bluuebunny/crossref_metadata_2025 huggingface dataset:
Introduction to Special Issue on The Missing Psychology in Cultural Anthropology's Key Words
Authors: Quinn Naomi , Strauss Claudia
Published: August 2006

It is common practice in anthropology to use terms with implicit psychological content (such as embodiment). This is consistent with contemporary developments in anthropological theory and practice that lead to a focus on individuals' voices and practices. Nevertheless, many cultural anthropologists are critical of psychology. This introduction considers and responds to some of the usual criticisms. As this introduction describes, the articles that follow each take one term that is widely used by anthropologists (agency, resistance, subjectivity, the imaginary, and the self) and show how the concept could be better illuminated, and some published case study better explained, through the use of person-centered methods and the selective application of psychological theories.
Late Aramaic: The Literary and Linguistic Context of the Zohar
Authors: Rapoport-Albert Ada , Kwasman Theodore
Published: August 2006

This article introduces a new research project focusing on the Aramaic language of the Zohar—the most influential work in the literary canon of the Jewish mystical tradition. The Zohar is generally assumed by scholars to have been written in Spain during the final decades of the thirteenth century, although traditional kabbalists and Orthodox Jews believe that it was authored by its main protagonist, Rabbi Shimon bar Yohai, in second-century Palestine. While not disputing the late medieval provenance of the work, this article challenges the standard scholarly opinion whereby the Aramaic in which it was written was an artificially manufactured idiom, drawing its vocabulary, grammar and syntax indiscriminately from a variety of 'genuine' Aramaic sources. Part I of this study demonstrates that some of the most distinctive 'flaws' of zoharic Aramaic are attested in a wide range of much earlier Aramaic sources. Part II, which will be published separately, as a sequel, concerns the related question of the Palestinian setting of the Zohar.
On the Etymology of Some Enigmatic Words in North-Eastern Neo-Aramaic
Authors: Mutzafi Hezy
Published: August 2006

The present article seeks to clarify the etymologies of several selected North-Eastern Neo-Aramaic (NENA) lexical oddities of unknown or uncertain origin. All lexical items in question are proven to be of Aramaic provenance, yet mere recourse to Classical Aramaic is inadequate for uncovering the origins of these puzzling words due to far-reaching diachronic changes that have distanced them from their precursors. Missing links, based on interdialectal studies within NENA, are therefore crucial for securing well-founded etyma for these lexical enigmas. In addition to adducing missing links found in cognate dialects, each etymological discussion specifies the diachronic processes involved in the development of the lexical item under consideration.
Early Marjolin’s Ulcer in Bureau-Barrière Syndrome
Authors: Momeni Arash , Stark G. Björn
Published: August 2006

Bureau-Barrière syndrome (BBS) describes a rare destructive process affecting skin and bone resulting from an acquired unilateral or bilateral polyneuropathy. Clinically, it is characterized by a triad of symptoms, namely, acral ulcerations, polyneuropathy, and bone lesions. To date, the development of Marjolin’s ulcer in the course of BBS has not been described to the authors’ knowledge.
A Review of the Microcirculation in Skin in Patients With Chronic Venous Insufficiency: The Problem and the Evidence Available for Therapeutic Options
Authors: Wollina Uwe , Abdel-Naser Mohamed Badawy , Mani Raj
Published: August 2006

Impairment of the cutaneous microcirculation is a major predisposing factor in inflammation and ulceration in patients with chronic venous insufficiency (CVI). Increase of capillary filtration rate predisposes to the formation of edema. Local lymphedema is a complication of CVI, often underdiagnosed. This review is focused on CVI but excludes the complication of ulceration. Treatment of microcirculatory dysfunction can be done by pharmacologic intervention or compression therapy or using a combination of both. This review is focused on drugs that have been evaluated by randomized prospective controlled trials. The following compounds are discussed: horse chestnut seed extracts, flavonoids, red vine leaves extracts, total triterpenic fraction of Centella asiatica (L), prociadins, calcium dobesilate, and pentoxifylline. The microcirculatory effects of compression therapy using bandages or stockings are also reviewed. The major microcirculatory effects that have been shown are the reduction of capillary filtration rate and improvements in levels of transcutaneous partial pressures of oxygen and carbon dioxide (TcPO2 and TcPCO2). Available data suggest that a combination of pharmacologic and compression therapy may have some additive effects.
The Causes of Skin Damage and Leg Ulceration in Chronic Venous Disease
Authors: Smith Philip Coleridge
Published: August 2006

