seismic anisotropy of shales shales are a major component of sedimentary basins and they play a decisive role in fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure shale anisotropy needs to be quantified to obtain reliable information on reservoir fluid lithology and pore pressure from seismic data and to understand time to depth conversion errors and non hyperbolic moveout a single anisotropy parameter thomsen s parameter is sufficient to explain the difference between the small offset normal moveout velocity and vertical velocity and to interpret the small offset avo response the sign of this parameter is poorly understood with both positive and negative values having been reported in the literature is sensitive to the compliance of the contact regions between clay particles and to the degree of disorder in the orientation of clay particles if the ratio of the normal to shear compliance of the contact regions exceeds a critical value the presence of these regions acts to increase and a change in the sign of from the negative values characteristic of clay minerals to the positive values commonly reported for shales may occur misalignment of the clay particles can also lead to a positive value of for transverse isotropy the elastic anisotropy parameters can be written in terms of the coefficients w 200 and w 400 in an expansion of the clay particle orientation distribution function in generalized legendre functions for a given value of w 200 decreasing w 400 leads to an increase in while for fixed w 400 increases with increasing w 200 perfect alignment of clay particles with normals along the symmetry axis corresponds to the maximum values of w 200 and w 400 given by w max 200 10 8 2 and w max 400 3 2 8 2 a comparison of the predictions of the theory with laboratory measurements shows that most shales lie in a region of the w 200 w 400 plane defined by w 400 w 200 w max 400 w max 200

identifying time temperature and mineralogical effects on chemical compaction in shales by rock physics relations the seismic response of a shale is a direct result of the original mineral composition textural configuration at deposition and degree of compaction the aim of this article is to show how the compactional processes and mineralogical effects can be directly identified by rock physics techniques and to emphasize the importance of having a thorough geological understanding when doing rock physics analysis to succeed we must first understand the fundamental relationships between sedimentology the compactional processes and the expected rock physics response that are not restricted to a particular basin or data set to achieve this we used wireline logs from 100 wells on the mid norwegian shelf to establish robust rock physics background trends in shales that were compared with the local responses in and around a target area the target was the tulipan well in the southwestern part of the mid norwegian shelf where thick deposits from the glacial marine north sea fan are located

core region of arctic oscillation and the main atmospheric events impact on the arctic 1 arctic oscillation ao is a seesaw pattern in which sea level pressure slp at the polar and middle latitudes in north hemisphere fluctuates between positive and negative phases it has been used as a representative atmospheric circulation index to express climate change the purpose of this paper is to reveal the regional difference of slp variation by calculating the correlation coefficients of ao index with all the gridded slps we have uncovered a special region named as arctic oscillation core region aocr where the running correlation coefficients rcc between gridded slp and ao index are all negative the averaged slp of this region correlates significantly with the ao index the correlations between local slps and ao index outside of aocr are weaker than those inside rcc analysis reveals several strong discrepant events different from ao these events occurred in the years of 1954 1955 1962 1971 1982 83 1995 1996 97 1998 and 1999 a comparison of these events and the enso or pdo indices suggests that the events in 1982 83 and 1998 are probably associated with the enso processes events centered in other years are likely connected with pdo which reached their minima in the years of 1950 1955 1962 and 1971 the result in this study provides an alternative insight to look at the mechanism of the variation of arctic oscillation

the link between the north atlantic oscillation and arctic sea ice export through fram strait abstract recently hilmer and jung have shown that the wintertime link between the north atlantic oscillation nao and the sea ice export through fram strait changed from zero correlation 1958 77 to about 0 7 1978 97 during the last four decades in the current study the authors focus on the question of how the two phenomena are linked in a long term context during wintertime december march this is done on a statistical basis using data from a century scale control integration of the coupled general circulation model echam4 opyc3 along with historical sea level pressure data for the period 1908 97 from the results of this study there is less indication that a significant link on interannual and decadal timescales between the nao and the sea ice export through fram strait is a characteristic property of the climate system at least under present day climate conditions this missing link can be explained by a vanishing net impact of the nao on sea ice thickness as well as sea ice drift near fram st

model uncertainty quantification in seismic tomography method and applications uncertainty is inherent in every stage of the oil and gas exploration and production e p business and understanding uncertainty enables mitigation of e p risks therefore quantification of uncertainty is beneficial for decision making and uncertainty should be managed along with other aspects of business for example decisions on well positioning should take into account the structural uncertainty related to the non uniqueness of a velocity model used to create a seismic depth image moreover recent advances in seismic acquisition technology such as full azimuth long offset techniques combined with high accuracy migration algorithms such as reverse time migration can greatly enhance images even in highly complex structural settings provided that an earth velocity model with sufficient resolution is available modern practices often use non seismic observation to better constrain velocity model building however even with additional information there is still ambiguity in our velocity models caused by the inherent non uniqueness of the seismic experiment many different earth velocity models exist that match the observed seismic and well data and this ambiguity grows rapidly away from well controls the result is uncertainty in the seismic velocity model and the true positions of events in our images tracking these uncertainties can lead to significant improvement in the quantification of exploration risk e g trap failure when well logging data are not representative drilling risk e g dry wells and abnormal pore pressure and volumetric uncertainties whilst the underlying ambiguity can never be fully eradicated a quantified measure of these uncertainties provides a valuable tool for understanding and evaluating the risks and for development of better risk mitigation plans and decision making strategies

