field measurements of duration limited growth of wind generated ocean surface waves at young stage of development abstract the issue of duration limited growth of wind generated waves is of importance to wave studies most analytical solutions for wind waves are given in time rather than fetch domain numerical modeling of wave development is also often conducted in temporal evolution mode experimental data of duration limited growth however are rare and do not cover a wide range of the wave development stage as a result theorists and modelers have to rely on fetch limited evolution data converting them into duration limited conditions on the basis of some assumptions during one of the field experiments of wind wave measurements a dataset was obtained that is almost ideal for duration limited wave growth analysis the dataset extends the range of coverage in dimensionless time of the existing database by about one order of magnitude the results of analysis provide strong support for the relation of space time conversion for rendering the fetch limited growth functions to duration limited growth functions qu

gnss r nonlocal sea state dependencies model and empirical verification global navigation satellite system reflectometry gnss r is an active bistatic remote sensing technique operating at l band frequencies gnss r signals scattered from a rough ocean surface are known to interact with longer surface waves than traditional scatterometery and altimetry signals a revised forward model for gnss r measurements is presented which assumes an ocean surface wave spectrum that is forced by other sources than just the local near surface winds the model is motivated by recent spaceborne gnss r observations that indicate a strong scattering dependence on significant wave height even after controlling for local wind speed this behavior is not well represented by the most commonly used gnss r scattering model which features a one to one relationship between wind speed and the mean square slope of the ocean surface the revised forward model incorporates a third generation wave model that is skillful at representing long waves an anchored spectral tail model and a gnss r electromagnetic scattering model in comparisons with the spaceborne measurements the new model is much better able to reproduce the empirical behavior

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

extreme curvature and extreme flexure analysis for fracture characterization from 3d seismic data new analytical algorithms and geologic implications abstractfracture characterization is fundamental to the reliable prediction of fractured reservoirs however it is difficult and expensive to obtain detailed fracture information required for reservoir prediction due to the lack of direct observational data in the subsurface here we develop seismic analysis methods to characterize fractured reservoirs based on reflection geometry related to bending and shearing of reservoir formations among various geometric attributes we focus on extreme curvature and extreme flexure that are considered effective at detecting fractures extreme curvature refers to the signed absolute maximum curvature at a specific azimuth where the curve shape is the tightest whereas extreme flexure refers to the signed absolute maximum gradient of curvature at a specific azimuth where the curve shape changes the most we implement new algorithms based on analytical equations to calculate extreme curvature and extreme flexure along with the corresponding azimuth from 3d seismic dat

rheological contrast at the continental moho effects of composition temperature deformation mechanism and tectonic regime abstract the rheological contrast at the moho is an important factor in continental tectonics this paper explores systematically the effects of composition temperature deformation mechanism and tectonic regime on the strength contrast considering four compositions for the lower crust felsic granulite mafic granulite wet diabase dry diabase and two for the lithospheric mantle dry and wet peridotite the strength contrast of the resulting eight compositional layerings is estimated as a function of moho temperature which is varied from 600 to 1500 k the moho temperature can be converted to surface heat flow if the thickness and composition of the crust are known besides a standard case crustal thickness 35 km the cases of a thick 50 km and thin 20 km crust are also considered with wet quartzite crustal rheology in the latter case results show a great variety of strength contrasts according to different conditions excluding the case of very low moho temperature tm 600 k when the behaviour of both lower crust and upper mantle is frictional brittle and therefore the strength contrast vanishes the strength contrast at a given strain rate is a strong function of composition temperature and tectonic conditions weak compositional stratification e g soft lower crust soft lithospheric mantle or hard lower crust hard lithospheric mantle results in lower contrasts than strong compositional stratification for any given compositional combination the absolute value of the strength contrast is higher in compressional as compared to extensional tectonic environments and tends to decrease with increasing temperature from a maximum of hundreds of mpa at low to intermediate moho temperatures 600 1200 k therefore rheological layering is favoured by strong intrinsic i e compositional strength contrasts between lower crust and upper mantle and relatively low moho temperatures

