bluuebunny/crossref_metadata_2025 huggingface dataset:
The FYVE domain in Smad anchor for receptor activation (SARA) is sufficient for localization of SARA in early endosomes and regulates TGF‐β/Smad signalling
Authors: Itoh Fumiko , Divecha Nullin , Brocks Lenny , Oomen Lauran , Janssen Hans , Calafat Jero , Itoh Susumu , Dijke Peter ten
Published: March 2003

Abstract Background: Transforming growth factor‐β (TGF‐β) initiates intracellular signalling by inducing the formation of a heteromeric complex between TGF‐β type I (TβR‐I) and TGF‐β type II serine/threonine kinase receptors (TβR‐II). After the activation of TβR‐I kinase by TβR‐II kinase, specific receptor‐regulated Smads (R‐Smads) are phosphorylated by TβR‐I kinase. Smad anchor for receptor activation (SARA), which contains a FYVE finger domain, regulates the subcellular localization of R‐Smads and presents them to TβR‐I. However, it is unclear where SARA is localized in the cell and which phospholipid(s) interacts with its FYVE domain.

Results: Wild‐type SARA and the FYVE domain of SARA (FYVE(SARA)) reveal a punctate staining pattern and co‐localize with the early endosomal markers, early endosomal antigen‐1 (EEA1) and hepatic growth factor‐regulated tyrosine kinase substrate (Hrs). The ectopic expression of dominant negative rab5, a critical regulatory molecule in endosome function, redistributes SARA from punctate to a diffuse cytosolic staining pattern. A lipid binding assay demonstrated that the recombinant FYVE domain from SARA predominantly interacts with phosphatidylinositol 3‐phosphate (PtdIns(3)P). Consistent with this result, wortmannin, a PI3 kinase inhibitor, resulted in both a redistribution of SARA from the endosomal compartment to the cytosol and the attenuation of both TGF‐β‐induced R‐Smad phosphorylation and transcriptional activation. Ectopic expression of the FYVE domain of SARA also induced the redistribution of wild‐type SARA and inhibited TGF‐β as well as BMP/Smad‐induced transcriptional responses.

Conclusion: The FYVE domain is sufficient and necessary for the early endosomal localization of SARA, probably through its interaction with PtdIns(3)P. Moreover, the localization of SARA in early endosomes is required for efficient TGF‐β/Smad signalling.
Association of frabin with specific actin and membrane structures
Authors: Kim Yongman , Ikeda Wataru , Nakanishi Hiroyuki , Tanaka Yoshinari , Takekuni Kyouji , Itoh Shinsuke , Monden Morito , Takai Yoshimi
Published: March 2003

Background: Frabin is an actin filament (F‐actin)‐binding protein with GDP/GTP exchange activity specific for Cdc42 small G protein. Expression of frabin forms filopodia‐like microspikes through the direct activation of Cdc42, and lamellipodia through indirect activation of Rac small G protein. Frabin consists of the F‐actin‐binding domain (FAB), the Dbl homology domain (DH), the first pleckstrin homology domain (PH1), the FYVE‐finger domain (FYVE), the second PH domain (PH2) from the N‐terminus in this order. Although DH and PH1 show exchange activity, FAB, in addition to DH and PH1, is required for the formation of microspikes, whereas FYVE and PH2, in addition to DH and PH1, are required for the formation of lamellipodia.

Results: Various truncated mutants of frabin were co‐expressed with a dominant active mutant (DA) of Cdc42, Rac1DA, or full‐length frabin in L fibroblasts. FAB was recruited to the Cdc42DA‐formed filopodia‐like microspikes. FAB and a fragment containing DH, PH1, FYVE and PH2 were recruited to the Rac1DA‐formed membrane ruffles. Furthermore, each of these fragments served as a dominant negative mutant of frabin when co‐expressed with full‐length frabin, and inhibited the full‐length frabin‐formed morphological changes.

Conclusion: These results suggest that frabin recognizes a specific actin structure(s) through FAB and a specific membrane structure(s) through FAB and the region containing DH, PH1, FYVE and PH2. It is likely that frabin associates with the specific actin and membrane structures and activates Cdc42 and Rac in the vicinity of these structures, eventually leading to morphological changes.
Inhibition of Nodal signalling by Lefty mediated through interaction with common receptors and efficient diffusion
Authors: Sakuma Rui , Ohnishi Yu‐ichiro , Meno Chikara , Fujii Hideta , Juan Hou , Takeuchi Jun , Ogura Toshihiko , Li En , Miyazono Kohei , Hamada Hiroshi
Published: March 2003

Background: Two TGFβ‐related proteins, Nodal and Lefty, are implicated in early embryonic patterning of vertebrates. Genetic data suggest that Nodal is a signalling molecule, while Lefty is an antagonist of Nodal, but their precise function remains unknown.

