sensitivity of extratropical cyclone characteristics to horizontal resolution in the ecmwf model the sensitivity to horizontal resolution of northern hemisphere extratropical cyclone characteristics during the wintertime december march is investigated using a set of seasonal forecasts 1982 2001 with the european centre for medium range weather forecasts ecmwf model three different horizontal resolutions tl95 tl159 and tl255 are employed in order to test the realism of the simulations the model results are compared with those obtained from era 40 re analysis data the cyclone tracking is accomplished by applying an automatic tracking scheme to six hourly mean sea level pressure data it is shown that many of the key characteristics of extratropical cyclones in the ecmwf model are highly sensitive to horizontal resolution with the low resolution version tl95 for example simulating only about 60 of the re analysed total number of extratropical cyclones regions found to be particularly sensitive include the northern pacific the arctic baffin bay and the labrador sea as well as the mediterranean sea for the latter region it is shown that even the relatively high resolution version of the model tl255 significantly underestimates the number of cases of genoa cyclogenesis furthermore it is shown that in some regions such as the entrance regions of the major northern hemisphere storm tracks model deficits are insensitive to increases in horizontal resolution the same analysis has been repeated for the high resolution operational ecmwf analysis 2000 2004 truncated at different total wave numbers tl95 tl159 tl255 and tl511 in order to separate dynamical effects of differences in resolution from those due to pure spectral truncation it is found that the dynamical effect of changing horizontal resolution dominates over the truncation effect for intense cyclones whereas the truncation effect dominates for shallow cyclones copyright 2006 royal meteorological society

identification of cyclone track regimes in the north atlantic a langrangian type climatology of north atlantic cyclones is established based on the high resolution european centre for medium range weather forecasts data set of the 1000 hpa height field first an algorithm is introduced to identify mid latitude cyclones and cyclone paths with as few constraints as possible cluster analysis of relative cyclone displacements yields three types of cyclone tracks characterizing stationary north eastward and zonally travelling storms the internal lagrangian statistics of these cyclone track types reveal representative life cycles for central pressure and geopotential height gradients and a power law scaling behaviour of cyclone displacements finally a basic climatology of north atlantic cyclone track regimes is deduced in terms of a time series and circulation statistics

reverse time migration a prospect of seismic imaging methodology abstract reverse time migration rtm is a seismic imaging method to map the subsurface reflectivity using recorded seismic waveforms the practice in exploration seismology has long established a two fold approach of seismic imaging using velocity modeling building to establish the long wavelength reference velocity models and using seismic migration to map the short wavelength reflectivity structures among various seismic migration methods for different situations rtm is the only method that is capable to use all seismic wave types that can be computed numerically being initiated in early 1980 s rtm seeks an image of the subsurface reflectivity as the best match in an image space between the extrapolation of time reversed waveform data and the prediction based on estimated velocity model and source parameters judging the image quality in the same space of forming the images is more advantageous than the approaches of modeling and inversion which seek the solution in the model space but judge its fitness in data space considering that most seismic migration applications today still use primary reflection as the only signal the capability of rtm to use all computable wave types is unique and helpful reducing the imaging artifacts due to mistaking non primary waves as primary reflections hence we refer to those rtm algorithms using only primary reflections as the first generation rtm methods and the rtm algorithms making a full use of primary reflections multiple reflections and other non primary waveform data as the second generation rtm methods this paper reviews the development history of the rtm along with its major challenges current solutions and future perspectives

three dimensional prestack plane wave migration of teleseismic p to s converted phases 1 theory 1 we present the theoretical foundations for a prestack migration technique to image teleseismic p to s converted phases the method builds on teleseismic p wave deconvolution pseudostation stacking neal and pavlis 1999 and on the idea of using a plane wave decomposition for imaging as introduced by treitel et al 1982 deconvolution operators are constructed by pseudostation stacking of the array aligned to the incident p wave arrival times to produce a space variable deconvolution operator the resulting data are then muted to remove the deconvolved direct p wave pulse and pseudostation stacked over a grid of feasible slowness vectors the pseudostation stack interpolates the wave field onto a regular grid along earth s surface producing a series one per slowness vector of uniformly sampled three dimensional data cubes two space variables and time the plane wave components can be propagated downward using a form of approximate ray tracing with a three dimensional earth model this yields a series of distorted cubes topologically equivalent to the original uniformly sampled data cubes these data volumes are summed as a weighted stack with the weights derived from an integration formula for inverse scattering based on the generalized radon transform this allows an image of the subsurface to be constructed on an event by event basis beneath the array we apply this technique to data from the lodore array that was deployed in northwestern colorado the results suggest the presence of a major lithospheric scale discontinuity defined by a south dipping boundary

imaging a crustal low velocity layer using reflected seismic waves from the 2014 earthquake swarm at long valley caldera california the magmatic system roof

developments in the characterization of complex rock slope deformation and failure using numerical modelling techniques recent advances in the characterization of complex rock slope deformation and failure using numerical techniques have demonstrated significant potential for furthering our understanding of both the mechanisms processes involved and the associated risk this paper illustrates how rock slope analyses may be undertaken using three levels of sophistication level i analyses include the conventional application of kinematic and limit equilibrium techniques with modifications to include probabilistic techniques coupling of groundwater simulations and simplistic treatment of intact fracture and plastic yield such analyses are primarily suited to simple translational failures involving release on smooth basal rear and lateral surfaces where the principle active damage mechanisms are progressive failure and or asperity breakdown level ii analyses involve the use of continuum and discontinuum numerical methods in addition to simple translation level ii techniques can be applied to complex translational rock slope deformations where step path failure necessitates degradation and failure of intact rock bridges along basal rear and lateral release surfaces active damage processes in this case comprise not only strength degradation along the release surface e g asperity breakdown but also a significant component of brittle intact rock fracture level iii analyses involve the use of hybrid continuum discontinuum codes with fracture simulation capabilities these codes are applicable to a wide spectrum of rock slope failure modes but are particularly well suited to complex translation rotational instabilities where failure requires internal yielding brittle fracturing and shearing in addition to strength degradation along release surfaces through a series of rock slope analyses the application of varied numerical methods are discussed particular emphasis is given to state of the art developments and potential use of level iii hybrid techniques d 2005 elsevier b v all rights reserved

influence of tectonic fractures zones on gravitational rock slope failures new insights from 2 d physical modeling 1 inherited structural discontinuities are known to play a dominant role in rock slope stability the influence of their density and persistence on failure kinematics resulting mobilized volume and slope morphology remains poorly constrained the influence of these parameters is addressed using a 2 d physical modeling technique rather than undertaking a parametric analysis we examine geologically stable model configuration based upon the well documented landslide at randa switzerland the models consisted of a homogeneous material in which several fracture zones were introduced in order to study simplified but realistic configurations of discontinuities results showed that the type of gravitational failure deep seated landslide or sequential failure and resulting slope morphology are very sensitive to the number and geometry of preexisting fracture zones first an increase in the density of fractures led to formation of the gravitational failure and increased the final mobilized volume second fracture persistence exerted a strong control upon the kinematics of slope movements but had little influence on the final volume of the mobilized mass

imaging p to s conversions with multichannel receiver functions we present a new methodology in the direct imaging of p to s converted phases recorded on broadband seismic arrays our approach is based on conventional three component array processing and receiver function techniques with the key addition of a weighted stack based on an aerial smoothing function this creates synthetic arrays with a specified aperture whose image points vary continuously across the array with this approach it is possible to interpolate data from an array of broadband stations onto an arbitrarily fine grid we have applied this technique to a single deep event recorded by the lodore broadband array located in northern colorado and southern wyoming the resulting images show distinct differences in crustal structure across the array and also image major upper mantle discontinuities

two dimensional waveform inversion of multi component data in acoustic elastic coupled media in order to account for the effects of elastic wave propagation in marine seismic data we develop a waveform inversion algorithm for acoustic elastic media based on a frequency domain finite element modelling technique in our algorithm we minimize residuals using the conjugate gradient method which back propagates the errors using reverse time migration without directly computing the partial derivative wavefields unlike a purely acoustic or purely elastic inversion algorithm the green s function matrix for our acoustic elastic algorithm is asymmetric we are nonetheless able to achieve computational efficiency using modern numerical methods numerical examples show that our coupled inversion algorithm produces better velocity models than a purely acoustic inversion algorithm in a wide variety of cases including both single and multi component data and low cut filtered data we also show that our algorithm performs at least equally well on real field data gathered in the korean continental shelf

