an integrated geophysical approach for water infiltration detection and characterization at monte cotugno rock fill dam southern italy abstract this study concerns with an integrated geophysical approach for the detection and spatial temporal characterization of the water infiltration into the monte cotugno dam embankment this strategic civil infrastructure is the largest rock fill dam in europe and represents the nodal point of the water system feeding the basilicata puglia and calabria regions southern italy here we propose an approach based on the combination of geophysical techniques as ground penetrating radar gpr and electrical resistivity tomography ert with thermal infrared mapping tir and geotechnical in situ measurements such an approach was applied for the diagnosis of the monte cotugno dam with the aim both to gain information about the geometry of visible micro fractures in the dam coverage and have a rapid mapping of the dam inner areas affected by water infiltration phenomena the sensing methods were deployed in a cascade modality where the thermal infrared tir method was used for surveying the dam along the overall length in order to achieve information about the dam coverage status in particular tir analysis allowed us to identify five areas affected by significant fractures and coating detachment afterwards gpr surveys were performed on the sloping side of the dam by investigating few areas among those identified by tir analysis in this way it was possible to get indications whether the water infiltration affected the deeper parts of the dam lastly electrical resistivity tomography ert method was applied in order to detect deeper inner areas affected by water leakages finally a joint interpretation of the three sensing methods was confirmed by shallow boreholes

investigation of upper mantle discontinuity structure beneath the central pacific using ss precursors 1 using a high quality broadband seismic data set of precursors to the phase ss we investigate the structure of upper mantle discontinuities beneath the central pacific including the hawaiian hot spot we image structure by stacking over 4000 records into geographic bins retaining periods down to 5 s we consider the effects of correcting for four separate tomographic models of mantle heterogeneity excluding data at distances containing phases that potentially interfere with precursors we find evidence for peak to peak topography of 15 20 km on the 670 km discontinuity and 7 28 km of topography on the 400 km discontinuity weak reflections are detected from discontinuities near 220 and 520 km depth the average transition zone thickness beneath our region is approximately 242 3 km very similar to previous estimates of the global average lateral transition zone thinning and thickening weakly correlate with reduced and increased transition zone shear velocity respectively consistent with a thermal origin to topographical variations on the discontinuities within our study region the transition zone beneath hawaii and to the east of the line island chain is thinned by up to 20 km in a province spanning nearly 1000 km suggesting an excess mantle temperature of 200 k in the oldest crustal regions of our study area 100 ma the 400 km discontinuity is relatively shallow and the transition zone is relatively thick 250 255 km a possible explanation for this pattern includes small scale convection in the upper mantle bringing colder material into the transition zone

low frequency vibroseis data with maximum displacement sweeps several recent advances in land seismic acquisition equipment and processing algorithms have encouraged exploration geophysicists to reconsider the potential benefits of energetic low frequencies for geophysical applications imaging beneath high velocity and highly absorbing formations deep imaging acoustic impedance inversion velocity model estimation in geophysically complex areas and inversion of surface waves to characterize near surface elastic properties

tracking slabs beneath northwestern pacific subduction zones article i nfo article history this study uses the amplitudes of bottom side reflected shear waves to constrain the morphology and dynam ics of subducted oceanic lithosphere beneath northwestern pacific subduction zones across honshu arc the 410 and 660 km seismic discontinuities are detected at the respective depths of 395 5 and 685 5 km within the wadati benioff zone their topographies are negatively correlated along slab dip showing the dominant effect of temperature on the olivine phase changes within the upper mantle transition zone the base of the upper mantle shows broad depressions as well as localized zones of shallow average depths be neath korea and northeast china the 15 km peak to peak topography west of the wadati benioff zones suggests that the stagnant part of the subducted pacific plate is not as flat as previously suggested eastward slab pile up is also possible at the base of the upper mantle across southern kuril arc the shear wave reflec tion coefficients of major olivine phase boundaries fall below 5 within the wadati benioff zone the appar ent reflection gaps and the spatial connection between a strong reflector at 900 km depth may imply 1 possible compositional variations at the top and bottom of the transition zone and 2 substantial mass heat flux across the 660 km seismic discontinuity we also identify strong reflectors within the subducted oceanic lithosphere at mid transition zone depths the depths and strengths of these reflectors are highly variable be tween honshu and southern kuril islands

do double ss precursors mean double discontinuities summary stacks of ss precursors have been widely used in the past two decades to investigate the existence and characteristics of upper mantle discontinuities on a global scale as well as in several regional cases here we present observations of ss precursors from an mb 6 7 earthquake recorded at the us transportable array in 2010 in this particular case the s660s precursors on the transverse component are strong enough to be identified on individual seismograms across the array without any stacking procedures two s660s precursors are observed seeming to suggest double discontinuities around 660 km depth in the bounce point region through careful analysis of 1 d and 3 d synthetic seismograms we however discover that although they have arrival times and slownesses that are very close to the theoretical values of ss precursors the apparent double precursors are artefacts because of mantle heterogeneity in the upper mantle near the receivers away from the bounce point region this suggests that caution must be taken about appropriate azimuthal coverage at the ss bounce point before interpreting double ss or pp precursors in terms of complex mineralogical transitions

near real time simulations of global cmt earthquakes summary we have developed a near real time system for the simulation of global earthquakes prompted by a trigger from the global centroid moment tensor cmt project the system automatically calculates normal mode synthetic seismograms for the preliminary reference earth model and spectral element synthetic seismograms for 3 d mantle model s362ani in combination with crustal model crust2 0 the 1 d and 3 d synthetics for more than 1800 seismographic stations operated by members of the international federation of digital seismograph networks are made available via the internet global shakemovie princeton edu and the incorporated research institutions for seismology data management center iris iris edu the record length of the synthetics is 100 min for cmt events with magnitudes less than 7 5 capturing r1 and g1 at all epicentral distances and 200 min for cmt events with magnitudes equal to or greater than 7 5 capturing r2 and g2 the mode simulations are accurate at periods of 8 s and longer whereas the spectral element simulations are accurate between periods from 17 to 500 s the spectral element software incorporates a number of recent improvements for example the mesh honours the moho as a first order discontinuity underneath the oceans and continents and the performance of the solver is enhanced by reducing processor cache misses and optimizing matrix matrix multiplication in addition to synthetic seismograms the system produces a number of earthquake animations as well as various record sections comparing simulated and observed seismograms

quantitative application of poststack acoustic impedance inversion to subsalt reservoir development the cost and complexity of deep water subsalt development wells is so great that a very limited spatial sampling of the target reservoir is achievable with well data thus the quantitative use of seismic data becomes of paramount importance poststack seismic amplitude inversion and poststack seismic attribute analysis and modeling are frequently employed to perform quantitative prediction of reservoir properties from surface seismic data several authors have shown that both absolute and relative acoustic impedance aai and rai respectively derived from poststack seismic amplitude inversion can be useful for quantitative estimates of summary reservoir properties such as average porosity net to gross and others this includes suprasalt and minibasin clastic reservoirs typically encountered in the middle and lower tertiary plays in the deep water gulf of mexico several of which are also encountered subsalt where depth to target can exceed 9000 m and highest frequencies at target are often rather l

imaging the upper mantle transition zone with a generalized radon transform of ss precursors we demonstrate the feasibility of using inverse scattering for high resolution imaging of discontinuities in the upper mantle beneath oceanic regions far from sources and receivers using broadband wavefield observations consisting of ss and its precursors the generalized radon transform grt that we developed for this purpose detects in the broadband data signals due to scattering from elasticity contrasts in earth s mantle synthetic tests with realistic source receiver distributions demonstrate that the grt is able to detect and image deep mantle interfaces even in the presence of noise depth phases ghosts phase conversions and multiples generated by reverberation within the transition zone as a proof of concept we apply the grt to 50 000 broadband seismograms to delineate interfaces in the depth range from 300 to 1000 km beneath the northwest pacific we account for smooth 3d mantle heterogeneity using first order perturbation theory and independently obtained global tomography models the preliminary results reveal laterally continuous but undulating scatter zones near 410 and 660 km depth and a weaker broader and more complex structure near 520 km depth the images also suggest the presence of multiple laterally intermittent interfaces near 350 km and between 800 and 1000 km depth that is above and below the transition zone sensu stricto filtering of the data we consider four pass bands 20 50 s 10 50 s 5 50 s and 2 50 s reveals a prominent frequency dependence of the magnitude width and complexity of the interfaces in particular of the scatter zone near 520 km depth such dependencies may put important constraints on the mineralogy and phase chemistry of the transition zone