diffusion creep of dry melt free olivine 1 deformation experiments were conducted on fine grained 3 6 m fully synthetic fo90 olivine aggregates in a gas medium apparatus at 300 mpa confining pressure and temperatures of 1150 1360 c the strain rates of the solution gelation derived and therefore genuinely melt free dry samples are about two orders of magnitude lower than the strain rates for nominally melt free aggregates at the same pressure and temperature conditions and grain size benchmark deformation tests with anita bay dunite and mild steel reproduce published data the creep strength of melt added sol gel olivine is similar to the published creep strength of dry melt bearing olivine derived from natural rocks nonlinear least squares fits to the melt free deformation data give an activation energy of 484 kj mol a stress exponent of 1 4 and a grain size exponent of 3 over a range of stresses from 15 to 210 mpa these results suggest that small amounts of melt may be similarly effective in reducing the creep strength of upper mantle rocks as small amounts of water however a possible contribution of grain boundary composition to the observed differences in rheology in the absence of melt cannot be conclusively ruled out by the current experiments

modeling waves and wind stress 1 a model for wave and wind stress prediction is constructed the source functions that drive the space time evolution of the energy spectra are developed in form based on theory and laboratory and field experiments the calibration factors proportionality constants of the source functions are determined from a comparison of modeled and observed significant height and mean period the observations are for the month of january 2005 and are derived from an array of laser range finders mounted on a bridge between two platforms in the ekofisk oil field in the north sea the model calculates the form stress on the waves and adds it vectorially to the sheltering modified skin stress the resulting drag coefficient versus wind speed is shown to have the observed structure low in light winds increasing in moderate winds and increasing more slowly in very strong winds modeled spectral shapes in the four quadrants of hurricane bonnie 1998 match the scanning radar altimeter measurements modeled spectral properties in hurricane ike 2008 are compared against ndbc buoy estimates with good results drag coefficients in the mixed seas produced by hurricanes show dependence on wave age of the wind sea swell propagation direction and water depth the need for wave and stress modeling for atmosphere ocean coupling is emphasized the new wave model has all the necessary attributes to be the basis for such a coupler

volumetric curvature attributes add value to 3d seismic data interpretation horizon based curvature attributes have been used in seismic data interpretation for predicting fractures since 1994 when lisle demonstrated the correlation of curvature values to fractures measured on an outcrop different measures of curvature such as gaussian strike and dip have been shown by different workers to be highly correlated with fractures and many more applications are also possible by definition all such applications need the interpretation of a seismic horizon which may be simple if data quality is good and the horizon of interest corresponds to a prominent impedance contrast

3d seismic flexure analysis for subsurface fault detection and fracture characterization seismic flexure is a new geometric attribute with the potential of delineating subtle faults and fractures from three dimensional 3d seismic surveys especially those overlooked by the popular discontinuity and curvature attributes although the concept of flexure and its related algorithms have been published in the literature the attribute has not been sufficiently applied to subsurface fault detection and fracture characterization this paper provides a comprehensive study of the flexure attribute including its definition computation as well as geologic implications for evaluating the fundamental fracture properties that are essential to fracture characterization and network modeling in the subsurface through applications to the fractured reservoir at teapot dome wyoming usa specifically flexure measures the third order variation of the geometry of a seismic reflector and is dependent on the measuring direction in 3d space among all possible directions flexure is considered most useful when extracted perpendicular to the orientation of dominant deformation and flexure offers new insights into qualitative quantitative fracture characterization with its magnitude indicating the intensity of faulting and fracturing its azimuth defining the orientation of most likely fracture trends and its sign differentiating the sense of displacement of faults and fractures