building tilted transversely isotropic depth models using localized anisotropic tomography with well information tilted transverse isotropytti is increasingly recognized as a more geologically plausible description of anisotropy in sedimentary formations than vertical transverse isotropy vti a lthough model building approaches for vti media are well understood similar approaches for tti media are in their infancy even when the symmetry axis direction is assumed known we describe a tomographic approach that builds localized anisotropic models by jointly inverting surface seismic and well data we present a synthetic data example of anisotropic tomography applied to a layered tti model with a symmetry axis tilt of 45 degrees we demonstrate three scenarios for constraining the solution in the first scenario velocity along the symmetry axis is known and tomography inverts for thomsen s and parameters in the second scenario tomography inverts for and velocity using surface seismic data and vertical check shot traveltimes in contrast to the vti case both these inversions are nonunique to combat nonuniqueness in the third scenario we supplement check shot and seismic data with the profile from an offset well this allows recovery of the correct profiles for velocity along the symmetry axis and we conclude that tti is more ambiguous than vti for model building additional well data or rock physics assumptions may be required to constrain the tomography and arrive at geologically plausible tti models furthermore we demonstrate that vti models with atypical thomsen parameters can also fit the same joint seismic and check shot data set in this case although imaging with vti models can focus the tti data and match vertical event depths it leads to substantial lateral mispositioning of the reflections

a regime view of northern hemisphere atmospheric variability and change under global warming the leading mode of wintertime variability in northern hemisphere sea level pressure slp is the arctic oscillation ao it is usually obtained using linear principal component analysis which produces the optimal although somewhat restrictive linear approximation to the slp data here we use a recently introduced nonlinear principal component analysis to find the optimal nonlinear approximation to slp data produced by a 1001 year integration of the cccma coupled general circulation model cgcm1 this approximation s associated time series is strongly bimodal and partitions the data into two distinct regimes the first and more persistent regime describes a standing oscillation whose signature in the mid troposphere is alternating amplification and attenuation of the climatological ridge over northern europe with associated decreasing and increasing daily variance over northern eurasia the second and more episodic regime describes a split flow south of greenland with much enhanced daily variance in the arctic in a 500 year integration with atmospheric co2 stabilized at concentrations projected for year 2100 the occupation statistics of these preferred modes of variability change such that the episodic split flow regime occurs less frequently while the standing oscillation regime occurs more frequently

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

projection of climate change onto modes of atmospheric variability two possible interpretations of forced climate change view it as projecting either linearly or nonlinearly onto the dominant modes of variability of the climate system an evaluation of these two interpretations is performed using annual mean sea level pressure slp and surface air temperature sat fields obtained from integrations of the geophysical fluid dynamics laboratory coupled general circulation model forced with varying concentrations of greenhouse gases the dominant modes of slp both represent much of the total variability and remain important in warmer climates with sat however the dominant modes are often related to variations in the sea ice edge and so do not remain important once the ice has retreated those unrelated to sea ice remain dominant in the warmer climates but represent smaller fractions of the total variability in general climate change tends to project most strongly onto the more dominant modes the change in slp projects partially onto the top two modes in the northern hemisphere reflecting both an overall decrease in hemispheric slp as well as the pattern of change in the southern hemisphere the change projects negligibly onto the dominant patterns between equilibrium climates but very strongly onto the antarctic oscillation like mode in the transient integrations changes in sat project partially onto the dominant modes but relate more to the mean warming rather than the pattern of change in general the change projects most strongly onto the more dominant modes in all slp domains the projection of climate change overwhelmingly manifests itself as a linear translation in the mode consistent with the linear interpretation in sat domains related to sea ice variability the projection reflects an increased tendency toward ice free regimes consistent with the nonlinear perspective however this nonlinear projection represents only a small portion of the overall climate change

applications of deterministic and stochastic rock physics modelling to anisotropic velocity model building modern anisotropic depth imaging requires transverse isotropy velocity models because the surface seismic experiment alone cannot uniquely determine all transverse isotropy parameters additional information is required traditional methods that use checkshots can only constrain anisotropy locally near the well and thus model building requires 3d extrapolation of well data we propose to use rock physics rock physics compaction modelling of shales and sandy shales can be used to constrain and predict anisotropic parameters of sediments whose depositional environment is governed by compaction in this study we present several applications of rock physics modelling to anisotropic velocity model building we show how both deterministic and stochastic rock physics modelling can be used for initial anisotropic velocity model building and as a constraint for anisotropic parameter estimation in all cases all predicted anisotropy models are physical and realizable in terms of effective medium theory and do not violate elasticity theory