facies and porosity 3d models constrained by stochastic seismic inversion to delineate paleocene fluvial lacustrine reservoirs in melut rift basin sudan abstract the paleocene sandstones of the yabus and samma formations are the main oil reservoirs in the melut rift basin of interior sudan in our study area we implemented a multi modeling approach to reveal heterogeneity and reservoir characteristics of this sandstone it estimates acoustic impedance from seismic data using deterministic and stochastic inversion algorithms we integrated petrophysical and geostatistical analyses of the well logs to produce facies and porosity 3d models the study populated and evaluated three different porosity models one from well logs only a second from well logs constrained by inversion results and a third from well logs constrained by inversion results and facies stochastic inversion reveals a significant vertical facies heterogeneity as less as two meters in yabus sandstone this heterogeneity is a lithology dependent and facies distribution is structurally controlled by major faults that developed during the third rift phase the geostatistical integration of seismic inversion sedimentologic and stratigraphic analyses reveal lateral facies distribution in the study area the significant correlation between facies distribution and porosity allows reliable mapping of thin sandbodies the facies and porosity 3d models indicate vertically stacked channels with isolated sandbodies in yabus sandstone this strongly suggests a meandering origin for this sandstone however the thick sandbodies observed in samma formation might indicate a braided channel setting the dominant claystone and mudstone facies deposited in melut formation indicate a shallow lacustrine setting the reservoir quality decreases with depth from the paleocene yabus and samma formations at the top towards the cretaceous melut formation at the bottom the porosity estimates support this conclusion as detected low porosity as less as 5 in melut formation with respect to higher porosity as high as 25 in yabus and samma formations the facies and porosity 3d models enhanced our understanding in predicting the reservoir heterogeneity quality and architecture of this sandstone

linearized avo and poroelasticity the technique of amplitude variation with offset avo allows geoscientists to extract fluid and lithology information from the analysis of prestack seismic amplitudes various avo parameterizations exist all of which involve the sum of three weighted elastic constant terms in present day avo approaches the weighting terms involve either knowledge of the incidence angle only or knowledge of both the incidence angle and the in situ vp vs ratio we have used the theory of poroelasticity to derive a generalized avo approximation that provides the estimation of fluid rigidity and density parameters we have combined two previously independent avo formulations thus reducing instead of adding to the total number of formulations this new approach requires knowledge of a third parameter to compute the weights the dry rock vp vs ratio we have derived a new equation and applied it to model and real data sets the new formulation has allowed us to estimate fluid properties of the reservoir in a more dire

multiparameter waveform inversion of a large wide azimuth low frequency land data set in oman abstractseveral 3d seismic acoustic full waveform inversions fwis of offshore data sets have been reported over the last five years a successful updating of the long to intermediate wavelengths of the earth model by fwi requires good quality wide angle long offset low frequency data recent improvements in acquisition make such data sets available on land too we evaluated a 3d application on a data set recorded in north oman the data contain low frequencies down to 1 5 hz long offsets and wide azimuths the application of acoustic fwi on land remains complicated because of the elastic effects notably the strong ground roll and many acquisition and human activity related noises the presence of fast carbonate layers in this region induces velocity inversions difficult to recover from diving or postcritical waves we accounted for anisotropic effects as we include fwi in a classical structural imaging workflow with a dedicated processing of the data and a simultaneous inversion of the nmo veloc

desiccation of a sensitive clay field experimental observations an excavation with three different levels was exposed to continuous evaporation during 35 days in order to observe and document the formation of shrinkage cracks in an intact and weathered sensitive marine clay desiccation of the intact saint alban clay under restrained conditions at an average evaporation rate of 0 018 cm h and an initial moisture content of 103 produced visible primary cracks after 17 h with an average spacing of 20 to 24 cm secondary cracks within each original polygon appeared after about 70 h of evaporation subhorizontal cracks at a depth of 6 to 8 cm were also created owing to differential strains induced by differential shrinkage of the soil polygons further evaporation resulted in the formation of a new set of vertical cracks after about 150 h of evaporation in the soil below the subhorizontal shear plane the shrinkage induced volume change associated with these different sets of cracks produced polygons with a protuberance at their bottom part indicating that the depth of crack propagation below the subhorizontal shear plane was about 3 to 4 cm in weathered clay at an initial moisture content of about 50 the average spacing was 10 to 12 cm indicating that spacing between primary cracks is related to soil type in the cohesionless topsoil no cracks were observed

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

seismic inversion as a predictive tool for porosity and facies delineation in paleocene fluvial lacustrine reservoirs melut basin sudan abstract the melut basin is a rift basin in the interior sudan linked to the mesozoic cenozoic central and western african rift system the paleocene yabus formation is the main reservoir deposited in heterogeneous fluvial lacustrine environment delineation of channel sandstone from shale is a challenge in reservoir exploration and development we demonstrate a detailed 3d quantitative seismic interpretation approach that integrates petrophysical properties derived from well logs analysis a porosity transform of acoustic impedance inversion provided a link between elastic and rock properties thus we used seismic porosity to discriminate between different facies with appropriate validation by well logs at the basin scale the results revealed lateral and vertical facies heterogeneity in the melut basin good reservoir quality is observed in the paleocene yabus formation the sand facies indicated high porosity 20 corresponding to low acoustic impedance 20000 24000 g ft cm3 s however lower quality reservoir is observed in the cretaceous melut formation the porosity of sand shale facies is low 5 corresponding to high acoustic impedance 29000 34000 g ft cm3 s this suggests that the yabus sandstone is potentially forming a better reservoir quality than melut formation at the reservoir scale we evaluated the facies quality of yabus formation subsequences using petrophysical analysis the subsequences yb1 to yb3 yb4 to yb7 and yb8 to yb10 showed relatively similar linear regressions respectively the subsequence of yb4 to yb7 is considered the best reservoir with higher porosity 25 however subsequence yb1 to yb3 showed lower reservoir quality with higher shale volume 30 this attributed to floodplain shale deposits in this subsequence similarly the high porosity 20 recognized in deeper subsequences yb6 to yb9 is due to clean sand facies we learnt a lesson that appropriate seismic preconditioning exhaustive petrophysical analysis and well log validation are important keys for improved reservoir quality prediction results in fluvial lacustrine basins

garnet and pyroxenes in the mantle a test of the majorite fractionation hypothesis experimental data are reported for the compositions of garnets and pyroxenes that coexist with liquid in the system cao mgo al2o3 sio2 cmas at 80 160 kbar all experiments were run using the uniaxial split sphere apparatus at stony brook our data have permitted a refinement of gasparik s 1990a thermodynamic analysis of garnets and pyroxenes that occur at arid below the solidus our results should provide precise estimates of the temperature pressure conditions at which peridotite and garnet xenoliths equilibrated in the mantle an examination is also made of the composition of garnet that crystallizes as a liquidus phase it is demonstrated to be a function of both composition and pressure pressure has the effect of changing the composition of garnet from pyropic at around 80 kilobars to pyroxene like majorite at pressures in excess of 140 kbar changes that mirror those seen for garnets in the subsolidus failure to consider the effects of pressure on the composition of liquidus garnet can result in an erroneous test of the hypothesis that garnet fractionation occurred in early earth history it is shown that primitive mantle peridotite could have formed as a liquid by 35 majorite garnet fractionation from a cv chondrite like allende at 200 260 kbar these results support the hypothesis that extensive or possibly total melting occurred during the growth of the earth by accretion of planetesimals e g davies 1985 abe and matsui 1985 stevenson 1987 wetherill 1990 and that majorite fractionation could have occurred during this time ohtani and sawamoto 1987 removal of majorite to the lower mantle during the crystallization of a magma ocean is a successful way of explaining differences in mgo sio2 and cao al2o3 between mantle peridotite and chondrite

reservoir lithology classification based on seismic inversion results by hidden markov models applying prior geological information abstract hidden markov models hmms have been applied to predict reservoir lithologies using seismic inversion results as inputs this approach takes into account the conditional probabilities between different lithologies i e the vertical transitions in sedimentary sequences these properties are used as prior geological information in order to relate the seismic inversion results to the true well log data hmms need to be trained based on the expectation maximization theory application of the resulting model on a synthetic example from the book cliffs utah usa showed that most lithologies are classified correctly even for some thin layers a comparison with point wise methods in which data samples are treated independently from each other such as k means and fuzzy logic classifiers leads to the conclusion that the spatial correlation in hmms allows better lithological predictions because the prior information accounts for the geological depositional processes a real case study with data from the vienna basin austria is performed in which lithologies in a 3d cube are obtained based on properties from seismic inversions via trained hmms while the vertical sequences are shown to be reasonably well predicted the horizontal continuities are not this indicates that the future research should focus on the lateral geological relationships