Results: The signalling pathway of Nodal was investigated with the use of a Nodal‐responsive assay system based on frog animal caps. Expression of dominant negative mutants of various receptors indicated that ALK4, and either ActRIIA or ActRIIB, function as type I and type II receptors for Nodal, respectively. A soluble form of Cripto lacking the COOH‐terminal region interacted with Nodal but failed to mediate Nodal signalling, indicating that the native Cripto protein functions as a membrane‐bound co‐receptor for Nodal. Processed forms of Lefty proteins, both smaller and larger forms, inhibited Nodal signalling. Such Lefty‐induced inhibition was rescued by excess ActRIIA or ActRIIB, suggesting that Lefty antagonizes Nodal signalling through competitive binding to the common receptor ActRIIA or ActRIIB. This idea was supported by the demonstration of a genetic interaction between lefty2 and ActRIIB in mouse. Behaviours of GFP‐Nodal and GFP‐Lefty2 proteins were also investigated in chick embryos. Both proteins could diffuse over a long distance, but the latter diffused faster than the former.

Conclusions: Efficient inhibition of Nodal signals by Lefty may involve competitive binding of Lefty to the common receptors and faster diffusion of Lefty.
ERBIN associates with p0071, an armadillo protein, at cell‐cell junctions of epithelial cells
Authors: Izawa Ichiro , Nishizawa Miwako , Tomono Yasuko , Ohtakara Kazuhiro , Takahashi Toshitada , Inagaki Masaki
Published: March 2003

Abstract

Working model for the ERBIN–p0071 interaction at cell‐cell adhesions. ERBIN is associated with p0071 at adherens junctions and desmosomes. p0071 is thought to interact with classic cadherins or desmosomal cadherins (Hatzfeld 1999). The subcellular localization of ERBIN may be regulated by the Rho family and other signals controlling cell polarity.

image

Background: ERBIN, an ErbB2 receptor‐interacting protein, belongs to a recently described family of proteins termed the LAP [leucine‐rich repeats and PSD‐95/dLg‐A/ZO‐1 (PDZ) domains] family which has essential roles in establishment of cell polarity.

Results: To identify new ERBIN‐binding proteins, we screened a yeast two‐hybrid library, using the carboxyl‐terminal fragment of ERBIN containing PDZ domain as the bait, and we isolated p0071 (also called plakophilin‐4) as an ERBIN‐interacting protein. p0071 is a member of the p120 catenin family, which are defined as proteins with 10 armadillo repeats, and localizes along the cell‐cell border. The ERBIN PDZ domain binds the COOH‐terminus of p0071 containing the PDZ domain‐binding sequence. Endogenous ERBIN was co‐immunoprecipitated with p0071. In fully polarized Madin–Darby canine kidney (MDCK) cells, ERBIN co‐localized largely with β‐catenin and partly with desmoplakin along the lateral plasma membrane domain. At these cell‐cell contact regions, ERBIN co‐localizes with p0071. Over‐expression of the dominant active forms of Cdc42, Rac1 or RhoA, Rho family small GTPases, resulted in a marked accumulation of ERBIN at the cell‐cell contacts of MDCK and HeLa cells.

Conclusion: These results show that ERBIN interacts in vivo with p0071 and that it may be involved in the organization of adherens junctions and the desmosomes of epithelia. In addition, we demonstrated that the subcellular localization of ERBIN might be regulated by Rho family small GTPases.
Yeast Whi2 and Psr1‐phosphatase form a complex and regulate STRE‐mediated gene expression
Authors: Kaida Daisuke , Yashiroda Hideki , Toh‐e Akio , Kikuchi Yoshiko
Published: March 2003

Background:  In response to various stressful situations, including diauxic conditions, the Msn2 and Msn4 transcription factors induce STRE‐mediated gene expression of many stress responsive genes in Saccharomyces cerevisiae. This is called the general stress response. The whi2 cells in the stationary phase are smaller than wild‐type cells.

Results:  Here we demonstrate that STRE‐mediated gene expression in whi2 cells is reduced to half of that in the wild‐type cells under various stress conditions. It is also delayed for several hours when the mutant cells enter the stationary phase. Using the two‐hybrid system, we isolated a WHI2‐interacting gene, PSR1, which is one of the redundant genes encoding plasma membrane phosphatases. whi2 and psr1 psr2 mutants had similar phenotypes, including reduced STRE‐mediated gene expression, higher sensitivity to sodium ions and heat shock, and hyper‐phosphorylation of Msn2. The phosphatase activity of Psr1 was necessary for the full activation of STRE‐mediated gene expression. Furthermore, both Psr1 and Msn2 were co‐immunoprecipitated with Whi2.

Conclusions:  Thus, Whi2 and its binding partner, Psr1‐phosphatase, are required for a full activation of the general stress response, possibly through the dephosphorylation of Msn2. These results may explain why stationary phase whi2 cells are small.
MBLR, a new RING finger protein resembling mammalian Polycomb gene products, is regulated by cell cycle‐dependent phosphorylation
Authors: Akasaka Takeshi , Takahashi Naomi , Suzuki Maki , Koseki Haruhiko , Bodmer Rolf , Koga Hisashi
Published: March 2003

Background: The RING finger proteins function in a variety of fundamental cellular processes. The products of some members of the Polycomb group (PcG) bear ring finger domains and are defined as a subclass of RING finger proteins. Among them are Drosophila posterior sex combs and suppressor 2 of zeste, whose RING fingers are conserved in vertebrate PcG proteins Mel18 and Bmi1.