least squares reverse time migration in a matrix based formulation this paper describes least squares reverse time migration the method provides the exact adjoint operator pair for solving the linear inverse problem thereby enhancing the convergence of gradient based iterative linear inversion methods in this formulation modified source wavelets are used to correct the source signature imprint in the predicted data moreover a roughness constraint is applied to stabilise the inversion and reduce high wavenumber artefacts it is also shown that least squares migration implicitly applies a deconvolution imaging condition three numerical experiments illustrate that this method is able to produce seismic reflectivity images with higher resolution more accurate amplitudes and fewer artefacts than conventional reverse time migration the methodology is currently feasible in 2 d and can naturally be extended to 3 d when computational resources become more powerful

numerical analysis of initiation and progressive failure in natural rock slopes the 1991 randa rockslide the 1991 randa rockslide in the swiss alps involved several complex mechanisms relating to geological mechanical and hydrological processes for which no clear trigger can be asserted this paper investigates the concept of progressive failure and the numerical modelling of rock mass strength degradation in natural rock slopes using the randa rockslide as a working example results from continuum i e finite element modelling are presented to illustrate a hypothesis suggesting that initiation of a progressive rock mass degradation process ultimately leading to failure began following deglaciation of the valley below discontinuum distinct element modelling is then applied to investigate the underlying mechanisms contributing to the episodic nature of the rockslide finally the use of a hybrid method that combines both continuum and discontinuum techniques to model fracture propagation are discussed in the context of modelling progressive slide surface development linking initiation and degradation to eventual catastrophic failure

experiments in migration processing of ss precursor data to image upper mantle discontinuity structure long period ss precursors result from underside reflections off upper mantle discontinuities by grouping and stacking global seismic data by ss bounce point location it is possible to map lateral variations in depths to the 410 and 660 km discontinuities a process analogous to common midpoint cmp stacking in reflection seismology because this method assumes horizontal reflectors energy arriving from dipping or intermittent reflectors may not be correctly imaged to address this possibility we experiment with techniques based on migration processing of shallow seismic reflection data the problem is complicated by the uneven distribution of sources and receivers for the ss precursor observations but the data are sufficiently dense beneath the northwest pacific ocean that reasonably good coverage can be obtained for this region we parameterize the model as a grid of point scatterers in latitude longitude and depth from the surface to 1000 km depth and compute travel times from each grid point to the source and receiver locations these times are used to construct a matrix equation that yields predicted ss precursor waveforms from the assumed scatterers to recover the model we experiment with both simple back projection and full inversions using a conjugate gradient method tests on noise free synthetic data generated using the same source receiver distribution as the actual data suggest that detailed resolution of discontinuity structure is possible at horizontal scales much smaller than the fresnel zone however the real data do not produce coherent results unless some degree of horizontal smoothing is imposed at least partially defeating the purpose of this approach results for the northwest pacific find structure on the 410 and 660 km discontinuities and hints of intermittent reflectors at other depths random resampling tests however suggest that most of these features are not reliably resolved with the exception of a depression on the 660 km discontinuity seen in the northwest pacific our experiments show that it is unlikely that small scale structure on the 660 km discontinuity near subducting slabs causes significant bias in maps of the large scale 660 km topography derived from long period ss precursor observations

multiparameter two dimensional inversion of scattered teleseismic body waves 2 numerical examples in this paper we investigate the formal inversion of synthetic teleseismic p coda waves for subsurface elastic properties using a ray theoretic approach which assumes single scattering bostock et al this issue we consider a model comprising an idealized lithospheric suture zone whose geometrical configuration is drawn from previous deep crustal seismic studies two dimensional pseudospectral synthetic seismograms representing plane waves propagating through this model are preprocessed to extract an estimate of the scattered wave field generated by short wavelength structure these data are employed in a series of numerical simulations which examine the dependence of multiparameter inversion results on a range of input parameters in particular we demonstrate 1 the contrasting sensitivity which forward and backscattered waves display to structural recovery 2 the diminution of the problem null space accompanied by increased source coverage 3 improvements in model reconstruction achieved through simultaneous treatment of multiple scattering modes and 4 the robustness of the method for data sets with noise levels and receiver geometries that approach those of field experiments

elastic reverse time migration elastic prestack reverse time finite difference migration of two component seismic surface data requires data extrapolation and application of an imaging condition data extrapolation involves synchronous driving of the vertical component and horizontal component finite difference meshes with the time reverse of the recorded vertical and horizontal traces respectively extrapolation uses the coupled elastic wave equation for variable velocity solved with a second order explicit finite difference scheme the imaging condition at any point in the grid is the one way traveltime from the source to that point elastic migrations of both synthetic test data and real two component common source gathers produce simpler images than acoustic migrations because of the coalescing of double reflections compressional waves and shear waves into single loci

composite rock slope kinematics at the current randa instability switzerland based on remote sensing and numerical modeling abstract kinematic analysis of slope instabilities in brittle rock is crucial for understanding the reaction of the rock mass to external forcing factors in steep terrain inaccessibility often limits collection of relevant data and remote sensing techniques must be applied this is the case at the current randa rock slope instability in southern switzerland where a total volume of about 5 6 million m3 moves at a rate of up to 30 mm yr a large portion of the unstable rock mass is exposed in an 800 m high inaccessible cliff the main scarp of the may 1991 rock slope failure between 2005 and 2007 a comprehensive suite of remote sensing techniques including photogrammetry lidar and gb dinsar was combined with 3d geodetic measurements to characterize the rock mass structure and displacement patterns photogrammetry and lidar data were measured simultaneously from a helicopter using a system allowing for oblique view angles which provided optimal observations of the steep rock cliff we used these datasets to map large scale structures and extract their orientation and minimum persistence as well as to characterize the 1991 failure scarp the northern part of the may 1991 failure surface shows a transition from stepped planar sliding at the base to failed rock bridges in the center to tensile failure close to the vertical head scarp kinematic analysis of the discontinuity sets in the currently moving rock mass shows that both toppling and translational sliding are feasible failure mechanisms toppling is more likely for steep faces above 2200 m whereas translational failure is more likely in the lower portion of the instability interpretation of gb dinsar displacement maps revealed similar kinematic behavior and also allowed identification of a basal rupture zone and lateral release plane bounding the instability displacement vectors derived from geodetic surveying provided new insights into the 3d kinematic behavior of the instability all information extracted from different data sets were integrated in a conceptual model which was then investigated with 2d numerical simulation using the discontinuum code udec the numerical models were able to reproduce the hypothesized kinematic behavior well

application of rtm 3d angle gathers to wide azimuth data subsalt imaging the availability of wide azimuth data and the use of reverse time migration rtm have dramatically increased the capabilities of imaging complex subsalt geology with these improvements the current obstacle for creating accurate subsalt images now lies in the velocity model one of the challenges is to generate common image gathers that take full advantage of the additional information provided by wide azimuth data and the additional accuracy provided by rtm for velocity model updating a solution is to generate 3d angle domain common image gathers from rtm which are indexed by subsurface reflection angle and subsurface azimuth angle we apply these 3d angle gathers to subsalt tomography with the result that there were improvements in velocity updating with a wide azimuth data set in the gulf of mexico

least squares reverse time migration inversion based imaging toward true reflectivity abstract as an inversion based imaging algorithm least squares reverse time migration lsrtm refines seismic images toward true reflectivity earth models it overcomes the shortcomings of conventional migration algorithms via iterative least squares inversion to gradually correct migration errors lsrtm also suppresses side lobes of image wavelets to generate images with high spatial resolution recovered weak events and steep dips are enhanced during iterations with balanced illumination the true amplitude behavior of lsrtm will greatly benefit quantitative seismic interpretations lsrtm can be a practical image domain broadband solution to generate high resolution images with fine layers as well as accurate complex structures

simulated decadal oscillations of the atlantic meridional overturning circulation in a cold climate state the significance of the atlantic meridional overturning circulation moc for regional and hemispheric climate change requires a complete understanding using fully coupled climate models here we present a persistent decadal oscillation in a coupled atmosphere ocean general circulation model while the present study is limited by the lack of comparisons with paleo proxy records the purpose is to reveal a new theoretically interesting solution found in the fully coupled climate model the model exhibits two multi century long stable states with one dominated by decadal moc oscillations the oscillations involve an interaction between anomalous advective transport of salt and surface density in the north atlantic subpolar gyre their time scale is fundamentally determined by the advection in addition there is a link between the moc oscillations and north atlantic oscillation nao like sea level pressure anomalies the analysis suggests an interaction between the nao and an anomalous subpolar gyre circulation in which sea ice near and south of the labrador sea plays an important role in generating a large local thermal anomaly and a meridional temperature gradient the latter induces a positive feedback via synoptic eddy activity in the atmosphere in addition the oscillation only appears when the nordic sea is completely covered by sea ice in winter and deep convection is active only near the irminger sea such conditions are provided by a substantially colder north atlantic climate than today