stress induced seismic azimuthal anisotropy in the upper crust across the north west shelf australia seismic azimuthal anisotropy saa is observed in many areas of the earth and fast polarized directions have been mapped using earthquake surface waves and teleseismic s wave splitting over large regional and tectonic scales higher resolution petroleum exploration data including 3 d seismic surveys and dipole shear logs often exhibit azimuthal anisotropy however we are unaware of any published studies mapping saa from exploration scale data to study large scale regional and tectonic saa trends the physical mechanisms causing saa in earthquake data are a subject of great interest comparing regional trends to the higher resolution exploration trends may help understand these mechanisms we present a saa analysis using seismic exploration data across the north west shelf nws of australia we map the fast polarization directions from 34 dipole shear logs and two 3 d seismic surveys and compare them to in situ maximum horizontal stress orientations h our results show that the and h trends correlate across a geographical area spanning almost 2000 km and are similar to published results in the region from earthquake seismology these results suggest that differential horizontal stress is the likely mechanism causing saa at a wide range of spatial scales on the nws of australia we also show that saa is not observed at exploration scales in some areas of the nws and propose a lithology dependent stress sensitivity model in which saa is strongest in clean unconsolidated quartz dominated sandstones and weaker or nonexistent in well consolidated cemented rocks and shale dominated sediments

mantle layering from scs reverberations 2 the transition zone this is the second paper in a four part sequence that examines the nature of mantle layering using the scsn phases and internal reflections observed within the reverberative interval of sh polarized seismograms mantle reflectivity profiles for 18 seismic corridors sampling portions of indonesia australia and the western and central pacific are constructed from low frequency 25 mhz scs reverberations i e scsn type phases reflected once from internal mantle discontinuities modeling the reflectivity profiles using synthetic seismograms yields precise path specific estimates of the travel times to the 410 km and 660 km discontinuities and their reflection coefficients the data are consistent with an olivine dominated model of the transition zone marked by two major phase transitions having average apparent depths of 414 2 km and 660 2 km and impedance contrasts of 0 046 0 010 and 0 072 0 010 respectively the interpath variations observed in the reverberation travel times imply that the topography on the two discontinuities is of the order of 20 km peak to peak and is negatively correlated consistent with an endothermic transition at 660 km whose clapeyron slope magnitude is comparable to that of the 410 km exothermic transition in the case of the 660 km discontinuity we have been able to supplement these long wavelength 1500 5000 km observations with an estimate of intrapath topography inferred from the frequency dependence of the 660 km reflection coefficient which gives peak to peak variations less than 40 km on scale lengths of 500 1500 km for the 660 km discontinuity the observed topography is significantly less than the dynamic topography expected for a simple compositional interface in regions of subduction however we do observed an intriguing negative correlation between the apparent depth and the reflection coefficient of the 660 km discontinuity which may involve small compositional variations plausible explanations for this correlation include heating of an initially cool chemical boundary layer gravitationally trapped above an endothermic phase transition loss of reflected energy due to local curvature or roughness of the reflector and or extreme topography occurring on a small compositional component to the discontinuity 40 of the total impedance contrast by stripping the 410 km and 660 km peaks from the composite path reflectivity profile we identify three minor reflectors at mean depths of 520 710 and 900 km the shallowest may mark the phase spinel phase transition the 710 km discontinuity can be attributed to the ilmenite gamet perovskite phase transition although changes in perovskite symmetry can potentially provide explanations for both the 710 km and 900 km features

gpr detection of several common subsurface voids inside dikes and dams ground penetrating radar gpr technique has been used in detecting several common subsurface voids inside dikes and dams in south of china and the results indicate that gpr can be successfully applied to uncovering termite nests inside dikes and dams and the technique proves to be advantageous in real time retrieval of detection data precise positioning and effect of application being basically not affected by locality and climate when it is compared to other available methods gpr is also effective in detecting cracks in the sloping clay core and proves to pose less impact on the normal operation of the detected hydraulic projects be more efficient and capable of retrieving more comprehensive detection data when compared with the method of artificial observation through holes chiseled out from the ground also gpr is capable of detecting ferralsol in tropical and subtropical regions to some depth and shows high value of application in detecting some hidden troubles such as caves and settlements with low to moderate depths inside dams in karst regions moreover gpr technique proves to be so capable of detecting carbonate rocks to certain depth and can yield precise results that it can be applied to analysis and discovery of leakage channels inside reservoirs in karst regions

determination and analysis of long wavelength transition zone structure using ss precursors summary global mapping of 410 and 660 km discontinuity topography and transition zone thickness has proven to be a powerful tool for constraining mantle chemistry dynamics and mineralogy numerous seismic and mineral physics studies suggest that the 410 km discontinuity results from the phase change of olivine to wadsleyite and the 660 km discontinuity results from the phase change of ringwoodite to perovskite and magnesiowustite underside reflections of the 410 and 660 km discontinuities arrive as precursors to ss with the recent development of a semi automated method of determining ss arrivals we have more than tripled the flanagan and shearer 1998a data set of handpicked ss waveforms we are able to increase resolution by stacking waveforms in 5 rather than 10 radius bins as well as increasing data coverage significantly in the southern hemisphere the resulting ss s410s and ss s660s times are heavily influenced by upper mantle velocity structure we perform a joint inversion for discontinuity topography and velocity heterogeneity as well as performing a simple velocity correction to the precursor differential times and find little difference between the two methods the 660 km discontinuity topography and transition zone thickness are correlated with velocities in the transition zone whereas the 410 km discontinuity topography is not in addition the 410 km discontinuity topography is not correlated with the 660 km discontinuity topography rather anticorrelated as expected due to the opposite signs of the clapeyron slopes of their respective phase changes these results suggest that whereas the topography of 660 km discontinuity could be dominated by thermal effects the topography of the 410 km discontinuity is likely dominated by compositional effects in addition unlike previous studies which find less topography on the 410 km discontinuity than on the 660 km discontinuity our 410 and 660 km topography have similar amplitudes

column on column structures as indicators of lava ice interaction ruapehu andesite volcano new zealand abstract lava flows of the mangawhero formation ca 15 60 ka on ruapehu volcano erupted during the last glaciation in a distal flow lobe at tukino on the east side of the mountain small secondary columns 10 20 cm thick have formed on the sides of large rectangular primary 0 5 3 m thick cooling columns thick 10 m zones of such small columns form a lateral and basal outer rind of the lobe as they do not mark glassy zones of quenching these secondary columns are interpreted as being formed by a second cooling event at temperatures below the boundary between the low creep and elastic regimes 600 c by rapid influx of copious amounts of water temperature drops deduced from extensional strains of the two sets of columns were used to gauge the viability of such a two stage process absence of reliable data on andesite contraction coefficients was overcome by using a sliding scale to assess a large range of values the estimates indicate that two stage chilling is feasible after flowing across relatively ice poor terrain the lava flow must have interacted with a valley glacier that provided water for further chilling the already formed primary columns and formation of the outer rind small columns given this evidence for lava ice interaction it is likely that prominent thick flows elsewhere in the mangawhero formation may have been constrained to their ridge top locations by ice conditions similar to those described by lescinsky and sisson lescinsky d t sisson t w 1998 ridge forming ice bounded lava flows at mount rainier washington geology 26 351 354

oceanic plateau of the hawaiian mantle plume head subducted to the uppermost lower mantle the hawaiian emperor seamount chain that includes the hawaiian volcanoes was created by the hawaiian mantle plume although the mantle plume hypothesis predicts an oceanic plateau produced by massive decompression melting during the initiation stage of the hawaiian hot spot the fate of this plateau is unclear we discovered a megameter scale portion of thickened oceanic crust in the uppermost lower mantle west of the sea of okhotsk by stacking seismic waveforms of ss precursors we propose that this thick crust represents a major part of the oceanic plateau that was created by the hawaiian plume head 100 million years ago and subducted 20 million to 30 million years ago our discovery provides temporal and spatial clues of the early history of the hawaiian plume for future plate reconstructions

fused spectral decomposition seismic attributes and forward seismic modelling to predict sand bodies in meandering fluvial reservoirs abstract understanding the hierarchical architectural elements of fluvial sand bodies is important for planning their development strategy and to enhance oil recovery red green blue rgb blending of multiple seismic attributes and forwarding seismic modelling are commonly used in the analysis of compound sand bodies however rgb blending of multiple seismic attributes can only qualitatively describe the boundaries and thickness of sand bodies the forward seismic modelling techniques previously documented in the literature are not effective when depicting the geometry of and stacking relationships between sand bodies i e reservoir compartmentalisation hence we propose in this work a new workflow that combines fused spectral decomposition seismic attributes sdsas and forwarding seismic modelling to quantitatively predict sand thickness and to characterise stacking relationships between sand bodies first we employ a support vector machine svm algorithm to fuse high middle and low frequency components attributes of seismic data so as to quantitatively predict the thickness of sand bodies second we define the seismic waveform response patterns corresponding to the typical conceptual stacked sand bodies with the constraints of waveform patterns and predicted sand thickness fused sdsas the geometry and stacking relationships of the sand bodies are characterised by forward seismic modelling to illustrate the effectiveness of our proposed workflow we apply it to the neogene minghuazhen formation nm of the qhd 32 6 oil field bohai bay basin china we define five architectural elements of a meandering fluvial reservoir by analysing the hierarchy of sand bodies using our workflow the predicted sand bodies in this workflow were further proven by horizontal drilling and production data

