bluuebunny/crossref_metadata_2025 huggingface dataset:
An adaptive finite‐difference method for traveltimes and amplitudes
Authors: Qian Jianliang , Symes William W.
Published: October 2002

The point‐source traveltime field has an upwind singularity at the source point. Consequently, all formally high‐order, finite‐difference eikonal solvers exhibit first‐order convergence and relatively large errors. Adaptive upwind finite‐difference methods based on high‐order Weighted Essentially NonOscillatory (WENO) Runge‐Kutta difference schemes for the paraxial eikonal equation overcome this difficulty. The method controls error by automatic grid refinement and coarsening based on a posteriori error estimation. It achieves prescribed accuracy at a far lower cost than does the fixed‐grid method. Moreover, the achieved high accuracy of traveltimes yields reliable estimates of auxiliary quantities such as take‐off angles and geometric spreading factors.
Reflection and transmission responses of a layered isotropic viscoelastic medium
Authors: Ursin Bjørn , Stovas Alexey
Published: October 2002

Transmission effects in the overburden are important for amplitude versus offset (AVO) studies and for true‐amplitude imaging of seismic data. Thin layers produce transmission effects which depend on frequency and slowness. We consider an inhomogeneous viscoelastic layered isotropic medium where the parameters depend on depth only. This takes into account both the effects of intrinsic attenuation and the effects of the layering (including changes in attenuation). The seismic wavefield is decomposed into up‐ and downgoing waves scaled with respect to the vertical energy flux. This gives important symmetry relations for the reflection and transmission responses. For a stack of homogeneous layers, the exact reflection response can be computed in a numerically stable way by a simple layer‐recursive algorithm.

The reflection and transmission coefficients at a plane interface are functions of the complex medium parameters (depending on frequency) and the real horizontal slowness parameter. Approximations for weak contrast and weak attenuation are derived and compared to the exact values in two numerical examples.

We derive first‐order approximations of the PP and SS transmission responses which are direct extensions of the well‐known O'Doherty‐Anstey formula. They consist of a phase shift and attenuation term from direct transmission through the layers and two attenuation terms from backscattered P‐ and S‐waves. The average of these transmission responses may be used for overburden corrections in AVO analysis. The first‐order PP and PS reflection responses have been computed for a stack of very thin layers corresponding to about 2800 m thickness. Because of a lack of data, the intrinsic attenuation was assumed to be constant in the layers. In the seismic frequency band, the intrinsic attenuation dominates the thin‐layer effects. Approximate and exact layer‐recursive modeling of the reflection responses for this layered medium are in good agreement.
Compatibility of high-altitude aeromagnetic and satellite-altitude magnetic anomalies over Canada
Authors: Ravat D. , Whaler K. A. , Pilkington M. , Sabaka T. , Purucker M.
Published: October 2002

Results from equivalent-source distributions derived jointly from high-altitude (average 4 km) aeromagnetic and Magsat-derived (average 400 km) magnetic anomalies over Canada indicate that long-wavelength components (500–2500 km) in these fields are extremely compatible with one another (with a correlation coefficient of 0.95). The jointly estimated anomaly field at the earth's surface can be used as a long-wavelength adjustment surface for regional near-surface magnetic anomaly compilations and in assessing the performance of other downward-continuation techniques. Because near-surface anomalies are not available over all regions of the world, we compare the jointly estimated anomaly field to the results of two different downward-continuation techniques: the evaluation of anomalies at the earth's surface from spherical harmonic coefficients derived from satellite-altitude data and the use of downward-continuation methods based on harmonic splines. Numerical and visual comparisons of these downward- continued fields with the jointly estimated anomaly field from the equivalent-source method indicate they are well correlated and could provide a useful method of deriving long-wavelength leveling surfaces for regional and worldwide magnetic anomaly maps.
A multimodel method for depth estimation from magnetic data
Authors: Thurston Jeffrey B. , Smith Richard S. , Guillon Jean-Claude
Published: October 2002

The local wavenumber and a multimodel wavenumber are complex attributes derived from a complex analytic signal. These quantities have been used to interpret anomalies arising from contacts, thin sheets, and horizontal cylinders. A new multimodel wavenumber can be used for computing depths of 2-D thick dikes and 2-D sloping steps. These two multimodel wavenumbers have been incorporated into a depth-estimation algorithm based on automatic curve matching. This algorithm works on profile data and has three appealing features: (1) the most appropriate of these five models is selected automatically; (2) the automatic curve matching uses a least-squares technique to reject responses that do not conform to the model assumptions; and (3) interference from distant sources can be accounted for as a base-level shift of the multimodel wavenumber curves.

Applying the automatic technique to survey data from the Western Canada sedimentary basin yields four thick dikes between 3400 and 4300 m below sensor. These depths are equivalent to 2.2 and 3.1 km below sea level, which is consistent with the basement depths derived from drillhole information.