Results: We have identified a new mammalian RING finger protein, termed MBLR due to its structural similarity to Mel18 and Bmi1 (Mel18 and Bmi1‐like RING finger protein). MBLR interacts with some PcG proteins: in vitro biochemical data support the idea of a direct interaction of MBLR’s RING finger domain with Ring1B, which is highly homologous to one of the mammalian PcG genes, Ring1A. We also show that MBLR acts as a transcriptional repressor in transiently transfected cells, as is the case for other PcG proteins. Immunocytochemical analysis reveals that MBLR protein is localized in a fine‐grained distribution throughout the nucleoplasm in interphase cultured cells and in a fainter diffuse cytoplasmic distribution in mitotic cells. In addition, we find that serine 32 of MBLR is specifically phosphorylated during mitosis, most likely by CDK7, a component of the basal transcriptional machinery.

Conclusion: Similarities to previously defined PcG proteins suggest that MBLR should be included in the same subclass of RING finger proteins as Mel18 and Bmi1. Although the biological relevance of the cell cycle‐related phosphorylation remains to be demonstrated, serine 32 phosphorylation could nevertheless be functionally important.
Cytoskeletal reorganization induced by insulin: involvement of Grb2/Ash, Ras and phosphatidylinositol 3‐kinase signalling
Authors: Tobe Kazuyuki , Asai Shohji , Matuoka Koozi , Yamamoto Tadashi , Chida Kazuhiro , Kaburagi Yasushi , Akanuma Yasuo , Kuroki Toshio , Takenawa Tadaomi , Kimura Satoshi , Nagai Ryozo , Kadowaki Takashi
Published: March 2003

Background:  Cytoskeletal reorganization is important for a wide variety of insulin‐mediated biological actions, including cell growth, migration and metabolism, but the intracellular signalling pathways leading to insulin‐induced cytoskeletal reorganization have largely been unknown. We therefore investigated the involvement of Grb2/Ash‐Ras and phosphatidylinositol (PI) 3‐kinase in the insulin‐induced morphological changes in fibroblasts over‐expressing human insulin receptors (HIRcB cells).

Results:  I nsulin, as well as 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) and 8‐bromo‐cAMP, induced a unique morphological change associated with actin cytoskeletal reorganization characterized by the disruption of actin stress fibres and thicker actin bundle formation. Microinjection of an anti‐Grb2/Ash antibody, but not control IgG, inhibited the insulin‐induced actin reorganization, whereas the TPA‐ and 8‐bromo‐cAMP‐induced morphological changes were not inhibited by microinjection of the anti‐Grb2/Ash antibody. In addition, microinjection of dominant negative ras p21 protein, but not the heat‐treated protein, inhibited insulin‐induced cytoskeletal reorganization. Microinjection of activated p21ras protein resulted in very similar cytoskeletal reorganization with actin bundle formation in the cytoplasm. The PI3‐kinase inhibitor wortmannin inhibited insulin‐induced cytoskeletal reorganization, but not the TPA‐ nor 8‐bromo‐cAMP‐induced reorganization. Interestingly, wortmannin also inhibited the activated p21ras‐induced morphological change.

Conclusions:  We concluded that Grb2/Ash‐Ras activation and probably Ras‐associated PI3‐kinase activation are involved in the insulin‐induced morphological change.
Regulation of c‐Fos and Fra‐1 by the MEK5‐ERK5 pathway
Authors: Terasawa Kazuya , Okazaki Kenji , Nishida Eisuke
Published: March 2003

Background: ERK5 is the newest subfamily member of the mitogen‐activated protein kinase (MAPK) family, and is activated by various extracellular signals including growth factors. MEK5 is a specific activator of ERK5. c‐Fos and Fra‐1, well‐known immediate early gene products, are members of the AP‐1 family. We previously reported that activation of the MEK5‐ERK5 pathway is able to induce expression of c‐Fos.

Results: We have found that activation of the MEK5‐ERK5 pathway causes the phosphorylation and stabilization of c‐Fos and Fra‐1. Phosphorylation of c‐Fos appears to be mediated by ERK5 and a kinase(s) lying downstream of ERK5, and the MEK5‐ERK5 pathway‐dependent phosphorylation sites on c‐Fos are different from the ERK1/2 pathway‐dependent ones. Interestingly, activation of the MEK5‐ERK5 pathway, but not that of the ERK1/2 pathway, is found to markedly increase the transactivation activity of c‐Fos. Furthermore, our results show that the C‐terminal half of ERK5 is necessary for the maximal activation of the transactivation activity of c‐Fos and Fra‐1.

Conclusion: These results reveal a role of the MEK5‐ERK5 pathway in modulating the function of the Fos family proteins which is different from the role of the ERK1/2 pathway.
Geophysical inversion with a neighbourhood algorithm—II. Appraising the ensemble
Authors: Sambridge Malcolm
Published: March 2003

Monte Carlo direct search methods, such as genetic algorithms, simulated annealing, etc., are often used to explore a finite-dimensional parameter space. They require the solving of the forward problem many times, that is, making predictions of observables from an earth model. The resulting ensemble of earth models represents all ‘information’ collected in the search process. Search techniques have been the subject of much study in geophysics; less attention is given to the appraisal of the ensemble. Often inferences are based on only a small subset of the ensemble, and sometimes a single member.

