bluuebunny/crossref_metadata_2025 huggingface dataset:
On unified dual fields and Einstein deconvolution
Authors: Loewenthal Dan , Robinson Enders A.
Published: October 2002

In many physical phenomena, the laws governing motion can be looked at as the relationship between unified dual fields which are continuous in time and space. Both fields are activated by a single source. The most notable example of such phenomena is electromagnetism, in which the dual fields are the electric field and the magnetic field. Another example is acoustics, in which the dual fields are the particle‐velocity field and the pressure field. The two fields are activated by the same source and satisfy two first‐order partial differential equations, such as those obtained by Newton’s laws or Maxwell’s equations. These equations are symmetrical in time and space, i.e., they obey the same wave equation, which differs only in the interface condition changing sign. The generalization of the Einstein velocity addition equation to a layered system explains how multiple reflections are generated. This result shows how dual sensors at a receiver point at depth provide the information required for a new deconvolution method. This method is called Einstein deconvolution in honor of Albert Einstein. Einstein deconvolution requires measurements of the pressure signal, the particle velocity signal, and the rock impedance, all at the receiver point. From these measurements, the downgoing and upgoing waves at the receiver are computed. Einstein deconvolution is the process of deconvolving the upgoing wave by the downgoing wave. Knowledge of the source signature is not required. Einstein deconvolution removes the unknown source signature and strips off the effects of all the layers above the receiver point. Specifically, the output of Einstein deconvolution is the unit‐impulse reflection response of the layers below the receiver point. Compared with the field data, the unit‐impulse reflection response gives a much clearer picture of the deep horizons, a desirable result in all remote detection problems. In addition, the unit‐impulse reflection response is precisely the input required to perform dynamic deconvolution. Dynamic deconvolution yields the reflectivity (i.e., reflection‐ coefficient series) of the interfaces below the receiver point. Alternatively, predictive deconvolution can be used instead of dynamic deconvolution.
Joint inversion of surface and three‐component borehole magnetic data
Authors: Li Yaoguo , Oldenburg Douglas W.
Published: October 2002

The inversion of magnetic data is inherently nonunique with respect to the distance between the source and observation locations. This manifests itself as an ambiguity in the source depth when surface data are inverted and as an ambiguity in the distance between the source and boreholes if borehole data are inverted. Joint inversion of surface and borehole data can help to reduce this nonuniqueness. To achieve this, we develop an algorithm for inverting data sets that have arbitrary observation locations in boreholes and above the surface. The algorithm depends upon weighting functions that counteract the geometric decay of magnetic kernels with distance from the observer. We apply these weighting functions to the inversion of three‐component magnetic data collected in boreholes and then to the joint inversion of surface and borehole data. Both synthetic and field data sets are used to illustrate the new inversion algorithm. When borehole data are inverted directly, three‐component data are far more useful in constructing good susceptibility models than are single‐component data. However, either can be used effectively in a joint inversion with surface data to produce models that are superior to those obtained by inversion of surface data alone.
Analysis and removal of multiply scattered tube waves
Authors: Herman Gérard C. , Milligan Paul A. , Dong Qicheng , Rector James W.
Published: October 2002

Because of irregularities in or near the borehole, vertical seismic profiling (VSP) or crosswell data can be contaminated with scattered tube waves. These can have a large amplitude and can interfere with weaker upcoming reflections, destroying their continuity. This type of organized noise cannot always be removed with filtering methods currently in use. We propose a method based on modeling the scattered tube‐wave field and then subtracting it from the total data set. We assume that the scattering occurs close to the borehole axis and therefore use a 1-D impedance function to characterize borehole irregularities. Estimation of this impedance function is one of the first steps. Our method also accounts for multiply scattered tube waves. We apply the method to an actual VSP data set and conclude that the continuity of reflected, upcoming events improves significantly in a washout zone.
Two‐dimensional, three‐component wave propagation in a transversely isotropic medium with arbitrary‐orientation—finite‐element modeling
Authors: Zhu Jianlin , Dorman Jim
Published: October 2002

Numerical modeling of seismic waves in transversely isotropic (TI) media is often restricted to special cases where the plane of isotropy coincides with a coordinate plane of the model medium. We remove this special limitation by developing a scheme in which symmetry axes of individual component TI media are oriented arbitrarily with respect to the coordinate axes of the composite model. In these general TI media, the elastic constants for each homogeneous anisotropic region are a 6 × 6 matrix of nonzero elements calculated by an arbitrary rotation. Then, 3-D modeling can readily deal with the coupling of the three components of wave motion. However, required computer memory and execution time may exceed practical limits. Therefore, we implement a finite‐element modeling process for TI media in which elastic properties vary only in two dimensions but component media have planes of isotropy in arbitrary directions. We compute three components of particle motion since the latter are coupled together in these media. The computational load is about twice that of the special cases where the planes of isotropy coincide with the coordinate planes. Three‐component synthetic profiles corresponding to two sample models clearly illustrate the behavior of seismic waves in anisotropic media, including shear‐wave splitting and coupling between the in‐line and cross‐line motion.
Using an induction coil sensor to indirectly measure theB-field response in the bandwidth of the transient electromagnetic method
Authors: Smith Richard S. , Annan A. Peter
Published: October 2002