Using these solutions as a starting point in an iterative forward modeling exercise, the measured data were explained with a geologically reasonable model.
Estimation of gas hydrate and free gas saturation, concentration, and distribution from seismic data
Authors: Lu Shaoming , McMechan George A.
Published: October 2002

Gas hydrates contain a major untapped source of energy and are of potential economic importance. The theoretical models to estimate gas hydrate saturation from seismic data predict significantly different acoustic/elastic properties of sediments containing gas hydrate; we do not know which to use. Thus, we develop a new approach based on empirical relations. The water‐filled porosity is calibrated (using well‐log data) to acoustic impedance twice: one calibration where gas hydrate is present and the other where free gas is present. The water‐filled porosity is used in a combination of Archie equations (with corresponding parameters for either gas hydrate or free gas) to estimate gas hydrate or free gas saturations.

The method is applied to single‐channel seismic data and well logs from Ocean Drilling Program leg 164 from the Blake Ridge area off the east coast of North America. The gas hydrate above the bottom simulating reflector (BSR) is estimated to occupy ∼3–8% of the pore space (∼2–6% by volume). Free gas is interpreted to be present in three main layers beneath the BSR, with average gas saturations of 11–14%, 7–11%, and 1–5% of the pore space (6–8%, 4–6%, and 1–3% by volume), respectively. The estimated saturations of gas hydrate are very similar to those estimated from vertical seismic profile data and generally agree with those from independent, indirect estimates obtained from resistivity and chloride measurements. The estimated free gas saturations agree with measurements from a pressure core sampler. These results suggest that locally derived empirical relations between porosity and acoustic impedance can provide cost‐effective estimates of the saturation, concentration, and distribution of gas hydrate and free gas away from control wells.
Elastic wave propagation in heterogeneous anisotropic media using the lumped finite‐element method
Authors: Zhang Jianfeng , Verschuur D. J.
Published: October 2002

A numerical technique for wave‐propagation simulation in 2‐D heterogeneous anisotropic structures is presented. The scheme is flexible in incorporating arbitrary surface topography, inner openings, liquid/solid boundaries, and irregular interfaces, and it naturally satisfies the free‐surface conditions of complex geometrical boundaries. The algorithm, based on a discretization mesh of triangles and quadrilaterals, solves the problem using integral equilibrium around each node instead of satisfying elastodynamic differential equations at each node as in the finite‐difference method. This study is an extension of previous work for the elastic‐isotropic case. Besides accounting for anisotropy, a simplified quadrilateral grid cell with low computational cost is introduced. The transversely isotropic medium with a symmetry axis on the horizontal or vertical plane, as typically caused by a system of parallel cracks or fine layers, is discussed in detail. A 2‐D algorithm is presented that can handle the situation where the symmetry axis of the anisotropy does not lie in the 2‐D plane. The proposed scheme is successfully tested against an analytical solution for Lamb's problem with a symmetry axis normal to the surface and agrees well with a numerical solution of the reflectivity method for a plane‐layered model in the isotropic case. Computed radiation patterns show characteristics such as shear‐wave splitting and triplications of quasi‐SV wavefronts, as predicted by the theory. Examples of surface‐wave propagation in an anisotropic half‐space with a semicylindrical pit on the surface and mixed liquid/(anisotropic) solid model with an inclined liquid/solid interface are presented. Moreover, seismograms are modeled for dome‐layered and plane‐layered anisotropic structures.
Discussions on Induced Polarization: Second Discussion
Authors: Wait James R.
Published: October 2002

It appears that the A’s do not agree with my comments. It might help to clarify my position if a more specific example is considered.
Reply by author to discussions by J. Cl. De Bremaecker and Charles E. Corbato
Authors: Nagy D.
Published: October 2002

I thank both Drs. Corbató and De Bremaecker for their references to earlier works in connection with the gravitational attraction of the prism. It may be of some interest, at least from the historical point of view, to give some further references, which were found after my paper went to press.
Discussion
Authors: Woods J. P.
Published: October 2002

We often discuss cooperation between the geologist and the geophysicist. Actually, I think the cooperation is very good; just the same, I believe that good always comes from discussions of this sort. We are in a gambling business. After we have used our best geophysical science and our best geological science, we are forced to fall back on human judgment.
Reply by Author to Dr. James R. Wait
Authors: Roy Amalendu
Published: October 2002

[Formula: see text] was defined by Dr. J. R. Wait for the purpose of studying the detectability of a core when surrounded by a “halo.” From the behavior of [Formula: see text] (and [Formula: see text]) in his Tables 1 and 2, Dr. Wait concludes: “For this particular definition of a shielding factor, there is no enhancement of the response of the core resulting from the presence of the shell.” He could not possibly have arrived at this conclusion unless he had equated [Formula: see text] (and [Formula: see text]) to the response (contribution) of the core (target) alone in presence of the outer shell.
Discussion of review of “Introduction to Geophysics,” B. F. Howell, Jr.
Authors: Krishan Shri
Published: October 2002

In your February 1960 issue, there appeared a review of the book “Introduction to Geophysics” by Dr. B. F. Howell, Jr. I want to point a flaw in the mathematical reasoning of the author. A publication of this and a subsequent explanation by the author will remove a great confusion in the minds of many readers.
Discussion of paper by A. R. Clark entitled “The Determination of the Long Dimension of Conducting Ore Bodies”
Authors: Kunz Bruno
Published: October 2002