the shapes of cold high mountains in sedimentary rocks abstract terzaghi geotechnique 12 1962 251 and young young a 1972 slopes oliver and boyd edinburgh 288 pp described the stable forms of slopes in sedimentary rock masses assuming penetrative discontinuities which are parallel to bedding and joints which are perpendicular to bedding the only movements considered were slides along bedding experience in the canadian rockies indicates that the cohesionless rock masses that exist at or above tree line may also move by toppling buckling and sliding along joints these processes also act to limit the inclinations of stable slopes rock strength is a factor in the critical height of a slope that buckles the processes can be represented as fields on a process diagram a plot of slope inclination against bedding dip using the basic friction angles of the rocks present the process diagram also separates five common mountain peak shapes which form on homoclinal sequences of beds castellate and matterhorn mountains occur in sub horizontal beds cuestas develop in gently to moderately dipping beds hogbacks formed in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes dogtooth mountains occur in steeply dipping sub vertical beds

mantle discontinuity structure beneath the colorado rocky mountains and high plains analysis of mantle discontinuity structure using converted p to s pas phases beneath colorado from the program for array seismic studies of the continental lithosphere passcal rocky mountain front rmf experiment reveals significant topography at the 410 and 660 km depth discontinuities and corresponding transition zone thickness variations a stack of all radial receiver functions resolves the 410 and 660 km discontinuities at average depths of 419 and 677 km respectively imaging of lateral variations in mantle discontinuity structure is accomplished by geographically binning the pds conversion points and then stacking the receiver functions in each bin to form spatial images analogous to common depth point stacking corrections for lateral velocity heterogeneity are calculated using the local s wave tomographic model of lee and grand 1996 and a constant lnvs lnvp scaling of 1 3 this scaling value is determined from the relative scaling between teleseismic p and s wave travel time residuals measured from the rocky mountain front deployment mantle discontinuity images using 150 km square bins show 20 km of 410 km discontinuity topography 30 km of 660 km discontinuity topography and up to 40 km of transition zone thickness variation features of the discontinuity structure include a 20 km depression of the 660 km discontinuity beneath western colorado and a gradual 10 km dip of the 410 km discontinuity beneath the high plains the thickening of the transition zone beneath southwest colorado is consistent with the presence of the subducted farallon slab in this region as imaged by van der lee and nolet 1997 in general our results show that the transition zone discontinuity structure is more complex than that predicted by the simple model of olivine phase boundaries modulated by vertically coherent thermal anomalies

numerical modelling of the gravity induced destabilization of a slope the example of the la clapiere landslide southern france abstract a finite difference two dimensional model with hooke mohr coulomb properties and topography derived from the dem are used to reproduce the la clapiere landslide the principal factor defining the gravity driven destabilization of the model is a gradual reduction in the cohesion this reduction simulates a degradation of the material properties with time because of weathering alteration processes the inelastic deformation fracturing and faulting first occur at mountain scale and results in normal fault formation causing crest sagging later the failure process is concentrated in the lower part of the slope and leads to the formation of a localized fault subparallel to the slope surface at a depth of ca 100 m this corresponds to the initiation of the la clapiere landslide and its propagation upslope a slow crest sagging continues during the whole model evolution

3d coupled acoustic elastic migration with topography and bathymetry based on spectral element and adjoint methods abstractin the context of the adjoint method we considered 3d coupled acoustic elastic migration in the presence of surface topography and or bathymetry isotropic elastic imaging involves three primary kernels related to mass density and shear and bulk moduli and various secondary kernels for example related to p wave impedance and compressional and shear wave speeds similar to reverse time migration these kernels reflect the constructive interference between a forward wavefield generated by active sources and an adjoint wavefield triggered by simultaneously back propagating recorded reflections from all receivers forward and adjoint wavefields were simulated using a spectral element method which due to its weak nature captures free surface topography in land surveys and bathymetry in marine acquisition to avoid storing the entire 3d forward wavefield required for calculating its interaction with the adjoint wavefield we only saved information on domain boundaries and reconstructed the forw

seismic imaging using microseismic events results from the san andreas fault system at safod 1 we have developed a new passive seismic imaging approach that consists of two steps first the hypocenter of the microseismic event is precisely located second this event is treated as a pseudo active seismic source and the reflections within the recorded wavefield are processed by using a directional migration algorithm in order to construct a high resolution image of the illuminated subsurface region in this paper we demonstrate the application of our approach to a number of microseismic events recorded by a borehole array in the san andreas fault observatory at depth main hole results obtained were high resolution 3 d images of different se nw oriented reflectors related to the san andreas fault saf system in the close vicinity of the borehole to support our approach we compared our findings with other active and passive seismic images and analyzed the correlation with borehole lithology we revealed a predominantly satisfactory agreement for both juxtapositions furthermore the stacked image of several microearthquakes provides a spatial characterization of the complex internal structure of the saf with much higher resolution than can be obtained from surface seismic reflection data

beyond receiver functions passive source reverse time migration and inverse scattering of converted waves 1 we present a wave equation prestack depth migration to image crust and mantle structures using multi component earthquake data recorded at dense seismograph arrays transmittedp and swaves recorded on the surface are back propagated using an elastic wave equation solver the wave modes are separated after the reverse time continuation of the wavefield from the surface and subjected to a cross correlation type imaging condition forming an inverse scattering transform reverse time migration rtm does not make assumptions about the presence or properties of interfaces notably it does not assume that interfaces are locally horizontal with synthetic experiments and different background models we show that passive source rtm can reconstruct dipping and vertically offset interfaces even in the presence of complex wave phenomena such as caustics and point diffraction and that its performance is superior to traditional receiver function analysis e g common conversion point ccp stacking in complex geological environments

poststack diffraction imaging using reverse time migration abstract we propose a method for imaging small scale diffraction objects in complex environments in which kirchhoff based approaches may fail the proposed method is based on a separation between the specular reflection and diffraction components of the total wavefield in the migrated surface angle domain reverse time migration was utilized to produce the common image gathers this approach provides stable and robust results in cases of complex velocity models the separation is based on the fact that in surface angle common image gathers reflection events are focused at positions that correspond to the apparent dip angle of the reflectors whereas diffracted events are distributed over a wide range of angles the high resolution radon based procedure is used to efficiently separate the reflection and diffraction wavefields in this study we consider poststack diffraction imaging the advantages of working in the poststack domain are its numerical efficiency and the reduced computational time the numerical results show that the proposed method is able to image diffraction objects in complex environments the application of the method to a real seismic dataset illustrates the capability of the approach to extract diffractions

structural constraints on deep seated slope deformation kinematics abstract a significant sackung type deep seated slope gravitational deformation dsgsd was recognised for the first time by the authors in the middle part of valfurva east of bormio rhaetian alps italy the reconstruction of its kinematics age and state of activity is presented through a detailed description of its morphological geomechanical and structural features an integrated multi disciplinary approach was performed to achieve a clear comprehension of the phenomenon field surveys and aero photo interpretation were carried out in order to clarify the structural geological and geomorphological setting in which the dsgsd developed a kinematic conceptual model of the slope deformation was developed through the analysis of morpho structures of their significance and relationships with lithological markers and quaternary deposits after a geomechanical characterisation of the rock mass involved in the slope deformation numerical modelling was performed to verify the hypotheses made on kinematics and driving factors of the phenomenon the sackung affects pre permian metapelites metabasites and marbles belonging to the upper austroalpine basement of the campo nappe as well as late pleistocene and holocene glacial and rock glacier deposits the deformation started after the late wurmian age 15 000 11 000 years b p and continued until few centuries ago not excluding a present day low rate activity deformation consists in a large oblique sagging along a deep confined sliding surface associated with gravitational reactivation of pre existing late alpine and recent tectonic brittle structures leading to the formation of n s and wnw ese trending gravitational morpho structures the evolution of the wnw ese trending system resulting in asymmetric trenches led to progressive failure of the lower part of the slope during the last 10 000 years as testified by large paleo landslide accumulations and it is still in progress numerical modelling indicates post glacial unloading as the main triggering factor of the slope deformation the importance of this deep seated slope deformation is enhanced by the occurrence of the 30 mm 3 active ruinon landslide in the lower part of the slope such landslide is subjected to rapid evolution and threatens the valley floor establishing an important risk factor connected to human lives and socio economic activities