3 d seismic attributes using a semblance based coherency algorithm seismic coherency is a measure of lateral changes in the seismic response caused by variation in structure stratigraphy lithology porosity and the presence of hydrocarbons unlike shaded relief maps that allow 3 d visualization of faults and channels from horizon picks seismic coherency operates on the seismic data itself and is therefore unencumbered by interpreter or automatic picker biases we present a more robust multitrace semblance based coherency algorithm that allows us to analyze data of lesser quality than our original three trace cross correlation based algorithm this second generation semblance based coherency algorithm provides improved vertical resolution over our original zero mean crosscorrelation algorithm resulting in reduced mixing of overlying or underlying stratigraphic features in general we analyze stratigraphic features using as narrow a temporal analysis window as possible typically determined by the highest usable frequency in the input seismic data in the limit one may confidently apply our new semblance based algorithm to a one sample thick seismic volume extracted along a conventionally picked stratigraphic horizon corresponding to a peak or trough whose amplitudes lie sufficiently above the ambient seismic noise in contrast near vertical structural features such as faults are better enhanced when using a longer temporal analysis window corresponding to the lowest usable frequency in the input data the calculation of reflector dip azimuth throughout the data volume allows us to generalize the calculation of conventional complex trace attributes including envelope phase frequency and bandwidth to the calculation of complex reflector attributes generated by slant stacking the input data along the reflector dip within the coherency analysis window these more robust complex reflector attribute cubes can be combined with coherency and dip azimuth cubes using conventional geostatistical clustering and segmentation algorithms to provide an integrated multiattribute analysis

the experimental deformation of dunite deformation experiments have been carried out on two dunites anita bay of 100 m grain size and aheim of 900 m grain size at strain rates from 10 3 to 10 6 s 1 and temperatures from 1000 c to 1300 c in a gas medium deformation apparatus at 300 mpa confining pressure most of the tests were under wet conditions defined by the presence of small amounts of water from hydrous minerals initially present constant strain rate and relaxation experiments covering ranges of flow stress down to about 70 mpa and 7 mpa respectively show that there is a change in flow law in going below about 100 mpa differential stress and that the coarser grained rock is stronger than the finer grained one power law parameters above the transition are n 4 48 0 31 and q 498 38 kj mol 1 for aheim dunite and n 3 35 0 17 and q 444 24 kj mol 1 for anita bay dunite while below the transition relaxation tests on anita bay dunite give n 2 44 0 18 and q 386 27 kj mol 1 it is concluded that there is a weakening effect of water that this effect is mainly in the grain boundaries and that grain boundary sliding is probably a significant deformation mechanism at the lower stresses under wet conditions

rheology of some continental lower crustal rocks abstract to gain insight into the rheology of selected feldspar bearing rocks from the continental lower crust clc three granulites from exposed lower crustal terrains and a microgabbro have been deformed to ca 10 strain at confining pressures of 0 8 1 0 gpa temperatures of 600 900 c and constant strain rates of 10 4 10 7 s 1 the most extensive work was done on the mafic pikwitonei and felsic adirondack granulites the pikwitonei mg hornblende plag an70 2 px has only a limited t range of apparent steady state behavior and strain softens at t 800 c at 10 5 10 6s 1 apparently associated with developing shear zones this strain softening is pressure insensitive from pc 0 8 1 0 gpa at t 850 c 10 6s 1 even though the dominant strain accommodation mechanisms change from semibrittle cataclastic to crystal plastic including dynamic recrystallization with increasing pressure plagioclase appears to bear more of the creep strain than amphibole at most experimental conditions except in those runs where both plagioclase and amphibole recrystallization occurs kapuskasing plag cpx gt granulite deformed at 800 c and at 850 c 10 6 s 1 has deformed in the steady state at stress levels only slightly greater than the pikwitonei the stillwater microgabbro and adirondack granulite are appreciably weaker and the latter exhibits homogeneous semibrittle steady state behavior over the entire range of conditions investigated for the adirondack 2 felds 2 px gt qtz granulite quartz 21 appears to control the creep rate at these low strains and steady state mechanical data fit well a creep power law with a 8 10 3 mpa ns 1 qc 243 kj mol and n 3 1 extrapolation of this flow law and of preliminary power law creep relations for the pikwitonei and microgabbro to a range of physical conditions assumed to encompass those at the continental moho supports geological and geophysical inferences that a mechanical discontinuity occurs at this transition zone with the lower crust generally being the weaker material in addition the stain softening exhibited by the pikwitonei may bear directly on the development of detachment zones at mid to lower crustal depths during prograde metamorphism