cyanobacterial blooms tied to volcanism during the 5 m y permo triassic biotic crisis comment 40 ar 39 ar ages obtained on volcanic ash layers from south china and volcanic rocks of the siberian traps st respectively xie et al argue that the volcanism associated with the st is predominantly younger than the p tr boundary age xie et al note that the majority of st 40 ar 39 ar ages e g reichow et al 2009 are similar to u pb zircon ages for two triassic boundaries and consequently that st volcanism was likely responsible for the prolonged stress in the early triassic ecosystems however the suggested age correlation is fl and the purpose of this comment is to challenge the comparison based on ages obtained by different methodologies and demonstrate that one of the conclusions drawn by xie et al is invalid ar

depth domain velocity analysis in vti media using surface p wave data is it feasible the main difficulties in anisotropic velocity analysis and inversion using surface seismic data are associated with the multiparameter nature of the problem and inherent trade offs between the model parameters for the most common anisotropic model transverse isotropy with a vertical symmetry axis vti media p wave kinematic signatures are controlled by the vertical velocity v0 and the anisotropic parameters e and however only two combinations of these parameters nmo velocity from a horizontal reflector vnmo 0 and the anellipticity coefficient can be determined from p wave reflection traveltimes if the medium above the reflector is laterally homogeneous while vnmo 0 and are sufficient for time domain imaging in vti media they cannot be used to resolve the vertical velocity and build velocity models needed for depth migration here we demonstrate that p wave reflection data can be inverted for all three relevant vti parameters v0 e and if the model contains nonhorizontal intermediate i

extracting seismic uncertainties from tomographic velocity inversion and their use in reservoir risk analysis structural information in subsurface seismic images is critical for reservoir delineation reserve estimation and well planning however by its very nature it is also uncertain one cause of the image uncertainty is the migration velocity model that directly affects the position of migrated events both laterally and vertically the term velocity is meant in the broad sense i e it also includes the anisotropy parameters we present a method that accounts for uncertainties in a velocity model estimated by tomography and translates them into the migrated domain standard deviation attributes on target horizon positions or layer thicknesses are extracted the method includes quality controls for validating the estimated uncertainty attributes before integration with other downstream or interpretative information the method is demonstrated on a north sea area covered by data from multiple seismic surveys we observe that uncertainties increase with model complexity or depth and decrease as the illu

the timing and extent of the eruption of the siberian traps large igneous province implications for the end permian environmental crisis we present new high precision 40ar 39ar ages on feldspar and biotite separates to establish the age duration and extent of the larger siberian traps volcanic province samples include basalts and gabbros from noril sk the lower tunguska area on the siberian craton the taimyr peninsula the kuznetsk basin vorkuta in the polar urals and from chelyabinsk in the southern urals most of the ages except for those from chelyabinsk are indistinguishable from those found at noril sk cessation of activity at noril sk is constrained by a 40ar 39ar age of 250 3 1 1 ma for the uppermost kumginsky suite the new 40ar 39ar data confirm that the bulk of siberian volcanism occurred at 250 ma during a period of less than 2 ma extending over an area of up to 5 million km2 the resolution of the data allows us to confidently conclude that the main stage of volcanism either immediately predates or is synchronous with the end permian mass extinction further strengthening an association between volcanism and the end permian crisis a sanidine age of 249 25 0 14 ma from bed 28 tuff at the global section and stratotype at meishan china allows us to bracket the p tr boundary to 0 58 0 21 myr and enables a direct comparison between the 40ar 39ar age of the traps and the permo triassic boundary section younger ages 243 ma obtained for basalts from chelyabinsk indicate that volcanism in at least the southern part of the province continued into the triassic

recent changes in the north atlantic it has long been recognized that the atlantic meridional overturning circulation moc is potentially sensitive to greenhouse gas and other climate forcing and that changes in the moc have the potential to cause abrupt climate change however the mechanisms remain poorly understood and our ability to detect these changes remains incomplete four main interrelated types of ocean change in particular are associated in the literature with greenhouse gas forcing these are a slowing of moc overturning rate changes in northern seas which might effect a change in atlantic overturning including changes in the freshwater flux from the arctic and changes in the transport and or hydrographic character of the northern overflows which ventilate the deep atlantic a change in the trans ocean gradients of steric height both zonal and meridional which might accompany a change in the moc and an intensification of the global water cycle though as yet we have no direct measure of the freshwater flux passing from the arctic to the atlantic either via the canadian arctic archipelago or along the east greenland shelf and no direct measure yet of the atlantic overturning rate we examine a wide range of time series from the existing hydrographic record for oceanic evidence of the other anticipated responses large amplitude and sustained changes are found or indicated by proxy over the past three to four decades in the southward transport of fresh waters along the labrador shelf and slope in the hydrography of the deep dense overflows from nordic seas in the transport of the eastern overflow through faroe bank channel and in the global hydrologic cycle though the type and scale of changes in ocean salinity are consistent with an amplification of the water cycle we find no convincing evidence of any significant concerted slowdown in the atlantic overturning circulation