When J. N. Hummel published his first apparent resistivity curves some 30 years ago, he used coordinates with a linear scale. A short time later it was found that such master curves are universally usable only when plotted on logarithmic scales. The reason for this is that the shape of the curves does not depend upon the absolute electrode spacing and the absolute resistivity values but only on the relative values. This, naturally, also holds true for the examples shown by A. R. Clark. The curves as shown by him reveal a resistivity ratio of [Formula: see text]. In the same way, the “Distance as a fraction of the Semimajor Axis” is a quotient. Both coordinates should therefore be presented in a logarithmic scale. When so plotted, the characteristic properties of the curves are much more conspciuous and are very different from those when linear scales are used. The remarks made by the author relative to the shape of the curves may have to be revised.
On: “On the Effects of Overburden on EM Anomalies—A Review” by Amalendu Roy (GEOPHYSICS, August 1970, p. 646–659)
Authors: Wait James R.
Published: October 2002

In a grossly inaccurate discussion, Roy (1970) criticizes my analysis of screening factors for the electromagnetic response of a conducting sphere (Wait, 1969). The screening factor [Formula: see text] was clearly defined in my paper as the ratio of two specified quantities.
Reply by Author to Discussion by S. K. Choudhury and R. Amaravadi
Authors: Peters Leo J.
Published: October 2002

I appreciate Dr. Choudhury’s discussion of my paper and would like to make the following remarks: Unfortunately, several errors in numerical values were made in the paper. Dr. Choudhury is correct in stating that the sign of the coefficient for [Formula: see text] in his equation (1), equation (24) in the paper, should be positive instead of negative.
On: “Quasi-static Transient Response of a Conducting Permeable Sphere” by J. R. Wait and K. P. Spies (GEOPHYSICS, October 1969, p. 789–792)
Authors: Hjelt Sven-Erik
Published: October 2002

Wait and Spies have calculated the transient step-function response of a conducting permeable sphere using the harmonic response and integral transformations. The result is given as a series of exponential functions instead of the higher functions used earlier (Wait, 1951). The exponential series solution can be obtained in another way by separating the time and spatial variables.
Reply by author to discussion by Robert P. Meyer and Keith McCamy
Authors: Laster Stanley J.
Published: October 2002

In answer, I think it is sufficient to point out that our paper is not a review or survey paper. In consequence, we have cited only those references which we personally consulted in preparation of the paper.
Reply by author to discussion by L. J. Katz and W. D. Wagner
Authors: Iyer H. M.
Published: October 2002

Nowhere in my paper have I questioned the validity of ground noise surveys as a geothermal exploration tool. My conclusions are specifically for the Mesa geothermal anomaly in Imperial Valley, California. I do believe that geothermal seismic noise exists and can be detected under favorable conditions, as was shown at Yellowstone (Iyer and Hitchcock, 1974). At Long Valley, in spite of “1000 head of cattle nibbling” at my geophones (did Drs. Katz and Wagner get the word from the cow’s mouth, perhaps) we found indications of “high‐velocity” seismic noise associated with the geothermal system in the area (Iyer and Hitchcock, 1976).
Reply to Peter Hubral by the Author
Authors: Michaels Paul
Published: October 2002

Peter Hubral’s extension of the raypath migration calculator program to include a lateral velocity gradient is quite ingenious. In such cases where the vertical and horizontal velocity gradients are constant, the net effect is a simple coordinate rotation. The theoretical raypath remains circular, but is only rotated about its intersection with the datum plane.
Reply to M. J. Kuhn by John R. Berryhill
Authors: Berryhill John R.
Published: October 2002

I wish to clarify the implications of my paper for cases more general than actually considered in the derivation for nonzero offset, and to present a quantitative example in accordance with Mr. Kuhn’s suggestion.
Reply to Discussion by J. R. Hearst and R. C. Carlson
Authors: Hearst J. R. , Carlson R. C.
Published: October 2002

Our equations (3) and (4) are correct. They represent the difference between the attraction of the shell viewed from [Formula: see text], the outer radius of the shell, and [Formula: see text], its inner radius. (The attraction of the shell viewed from [Formula: see text] is zero.) On the other hand, equations (5) and (6) of Fahlquist and Carlson represent the difference in attraction of the entire earth from the same viewpoints and thus, as they say, include a free‐air gradient term. However, their equation (5) would be correct only if the mean density of the earth were equal to that of the shell, and the free‐air gradient obtained by their equation (10) is correct only under these circumstances.
Reply to W. C. Kellogg by H. L. Yarger, R. R. Robertson, and R. L. Wentland
Authors: Yarger Harold L. , Robertson Robert R. , Wentland Robert L.
Published: October 2002

We appreciate Mr. Kellogg’s interest in bringing his previous discussion to our attention (Kellogg, 1966). It is certainly possible that our paper has duplicated, in part or whole, work done by Milton Glicken. Since Mr. Kellogg does not supply a reference for Glicken’s work, we assume it was never published, thus making it of little use to us or anyone else. In fact, we were driven to developing our own method due to the apparent lack of published material on modern approaches to diurnal drift removal from digitally recorded aeromagnetic data.
Reply by the authors to R. L. Grasty and J. M. Carson
Authors: Crossley D. J. , Reid A. B.
Published: October 2002