bidimensional diagnostics variability and trends of northern hemisphere blocking abstractin this paper northern hemisphere winter blocking is analyzed through the introduction of a set of new bidimensional diagnostics based on geopotential height that provide information about the occurrence the duration the intensity and the wave breaking associated with the blocking this analysis is performed with different reanalysis datasets in order to evaluate the sensitivity of the index and the diagnostics adopted in this way the authors are able to define a new category of blocking placed at low latitudes that is similar to midlatitude blocking in terms of the introduced diagnostics but is unable to divert or block the flow furthermore over the euro atlantic sector it is shown that it is possible to phenomenologically distinguish between high latitude blocking occurring over greenland north of the jet stream and dominated by cyclonic wave breaking and the traditional midlatitude blocking localized over europe and driven by anticyclonic wave breaking these latter events are uniform

a method for the study of crack propagation in rock structures a method is presented for analysing the stability of rock structures based on the propagation of geological discontinuities discontinuities are modelled as flat cracks and their propagation is analysed using fracture mechanics methods as rock structures are brittle these phenomena can be studied using linear elastic fracture mechanics lefm problems in the application of lefm methods are analysed with regard to the states of compressive stress present in rock a numerical procedure is described which simulates the propagation of natural discontinuities in rock the crack propagation trajectories determined from this analysis are compared with experimental results obtained on mortar specimens the applicability of the method to the study of rock mass stability is shown with reference to the behaviour of rock slopes l article presente une methode permettant d analyser la stabilite de structures rocheuses cette methode est fondeve sur petude de la propagation de discontinuites geologiques ces discon

gaussian beam migration just as synthetic seismic data can be created by expressing the wave field radiating from a seismic source as a set of gaussian beams recorded data can be downward continued by expressing the recorded wave field as a set of gaussian beams emerging at the earth s surface in both cases the gaussian beam description of the seismic wave propagation can be advantageous when there are lateral variations in the seismic velocities gaussian beam downward continuation enables wave equation calculation of seismic propagation while it retains the interpretive raypath description of this propagation this paper describes a zero offset depth migration method that employs gaussian beam downward continuation of the recorded wave field the gaussian beam migration method has advantages for imaging complex structures like finite difference migration it is especially compatible with lateral variations in velocity but gaussian beam migration can image steeply dipping reflectors and will not produce unwanted reflectio

influence of structural heterogeneities and of large scale topography on imbricate gravitational rock slope failures new insights from 3 d physical modeling and geomorphological analysis initial topography and inherited structural discontinuities are known to play a dominant role in rock slope stability previous 2 d physical modeling results demonstrated that even if few preexisting fractures are activated propagated during gravitational failure all of those heterogeneities had a great influence on mobilized volume and its kinematics the question we address in the present study is to determine if such a result is also observed in 3 d as in 2 d previous models we examine geologically stable model configuration based upon the well documented landslide at randa switzerland the 3 d models consisted of a homogeneous material in which several fracture zones were introduced in order to study simplified but realistic configurations of discontinuities e g based on natural example rather than a parametric study results showed that the type of gravitational failure deep seated landslide or sequential failure and resulting slope morphology evolution are the result of the interplay of initial topography and inherited preexisting fractures orientation and density the three main results are i the initial topography exerts a strong control on gravitational slope failure indeed in each tested configuration even in the isotropic one without fractures the model is affected by a rock slide ii the number of simulated fracture sets greatly influences the volume mobilized and its kinematics and iii the failure zone involved in the 1991 event is smaller than the results produced by the analog modeling this failure may indicate that the zone mobilized in 1991 is potentially only a part of a larger deep seated landslide and or wider deep seated gravitational slope deformation

reverse time migration migration of stacked or zero offset sections is based on deriving the wave amplitude in space from wave field observations at the surface conventionally this calculation has been carried out through a depth extrapolation we examine the alternative of carrying out the migration through a reverse time extrapolation this approach may offer improvements over existing migration methods especially in cases of steeply dipping structures with strong velocity contrasts this migration method is tested using appropriate synthetic data sets

microseismic reflection imaging of the central andean crust the coda of passive seismic recordings is often rich in arrivals that are coherent across several stations if reflections can be extracted then they may be used for seismic reflection subsurface imaging with the objective to image the upper crust of the north chilean precordillera central andes approximate location 21 s 69 w we developed a workflow to process passive seismic data into subsurface reflection images we analysed the waveform recordings of several hundred microseismic events using signal processing and imaging techniques adapted from active controlled source seismic imaging as used in the oil industry key processing steps involved precise arrival time picking and hypocentre determination removing signal amplitude variations due to varying source radiation patterns identification and separation of reflections from coherent noise and transformation of the processed waveforms into images of the subsurface reflectivity when designing our microseismic reflection imaging workflow we took advantage of the fact that the passive seismic recording geometry with the hypocentres located at depth and the receivers positioned at the surface resembles a reverse vertical seismic profiling experiment the resultant p and s wave reflection images reveal several reflective features such as an approximate 15 westward dipping reflector over the 5 25 km depth range that largely coincides with a distinct seismicity boundary we interpret the imaged interface as the brittle ductile transition zone boundary possibly enhanced by a tectonic shear zone for the area of the north chilean precordillera the deduced microseismic reflection sections with horizontal extensions of about 50 km represent the first high resolution images of the shallow crust which could not be obtained from previous active source seismic reflection data

imaging complex geologic structure with single arrival kirchhoff prestack depth migration we compare various forms of single arrival kirchhoff prestack depth migration to a full waveform finite difference migration image using synthetic seismic data generated from the structurally complex 2 d marmousi velocity model first arrival traveltime kirchhoff migration produces severe artifacts and image contamination in regions of the depth model where significant reflection energy propagates as late or multiple arrivals in the total reflection wavefield kirchhoff migrations using maximum energy arrival traveltime trajectories significantly improve the image in the complex zone of the marmousi model but are not as coherent as the finite difference migration image by carefully incorporating continuous phase estimates with the associated maximum energy arrival traveltimes we obtain single arrival kirchhoff images that are similar in quality to the finite difference migration image furthermore maximum energy green s function traveltime and phase values calculated within the seismic frequency ban

p and s wave receiver function imaging of subduction with scattering kernels a method for scattered wave imaging in 3d with both teleseismic p and s wave receiver function data is introduced the approach relies on body wave scattering kernels that are derived from the adjoint data sensitivity kernels which are typically used for full waveform tomography the forward problem is approximated using ray theory yielding a computationally efficient imaging algorithm that can resolve dipping and discontinuous interfaces using both p and s wave receiver functions travel time fields for the incident teleseismic arrivals and the receiver point sources are obtained by solving the eikonal equation using a fast marching code which can handle a 3d reference velocity model an energy stable finite difference method is used to simulate elastic wave propagation in a 2d hypothetical subduction zone model the resulting synthetic p and s wave receiver function datasets are used to validate the imaging method the kernel images are compared with those generated by the generalized radon transform and common conversion point stacking methods these results demonstrate the potential of the kernel imaging approach for constraining lithospheric structure in complex geologic environments with sufficiently dense recordings of teleseismic data potential imaging targets include short wavelength compositional variations in the mantle wedge and the slab s lithosphere asthenosphere boundary

implementation of elastic reverse time migration using wavefield separation in the frequency domain summary considerable effort has been devoted to the migration of multicomponent data in elastic media with wavefield separation techniques being the most successful most of this work has been carried out in the time domain in this paper we formulate a multicomponent migration technique in the frequency domain reverse time migration can be viewed as the zero lag cross correlation between virtual source and back propagated wavefields cross correlating the helmholtz decomposed wavefields rather than directly correlating the vector displacement fields results in sharper more interpretable images contaminated by fewer crosstalk artefacts the end products are separate p and s wave and if desired ps and sp migration images we test our migration algorithm on synthetic seismic data generated using the seg eage salt dome overthrust and marmousi 2 models we correctly image the location and shape of the target zone for oil exploration using these data sets furthermore we demonstrate that our new migration technique provides good images even when the initial velocity model is only approximate

influence of inherited topography on gravitational slope failure three dimensional numerical modelling of the la clapiere slope alpes maritimes france gravitational slope failure involves rock slopes at various scales nowadays it is accepted that different factors influence slope destabilization including topography in many cases slope failure occurs between tributary valleys cutting the slope in this study we ask what influence tributary valleys have on slope failure to tackle this question we developed a 3 d numerical model of the la clapiere slope and then examined a series of simplified 3 d models with different geometries of tributary valleys spacing and depth our results show that 1 whatever considered in situ stresses are including the third dimension reduces the destabilization threshold compared with 2 d models and 2 the spacing and the depth of tributary valleys influence slope failure for shallow incisions increasing the lateral spacing between tributary valleys does not affect failure localization but does increase slope damage to a stable value from 2000 m however deeper incision does not affect slope damage but does contribute to failure localization when the spacing is less than 1500 m the part of the slope between tributary valleys is not involved in the failure process but for spacings above 1500 m slope failure occurs between tributary valleys