the elastic anisotrophy of shales shales constitute about 75 of the clastic fill sedimentary basins and have a decisive effect on fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure the elastic stiffnesses of a shale with partially oriented clay particles is expressed in terms of the coefficients w sub lmn in an expansion of the clay particle orientation distribution function in generalized legendre functions application is made to the determination of the anellipticity of shales for transverse isotrophy the anellipticity quantifies the deviation of the p wave slowness curve from an ellipse and is shown to depend on a single coefficient w sub 400 in the expansion of the clay particle orientation distribution function if w sub 400 is small the anellipticity may be neglected as is apparently the case for a near surface late tertiary shale studied by winterstein and paulson strongly aligned clay particles result in a positive value of w sub 400 and a positive anellipticity in agreement with the majority of the field measurements however less well ordered shales could have a significantly positive second moment w sub 200 but only a small positive or even negative value of w sub 400 for such shales the anellipticity would be small or negative despite amore preferred alignment of clay particles in the bedding plane numerical examples of clay particle orientation distribution functions leading to zero or negative anellipticity are given less

effect of grain scale alignment on seismic anisotropy and reflectivity of shales the elastic properties and anisotropy of shales are strongly influenced by the degree of alignment of the grain scale texture in general an orientation distribution function odf can be used to describe this alignment which in practice can be characterized by two legendre coefficients we discuss various statistical odfs that define the alignment by spreading from a mean value in particular the gaussian fisher and bingham distributions we compare the statistical models with an odf resulting from pure vertical compaction no shear strain of a sediment the compaction odf may be used to estimate how the elastic properties and anisotropy evolve due to burial of clayey sediments our study shows that the three statistical odfs produce almost identical correspondence between the two legendre coefficients as a function of the spreading parameter so that the spreading parameter of one odf can be converted to the spreading parameter of another odf in most cases it is then sufficient to apply the spreading parameter for the odf instead of the two legendre coefficients the effect of compaction on the odf gives a slightly different correspondence between the two legendre coefficients from that for the other models in principle this opens up the possibility of distinguishing anisotropy effects due to compaction from those due to other processes we also study reflection amplitudes versus angle of incidence ava for all wave modes where shales having various odfs overlie an isotropic medium the ava responses are modelled using both exact and approximation formulae and their intercepts and gradients are compared the modelling shows that the s wave velocity is sensitive to any perturbation in the spreading parameter while the p wave velocity becomes increasingly sensitive to a perturbation of a less ordered system similar observations are found for the ava of the p p and p sv waves modelling indicates that a combined use of the amplitude versus offset of p p and p sv reflected waves may reveal certain grain scale alignment properties of shale like rocks

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

a decade of tomography over the past 10 years ray based postmigration grid tomography has become the standard model building tool for seismic depth imaging while the basics of the method have remained unchanged since the late 1990s the problems it solves have changed dramatically this evolution has been driven by exploration demands and enabled by computer power there are three main areas of change first standard model resolution has increased from a few thousand meters to a few hundred meters this order of magnitude improvement may be attributed to both high quality complex residual moveout data picked as densely as 25 m to 50 m vertically and horizontally and to a strategy of working down from long wavelength to short wavelength solutions second more and more seismic data sets are being acquired along multiple azimuths for improved illumination and multiple suppression high resolution velocity tomography must solve for all azimuths simultaneously to prevent short wavelength velocity heterogeneity from being mistaken for azimuthal anisotropy third there has been a shift from predominantly isotropic to predominantly anisotropic models both vti and tti with four component data anisotropic grid tomography can be used to build models that tie pz and ps images in depth

the application of map migration to 2 d migrated data two dimensional migrated time interpretations are used in a novel application of map migration this is done by following the seismic migration along the 2 d lines by a map migration in a direction orthogonal to the lines thus achieving a fully 3 d migrated representation of the subsurface in addition to modifying the 2 d times and positions this approach corrects the amplitudes of the 2 d migrated data which suffer from being corrupted by focusing or defocusing because of the reflector curvature orthogonal to the line direction a gulf of mexico case study illustrates how this map migration technique simplifies the time structure map and explains anomalous amplitude variations

recent temperature changes in the western arctic during spring abstract the lower troposphere of the western arctic eastern siberia to northern canada was relatively warm during spring in the 1990s based on the ncep ncar reanalysis supplemented by the television infrared observational satellite tiros operational vertical sounder tovs polar pathfinder dataset this warmth is a result of a recent increase in the frequency of warm months compared to the previous four decades the primary difference between four notably warm springs in the 1990s and four cold springs in the 1980s was the sense of the horizontal advection term in a lower tropospheric heat budget for northern alaska southern beaufort sea while the horizontal advection of heat was highly episodic it was related to changes in the mean circulation at low levels in particular a shift from anomalous northeasterly flow in the 1980s to anomalous southwesterly flow in the 1990s during march and april this change in the low level winds in the western arctic coincided with a systematic shift in the arct