The main purpose of our original paper was to establish a procedure for comparing the performances of channels and windows in radiometric interpretation, especially using multichannel spectrometer data. As a result of the application of the method to data made available by the South African Geological Survey (SAGS), we were led to speculate that, among other things, the cosmic background component may be more variable in time than had previously been assumed.
Clarification of the discussion on: “The deconvolution of phase‐shifted wavelets”
Authors: Bickel Samuel H.
Published: October 2002

The only assumption made in deriving equation (6) is that the inverse v⁁(t) is complex. Complex does not imply analytic. Clearly, we remove a degree of freedom if we restrict the real and imaginary parts of the inverse to be related by a Hilbert transform. No deconvolution algorithm that leads to such a restriction can produce results that could not be obtained by simply inverting the real wavelet.
Reply by authors to discussion by Amalendu Gupta
Authors: Choudhury S. K. , Datta A. N.
Published: October 2002

We thank Gupta for his interest in our paper. In his rather lengthy discussion, Gupta has questioned the validity of the following: (a) The distribution and thickness of Rajmahal Trap, (b) presence of Gondwanas below the Rajmahal Trap, (c) density value of the Gondwanas used in computation, and (d) regional trend. Furthermore, he has commented about the omission in providing the theoretical subtrap gravity values.
Reply by the authors to Richard D. Rechtien
Authors: Kuo John T. , Dai Ting‐fan
Published: October 2002

It may not be completely obvious that in our Kirchhoff elastic wave‐migration formulation for the case of noncoincident source and receiver the traction vector [Formula: see text] and the displacement vector field [Formula: see text] on the boundary of a region in our equation (1) are indeed the total traction vector and the total displacement vector field. Therefore, the boundary condition [Formula: see text] on the free surface specified by S′ is correctly imposed.
Reply by the author to A. T. Herring
Authors: Hammer Sigmund
Published: October 2002

The criticisms in Herring’s Discussion have been largely covered in my recent reply to Steenland (Hammer, 1984), but some points of fact and discussion warrant additional comment.
Reply by J. Morlet to J. D. Laski
Authors: Morlet J.
Published: October 2002

Point (a): I agree with this remark. Here for 3‐D propagation medium, one must use the bulk modulus K rather than Young’s modulus E, which must be strictly restricted to the case of a 1‐D propagation medium (i.e., a rod or a string).
Reply by authors to J. A. Hudson and S. Crampin
Authors: Schoenberg M. , Muir F.
Published: October 2002

We are glad that some people are reading our paper critically, and welcome their comments. This is particularly important since we are aware of many groups who are using the calculus to get a handle on what kinds of effects to expect when certain elements are combined in the model of a rock mass. In addition, there is an unexpected application to modeling irregular boundaries (Muir et al., 1991) and an extension to modeling stiffeners in layered permeable systems (Schoenberg, 1991). Hudson and Crampin touch on one aspect of our paper, and we offer the following comments.
Response by J. Roy to the reply by the authors
Authors: Roy Jean
Published: October 2002

On platform attitude measurement: The integration of platform attitude measurements with existing geophysical platforms was done regularly in all airborne geophysical platforms equipped with the Geonics EM‐18 VLF system where roll and pitch compensation was done with a gyroscope‐derived signal (Geonics 1982 Catalog, EM‐18 data sheet). Also, the integration of full platform attitude measurement (pitch, yaw, and roll) with a geophysical platform was done as an example by SGC. Their platform carried, among others, a three‐component magnetometer (SGC TRIX‐03 data sheet) and a RAMA‐style VLF system (Granar, 1981). Pendulum‐based systems have also been used in both fixed wing aircrafts and helicopter towed birds. Current developments in platform attitude measurements include multiple GPS antennas and receivers with measuring tolerances lower than one degree (among others, NASA, 1992).
Reply by the authors to J. G. Saha, C. H. Mehta, and S. Benjamin
Authors: Eisner Elmer , Hampson Gary
Published: October 2002

We appreciate the interest that Saha et al. have shown in our paper and thank them for their prompt response to our request for specific details of their numerical experiments. Our interpretation of these details is given in Appendix A.
Reply by the author to K. Duckworth
Authors: Guptasarma D.
Published: October 2002

Duckworth is evidently in agreement with some of the conclusions of my paper. But since he does not indicate specifically which conclusions he considers invalid, but questions the validity of my conclusions in general, I can only clarify the doubts specifically mentioned by him.
Reply by the authors to Robert S. Pawlowski
Authors: Blakely Richard J. , Simpson Robert W.
Published: October 2002

We appreciate Robert S. Pawlowski’s interest in our paper, and we agree that his equation for [Formula: see text] provides values identical to ours, regardless of the value of d. Given our expressions for a and b, there is an error in our equation for [Formula: see text] which becomes apparent if one considers the units of the various terms in the summation.
Reply by the authors to R. S. Smith
Authors: Flis M. F. , Newman G. A.
Published: October 2002