Chronic venous disease with skin changes of the leg is a common condition affecting up to 1 in 20 people in westernized countries. The causes of this problem are not fully understood, although research in recent years has revealed a number of important mechanisms that contribute to the disease process. Patients with chronic venous disease suffer persistently raised pressures in their deep and superficial veins in the lower limb. Leucocytes become “trapped” in the circulation of the leg during periods of venous hyper-tension produced by sitting or standing. Studies of the plasma levels of neutrophil granule enzymes shows that these are increased during periods of venous hypertension, suggesting that this causes activation of the neutrophils. Investigation of the leucocyte surface ligands CD11b and CD62L shows that the more activated neutrophils and monocytes are sequestered during venous hypertension. Measurement of plasma levels of the soluble parts of the endothelial adhesion molecules VCAM, ICAM, and ELAM show that these are all elevated in patients with chronic venous disease compared to controls. Following 30 minutes of venous hypertension produced by standing, these levels are further increased. These data suggest that venous hypertension causes neutrophil and monocyte activation, which in turn causes injury to the endothelium. Chronic injury to the endothelium leads to a chronic inflammatory condition of the skin that we know clinically as lipodermatosclerosis. This is mediated by perivascular inflammatory cells, principally macrophages, in the skin microcirculation. These stimulate fibroblasts in the skin leading to tissue remodeling and laying down of fibrous tissue. Vascular endothelial growth factor stimulates proliferation of capillaries within the skin. Skin in this state has the potential to ulcerate in response to minor injury.
Differences in the frequency and function of HHV8-specific CD8 T cells between asymptomatic HHV8 infection and Kaposi sarcoma
Authors: Lambert Marion , Gannagé Monique , Karras Alexandre , Abel Michal , Legendre Christophe , Kerob Delphine , Agbalika Felix , Girard Pierre-Marie , Lebbe Celeste , Caillat-Zucman Sophie
Published: August 2006

It is unclear how the immune response controls human herpesvirus 8 (HHV8; also known as Kaposi sarcoma–associated herpesvirus [KSHV]) replication and thereby prevents Kaposi sarcoma (KS). We compared CD8 T-cell responses to HHV8 latent (K12) and lytic (glycoprotein B, ORF6, ORF61, and ORF65) antigens in patients who spontaneously controlled the infection and in patients with posttransplantation, AIDS-related, or classical KS. We found that anti-HHV8 responses were frequent, diverse, and strongly differentiated toward an effector phenotype in patients who controlled the infection. Conversely, HHV8-specific CD8 cells were very rare in patients who progressed to KS, and were not recruited to the tumoral tissue, as visualized by in situ tetramer staining of KS biopsies. Last, HHV8-specific CD8 T cells were observed in a seronegative recipient of an HHV8infected graft who remained persistently aviremic and antibody negative, suggesting that specific cytotoxic T lymphocytes (CTLs) may provide protection from persistent HHV8 infection. These results support the crucial role of cellular immune responses in controlling HHV8 replication, in preventing malignancies in latently infected subjects, and in conferring genuine resistance to persistent infection. They may also have important implications for the design of prophylactic and therapeutic HHV8 vaccines, and for adoptive immunotherapy of KS.
Most human thymic and peripheral-blood CD4+CD25+ regulatory T cells express 2 T-cell receptors
Authors: Tuovinen Heli , Salminen Jukka T. , Arstila T. Petteri
Published: August 2006

Lack of allelic exclusion in the T-cell receptor (TCR) α locus gives rise to 2 different TCRs in 10% to 30% of all mature T cells, but the significance of such dual specificity remains controversial. Here we show that human CD4+CD25+ regulatory T (Treg) cells express 2 distinct Vα chains and thus 2 TCRs at least 3 times as often as other T cells. Extrapolating from flow cytometric analysis using Vα2-, Vα12-, and Vα24-specific monoclonal antibodies (mAbs), we estimated that between 50% and 99% of the CD25+ Treg cells were dual specific, as compared with about 20% of their CD25– counterparts. Moreover, both TCRs were equally capable of transmitting signals upon ligation. Cells with 2 TCRs also expressed more FOXP3, the Treg-cell lineage specification factor, than cells with a single TCR. Our findings suggest that expression of 2 TCRs favors differentiation to the Treg-cell lineage in humans and raise the question of the potential functional consequences of dual specificity.
A transgenic zebrafish model of neutrophilic inflammation
Authors: Renshaw Stephen A. , Loynes Catherine A. , Trushell Daniel M.I. , Elworthy Stone , Ingham Philip W. , Whyte Moira K.B.
Published: August 2006

We have established an in vivo model for genetic analysis of the inflammatory response by generating a transgenic zebrafish line that expresses GFP under the neutrophil-specific myeloperoxidase promoter. We show that inflammation is induced after transection of the tail of zebrafish larvae and that this inflammation subsequently resolves over a similar time course to mammalian systems. Quantitative data can be generated from this model by counting of fluorescent cells or by digital image analysis. In addition, we show that the resolution of experimentally induced inflammation can be inhibited by the addition of a pancaspase inhibitor, zVD.fmk, demonstrating that experimental manipulation of the resolution of inflammation is possible in this model.
Increased blood pressure in adult offspring of families with Balkan Endemic Nephropathy: a prospective study
Authors: Dimitrov Plamen S , Simeonov Valeri A , Tsolova Svetlana D , Bonev Angel G , Georgieva Rossitza B , Karmaus Wilfried J
Published: August 2006

Background

Previous studies have linked smaller kidney dimensions to increased blood pressure. However, patients with Balkan Endemic Nephropathy (BEN), whose kidneys shrink during the course of the disease, do not manifest increased blood pressure. The authors evaluated the relationship between kidney cortex width, kidney length, and blood pressure in the offspring of BEN patients and controls.

