sediments also showed different behavior specific non specific adsorption is relevant for cu and zn in the upstream branch of ribeira da agua forte with acid drainage conditions whereas the mixture with the waste water causes that the association of these metals with oxyhydroxide to be more important metals bound to oxyhydroxides are on the order of 60 70 for pb 50 for cu and 30 60 for zn organic matter is only marginally important around the waste water input area showing 2 8 cu bound to this phase these results also show that although the mixing process of both acid and organic rich waters can suppress and briefly mitigate some adverse effects of acid drainage the continuing discharge of these waste waters into a dry stream promotes the remobilization of metals fixed in the secondary solid phases in the stream bed back into solution a situation that can hardly be amended back to its original state

source provenance of andesite artefacts using non destructive xrf analysis x ray fluorescence spectrometry is a common technique in determining the elemental composition of lithic materials with the exception of glassy volcanic rocks like obsidian most rock types are prepared for analysis by conversion of specimens to powder or glass in order to reduce the effects of irregular surface topography and internal inhomogeneity concern for artefact conservation necessitates a less destructive preparation technique which has not been widely investigated except with respect to obsidian artefacts a series of analyses of andesitic and dacitic rocks explore the degree of influence of surface topography and inhomogeneity to determine if less destructive procedures can distinguish effectively between different geological sources focusing primarily on major elements results suggest that source discrimination can be achieved using data produced by any of the three sample preparation procedures investigated quantitative chemical data from glass beads semi quantitative chemical data from polished rock billets or x ray intensity ratios from unmodified flakes or polished billets

a past giant lateral collapse and present day flank instability of fogo cape verde islands fogo island is a large and extremely steepsided oceanic island volcano in the cape verde archipelago it has a large ca 9 km across east facing summit collapse structure the monte amarelo collapse with a probable volume of at least 150 200 km3 for most of its history the monte amarelo volcano had a small but productive central vent complex and radial rift zones fed by laterally propagating dykes shortly before the collapse the latter were replaced by north south trending arrays of en echelon vertically propagating dykes since the monte amarelo collapse the scar has partly filled with a new volcano the cha das caldeiras volcano the summit cone of this volcano the pico do fogo is a very young feature but has been abandoned in the most recent phase of activity from the 18th century onwards the same period has also seen the abandonment of earlier radial rift zones with laterally propagating dykes and their replacement with en echelon arrays of vents fed by vertically propagating dykes these form an n s trending array within the older collapse structure and are associated with seaward displacement of the eastern flank of the volcano within the old collapse structure the most recent eruptions those of 1951 and 1995 appear to be associated with episodes of flank instability manifested in n s surface fissuring and east facing normal faults these recent structural changes in the volcano parallel those which took place in the monte amarelo volcano prior to its collapse

radon transform wave field separation for vertical seismic profiling data the data obtained by the vertical seismic profiling vsp method require unique processing before interpretation an important step is the separation of upgoing and downgoing signals by application of an f k velocity filter and muting of the direct wave similarly if the vsp section is transformed to the p plane the upgoing and downgoing wave fields become separable because they map to different p quadrants according to their dips this allows either wave field to be reconstructed by application of the inverse radon transform after windowing in the p plane results obtained by the radon transform wave field separation rtws method are similar to those obtained by f k velocity filtering however by implementing an amplitude ratio testing filter in the forward slant stack the quality of the reconstructed wave field is much improved for a specific range of p stack values in the forward transform this filter sorts and removes the unwanted events from the desired ones by testing their consistency

