bluuebunny/crossref_metadata_2025 huggingface dataset:
Aeromagnetic expression of faults that offset basin fill, Albuquerque basin, New Mexico
Authors: Grauch V. J. S. , Hudson Mark R. , Minor Scott A.
Published: October 2002

High‐resolution aeromagnetic data acquired over the Albuquerque basin show widespread expression of faults that offset basin fill and demonstrate that the aeromagnetic method can be an important hydrogeologic and surficial mapping tool in sediment‐filled basins. Aeromagnetic expression of faults is recognized by the common correspondence of linear anomalies to surficial evidence of faulting across the area. In map view, linear anomalies show patterns typical of extensional faulting, such as anastomosing and en echelon segments. Depths to the tops of faulted magnetic layers showing the most prominent aeromagnetic expression range from 0 to 100 m. Sources related to subtler fault expressions range in depths from 200 to 500 m. We estimate that sources of the magnetic expressions of the near‐surface faults likely reside within the upper 500–600 m of the subsurface. The linear anomalies in profile form show a range of shapes, but all of them can be explained by the juxtaposition of layers having different magnetic properties. One typical anomaly differs from the expected symmetric fault anomaly by exhibiting an apparent low over the fault zone and more than one inflection point. Although the apparent low could easily be misinterpreted as representing multiple faults or an anomalous fault zone, geophysical analysis, magnetic‐property measurements, and geologic considerations lead instead to a “thin‐thick model” in which magnetic layers of different thickness are juxtaposed. The general geometry of this model is a thin magnetic layer on the upthrown block and a thick magnetic layer on the downthrown block. The thin‐thick model can be represented geologically by growth faulting and syntectonic sedimentation, where relatively coarse‐grained sediment (which is more magnetic than fine‐grained material) has accumulated in the hanging wall. This implies that the aeromagnetic data have potential for mapping growth faults and locating concentrations of coarse‐grained material that may have high hydraulic transmissivity. Although cementation along fault zones is common in portions of the area, we found no evidence that this secondary process results in measurable aeromagnetic anomalies. This observation differs from the findings in other sedimentary basins suggesting that magnetic anomalies arise from secondary magnetization along fault planes.
Migration‐based traveltime waveform inversion of 2-D simple structures: A synthetic example
Authors: Clément François , Chavent Guy , Gómez Susana
Published: October 2002

Migration‐based traveltime (MBTT) formulation provides algorithms for automatically determining background velocities from full‐waveform surface seismic reflection data using local optimization methods. In particular, it addresses the difficulty of the nonconvexity of the least‐squares data misfit function. The method consists of parameterizing the reflectivity in the time domain through a migration step and providing a multiscale representation for the smooth background velocity. We present an implementation of the MBTT approach for a 2-D finite‐difference (FD) full‐wave acoustic model. Numerical analysis on a 2-D synthetic example shows the ability of the method to find much more reliable estimates of both long and short wavelengths of the velocity than the classical least‐squares approach, even when starting from very poor initial guesses. This enlargement of the domain of attraction for the global minima of the least‐squares misfit has a price: each evaluation of the new objective function requires, besides the usual FD full‐wave forward modeling, an additional full‐wave prestack migration. Hence, the FD implementation of the MBTT approach presented in this paper is expected to provide a useful tool for the inversion of data sets of moderate size.
Numerical simulation of the Biot slow wave in water‐saturated Nivelsteiner Sandstone
Authors: Arntsen Børge , Carcione José M.
Published: October 2002

The development of rock acoustic models is important for interpreting seismic data. These models should relate seismic properties such as wave velocity and attenuation to the production and lithological properties of reservoir rocks, such as porosity, permeability, fluid type, and fluid saturation.
Comprehensive assessment of seismic acquisition geometries by focal beams—Part I: Theoretical considerations
Authors: Berkhout A. J. , Ongkiehong L. , Volker A. W. F. , Blacquière G.
Published: October 2002

The starting point for a relatively simple approach to data acquisition design can be found in the common focus point (CFP) philosophy, which describes seismic migration as a double focusing process. The migration output is presented as the combined result of focused source beams and focused detector beams for a given velocity model, revealing the potential amplitude accuracy and spatial resolution of a specific field geometry. In addition, any noise model can be fed into the input, and the subsequent beam‐forming operations can be applied to predict the potential noise suppression rate. The economical optimization comes from the possibility of balancing the source and detector efforts as well as the acquisition and processing efforts.
DETERMINATION OF THE BOUGUER CORRECTION CONSTANT
Authors: Siegert A. J. F.
Published: October 2002

A formula is given which eliminates some of the usual graphical work and makes the result independent of the judgment of the computer. The probable error can be determined easily.
THE EFFECT OF MUD RESISTIVITIES ON THE INTENSITIES OF ELECTRICAL LOGS
Authors: Bowsky M. C.
Published: October 2002