This paper presents a new approach to the appraisal problem. To our knowledge this is the first time the general case has been addressed, that is, how to infer information from a complete ensemble, previously generated by any search method. The essence of the new approach is to use the information in the available ensemble to guide a resampling of the parameter space. This requires no further solving of the forward problem, but from the new ‘resampled’ ensemble we are able to obtain measures of resolution and trade-off in the model parameters, or any combinations of them.

The new ensemble inference algorithm is illustrated on a highly non-linear wave-form inversion problem. It is shown how the computation time and memory requirements scale with the dimension of the parameter space and size of the ensemble. The method is highly parallel, and may easily be distributed across several computers. Since little is assumed about the initial ensemble of earth models, the technique is applicable to a wide variety of situations. For example, it may be applied to perform ‘error analysis’ using the ensemble generated by a genetic algorithm, or any other direct search method.
Microlevelling procedures applied to regional aeromagnetic data: an example from the Transantarctic Mountains (Antarctica)
Authors: Ferraccioli Fausto , Gambetta Marco , Bozzo Emanuele
Published: March 2003

The extensive application of digital enhancement and filtering as a powerful tool for aeromagnetic interpretation, not only of high resolution but also of regional data, requires an improved levelling. Two microlevelling techniques were thus compared in order to find an effective but relatively simple procedure to remove, or at least to reduce, residual magnetic errors remaining after standard levelling processes. This study was carried out on regional aeromagnetic data recently acquired at high magnetic latitudes along the Transantarctic Mountains in Antarctica, where it is particularly critical to remove time‐dependent magnetic variations. Two‐dimensional FFT filters applied to the gridded data, namely the Butterworth and a directional cosine filter, proved to be more effective than previously proposed one‐dimensional space‐domain filters in the reduction of the ‘residual corrugation’ not removed by statistical levelling. Tectonic interpretation of trends detected in the total field magnetic anomaly map and in the 3D analytic signal improved after application of frequency‐domain microlevelling. However, we also show that when interpreting microlevelled data, two factors must be considered: (i) the possible presence of real geological trends aligned along the flight lines; (ii) modifications in the results yielded by depth estimates of magnetic sources due to the FFT filters applied during the microlevelling procedure. Such changes were seen both in the well‐established 2D FFT method, based on the slope of the energy spectrum, and in the more recent 3D Euler deconvolution technique. Overall our results indicate that microlevelling could profitably be applied to older gridded aeromagnetic data sets in Antarctica, thus improving the accuracy and geological significance of future regional magnetic compilations, as already seen in other continents.
Multiple prediction using the homeomorphic‐imaging technique
Authors: Keydar Shemer , Landa Evgeny , Gelchinsky Boris , Belfer Igor
Published: March 2003

A new method for predicting different kinds of multiples and peg‐leg reflections in unstacked seismic data is discussed. The basis for this method is the fact that kinematic properties of multiples can be represented as a combination of kinematic properties of primary reflections. The prediction is made using a two‐step process. In the first step, the values for the angle of emergence and radius of curvature of the wavefront for primary reflections from ‘multiple‐generating’ interfaces are obtained. These parameters are estimated directly from unstacked data for every source point using the homeomorphic‐imaging technique. The second step consists of prediction of multiples from primary reflections that satisfy a so‐called ‘multiple condition’. This condition is the equality of the absolute values of the angles of emergence calculated from the first step. This method is effective even in complex media and information on the subsurface geology is not required. The parameters are estimated directly from the unstacked data and do not require any computational efforts such as in wavefield extrapolation of data.
A comparison between airguns and explosives as wide‐angle seismic sources
Authors: Staples  , Hobbs  , White
Published: March 2003

The relative merits of a 48‐gun, 9324 cu. in. (153 litre) airgun array and a 200 kg explosive source are considered for the purposes of long‐range (0–400 km) refraction seismic work, with particular reference to traveltime modelling. Theoretical source calculations indicate that in the frequency range 2.5–12.0 Hz, the airgun source will produce an RMS pressure ∼ 8% of that produced by the explosive source and an initial burst pressure ∼17% of that produced by the explosive source. Observed data support these calculations at short ranges and illustrate the greater attenuation of the airgun signal with range due to its lack of very low frequency (< 5 Hz) content. At short offsets, the airgun array provides a preferable seismic source to the explosives, due to densely spaced shots and a consistent waveform resulting in excellent trace‐to‐trace coherence. With increasing offsets, it may be necessary to stack the airgun data to enhance its signal‐to‐noise ratio: here we use a 4‐fold stack. Large explosive shots, although more powerful, produce a less consistent waveform and are more widely spaced due to operational constraints. The offset at which airguns provide a preferable source is dependent on the ambient noise. This practical comparison of real sources demonstrates that, even without advanced processing, a well‐tuned airgun array may provide a preferable source to explosives at offsets up to 160 km, under favourable experimental conditions.
Measurement of magnetic properties of steel sheets
Authors: Eskola  , Puranen  , Soininen
Published: March 2003

Magnetic methods are used in detection of environmental, engineering and military objects fabricated of thin ferromagnetic sheets having volume susceptibilities higher than 100 SI units. Magnetic modelling of such objects would be advantageous, but it requires knowledge of the susceptibility and remanence values of sheet materials, which is scarce. We introduce a magnetometer method for the determination of susceptibility and remanence on thin steel samples. The area of the sample must be so large that its within‐sheet magnetization remains below the saturation state. The measurements are made in normal office surroundings in the Earth's magnetic field with an ordinary fluxgate magnetometer.