Methods

102 offspring of BEN patients and 99 control offspring of non-BEN hospital patients in the Vratza District, Bulgaria, were enrolled in a prospective study and examined twice (2003/04 and 2004/05). Kidney dimensions were determined using ultrasound, blood pressure was measured, and medical information was collected. The parental disease of BEN was categorized into three groups: mother, father, or both parents. Repeated measurements were analyzed with mixed regression models.

Results

In all participants, a decrease in minimal kidney cortex width of 1 mm was related to an increase in systolic blood pressure of 1.4 mm Hg (p = 0.005). There was no association between kidney length and blood pressure. A maternal history of BEN was associated with an increase in systolic blood pressure of 6.7 mm Hg (p = 0.03); paternal BEN, +3.2 mm Hg (p = 0.35); or both parents affected, +9.9 mm Hg (p = 0.002). There was a similar relation of kidney cortex width and parental history of BEN with pulse pressure; however, no association with diastolic blood pressure was found.

Conclusion

In BEN and control offspring, a smaller kidney cortex width predisposed to higher blood pressure. Unexpectedly, a maternal history of BEN was associated with average increased systolic blood pressure in offspring.
Differential DNA methylation profiles in gynecological cancers and correlation with clinico-pathological data
Authors: Yang Hui-Juan , Liu Vincent WS , Wang Yue , Tsang Percy CK , Ngan Hextan YS
Published: August 2006

Background

Epigenetic gene silencing is one of the major causes of carcinogenesis. Its widespread occurrence in cancer genome could inactivate many cellular pathways including DNA repair, cell cycle control, apoptosis, cell adherence, and detoxification. The abnormal promoter methylation might be a potential molecular marker for cancer management.

Methods

For rapid identification of potential targets for aberrant methylation in gynecological cancers, methylation status of the CpG islands of 34 genes was determined using pooled DNA approach and methylation-specific PCR. Pooled DNA mixture from each cancer type (50 cervical cancers, 50 endometrial cancers and 50 ovarian cancers) was made to form three test samples. The corresponding normal DNA from the patients of each cancer type was also pooled to form the other three control samples. Methylated alleles detected in tumors, but not in normal controls, were indicative of aberrant methylation in tumors. Having identified potential markers, frequencies of methylation were further analyzed in individual samples. Markers identified are used to correlate with clinico-pathological data of tumors using χ2 or Fisher's exact test.

Results

APC and p16 were hypermethylated across the three cancers. MINT31 and PTEN were hypermethylated in cervical and ovarian cancers. Specific methylation was found in cervical cancer (including CDH1, DAPK, MGMT and MINT2), endometrial cancer (CASP8, CDH13, hMLH1 and p73), and ovarian cancer (BRCA1, p14, p15, RIZ1 and TMS1). The frequencies of occurrence of hypermethylation in 4 candidate genes in individual samples of each cancer type (DAPK, MGMT, p16 and PTEN in 127 cervical cancers; APC, CDH13, hMLH1 and p16 in 60 endometrial cancers; and BRCA1, p14, p16 and PTEN in 49 ovarian cancers) were examined for further confirmation. Incidence varied among different genes and in different cancer types ranging from the lowest 8.2% (PTEN in ovarian cancer) to the highest 56.7% (DAPK in cervical cancer). Aberrant methylation for some genes (BRCA1, DAPK, hMLH1, MGMT, p14, p16, and PTEN) was also associated with clinico-pathological data.

Conclusion

Thus, differential methylation profiles occur in the three types of gynecologic cancer. Detection of methylation for critical loci is potentially useful as epigenetic markers in tumor classification. More studies using a much larger sample size are needed to define the potential role of DNA methylation as marker for cancer management.
Suppressing near-receiver scattered waves from seismic land data
Authors: Campman Xander H. , Herman Gérard C. , Muyzert Everhard
Published: August 2006

Upgoing body waves that travel through a heterogeneous near-surface region can excite scattered waves. When the scattering takes place close to the receivers, secondary waves interfere with the upcoming reflections, diminishing the continuity of the wavefront. We estimate a near-surface scattering distribution from a subset of a data record and use this scattering distribution to predict the secondary waves of the entire data record with a wave-theoretical model for near-receiver scattering. We then subtract the predicted scattered waves from the record to obtain the wavefield that would have been measured in the absence of near-surface heterogeneities. We apply this method to part of a field data set acquired in an area with significant near-surface heterogeneity. The main result of our processing scheme is that we effectively remove near-surface scattered waves. This, in turn, increases trace-to-trace coherence of reflection events. Moreover, application of our method improves the results obtained from just an application of a dip filter because we remove parts of the scattered wave with apparent velocities that are typically accepted by the pass zone of the dip filter. Based on these results, we conclude that our method for suppressing near-receiver scattered waves works well on densely sampled land data collected in areas with strong near-surface heterogeneity.
Two methods for determining geophone orientations from VSP data
Authors: Zeng Xiaoxian , McMechan George A.
Published: August 2006