the role of the siberian high in northern hemisphere climate variability the dominant mode of sea level pressure slp variability during the winter months in the northern hemisphere nh is characterized by a dipole with one anomaly center covering the arctic with the opposite sign anomaly stretched across the mid latitudes associated with the slp anomaly is a surface temperature anomaly induced by the anomalous circulation we will show that this anomaly pattern originates in the early fall on a much more regional scale in siberia as the season progresses this anomaly pattern propagates and amplifies to dominate much of the extratropical nh making the siberian high a dominant force in nh climate variability in winter also since the slp and surface temperature anomalies originate in a region of maximum fall snow cover variability we argue that snow cover partially forces the phase of winter variability and can potentially be used for the skillful prediction of winter climate

regional and hemispheric circulation patterns in the northern hemisphere winter or the nao and the ao 1 two different scales of teleconnection patterns are found over the euro atlantic region during the winter one is a regional seesaw between iceland and the azores and the other is a hemispheric seesaw between the mediterranean and the polar siberia region the north atlantic oscillation nao and the arctic oscillation ao indices are sensitive to both modes although the nao index reflects the more regional one the principal process producing a hemispheric seesaw pattern in the surface pressure is changing in vertical winds in the polar troposphere driven by wave forcings upward motion in the polar region induces meridional flows near the surface especially around the norwegian sea and bering strait which induce wavy patterns in the surface pressure the importance of distinguishing the two modes in understanding recent trends is also addressed

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

age and timing of the permian mass extinctions u pb dating of closed system zircons the age and timing of the permian triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts zircons from nine ash beds within the shangsi and meishan sections china pretreated by annealing followed by partial attack with hydrofluoric acid result in suites of consistent and concordant uranium lead u pb ages eliminating the effects of lead loss the u pb age of the main pulse of the extinction is 252 6 0 2 million years synchronous with the siberian flood volcanism and it occurred within the quoted uncertainty

the southern annular mode seen through weather regimes abstractthis article investigates the prominent features of the southern hemisphere south of 20 s atmospheric circulation when extracted using eof analysis and a k means clustering algorithm the focus is on the southern annular mode sam the nature of its recent trend and the zonal symmetry of associated spatial patterns the study uses the ncep department of energy atmospheric model intercomparison project ii reanalysis ncep 2 period 1979 2009 to obtain robust patterns over the recent years and the twentieth century reanalysis project period 1871 2008 to document decadal changes also presented is a comparison of these signals against a station based reconstruction of the sam index and a gridded interpolated dataset hadley centre sea level pressure dataset version 2 hadslp2 over their common period both reanalyses are in fair agreement both in terms of spatial patterns and temporal variability in particular both datasets show weather regimes that can be interpreted as the opposite pha

the preferred structure of variability of the northern hemisphere atmospheric circulation a nonlinear generalisation of principal component analysis pca is applied to the 500mb geopotential height field of the northern hemisphere extratropical atmosphere it is found that the low frequency variability of the mid troposphere is characterised by three distinct quasi stationary states the states are described and compared to those obtained from applications of cluster analyses and linear pca to the height field evidence is provided that modes obtained through pca notably the arctic oscillation ao are not independent dynamical modes of variability of the northern hemisphere extratropics rather they arise as the optimal linear compromise between the preferred quasi stationary states of the circulation

cyanobacterial blooms tied to volcanism during the 5 m y permo triassic biotic crisis reply we welcome the comment from reichow and saunders 2011 1 and are glad that they agree with our main conclusion on the relationship among cyanobacterial blooms volcanism and carbon isotope excursions across the permian triassic boundary xie et al 2010 2 they do challenge however

recurrent climate winter regimes in reconstructed and modelled 500 hpa geopotential height fields over the north atlantic european sector 1659 1990 recurrent climate winter regimes are examined from statistically reconstructed and modelled 500 hpa geopotential height fields over the north atlantic european sector for the period 1659 1990 we investigate the probability density function of the state space spanned by the first two empirical orthogonal functions of combined winter data regimes are detected as patterns that correspond to areas of the state space with an unexpected high recurrence probability using a monte carlo approach the reconstruction and the model reveal four recurrent climate regimes they correspond to the two phases of the north atlantic oscillation and two opposite blocking patterns complemented by the investigation of the temporal evolution of the climate regimes this leads to the conclusion that the reconstructed and the modelled data for this geographic sector reproduce low frequency atmospheric variability in the form of regime like behaviour the overall evidence for recurrent climate regimes is higher for the model than for the reconstruction however comparisons with independent data sources for the period 1659 1990 revealed a more realistic temporal evolution of the regimes for the reconstructed data