We appreciate the interest Richard Smith has shown in our paper and welcome the opportunity to respond. The main thrust of Smith’s comments is aimed at our choice of using a dc limit in the Cole‐Cole impedance model. Unlike the high‐frequency limit, the dc limit is not affected by the inductive limit of the conductor and so is by far the most logical choice. Any inherent increase in the TEM response at early time, because of the decrease in resistivity to [Formula: see text], is part of the IP effect and should not be discounted as mathematically spurious.
Reply by the author to C. Lomnitz and J. Adauto de Souza
Authors: Knapp Ralph W.
Published: October 2002

I am pleased to see my work used to confirm the thoughts and observations of another. Lomnitz and Adauto de Souza use my paper to confirm the existence of body waves with velocities less than the velocity of sound in air. Contrary to one of their statements, I consider this to be the normal case rather than the exception. Shallow reflection seismology is perpetually faced with field records that show a direct body‐wave arrival following the arrival of the air‐coupled wave. A particular example is shown by Birkelo et al. (1987), who even applied a stacking velocity less than the velocity of sound in air to process a very shallow reflector. I have measured the time shift from reflectors recorded by vertically separated geophones in soils and determined direct propagation velocities as low as 100 m/s.
Reply by authors to discussion by Ellis Strick
Authors: White J. E. , Walsh D. J.
Published: October 2002

A short quotation from the paper under discussion may help provide the background for this rebuttal: “The intended message of this paper is quite simple: Attenuation very nearly proportional to frequency over a wide frequency range does not demand substantial velocity variation within this frequency band and does not require any unusual velocity variation at low frequencies. The approach is to present one counter‐example to the published allegations that such velocity variation is essential, in view of casuality and mathematical considerations.” The counter‐example, a lumped‐element model, is full and complete and the reader is invited to refer to the paper. The authors did not propose this model as the ultimate description of seismic wave propagation in rocks. In fact, the paper contained this encouragement for further research.
Reply by the author to R. Ignetik
Authors: Raiche Art P.
Published: October 2002

The failure of Ignetik to recognize the logic underlying my approach to polygonal‐loop modeling demonstrates a need to present some points more clearly. The starting point was that I wanted to represent the transmitter as an array of vertical magnetic dipoles rather than horizontal linear dipoles. The reason for this was to minimize the computation needed for downhole receivers and multiple transmitter loops. The layered‐earth Green’s tensor elements for horizontal linear dipoles for a general “receiver” point are very complicated for the N‐layer case. Those for the vertical dipole are very simple and require much less computation.
Reply by the author to G. D. Garland.
Authors: Sissons B. A.
Published: October 2002

Although the Tokaanu experiment does contradict the proposal that the gravitational constant G increases with scale, the result is not significant. The standard error in the least‐squares adjustment is at least 1 percent, which exceeds the predicted variation in G. The uncertainty in mean density is nearer 5 percent. Gravity data with sufficient precision to test for a scale effect in G are obtainable; the main problem appears to be the uncertainty in density determinations. Stacey et al (1981) made a least‐squares determination of G using gravity and density measurements from a mine. However, the pattern of residuals obtained indicated the presence of anomalous masses not adequately accounted for by their density averaging. The method I have used which models the spatial variation in density offers the possibility of obtaining a least‐squares fit for G with a satisfactory residual distribution. However, the problem of the effect on bulk density of joints and voids not sampled in hand specimens remains.
Reply by the author to Dr. G. R. Olhoeft
Authors: Kayal J. R. , Christoffel D. A.
Published: October 2002

We thank Dr. Olhoeft for his criticism of our short note and reply as follows. Checks were made for possible local “convection cells” in regions of high thermal gradient within the boreholes, using the criteria of Beck (1976).
Reply by the author to A. Apparao
Authors: Guptasarma D.
Published: October 2002

Apparao’s discussion of my paper contains five sections. The following reply refers to these sections in the same order.
Reply by the authors to Nobes, Schneider, and Hodgson
Authors: Han D. , Nur A. , Morgan D.
Published: October 2002

We agree with Nobes et al. that our own bias, like theirs, is that “If at all possible equations relating one physical property to another should be based on some physical model,” but in addition we believe also that such a model must be correct, or at least physically sound. It is on the issue of the soundness of the traveltime average model that we fundamentally disagree with Nobes et al.
Reply by the author to M. Schoenberger and F. K. Levin
Authors: Jacobson R. S.
Published: October 2002

Dr. Schoenberger and Dr. Levin correctly point out significant differences between their original figure demonstrating compensated transmission loss (Schoenberger and Levin, 1978, Figure 7) and my adapted version of their figure (Figure 2).
Reply by the author to B. Ursin
Authors: Levin Franklyn K.
Published: October 2002

I thank Dr. Ursin for providing a firm foundation to what was essentially a numerical study. I find Dr. Ursin’s comments on interface waves particularly interesting and appreciate his remarks on what happens when the denominator of the reflection coefficient expression becomes zero.
Reply to B. Zhou by the author
Authors: Compani‐Taurizi B.
Published: October 2002