Vertical seismic profile (VSP) data are usually acquired with three-component geophones of unknown azimuthal orientation. The geophone orientation must be estimated from the recorded data as a prerequisite to processing such as P- and S-wave separation, calculation of wave-incident directions, and 3D migration. We compare and combine two methods for estimating azimuthal orientation by least-squares fitting over a large number of shots. Combining the two methods can be done in an automated manner, which provides more accurate estimates of the geophone orientations than previous methods. In the polarization-plane method, we calculate the polarization plane of the first P-wave arrival. Then we subtract the source azimuth to determine the geophone orientation, independently for each geophone, with an angular uncertainty of [Formula: see text], and with no accumulated errors. In the relative-angle method, we obtain relative angles between adjacent geophone pairs using trace crosscorrelations, and operate on all coherent signals (even noise). Swapped geophone components can be detected automatically using the polarization-plane method. The main limitation of these (and all other known) methods is that uncertainties associated with path refraction are not estimated, unless some geophones have a priori known orientations, or we have a known earth model to correct for refraction.
Coherent interferometric imaging in clutter
Authors: Borcea Liliana , Papanicolaou George , Tsogka Chrysoula
Published: August 2006

Coherent interferometry is an array-imaging method in which we back-propagate, or migrate, crosscorrelations of the traces over appropriately chosen space-time windows rather than the traces themselves. The size of the space-time windows is critical and depends on two parameters. One is the decoherence frequency, which is proportional to the reciprocal of the delay spread in the traces produced by the clutter. The other is the decoherence length, which also depends on the clutter. As is usual, the clutter is modeled by random fluctuations in the medium properties. In isotropic clutter, the decoherence length is typically much shorter than the array aperture. In layered random media, the decoherence length along the layers can be quite long. We show that when the crosscorrelations of the traces are calculated adaptively, coherent interferometry can provide images that are statistically stable relative to small-scale clutter in the environment. This means that the images we obtain are not sensitive to the detailed form of the clutter. They only depend on its overall statistical properties. However, clutter does reduce the resolution of the images by blurring. We show how the amount of blurring can be minimized by using adaptive interferometric imaging algorithms and discuss the relation between the coherence properties of the array data and the loss in resolution caused by the blurring.
Salt-flank delineation by interferometric imaging of transmitted P- to S-waves
Authors: Xiao Xiang , Zhou Min , Schuster Gerard T.
Published: August 2006

We describe how vertical seismic profile (VSP) interferometric imaging of transmitted P-to-S (PS) waves can be used to delineate the flanks of salt bodies. Unlike traditional migration methods, interferometric PS imaging does not require the migration velocity model of the salt and/or upper sediments in order to image the salt flank. Synthetic elastic examples show that PS interferometric imaging can clearly delineate the upper and lower boundaries of a realistic salt-body model. Results also show that PS interferometric imaging is noticeably more accurate than conventional migration methods in the presence of static shifts and/or migration velocity errors. However, the illumination area of the PS transmitted waves is limited by the width of the shot and geophone aperture, which means wide shot offsets and deeper receiver wells are needed for comprehensive salt-flank imaging. Interferometric imaging results for VSP data from the Gulf of Mexico demonstrate its superiority over the traditional migration method. We also discuss other arrivals that can be used for interferometric imaging of salt flanks. For comparison, reduced-time migration results are presented, which are similar in quality to those obtained for interferometric imaging. We conclude that PS interferometric imaging of VSP data provides the geophysicist with a new tool by which salt flanks can be viewed from both above and below VSP geophone locations.
Imaging passive seismic data
Authors: Artman Brad
Published: August 2006

Imaging passive seismic data is the process of synthesizing the wealth of subsurface information available from reflection seismic experiments by recording ambient sound using an array of geophones distributed at the surface. Crosscorrelating the traces of such a passive experiment can synthesize data that are identical to actively collected reflection seismic data. With a correlation-based imaging condition, wave-equation shot-profile depth migration can use raw transmission wavefields as input for producing a subsurface image. Migration is even more important for passively acquired data than for active data because with passive data, the source wavefields are likely to be weak compared with background and instrument noise — a condition that leads to a low signal-to-noise ratio. Fourier analysis of correlating long field records shows that aliasing of the wavefields from distinct shots is unavoidable. Although this reduces the order of computations for correlation by the length of the original trace, the aliasing produces an output volume that may not be substantially more useful than the raw data because of the introduction of crosstalk between multiple sources. Direct migration of raw field data still can produce an accurate image, even when the transmission wavefields from individual sources are not separated. To illustrate direct migration, I use images from a shallow passive seismic investigation targeting a buried hollow pipe and the water-table reflection. These images show a strong anomaly at the 1-m depth of the pipe and faint events that could be the water table at a depth of around [Formula: see text]. The images are not clear enough to be irrefutable. I identify deficiencies in survey design and execution to aid future efforts.
Seismic interferometry: Reconstructing the earth’s reflection response
Authors: Draganov Deyan , Wapenaar Kees , Thorbecke Jan
Published: August 2006

In 1968, Jon Claerbout showed that the reflection response of a 1D acoustic medium can be reconstructed by autocorrelating the transmission response. Since then, several authors have derived relationships for reconstructing Green’s functions at the surface, using crosscorrelations of (noise) recordings that were taken at the surface and that derived from subsurface sources.