arctic oscillation or north atlantic oscillation abstract the definition and interpretation of the arctic oscillation ao are examined and compared with those of the north atlantic oscillation nao it is shown that the nao reflects the correlations between the surface pressure variability at its centers of action whereas this is not the case for the ao the nao pattern can be identified in a physically consistent way in principal component analysis applied to various fields in the euro atlantic region a similar identification is found in the pacific region for the pacific north american pna pattern but no such identification is found here for the ao the ao does reflect the tendency for the zonal winds at 35 and 55 n to anticorrelate in both the atlantic and pacific regions associated with the nao and pna because climatological features in the two ocean basins are at different latitudes the zonally symmetric nature of the ao does not mean that it represents a simple modulation of the circumpolar flow an increase in the ao or nao implies stro

well constrained seismic estimation of pore pressure with uncertainty the safe drilling of wells for hydrocarbon exploration or production requires that the wellbore pressure be maintained between the formation pore pressure and the maximum pressure the formation can withstand without fracturing this task is made more difficult when drilling in overpressured areas which require a quantitative predrill prediction of pore pressure with uncertainty to be made a predrill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform calibrated by offset well data however the uncertainty in velocity is often not quantified this example from the gulf of mexico uses seismic velocities with uncertainty derived by combining seismic velocities with well data den boer et al 2006 parameters in the velocity to pore pressure transform are estimated using seismic velocities density logs pressure information and well velocities derived by inverting time depth pairs from check shots in the area pore pressure and associated uncer

long term characteristics of simulated ice deformation in the baltic sea 1962 2007 1 the north atlantic oscillation nao index is a frequently used measure for the mean winter conditions in northern europe a positive high index is associated with strong westerlies and anomalous warm temperatures the effects on sea ice conditions in the baltic sea are twofold warm temperatures prevent sea ice formation if ice is present nevertheless the strong winds can promote the formation of ice ridges which hinders ship traffic we use an ocean sea ice model to investigate the nao impact on the ridged ice area fraction in the baltic during 1962 2007 our simulations indicate that in the northern bothnian bay a high nao index is related to an anomalous accumulation of ridges while in the rest of the baltic sea the relationship is contrary the nao explains locally at most only 20 25 of the ridged ice fraction interannual variability which indicates the systems complexity however we find high skill with local correlations around 0 8 for annually averaged ridged ice fraction reconstructed from multilinear regression using winter averaged wind extremes surface air temperature and sea surface temperature sst this suggests that the amount of ridged ice in late winter can be derived from these routinely measured quantities in large parts of the basin it is sufficient to use the atmospheric parameters as a predictor while in the eastern bothnian bay and southern gulf of finland the sst is required to reconstruct the bulk of the ridged ice fraction

estimating the model resolution matrix for large seismic tomography problems based on lanczos bidiagonalization with partial reorthogonalization summary the propack package developed by larsen is able to efficiently and accurately estimate singular values and vectors for large matrices based on the lanczos bidiagonalization with partial reorthogonalization we incorporate the pavtial reorthogonalization package propack package into the double difference seismic tomography code tomodd and estimate the model resolution matrix for large seismic tomography problems compared to previous least squares qr lsqr based methods for estimating the model resolution matrix the propack based method calculates the full resolution matrix and thus gives a complete description of how well the model is resolved several observations are drawn from the application to data from the 2001 eruption of mt etna for this example it is reasonable to use ray sampling density information to characterize the model resolution qualitatively the model resolution resulting from just velocity inversion bears a close linear relationship to that from simultaneous inversion but always overestimates resolution and the inversion system using differential times has a greater ability to resolve the source region structure than the system using absolute times

skewness of low frequency fluctuations in the tropospheric circulation during the northern hemisphere winter abstract departures of lowpass filtered 500 mb height and sea level pressure anomalies from a gaussian distribution have been examined based on northern hemisphere operational analyses for 30 winters at each gridpoint we evaluated several indices that are measures of the differences between the amplitudes and frequencies of the persistent anomalies with positive and negative polarities and differences in the temporal variability observed within extended periods of positive and negative anomalies the spatial patterns for these indices are all quite similar and they resemble the distribution of the moment coefficient of skewness documented by white positive skewness is observed to the north of the stormtrack latitudes and the negative to the south of them the skewness pattern in the sea level pressure field is weaker particularly at high latitudes and it exhibits a bias toward negative skewness anomalies with amplitudes larger than two standard deviations which occur about 5 of the time account

solar cycle modulation of the north atlantic oscillation implication in the spatial structure of the nao 1 the spatial extent of the north atlantic oscillation nao is investigated the results suggest that the spatial structure of the nao differs significantly according to the phase of the solar cycle during the solar maximum phases the nao has a hemispherical structure extending into the stratosphere which is similar to the arctic oscillation ao except for the pacific sector however during the minimum phase the nao is confined to the eastern atlantic sector in the troposphere whether or not the nao is modulated by the solar cycle these results may shed new light on the controversy of the physical reality of the two modes of variability the nao and the ao

