internal tide scattering at seamounts ridges and islands 1 the scattering of mode 1 internal tides from idealized gaussian topography in a nonrotating ocean with constant and realistic stratifications is examined with a primitive equation numerical model incident mode 1 energy fluxes of 20 and 2000 w m 1 are used to examine the linear regime and a more realistic situation simulations using two dimensional or infinite ridges compare well with ray tracing methods and illustrate how the size and shape of the topography influence wave scattering the height affects energy transmission and reflection while the slope and width determine the conversion of low mode internal tides into beams or higher modes three dimensional topographic scattering is considered for seamounts finite width ridges and islands scattering from finite ridges focuses wave energy directly downstream while scattering from seamounts produces azimuthal energy dispersion scattering to higher wave modes occurs in the lee of near critical and supercritical seamounts and ridges nonlinear interactions transfer energy into the mode 1 m4 internal tide the mellor yamada level 2 5 submodel parameterizes turbulent mixing for the near critical and supercritical ridges with realistic stratification elevated mixing is found over the leading edge of the topography and along a tidal beam up to the first surface bounce a transition from a beam structure near the topography to a low mode structure farther away occurs due to an increased contribution from the mode 1 internal tide as it refracts around the topography and not due to turbulent dissipation internal tide scattering at topography leads to a loss of energy to mixing and to a redistribution of energy flux in space frequency and mode number

joint probabilistic petrophysics seismic inversion based on gaussian mixture and markov chain prior models abstractseismic reservoir characterization focuses on the prediction of reservoir properties based on the available geophysical and petrophysical data the inverse problem generally includes continuous properties such as petrophysical and elastic attributes and discrete properties such as lithology fluid classes we have developed a joint probabilistic inversion methodology for the prediction of petrophysical and elastic properties and lithology fluid classes that combined statistical rock physics and bayesian seismic inversion the elastic attributes depend on continuous petrophysical variables such as porosity and clay content and discrete lithology fluid classes through a nonlinear rock physics relationship together the seismic model relates the elastic attributes such as velocities and density to their seismic response reflectivity traveltime and amplitudes the advantage of our integrated approach is that the inversion method accounts for the uncertainty associated to each step of the mo

probabilistic petrophysical properties estimation integrating statistical rock physics with seismic inversion a joint estimation of petrophysical properties is proposed that combines statistical rock physics and bayesian seismic inversion because elastic attributes are correlated with petrophysical variables effective porosity clay content and water saturation and this physical link is associated with uncertainties the petrophysical properties estimation from seismic data can be seen as a bayesian inversion problem the purpose of this work was to develop a strategy for estimating the probability distributions of petrophysical parameters and litho fluid classes from seismics estimation of reservoir properties and the associated uncertainty was performed in three steps linearized seismic inversion to estimate the probabilities of elastic parameters probabilistic upscaling to include the scale changes effect and petrophysical inversion to estimate the probabilities of petrophysical variables andlitho fluid classes rock physics equations provide the linkbetween reservoir properties and velocities and lin

hierarchical bayesian lithology fluid prediction a north sea case study seismic 3d amplitude variation with offset avo data from the alvheim field in the north sea are inverted into lithology fluid classes elastic properties and porosity lithology fluid maps over hydrocarbon prospects provide more reliable estimates of gas oil volumes and improve the decision concerning further reservoir assessments the alvheim field is of turbidite origin with complex sand lobe geometry and appears without clear fluid contacts across the field the inversion is phrased in a bayesian setting the likelihood model contains a convolutional linearized seismic model and a rock physics model that capture vertical trends due to increased sand compaction and possible cementation the likelihood model contains several global model parameters that are considered to be stochastic to adapt the model to the field under study and to include model uncertainty in the uncertainty assessments the prior model on the lithology fluid classes is a markov random field that captures local vertical horizonta

internal tide scattering at the line islands ridge 1 scattering of the m2 mode one internal tide from the line islands ridge is examined with a primitive equation numerical model model runs with baroclinic and barotropic forcing are performed to distinguish scattered from locally generated internal tides tpxo 5 tidal model sea surface elevations provide barotropic forcing while for the run with baroclinic forcing a mode one m2 energy flux of 1000 w m 1 is used to represent energy fluxes emanating from the hawaiian ridge scattering redistributes more energy flux from mode one than is locally generated in mode one for the higher modes scattering and generation contribute equally in terms of the overall energy flux spatial and modal distributions of energy density and flux show internal tide scattering dominates at hutchinson seamount while higher modes are generated locally at sculpin ridge hutchinson seamount s slopes are steeper over a greater continuous area than sculpin ridge scattered energy is found downstream of the steepest topographies similar to simulations with idealized gaussian ridges at the line islands ridge 37 of the incident mode one energy flux is lost because of scattering into modes 2 5 19 dissipation by the model s turbulence parameterization 15 and nonlinear transfer to the m4 internal tide 3 two topex ground tracks pass through the model domain roughly normal to the ridge topography and confirm the general features of the modal and spatial distribution found in the model in the topographically rough western pacific internal tide scattering may be a significant source of energy for mixing away from topography