stress strength relationship in the lithosphere during continental collision lithospheric strength profiles generated for a shortening continental lithosphere generally predict excessively high differential stresses in the sub moho continental mantle this seems inconsistent with the relative scarcity of earthquakes at this depth this inconsistency was put forward as evidence for weak mantle rheology however this argument implicitly assumes that strength envelopes are valid in actively deforming regions we test this assumption on two end member model lithospheres having identical upper crustal rheologies but with 1 a weak lower crust and strong mantle and 2 a strong lower crust and weak mantle for this purpose we compare one dimensional 1 d with 2 d visco elastoplastic numerical models of continental shortening the 2 d models show that strongly heterogeneous deformation typically follows initially homogeneous deformation lithospheric scale buckle folds and shear zones result in strain rate variations of as much as three orders of magnitude differential stresses in the upper crust are close to yield as predicted by 1 d models stresses in deeper lithospheric regions however are significantly smaller than in 1 d models especially in actively deforming regions systematic numerical simulations as a function of temperature and deformation rate reveal that 1 d models are reliable in hot and or slowly deforming lithospheres only the relative scarcity of earthquakes at mantle levels should thus be interpreted as an intrinsic consequence of strong lithospheric deformation rather than as evidence for a weak upper mantle

the role of rheology in extensional basin formation modelling the rheology of the lithosphere determines its deformation under given initial and boundary conditions this paper presents a critical discussion on how rheological properties are taken into account in extensional basin modelling since strength envelopes are often used in models we review the uncertainties in temperature and rheological parameters and assumptions in type of rheology and mode of deformation involved in their construction models of extensional basins are classified into three groups kinematic kinematic with rheological constraints and dynamic rheology enters kinematic models only implicitly in the assumption of an isostatic compensation mechanism we show that there is a critical level of necking that reconciles local isostasy with the finite strength of the lithosphere which requires a flexural response kinematic models with rheological constraints make use of strength envelopes to assess the initial lateral variations of lithospheric strength and its evolution with time at the site of extension dynamic models are the only ones to explicitly introduce rheological constitutive equations usually in plane strain or plane stress they usually however require the presence of an initial perturbation thickness variations pre existing faults thermal inhomogeneities rheological inhomogeneities the mechanical boundary conditions kinematic and dynamic and the thermal boundary conditions constant temperature or constant heat flux at the lower boundary of the lithosphere may result in negative positive feedbacks leading to cessation acceleration of extension we conclude that while kinematic models with rheological constraints if possible are very successful in accounting for the observed characteristics of sedimentary basins dynamic models are necessary to gain insight into the physical processes underlying basin formation and evolution

combining outcrop data and three dimensional structural models to characterize fractured reservoirs an example from wyoming combining a detailed outcrop characterization of fracture and fault occurrence with attributes from a three dimensional model of an anticlinally folded clastic reservoir body we determine which characteristics of the structural form and evolution are most closely related to the development of important reservoir scale structures our example reservoir body studied is the frontier formation 1 sandstone in oil mountain an asymmetric anticline on the western flank of casper arch in central wyoming the three dimensional model of the structure was constructed using an iterative scheme designed to maximize interpretation accuracy and precision the model was analyzed to determine the spatial variance in morphologic and kinematic attributes using a quantitative testing approach we found that the intensity of tectonically produced fractures is closely related spatially to rate of dip change and total curvature with the former having the strongest correlation this folding is a low strain process compared to tear faulting which has the strongest spatial correlation to larger strains the location and magnitude of these higher strain areas can be adequately predicted by three dimensional restoration and forward modeling of the upper bounding surface of the reservoir body we use these results to build a predictive model for fault and fracture distribution at oil mountain and to discuss how this approach can aid in the exploitation of analogous producing reservoirs

enhanced structural interpretation from 3d seismic data using hybrid attributes new insights into fault visualization and displacement in cretaceous formations of the scotian basin offshore nova scotia abstract meta or hybrid attributes extracted from seismic data through artificial neural networks enhance structural details in subsurface strata cretaceous units within the penobscot prospect are devoid of such interpretations although these units are plausible zones for hydrocarbon generation and accumulation the role of geologic structures responsible for such entrapment is poorly understood the present study enlightens these latter geological structures through a case study that uses 3d time migrated seismic data from the penobscot prospect in the scotian basin a modern data conditioning approach used together with multi attribute analyses and a supervised neural network have brought out the minute details of subsurface geologic structures through a hybrid attribute called the fault probability cube fpc the present fault displacement analysis reveals that the major fault of the prospect has evolved by the coalescence of different fault segments grown over space and time and has demonstrated a predominant nnw sse structural trend such a geometry has structurally modulated the cretaceous units the logan canyon the dawson canyon and the wyandot formations giving rise to different horst graben structures and fracture networks as shown by the fpc attribute this generates complicated structural deformation and accommodation space thereby enabling different trapping zones for hydrocarbon accumulation within these units such a detailed structural understanding will provide significant input to the future exploration and development programme in the penobscot prospect