study of the lithospheric and upper mantle discontinuities beneath eastern asia by ss precursors summary we analyse broad bandss waveform data recorded by several networks in europe with sources mainly in the west pacific to study the underside reflections of teleseismic ss waves in the lithosphere and the upper mantle beneath eastern asia and the nw pacific ocean ss bounce points sample a corridor from the aleutian kamchatka and japan subduction zones through the north china craton and central asian orogenic belt to the tibetan plateau the corridor passes through different tectonic units such as subduction zones an old continental shield a fold belt and a high plateau we investigate the seismic structure of the lithosphere and the mantle transition zone beneath the different geotectonic units along the profile and infer the correlation of geodynamic processes at different depths we explore the short period frequency content in the ss waveform data and use moveout correction and common midpoint stack to acquire profiles with high lateral and depth resolution from the crust to the mantle transition zone clear ss precursors of the 410 and 660 km discontinuities show the effects of the interaction between the subducted oceanic lithosphere and the mantle transition zone beneath the nw pacific subduction zones a low velocity layer has also been detected beneath the 410 km discontinuity and can be traced along the entire profile due to the improved resolution acquired by the method presented here we have been able to study the shallower structures such as the moho and the lithosphere asthenosphere boundary by ss precursors the continental moho can be clearly seen along this corridor the depth variation agrees well with earlier receiver function results we also see negative reflectors along the profile at varying depths which can be interpreted as the lithosphere asthenosphere boundary

seismic imaging of transition zone discontinuities suggests hot mantle west of hawaii the hawaiian hotspot is often attributed to hot material rising from depth in the mantle but efforts to detect a thermal plume seismically have been inconclusive to investigate pertinent thermal anomalies we imaged with inverse scattering of ss waves the depths to seismic discontinuities below the central pacific which we explain with olivine and garnet transitions in a pyrolitic mantle the presence of an 800 to 2000 kilometer wide thermal anomaly tmax 300 to 400 kelvin deep in the transition zone west of hawaii suggests that hot material does not rise from the lower mantle through a narrow vertical plume but accumulates near the base of the transition zone before being entrained in flow toward hawaii and perhaps other islands this implies that geochemical trends in hawaiian lavas cannot constrain lower mantle domains directly

ss wave sensitivity to upper mantle structure implications for the mapping of transition zone discontinuity topographies 1 studies of the depths of the upper mantle discontinuities have relied on the differential travel times between the ss wave and its precursors we examine the effect of velocity heterogeneities on these differential travel time data ray theory which is used to correct these data for the effect of velocity heterogeneities is shown to be inaccurate if the characteristic heterogeneity length scales are similar to those seen in regional models or if the station is near the ss wave radiation nodal plane

sensitivity of ss precursors to topography on the upper mantle 660 km discontinuity the sensitivity of ss precursors to the presence of topography on the 660 km discontinuity is addressed using an axisymmetric finite difference approximation to the sh wave propagation in the earth mantle numerical experiments are lead to quantify the bias in both wavelength and amplitude committed in estimating depth information on the upper mantle discontinuities from ray inversion of sds arrival times it is further shown that long period s660s arrival times do not provide information on the deepening of the 660 in presence of a velocity increase expected as the thermal signature of a subducting slab

broadband array observations of the 300 km seismic discontinuity 1 intermittent seismic discontinuities near 250 300 km depth beneath south america and the pacific basin are detected with high resolution seismic array methods that use ss and pp precursors recorded at the high lava plains seismic experiment and the earthscope transportable array the transformation of coesite to stishovite in an eclogite rich mantle composition produces a seismic discontinuity near 300 km depth lateral changes in basalt fraction of the upper mantle will thus produce an intermittent seismic discontinuity the sensitivity of the precursors to intermittent seismic structure is addressed using an axisymmetric finite difference model of wave propagation in the mantle these numerical experiments find that the precursors are sensitive to structures 500 km in lateral extent and that the observations of this discontinuity are plausibly tied to lateral variations in basaltic composition of the upper mantle related to dynamics such as plumes and subduction

integration of knowledge based seismic inversion and sedimentological investigations for heterogeneous reservoir abstract conventional geological modelling methods are not capable to provide precise and comprehensive model of the subsurface structures when dealing with insufficient data knowledge based methods employing rule bases techniques are found vast applications in geoscience studies these methods are applicable for petroleum reservoir geological modelling and characterizations specifically for geologically complex structures in this study we present a knowledge based seismic acoustic impedance inversion method which employs rule based method for porosity estimation the back propagation algorithm and the fuzzy neural network are also used in the methodology for parameter optimization and definition of nonlinear relationship between seismic attributes and porosity of the reservoir rock the methodology initiates by seismic acoustic impedance inversion followed by conventional porosity estimation subsequently a knowledgebase was designed by investigation on more than 24 published case studies this knowledgebase was used for definition of rules and optimization number of rules and improve efficiency of the inference engine the porosity model obtained by conventional method in previous step would be used for primary evaluation of the rules the extracted rules and optimized number rules then would be used for rule based porosity estimation the methodology was applied on a petroleum field containing two heterogeneous reservoir formations result of application of the proposed approach was evaluated with core analysis thin sections and drilling data consistency of result obtained by the proposed method with geological data has shown its capability to resolve problem of insufficient data in reservoir geological modelling

multiple seismic discontinuities near the base of the transition zone in the earth s mantle the seismologically defined boundary between the transition zone in the earth s mantle 410 660 km depth and the underlying lower mantle is generally interpreted to result from the breakdown of the gamma spinel phase of olivine to magnesium perovskite and magnesiowustite laboratory measurements of these transformations of olivine have determined that the phase boundary has a negative clapeyron slope and does indeed occur near pressures corresponding to the base of the transition zone but a computational study has indicated that because of the presence of garnet minerals multiple seismic discontinuities might exist near a depth of 660 km ref 4 which would alter the simple negative correlation of changes in temperature with changes in the depth of the phase boundary in particular garnet minerals undergo exothermic transformations near this depth acting to complicate the phase relations and possibly effecting mantle convection processes in some regions here we present seismic evidence that supports the existence of such multiple transitions near a depth of 660 km beneath southern california the observations are consistent with having been generated by garnet transformations coupling with the dissociation of the gamma spinel phase of olivine temperature anomalies calculated from the imaged discontinuity depths using clapeyron slopes determined for the various transformations generally match those predicted from an independent p wave velocity model of the region

stabilizing the low frequencies acoustic and elastic impedance sections have two main uses firstly they look more like geology than traditional reflectivity data and enable us to better communicate the subsurface images to our non geoscientist colleagues e g reservoir engineers and drillers secondly inverted data can be directly calibrated to rock and fluid reservoir properties such as porosity net to gross or net pay facilitating its quantitative use

an analysis of ss precursors using spectral element method seismograms summary the traveltimes of underside shear wave reflections i e ss precursors are widely used data for mapping the topography of mantle discontinuities in the upper mantle here we examine the accuracy of ray theory in estimating the contribution of shear velocity heterogeneity in the mantle to ss s400s ss s670s and s400s s670s traveltimes we analyse stacks of spectral element method waveforms computed for 34 shallow earthquakes and 16 020 globally distributed virtual seismometers the waveforms are computed for three versions of shear velocity model s20rts with variable strengths of the volumetric shear velocity perturbations within the layered structure of the preliminary reference earth model we find that ray theoretical corrections account for only 50 per cent of the traveltime variation due to large scale velocity heterogeneity for current tomographic models as represented by s20rts this translates into unpredictable long and short wavelength errors in maps of mantle discontinuity depths of about 5 km this amounts to roughly 10 per cent of published variations in mantle discontinuity depths however relative errors will be significantly larger if ray theoretical traveltime corrections are based on forthcoming models of shear velocity with much stronger heterogeneity at the smallest scales

elastic impedance inversion of multichannel seismic data from unconsolidated sediments containing gas hydrate and free gas the elastic properties of hydrated sediments are not well known which leads to inaccuracy in the evaluation of the amount of gas hydrate worldwide elastic impedance inversion is useful in estimating the elastic properties of sediments containing gas hydrate or free gas trapped beneath the gas hydrate from angle dependent p wave reflections we reprocess the multichannel u s geological survey seismic line bt 1 from the blake ridge off the east coast of north america to obtain migrated common angle aperture data sets which are then inverted for elastic impedance two new algorithms to estimate p impedance and s impedance from the elastic impedance are developed and evaluated using well log data from ocean drilling program odp leg 164 these new algorithms are stable even in the presence of modest noise in the data the vs vp ratio poisson s ratio and lame parameter terms and are estimated from the p impedance and s impedance the hydrated sediments have high elastic impedance high p impedan

the nature of the 660 kilometer discontinuity in earth s mantle from global seismic observations of pp precursors the 660 kilometer discontinuity which separates earth s upper and lower mantle has been detected routinely on a global scale in underside reflections of precursors to ss shear waves here we report observations of this discontinuity in many different regions using precursors to compressional pp waves the apparent absence of such precursors in previous studies had posed major problems for models of mantle composition we find a complicated structure showing single and double reflections ranging in depth from 640 to 720 kilometers that requires the existence of multiple phase transitions at the base of the transition zone the results are consistent with a pyrolite mantle composition