the impact of a weak horizon on kinematics and internal deformation of a failure mass using discrete element method abstract weak horizons within slopes may induce and or accelerate failure of slopes in this study we focus on the effect of orientation location and dimension of a weak horizon on the mode and kinematics of downslope movement of a failure mass using discrete element method two kinds of cases with weak horizons were studied one unstable homogeneous slope with low shear strength c 50 kpa 0 57 and two stable homogeneous slopes with high shear strength c 60 kpa 0 57 or c 50 kpa 0 7 in the three sets of slope models there was a weak horizon with a finite thickness embedded within the slope in each set of slope models two different thicknesses and locations for the weak horizons were considered to systematically investigate the effect of these parameters on the mass movement in addition the dip of the weak horizon was changed where in some models it was parallel to the slope and in others it was dipping either steeper or gentler than the slope we analyzed both kinematics and internal deformation of the failure mass in all models and conclude that the presence and geometry i e thickness location and dip of a weak horizon changes the mode and kinematics of mass movement and governs the location of the failure surface

simulated winter circulation types in the north atlantic and european region for preindustrial and glacial conditions 1 winter circulation types under preindustrial and glacial conditions are investigated and used to quantify their impact on precipitation the analysis is based on daily mean sea level pressure fields of a highly resolved atmospheric general circulation model and focuses on the north atlantic and european region we find that glacial circulation types are dominated by patterns with an east west pressure gradient which clearly differs from the predominantly zonal patterns for the recent past this is also evident in the frequency of occurrence of circulation types when projecting preindustrial circulation types onto the glacial simulations the elevation of the laurentide ice sheet is identified as a major cause for these differences in areas of strong precipitation signals in glacial times the changes in the frequencies of occurrence of the circulation types explain up to 60 of the total difference between preindustrial and glacial simulations

reversed time migration in spatial frequency domain during the past decade finite difference methods have become important tools for direct modeling of seismic data as well as for certain interpretation processes one of the earliest applications of these methods to seismics is the pioneering contribution of alterman who in a series of papers alterman and karal 1968 alterman and aboudi 1968 alterman and rotenberg 1969 alterman and loewenthal 1972 demonstrated the usefulness of such numerical computations for the propagation of seismic waves in elastic media a clear exposition of these techniques as well as a comparison of results obtained from them with the corresponding analytical solutions can be found in alterman and karal 1968 this subject was further developed and extended to more complicated models by boore 1970 ottaviani 1971 and kelly et al 1976 claerbout introduced a somewhat different finite difference approach claerbout 1970 claerbout and johnson 1971 for modeling the acoustic waves which often dominate the reflection seismogram in his approach the original wave equation which governs the propagation of the acoustic waves is modified in such a way so as to allow the propagation of either only upcoming or only downgoing waves by moving the coordinate frame with the downgoing waves claerbout showed that one could greatly reduce computation time using the same concepts he showed claerbout and doherty 1972 how to use a similar scheme for migrating a seismic section by downward continuation of the upcoming waves this migration method is an interesting extension of the ideas of hagedoorn 1954 and was found to be extremely useful with real data larner and hatton 1976 loewenthal et al 1976

scattering and dip angle decomposition based on subsurface offset extended wave equation migration abstractan angle dependent reflection coefficient is recovered by seismic migration in the angle domain we have developed a postmigration technique for computing scattering and dip angle common image gathers cigs from seismic images extended by the subsurface offset based on wave equation migration methods our methodology suggests a system of radon transform operators by introducing local transform relations between the subsurface offset image and the angle domain components in addition to the commonly used decomposition of the scattering angle the methodology associates the wave equation migration with dip domain images as well the same postmigration subsurface offset image is used to decompose scattering and dip angle cigs individually or to decompose a multiangle cig by showing simultaneously both angles on the gather s axis we show that the dip angle response of seismic reflections is a spot like signature focused at the specular dip of the subsurface reflector it differs from the well stu

from the hagedoorn imaging technique to kirchhoff migration and inversion the seminal 1954 paper by j g hagedoorn introduced a heuristic for seismic reflector imaging that heuristic was a construction technique a string construction or ruler and compass method for finding reflectors as an envelope of equal traveltime curves defined by events on a seismic trace later kirchhoff migration was developed this method is based on an integral representation of the solution of the wave equation for decades kirchhoff migration has been one of the most popular methods for imaging seismic data parallel with the development of kirchhoff wave equation migration has been that of kirchhoff inversion which has as its objectives both structural imaging and the recovery of angle dependent reflection coefficients the relationship between kirchhoff migration inversion and hagedoorn s constructive technique has only recently been explored this paper addresses this relationship presenting the mathematical structure that the kirchhoff approach adds to hagedoorn s constructive method and showing the relationship between the two

angle domain common image gathers for migration velocity analysis by wavefield continuation imaging we analyze the kinematic properties of offset domain common image gathers cigs and angle domain cigs adcigs computed by wavefield continuation migration our results are valid regardless of whether the cigs were obtained by using the correct migration velocity they thus can be used as a theoretical basis for developing migration velocity analysis mva methods that exploit the velocity information contained in adcigs we demonstrate that in an adcig cube the image point lies on the normal to the apparent reflector dip that passes through the point where the source ray intersects the receiver ray the image point position on the normal depends on the velocity error when the velocity is correct the image point coincides with the point where the source ray intersects the receiver ray starting from this geometric result we derive an analytical expression for the expected movements of the image points in adcigs as functions of the traveltime perturbation caused by velocity errors by applying this ana

three dimensional passive seismic waveform imaging around the safod site california using the generalized radon transform 1 we apply a three dimensional 3d generalized radon transform grt to scattered p waves from 575 local earthquakes recorded at 68 temporary network stations for passive source imaging of near vertical structures close to the san andreas fault observatory at depth safod site the grt image profiles through or close by the safod site reveal near vertical reflectors close to the fault zone as well as in the granite to the southwest and the franciscan melange to the northeast of the main fault although slightly lower in resolution these structures are generally similar to features in 2d images produced with steep dip prestack seismic migration of data from active source seismic reflection and refraction surveys our grt images however also reveal several vertical reflectors to the northeast of the saf that do not appear in the migration images but which are consistent with local geology these results suggest that in a seismically active area inverse scattering of earthquake data for instance with the grt can be a viable and in 3d economic alternative to an active source survey

three dimensional physical modeling of deep seated landslides new technique and first results 1 a new technique for physical experimental modeling of landsliding and the first results are presented the technique is based on the use of new elasto brittle plastic analogue materials and an original vertical accelerator device enabling an increase in the gravity acceleration this technique allows slope stability to be addressed in a full three dimensional large strain formulation involving brittle and ductile rupture of the material three sets of experiments on the scale of a mountain 1 km high are presented the first one was designed to define the conditions and the mode of instability deformation in a homogeneous unfractured model instability occurs when the effective compressive strength c of the mountain is as small as 107 pa i e about 1 order of magnitude lower than the typical strength of small rock samples the deformation and rupture involve the whole mountain and correspond to well known deep seated gravitational slope deformation in the second set of experiments we introduced inherited tectonic faults which considerably reduce mountain stability with deformation again developing at the mountain scale the introduction of the local small scale fractures and weak zones in the last set of experiments resulted in smaller scale shallow landslides

anisotropic upper mantle stratigraphy and architecture of the slave craton the earth s physical properties show a dominantly radial structure which is the result of compositional differentiation isochemical phase changes1 and rheological layering2 rheological layering is perhaps the most difficult to investigate using conventional seismological techniques because the seismic manifestation of this property elastic anisotropy may closely mimic the effects of isotropic heterogeneity3 nonetheless an improved characterization of earth s rheological structure promises important insights into such processes as plate dynamics and continental evolution here i present a methodology for effectively characterizing sharp transitions in anisotropic upper mantle structure using the coda of teleseismic p waves application to seismograms from the slave craton reveals a well developed stratigraphy at least in part anisotropic with major boundaries occurring at nominal depths of 75 135 and 195 km the geometry and sharpness of these discontinuities suggest a structural origin perhaps involving shallow subduction