Mr. Zhou’s interest in the article is appreciated. I do not get reflections from the edges of the model in the nonabsorptive case when the model fills the entire computational space. When absorptive potentials are used, reflections occur at the edges. However, then the useful modeling space is not the entire computational space, but the computational space minus the absorptive region. Another case of interest occurs when the model is irregular in shape and is made to be a subset of the computational space with the infinite background surrounding it. In this case the contrast in velocity at the model edges produces reflections. If these reflections are to be eliminated in order to focus on the response of a particular target, then an absorptive potential may be used to simultaneously eliminate wraparound, reflections due to velocity contrast, and reflections due to absorption contrast.
Reply by the authors to S. N. Domenico
Authors: Larner Kenneth L. , Beasley Craig J. , Lynn Walter S.
Published: October 2002

Many issues must be taken into account in attempts to image steep reflectors, such as salt‐dome flanks, with full accuracy. Dr. Domenico has correctly pointed out that an important issue is the faithful preservation of steep reflections by the stacking process, and we thank him for bringing to the reader’s attention the outstanding paper of May and Covey. (Although our paper was not intended to be a discussion of all techniques for imaging salt domes, we commend the May and Covey paper to readers for its insights and practical demonstration of important issues in imaging of salt‐dome flanks.)
Reply by the author to M. Schoenberger
Authors: Ziolkowski A. M.
Published: October 2002

I thank Michael Schoenberger for his comments. At issue are my remarks on the extraction of a wavelet from stacked data using the well‐log based reflectivity.
Reply by the authors to V. J. Lunardini
Authors: Larson Timothy H. , Hsui Albert T.
Published: October 2002

Our analysis was orginally designed for groundwater investigations in which heat capacities of different soil formations are practically identical (Hillel, 1980). In our generalization, we inadvertently neglected to relax this restriction. We thank V. J. Lunardini for pointing out this small oversight. We agree that the interface boundary condition involves thermal conductivity (K) and not thermal diffusivity (κ). Our equation (A‐20) should read [Formula: see text].
Reply by the authors to David W. Eaton
Authors: Vernik Lev , Nur Amos
Published: October 2002

In the business of laboratory anisotropy measurements in rocks with hexagonal symmetry, an experimentalist faces two major sources of error when estimating the δ parameter even after the core homogeneity and sample orientation with respect to the symmetry axis have been ensured. The first source is the accuracy of a [Formula: see text] (45 degrees) measurement (about 1 percent) which is dramatically magnified when propagating through equations (1) and (2) in Vernik and Nur (1992; see also Thomsen, 1986). The second source, which is superposed on the first one, is a certain degree of uncertainty with the plane wave assumption and, respectively, treating the first break velocity at 45 degrees to the symmetry axis as a phase rather than a group velocity.
Reply by the authors to E. Lichman
Authors: Reed Michael J. , Nguyen Hung V. , Chambers Ronald E.
Published: October 2002

We would like to thank Eugene Lichman for his careful reading of our short note “Computing the Fourier Transform in Geophysics with the Transform Decomposition DFT.” As he correctly states, there is indeed an error in equation (2).
Reply by the authors to Steve Webster
Authors: Cooper Nick , Swift Roland
Published: October 2002

The authors agree with Steve Webster’s comments. The sentence he quotes refers specifically to Cyprus‐type deposits in the Cypriot environment and could be reworded, “it is unlikely that a Cypriot Cyprus‐type deposit could be detected using TEM alone.”
Localization of maximum‐depth gravity anomaly sources by a distribution of equivalent point masses
Authors: Mauriello Paolo , Patella Domenico
Published: October 2002

A method is proposed for localizing the maximum depth sources of a gravity anomaly data set collected on a generally uneven, free surface topography. First, the Newtonian‐type integral defining the Bouguer anomaly function is solved as a sum of elementary contributions from pointlike mass contrast (Δ‐mass) elements. Using this solution, the power associated with the Bouguer effect is derived as a sum of crosscorrelation integrals between the Bouguer anomaly data function and a scanner function expressing the gravity effect from a pointlike Δ‐mass element. Finally, applying Schwarz’s inequality to a single crosscorrelation power term, a Δ‐mass occurrence function is introduced as a suitable tool for localizing the maximum‐depth sources (MDS) of a given gravity anomaly field. The MDS localization procedure consists of scanning the half‐space below the survey area by a unit strength Δ‐mass element and calculating the Δ‐mass occurrence function at the nodes of a 3‐D regular grid. The grid values exceeding in modulus a prefixed threshold can be contoured to single out the zones underground where the Δ‐mass occurrence function shows the highest values. These zones are interpreted as the equivalent MDS pattern for the observed gravity field. Synthetic examples demonstrate that the MDS localization approach is a powerful tool especially suited for analyzing unconstrained gravity data. In the case of an isometric source body, we show that the maximum depth of the equivalent point mass virtually coincides with the position of the actual source center. In the case where the source is not isometric, besides giving the maximum depth of the equivalent point mass, the method also allows obtaining useful information on the upper limit for the source depth. An application to a real case in the field of volcanology (Mt. Etna volcano, Sicily, Italy) is finally presented and discussed.
Phase correction in separatingP‐ andS‐waves in elastic data
Authors: Sun Robert , Chow Jinder , Chen Kuang‐Jung
Published: October 2002