elastic imaging and time lapse migration based on adjoint methods we have drawn connections between imaging in exploration seismology adjoint methods and emerging finite frequency tomography all of these techniques rely on spatial and temporal constructive interference between observed and simulated waveforms to map locations of structural anomalies modern numerical methods and computers have facilitated the accurate and efficient simulation of 3d acoustic an elastic and poroelastic wave propagation using a 2d cross section of the seg eage salt model we have determined how such waveform simulations might be harnessed to improve onshore and offshore seismic imaging strategies and capabilities we have found that the density sensitivity kernel in adjoint tomography is related closely to the imaging principle in exploration seismology and that in elastic modeling the impedance kernel actually is a better diagnostic tool for reflector identification the shear and compressional wave speed sensitivity kernels in adjoint tomography are related closely to finite frequency banana doughnut kernels and these kernels are well suited for mapping larger scale structure i e for transmission tomography these ideas have been substantiated by addressing problems in subsalt time lapse migration

jarosite argon diffusion and dating aqueous mineralization on earth and mars abstract jarosite 40 ar 39 ar ages can be used to date surface processes such as weathering and environmental transitions i e aridification on earth and mars to better interpret jarosite ages from a thermochronological perspective the diffusion kinetics of argon in jarosite were determined incremental fractional loss measurements indicate an activation energy e of 37 8 1 5 kcal mol and a log d o a 2 of 5 68 0 63 s 1 corresponding to a closure temperature of 143 28 c assuming a cooling rate 100 c ma downward extrapolation of these parameters to martian surface temperatures 22 c predicts 40 ar 39 ar age spectra using the least retentive e d o a 2 pairs predict that if held at 22 c or less for 4 0 ga supergene jarosite would preserve original growth ages manifest as plateau ages consisting of 95 of the gas release because of its susceptibility to mineralogical breakdown 40 ar 39 ar ages on preserved martian jarosite will reflect the time since water was present at a location that has since undergone aridification and remained hydrologically inactive and thermally quiescent

observations of high frequency harmonic tremor in fogo cape verde islands abstract we report observations of high frequency hf volcanic tremor with spectral peaks in the band 5 20 hz recorded in fogo island cape verde archipelago several occurrences are characterized by regularly spaced spectral peaks but the fundamental frequency is missing the signal is strong enough to be weakly detected on the southern islands of the archipelago at distances of 20 80 and 120 km from fogo this widespread detection of the hf tremor suggests that the propagation of the energy is made as t waves propagating in the ocean sound channel after correcting for site effects the spatial pattern of amplitudes in fogo and brava islands clearly indicates an offshore source active seamounts recently discovered in the vicinity of fogo and brava islands hansteen t h grevemeyer i hanel k kraus g schneider j masson d g le bas t faria b 2006 seamounts at the cape verde islands the geosphere hydrosphere biosphere connection seamount biogeosciences network workshop volume la jolla march 24 25 2006 27 29 are proposed to be the source of the hf tremor

a plane wave decomposition for elastic wave fields applied to the separation of p waves and s waves in vector seismic data we describe a method to decompose a two dimensional 2 d elastic wave field recorded along a line into its longitudinal and transverse parts that is into compressional p waves and shear s waves separation of the data into p waves and s waves is useful when analyzing vector seismic measurements along surface lines or in boreholes the method described is based on a plane wave expansion for elastic wave fields and is illustrated with a synthetic example of an offset vertical seismic profile vsp in a layered elastic medium

fresnel volume migration of multicomponent data if the aperture of a seismic reflection experiment is strongly limited kirchhoff migration suffers from strong artifacts attributable to incomplete summation this can be overcome by restricting the migration operator to the region that physically contributes to a reflection event examples of such limited aperture experiments include data acquisition in boreholes tunnels and mines we present an extension to three component 3c kirchhoff prestack depth migration where the migration operator is restricted to the fresnel volume of the specular reflected raypath we use the measured polarization direction at a 3c receiver to determine points of specular reflection in homogeneous media the polarization angle of 3c data can be used directly to decide whether a certain image point belongs to the fresnel volume of a specular reflection in heterogeneous media the fresnel volume around an image point is approximated by means of paraxial ray tracing the method is tested on a synthetic vertical seismic profiling experiment with strongly limited aperture migration artifacts and crosstalk effects from converted waves are strongly reduced compared with standard migration schemes the method is successfully applied to seismic data acquired in a tunnel