engineering geological assessment of the proposed urus dam turkey abstract this paper describes the results of the engineering geological investigations and rock mechanics studies carried out at the proposed urus dam site analyses were carried out in terms of rock mass classifications for diversion tunnel kinematic analysis of excavation slopes permeability of the dam foundation and determination of rock mass strength parameters urus dam is a rock filled dam with upstream concrete slab the dam will be built on the suveri river in the central part of turkey the foundation rocks are volcanic rocks which consist of andesite basalt and tuff of neogene age studies were carried out both at the field and the laboratory field studies include engineering geological mapping intensive discontinuity surveying core drilling pressurized water tests and sampling for laboratory testing uniaxial triaxial and tensile strength tests were performed and deformation parameters unit weight and porosity were determined on the intact rock specimens in the laboratory rock mass strength and modulus of elasticity of rock mass are determined using the hoek brown empirical strength criterion rock mass classifications have been performed according to rmr and q systems for the diversion tunnel engineering geological assessment of the proposed dam and reservoir area indicated that there will be no foundation stability problems detailed geotechnical investigations are required for the final design of the dam

tectonostratigraphic development of the interior sudan rifts central africa abstract in the muglad melut and blue nile rift basins of interior sudan three major episodes of rifting concomitant subsidence and nonmarine nonvolcanic sedimentation are recognized these three rifting cycles which spanned 140 to 95 ma fl 95 to 65 ma f2 and 65 to 30 ma f3 resulted in the accumulation of up to 5400 4200 and 5400 m of sediments respectively in the muglad basin the best known and largest of the sudan rift basins each rifting cycle consists of 1 a basal sandstone unit at least near rift margins that is followed by 2 an upward coarsening section of lacustrine shale grading through marginal lacustrine mudstone and sandstone into fluvial mudstone and sandstone and 3 a capping blanket of fluvial and alluvial sandstone the shale dominated portions of these cycles were deposited in a closed drainage basin during active faulting the fluvial and alluvial blanket sands were deposited in an open drainage basin during the thermal sag phase following each tectonic cycle the early cretaceous f1 intracontinental rifts of interior sudan were linked to major rifts spreading centres in the proto south atlantic by the dextral wsw trending central african shear zone and to the indian ocean via the nw trending anza rift in kenya in the muglad basin f1 deformation involved high strain rates rapid syn rift crustal stretching and subsidence and the formation of deep fault bounded tensional and transtensional pull apart basins during the f2 and f3 deformations the rates of subsidence and stretching were much lower and were focused within smaller geographic areas structural elements include asymmetric half grabens and less common full grabens with central highs the three superimposed tectonic episodes resulted in the subsidence of nnw to nw trending rift sub basins this gave rise to a wide variety of normal fault geometries displacements and growth histories planar domino style and listric normal f1 fault arrays are modeled the rotated f1 basement blocks typically are asymmetric and low standing and favour ne directed growth and material transport the f2 and f3 normal faults which have both ne and sw directed polarities often are listric and decouple younger syn rift strata from older f1 rotated and locked planar basement faults palinspastic restorations and forward modeling of three regional cross sections suggest that f1 faults account for 65 80 of total crustal extension stretching factors across the interior sudan rifts vary between 1 25 and 1 40 this range is considered to be a minimum since restored sections do not cross f3 depocenters total crustal extension across the muglad plus the melut rift basins exceeds 75 km

multiresolution imaging of mantle reflectivity structure using ss and p p precursors summary knowledge of the mantle reflectivity structure is highly dependent on our ability to efficiently extract and properly interpret small seismic arrivals among the various data types and techniques long period ss pp precursors and high frequency receiver functions are routinely utilized to increase the confidence of the recovered mantle stratifications at distinct spatial scales however low resolution and a complex fresnel zone are glaring weaknesses of ss precursors while over reliance on receiver distribution is a formidable challenge for the analysis of converted waves from oceanic regions a promising high frequency alternative to receiver functions is ppprecursors which are capable of resolving mantle structures at verticalandlateralresolutionof 5and 200km respectively owingtotheirspectralcontent shallow angle of incidence and near symmetric fresnel zones this study presents a novel processing method for both ss or pp and ppprecursors based on deconvolution stacking radon transform and depth migration a suite of synthetic tests is performed to quantify the fidelity and stability of this method under different data conditions our multiresolution survey of the mantle at targeted areas near nazca south america subduction zone reveal both olivine and garnet related transitions at depths below 400km we attribute a depressed 660 to thermal variations whereas compositional variations atop the upper mantle transition zone are needed to explain the diminished or highly complex reflected scattered signals from the 410km discontinuity we also observe prominent ppreflections within the transition zone and the anomalous amplitudes near the plate boundary zone indicate a sharp 10km thick transition that likely resonates with the frequency content of ppprecursors the migration of ss precursors in this study shows no evidence of split 660 reflections but potential majorite ilmenite 590 640km and ilmenite perovskite transitions 740 750km areidentifiedbasedonsimilarlyprocessedhigh frequencyppprecursors additionalfindings of severely scattered energy in the lithosphere and distinct lower mantle reflections at 800km could be potentially important but require further verifications overall our improved imaging methods and the strong sensitivity of ppprecursors to the existence depth sharpness and strengthofreflective structuresoffersignificant futurepromisefortheunderstanding ofmantle mineralogy and dynamics

subducted lithosphere beneath the kuriles from migration of pp precursors abstract we seismically image both thermal and chemical heterogeneity of the mantle beneath the kurile subduction zone using p wave energy reflected from the underside of discontinuities arriving as precursors to the seismic phase pp we take advantage of new broadband seismic data provided by the high lava plains seismic experiment and earthscope s usarray collecting a dataset of 31 high quality sumatran earthquakes sampling beneath the kuriles we employ high resolution array analysis techniques including migration and vespagrams to identify precursory arrivals and study lateral variations in discontinuity depth sharpness and impedance of the mantle transition zone we find the 410 km boundary is at 395 km near the subducting kurile slab though the boundary is 410 425 km deep elsewhere in regions away from subduction we do not detect a laterally continuous underside reflection of p waves from the 660 km discontinuity however in the vicinity of the subducting kurile slab we detect robust p660p reflections from interfaces near 620 670 km depth signifying an increase in the impedance contrast at 660 km depth we also detect deeper reflectors down to 720 km depth beneath the kurile slab in a localized area cold aluminum depleted harzburgitic lithosphere residing at the base of the transition zone best explains the local enhancement of the 660 km discontinuity p wave impedance contrast our new discontinuity measurements support the hypothesis of cold depleted lithosphere stagnating at the 660 km discontinuity beneath the kuriles subduction zone and imply the 660 km boundary can locally impede mantle flow and produce chemical heterogeneity within the transition zone

ava inversion of the top utsira sand reflection at the sleipner field amplitude variation with angle ava inversion is performed on the top utsira sand reflector at the sleipner field north sea norway this interface is of particular interest because of the accumulation of co 2 injected from a point deeper in the utsira sand the focus is on the postmigration processing of angle gathers together with the actual inversion procedure the processing treats amplitude extraction offset to angle mapping and global scaling in detail two algorithms are used for the inversion of ava data one that assesses uncertainties and one fast least squares variant both are very suitable for this type of problem because of their covariance matrices and built in regularization in addition two three parameter approximations of the zoeppritz equations are used one is linear approximation and the other is quadratic the results show significant signals for all three elastic parameters but the substitution of brine by co 2 using gassmann s equation indicates that the contrasts in s wave

constraints on upper mantle discontinuities from observations of long period reflected and converted phases stacked images combining over 5 years of long period global digital seismograph network data reveal many phases associated with reflections and conversions from upper mantle discontinuities these images show travel time and amplitude relative to a reference phase which is aligned and normalized on all seismograms prior to stacking results obtained for p s ss and pp reference arrivals resolve numerous phases from discontinuities near 410 and 660 km while some of the stacks also show evidence for a weaker discontinuity near 520 km phases of particular interest include p and sh multiples resulting from topside reflections precursors to ss from underside reflections and p to sv converted phases these phases can be clearly seen both in the waveform stacks and in cross correlation analysis of individual seismograms travel times for these arrivals are converted to discontinuity depths relative to velocities in the preliminary reference earth model and empirical corrections are applied for the effects of lateral velocity variations in the upper mantle average apparent depths to the discontinuities for the different phases agree to within 3 km for the 410 km discontinuity to within 4 km for the 520 km discontinuity and to within 8 km for the 660 km discontinuity the best global averages are obtained from the ss precursor data which indicate discontinuities at 415 519 and 659 km discontinuity depths obtained from the p to sv converted phases at over 35 individual seismic stations exhibit variations of less than 20 km apparent depths to the 660 km discontinuity consistently show greater variability than depths to the 410 km discontinuity supporting recent laboratory results which indicate that the clapeyron slope for the 660 km discontinuity is significantly larger in magnitude than the slope for the 410 km discontinuity precursors to ss seen between 110 and 180 are particularly useful for mapping possible lateral variations in discontinuity depths since each arrival can be associated with a single underside reflection point apparent discontinuity depths computed from ss precursors for different tectonic regions agree to within about 5 km the ss precursors have especially good coverage near the subducting slabs in the northwest pacific analysis of apparent discontinuity depths in this area suggests the presence of a broad 1000 to 1500 km wide region near the slab in which the 660 km discontinuity is depressed by about 20 km measuring absolute amplitudes for these phases is difficult due to the large corrections required to compensate for the effects of incoherent stacking relative amplitude analysis suggests that the p and s wave impedance changes at 410 km are about 0 8 1 1 times the size of the changes at 660 km and that the contrasts at 520 km are between 0 3 and 0 6 of the changes at 410 km