observations of strong mid pacific internal tides above horizon guyot abstract large semidiurnal current and isotherm oscillations were observed by one current meter continuously for 9 months in the waters above horizon guyot a seamount located in the central pacific the m2 tides dominated the current meter record the m2 current ellipse was oriented along 142 the semi major amplitude was 7 6 cm s 1 and the currents rotated in a clockwise direction the m2 isotherm deflection amplitude was 20 m the m2 currents observed above the guyot were two to three times larger than m2 currents either observed in or predicted for this region of the mid pacific evidence suggests that the semidiurnal tide was predominantly an internal tide that was generated at the guyot the observed internal tide had a narrow bandwidth and a constant amplitude and phase for 9 months and had characteristics similar to a vertically propagating rather than a vertically standing internal wave

scattering of internal waves at finite topography in two dimensions part i theory and case studies abstract the scattering of internal gravity waves at finite topography in two dimensions is studied theoretically and numerically for a finite depth ocean a formal solution is derived using a mapping function based on ray tracing the solution satisfies radiation conditions energy is conserved the incoming energy flux is redistributed in physical and modenumber space numerical solutions are calculated for a single plane wave propagating from the ocean side onto slope shelf configurations where a flat shallow shelf is connected to a flat deep ocean by linear slopes staircases convex or concave parabolic profiles and half cosine slopes the fraction of the incoming energy flux transmitted onto the shelf and reflected back to the deep ocean and the distribution of these fluxes in modenumber space are calculated the results depend on the parameters of the incident wave and of the topography especially important is the distinction between supercritical topography where the slope of the topography exc

lithology and fluid prediction from prestack seismic data using a bayesian model with markov process prior lithology and fluid prediction from prestack seismic data using a bayesian model with markov process prior

improved resolution in bayesian lithology fluid inversion from prestack seismic data and well observations part 2 real case study we have performed lithology fluid inversion based on prestack seismic data and well observations from a gas reservoir offshore norway the prior profile markov random field model captures horizontal continuity and vertical sequencing of the lithology fluid variables the prior model is also locally adjusted for spatially varying lithology fluid proportions the likelihood model is inferred from basic seismic theory and observations in wells an approximate posterior model is defined which can be simulated from by an extremely computer efficient algorithm the lithology fluid inversion results are compared to manual interpretations and evaluated by cross validation in one well moreover inversions based on simplified prior models are developed for comparative reasons both lithology fluid realizations and predictions look geologically reasonable the results seem to reflect general reservoir experience and information provided by the prestack seismic data and well observations the lithology fluid propor

seismic inversion for reservoir properties combining statistical rock physics and geostatistics a review there are various approaches for quantitative estimation of reservoir properties from seismic inversion a general bayesian formulation for the inverse problem can be implemented in two different work flows in the sequential approach first seismic data are inverted deterministically or stochastically into elastic properties then rock physics models transform those elastic properties to the reservoir property of interest the joint or simultaneous work flow accounts for the elastic parameters and the reservoir properties often in a bayesian formulation guaranteeing consistency between the elastic and reservoir properties rock physics plays the important role of linking elastic parameters such as impedances and velocities to reservoir properties of interest such as lithologies porosity and pore fluids geostatistical methods help add constraints of spatial correlation conditioning to different kinds of data and incorporating subseismic scales of heterogeneities

impact of rock physics depth trends and markov random fields on hierarchical bayesian lithology fluid prediction early assessments of petroleum reservoirs are usually based on seismic data and observations in a small number of wells decision making concerning the reservoir will be improved if these data can be integrated and converted into a lithology fluid map of the reservoir we analyze lithology fluid prediction in a bayesian setting based on prestack seismic data and well observations the likelihood model contains a convolved linearized zoeppritz relation and rock physics models with depth trends caused by compaction and cementation well observations are assumed to be exact the likelihood model contains several global parameters such as depth trend wavelets and error parameters the inference of these is an integral part of the study the prior model is based on a profile markov random field parameterized to capture different continuity directions for lithologies and fluids the posterior model captures prediction and model parameter uncertainty and is assessed by markov chain monte carlo simulation base