a study of the application of vsp to exploration ahead of a tunnel the vertical seismic profiling technique vsp was applied to the exploration ahead of a railway tunnel near ingolstadt germany before processing the field data the potential of vsp under the geometrical constraints of a tunnel is demonstrated with synthetic data the field test comprised two receiver sections with four receivers each in radially drilled boreholes the seismic waves were generated by blasting at the tunnel face despite the unfavourable geology very inhomogeneously weathered rock with no large scale discontinuities the most prominent geological feature a transition to better rock quality could be identified 40 m ahead of the tunnel face as an item for further improvement we discuss the ambiguous determination of the static corrections and the velocity field

sub basalt decoupled walkaway vsp imaging walkaway vertical seismic profile vsp data acquired in basalt covered areas can be used to improve knowledge of the sub basalt structure a synthetic example and a case study from the north atlantic uk show that elastic two way downward continuation migration combined with the stationary phase principle is well suited to the processing of vsp data vector data are processed using decoupled elastic migration algorithms in both isotropic and anisotropic media to illustrate the value of decoupled imaging equations conventional pp imaging is carried out on the enhanced vsp data and compared with the decoupled scheme decoupled vector migration operates directly on the displacement vector and uses various wave modes downgoing waves are migrated to image basalt lava flows and measure their anisotropy upgoing waves are used for high resolution sub basalt imaging

separation of p and s waves in combined p and sv observations with vertical and in line horizontal geophones recognition and separation of the individual p and s arrivals may form a considerable problem due to the geophone receiving characteristics p and s waves are observed on both horizontal and vertical geophones a new method of separating p and s waves is presented that inverts the geophone records for the receiving characteristics thereby separating the two wavetypes the filter coefficients are determined from the near surface p and s wave velocity and from the geometry of the geophone groups the p s separation filter was tested on synthetic data with good results even ps and sp converted reflections which are completely coinciding for horizontal reflectors could be well separated the filter appears to be stable and to have low sensitivity to noise in the data or to errors in the near surface p and s wave velocity the filter is superior to other separation methods which were applied to the same dataset for comparison this method can also be applied to vsp data

vertical seismic profiling vertical seismic profiling is one of the rapidly developing areas of geophysical technology for exploring in mature basins the measurement basically involves recording the total upgoing and downgoing seismic wave fields propagating through a stratigraphic section by means of geophones clamped to the wall of a drilled well

reflection seismic imaging and physical properties of base metal and associated iron deposits in the bathurst mining camp new brunswick canada the bathurst mining camp northern new brunswick canada is a major base metal producing region that includes the brunswick no 12 and smaller past producing brunswick no 6 deposit sustaining mining activity in the camp requires exploration of orebodies near and adjacent to existing mines in this paper we recovered re processed modeled and interpreted a 2d high resolution reflection seismic profile in the vicinity of the brunswick no 6 open pit with the aim of providing key information on the geological structures associated with mineral deposits at depth the seismic data quality is good to excellent with numerous strong reflections in raw shot gathers resulting from a careful survey design that included test shots and a priori considerations for the geological environment physical properties of lithological units and mineralized zones including gamma gamma conductivity magnetic susceptibility density and sonic data were studied from borehole geophysical measurements conducted near the mine this helped to correlate seismic data and shows that the brunswick horizon a key ore prospecting horizon and associated lithological contacts are strongly reflective the results demonstrate that reflection seismic imaging has been particularly effective for imaging steeply dipping structures of the brunswick no 6 deposit many of which intersect the surface and thus allow for correlation with surface geology massive sulfides and iron formation of the brunswick horizon are identifiable locally within a distinctive reflective package that can be used as a broad guide in the region for the exploration of deep base metal deposits in several locations a change from highly reflective to semi transparent seismic character is explained by the presence of faults that juxtapose highly reflective lithological units with seismically transparent lithologies