For acoustic media, we review relations between the reflection response and the transmission response in 3D inhomogeneous lossless media. These relations are derived from a one-way wavefield reciprocity theorem. We use modeling results to show how to reconstruct the reflection response in the presence of transient subsurface sources with distinct excitation times, as well as in the presence of simultaneously acting noise sources in the subsurface. We show that the quality of reconstructed reflections depends on the distribution of the subsurface sources. For a situation with enough subsurface sources — that is, for a distribution that illuminates the subsurface area of interest from nearly alldirections — the reconstructed reflection responses and the migrated depth image exhibit all the reflection events and the subsurface structures of interest, respectively. With only a few subsurface sources, that is, with insufficient illumination, the reconstructed reflection responses are noisy and can even become kinematically incorrect. At the same time, however, the depth image, which was obtained from their migration, still shows clearly all the illuminated subsurface structures at their correct positions.

For the elastic case, we review a relationship between the reflection Green’s functions and the transmission Green’s functions derived from a two-way wavefield reciprocity theorem. Using modeling examples, we show how to reconstruct the different components of the particle velocity observed at the surface and resulting from a surface traction source. This reconstruciton is achieved using crosscorrelations of particle velocity components measured at the surface and resulting from separate P- and S-wave sources in the subsurface.
Joint gravity and magnetic inversion in 3D using Monte Carlo methods
Authors: Bosch Miguel , Meza Ronny , Jiménez Rosa , Hönig Alfredo
Published: August 2006

We jointly invert gravity and magnetic data following a Monte Carlo method that provides estimation for a 3D model of the structure and physical properties of the medium. In particular, the model layer geometry and the density and magnetic susceptibility fields within layers are estimated, and their uncertainties are described with posterior probabilities. This method combines the gravity and magnetic data with prior information of the mass density and magnetic susceptibility statistics, and statistical constraints on the model interface positions. The resulting model realizations jointly comply with the observations and the prior statistical information.
High-resolution geophysical characterization of shallow-water wetlands
Authors: Mansoor Nasser , Slater Lee , Artigas Francisco , Auken Esben
Published: August 2006

We describe a procedure for rapid characterization of shallow-water, contaminated wetlands. Terrain-conductivity (TC), vertical-magnetic-gradiometry, and surface-water-chemistry data were obtained from a shallow-draft paddleboat operable in as little as [Formula: see text] of water. Measurements were taken every [Formula: see text], with data-acquisition rates exceeding [Formula: see text] of line ([Formula: see text] data points) per 8-hr field day.

We applied this procedure to an urban wetland that is affected by point and nonpoint sources of pollution. We used a one-dimensional, laterally constrained inversion algorithm to invert the apparent-conductivity data set obtained from the TC survey and to create a pseudo-2D image of sediment conductivity. The continuously recorded surface-water depth and conductivity values were input as a priori information in the inversion. We used soil chemistry determined for 28 sediment samples collected from the site, as well as lithologic logs from across the wetland, to constrain interpretation of the geophysical data. The inverted sediment conductivity describes a pattern of contamination probably attributable to leachates from adjacent landfills and/or to saltwater ingress from a partial tidal connection that is not obvious in the surface-water data. Magnetic-gradiometry values and the in-phase component of an EM31 response both reflect primarily the distribution of junk metal associated with a legacy of illegal dumping. Historic aerial photographs suggest that this distribution reflects land-use history and defines the maximum previous extent of an adjacent landfill and a pattern of dumping correlated with historic roadways.
Comparison of integral equation and physical scale modeling of the electromagnetic responses of models with large conductivity contrasts
Authors: Farquharson Colin G. , Duckworth Ken , Oldenburg Douglas W.
Published: August 2006