the effect of large scale shear velocity heterogeneity on ss precursor amplitudes 1 precursors to the ss wave have been analyzed extensively to characterize seismic discontinuities in the upper mantle we examine the influence of shear velocity heterogeneity on the amplitude of underside shear wave reflections off the 410 i e s410s and 660 i e s660s discontinuities using waveform data from global seismic networks and spectral element method synthetics for four tomographic models of the crust and mantle on average the s660s ss amplitude ratio is smaller than values predicted for the preliminary reference earth model prem and tomographic models of shear velocity perturbations from prem the variation of s410s ss and s660s ss ratios determined for the 3 d models is significant its amplitude depends on the amplitude of shear velocty heterogeneity in the mantle and on the incorporated model for the crust the s410s ss and s660s ss amplitude variations are stronger in the data and do not correlate spatially with the simulated ratios it is therefore not certain that the spatial variation of s410s ss and s660s ss as expressed by cap averaging can be related to compositional heterogeneity in the mantle given the profound influence of the heterogeneous crust and mantle

towards more realistic values of elastic moduli for volcano modelling abstract the accuracy of elastic analytical solutions and numerical models widely used in volcanology to interpret surface ground deformation depends heavily on the young s modulus chosen to represent the medium the paucity of laboratory studies that provide young s moduli for volcanic rocks and studies that tackle the topic of upscaling these values to the relevant lengthscale has left volcano modellers ill equipped to select appropriate young s moduli for their models here we present a wealth of laboratory data and suggest tools widely used in geotechnics but adapted here to better suit volcanic rocks to upscale these values to the scale of a volcanic rock mass we provide the means to estimate upscaled values of young s modulus poisson s ratio shear modulus and bulk modulus for a volcanic rock mass that can be improved with laboratory measurements and or structural assessments of the studied area but do not rely on them in the absence of information we estimate upscaled values of young s modulus poisson s ratio shear modulus and bulk modulus for volcanic rock with an average porosity and an average fracture density quality to be 5 4 gpa 0 3 2 1 gpa and 4 5 gpa respectively the proposed young s modulus for a typical volcanic rock mass of 5 4 gpa is much lower than the values typically used in volcano modelling we also offer two methods to estimate depth dependent rock mass young s moduli and provide two examples using published data from boreholes within k lauea volcano usa and mt unzen japan to demonstrate how to apply our approach to real datasets it is our hope that the data and analysis presented herein will assist in the selection of elastic moduli for volcano modelling to this end we provide a microsoft excel spreadsheet containing the data and necessary equations to calculate rock mass elastic moduli that can be updated when new data become available the selection of the most appropriate elastic moduli will provide the most accurate model predictions and therefore the most reliable information regarding the unrest of a particular volcano or volcanic terrain

detecting seismic anisotropy above the 410 km discontinuity using reflection coefficients of underside reflections abstract we investigate the effect of various types of deformation mechanisms on the reflection coefficients of p and s waves underside reflections off the 410 km discontinuity to develop a diagnostic tool to detect the style of deformation at boundary layers we calculate the reflection coefficient for p and sh underside reflections using velocity perturbations resulting from aligned minerals above the 410 km discontinuity for different deformation scenarios the results show that in the case of an anisotropic olivine layer above an isotropic wadsleyite layer the p wave reflection coefficient amplitudes are only slightly influenced by the joint effect of angle of incidence and the strength of imposed deformation without any polarity reversal and for all deformation styles for the sh wave underside reflections the incidence angle for which a polarity reversal occurs changes with distance for all scenarios and in addition changes with azimuth for shear deformation scenarios these differences in amplitude and polarity patterns of reflection coefficients of different deformation geometries especially for s wave at shorter distances potentially provide a possibility to distinguish between different styles of deformation at a boundary layer we also show a first test using currently available elastic constants of anisotropic wadsleyite beneath anisotropic olivine

3 d shear wave radially and azimuthally anisotropic velocity model of the north american upper mantle summary using a combination of long period seismic waveforms and sks splitting measurements we have developed a 3 d upper mantle model sawum na2 of north america that includes isotropic shear velocity with a lateral resolution of 250 km as well as radial and azimuthal anisotropy with a lateral resolution of 500 km combining these results we infer several key features of lithosphere and asthenosphere structure a rapid change from thin 70 80 km lithosphere in the western united states wus to thick lithosphere 200 km in the central cratonic part of the continent closely follows the rocky mountain front rmf changes with depth of the fast axis direction of azimuthal anisotropy reveal the presence of two layers in the cratonic lithosphere corresponding to the fast to slow discontinuity found in receiver functions below the lithosphere azimuthal anisotropy manifests a maximum stronger in the wus than under the craton and the fast axis of anisotropy aligns with the absolute plate motion as described in the hotspot reference frame hs3 nuvel 1a in the wus this zone is confined between 70 and 150 km decreasing in strengthwithdepthfromthetop fromthermftothesanandreasfaultsystemandthejuande fuca gorda ridges this result suggests that shear associated with lithosphere asthenosphere couplingdominatesmantledeformationdowntothisdepthinthewesternpartofthecontinent the depth extent of the zone of increased azimuthal anisotropy below the cratonic lithosphere is not well resolved in our study although it is peaked around 270 km a robust result radial anisotropy is such that predominantly 1 where vsh vsv 2 under the continent and its borders down to 200 km with stronger in the bordering oceanic regions across the continent and below 200 km alternating zones of weaker and stronger radial anisotropy with predominantly 1 correlate with zones of small lateral changes in the fast axis direction of anisotropy and faster than average vs below the lab suggesting the presence of small scale convection with a wavelength of 2000 km finally in the western united states complex 3 d patterns of isotropic velocity and anisotropy reflect mantle dynamics associated with the rich tectonic history of the region

upper mantle discontinuity topography from thermal and chemical heterogeneity using high resolution stacks of precursors to the seismic phase ss we investigated seismic discontinuities associated with mineralogical phase changes approximately 410 and 660 kilometers km deep within earth beneath south america and the surrounding oceans detailed maps of phase boundary topography revealed deep 410 and 660 km discontinuities in the down dip direction of subduction inconsistent with purely isochemical olivine phase transformation in response to lowered temperatures mechanisms invoking chemical heterogeneity within the mantle transition zone were explored to explain this feature in some regions multiple reflections from the discontinuities were detected consistent with partial melt near 410 km depth and or additional phase changes near 660 km depth thus the origin of upper mantle heterogeneity has both chemical and thermal contributions and is associated with deeply rooted tectonic processes

mantle transition zone structure along a profile in the sw pacific thermal and compositional variations summary events from the south pacific recorded in the tien shan region are studied with a migration method to measure discontinuity depth along a profile between the mariana and molucca sea subduction zones deflections of the upper mantle discontinuities within and between the subduction zones are investigated using pp precursors filtered to periods of 3 to 10 s we find p wave reflections near the 410 520 and 660 km discontinuities the 410 km discontinuity is elevated in the subduction region and near the predicted depth 410 km in the average velocity region in some cases we find negative polarities of the reflection from the 410 km discontinuity which may indicate water induced melting above the olivine to wadsleyite transition the 520 km discontinuity is shallow between the two subduction zones and deepens towards the mariana backarc region this discontinuity topography may be due to detection of both the wadsleyite to ringwoodite transition in a depleted downwelling elevated region and the formation of calcium perovskite in a more fertile upwelling depressed region the 660 km discontinuity is split in the halmahera slab with one reflection each near 600 and 700 km depth consistent with a cold sinking slab and detection of phase transitions for both garnet and olivine to perovskite respectively in the region between the subduction areas we find a downward deflection of the 660 km discontinuity with short length scale 100 300 km undulations that may reflect compositional variation