The traditional sensor used in transient electromagnetic (EM) systems is an induction coil. This sensor measures a voltage response proportional to the time rate of change of the magnetic field in the EM bandwidth. By simply integrating the digitized output voltage from the induction coil, it is possible to obtain an indirect measurement of the magnetic field in the same bandwidth. The simple integration methodology is validated by showing that there is good agreement between synthetic voltage data integrated to a magnetic field and synthetic magnetic‐field data calculated directly. Further experimental work compares induction‐coil magnetic‐field data collected along a profile with data measured using a SQUID magnetometer. These two electromagnetic profiles look similar, and a comparison of the decay curves at a critical point on the profile shows that the two types of measurements agree within the bounds of experimental error. Comparison of measured voltage and magnetic‐field data show that the two sets of profiles have quite different characteristics. The magnetic‐field data is better for identifying, discriminating, and interpreting good conductors, while suppressing the less conductive targets. An induction coil is therefore a suitable sensor for the indirect collection of EM magnetic‐field data.
Optimization of signal‐to‐noise ratio in dc soundings
Authors: Stoll Johannes B. , Bahr Karsten
Published: October 2002

Geoelectric (dc) sounding methods are usually limited to electrode spacings smaller than 1 km, which restrict the depth of investigation to only several hundreds of meters. Greater depths of investigation require both a larger electrode spacing and motor‐generator driven transmitters. In order to increase the depth of investigation into the middle crust, the distance between transmitter and receiver dipole must be increased up to 100 km as well. Instead of a Schlumberger electrode configuration, we use a dipole‐dipole electrode arrangement, which avoids cable connections of several tens of kilometers. It takes less logistics in the field and requires less precautions to control the cable circuits. However, the electric field of a grounded dipole decays by the power of 3. Even if a strong current source with a power of 30 kW is employed, at distances beyond 10 km the amplitude of the transmitted dc signal becomes considerably smaller than the naturally inductive field and cultural noise. Here, we present a technique which resolves the transmitted dc signal at sites up to 60 km apart using an electric dipole source. The suggested technique removes the inductive part in the time series and, therefore, reduces the noise level. It requires applying the magnetotelluric technique before and/or after the geoelectrical sounding. Both the magnetic and electric variational fields are recorded during geoelectrical sounding. If the magnetotelluric transfer function is obtained at a site, then the natural inductive electric field can be predicted, which in turn is used to remove the inductive electrical part from the receiver dipole record.
Estimation of fracture parameters from reflection seismic data—Part II: Fractured models with orthorhombic symmetry
Authors: Bakulin Andrey , Grechka Vladimir , Tsvankin Ilya
Published: October 2002

Existing geophysical and geological data indicate that orthorhombic media with a horizontal symmetry plane should be rather common for naturally fractured reservoirs. Here, we consider two orthorhombic models: one that contains parallel vertical fractures embedded in a transversely isotropic background with a vertical symmetry axis (VTI medium) and the other formed by two orthogonal sets of rotationally invariant vertical fractures in a purely isotropic host rock. Using the linear‐slip theory, we obtain simple analytic expressions for the anisotropic coefficients of effective orthorhombic media. Under the assumptions of weak anisotropy of the background medium (for the first model) and small compliances of the fractures, all effective anisotropic parameters reduce to the sum of the background values and the parameters associated with each fracture set. For the model with a single fracture system, this result allows us to eliminate the influence of the VTI background by evaluating the differences between the anisotropic parameters defined in the vertical symmetry planes. Subsequently, the fracture weaknesses, which carry information about the density and content of the fracture network, can be estimated in the same way as for fracture‐induced transverse isotropy with a horizontal symmetry axis (HTI media) examined in our previous paper (part I). The parameter estimation procedure can be based on the azimuthally dependent reflection traveltimes and prestack amplitudes of P-waves alone if an estimate of the ratio of the P- and S-wave vertical velocities is available. It is beneficial, however, to combine P-wave data with the vertical traveltimes, NMO velocities, or AVO gradients of mode‐converted (PS) waves. In each vertical symmetry plane of the model with two orthogonal fracture sets, the anisotropic parameters are largely governed by the weaknesses of the fractures orthogonal to this plane. For weak anisotropy, the fracture sets are essentially decoupled, and their parameters can be estimated by means of two independently performed HTI inversions. The input data for this model must include the vertical velocities (or reflector depth) to resolve the anisotropic coefficients in each vertical symmetry plane rather than just their differences. We also discuss several criteria that can be used to distinguish between the models with one and two fracture sets. For example, the semimajor axis of the P-wave NMO ellipse and the polarization direction of the vertically traveling fast shear wave are always parallel to each other for a single system of fractures, but they may become orthogonal in the medium with two fracture sets.
Application of 3-D seismics to mine planning at Vaal Reefs gold mine, number 10 shaft, Republic of South Africa
Authors: Pretorius C. C. , Trewick W. F. , Fourie A. , Irons C.
Published: October 2002