A comparison is made between the results from two different approaches to modeling geophysical electromagnetic responses: a numerical approach based upon the electric-field integral equation and the physical scale modeling approach. The particular implementation of the integral-equation solution was developed recently, and the comparison presented here is essentially a test of this new formulation. The implementation approximates the region of anomalous conductivity by a mesh of uniform cuboidal cells and approximates the total electric field within a cell by a linear combination of bilinear edge-element basis functions. These basis functions give a representation of the electric field that is divergence free but not curl free within a cell, and whose tangential component is continuous between cells. The charge density (which arises from the discontinuity of the normal com-ponent of the electric field across interfaces between cells of different conductivities and between cells and the background) is incorporated in a similar manner to integral equation solutions to dc resistivity modeling. The scenarios considered for the comparison comprise a graphite cube of [Formula: see text] conductivity and 14-cm length in free space and in brine ([Formula: see text] conductivity). The transmitter and receiver were small horizontal loops; measurements and computations were made for various fixed transmitter-receiver separations and various heights of the transmitter-receiver pair for frequencies ranging from [Formula: see text]. The agreement between the numerical results from the integral-equation implementation and the measurements from the physical scale modeling was very good, contributing to the verification of this particular implementation of the integral-equation solution to electromagnetic modeling.
Flattening without picking
Authors: Lomask Jesse , Guitton Antoine , Fomel Sergey , Claerbout Jon , Valenciano Alejandro A.
Published: August 2006

We present an efficient full-volume automatic dense-picking method for flattening seismic data. First local dips (stepouts) are calculated over the entire seismic volume. The dips are then resolved into time shifts (or depth shifts) using a nonlinear Gauss-Newton iterative approach that exploits fast Fourier transforms to minimize computation time. To handle faults (discontinuous reflections), we apply a weighted inversion scheme. The weight identifies locations of faults, allowing dips to be summed around the faults to reduce the influence of erroneous dip estimates near the fault. If a fault model is not provided, we can estimate a suitable weight (essentially a fault indicator) within our inversion using an iteratively reweighted least squares (IRLS) method. The method is tested successfully on both synthetic and field data sets of varying degrees of complexity, including salt piercements, angular unconformities, and laterally limited faults.
Modeling and inversion of PS-wave moveout asymmetry for tilted TI media: Part I — Horizontal TTI layer
Authors: Dewangan Pawan , Tsvankin Ilya
Published: August 2006

One of the distinctive features of mode-converted waves is their asymmetric moveout (i.e., the PS-wave traveltime in general is different if the source and receiver are interchanged) caused by lateral heterogeneity or elastic anisotropy. If the medium is anisotropic, the PS-wave moveout asymmetry contains valuable information for parameter estimation that cannot be obtained from pure reflection modes.

Here, we generalize the so-called [Formula: see text] method, which is designed to replace reflected PS modes in velocity analysis with pure (unconverted) SS-waves, by supplementing the output SS traces with the moveout-asymmetry attributes of PS-waves. The time-asymmetry attribute [Formula: see text] is computed in the slowness domain as the difference between the paired traveltimes of the PS arrivals corresponding to ray parameters (horizontal slownesses) of equal magnitude but opposite sign. Another useful asymmetry attribute is the offset [Formula: see text] of the PS-wave traveltime minimum on a common-midpoint (CMP) gather.

We demonstrate the effectiveness of the developed algorithmand the importance of including the asymmetry attributes of PS-waves in anisotropic velocity analysis for a horizontal transversely isotropic layer with a tilted symmetry axis (or TTI) medium. Simple analytic expressions for the moveout asymmetry of PSV-waves, derived in the weak-anisotropy approximation, are verified by anisotropic ray tracing. The attribute [Formula: see text] is proportional to the anellipticity parameter [Formula: see text] and reaches its maximum when the symmetry axis deviates by 20°–30° from the vertical or horizontal direction.

All relevant parameters of a TTI layer can be estimated by a nonlinear inversion of the NMO velocities and zero-offset traveltimes of PP- and SS- (SVSV) waves combined with the moveout-asymmetry attributes of the PSV-wave. The inversion of pure-mode (PP and SS) moveouts alone is nonunique, while the addition of the attributes [Formula: see text] and [Formula: see text] yields stable parameter estimates from 2D data acquired in the vertical symmetry-axis plane. If the TTI model is formed by obliquely dipping fractures, the anisotropic parameters can be inverted further for the fracture orientation and compliances.
Velocity-independent layer stripping of PP and PS reflection traveltimes
Authors: Dewangan Pawan , Tsvankin Ilya
Published: August 2006

Building accurate interval velocity models is critically important for seismic imaging and AVO (amplitude variation with offset) analysis. Here, we adapt the [Formula: see text] method to develop an exact technique for constructing the interval traveltime-offset function in a target zone beneath a horizontally layered overburden. All layers in the model can be anisotropic, with an essential assumption that the overburden has a horizontal symmetry plane (i.e., up-down symmetry).

Our layer-stripping algorithm is entirely data-driven and, in contrast to the generalized Dix equations, does not require knowledge of the velocity field anywhere in the medium. Important advantages of our approach compared to the Dix-style formalism also include the ability to handle mode-converted waves, long-offset data, and laterally heterogeneous target layers with multiple, curved reflectors. Numerical tests confirm the high accuracy of the algorithm in computing the interval traveltimes of both PP- and PS-waves in a dipping, transversely isotropic layer with a tilted symmetry axis (TTI medium) beneath an anisotropic overburden.