anisotropic model building with wells and horizons gulf of mexico case study comparing different approaches anisotropic depth imaging with ver tical transversely isotropic vti models has become the dominant practice in the industry however anisotropic parameters for these models continue to be derived by basic practices without the use of tomography hanging a single profile of thomsen s parameters from the water bottom still remains the most common practice in a simple structural setting it is usually possible to focus the data and obtain a good image despite having a simple and unrealistic model for thomsen s parameters however depth positioning of such images is usually suboptimal better positioning requires more geologically plausible models in addition imaging in complex settings may require tilted transversely isotropic tti models

estimating and interpreting velocity uncertainty in migrated images and avo attributes estimating a suitable velocity field for use in prestack depth migration is inherently uncertain because of limitations on the available data and estimation techniques this uncertainty affects both the migrated depth of structures and their amplitudes in the inverted images these effects can be estimated by performing multiple migrations with a set of velocity fields and colocating features in the migrated images this lets us examine the imaging procedure s sensitivity to changes in the velocity field so we can assess both structural and amplitude uncertainties in migrated images these two types of uncertainties affect interpretation in different ways for instance with structural uncertainty interpretation we consider the change in migrated location of structures when deciding on drilling locations optimizing well trajectories or computing uncertainty in volumetric calculations with amplitude uncertainty or amplitude versus offset avo uncertainty interpretation we consider 1 uncertainty in c

time depth relationships for multilayer depth conversion the conversion of seismic time to depth through the use of analytical functions has been a common procedure in seismic work for many decades with the exception of recent examples dealing with the linear function none of the published time depth relationships corresponding to these functions is applicable to multilayer depth conversion the present work redresses this situation it presents formulae applicable to multilayer depth conversion for a large number of analytical functions the derivation is based on a procedure generally similar to that presented by japsen 1993 most of the functions considered date back to a publication by kaufman in 1953 and earlier publications a number of other functions hitherto not known in the industry are also presented

resolution uncertainty and whole earth tomography 1 using the arrival times of 10 distinct phases from the international seismological center catalogue p s pp pcp ss scs pkpab pkpbc pkpdf sksac and two sets of differential times ss s410s and ss s660s we estimate the p and s velocity structure of the whole earth mantle outer core and inner core boundary topography of four interfaces within the earth hypocentral relocation parameters and station corrections the entire catalogue is relocated and reassociated using the radial velocity model ak135 both p and s phases are used in the relocation of over 41 000 events in depth isotropic velocity variations within the earth are parameterized by 22 layers lateral variations in shear and compressional velocity within the layers are represented by one of two grids in the mantle each layer is subdivided into 4560 equal volume cells of dimension 3 3 at the equator however in the outer and inner core the cell size is increased to 6 6 this change in grid spacing accounts for decreasing cell volumes with depth and variations in sampling between the mantle and core previous attempts using a fine grid throughout the earth resulted in poor resolution of core structure with the current grid the resolution of velocity heterogeneity in the mantle and outer core is comparable in the upper and midmantle the well resolved cells lie beneath eurasia and a narrow zone surrounding the mantle beneath the pacific basin in the lowest mantle the resolution decreases significantly an examination of the averaging kernels associated with six locations near the base of the mantle reveals the significant lateral and vertical averaging inherent in estimates of compressional velocity in well sampled regions of the outer core we are able to resolve compressional velocity variations in our 6 6 cells however velocity variations in the inner core are poorly constrained at the scale of our blocks in well sampled regions of the mantle and outer core model parameter standard deviations remain below 0 25 for much of the inner core the standard deviations are quite large exceeding 0 5 narrow high velocity anomalies are imaged in the upper mantle associated with subduction zones in a number of locations such as beneath the americas these features extend well into the lower mantle in the outer core heterogeneity is generally lower in magnitude of the order of 0 5 the most notable feature in the outer core is a systematic shift to slightly higher velocity in addition we find a roughly symmetric distribution of heterogeneity at the base of the outer core compressional velocities are generally higher in the equatorial regions and lower at the poles

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

cyanobacterial blooms tied to volcanism during the 5 m y permo triassic biotic crisis widespread but episodic deposition of cyanobacterial mats occurred during the 5 m y permo triassic biotic crisis providing a critical record to decipher the long term stressful environmental conditions and thus a linkage with the killer here we document the timing and duration of these blooms indicated by lipid biomarkers and microbialites throughout south china and compare them to the timing of volcanic activity the initial cyanobacterial bloom has the longest duration and is associated with a prominent eu anomaly in southwestern china where the most intensive volcanism has been proposed to occur suggesting a causal relationship subsequent cyanobacterial blooms in the early triassic are associated with known volcanic events in south china and also with the most voluminous siberian flood basalts and with the largest negative carbon isotope excursions thus it appears that volcanic activity has had a significant impact on microbial development in south china south china volcanism around the permian triassic boundary ptb could have played a much larger role in biotic changes of both bacterial and calcified faunal ecosystems than previously thought the well known siberian volcanism is proposed herein on the basis of the current compilation of dating data to protract the early triassic faunal recovery rather than to cause the end permian extinction