The square‐shaped sheet samples measured in this work have an edge length of 17.5 cm and a thickness in the range 0.5–1.0 mm. During the measuring procedure the sample is placed in four positions on a subvertical measurement board. For each position, the magnetic field in the dip direction of the board plane is measured on the opposite sides of the sample. The secondary field values are averaged for each sample position in order to reduce the effect of sample inhomogeneities. With these data, the susceptibility and remanence of the sample in its edge directions are then determined, based on a model curve which is calculated numerically using thin‐sheet integral equations.

The susceptibilities measured for different steel types (cold rolled and hot‐dip zinc‐coated steel sheets) varied in the range 200–500 SI units, and the remanence varied in the range 1000–20 000 A/m. No systematic differences were observed between the magnetic properties of various steel types. The repeatability of the susceptibility measurements was good (variations < 5%) but the remanence could be changed by 50% between repeated determinations.

The measured susceptibility range signifies that pieces of steel with a typical thickness of 0.5 mm remain below magnetic saturation when their edge dimension is larger than 5 cm. Therefore magnetic modelling of larger steel pieces must be made using the thin‐sheet theory with known magnetic properties, whereas smaller saturated pieces can be alternatively modelled as an equipotential system.
Filter formulation and wavefield separation of cross‐well seismic data
Authors: Mars Jérôme , Rector Iii James W. , Lazaratos Spyros K.
Published: March 2003

Multichannel filtering to obtain wavefield separation has been used in seismic processing for decades and has become an essential component in VSP and cross‐well reflection imaging. The need for good multichannel wavefield separation filters is acute in borehole seismic imaging techniques such as VSP and cross‐well reflection imaging, where strong interfering arrivals such as tube waves, shear conversions, multiples, direct arrivals and guided waves can overlap temporally with desired arrivals. We investigate the effects of preprocessing (alignment and equalization) on the quality of cross‐well reflection imaging wavefield separation and we show that the choice of the multichannel filter and filter parameters is critical to the wavefield separation of cross‐well data (median filters, f–k pie‐slice filters, eigenvector filters). We show that spatial aliasing creates situations where the application of purely spatial filters (median filters) will create notches in the frequency spectrum of the desired reflection arrival. Eigenvector filters allow us to work past the limits of aliasing, but these kinds of filter are strongly dependent on the ratio of undesired to desired signal amplitude. On the basis of these observations, we developed a new type of multichannel filter that combined the best characteristics of spatial filters and eigenvector filters. We call this filter a ‘constrained eigenvector filter’. We use two real data sets of cross‐well seismic experiments with small and large well spacing to evaluate the effects of these factors on the quality of cross‐well wavefield separation. We apply median filters, f–k pie‐slice filters and constrained eigenvector filters in multiple domains available for these data sets (common‐source, common‐receiver, common‐offset and common‐midpoint gathers). We show that the results of applying the constrained eigenvector filter to the entire cross‐well data set are superior to both the spatial and standard eigenvector filter results.
Quantitative estimate of VTI parameters from AVA responses
Authors: Plessix René‐Edouard , Bork Jonathan
Published: March 2003

The influence of the vertical transverse isotropy (VTI) on amplitude versus angle (AVA) responses is first studied on the linearized formula of the PP‐reflection coefficient. Up to medium angles of incidence, as in the isotropic case, only two quantities can be retrieved, the second with less accuracy than the first. These quantities are the P‐impedance and the S‐impedance multiplied by 1− δ/2, where δ is one of the two anisotropic parameters introduced by Thomsen. To extend these results to the exact formulae, the AVA analysis is then formulated as an inverse problem and a least‐squares cost function is defined. A study of the eigenvalues and eigenvectors of the Hessian of the least‐squares cost function confirms these results. Though these results are dependent on the amount of data and on the maximum angle of incidence available, they are appropriate for small and medium angles of incidence. Thanks to this inverse formulation, this work can be extended to the case of multicomponent AVA responses. The addition of PS‐reflection data further constrains the problem, but the S‐impedance and δ are still coupled. However, the addition of SS‐reflection data gives an estimation of both P‐ and S‐impedances and δ. The last two parameters, the density and the second anisotropic parameter ɛ, remain difficult to determine, at least with small‐to‐medium angular apertures.
GPR study of pore water content and salinity in sand
Authors: Al Hagrey  , Müller
Published: March 2003

High‐resolution studies of hydrological problems of the near‐surface zone can be better accomplished by applying ground‐probing radar (GPR) and geoelectrical techniques. We report on GPR measurements (500 and 900 MHz antennae) which were carried out on a sorted, clean sand, both in the laboratory and at outdoor experimental sites. The outdoor sites include a full‐scale model measuring 5 × 3 × 2.4 m3and a salinity site measuring 7.0 × 1.0 × 0.9 m3with three buried sand bodies saturated with water of various salinities. Our studies investigate the capability of GPR to determine the pore water content and to estimate the salinity. These parameters are important for quantifying and evaluating the water quality of vadose zones and aquifers. The radar technique is increasingly applied in quantifying soil moisture but is still rarely used in studying the problems of water salinity and quality.