topographically induced mixing around a shallow seamount measurements of the rate of dissipation of kinetic energy around a shallow seamount in the eastern north pacific show that mixing there is 100 to 10 000 times as large as that far away from the seamount if such values are typical of other seamounts mixing across density surfaces in the ocean occurs mainly at their boundaries and topographically induced mixing may help to explain the discrepancy between the observed intensity of mixing in the interior of the oceans and that required to satisfy models of ocean circulation

ground water radon anomaly before the kobe earthquake in japan radon concentration in ground water increased for several months before the 1995 southern hyogo prefecture kobe earthquake on 17 january 1995 from late october 1994 the beginning of the observation to the end of december 1994 radon concentration increased about fourfold on 8 january 9 days before the earthquake the radon concentration reached a peak of more than 10 times that at the beginning of the observation before starting to decrease these radon changes are likely to be precursory phenomena of the disastrous earthquake

bayesian lithology fluid prediction and simulation on the basis of a markov chain prior model a technique for lithology fluid lf prediction and simulation from prestack seismic data is developed in a bayesian framework the objective is to determine the lf classes along 1d profiles through a reservoir target zone a stationary markov chain prior model is used to model vertical continuity of lf classes along the profile the likelihood relates the lf classes to the elastic properties and to the seismic data and it introduces vertical correlation because the seismic data are band limited an approximation of the likelihood model provides an approximate posterior model that is a markov chain the approximate posterior can be assessed by an exact and efficient recursive algorithm the lf inversion approach is evaluated on a synthetic 1d profile that is inspired by a north sea sandstone reservoir with a realistic wavelet colored noise model and a s n ratio of three in the seismic data the results are reliable the lf classes and the interfaces between zones are largely correct the prediction unce

radon as an anthropogenic indoor air pollutant as exemplified by radium dial watches and other uranium and radium containing artefacts radon is generally regarded as a naturally occurring radiological hazard but we report here measurements of significant hazardous radon concentrations that arise from man made sources e g radium dial watches this study is an examination and assessment of health risks from radium and uranium found in historical artefacts and the radon that emanates from them this includes radium dial watches the main focus plus clocks aircraft instruments and ornaments and artefacts made of uranium glass uranium glazed such objects were very popular in the 1930s and 1940s and are still readily available today a collection of 30 radium dial pocket and wrist watches was measured and shown to be capable of giving rise to radon concentrations two orders of magnitude greater than the uk domestic action level of 200 bq m 3 in unventilated or poorly ventilated rooms furthermore individual watches are capable of giving rise to radon concentrations in excess of the uk domestic action level we also highlight a gap in remediation protocols which are focused on preventing radon entering buildings from outside with regard to internally generated radon hazards radon as arising from man made objects such as radium dial watches should be considered appropriately in radon protocols and guidelines

the generation of internal tides at the hawaiian ridge previous analyses of altimeter and acoustic data indicate that the hawaiian ridge is a significant generation site for semidiurnal m2 period internal waves owing to tidal flow over topography such waves likely play an important role connecting the dissipation of tidal energy to ocean mixing here a primitive equation numerical model with realistic stratification bathymetry and tidal forcing is used to simulate the generation of these waves in a manner consistent with altimeter sea surface observations the highest amplitude waves originate at three generation sites located at both the island and seamount portions of the chain these sites have in common both enhanced flows across ridge shaped topography and maxima in model calculated body force which couples barotropic and baroclinic motions the model vertical structure suggests the presence of multiple dynamical modes within 100 km of the ridge and not just the lowest modes that have been detected at the sea surface

bayesian lithology and fluid prediction from seismic prestack data a fast bayesian inversion method for 3d lithology and fluid prediction from prestack seismic data and a corresponding feasibility analysis were developed and tested on a real data set the objective of the inversion is to find the probabilities for different lithology fluid classes from seismic data and geologic knowledge the method combines stochastic rock physics relations between the elastic parameters and the different lithology fluid classes with the results from a fast bayesian seismic simultaneous inversion from seismic data to elastic parameters a method for feasibility analysis predicts the expected modification of the prior probabilities to posterior probabilities for the different lithology fluid classes the feasibility analysis can be carried out before the seismic data are analyzed both the feasibility method and the seismic lithology fluid probability inversion were applied to a prospect offshore norway the analysis improves the probability for gas sand from 0 1 to about 0 2 0 4 with s

bayesian wavelet estimation from seismic and well data a bayesian method for wavelet estimation from seismic and well data is developed the method works both on stacked data and on prestack data in form of angle gathers the seismic forward model is based on the convolutional model where the reflectivity is calculated from the well logs possible misties between the seismic traveltimes and the time axis of the well logs errors in the log measurements and seismic noise are included in the model the estimated wavelets are given as probability density functions such that uncertainties of the wavelets are an integral part of the solution the solution is not analytically obtainable and is therefore computed by markov chain monte carlo simulation an example from sleipner field shows that the estimated wavelet has higher amplitude compared to wavelet estimation where well log errors are neglected and the uncertainty of the estimated wavelet is lower