vb cyclones synchronized with the arctic north atlantic oscillation vb cyclones typically emerge in the western mediterranean and propagate to the northeast into central europe this paper explores the temporal characteristics of vb cyclone occurrence based on cyclone tracks identified at the atmospheric levels of z700 and sea level pressure using jra 55 reanalysis data for the period 1959 2015 the risk of vb occurrence was significantly high in the 1960s and has remained at a lower level since then vb cyclones do not occur fully randomly according to a poisson point process eleven well separated and distinct clusters as well as 11 hiatus periods are identified with average occurrence rates of 21 5 and 5 2 yrea 1 respectively during the event of vb the large scale atmospheric circulation is changed into a state favoring the development of successive vb cyclones clustering is very prominent in the case of genoan vb cyclones in summer as well as those vb cyclones developing over the iberian peninsula or the north african coast in winter superposition of the polar and the subtropical jet stream over the western mediterranean is identified as a main feature at the onset of vb cyclones vb cyclone occurrence appears to be synchronized with the northern atlantic oscillation nao at z500 and arctic oscillation ao at z1000 clusters have occurred when both nao and ao were negative this relation applies to western mediterranean cyclones not following a vb track as well however to a much weaker extent in contrast vb cyclone frequency was particularly low from 1988 to 1997 during a sustained positive phase of both nao and ao

the cheyenne belt analysis of a proterozoic suture in southern wyoming abstract the cheyenne belt of southeastern wyoming is a major shear zone which separates archean rocks of the wyoming province to the north from 1800 1600 ma old eugeoclinal gneisses to the south miogeoclinal rocks 2500 2000 ma old unconformably overlie archean basement immediately north of the shear zone and were deposited under transgressive conditions along a rift formed continental margin intrusive tholeiitic sills and dikes are interpreted as rift related intrusions and a date of 2000 ma on a felsic differentiate of these intrusions gives the approximate age of rifting there are no known post 2000 ma felsic intrusions north of the cheyenne belt volcanogenic gneisses and abundant syntectonic calc alkaline plutons of the southern terrane are interpreted as island are volcanic and plutonic rocks the volcanics are a bimodal basalt rhyolite assemblage plutons include large gabbroic complexes and quartz diorite 1780 ma syntectonic granitoids 1730 1630 ma and post tectonic anorthosite and granite 1400 ma there is no evidence for archean crust south of the cheyenne belt structural data thrusts in the miogeoclinal rocks vertical stretching lineations and the same fold geometries north and south of the shear zone suggest that juxtaposition of the two terranes took place by thrusting of the southern terrane island arc over the northern terrane craton and miogeocline probably as a continuation of the south dipping subduction which generated calc alkaline plutons of the southern terrane a metamorphic discontinuity across the shear zone with greenschist facies rocks to the north and upper amphibolite facies rocks and migmatites to the south also suggests thrusting of the southern terrane deeper crustal levels over the northern terrane shallower levels the cheyenne belt may be a deeply eroded master decollement perhaps analogous to a ramp in the master decollement in the southern appalachians this interpretation of the cheyenne belt as a proterozoic suture zone provides an explanation for the geologic geochronologic geophysical metallogenic and metamorphic discontinuities across the shear zone

structural analysis of turtle mountain alberta using digital elevation model toward a progressive failure abstract in 1903 the eastern slope of turtle mountain alberta was affected by a 30 m m 3 rockslide named frank slide that resulted in more than 70 casualties assuming that the main discontinuity sets including bedding control part of the slope morphology the structural features of turtle mountain were investigated using a digital elevation model dem using new landscape analysis techniques we have identified three main joint and fault sets these results are in agreement with those sets identified through field observations landscape analysis techniques using a dem confirm and refine the most recent geology model of the frank slide the rockslide was initiated along bedding and a fault at the base of the slope and propagated up slope by a regressive process following a surface composed of pre existing discontinuities the dem analysis also permits the identification of important geological structures along the 1903 slide scar based on the so called sloping local base level slbl an estimation was made of the present unstable volumes in the main scar delimited by the cracks and around the south area of the scar south peak the slbl is a method permitting a geometric interpretation of the failure surface based on a dem finally we propose a failure mechanism permitting the progressive failure of the rock mass that considers gentle dipping wedges 30 the prisms or wedges defined by two discontinuity sets permit the creation of a failure surface by progressive failure such structures are more commonly observed in recent rockslides this method is efficient and is recommended as a preliminary analysis prior to field investigation

internal structure and deformation of an unstable crystalline rock mass above randa switzerland part i internal structure from integrated geological and geophysical investigations 6m 3 of material occurred in fractured gneissic rock whose principal foliation faults and fracture zones dip into the slope above the scarp of the second rockslide the mountain continues to move at rates of up to 2 cm year in an attempt to understand failure mechanisms in fractured crystalline rock masses we have carried out a comprehensive multidisciplinary study that included detailed geological mapping borehole logging and imaging and surface and borehole geophysical surveys an integrated interpretation of the resultant data has revealed the presence of three prominent fault and fracture zone sets that define the internal structure of the rock mass some faults and fracture zones could be traced up to 85 m into the subsurface using borehole radar reflection methods the dips of the faults and fracture zones estimated from surface mapping matched those from radar reflection and borehole televiewer surveys no evidence was found for significant faults or persistent weakness planes that paralleled the 1991 rockslide failure surfaces instead the new observations were consistent with dominant failure mechanisms that involve the progressive development of major shear and brittle fracturezones and the eventual destruction of intact rock bridges immediately prior to catastrophic collapse this integrated study provides the first reliable model of the 3 d fault structure associated with and contributing to a large rock slope instability in a brittle crystalline rock mass

features of glacial valley profiles simply explained 1 glacial occupation of alpine valleys results in a distinct signature in the long valley profile including steepening of the profile in the headwaters flattening at lower elevations and a step in the profile at the convergence of headwater tributaries we present analytic results for glacial erosion patterns by making the following assumptions 1 the initial profile is linear 2 the width of the valley is uniform 3 the annual mass balance varies linearly with elevation 4 the glacier at any time is quasi steady 5 the erosion rate is proportional to ice discharge per unit valley width and 6 glacial erosion rates far exceed fluvial erosion rates a steady glacier under these conditions would erode a parabolic divot in the longitudinal valley profile with its maximum depth coinciding with the down valley position of the equilibrium line altitude ela the calculated flattening of the valley floor down valley of the ela and the steepening of it up valley captures the essence of the glacial signature when a reasonable probability distribution of elas is allowed the predicted erosion peaks at 30 40 of the down valley distance to the glacial limit and the pattern merges smoothly with the steeper fluvial profile downstream of the glacial limit profiles of mass balance that are capped at a maximum value produce shorter glaciers and a slight asymmetry in the expected erosion pattern only when we mimic the tributaries of glacial headwaters by specifying a valley width distribution do we obtain the upper step observed in many valley profiles

perspicacious indicators of atmospheric blocking 1 a novel dynamically based approach is introduced to identify describe and diagnose atmospheric blocking events the approach is based upon the potential vorticity perspective and takes into account the three dimensional structure of the phenomenon it is argued that the essence of a blocking anomaly is located in the upper troposphere just below the tropopause the associated novel blocking indicators are derived from two dimensional fields at 6 hourly temporal resolution and provide information on the spatial scale shape amplitude and movement of blocks a northern hemisphere winter djf climatology for the era15 period 1979 1993 is presented and comments are made on the relationship between the indicators and previous blocking indices

full azimuth subsurface angle domain wavefield decomposition and imaging part i directional and reflection image gathers we present a new subsurface angle domain seismic imaging systemforgeneratingandextractinghigh resolutioninformation about subsurface angle dependent reflectivity the system enables geophysicists to use all recorded seismic data in a continuousfashiondirectlyinthesubsurfacelocalangledomainlad resulting in two complementary full azimuth common imageangle gather systems directional and reflection the complete setofinformationfrombothtypesofanglegathersleadstoaccurate high resolution reliable velocity model determination and reservoir characterization the directional angle decomposition enables the implementation of specular and diffraction imaging in real 3d isotropic anisotropic geological models leading to simultaneous emphasis on continuous structural surfaces and discontinuous objects such as faults and small scale fractures structural attributes at each subsurface point e g dip azimuth andcontinuity canbederiveddirectlyfromthedirectionalangle gathers the reflection angle gathers display reflectivity as a function of the opening angle and opening azimuth these gathers are most meaningful in the vicinity of actual local reflecting surfaces wherethereflectionanglesaremeasuredwithrespectto the derived background specular direction the reflection angle gathers are used for automatic picking of full azimuth angle domainresidualmoveoutsrmowhich togetherwiththederived background orientations of the subsurface reflection horizons provide a complete set of input data to isotropic anisotropic tomography the full azimuth angle dependent amplitude variations are used for reliable and accurate amplitude versus angle andazimuthavazanalysisandreservoircharacterization the proposed system is most effective for imaging and analysis below complex structures such as subsalt and subbasalt high velocity carbonate rocks shallow low velocity gas pockets and others in addition it enables accurate azimuthal anisotropic imaging and analysis providing optimal solutions for fracture detectionandreservoircharacterization