thermomechanical structure of european continental lithosphere constraints from rheological profiles and eet estimates summary the eet equivalent elastic thickness of the lithosphere is a measure of the integrated lithospheric strength it is directly related to the mechanical thickness and rheology of the crustal and mantle lithosphere we present a comparison of eet estimates and strength profiles based on the extrapolation of rock mechanics data for different parts of the european and eurasian continental lithosphere we discuss the temporal and spatial variations in the mechanical thickness and strength inferred from data for precambrian segments of europe s lithosphere variscan europe and the alpine collision belt this analysis demonstrates important spatial and temporal variations in lithospheric rigidity for orogenic belts and sedimentary basins in eastern and western europe and asian parts of eurasia the eet estimates based on synthetic rheological profiles constrained by newly available geophysical data are consistent with the estimates of eet derived from flexural studies of sedimentary basins forelands and orogenic belts these rheological profiles suggest weakening of the major parts of the european and eurasian continental lithosphere by decoupling of the crustal and upper mantle parts a comparison with the seismicity depth distribution for some selected sites suggests that the intra plate seismicity is essentially restricted to the upper crustal parts of europe s lithosphere providing additional support to the notion of the decoupled lithosphere the presence of intra plate stress fields can explain a significant part of the observed variations in eet estimates within individual thermotectonic age groups a comparison of wavelengths of crustal and lithospheric folding with observations shows these wavelengths to be consistent with estimates of eet inferred from the rheological response of basins and orogens at more moderate levels of intra plate stress

a two level concept of plate tectonics application to geodynamics abstract a two level plate tectonics concept is developed on the basis of data on lithosphere rheological stratification this approach differentiates between crust and subcrust plate ensembles separated by a lower crust viscoplastic asthenolayer similarly to classical plate tectonics three types of boundaries are distinguished in the lower layer which do not always coincide with crust plate boundaries especially for continents applications of this concept to geodynamics are considered and a corresponding quantitative analysis for several important processes is carried out a quantitative model of mountain formation and collision plateau origins is proposed also a geodynamic model of the evolution of passive margins taking into account a lower crust viscous flow is considered and its geological consequences are discussed a mechanism of rifting taking into consideration rheological lithospheric layering and its vertical movements caused by extension is developed both a qualitative scheme and quantitative analysis of the slow evolution of intracraton structures of shield basin type taking into account erosion and sedimentation processes are worked through also historical aspects of plate tectonics are discussed from the point of view of the proposed concept

semi automatic fault fracture interpretation based on seismic geometry analysis abstract fault and fracture interpretation is a fundamental but essential tool for subsurface structure mapping and modelling from 3d seismic data the existing methods for semi automatic automatic fault picking are primarily based on seismic discontinuity analysis that evaluates the lateral changes in seismic waveform and or amplitude which is limited by its low resolution on subtle faults and fractures without apparent vertical displacements in seismic images this study presents an innovative workflow for computer aided fault fracture interpretation based on seismic geometry analysis first the seismic curvature and flexure attributes are estimated for highlighting both the major faults and the subtle fractures in a seismic volume then fault probability is estimated from the curvature and flexure volumes for differentiation between the potential faults and non faulting features in the geometric attributes finally the seeded fault picking is implemented for interpreting the target faults and fractures guided by the knowledge of interpreters to avoid misinterpretation and artefacts in the presence of faulting complexities as well as coherent seismic noises applications to two 3d seismic volumes from the netherlands north sea and the offshore new zealand demonstrate the added values of the proposed method in imaging and picking the subtle faults and fractures that are often overlooked in the conventional seismic discontinuity analysis and the following fault interpretation procedures