In combination with the inversion techniques developed for homogeneous TTI models, the proposed layer stripping of PP and PS data can be used to estimate the interval parameters of TTI formations in such important exploration areas as the Canadian Foothills. Potential applications of this methodology also include the dip-moveout inversion for the P-wave time-processing parameter [Formula: see text] and stable computation of the interval long-spread (nonhyperbolic) moveout for purposes of anisotropic velocity analysis.
Positioning drill-bit and look-ahead events using seismic traveltime data
Authors: Eidsvik Jo , Hokstad Ketil
Published: August 2006

We study seismic traveltime measurements acquired in the borehole, including vertical seismic profiling, seismic measurements while drilling, and drill-bit noise generated data. These traveltime data are used to assess informative parameters, including drill-bit position, distance to drilling target, and parameters of the velocity model. First, we analyze seismic traveltime data using a simple hyperbolic traveltime equation for rays between surface sampling locations and the drill bit. Second, we describe a model for estimating both the position of the drill bit and the relative distance to geologic interfaces ahead of the bit. Finally, we present a dynamic Bayesian strategy for real-time prediction of drill-bit positions, velocity parameters, and distances to geologic markers. Walk-away vertical seismic profiling data from the Norwegian Sea are used to demonstrate our methods. For this data set, we pick five key reflectors ahead of the drill bit. The deepest reflector is estimated to be [Formula: see text] ahead of the drill bit, using seismic traveltime data alone. The effects of aperture and surface sampling locations are large on our estimates and their associated uncertainties, and we observe that large offset is preferable to dense sampling in terms of positioning accuracy.
AVA simultaneous inversion of partially stacked seismic amplitude data for the spatial delineation of lithology and fluid units of deepwater hydrocarbon reservoirs in the central Gulf of Mexico
Authors: Contreras Arturo , Torres-Verdín Carlos , Fasnacht Tim
Published: August 2006

This paper describes the successful application of amplitude-versus-angle (AVA) inversion of prestack-seismic amplitude data to detect and delineate deepwater hydrocarbon reservoirs in the central Gulf of Mexico. Detailed AVA fluid/lithology sensitivity analysis was conducted to assess the nature of AVA effects in the study area based on well-log data. Standard techniques such as crossplot analysis, Biot-Gassmann fluid substitution, AVA reflectivity modeling, and numerical simulation of synthetic gathers were part of the AVA sensitivity analysis.

Crossplot and Biot-Gassmann analyses indicate significant sensitivity of acoustic properties to fluid substitution. AVA reflectivity and angle-gather modeling indicate that the shale/sand interfaces represented by the top and base of the M-10 reservoir are associated with typical Class III AVA responses caused by relatively low-impedance gas-bearing sands. Consequently, prestack seismic inversion provided accurate and reliable quantitative information about the spatial distribution of lithology and fluid units within the turbidite reservoirs based on the interpretation of fluid/lithology-sensitive modulus attributes. From the integration of inversion results with analogous depositional models, the M-series reservoirs were interpreted as stacked terminal turbidite lobes within an overall fan complex. This interpretation is consistent with previous regional stratigraphic/depositional studies.
Comparison between interferometric migration and reduced-time migration of common-depth-point data
Authors: Zhou Min , Jiang Zhiyong , Yu Jianhua , Schuster Gerard T.
Published: August 2006

One of the difficulties in seeing beneath salt is that the migration velocity in the salt and above it is not well known. This can lead to defocusing of migration images beneath the salt. In this paper, we show that reduced-time migration (RTM) and interferometric migration (IM) can partly mitigate this problem. RTM time-shifts the traces with the time difference between the calculated arrival time [Formula: see text] and the natural arrival time [Formula: see text] of a reference reflection, where [Formula: see text] and [Formula: see text] denote the source and receiver locations on the surface, respectively. We use the terms natural and calculated to represent, respectively, the arrival times that are velocity-independent (traveltimes directly extracted from the data without knowledge of the velocity model) and velocity-dependent (traveltimes calculated by ray tracing through a given velocity model). The benefit of RTM is a significant reduction of defocusing errors caused by errors in the migration velocity. IM, on the other hand, requires extrapolation of the surface data below salt using the natural arrival times [Formula: see text] of the subsalt reference reflector, and migration of the extrapolated data below the salt. The benefit with IM is that no salt velocity model is needed, so the model-based defocusing errors are, in theory, eliminated. To reduce computational time, we implement IM with a seminatural Green’s function (combination of model-based calculated and picked natural traveltimes). Because no explicit data extrapolation is needed, IM with seminatural Green’s functions is more cost-efficient than the standard IM. In this paper, we tested both RTM and IM with seminatural Green’s functions on a synthetic and a field common-depth-point (CDP) data set, the latter from the Gulf of Mexico (GOM). Results show that both RTM and IM can remove the significant kinematic distortions caused by the overburden without knowledge of the overburden velocity.
Interferometric modeling of wave propagation in inhomogeneous elastic media using time reversal and reciprocity
Authors: van Manen Dirk-Jan , Curtis Andrew , Robertsson Johan O.
Published: August 2006