kirchhoff elastic wave migration for the case of noncoincident source and receiver in taking into account both compressional p and shear s waves more geologic information can likely be extracted from the seismic data the presence of shear and converted shear waves in both land and marine seismic data recordings calls for the development of elastic wave migration methods the migration method presently developed consists of simultaneous migration of p and s waves for offset seismic data based on the kirchhoff helmholtz type integrals for elastic waves a new principle of simultaneously migrating both p and s waves is introduced the present method named the kirchhoff elastic wave migration has been tested using the 2 d synthetic surface data calculated from several elastic models of a dipping layer including a horizontal layer a composite dipping and horizontal layer and two layers over a half space the results of these tests not only assure the feasibility of this migration scheme but also demonstrate that enhanced images in the migrated sections are well formed moreove

influence of major inherited faults zones on gravitational slope deformation a two dimensional physical modelling of the la clapiere area southern french alps abstract inherited faults are known to influence rock slope stability and gravitational deformation in spite of that in many studies few faults are identified in field and properly used in models of gravitational slope deformation the aim of this work is to study the influence of inherited faults zone density and geometry on gravitational failure processes at the massif scale using a physical modelling technique which satisfies the similarity criteria models are scaled to the well documented natural example of la clapiere in the southern french alps experiments were conducted using mechanically homogeneous material with variable fault geometry in each of tested configurations the mobilized volume was almost the same results confirmed the hypothesis that the la clapiere landslide is a shallow section of a deep seated gravitational slope deformation furthermore among the various configurations tested only one is enable to reproduce the observed superficial deformation on the la clapiere hillside this result demonstrated that the geometry of the faults at depth plays a major role on the style of gravitational deformation patterns regarding the particular case of la clapiere our results give new insights on the shape of the faults affecting the massif at depth in particular normal listric faults seem to have shallow inflexions compared to a deep seated thrust fault that was either gravitationally formed or pre existing but inactive i e sealed before slope destabilization and then gravitationally reactivated

interferometry by deconvolution part 2 theory for elastic waves and application to drill bit seismic imaging deconvolution interferometry successfully recovers the impulse response between two receivers without the need for an independent estimate of the source function here we extend the method of interferometry by deconvolution to multicomponent data in elastic media as in the acoustic case elastic deconvolution interferometry retrieves only causal scattered waves that propagate between two receivers as if one acts as a pseudosource of the point force type interferometry by deconvolution in elastic media also generates artifacts because of a clamped point boundary condition imposed by the deconvolution process in seismic while drilling swd practice the goal is to determine the subsurface impulse response from drill bit noise records most swd technologies rely on pilot sensors and or models to predict the drill bit source function whose imprint is then removed from the data interferometry by deconvolution is of most use to swd applications in which pilot records are absent or provide unreliable estimates of bit excitation with a numerical swd subsalt example we show that deconvolution interferometry provides an image of the subsurface that cannot be obtained by correlations without an estimate of the source autocorrelation finally we test the use of deconvolution interferometry in processing swd field data acquired at the san andreas fault observatory at depth safod because no pilot records were available for these data deconvolution outperforms correlation in obtaining an interferometric image of the san andreas fault zone at depth

3d acoustic reverse time migration1 acoustic reverse time finite difference migration for zero offset data is extended from two to three dimensional media the formulation is based on the full three dimensional acoustic wave equation and so has no dip restrictions and it involves extrapolation in a velocity distribution variable in three dimensions the algorithm is demonstrated by successful migration of synthetic data sets for three models a point diffractor an oblique pinch out and a dome overlying a planar reflector

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

migration by extrapolation of time dependent boundary values migration of an observed zero offset wavefield can be performed as the solution of a boundary value problem in which the data are extrapolated backward in time this concept is implemented through a finite difference solution of the two dimensional acoustic wave equation all depths are imaged simultaneously at time 0 the imaging condition and all dips right up to vertical are correctly migrated numerical examples illustrate this technique in both constant and variable velocity media

influence of large scale topography on gravitational rock mass movements new insights from physical modeling 1 gravitational slope failures and associated rock mass movements can be observed at various scales in the same area it seems obvious that the different movement scales should be interrelated but their relationships are poorly understood we address this problem using 3 d physical modeling experiments were conducted with mechanically homogeneous models with two scale topographic features a large scale corresponds to the whole mountain several kilometers and a smaller one to a part of a mountain slope one kilometer results show that large scale relief induces large scale large volume gravitational movements introduction of small scale topographic features results not only in the generation of smaller scale landslides but also in considerable changes in the deformation pattern the various scale processes occur simultaneously and affect each other to predict the evolution of a landslide it is therefore necessary to take into account the topography and deformation pattern at various scales

structural characterization of turtle mountain anticline alberta canada and impact on rock slope failure abstract this paper proposes a structural investigation of the turtle mountain anticline alberta canada to better understand the role of the different tectonic features on the development of both local and large scale rock slope instabilities occurring in turtle mountain the study area is investigated by combining remote methods with detailed field surveys in particular the benefit of terrestrial laser scanning for ductile and brittle tectonic structure interpretations is illustrated the proposed tectonic interpretation allows the characterization of the fracturing pattern the fold geometry and the role of these tectonic features in rock slope instability development ten discontinuity sets are identified in the study area their local variations permitting the differentiation of the study zone into 20 homogenous structural domains the anticline is described as an eastern verging fold that displays considerable geometry differences along its axis and developed by both flexural slip and tangential longitudinal strain folding mechanisms moreover the origins of the discontinuity sets are determined according to the tectonic phases affecting the region pre folding folding post folding the localization and interpretation of kinematics of the different instabilities revealed the importance of considering the discrete brittle planes of weakness which largely control the kinematic release of the local instabilities and also the rock mass damage induced by large tectonic structures fold hinge thrust

lithosphere scale seismic image of the southern urals from explosion source reflection profiling explosive source deep seismic reflection data from the southern ural mountains of central russia provided a lithosphere scale image of the central eurasian plate that reveals deep reflections 35 to 45 seconds in travel time 130 to 170 kilometers deep from the mantle the data display laterally variable reflectivity at the base of the crust that deepens beneath the central part of the profile documenting a crustal thickness of 55 to 60 kilometers beneath the axis of the orogen these data provide an image of the structure of the crust and underlying mantle lithosphere in a preserved collisional orogen perhaps to the base of the lithosphere

an introductory review on gravitational deformation induced structures fabrics and modeling abstract recent studies have pointed out a similarity between tectonics and slope tectonic induced structures numerous studies have demonstrated that structures and fabrics previously interpreted as of purely geodynamical origin are instead the result of large slope deformation and this led in the past to erroneous interpretations nevertheless their limit seems not clearly defined but it is somehow transitional some studies point out continuity between failures developing at surface with upper crust movements in this contribution the main studies which examine the link between rock structures and slope movements are reviewed the aspects regarding model and scale of observation are discussed together with the role of pre existing weaknesses in the rock mass as slope failures can develop through progressive failure structures and their changes in time and space can be recognized furthermore recognition of the origin of these structures can help in avoiding misinterpretations of regional geology this also suggests the importance of integrating different slope movement classifications based on distribution and pattern of deformation and the application of structural geology techniques a structural geology approach in the landslide community is a tool that can greatly support the hazard quantification and related risks because most of the physical parameters which are used for landslide modeling are derived from geotechnical tests or the emerging geophysical approaches

representation of extratropical cyclones blocking anticyclones and alpine circulation types in multiple reanalyses and model simulations abstractatmospheric circulation types blockings and cyclones are central features of the extratropical flow and key to understanding the climate system this study intercompares the representation of these features in 10 reanalyses and in an ensemble of 30 climate model simulations between 1980 and 2005 both modern full input reanalyses and century long surface input reanalyses are examined modern full input reanalyses agree well on key statistics of blockings cyclones and circulation types however the intensity and depth of cyclones vary among them reanalyses with higher horizontal resolution show higher cyclone center densities and more intense cyclones for blockings no strict relationship is found between frequency or intensity and horizontal resolution full input reanalyses contain more intense blocking compared to surface input reanalyses circulation type classifications over central europe show that both versions of the twentieth century reanalysis dataset contain more easterlies and