During 1994, a 3-D seismic reflection survey was undertaken at Vaal Reefs No. 10 shaft with the objective of mapping the detailed structure of the Ventersdorp contact reef gold orebody. This would provide vital input into future mine planning and development. The survey benefitted from 10 years of 2-D seismic experience and one previous 3-D mine survey, conducted in the Witwatersrand Basin. The seismic survey at No. 10 shaft accurately and spectacularly delineated the 3-D structure of the Ventersdorp contact reef at depths ranging from 1000 to 3500 m, imaging faults with throws in the 20- to 1200-m range. The resultant structure plans were satisfactorily validated by subsequent surface drilling and underground mapping mining operations during the period 1994 to 1996. These plans have been merged with drillhole, underground, and sampling data into an integrated mine modeling, gold reserve estimation, and mine scheduling package. The geology department now manages the planning function at No. 10 shaft, and 3-D seismics has played a significant role in placing this important responsibility firmly within the geologists’ domain. Building on the success of the No. 10 shaft survey, two other 3-D seismic surveys were concluded over mines during 1996 and 1997.
The detection of potassic alteration by gamma‐ray spectrometry—Recognition of alteration related to mineralization
Authors: Shives Robert B. K. , Charbonneau B. W. , Ford K. L.
Published: October 2002

Canadian case histories document the use of airborne and ground gamma‐ray spectrometry to detect and map potassium alteration associated with different styles of mineralization. These include: volcanic‐hosted massive sulfides (Cu‐Pb‐Zn), Pilley’s Island, Newfoundland; polymetallic, magmatic‐hydrothermal deposits (Au‐Co‐Cu‐Bi‐W‐As), Lou Lake, Northwest Territories; and porphyry Cu‐Au‐(Mo) deposits at Mt. Milligan, British Columbia and Casino, Yukon Territory. Mineralization in two of these areas was discovered using airborne gamma‐ray spectrometry. In each case history, alteration produces potassium anomalies that can be distinguished from normal lithologic potassium variations by characteristic lows in eTh/K ratios. Interpretations incorporating airborne and ground spectrometry, surficial and bedrock geochemistry and petrology show that gamma‐ray spectrometric patterns provide powerful guides to mineralization. This information complements magnetic, electromagnetic, geological, and conventional geochemical data commonly gathered during mineral exploration programs.
Some aspects of interval velocity analysis using 3-D depth‐migrated gathers
Authors: Reshef Moshe
Published: October 2002

Analysis of depth‐migrated gathers is the basis of most interval velocity estimation techniques. These gathers, known as common image gathers (CIGs), should consist of flat events when the velocity used for the migration is correct (Faye and Jeannot, 1986; Al‐Yahya, 1989). As a result of this assumption, interval velocity analysis has become a procedure of flattening events in CIGs.
Elimination of free‐surface related multiples without need of the source wavelet
Authors: Amundsen Lasse
Published: October 2002

This paper presents a new, wave‐equation based method for eliminating the effect of the free surface from marine seismic data without destroying primary amplitudes and without any knowledge of the subsurface. Compared with previously published methods which require an estimate of the source wavelet, the present method has the following characteristics: it does not require any information about the marine source array and its signature, it does not rely on removal of the direct wave from the data, and it does not require any explicit deghosting. Moreover, the effect of the source signature is removed from the data in the multiple elimination process by deterministic signature deconvolution, replacing the original source signature radiated from the marine source array with any desired wavelet (within the data frequency‐band) radiated from a monopole point source. The fundamental constraint of the new method is that the vertical derivative of the pressure or the vertical component of the particle velocity is input to the free‐surface demultiple process along with pressure recordings. These additional data are routinely recorded in ocean‐bottom seismic surveys. The method can be applied to conventional towed streamer pressure data recorded in the water column at a depth which is greater than the depth of the source array only when the pressure derivative can be estimated, or even better, is measured. Since the direct wave and its source ghost is part of the free‐ surface demultiple, designature process, the direct arrival must be properly measured for the method to work successfully. In the case when the geology is close to horizontally layering, the free‐surface multiple elimination method greatly simplifies, reducing to a well‐known deterministic deconvolution process which can be applied to common shot gathers (or common receiver gathers or common midpoint gathers when source array variations are negligible) in the τ-p domain or frequency‐wavenumber domain.
An analysis of the accuracy of magnetic source‐body geometry determined from the 3-D analytic signal
Authors: Zhang Jisheng
Published: October 2002