Two‐dimensional elastic data containing reflected P‐waves and converted S‐wave generated by a P‐source may be separated using dilatation and rotation calculation (Sun, 1999). The algorithm is a combination of elastic full wavefield extrapolation (Sun and McMechan, 1986; Chang and McMechan, 1987, 1994) and wave‐type separation using dilatation (divergence) and rotation (curl) calculations (Dellinger and Etgen, 1990). It includes (1) downward extrapolating the (multicomponent) elastic data in an elastic velocity model using the elastic wave equation, (2) calculating the dilatation to represent pure P‐waves and calculating the rotation to represent pure S‐waves at some depth, and (3) upward extrapolating the dilatation in a P‐velocity model and upward extrapolating the rotation in an S‐velocity model, using the acoustic wave equation for each.
Estimation of pulse shaping for well logs
Authors: Sølna K.
Published: October 2002

A wavelet propagating in a finely layered lossless medium is subject to apparent attenuation that changes its shape. Can a sonic log be used to characterize this change? I show that numerical simulations with the well‐log as medium give an apparent attenuation or diffusion of the pulse that is very different from the attenuation in the real medium. This is due to the smoothing effect of the well‐log tool. Based on a version of the O’Doherty‐Anstey approximation, I derive an expression that reveals the role of the tool. Using a sonic log, I verify the theory and show how tool effects can be mitigated by deconvolution. I also propose a two‐scale stochastic model for the sonic log and a procedure for estimation of its parameters. One application of sonic logs is to quantify apparent attenuation and, in this context, my results are important.
Reducing source‐generated noise in shallow seismic data using linear and hyperbolic τ‐ptransformations
Authors: Spitzer Roman , Nitsche Frank O. , Green Alan G.
Published: October 2002

High‐resolution seismic reflection data recorded at many locations on the earth are plagued by the overwhelming effects of direct, refracted, guided, and surface waves. These different components of source‐generated noise may completely mask reflections at traveltimes <∼50–100 ms. Conventional processing methods that include the time‐consuming application of mute functions may lead to the misprocessing of source‐generated noise (especially guided waves) as reflected events and/or the unintentional removal of important shallow reflections. We introduce a combined linear and hyperbolic τ‐p processing scheme that results in the effective separation of reflections from source‐generated noise. After applying linear moveout terms that adjust the direct, refracted, and guided arrivals to appear horizontal to subhorizontal, the reduced traveltime shot gathers are transformed into the linear τ‐p domain. It is then straightforward to design a single τ‐p filter that eliminates most of the source‐generated noise throughout the entire data set. Following inverse linear τ‐p transformation and removal of the linear moveout terms, the filtered shot gathers contain reflections and residual elements of the source‐generated noise. Because summing along hyperbolas favors reflections, transforming the filtered shot gathers into the hyperbolic τ‐p domain leads to significant enhancements in the S/N ratio. A simple rescaling of data values in the hyperbolic τ‐p domain, which results in the loss of true amplitude information, increases further the relative strength of the reflected signals. Finally, inverse hyperbolic transformation yields shot gathers dominated by reflections. In tests of the combined τ‐p processing scheme on a synthetic shot gather and on a complete shallow seismic reflection data set recorded in northern Switzerland, significant improvements in the quality of reflections in the prestacked data and on a fully processed section are readily apparent. According to the results of these tests, the new scheme works well for reflections originating from flat and dipping horizons.
Seismic models of a mixed carbonate‐siliciclastic shelf margin: Permian upper San Andres Formation, Last Chance Canyon, New Mexico
Authors: Kenter J. A. M. , Bracco Gartner G. L. , Schlager W.
Published: October 2002

Seismic models based on randomly distributed samples from the Permian upper San Andres Formation (Last Chance Canyon, New Mexico) verify that the most prominent seismic reflections are related to stratal geometry. However, at least some reflections arise from lateral facies transitions that are commonly associated with highly prograding mixed carbonate‐siliciclastic sediments. Understanding seismic reflections and reflection terminations in sedimentary rocks requires simulation of at least 2‐D cross‐sections of the impedance distribution. To investigate the cause of reflections in strongly prograding mixed carbonate‐siliciclastic shelf margins, acoustic velocity and bulk density were measured on more than 60 plugs that spatially cover one higher order genetic sequence. The resulting impedance values were gridded and contoured, and the genetic sequence was repeated to create a cross‐section. Averaging impedance values for each lithofacies zone generated a second impedance cross‐section. Seismic models of both impedance cross‐sections revealed the following observations: (1) reflections associated with the sequence boundaries are subject to amplitude and polarity phase changes and (2) at least one reflection within the high‐order sequences is related to subhorizontal facies changes and is associated with two pseudounconformities. The contoured impedance model is suggested to closer resemble the true impedance function in outcrop and shows subtle vertical shifts and significantly higher impedance contrasts.
Application of Alford rotation to ground-penetrating radar data
Authors: Van Gestel Jean‐Paul , Stoffa Paul L.
Published: October 2002