Time reversal of arbitrary, elastodynamic wavefields in partially open media can be achieved by measuring the wavefield on a surface surrounding the medium and applying the time reverse of those measurements as a boundary condition. We use a representation theorem to derive an expression for the time-reversed wavefield at arbitrary points in the interior. When this expression is used to compute, in a second point, the time-reversed wavefield originating from a point source, the time-reversed Green’s function between the two points is observed. By invoking reciprocity, we obtain an expression that is suitable for modeling of wave propagation through the medium. From this we develop an efficient and flexible two-stage modeling scheme. In the initial phase, the model is illuminated systematically from a surface surrounding the medium using a sequence of conventional forward-modeling runs. Full waveforms are stored for as many points in the interior as possible. In the second phase, Green’s functions between arbitrary points in the volume can be computed by crosscorrelation and summation of data computed in the initial phase. We illustrate the method with a simple acoustic example and then apply it to a complex region of the elastic Pluto model. It is particularly efficient when Green’s functions are desired between a large number of points, but where there are few common source or receiver points. The method relies on interference of multiply scattered waves, but it is stable. We show that encoding the boundary sources using pseudonoise sequences and exciting them simultaneously, akin to daylight imaging, is inefficient and in all explored cases leads to relatively high-noise levels.
Correlation of random wavefields: An interdisciplinary review
Authors: Larose Eric , Margerin Ludovic , Derode Arnaud , van Tiggelen Bart , Campillo Michel , Shapiro Nikolai , Paul Anne , Stehly Laurent , Tanter Mickael
Published: August 2006

This paper presents an interdisciplinary review of the correlation properties of random wavefields. We expose several important theoretical results of various fields, ranging from time reversal in acoustics to transport theory in condensed matter physics. Using numerical simulations, we introduce the correlation process in an intuitive manner. We establish a fruitful mapping between time reversal and correlation, which enables us to transpose many known results from acoustics to seismology. We show that the multiple-scattering formalism developed in condensed matter physics provides a rigorous basis to analyze the field correlations in disordered media. We discuss extensively the various factors controlling and affecting the retrieval of the Green’s function of a complex medium from the correlation of either noise or coda. Acoustic imaging of complex samples in the laboratory and seismic tomography of geologic structures give a glimpse of the promising wide range of applications of the correlation method.
Improved Green’s functions for passive-source structural studies
Authors: Mercier Jean-Philippe , Bostock Michael G. , Baig Adam M.
Published: August 2006

Over the past two decades, teleseismic receiver functions have proved to be a useful tool to investigate crustal structure. Because they represent a first-order approximation to the [Formula: see text]-wave component of the teleseismic-[Formula: see text] Green’s function, receiver functions provide valuable information on physical properties related to shear modulus. However, the implicit use of the [Formula: see text]-component seismogram as a proxy for the source precludes the recovery of information on discontinuous structure involving contrasts in compressional modulus. By deconvolving improved estimates of complex source time functions generated by earthquakes, one may move beyond the conventional receiver function paradigm to a more accurate approximation of the earth’s Green’s function. Using a new deconvolution method, we present estimates of the [Formula: see text]-component of the teleseismic-[Formula: see text] Green’s functions at several stations of the Canadian National Seismic Network (CNSN) that clearly show the receiver-side pure [Formula: see text]-wave crustal multiple. The identification and characterization of these signals in studies of the lithosphere will afford better constraints on subsurface lithology and represent a narrowing of the gap between active- and passive-source seismic imaging.
On estimating the impulse response between receivers in a controlled ultrasonic experiment
Authors: van Wijk K.
Published: August 2006

A controlled ultrasonic laboratory experiment provides a detailed analysis of retrieving a band-limited estimate of the Green's function between receivers in an elastic medium. Instead of producing a formal derivation, this paper appeals to a series of intuitive operations, common to geophysical data processing, to understand the practicality of seismic interferometry. Whereas the retrieval of the full Green's function is based on the crosscorrelation of receivers in the presence of equipartitioned signal, an estimate of the impulse response is recovered successfully with 40 sources in a line covering six wavelengths at the surface.
A weak-anisotropy approximation to multicomponent induction responses in cross-bedded formations
Authors: Wang Tsili
Published: August 2006

The multicomponent induction logging response to a cross-bedded formation has been modeled under a weak-anisotropy approximation. With the approximation, a cross-bedded formation can be modeled as a transversely isotropic (TI) medium. The validity of the approximation has been tested for the main (coplanar and coaxial) components of the induction response. The conditions for the weak-anisotropy approximation to be valid depend on the component of the response. For the coplanar components, the approximation is valid for an anisotropy ratio up to 2 if the relative dipping angle between the cross-bedded formation and the borehole axis is below [Formula: see text]. For the coaxial component, the approximation reduces to a previously established result that the apparent resistivity for such a component is the geometric average of the resistivities, parallel and perpendicular to the bedding planes of an anisotropic formation, respectively, if the borehole is ignored. Hence, the approximation holds for the coaxial component regardless of the anisotropy ratio.