Since the early 1970s, the analytic signal technique has been successfully used to estimate the depth and position of geologic boundaries (e.g., contacts, faults) because it requires no assumption about the source magnetization. Nabighian (1972) defines the 2-D analytic signal and shows how it can be used to determine the depth to the top and the horizontal position of thin, elongated bodies. This concept was extended to 3-D (Nabighian, 1984), but only later was a practical method to process data from 3-D sources presented (Roest et al., 1992). Hsu et al. (1996) extends the concept of analytic signal for the 3-D case by defining the nth‐order enhanced analytic signal. Roest et al. (1992) and Hsu et al. (1996) point out that even in the 3-D case, the analytic signal produces good estimates of the source depth and position only if the source is elongated and free of interference from other sources, that is, if its horizontal dimension is much larger than the depth of its top.
Magnetic source parameters of two‐dimensional structures using extended Euler deconvolution
Authors: Mushayandebvu Martin F. , van Driel P. , Reid Alan B. , Fairhead James Derek
Published: October 2002

The Euler homogeneity relation expresses how a homogeneous function transforms under scaling. When implemented, it helps to determine source location for particular potential field anomalies. In this paper, we introduce an additional relation that expresses the transformation of homogeneous functions under rotation. The combined implementation of the two equations, called here extended Euler deconvolution for 2-D structures, gives a more complete source parameter estimation that allows the determination of susceptibility contrast and dip in the cases of contact and thin‐sheet sources. This allows for the structural index to be correctly chosen on the basis of a priori knowledge about susceptibility and dip. The pattern of spray solutions emanating from a single source anomaly can be attributed to interfering sources, which have their greatest effect on the flanks of the anomaly. These sprays follow different paths when using either conventional Euler deconvolution or extended Euler deconvolution. The paths of these spray solutions cross and cluster close to the true source location. This intersection of spray paths is used as a discriminant between poor and well‐constrained solutions, allowing poor solutions to be eliminated. Extended Euler deconvolution has been tested successfully on 2-D model and real magnetic profile data over contacts and thin dikes.
GEOPHYSICS IN CANADA—ABSTRACT
Authors: Freeman L. I.
Published: October 2002

Geophysical methods applied to oil exploration have been used in Canada shortly after their introduction in the United States. Apparently the brevity of each survey by any method precluded any particular success. Unfortunately their first application was to areas in which no great success has been attained since. Within the past five years, however, due to the introduction of the gravity meter and the improvement in reflection seismograph methods and instruments, Canada is well along in its exploration with geophysics.
LEAST SQUARES DETERMINATION OF THE VELOCITY FUNCTION V=V0+kz FOR ANY SET OF TIME DEPTH DATA
Authors: Legge J. A. , Rupnik J. J.
Published: October 2002

A method is presented by means of which a least square fit of the circular ray path plotting function to time‐depth data is obtained. An example is worked out illustrating the application of the method to an actual case.
Transcontinental Gravitational and Magnetic Profile of North America and Its Relation to Geologic Structure. George P. Woollard. Bulletin of the Geological Society of America, Vol. 54, Pages 747–790. June 1, 1943.
Authors: Nettleton L. L.
Published: October 2002

This paper is the final publication of the results of the transcontinental traverse of gravity and magnetic measurements carried out by Prof. Woollard in the summer of 1940. The first public announcement of the results of this work was given at the Houston meeting of the S.E.G. in 1941, when a paper with substantially the same title was listed to be read by title and an extensive abstract was published in the program of the meeting. A large chart corresponding approximately to Plate 1 of Woollard’s present paper was shown at that meeting and was discussed informally, although Prof. Woollard himself was not able to be present.
HOW NOT TO FIND AN OIL FIELD
Authors: Sloat John
Published: October 2002

This paper discusses causes and cases of seismograph misinterpretation, with examples of errors resulting from certain spreads, from weathering computations, and from incorrect velocity assumptions. The question is raised as to whether subterranean weathering corrections, echo reflections, transverse waves or regional velocity gradients have caused serious mis‐mapping of structure. The evaluation of results from dip shooting is reviewed, with cases showing how oil fields have been missed. The psychological factor in picking records is stressed and the use of marked records in correlation is questioned. The need for a better criterion of correlation is expressed, and it is suggested that a more complete study of results might result in fewer dry holes.
ANALYSIS FOR HYDROCARBONS IN THE PRESENCE OF NITROUS OXIDE
Authors: Kriegel Monroe W.
Published: October 2002

The technique for the analysis of soil air for small quantities of hydrocarbons is reviewed. Various methods of expressing results and the basis for the calculation of each are given. Field data on expansion ratios are presented to show that there exists in the soil air a gas, other than the saturated hydrocarbons, which is not removed by the screening agents and is retained in the condensation trap. The reasons for believing that this gas is nitrous oxide are given, together with plausible sources of this gas in the soil air. Laboratory data are presented on the analysis of pure hydrocarbons in the presence and in the absence of this gas. Calculations made by each of the methods show that when results are based on after‐burning readings, a true measure of the hydrocarbon content is evolved, regardless of the presence of nitrous oxide.
PRECISE MEASUREMENT OF DEEP ELECTRICAL ANOMALIES
Authors: West Thomas S. , Beacham Clarence C.
Published: October 2002