The reflection coefficient at interfaces is obtained from the amplitude spectrum in the frequency and time domains and is confirmed by 1D wavelet modelling. In addition, the GPR velocity to a target at a known depth is determined using techniques of two‐way traveltime, CMP semblance analysis and fitting an asymptotic diffraction curve.

The results demonstrate that the reflection coefficient increases with increasing salinity of the moisture. These results may open up a new approach for applications in environmental problems and groundwater prospecting, e.g. mapping and monitoring of contamination and evaluating of aquifer salinity, especially in coastal areas with a time‐varying fresh‐water lens. In addition, the relationship between GPR velocity and water content is established for the sand. Using this relationship, a subsurface velocity distribution for a full‐scale model of this sand is deduced and applied for migrated radargrams. Well‐focused diffractions separate single small targets (diameter of 2–3 cm, at a depth of 20–180 cm and a vertical interval of 20 cm). The results underscore the high potential of GPR for determining moisture content and its variation, flow processes and water quality, and even very small bodies inside the sand or soil.
A parallel laboratory for simulation and visualization of seismic wavefields
Authors: Sabadell F. Javier , Serón Francisco J. , Badal José
Published: March 2003

The use of parallel computers makes simulation of elastic waves feasible throughout large structures by means of recent advances in domain decomposition methods. We introduce a competitive parallel algorithm for the propagation of elastic waves in complex heterogeneous media using finite‐element discretization. This parallel method, called the multiblock method, performs more efficiently than classical domain decomposition techniques based on substructuration, such as the Schur complement technique. It reduces considerably the amount of communication amongst processors because the interface problem between subdomains is solved by taking advantage of Huygens' principle for wave propagation. We provide some numerical examples and detailed studies on the efficiency and performance of the algorithm, proving that it is competitive and less costly, from the computational viewpoint, than algorithms based on the Schur technique.
Estimation of an optimal mixed‐phase inverse filter
Authors: Ursin Bjorn , Porsani Milton J.
Published: March 2003

Inverse filtering is applied to seismic data to remove the effect of the wavelet and to obtain an estimate of the reflectivity series. In many cases the wavelet is not known, and only an estimate of its autocorrelation function (ACF) can be computed. Solving the Yule‐Walker equations gives the inverse filter which corresponds to a minimum‐delay wavelet. When the wavelet is mixed delay, this inverse filter produces a poor result.

By solving the extended Yule‐Walker equations with the ACF of lag α on the main diagonal of the filter equations, it is possible to decompose the inverse filter into a finite‐length filter convolved with an infinite‐length filter. In a previous paper we proposed a mixed‐delay inverse filter where the finite‐length filter is maximum delay and the infinite‐length filter is minimum delay.

Here, we refine this technique by analysing the roots of the Z‐transform polynomial of the finite‐length filter. By varying the number of roots which are placed inside the unit circle of the mixed‐delay inverse filter, at most 2α different filters are obtained. Applying each filter to a small data set (say a CMP gather), we choose the optimal filter to be the one for which the output has the largest Lp‐norm, with p=5. This is done for increasing values of α to obtain a final optimal filter. From this optimal filter it is easy to construct the inverse wavelet which may be used as an estimate of the seismic wavelet.

The new procedure has been applied to a synthetic wavelet and to an airgun wavelet to test its performance, and also to verify that the reconstructed wavelet is close to the original wavelet. The algorithm has also been applied to prestack marine seismic data, resulting in an improved stacked section compared with the one obtained by using a minimum‐delay filter.
Large‐offset approximation to seismic reflection traveltimes
Authors: Causse Emmanuel , Haugen Geir Ultveit , Rommel Björn Eino
Published: March 2003

Conventional approximations of reflection traveltimes assume a small offset‐to‐depth ratio, and their accuracy decreases with increasing offset‐to‐depth ratio. Hence, they are not suitable for velocity analysis and stacking of long‐offset reflection seismic data. Assuming that the offset is large, rather than small, we present a new traveltime approximation which is exact at infinite offset and has a decreasing accuracy with decreasing offset‐to‐depth ratio. This approximation has the form of a series containing powers of the offset from 1 to −∞. It is particularly accurate in the presence of a thin high‐velocity layer above the reflector, i.e. in a situation where the accuracy of the Taner and Koehler series is poor. This new series can be used to gain insight into the velocity information contained in reflection traveltimes at large offsets, and possibly to improve velocity analysis and stacking of long‐offset reflection seismic data.
Salt‐water intrusion mapping by geoelectrical imaging surveys
Authors: Abdul Nassir S.S. , Loke M.H. , Lee C.Y. , Nawawi M.N.M.
Published: March 2003

The geoelectrical imaging method is a tool for mapping the intrusion boundary between fresh water and saline water due to its inherent capability to delineate the lateral changes in pore‐water salinity. A new field survey technique that can be used for environmental and geotechnical investigations has been developed. This study evaluates the multiscale survey technique as a tool employed in electrical imaging to detect the salt‐water intrusion boundary in Yan, State of Kedah, northwest Malaysia. The technique was incorporated into these surveys, and it has proved to be a robust method for accurately mapping the fresh‐water/saline‐water boundary. The resulting resistivity sections from these surveys were consistent with both the available geological and borehole information from the area and the previous resistivity surveys conducted by the Geological Survey of Malaysia at those sites.
Detection and identification of north–south trending magnetic structures near the magnetic equator
Authors: Beard Les P.
Published: March 2003