sackung and enigmatic mass movement folds on a structurally controlled mountain ridge abstract the recently emerged concept of slope tectonics suggests that mass movement processes can produce structures similar in morphological expression to that of extensional strike slip and compressional tectonic deformations further there has long been debate about the tectonic or gravitational origin of lineaments found on hillslopes here we present cases of where geological structure and inherited tectonic structures have preconditioned the development of mass movements and creation of slope tectonic features on a monoclinal ridge smrk mt in the outer western carpathians czechia geomorphic mapping from lidar derived topography structural measurements electrical resistivity tomography and ground penetrating radar were used to map synthetic and antithetic scarps thrusts and folds and assess their relation to geological and tectonic structures the scarps are found to be strongly related to transverse nnw to nne trending inherited normal and strike slip faults and mainly cross cut the topography of the mountain ridge some of the folds are thought to have originated from buckling or compression in the distal parts of landslides in other places transpressional folds have developed oblique to major lateral shear surfaces interpreted to be sackung mass movement scarps that have been inherited from tectonic faults the transpressional folds developed due to localized contraction along bends in the lateral shear surface as mass movement proceeded ramp flat thrust folds developed in the compressional parts of landslides where the landslide intersects with slope parallel sackung and or inherited fault planes inclined to the slope altogether this study demonstrates a connection between kinematics of deep seated gravitational slope deformations dsgsds shallower landslides and the origin of transpressive ramp flat thrust and detachment structures in rock slopes

slope tectonics a short introduction geomorphology structuralgeologyandengineeringgeology allow description of the main character istics of a slope in distinct ways that can be com bined to provide a complementary view of theoperative slope processes the subjects presentedin this special publication include slope mor phology and evolution mechanical behaviour ofthe material modes of failure and collapse in u ence of lithology and structural features and therole played by controlling factors this slope tec tonics volume comprises a series of very differentcontributions that attempt to underline a multidisci plinary approach thatshould form the framework ofslope instability studies slope tectonics is adopted in this volume tomeandeformationthatisinducedorfullycontrolledbytheslopemorphologyandthatgeneratesfeaturesthatcanbecomparedtotectonicfeatures thestress eld in a slope is the result of gravity topographyand the geological setting created by an ensembleof geodynamic processes active tectonics alsocalled neotectonics generates a stress eld thatcancontrolslopeprocesses astrongfeedbackexist ingbetween geological history tectonics lithology geomorphological evolution and topography as a consequence a list of factors and theirrela tive in uence can be presented 1 fabric induced by a local stress eld within aslope discontinuities and local faults with cata clastic bands of variable thickness folds fig 1 associated predominantlywith brittle structures complex failure paths stepped or multi surface localfailures rockbridgefailuresorexten sional failures graben like or pseudo graben like subsidence due to weak or soluble mate rials causing complex sliding topplingphenomena 2 reactivation of pre existing faults disconti nuities joints foliations or rock anisotropies surfaces characterized by residual or lowerthan peak strength formation of composite failure surfaces 3 regional tectonic movements inducing newslope morphologies uplift major fault movement pull apart zones folding the boundary between classical tectonics andslope deformations especially at a large scale hasalways been indistinct as emphasized by antoine 1988 schultz ela 2001 in his paper antoinediscussed mechanisms like diverticulation def ined by lugeon 1943 and badoux 1963 wherepart of pre alpine nappes were reversed in geo metry by huge landslides inverting the stratigraphy antoine 1988 a remarkable geometrical analogyexists between basin extensional tectonics wer nicke 1981 and certain landslide spreading inclays voight 1973 varnes 1978 hutchinson1988 this is despite the fact that wernicke shypothesis demonstrated that basin and rangeregions were not produced by huge landslides butby low angle faulting induced by geodynamic pro cesses regional extension has produced changesin topography and as a consequence signi cantgravity induced deformations therefore we suggest that the term slope tec tonics is justi ed and must be recognized as animportant component in slope deformation slopeinstability implies movements driven by gravitythat can produce irreversible deformations in thepast slopes were viewed as privileged erosionzones de la noe de margerie 1888 strahler1950 whereas few erosion processes were attribu ted to landslides young 1972 since the work ofsimonett 1967 and hovius et al 1997 the link

analysis of the distributions of stress in natural ridge forms implications for the deformation mechanisms of rock slopes and the formation of sackung abstract stress distributions in general asymmetric ridge forms derived from 13 ridges in british columbia and colorado are modelled in two dimensions with a finite difference method in each of the 13 ridges sackung scarps tension cracks trenches can be found spatial correlations between stress concentrations and these sackungen landforms are investigated for the mean ridge forms rock mass properties for the modelled ridges are developed using the hoek brown criterion and the geological strength index gsi gravity loading and combined gravity tectonic loading on the ridge forms are considered the importance of representing in situ rock masses with an elastoplastic as opposed to elastic constitutive criterion is discussed the resulting stress distributions for the three general ridge classes indicate that different processes are responsible for the formation of sackungen landforms and slope deformations in each type of ridge

3 d numerical modelling of the influence of pre existing faults and boundary conditions on the distribution of deformation example of north western ghana abstract high strain zones bound and separate the high grade tectono metamorphic terranes from low grade greenstone belts in the north western parts of ghana these belts are bounded by granitoid domains characterized by two main episodic pulses of magmatic intrusive events which occurred between 2213 ma and 2086 ma high strain zones are thought to play a significant role in creating fluid pathways particularly for partially molten material from lower crustal sources to the upper crust in this study a three dimensional thermo mechanical model has been used to explore the evolution of high strain zones and relief under compressional and simple shear boundary conditions different orientations of a system of branched strike slip faults were tested the effects of the frictional angle and density contrast on the evolution of relief were also compared in this study the resulting model indicates domains of tensile vs compressional strain as well as shear zones this shows that the internal fault zones as well as the host rock in between the faults behave as relatively weaker domains than the external regions under both applied compressive and simple shear boundary conditions these weakened domains constitute preferential zones of tensile and shear strain accommodations in the upper crust which may favour infilling by deeper partially molten rocks this processes is suggested by the authors as the most likely processes to have occurred in pre existing branched shear zones systems in north western ghana during the eburnean orogeny around 2 20 2 10 ga the orientations of faults in these models play an important role in controlling the evolution of relief and localized deformation in particular greatest the largest relief is obtained when faults dip parallel to each other and when they are inclined at depth as they thus facilitate strain rotation and material transfer from depth the host rock density does not play a primary role in producing relief compared to variations in friction angle at crustal scale of our model relief increases by 200 300 m when the host rock density is increased by 200 kg m3 whereas relief reduces by about 1200 m when decreasing the host rock friction from 20 to 10 this study suggests a model for interpreting the evolution and locus of exhumation of partially molten rocks in north western ghana

use of rtm full 3d subsurface angle gathers for subsalt velocity update and image optimization case study at shenzi field various reverse time migration rtm angle gather generation techniques have been developed to address poor subsalt data quality and multiarrival induced problems in gathers from kirchhoff migration but these techniques introduce new problems such as inaccuracies in 2d subsurface angle gathers and edge diffraction artifacts in 3d subsurface angle gathers the unique rich azimuth data set acquired over the shenzi field in the gulf of mexico enabled the generally artifact free generation of 3d subsurface angle gathers using this data set we carried out suprasalt tomography and salt model building steps and then produced 3d angle gathers to update the subsalt velocity we used tilted transverse isotropy rtm with extended image condition to generate full 3d subsurface offset domain common image gathers which were subsequently converted to 3d angle gathers the angle gathers were substacked along the subsurface azimuth axis into azimuth sectors residual moveout analysis was carried out and ray based tom

blocking and rossby wave breaking on the dynamical tropopause in the southern hemisphere abstract rossby wave breaking on the dynamical tropopause in the southern hemisphere the 2 pvu surface is investigated using the era 40 dataset the indication of wave breaking is based on reversal in the meridional gradient of potential temperature and persistent large scale wave breaking is taken as a strong indication that blocking may be present blocking in the midlatitudes is found to occur predominantly during wintertime in the pacific and is most vigorous in the east pacific while during summertime the frequency of blocking weakens and its extent becomes confined to the west pacific the interannual variability of blocking is found to be high wave breaking occurs most frequently on the poleward side of the polar jet and has some but not all of the signatures of blocking so it is referred to as high latitude blocking in general cyclonic wave breaking occurs on the poleward side of the polar jet otherwise anticyclonic breaking occurs however at least in wintertime wave breaking in th