A method of electrical prospecting has been developed in which the deleterious effects of superficial inhomogeneities in resistivity are eliminated. An electrode configuration is used consisting of a current electrode at “infinity,” a pair of current electrodes with a constant separation of a few hundred feet which are used alternately, and a pair of potential electrodes with a constant separation of a few hundred feet, collinear with the pair of current electrodes, and at a distance from them which is varied to secure depth resolution. It is demonstrated that superficial influences are eliminated by forming the resistivity increment, the ratio between apparent resistivity determined by use of the closer current electrode of the alternate pair and that determined by use of the farther current electrode of the alternate pair. It is also demonstrated that the area explored is below a point approximately half‐way between the alternate pair of current electrodes. Resistivity increment curves, called Resistologs by the authors, can be correlated from station to station, and after they are correlated the lateral variation in the electrical properties of selected subsurface zones can be studied. As a result of the latter characteristic of the measurements, a possibility exists for the direct location of oil and gas, observational evidence for which is presented. The results of surveys made in Hart County, Kentucky, and in the Sam Fordyce, Seven Sisters, Pettus, Branyon, Dunlap, Oakville, and Rhode Ranch fields of Southwest Texas are displayed.
Application of a high‐resolution seismic investigation in a Greek coal mine
Authors: Tselentis G.‐Akis , Paraskevopoulos Paraskevas
Published: October 2002

High‐resolution seismic methods were applied to map the detailed structure and thickness of the Domeniko coal basin (central Greece) and to search for lateral discontinuities, such as pinch‐outs and faults. Extensive tests were performed to optimize recording parameters and equipment. Reflection events which can be attributed to coal layers can be interpreted from depths of approximately 30 to 150 m on CDP stacked and inverted sections. Several low‐throw faults have been interpreted from the sections. Results obtained from the high‐resolution seismic reflection survey combined with drillhole information clearly revealed the 3‐D model of the coal field.

Using geostatistical methods, the results of the high‐resolution reflection seismic survey were combined with the information from the borehole program to clearly reveal the 3‐D model of the basin.
Postmap migration of crosswell reflection seismic data
Authors: Byun Joongmoo , Rector III James W. , Nemeth Tamas
Published: October 2002

Vertical seismic profiling/common depth point (VSP‐CDP) mapping is often preferred to crosswell migration when imaging crosswell seismic reflection data. The principal advantage of VSP‐CDP mapping is that it can be configured as a one‐to‐one operation between data in the acquisition domain and data in the image domain and therefore does not smear coherent noise such as tube waves, guided waves, and converted waves as crosswell migration could. However, unlike crosswell migration, VSP‐CDP mapping cannot collapse diffractions; therefore, the lateral resolution of reflection events suffers.

We present a migration algorithm that is applied to the crosswell data after they have been mapped. By performing crosswell migration in two distinct steps—mapping followed by diffraction stacking—noise events can be identified and filtered in the mapped domain without smearing effects commonly associated with conventional crosswell migration operators. Tests on noise‐free synthetic crosswell data indicate that the two‐step migration yields results nearly identical with conventional crosswell migration.

Our specific implementation of the two‐step migration algorithm maps the data using an estimate of the interwell velocity field and then performs diffraction stacking using a constant‐velocity assumption. The migrated results are confined to the mapped region to reduce edge effects commonly associated with conventional crosswell migration. Results from synthetic data indicate that the constant‐velocity assumption used for diffraction stacking is remarkably robust, even for models with large vertical velocity variation. It is, however, important that the data are mapped with the correct interwell velocity model. After applying postmap migration to two field data sets mapped by VSP‐CDP mapping, better fault resolution was achieved and the lateral resolution was improved significantly.
On: “USE OF THE GRAVITY METER IN ESTABLISHMENT OF GRAVITY BENCH MARKS”
Authors: Lambert Walter D.
Published: October 2002

The Coast and Geodetic Survey is planning, when circumstances permit, to use gravity meters freely for the determination of g. This innovation will not mean the abandonment of pendulum determinations of g, but the two methods should be closely coordinated; hence the number and location of new pendulum stations will be profoundly affected by the use of gravity meters.
Reply to A. Roy by A. A. R. Zohdy
Authors: Zohdy Adel A. R.
Published: October 2002

In the article discussed, Figure 2 is vertically exaggerated five times (as indicated on the figure), consequently the departure of the model from quasi‐horizontal layers is also exaggerated five times. Furthermore, as slated in the article, the geoelectric section is divided into three segments: northwestern, middle, and southeastern. The lateral continuity and the successful correlation of the intermediate and deeper layers within each segment (especially in the target area) were demonstrated by the quantitative interpretations of the various soundings. Therefore, the assumption of horizontal layering is still an acceptable approximation except at the boundaries of the geothermal system. The lack of completely generalized two‐ or three‐dimensional modeling techniques (except for oversimplified structures) prevented us from calculating an even more sophisticated model.
Reply by the authors to S. H. Bickel
Authors: Levy S. , Oldenburg D.
Published: October 2002