petroleum geology of cretaceous tertiary rift basins in niger chad and central african republic this overview of the petroleum geology of rift basins in niger chad and central african republic car is based on exploration work by exxon and partners in the years 1969 1991 the work included 50 000 km of modern reflection seismic 53 exploration wells 1 000 000 km2 of aeromagnetic coverage and about 10 500 km of gravity profiles the results outline ten cretaceous and tertiary rift basins which constitute a major part of the west and central african rift system wcars the rift basins derive from a multiphased geologic history dating from the pan african approximately 750 550 ma to the holocene main rifting was probably caused by the stretching and subsidence of african crustal blocks during the breakup of gondwana in the early cretaceous and by r activated plate movements in the early tertiary wcars in the study area is divided into the west african rift subsystem was and the central african rift subsystem cas was basins in niger and chad are chiefly extensional and are filled by up to 13 000 m of lower cretaceous to holocene continental and marine clastics the basins contain five oil 19 43 api and two oil and gas accumulations in upper cretaceous and eocene sandstone reservoirs the hydrocarbons are sourced and sealed by upper cretaceous and eocene marine and lacustrine shales the most common structural styles and hydrocarbon traps usually are associated with normal fault blocks cas rift basins in chad and car are extensional and transtensional and are filled by up to 7500 m of chiefly lower cretaceous continental clastics the basins contain eight oil 15 39 api and one oil and gas discovery in lower and upper cretaceous sandstone reservoirs the hydrocarbons are sourced by lower cretaceous shales and sealed by interbedded lacustrine and flood plain shales structural styles range from simple fault blocks through complex flower structures the main hydrocarbon traps are in contractional anticlines geological conditions favor the discovery of potentially commercial volumes of oil in wcars basins of niger chad and car

avo inversion for a non welded interface estimating compliances of a fluid filled fracture though well known for layer boundaries the use of amplitude versus offset avo variations for non welded boundaries like fractures is not yet investigated depending on the seismic wavelength used fractures can be regarded as thin compliant zones in rocks in different scales we explore the potential of multiangle avo inversion of p p and p s reflections from a fracture to estimate fracture properties we conduct laboratory experiments to measure reflection responses of dry and wet fractures the observed p p reflections of the wet fracture and the fracture aperture are very well predicted by the non welded interface model we invert the angle dependent p p reflectivity of the fracture to estimate both normal and tangential fracture compliances the estimated value of the normal compliance is accurate and it is also possible to obtain the value of the non zero tangential compliance we find that supplementing the information of converted p s reflections in theavoinversion greatly improves the estimate of the tangential compliance the calculated compliance ratio clearly shows the existence of fluid in the fracture this finding can be crucial for new applications in a wide range of scale from earthquake seismology deep and shallow seismic exploration to non destructive material testing

geophysical benefits from an improved seismic vibrator the seismic vibrator has become a very important source for land data acquisition and there have been dramatic improvements in recent times in the application of the vibroseis technique these improvements have led to much increased productivity and in many cases much denser source sampling at the same time the vibrator itself has seen little improvement over the last couple of decades there are needs in a few areas where an improvement in the vibrator itself can bring benefits to the quality of the seismic data acquired this paper describes progress in four such areas low frequency performance high frequency performance an improved estimate of the vibrator groundforce and source signature consistency over variable ground conditions each of these vibrator characteristics will be discussed in turn meanwhile two field test results in which the performance of two different vibrators in these four areas are compared

internal characterization of embankment dams using ground penetrating radar gpr and thermographic analysis a case study of the medau zirimilis dam sardinia italy abstract the stability of embankment dams without an impermeable core depends on the characteristics of the face slab that prevents internal erosion piping and eventual collapse of the structure under a mediterranean climate the impermeable asphaltic face slab is subjected to high solar radiation and consequent temperature changes which can generate the creation of cracks and joints the medau zirimilis dam located in the casteddu river sardinia is an embankment dam that has undergone seepage and continuous repairs in its asphalt face slab these reparations have been conducted because of the occurrence of cracks and relative movement of different segments of the slab to evaluate if seepage endangers the integrity of the dam gpr was used with different antennas 100 250 and 500 mhz along its crest and upstream and downstream faces and the data were integrated with infrared thermographic images although geophysical data do not show structural changes affecting the main dam structure deformation structures at shallow levels and in particular in the upstream face and along the crest of the dam have been identified such deformation affects the road atop the crest the face slab and underlying levels resulting in landslides that include material from several meters below the surface the analysis permitted the identification of the origin of surficial cracks and their effects on the face slab these sectors independent of current movement define the most unstable areas against water level changes that can affect the dam integrity gpr analysis at the embankments usually has the handicap of high clay content that precludes electromagnetic wave penetration however in this case the obtained resolution and extent of penetration using the different antennas was sufficient due to the absence of an inner waterproof unit and permitted the evaluation of the inner structure of the dam and the application of gpr for construction quality surveillance internal structural characterization and dam monitoring

imaging mantle transition zone thickness with sds ss finite frequency sensitivity kernels summary we invert differential sds ss traveltime residuals measured from stacked waveforms and finitefrequency sensitivity kernels for topography on the 410 and 660 km discontinuities this approach yields higher resolution images of transition zone thickness than previous stacking methods which simply average smooth over topographic features apparent structure measured using simple stacking is highly dependent upon the bin size of each stack by inverting for discontinuity topography with a variety of bin sizes we can more accurately calculate the true structure the inverted transition zone model is similar to simple stack models with an average thickness of 242 km but the lateral variations in thickness are larger in amplitude and smaller in scale fast seismic velocities in 3 d mantle models such as sb4l18 correlate with areas of thicker transition zone the elongated curvilinear regions of thickened transition zone that occur near subduction zones are narrow and high amplitude which suggests relatively little lateral spreading and warming of subducted lithosphere within the transition zone the anomalously thin transition zone regions are laterally narrow and not broadly continuous if these variations in transition zone thickness are interpreted as thermal in nature then this model suggests significant temperature variations on small lateral scales

stagnant slab a review a stagnant slab is a subducted slab of oceanic lithosphere subhorizontally deflected above across or below the 660 km discontinuity this phenomenon has now been widely recognized beneath subduction zones around the circum pacific and in the mediterranean collaboration of seismic and electromagnetic observations mineral physics measurements and geodynamic modeling has begun to provide a consistent picture of stagnant slab

shear wave reflectivity imaging of the nazca south america subduction zone stagnant slab in the mantle transition zone 1 in this study we utilize over 5000 ss waveforms to investigate the high resolution mantle reflectivity structure down to 1200 km beneath the south american convergent margin our results indicate that the dynamics of the nazca subduction are more complex than previously suggested the 410 and 660 km seismic discontinuities beneath the pacific ocean and amazonian shield exhibit limited lateral depth variations but their depths vary substantially in the vicinity of the subducting nazca plate the reflection amplitude of the 410 km discontinuity is greatly diminished in a 1300 km wide region in the back arc of the subducting plate which is likely associated with a compositional heterogeneity on top of the upper mantle transition zone the underlying 660 km discontinuity is strongly depressed showing localized depth and amplitude variations both within and to the east of the wadati benioff zone the width of this anomalous zone 1000 km far exceeds that of the high velocity slab structure and suggesting significant slab deformation within the transition zone the shape of the 660 km discontinuity and the presence of lower mantle reflectivity imply both stagnation and penetration are possible as the descending nazca slab impinges upon the base of the upper mantle citation contenti s y j gu a okeler and m d sacchi 2012 shear wave reflectivity imaging of the nazca south america subduction zone stagnant slab in the mantle transition zone geophys res lett 39 l02310 doi 10 1029 2011gl050064

waveform inversion of ss precursors an investigation of the northwestern pacific subduction zones and intraplate volcanoes in china abstract the arrival time and amplitude of underside reflections from mantle seismic discontinuities ss precursors have made major contributions to the understanding of mantle composition and dynamics in this study we introduce a nonlinear waveform inversion technique to simultaneously constrain shear velocities and discontinuity depths beneath the northwestern pacific subduction system based exclusively on a large ss precursor waveform dataset we are able to clearly delineate the morphology of the descending pacific plate which flattens at the base of the upper mantle and extends westward by 1500 km toward northern central china our grid search yields the maximum correlation between shear velocity and transition zone thickness at an angle of 30 consistent with the reported average slab dip beneath the study region the strongly positive correlation suggests predominantly thermal rather than compositional variations along the descending pacific plate the joint depth velocity solution also shows a 5 10 km depression of the 410 km discontinuity and an average decrease of 1 2 in upper mantle shear velocity beneath the intraplate volcanic fields in northeastern china this anomaly which reaches the middle of the upper mantle transition zone beneath the changbai hotspot initiates at a significantly shallower 320 km depth beneath the wudalianchi region high amplitude reflections at depths greater than 410 km suggest a water poor melt layer in possible association with 1 decompression melting from passive upwelling and or 2 active upwelling through a slab window