We investigate the application of Alford rotation to ground‐penetrating radar (GPR) data. By recording the reflected field amplitudes using four different configurations, we extract information about the orientation of buried objects that have angle‐dependent reflectivity. In theory this method can be successfully applied to find the orientation of dipping layers, cylinders, and vertical fractures. Modeling results show angle‐dependent reflections in all three cases; as a result, we can exactly determine the orientation of these targets. Analysis of a field survey at a controlled GPR test site in which reflections were collected from an elongate cylinder buried in a homogeneous soil show good prediction of the angle of orientation of the cylinder and confirm the expected theoretical and modeling results. The Alford rotation method requires accurate data acquisition for effective practical implementation. Improved results will require exact knowledge of the radiation pattern of the GPR antennas under different circumstances.
Common‐angle migration: A strategy for imaging complex media
Authors: Xu Sheng , Chauris Hervé , Lambaré Gilles , Noble Mark
Published: October 2002

Complex velocity models characterized by strong lateral variations are certainly a great motivation, but also a great challenge, for depth imaging. In this context, some unexpected results can occur when using depth imaging algorithms. In general, after a common shot or common offset migration, the resulting depth images are sorted into common‐image gathers (CIG), for further processing such as migration‐based velocity analysis or amplitude‐variation‐with‐offset analysis. In this paper, we show that CIGs calculated by common‐shot or common‐offset migration can be strongly affected by artifacts, even when a correct velocity model is used for the migration. The CIGs are simply not flat, due to unexpected curved events (kinematic artifacts) and strong lateral variations of the amplitude (dynamic artifacts). Kinematic artifacts do not depend on the migration algorithm provided it can take into account lateral variations of the velocity model. This can be observed when migrating the 2‐D Marmousi dataset either with a wave‐equation migration or with a multivalued Kirchhoff migration/inversion. On the contrary, dynamic artifacts are specific to multi‐arrival ray‐based migration/inversion. This approach, which should provide a quantitative estimation of the reflectivity of the model, provides in this context dramatic results. In this paper, we propose an analysis of these artifacts through the study of the ray‐based migration/inversion operator. The artifacts appear when migrating a single‐fold subdata set with multivalued ray fields. They are due to the ambiguous focusing of individual reflected events at different locations in the image. No information is a priori available in the single‐fold data set for selecting the focusing position, while migration of multifold data would provide this information and remove the artifacts by the stack of the CIGs. Analysis of the migration/inversion operator provides a physical condition, the imaging condition, for insuring artifact free CIGs. The specific cases of common‐shot and common‐offset single‐fold gathers are studied. It appears clearly that the imaging condition generally breaks down in complex velocity models for both these configurations. For artifact free CIGs, we propose a novel strategy: compute CIGs versus the diffracting/reflecting angle. Working in the angle domain seems the natural way for unfolding multivalued ray fields, and it can be demonstrated theoretically and practically that common‐angle imaging satisfies the imaging condition in the great majority of cases. Practically, the sorting into angle gathers can not be done a priori over the data set, but is done in the inner depth migration loop. Depth‐migrated images are obtained for each angle range. A canonical example is used for illustrating the theoretical derivations. Finally, an application to the Marmousi model is presented, demonstrating the relevance of the approach.
Seismic imaging beyond depth migration
Authors: Berkhout A. J. , Verschuur D. J.
Published: October 2002

If seismic imaging is formulated in terms of two focusing steps—focusing in emission and focusing in detection (or vice versa)—the output of the first focusing step yields a new type of seismic gather, the common‐focus‐point (CFP) gather, which is available for data analysis and information extraction. One important consequence of this novel option is that the involved focusing operators can be updated without updating the underlying velocity model. Introducing the concept of “dynamic focusing,” it is proposed to verify the validity of focusing operators by comparing the “gather of focus‐point responses” with the “gather of focusing operators.” Compared with velocity‐driven time and depth migration, operator‐driven CFP migration can be considered as the most general approach to seismic imaging: it does not require a velocity model, and it automatically takes into account unknown complex propagation effects such as conversion, anisotropy, and dispersion. In addition, in CFP migration, the second focusing step can be extended to produce both angle‐averaged reflection information and angle‐dependent reflection information. The CFP approach to seismic migration allows new solutions in the situation of complex near‐surface layers, subsalt targets, multicomponent processing, and time lapse analysis.
Novel Targets for Lung Cancer Therapy: Part II
Authors: Dy Grace K. , Adjei Alex A.
Published: October 2002

ABSTRACT: Lung cancer is the second most common form of cancer in the United States, and although it accounts for 15% of all cancers, it is the most lethal, accounting for approximately 28% of cancer deaths. In 2002, it is estimated that 177,000 new cases of lung cancer will be diagnosed in the United States, and an estimated 160,000 men and women will die from the disease. This mortality rate is greater than that attributable to colorectal, breast, and prostate cancer combined. Systemic treatments for lung cancer with standard chemotherapy agents are still relatively ineffective. Agents targeting novel proliferative and survival pathways in lung cancer are needed to improve treatment outcomes.

In recent years, numerous agents inhibiting aberrant processes in tumor cells have undergone clinical evaluation. This review is the second of a two-part series that summarizes pertinent preclinical and clinical information on novel drugs that target critical abnormalities in lung cancer. In this article, agents that were developed to inhibit various aspects of tumor protein trafficking and protein degradation, cell cycle regulation, angiogenesis, and antigenicity are described. Future approaches to treatment are suggested.