In our paper on the deconvolution of phase‐shifted wavelets, we adopted the convolutional model of the seismogram from the outset. This showed that the seismogram can be represented as the real part of the convolution of the complex reflectivity function with an analytic wavelet. Our goal was to devise a mathematical and algorithmic procedure whereby the complex model could be recovered.
Reply by the author to D. F. Winterstein
Authors: Ensley R. A.
Published: October 2002

Mr. Winterstein is entirely correct in pointing out that the S‐wave data presented in my paper were a brute stack. In addition, the P‐wave data presented were also a brute stack.
Reply by the author to F. A. Dahlen and R. I. Odom
Authors: Eisner E.
Published: October 2002

The mathematical conditions for application of reciprocity almost preclude their strictly correct application to real experiments. Hence it is of interest to have a robust intuitive understanding as well, to serve as a guide to proper application. The apparent paradox under discussion has served to bring into focus certain aspects of reciprocity that are not readily apparent from the mathematical formulation. As I now see it, a nonparadoxical way to view the situation under discussion is as follows.
Reply by the authors to M. Goldman
Authors: Hesse A. , Jolivet A. , Tabbagh Alain
Published: October 2002

We thank M. Goldman for his relevant criticism. In cylindrical coordinates the θ component of the Laplacian vector comprises six terms and equation (3) of our paper must be written: [Formula: see text]
Reply by the authors to V. I. Starostenko
Authors: Lahmeyer Bernd , Götze Hans J.
Published: October 2002

We would like to thank V. I. Starostenko for his interest in our paper and his historical remarks on the development of 3‐D modeling formulas in gravity and magnetics. The main objective of our paper was to publish a user‐friendly fast interpretation tool for 3‐D modeling including interactive computer graphics. Therefore, it does not deal with an extended derivation of the formulas used in potential field theory.
Reply by the authors to M. S. Reford
Authors: Grauch V. J. S. , Campbell D. L.
Published: October 2002

We appreciate the interest Mr. Reford has shown by examining the dike anomaly as it relates to draped versus level surveys. We agree that draped survey data are not much harder to interpret than level survey data, but, as Mr. Reford shows, one must make allowances for the difference while interpreting data. That one must make these allowances was the point of our Figure 4; we were not attempting accurate measurements. The method we used to estimate the vertical depth to the dikes (slope‐distance method) is not only approximate but subjective as well. It is not surprising then that our depth estimate errors were large.
On: “Seismic signature of a Swan Hills (Frasnian) reef reservoir, Snipe Lake, Alberta” by N. L. Anderson, R. J. Brown, R. C. Hinds, and L. V. Hills (GEOPHYSICS, 54, 148–157, February 1989).
Authors: Yao George Chia‐Chi
Published: October 2002

As a user of the GMA Stratigraphic Modeling System (Geophysical Micro Computer Applications Ltd., Calgary), I was surprised to see a label of “RICKER 0‐PHASE, 30 ms, 28 Hz.” in Figures 6, 7, and 11 of the above article. The usual label from GMA is “Ricker 0 Phase, 30 ms, 26 Hz.”
Reply by the authors to Hilton B. Evans
Authors: Llera F. J. , Sato M. , Nakatsuka K. , Yokoyama H.
Published: October 2002

We thank Prof. Evans for his interest in our paper and welcome the opportunity to respond to his comments. Evans’ discussion focuses on the consistency of our experimental data for rock resistivity with the saturating solution resistivity and Archie’s relationship.
Reply by the author to D. F. Winterstein
Authors: Lynn Heloise Bloxsom
Published: October 2002

I thank Don Winterstein for his relevant and perceptive discussion. As he stated, I have indeed used the term azimuthal anisotropy as a synonym for vertical S‐wave birefringence. This usage he deprecates. By no means do I wish to indicate by my usage lack of support for his work, “Anisotropy terminology for geophysicists” (Winterstein, 1990). There is a need for exact and correct terminology, and his work is worthy of implementation.
Response by the author to A. R. Brown
Authors: Feagin Frank J.
Published: October 2002

I appreciate Dr. Brown’s interest and comments on the paper. I thank him for creating an opportunity for further discussion. The paper, as he points out, does not address the important subjects of perceptibility of seismic character and stratigraphic detail. Neither does it attempt to evaluate the use of color in seismic displays. These and other aspects of display technology are deserving of much more objective and fundamental research than they have received—or at least more than has been reported.
Reply by author to J. G. Saha, N. D. J. Rao, and M. C. Agrawal.
Authors: Taner M. T. , Koehler F. , Sheriff R. E.
Published: October 2002

In reply to the discussion on the “Complex Seismic Trace” coauthored by Taner, Koehler, and Sheriff, we have no substantial disagreement with the remarks of Saha, Rao, and Agrawal. Sharp termination of the Hilbert operator does lead to inaccuracies.
Reply by the author to Brian R. Spies and James R. Wait
Authors: Das Umesh C.
Published: October 2002