unusual high acidity oils from the great palogue field melut basin sudan abstract crude oils produced from the great palogue field in the melut basin sudan display unusually high total acid number values tan up to 10 4 mg koh g oil this field was discovered in 2002 and produces oils of highly variable 15 31 api gravity the main production comes from the paleogene samma and yabus formations with the upper cretaceous melut formation being a minor contributor the effective hydrocarbon source rocks are most likely within lower cretaceous lacustrine shales deposited during the syn rift stages of the basin s evolution this study addressed 20 crude oil samples from five exploration and appraisal wells in the great palogue field and four oil samples from other oil fields in the basin to represent the various production fluids from the upper cretaceous and paleogene pay zones these oil samples were characterized using routine molecular geochemical techniques to determine the primary geological and geochemical controls on oil acidity based on source and maturity constraints two genetic types of high acidity oils have been recognized from the melut basin the first group of high acidity oils is likely primary high tan oils with a tan value of 0 5 0 99 mg koh g oil they are buried deeper than 2000 m where the temperature is higher than 80 c these include the oils only in the upper cretaceous melut formation of the anbar 1 and palogue south 2 blocks the second group of high acidity oils show higher tan values 1 0 mg koh g oil and various levels of biodegradation these oils represent the dominant oil type in the melut basin occurring mainly in the paleogene yabus and samma formations a multiple phase oil charging model is proposed to explain the horizontal and vertical variation in the oil tan values across the great palogue field

p p precursors under africa evidence for mid mantle reflectors observations of precursors to p p from a recent exceptionally large deep earthquake in the fiji islands moment magnitude 7 6 at an array of broadband stations in california revealed mid mantle reflectors near depths of 785 kilometers and 1200 kilometers under the southern african rift such observations previously reported primarily in subduction zones suggest that these reflectors may have a global character our analysis which also indicated a sharp uplifted 670 kilometer discontinuity demonstrates the power of sparse regional broadband arrays for the study of weak frequency dependent features in deep earth structure

three dimensional radial anisotropic structure of the north american upper mantle from inversion of surface waveform data summary seismic anisotropy provides insight into palaeo and recent deformation processes and there fore mantle dynamics in a first step towards a model for the north american upper mantle with anisotropy characterized by a symmetry axis of arbitrary orientation aimed at filling the gap between global tomography and sks splitting studies we inverted long period waveform data simultaneously for perturbations in the isotropic s velocity structure and the anisotropic parameter v 2 sh v2 in the framework of normal mode asymptotic coupling theory nact the resulting 2 d broad band sensitivity kernels allow us to exploit the information contained in long period seismograms for fundamental and higher mode surface waves at the same time to ensure high quality of the retrieved regional upper mantle structure accurate crustal cor rections are essential here we follow an approach which goes beyond the linear perturbation approximation and split the correction into a linear and non linear part the inverted data set consists of more than 40 000 high quality three component fundamental and overtone sur face waveforms recorded at broad band seismic stations in north america from teleseismic events and provides a fairly homogeneous path and azimuthal coverage the isotropic part of our tomographic model shares the large scale features of previous regional studies for north america we confirm the pronounced difference in the isotropic velocity structure between the western active tectonic region and the central eastern stable shield as well as the presence of subducted material juan de fuca and farallon plate at transition zone depths the new regional 3 d radial anisotropic model indicates the presence of two distinct anisotropic layers beneath the cratonic part of the north american continent a deep asthenospheric layer con sistent with present day mantle flow and a shallower lithospheric layer possibly a record of ancient tectonic events

broadband seismic amplitude variation with offset inversion abstractseismic amplitude variation with offset avo inversion is well known as a popular and pragmatic tool used for the prediction of elastic parameters in the geosciences low frequencies missing from conventional seismic data are conventionally recovered from other geophysical information such as well log data for estimating the absolute rock properties which results in biased inversion results in cases of complex heterogeneous geologic targets or plays with sparse well log data such as marine or deep stratum broadband seismic data bring new opportunities to estimate the low frequency components of the elastic parameters without well log data we have developed a novel avo inversion approach with the bayesian inference for broadband seismic data the low frequency components of the elastic parameters are initially estimated with the proposed broadband avo inversion approach with the bayesian inference in the complex frequency domain because seismic inversion in the complex frequency domain is he

a prestack basis pursuit seismic inversion abstractresolving thin layers and clearly delineating layer boundaries in inverted seismic sections are very important goals for exploration and production many seismic inversion methods based on a least squares optimization approach with tikhonov type regularization can lead to unfocused transitions between adjacent layers a basis pursuit inversion bpi algorithm based on the l1 norm optimization method can however resolve sharp boundaries between layers we have formulated a bpi algorithm for amplitude versus angle inversion and investigated its potential to improve contrasts between layers like the bpi for poststack case the sparse layer constraint rather than the sparse spike constraint is used to construct the model space as a wedge dictionary all the elements of the dictionary are bed reflectivities which include solutions consisting of thin beds as well with this dictionary we use an l1 norm optimization framework to derive three reflectivities namely rp rs and r although bpi doe

global variability of transition zone thickness 1 we analyze recordings from more than 3000 shallow earthquakes and measure s410s s660s differential travel times on a global scale these differential times are obtained using a novel cross correlation technique that eliminates effects associated with a priori assumptions of crustal thickness and velocity variations above the upper mantle transition zone our measurements show absolute perturbations up to 8 s from the global average 242 km which imply transition zone thickness variations of 20 km on a length scale of 2000 km the transition zone under major subduction zones e g the western pacific and south america is significantly thicker than the global average this could be associated with large scale depressions of the 660 km discontinuity due to the accumulation of cold oceanic lithosphere at the base of the upper mantle a narrow transition zone is observed under the central pacific and northern atlantic oceans we also observe a modest anticorrelation between s410s s660s times and the delay times of shear waves predicted using s12 wm13 su et al 1994 in the transition zone which suggests considerable thermal influence on the large scale topography of the 410 and 660 km discontinuities the lack of a stronger anticorrelation suggests that 1 compositional heterogeneities may be present and 2 a significant fraction of thermal anomalies near the transition zone do not extend through the transition zone and influence both the 410 and the 660 km discontinuities a regional analysis shows that the transition zone is on average 6 8 km thicker under continents than under oceans this implies a temperature difference of 50 70 c however we do not observe a clear correlation between thickness and the age of the crust

computation of seismic profiles from mineral physics the importance of the non olivine components for explaining the 660 km depth discontinuity the recent increasing number of experimental works leads us to review the elastic properties and mineralogical transformations of mantle minerals the updated data set is used to compute seismic profiles for two petrological models along three adiabatic temperature profiles these profiles are chosen to stress out the influence of non olivine minerals on seismic parameters and to represent cold and horizontally averaged temperature profiles of the earth s mantle in a first part starting compositions of pyrolite and piclogite and a single layer convection are assumed the results clearly point out the importance of the non olivine part of the mineralogy two scenarios are found to explain the 660 km depth discontinuity

engineering geological assessment of the obruk dam site corum turkey engineering geological properties of rock masses such as discontinuities degree of weathering strength and hydraulic conductivities along the dam axis and the excavatibility of diversion tunnels power tunnels and spillways were investigated in order to determine probable problems and necessary precautions to be taken prior to construction in this study the obruk dam site constructed on the kizilirmak river to the north of corum central anatolia was investigated from the standpoint of the aforementioned engineering geological aspects quaternary alluvium at the dam site has a thickness of about 65 m and overlies the eocene basalt basement diversion and power tunnels were constructed in the basalts in order to determine the distribution of the basalt both horizontally and vertically core samples were collected from preliminary geotechnical boreholes drilled by the general directorate of the state hydraulic works dsi and the depth to groundwater was measured in these boreholes the geological and geomechanical properties of the basalt are controlled by tectonism and weathering and these properties vary over short distances the mineralogical petrographical and geomechanical properties of the basalt core samples were determined based on these test results the rock mass cropping out at the dam site has been classified for tunneling and possible support systems suggested

seismic studies of a bottom simulating reflection related to gas hydrate beneath the continental margin of the beaufort sea the upper continental margin of the beaufort sea north of alaska is underlain by a strong bottom simulating reflection bsr that lies 300 to 700 m beneath the seafloor and corresponds to the phase boundary between interstitial water and natural gas below and solid gas hydrate above bsrs of similar origin are common worldwide where they are usually interpreted to mark the base of gas hydrate bearing clastic sediment with or without underlying free gas in the sediment surprisingly little is known about the origin of these strong reflections in this paper we analyze the contrasting physical properties which produce bsrs by comparing synthetic bsr amplitudes and waveforms for varying source receiver offsets with multichannel seismic reflection data across the well developed bsr of the beaufort sea in order to discriminate whether free gas is present under the bsr or not it was necessary to supplement near vertical incidence data with prestack offset data the amplitude versus offset avo analysis indicates that the bsr is produced mainly by the existence of free gas in the clastic sediments beneath the bsr the zone of free gas is based on vertical incidence synthetics estimated to be thinner than 11 16 m it is possibly thicker than 16 m if the gas concentration decreases with depth saturation of gas hydrate in the sediment above the bsr is tentatively estimated from the avo modeling to be less than 10 of the pore volume