characterizing and comparing the control run variability of eight coupled aogcms and of observations part 2 precipitation we examine the spatial patterns of variability of annual mean temperature in the control runs of eight coupled atmosphere ocean general circulation models aogcms and of observations we characterize the patterns of variability using empirical orthogonal functions eofs and using a new technique based on what we call quasi eofs the quasi eofs are computed based on the spatial pattern of the correlation between the temperature variation at a given grid point and the temperature defined over a pre determined reference region with a different region used for each quasi eof for the first four quasi eofs the reference regions are the entire globe the nino3 region western europe and siberia since the latter three regions are the centers of strong anomalies associated with the el nino north atlantic and siberian oscillations respectively the spatial pattern of the covariance with temperature in these regions gives the structure of the model or observed el nino north atlantic and siberian components of variability when eof analysis is applied to the model control runs the patterns produced generally have no similarity to the eof patterns produced from observational data this is due in some cases to large nao like variability appearing as part of eof1 along with enso like variability rather than as separate eof modes this is a disadvantage of eof analysis the fraction of the model time space variation explained by these unrealistic modes of variability is generally greater than the fraction explained by the principal observed modes of variability when qeof analysis is applied to the model data all three natural modes of variability are seen to a much greater extent however the fraction of global time space variability that is accounted for by the model enso variability is in our analysis less than observed for all models except the hadcm2 model but within 20 for another three models the space time variation accounted for by the other modes is comparable to or somewhat larger than that observed in all models as another teleconnection indicator we examined both southern oscillation index soi and its relation to tropical pacific ocean temperature variations the qeof2 amplitude and the north atlantic oscillation index naoi and its relation to north atlantic region temperatures the qeof3 amplitude all models exhibit a relationship between these indices and the qeof amplitudes are comparable to those observed furthermore the models show realistic spatial patterns in the correlation between local temperature variations and these indices

elastic and resistivity anisotropy of shale during compaction and diagenesis joint effective medium modeling and field observations abstractshales are anisotropic materials which have been observed to have both electrical and elastic anisotropy shales also comprise most of the sedimentary column in clastic basins and thus the ability to model shale response to electrical and seismic fields may improve our ability to better resolve anisotropy by using different measurements compacting shale effective media modeling which captures the geological process of porosity reduction and geochemical compaction was formulated in this research in microstructural parameters associated with particle alignment and pore shape deformation the state of compaction captured by the porosity of the soft sediment governs the pore aspect ratio and the amount of particle alignment diagenetic processes are captured using temperature dependent mineral elasticity and conductivity the model uses the same microstructural parameters and equivalent effective medium approximation scheme to predict electrical and elastic anisotropy in situ measurements of e

interpretation of velocity estimates from coherency inversion velocity estimation by coherency inversion provides a velocity depth macro model of the subsurface the accuracy of this model is critical for imaging techniques such as depth migration and inversion therefore the reliability of seismic interpretation is strongly dependent on the accuracy of the derived model uncertainties in the velocity and depth estimates for the model can be calculated using a combination of the response surface technique and the dix equation in the layer stripping strategy the method takes into account the local errors connected mainly to the current layer and the global errors connected to the derived overburden examples using synthetic and real data show that the coherency inversion produces accurate macro models

optimal nonlinear design of marine borehole seismic surveys abstractwe explore dn optimization a recently introduced method in optimal experimental design theory as a tool to minimize the forecasted postinversion model uncertainty in marine borehole seismic applications the dn criterion is a design objective function crafted specifically for nonlinear data model relationships and when used in conjunction with greedy sequential optimization algorithms is among the first of its kind to be computationally efficient enough for industrial scale applications the benefits and disadvantages of greedy algorithms are briefly discussed and one of the most popular the construction algorithm is confirmed to take nearly linear time as predicted by theory the dn criterion is rederived here to show that restrictive assumptions in its original derivation were unnecessary this new derivation is cast in terms of expected likelihood ratios which quantify the discriminability of geomodels constrained by observed seismic data a 3d vertical seismic profiling vsp surve

anisotropic velocity analysis1 results from walkaway vsp and shale laboratory experiments show that shale anisotropy can be significantly anelliptic heterogeneity and anellipticity both lead to non hyperbolic moveout curves and the resulting ambiguity in velocity analysis is investigated for the case of a factorizable anisotropic medium with a linear dependence of velocity on depth more information can be obtained if there are several reflectors the method of dellinger et al for anisotropic velocity analysis in layered transversely isotropic media is examined and is shown to be restricted to media having relatively small anellipticity a new scheme based on an expansion of the inverse squared group velocity in spherical harmonics is presented this scheme can be used for larger anellipticity and is applicable for horizontal layers having monoclinic symmetry with the symmetry plane parallel to the layers the method is applied to invert the results of anisotropic ray tracing on a model sand shale sequence for transversely isotropic media with small anisotropy the scheme reduces to the method of byun et al and byun and corrigan the expansion in spherical harmonics allows the p phase slowness surface of each layer to be determined in analytic form from the layer parameters obtained by inversion without the need to assume that the anisotropy is weak