I have made no fundamental errors in my paper (Das, 1995a). Unlike conventional mutual coupling ratio (MCR) data which are normalized one component measurements at a transmitter‐receiver T‐R separation (or a frequency) at a number of frequencies (or a number of T‐R separations), the “new processing” uses multisystem, multifrequency, multireceiver MCR data. Processing (combining and integrating in a way given in my paper) of two‐component MCR measurements at one frequency at a large number of T‐R separations produces only one apparent resistivity value [Formula: see text]. This is repeated at other frequencies to obtain an apparent resistivity sounding curve (cf. Figures 3 and 4; Das, 1995b). Thus, disappearance of equivalence in MCR is the result of data redundancy in the new processing at each frequency in apparent resistivity domain and the fact that “different electromagnetic components do have different sensitivity to earth parameters”.
Reply by author to discussion by Dr. S. K. Singh
Authors: Verma Saurabh K.
Published: October 2002

Dr. Singh rightly points out that in this paper the transient response was obtained through the inversion of the already available frequency response (Wait, 1952). The neglect of the monopolar contribution ([Formula: see text] term) by Dr. Wait remained unnoticed, rather surprisingly, for well over two decades! The results obtained in my paper would, therefore, appear to be misleading, or more appropriately, incomplete. There are some significant factors, however, which reveal that the apparent fallacy in the presented interpretation scheme is only of a trivial nature. This is elaborated below.
Reply by authors to discussion by Gudmundur Gudmundsson
Authors: Spector Allan , Grant Fraser S.
Published: October 2002

The authors appreciate the interest shown by Gudmundsson in their paper. They wish also to correct his observation that there is a fundamental difference between the mathematical expression for the Fourier transform of the total field anomaly due to a prism, given by Bhattacharyya (1966), and the basis of that given in their paper.
Reply by Authors to Discussion by R. Jerry Brod
Authors: Behrendt John C. , Wotorson Cletus S.
Published: October 2002

Brod appears to doubt the adequacy of the radioactivity survey. Although we were not involved in the planning or execution of the survey, we believe that the design was consistent with obtaining the maximum data for the funds available and that the contractor’s work was satisfactory in all aspects. Admittedly, more definitive gamma‐ray spectral radiation data could have been obtained (at a considerable increase in cost) but we are convinced that the data obtained are adequate for the interpretations reported. The objectives of both surveys, as stated, were to contribute to the reconnaissance geologic mapping program in Liberia.
Reply by the author to N. C. McNaughton
Authors: Robinson John C.
Published: October 2002

A first reaction to McNaughton’s discussion was that it is irrelevant to the subject paper. After all, the purpose of that paper was to show an algorithm for implementing Futterman’s (1962) dispersion relationship—not to defend the universality of its applications or the terminology used to describe it. However, there hasn’t been much published in the recent geophysical literature about dispersion, and McNaughton’s question seems a relevant one in the general context of the dispersion subject. Not having an immediate answer to McNaughton’s question and being sufficiently intrigued with it, the decision was made to look further into the published literature for an answer.
Reply by the author to C. J. Swain
Authors: Karl John H.
Published: October 2002

As Dr. Swain observes, my 4πγ[Formula: see text] effect results from a global average, and as such says nothing about the vertical gradient at any given location. That’s my point. If my average value is correct (no one has disagreed with that) and measured values agree with the normal gradient, then there must be anomalies that are even larger than 4πγ[Formula: see text] somewhere. It is likely that these anomalous values occur in mountainous regions—just the place where the elevation correction is most important.
Reply by the authors to R. Pauls
Authors: Mohan N. L. , Sundararajan N. , Rao S. V. Seshagiri
Published: October 2002

We appreciate the keen interest evinced by Mr. Rob Pauls on our article “Interpretation of some two‐dimensional magnetic bodies using Hilbert transforms.” We are very sorry to note that Mr. Pauls has made hasty comments without going through our article critically.
Reply by the author to G. W. Leney
Authors: Corry Charles E.
Published: October 2002

I find no valid criticism of my paper in the comments by G. W. Leney and he provides no evidence to support his arguments. In several instances he misstates my conclusions or misrepresents the data. While my proposed mechanism is based on electrochemistry, Leney assumes linear circuit theory and Ohm’s law without providing any logical connection.
Reply by the authors to D. M. Pai
Authors: Kosloff Dan , Kessler David
Published: October 2002

We regret not having referenced the work of Pai (1985), but we disagree completely with the contents of his discussion. Briefly summarized, the downward continuation in our article includes the following steps.
On: “Lithology discrimination for thin layers using wavelet signal parameters” by J. N. Lange and H. A. Almoghrabi (GEOPHYSICS, 53, 1512–1519, December 1988).
Authors: Sengupta M. K.
Published: October 2002

Lange and Almoghrabi have shown correctly that seismic frequency is an important parameter for discriminating among seismic lithologies and pore‐fluid types for thin layers. I would like to draw attention to Figure 3 of this paper and to the last paragraph of their conclusions, which state, “The crux of the multiparameter algorithms…is the thin layer’s frequency‐dependent reflectivity, which can be used to discriminate reflector lithologies and pore fluid type.”
Reply by authors to G. J. O. Vermeer
Authors: Morse Peter F. , Hildebrandt George F.
Published: October 2002