Long, structurally undeformed north–south trending structures show no magnetic anomaly at the magnetic equator, except at the north and south truncations of the structure. However, folding, faulting, differential erosion or other structural deformation can produce detectable magnetic anomalies in a generally north–south trending equatorial structure. Spatial variation in magnetic susceptibility or remanent magnetization can also produce anomalies in equatorial north–south structures. These anomaly patterns are often more complicated than patterns produced by similar structures at high latitudes, but interpretational insight can be gained through numerical modelling of common structures. Reduction‐to‐pole and analytic signal filters can aid in interpretation of equatorial anomalies, but these must be applied carefully because of instabilities deriving from filter design and noise amplification.
A brief study of applications of the generalized reciprocal method and of some limitations of the method
Authors: Sjögren Bengt
Published: March 2003

An analysis of the generalized reciprocal method (GRM), developed by Palmer for the interpretation of seismic refraction investigations, has been carried out. The aim of the present study is to evaluate the usefulness of the method for geotechnical investigations in connection with engineering projects. Practical application of the GRM is the main object of this study rather than the theoretical/mathematical aspects of the method.

The studies are partly based on the models and field examples presented by Palmer. For comparison, some other refraction interpretation methods and techniques have been employed, namely the ABC method, the ABEM correction method, the mean‐minus‐T method and Hales' method. The comparisons showed that the results, i.e. the depths and velocities determined by Palmer, are partly incorrect due to some errors and misinterpretations when analysing the data from field examples.

Due to the limitations of the GRM, some of which are mentioned here, stated by Palmer in his various publications, and other shortcomings of the method (e.g. the erasing of valuable information), the GRM must be regarded as being of limited use for detailed and accurate interpretations of refraction seismics for engineering purposes.
Seismic data compression by an adaptive local cosine/sine transform and its effects on migration
Authors: Wang Yongzhong , Wu Ru‐Shan
Published: March 2003

The local cosine/sine basis is a localized version of the cosine/sine basis with a window function which can have arbitrary smoothness. It has orthogonality and good time and frequency localization properties. The adaptive local cosine/sine basis is a best‐basis obtained from an overabundant library of cosine/sine packets based on a cost‐functional. We propose a 2D semi‐adaptive (time‐adaptive or space‐adaptive) local cosine transform (referred to as a 2D semi‐ALCT) and apply it to the SEG–EAEG salt model synthetic data set for compression. From the numerical results, we see that most of the important features of the data set can be well preserved even in the high compression ratio (CR=40:1) case. Using reconstructed data from the highly compressed ALCT coefficients (CR=40:1) for migration, we can still obtain a high‐quality image including subsalt structures. Furthermore, we find that the window partition, generated by the 2D semi‐ALCT, is well adapted to the characteristics of the seismic data set, and the compression capability of the 2D semi‐ALCT is greater than that of the 2D uniform local cosine transform (2D ULCT). We find also that a (32, 32) or (32, 64) minimum (time, space) window size can generate the best compression results for the SEG–EAEG salt data set.
Sensitivity study using a genetic algorithm: inversion of amplitude variations with slowness
Authors: Ji Ying , Singh Satish C. , Hornby Brian E.
Published: March 2003

A sensitivity study of elastic parameters in amplitude‐variation‐with‐slowness (AVS) for small‐ and large‐offset seismic data is presented. In order to handle the non‐linearity associated with waveform or amplitude beyond the critical slowness, an inversion algorithm based on Bayes' theory is used. A genetic algorithm was used to obtain the a posteriori probability density (PPD) function. The sensitivity analysis is performed on synthetic data containing P‐wave as well as converted S‐wave reflections. Four different two‐layer models, which represent the typical range of AVS responses associated with the gas‐sands normally encountered in exploration, were used to examine how well the elastic parameters can be inverted for different parametrizations by comparing the PPD functions. The sensitivity study results suggest that including wide‐angle data in the inversion can greatly enhance the quality of inversion. The converted S‐wave reflections can provide valuable extra information that can be used to extract elastic parameters. The results with noisy data demonstrate that the contrast of density and three velocity ratios can be estimated robustly with wide‐angle reflection data.
Electromagnetic profiling interpretation across vertical faults and dikes
Authors: Sampaio Edson E.S. , Dias Carlos A.
Published: March 2003

When a vertical fault or dike scatters a normally incident TE‐mode plane wave, the horizontal components of the electric and the magnetic fields vary along the direction perpendicular to the strike. This scattering is also responsible for the formation of a vertical component of the magnetic field, which also varies along the direction perpendicular to the strike. Analysis of the lateral variations of the field components permits the identification of the type of geological structure, either fault or dike, as well as an estimate of the position of the geological contacts and the electrical conductivity of each medium. Previous exact analytical solutions have shown that two Fourier cosine integrals can express each field component. A series of functions specified for each model represent the kernel of each integral. From the field components obtained from the first non‐zero term of each series, we calculated the following functions: the dip angle and the ellipticity of the vertical polarization ellipse in a plane perpendicular to the strike of the structure, and the azimuth and the ellipticity of the horizontal ellipse. We established master‐curves of these functions for the interpretation of vertical faults and dikes for the polarization ellipsoid, for instance VLF or audio‐frequency methods. This representation has as variable the induction number , and as parameters σ2/σ1 and