radon health and natural hazards a signpost for assessment and protection in the 21st century this volume draws together the final outputs of the five year unesco iugs igcp project 571 and presents new data on radon in the built and natural environments radon as a diagnostic tool of geophysical phenomena reflections and recommendations on the future of radon research and a critique of radon s asserted use as a therapy in recent years there has been an increasing interest in radon from a range of different aspects and we would suggest that radon science has the potential to be a useful tool in understanding our environment as well as its impacts on human health

internal tide generation by seamounts ridges and islands a numerical investigation is made into the generation of semidiurnal internal tides by tidal flow over steep topographic features in the deep ocean a fully three dimensional free surface nonlinear hydrostatic model the princeton ocean model is used with real stratification representative tidal forcing and gaussian shaped seamounts ridges and islands for the topography the efficiencies of the different topographies in extracting energy from the barotropic tide and in generating an internal tide are considered each topography produces an internal tide characterized by signals propagating away from the feature as beams that follow internal wave characteristic paths the strength of the signals however varies markedly for different topographies this is largely attributed to the way in which the barotropic tide interacts with the three dimensional topography internal wave generation requires a significant vertical displacement of stratified water by the barotropic tide as it flows over topography it is found that for symmetric seamounts and islands the barotropic flow tends to go around the feature producing only a weak internal tide when elongated into a ridge barotropic flow is forced across isobaths generating an energetic internal tide changing the horizontal aspect ratio of the topography from 1 1 a seamount to 3 1 a ridge increases the resulting baroclinic energy flux by nearly an order of magnitude the slope of the topography relative to that of the internal wave characteristics is also shown to be important with strongest generation occurring at regions of critical or supercritical topographic slope

improved resolution in bayesian lithology fluid inversion from prestack seismic data and well observations part 1 methodology the focus of our study is lithology fluid inversion with spatial coupling from prestack seismic amplitude variation with offset avo data and well observations the inversion is defined in a bayesian setting where the complete solution is the posterior model the prior model for the lithology fluid lf characteristics is defined as a profile markov random field model with lateral continuity each vertical profile is further given as an inhomogeneous markov chain model upward through the reservoir the likelihood model is defined by profile and it relates the lf characteristics to the seismic data via a set of elastic material parameters and a convolution model the likelihood model is approximated the resulting approximate posterior model is explored using an efficient block gibbs simulation algorithm the inversion approach is evaluated on a synthetic realistic 2d reservoir seismic avo data and well observations are integrated in a consistent manner to obtain predictions of the lf characteristics wi

significant annual and sub annual cycles in indoor radon concentrations seasonal variation and correction the majority of radon measurements in the built environment are made over sub year periods and are then generally seasonally corrected i e scaled by an appropriate seasonal correction factor scf to estimate the annual average radon concentration scfs are statistically derived and assume an underlying annual cycle reflecting the widely observed seasonal variation in indoor radon concentrations in the uk public health england has pioneered the calculation and use of a national scf set using an annual sinusoidal model for variations in radon concentration and averaging across the entire country to test the validity of that model a four year record of weekly radon data from four houses in brixworth northamptonshire uk was analysed in conjunction with corresponding weather data for the period from a nearby weather station the radon data showed a statistically significant annual cycle comprising both annual sinusoidal and second harmonic i e six month period terms two sets of scfs were calculated first using a conventional annual sinusoidal model which explained 21 2 of the variance in the radon data second a second harmonic term was included in the model which explained 24 6 of the variance this represents an improvement of 3 4 percentage points 15 9 and thus will result in better scfs

stochastic inversion by matching to large numbers of pseudo wells abstractwe have developed a 1d stochastic algorithm for estimating reservoir properties based on matching large numbers of pseudo wells to seismic angle stacks the pseudo wells are part deterministic and part stochastic 1d stratigraphic profiles with consistent elastic and reservoir properties pseudo wells are sampled from a prior distribution defined by the geological interpretation a rock physics model and a model for the vertical statistics that provides close control of the lithofacies proportions a new set of pseudo wells typically 103 104 tied to the local stratigraphy is constructed for each seismic trace synthetics derived from the pseudo wells using extended elastic impedance are matched to either one or two seismic angle stacks and the best matches are selected and averaged to provide a joint estimate of reservoir properties and impedances and the associated uncertainties the algorithm has been tested on a number of data sets and validated by blind well ties the algorithm is 1d with