developing a model discrete fracture network drilling and enhanced oil recovery strategy in an unconventional naturally fractured reservoir using integrated field image log and three dimensional seismic data in this study we develop a model discrete fracture network dfn for the unconventional naturally fractured tensleep sandstone oil reservoir at teapot dome wyoming reservoir characterization is based on three dimensional 3d seismic data fracture image logs from teapot dome and field observations of the tensleep exposure in the alcova anticline and fremont canyon areas image logs reveal that the dominant reservoir fracture set trends parallel to the present day maximum horizontal compressive stress inferred from drilling induced fractures analog field studies of the alcova anticline and fremont canyon suggest fracture heights and lengths are power law distributed while the fracture spacing distribution is best described as log normal image log derived fracture apertures are also log normally distributed these properties are incorporated into a model dfn we assume subseismic folds faults and fracture zones control fracture intensity distribution and use composite 3d seismic attributes to locate subtle changes in seismic response interpreted to result from subseismic structure directional curvature defines aperture opening strain normal to the dominant reservoir fracture set seismic attributes are scaled and combined to control fracture intensity variations in the model grid cell porosity and permeability distributions derived from the dfn suggest the presence of northeast southwest trending reservoir compartments we suggest that enhanced oil recovery operations may be optimized using lateral injection and production wells oriented along interpreted compartment boundaries at high angles to this combination of injection and production laterals could help maximize storage and hydrocarbon recovery in depleted reservoirs and in down dip residual oil zones

scattering of gps signals from the ocean with wind remote sensing application a theoretical model that describes the power of a scattered global positioning system gps signal as a function of geometrical and environmental parameters has been developed this model is based on a bistatic radar equation derived using the geometric optics limit of the kirchhoff approximation the waveform i e the time delayed power obtained in the delay mapping technique depends on a wave slope probability density function which in turn depends on wind waveforms obtained for aircraft altitudes and velocities indicate that altitudes within the interval 5 15 km are the best for inferring wind speed in some regimes an analytical solution for the bistatic radar equation is possible this solution allows converting trailing edges of waveforms into a set of straight lines which could be convenient for wind retrieval a transition to satellite altitudes together with satellite velocities makes the peak power reduction and the doppler spreading effect a significant problem for wind retrieval based on the delay mapping technique at the same time different time delays and different doppler shifts of the scattered gps signal could form relatively small spatial cells on sea surface suggesting mapping of the wave slope probability distribution in a synthetic aperture radar sar fashion this may allow more accurate measurements of wind velocity and wind direction

effect of brittle fracture on the rheological structure of the lithosphere and its application in the ordos abstract an empirical formula for the fracture strength of the principal rock type in the lithosphere is obtained based on the experimental data from previous studies in which the effects of the confining pressure size of the rock sample temperature strain rate and the pore pressure are taken into account the empirical formulae for the effects of them are also presented by comparing the frictional strength to the fracture strength calculated using the new empirical formula it is shown that frictional sliding is dominant in the upper crust but brittle fracture is dominant in the lower part of the crust and the lithosphere beneath the crust therefore the fracture mechanism must be taken into account in the study of the rheological structure of the lithosphere the empirical formula for the fracture strength is applied to study the rheological structure of the lithosphere in the ordos block brittle regime in the rheological structure can be divided into two sub regions in one of which brittle fracture and in the other frictional sliding are dominant respectively unlike previous conventional studies in which frictional sliding is assumed to be the only factor the magnitude of the rheological strength of the lithosphere calculated by the empirical formula is also lower than that obtained in previous conventional studies

3d volumetric multispectral estimates of reflector curvature and rotation one of the most accepted geologic models is the relation between reflector curvature and the presence of open and closed fractures such fractures as well as other small discontinuities are relatively small and below the imaging rangeofconventionalseismicdata dependingonthetectonic regime structural geologists link open fractures to either gaussian curvature or to curvature in the dip or strike directions reflector curvature is fractal in nature with different tectonic and lithologic effects being illuminated at the 50 m and1000 m scales untilnow suchcurvatureestimateshave been limited to the analysis of picked horizons we have developed what we feel to be the first volumetric spectral estimates of reflector curvature we find that the most positive and negative curvatures are the most valuable in the conventional mapping of lineations including faults folds and flexures curvatureismathematicallyindependentof andinterpretatively complementary to the well established coherence geometric attribute we find the long spectral wavelengthcurvatureestimatestobeofparticularvalueinextracting subtle broad features in the seismic data such as folds flexures collapse features fault drags and under and overmigrated fault terminations we illustrate the value of these spectral curvature estimates and compare them to other attributes through application to two land data sets a salt domefromtheonshorelouisianagulfcoastandafractured karsteddatavolumefromfortworthbasinofnorthtexas