, where a denotes the half‐thickness of the dike. The interpretation procedure using curve fitting is possible because the induction number is represented on a logarithmic scale. This procedure represents an important step before automatic interpretation is carried out. Two case histories using field data illustrate the effectiveness of the procedure and the type of quantitative interpretation obtained from it.
Preliminary laboratory investigations into the attenuation of compressional and shear waves on near‐surface marine sediments
Authors: Ayres Arthur , Theilen Friedrich
Published: March 2003

The attenuation of compressional and shear waves (Qp and Qs) has been studied by several authors but most of these investigations were performed on deep buried reservoir sandstones in order to distinguish between gas and condensate reservoirs and water‐saturated sandstones. We present a preliminary investigation into the use of seismic wave attenuation as a measure of the geotechnical parameters of the near‐surface marine sediments, a little‐studied geological setting. A 6.9 m‐long gravity core was taken from the continental slope of the Barents Sea at a water depth of 2227 m. The core was primarily composed of brown to olive‐grey clayey mud, having a high content of foraminifers and being locally bioturbated. The values of Qp and Qs were determined using the rise‐time method at 19 and 18 different points of the core, respectively, and they were correlated with geotechnical parameters such as wet bulk density, porosity, water content, shear strength and C/P ratio (the ratio of shear strength to overburden pressure). The calculated correlation coefficients for all correlations ranged from −0.39 to 0.41, suggesting that the attenuation characteristics of seismic waves could not be used to derive geotechnical parameters of marine sediments. However, with such a small data set it is difficult to determine clearly whether attenuation is primarily a frequency‐dependent parameter and consequently not related to sediment properties, or whether the limited number of data points is the main factor responsible for the low correlation coefficients observed. Moreover, several different methods are available for the computation of the quality factor Q, and the rise‐time method may not be the most appropriate means of determining the attenuation on near‐surface marine sediments.
Fast repeat‐modelling of time‐lapse seismograms
Authors: Kirchner Andreas , Shapiro Serge A.
Published: March 2003

In order to plan surveys for seismic time‐lapse studies, seismograms are usually simulated for a set of earth models corresponding to different stages of the oil production process. This can be expensive because, for reasons of accuracy, finite‐difference (FD) modelling is very often applied.We present the Born repeat‐modelling technique (BRM), which is a combination of FD modelling and perturbation theory. Production effects are considered as small perturbations of the earth model, and the Born approximation is used to compute the change in the wavefield due to production‐induced modifications to the reservoir properties. This is very efficient in the situation described above.We give a detailed description of the proposed modelling scheme and discuss its applicability. The theoretical foundations of BRM are presented for onshore seismic experiments, and an extension to the case of marine (pressure) seismograms is derived. In addition, the performance of BRM is demonstrated with several numerical examples.
Limiting apparent‐resistivity values for dipping‐bed earth models
Authors: Hunt Paul , Powell Nigel , Watson Kathryn A.
Published: March 2003

Consideration is given to some special features of normalized apparent‐resistivity (NAR) curves, resulting from the deployment of Wenner electrode arrays on the surface above dipping earth structures. Limiting values of the potential are derived when a direct‐current source is located at points on the surface above a simple two‐region dipping‐bed earth model and their influence on corresponding NAR curve characteristics is investigated. Particular attention is given to the exploitation of such features to provide a new and direct approach to model parameter estimation, either as an alternative to traditional curve‐matching techniques or as a source of supporting information when other earth model characterization methods have been employed. Throughout, the emphasis is on the single‐dipping‐bed model, but application to more complex structures is discussed, including examples of two dipping beds, dipping dikes and more general tilted unconformities.
Calibrate yourself to your data! A vital first step in seismic interpretation
Authors: Brown Alistair R.
Published: March 2003

Stratigraphic, reservoir and fluid interpretation demands a thorough understanding of the seismic‐to‐well tie. Data phase, polarity and tuning effects significantly influence this tie and are often poorly understood. By relating seismic character to known subsurface geology, the interpreter should gain better understanding and be able to calibrate himself to his data. This is an important preliminary stage in any seismic interpretation beyond structure.
From the Hagedoorn imaging technique to Kirchhoff migration and inversion
Authors: Bleistein Norman , Gray Samuel H.
Published: March 2003

The seminal 1954 paper by J.G. Hagedoorn introduced a heuristic for seismic reflector imaging. That heuristic was a construction technique – a ‘string construction’ or ‘ruler and compass’ method – for finding reflectors as an envelope of equal traveltime curves defined by events on a seismic trace. Later, Kirchhoff migration was developed. This method is based on an integral representation of the solution of the wave equation. For decades Kirchhoff migration has been one of the most popular methods for imaging seismic data. Parallel with the development of Kirchhoff wave‐equation migration has been that of Kirchhoff inversion, which has as its objectives both structural imaging and the recovery of angle‐dependent reflection coefficients. The relationship between Kirchhoff migration/inversion and Hagedoorn's constructive technique has only recently been explored. This paper addresses this relationship, presenting the mathematical structure that the Kirchhoff approach adds to Hagedoorn's constructive method and showing the relationship between the two.