We thank Gijs Vermeer for his interesting comments on our article. The focus of his discussion is to explain why residual ground roll remains on the stacked sections of Figures 13 and 14 even after using the optimal stackarray. He reasons that right‐dipping residual ground‐roll events can be explained by the presence of off‐line scatterers. He further argues that symmetric sampling of the ground roll in both shot‐and‐receiver domains would mitigate this effect, and proposes a quick test involving reprocessing of our Humble data using only every fifth receiver group (which would result in symmetric sampling).
Reply by the authors to N. S. Rajan
Authors: Saatcilar R. , Ergintav S. , Camtez N.
Published: October 2002

‵We understand that the author fastidiously examined our paper (Saatcilar et al., 1990) to see if there are any errors in the formulas or misleading expressions in the text. Indeed he discovered the typographical error in the definition of the Hartley kernel which was introduced by an officious person at the printing company at the last moment thinking that we have mistyped “css” and he/she replaced it with “cos” in formulas (1), (2), (3), (16), (21), (22). An “Eratta” has been written in “Geophysics, vol. 56, n. 9, p. 1514” in which the editor corrected only formulas (1) and (2) of our original paper. Rajan probably has not seen it. All his discussions depend on these mistypings. With this occasion, he also gives some details related to the Hartley transform and unnecessarily repeats some of our discussions. The mistyped formulas in our original paper follow.
Reply by the authors to J. Mars and J. W. Rector III
Authors: Zhou B. , Greenhalgh S. A.
Published: October 2002

We thank J. Mars and J. W. Rector III for their interest in our paper and for demonstrating that asymmetry in the range of p values used by us in forming Figures 3a and 3b has contributed to the phase distortion in Figure 4a. For the flat event we were considering in Figure 2, both positive and negative p values should strictly have been used in taking the forward and inverse transforms. For a dipping event, this would be unnecessary. There is no requirement that the p range be symmetric about the origin, just that it brackets the slowness values forming the event. Unfortunately, the conclusion reached by Mars and Rector, that the phase distortion ‘is due entirely to the choice of p values and that p‐direction deconvolution is unnecessary, is incorrect, and detracts from one of the main points of our paper.
Response by J. Mars and J. W. Rector III to the reply by the author
Authors: Mars Jerome , Rector James W.
Published: October 2002

We thank B. Zhou and S.A. Greenhalgh for their response. We would first like to correct Zhou and Greenhalgh. Our comments in the preceding discussion apply only to the invertibility of the τ‐p transform.
Response by Arthur E. Barnes to the reply by the authors
Authors: Barnes Arthur E.
Published: October 2002

I appreciate the thoughtful and thorough response given by Tygel et al. They point out that even for a single dipping reflector imaged by a single non‐zero offset raypath, pulse distortion caused by “standard processing” (NM0 correction‐CMP sort‐stack‐time migration) and pulse distortion caused by prestack depth migration are not really the same, because the reflecting point is mispositioned in standard processing. Within a CMP gather, this mispositioning increases with offset, giving rise to “CMP smear.” CMP smear degrades the stack, introducing additional pulse distortion. Where i‐t is significant, and where lateral velocity variations or reflection curvature are large, such as for complex geology, the pulse distortion of standard processing can differ greatly from that of prestack depth migration.
A new method for shape and depth determinations from gravity data
Authors: Abdelrahman El‐Sayed M. , El‐Araby Tarek M. , El‐Araby Hesham M. , Abo‐Ezz Eid R.
Published: October 2002

We have developed a simple method to determine simultaneously the shape and depth of a buried structure from residualized gravity data using filters of successive window lengths. The method is similar to Euler deconvolution, but it solves for shape and depth independently. The method involves using a relationship between the shape factor and the depth to the source and a combination of windowed observations. The relationship represents a parametric family of curves (window curves). For a fixed window length, the depth is determined for each shape factor. The computed depths are plotted against the shape factors, representing a continuous, monotonically increasing curve. The solution for the shape and depth of the buried structure is read at the common intersection of the window curves. This method can be applied to residuals as well as to the Bouguer gravity data of a short or long profile length. The method is applied to theoretical data with and without random errors and is tested on a known field example from the United States. In all cases, the shape and depth solutions obtained are in good agreement with the actual ones.
Moisture permeability measurement using a surface air dew-point probe: a feasibility study
Authors: Yik F WH , Chau C K
Published: October 2002

Moisture permeability of building materials is essential information to predicting moisture transfer in buildings. The conventional way of measuring the permeability of a material is the standard cup test method, which is very time consuming. The paper describes an investigation into the feasibility of using a surface air dew-point probe (SADP), which was first designed by Tsuchiya, to significantly shorten the measurement time. An analysis is presented to show the degree of accuracy required of the measurement of the moisture content changes of the air flowing through the SADP in order that accurate measurement of permeability can be achieved. The requirement, however, may not be achievable with the dew-point temperature sensors currently available. An experimental method for solving this problem is suggested, based on experience gained in trial experiments.