3 d seismic discontinuity for faults and stratigraphic features the coherence cube seismic data are usually acquired and processed for imaging reflections this paper describes a method of processing seismic data for imaging discontinuities e g faults and stratigraphic features one application of this nontraditional process is a 3 d volume or cube of coherence coefficients within which faults are revealed as numerically separated surfaces figure 1 compares a traditional 3 d reflection amplitude time slice with the results of the new method to our knowledge this is the first published method of revealing fault surfaces within a 3 d volume for which no fault reflections have been recorded

how rigid is europe s lithosphere 1 the integrated strength distribution and variations of the effective elastic plate thickness te have been estimated for the european lithosphere based on thermal and rheological data for the crust and upper mantle the new results show a significant spatial variability demonstrating that both jelly sandwich and creme brulee models might be valid depending on lithospheric physical conditions in most of europe crustal strength provides a relatively large contribution 50 to the lithospheric strength western europe appears mostly characterized by mechanically decoupled lithospheric layers low strength and te 30 km the contribution of the mechanically strong mantle to te is low in most parts of western europe no clear relationship between te and thermal age is found in the continent the values for the tectonic provinces older than 85 ma are significantly smaller than theoretically expected for their age and crustal thickness whereas the opposite is true for the younger provinces

curvature attribute applications to 3d surface seismic data identifying subtle faults at or below the limits of seismic resolution and predicting fractures associated with folds and flexures is one of the major objectives of careful seismic interpretation with the advent of common use of 3d seismic in the late 1980s first derivative based horizon dip magnitude and dip azimuth were found to enhance faults that were otherwise difficult to see more recently second derivative based curvature maps have carried this process a step further horizon based curvature computation is now available in the commercial workstation environment putting these tools in the hands of geoscientists who do not have access to processing software and do not have time or inclination to program

efficient volumetric extraction of most positive negative curvature and flexure for fracture characterization from 3d seismic data most positive negative curvature and flexure are among the most useful seismic attributes for detecting faults and fractures in the subsurface based on the geometry of seismic reflections when applied to fracture characterization and modelling of a fractured reservoir their magnitude and azimuth help quantify both the intensity and orientation of fracturing respectively however previous efforts focus on estimating only the magnitude of both attributes whereas their associated azimuth is ignored in three dimensional 3d seismic interpretation this study presents an efficient algorithm for simultaneously evaluating both the magnitude and azimuth of most positive negative curvature and flexure from 3d seismic data the approach implemented in this study is analytically more accurate and computationally more efficient compared with the existing approach the added value of extracting most positive negative curvature and flexure is demonstrated through the application to a fractured reservoir at teapot dome wyoming first the newly extracted attributes make computer aided fault fracture decomposition possible this allows interpreters to focus on one particular component for fracture characterization at a time so that a composite fractured reservoir could be partitioned into different components for detailed analysis second curvature flexure azimuth allows interpreters to plot fracture histogram and or rose diagram in an automatic and quantitative manner compared with the conventional plotting rose diagram based on manual measurements automatic plotting is more efficient and offers unbiased insights into fracture systems by illuminating the most likely orientations of natural fractures in fractured reservoirs

improved estimates of seismic curvature and flexure based on 3d surface rotation in the presence of structure dip abstractfracture characterization is critical to reliable prediction of fractured reservoirs fractures formed by folding and or shearing of reservoir formations can be detected using seismic curvature and flexure analysis previous curvature and flexure analysis methods often have limitations in accuracy and efficiency in the presence of structural dip we have developed new algorithms for volumetric curvature and flexure analysis based on 3d surface rotation using the local reflector dip to improve the accuracy and efficiency for curvature and flexure analysis in structurally complex settings among the various measures of curvature and flexure in 3d space we have focused on signed maximum curvature and flexure that are considered to be most effective for predicting intensity and orientation of faults and fractures in fractured reservoirs the application of the algorithms to a 3d seismic survey from teapot dome wyoming demonstrated that the new methods help resolve subtle structural details that ar

the equivalent elastic thickness te seismicity and the long term rheology of continental lithosphere time to burn out creme brulee insights from large scale geodynamic modeling abstract depending on the conditions and time scale the lithosphere exhibits elastic brittle plastic or viscous ductile properties as suggested by rock mechanics experiments a large part of the long term lithospheric strength is supported in the ductile regime unfortunately these data validated for strain rates 10 6 s 1 small scales few cm and simplified conditions cannot be univocally interpolated to geological time and spatial scales strain rates 10 17 10 13 s 1 100 1000 km spatial scales complex conditions without additional parameterization an adequate parameterization has to be based on real time observations of large scale deformation indeed for the oceanic lithosphere the goetze and evan s brittle elastic ductile yield strength envelopes derived from data of experimental rock mechanics were successfully validated by a number of geodynamic scale observations such as the observations of plate flexure and the associated t e equivalent elastic thickness estimates yet for continents the uncertainties of flexural models and of the other data sources are much stronger due to the complex structure and history of continental plates for example in one continental rheology model dubbed jelly sandwich the strength mainly resides in the crust and mantle while in another dubbed creme brulee the mantle is weak and the strength is limited to the upper crust these models have arisen because of conflicting results from distributed earthquake elastic thickness t e and rheology data we address these problems by examining the plausibility of each rheological model from general physical considerations we review the elastic thickness t e estimates and their relationship to the seismogenic layer thickness t s to show that these two quantities have no direct physical relation we also show that some of small t e must be artifacts of inconsistent formulation of the mechanical problem in some free air anomaly admittance models we point out that this does not necessarily detract from the admittance method itself but refers to its incorrect application in the continental domain we then explore by analytical and numerical thermo mechanical modeling the implications of a weak and strong mantle for tectonic structural styles we conclude that rheological models such as creme brulee which invoke a weak lithosphere mantle are generally incompatible with observations the jelly sandwich is in better agreement and we believe provides a useful first order explanation for the long term support of the earth s main surface features

integrating 3d seismic curvature and curvature gradient attributes for fracture characterization methodologies and interpretational implications abstractin 3d seismic interpretation curvature is a popular attribute that depicts the geometry of seismic reflectors and has been widely used to detect faults in the subsurface however it provides only part of the solutions to subsurface structure analysis this study extends the curvature algorithm to a new curvature gradient algorithm and integrates both algorithms for fracture detection using a 3d seismic test data set over teapot dome wyoming in fractured reservoirs at teapot dome formed by tectonic folding and faulting curvature helps define the crestal portion of reservoirs that is associated with strong seismic amplitude and high oil productivity in contrast curvature gradient helps define the regional northwest trending and the cross regional northeast trending lineaments that are associated with weak seismic amplitude and low oil productivity in concert with previous reports from image logs cores and outcrops an integrated seismic curvature and curvature gradient analysis suggests t

quantitative prediction of lower order faults based on the finite element method a case study of the m35 fault block in the western hanliu fault zone in the gaoyou sag east china

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

lithosphere strength inferred from fracture strength of rocks at high confining pressures and temperatures abstract a model is proposed for the strength of the crust or lithosphere in which the peak strength is in the brittle regime but not on the brittle ductile transition the model is based on experimental evidence which suggests that the fracture mechanism changes from ordinary brittle fracture to a high pressure type when the compressive strength equals the frictional strength the model assumes that a high pressure type of fracture is dominant in the earth s lower crust except where very high pore pressures exist it takes account of the scale effect on the strength of rocks the strength of the high pressure regime is estimated as a function of depth or pressure and temperature using experimental results derived at high confining pressures and temperatures in the upper part of the brittle zone where the frictional strength is lower than the compressive strength byerlee s friction law is used in the ductile regime the steady state creep law is used two cases of lithospheric strength dry and wet hydrostatic water pressure respectively are evaluated for thrust strike slip and normal faulting mechanisms with the exception of a wet lithosphere and a normal faulting mechanism the strength between the frictional and creep regimes is approximately constant with depth although the peak strength is in this part