The drilling mud is one of the variables that prevents comparing the actual intensities of electrical logs. This paper deals with the effect of the resistivity of the drilling mud on the intensities of the natural potential and normal apparent resistivity curves.
RADIOACTIVITY ANALYSES OF OIL WELL SAMPLES
Authors: Pontecorvo Bruno
Published: October 2002

A laboratory method of analyzing the radioactivity of rock samples is described in which the laboratory tests are designed to simulate the conditions which prevail when radioactivity logs of wells are made. Thus the radioactivity of samples may be correlated with the results of such well logs and their interpretation improved thereby.
CURVED PATH METHODS APPLIED TO VERTICALS AND TO WIDE SHOT SPREADS
Authors: Mott‐Smith Morton
Published: October 2002

The ray path‐wave front chart and similar methods used for vertical shots are briefly described, and the possibility and the advantages of applying the linear time law to these methods is pointed out. A short method of fitting the linear depth law to the observed velocity is described. The possibility of extending any method applicable to verticals to wide shot spreads is shown, and a method of correcting straight path dips for curvature in the case of verticals is pointed out.
GEOPHYSICS IN THE PERMIAN BASIN
Authors: Wilson John H.
Published: October 2002

The application of geophysics in the Permian Basin to war and postwar problems is largely one of location of new oil reserves. Given governmental approval, allocation of essential supplies and adequate financial incentive, which involves such factors as price, allowables, outlets, etc., geophysical work may be expected to continue in fair volume during the war because the Permian Basin still contains many highly prospective areas not yet satisfactorily explored by geophysical methods.
LOCAL AREAL DISTRIBUTION OF VELOCITIES IN THE TEXAS GULF COAST
Authors: Swan B. G.
Published: October 2002

This paper presents velocity data obtained from long reversed profile surface shooting on three Texas Gulf Coast projects. Velocity determinations were distributed areally in sufficient detail to permit construction of “Isotime” contour maps representing velocities to a time datum. Maps are presented showing the resulting corrected seismic structure. Also presented are Time‐Depth curves of two profiles with curves of nearby well velocity surveys. Two comparisons are made of velocities at common points determined by the long velocity profiles and by Time-Δt analysis of shorter spreads. Data presented show that velocities determined in the manner described are quite variable over local areas, but can be contoured into fairly regular patterns, and that if applied to the ordinary seismic data profound changes in structural interpretation are effected; that major discontinuities in velocity stratification may be detected; that in the two examples described, velocities obtained from 5400 foot reversed reflection profiles are higher than those obtained by Time-Δt analysis of 1800 foot reversed profiles; and that velocity anomalies determined from surface profile shooting may be associated with faulting in the subsurface beds.
NOTE ON THE TRANSMISSION OF RADIO WAVES THROUGH THE EARTH
Authors: Silverman Daniel , Sheffet David
Published: October 2002

Experiments are described and data reported on the attenuation suffered by radio signals in passing through shallow layers of the earth. Comparison is made between the measured attenuations and values computed from published formulae.
COMPUTATION OF SEISMIC DIPS BELOW AN UNCONFORMITY
Authors: Dix C. Hewitt , Lawlor Reed C.
Published: October 2002

Formulas giving the strike and dip of a plane reflector beneath a series of layers separated by interfaces of known strike and dip are developed in terms of seismic data obtained at the surface. The formulas for the position of a plane reflector beneath a single unconformity are also developed. Examples show the extent of the influence of the strike and dip of a single unconformity on the computation of the strike, dip, and position of the reflector yielding a given set of surface data.
MECHANISM OF DETONATION IN EXPLOSIVES
Authors: Lawrence Robert W.
Published: October 2002

Results of photographic work on the detonation of high explosives are presented and discussed in their relationship to the hydrodynamic theory of detonation. The two most important properties of an explosive are its strength and its detonation velocity. Methods for determining these quantities are described. A moving film camera of the rotating drum type is especially useful in determining detonation velocity and in studying the nature of detonation. The photographic results, which are illustrated by a number of pictures, are helpful in demonstrating various elements of the theory. These photographs illustrate the nature of detonation waves in explosives and of shock waves in air. The duration of the detonation waves in nitroglycerin and blasting gelatin is less than one millionth of a second and the duration of the shock waves produced by these explosives in air is of the same order. The high temperature of shock waves which is predicted by theory is confirmed by the intense luminosity shown in photographs. The relatively low temperature predicted for shock waves in liquids is similarly confirmed by the absence of luminous shock waves in water. Photographs are included showing the propagation of detonation from one cartridge of blasting gelatin to another across air gaps and water gaps. In the latter case no visible shock wave is produced in the water and the highly luminous after‐burning is eliminated. Calculated values of the detonation velocity for nitroglycerin, blasting gelatin and 60% gelatin dynamite are in approximate agreement with the experimentally determined values. Calculations indicate that pressures in the detonation wave may run as high as 140,000 atmospheres and temperatures to 4300°C. The shape of the detonation wave front in a high velocity explosive like blasting gelatin is apparently planar whereas in low velocity explosives it is convex. The actual mechanism of energy propagation in detonation is not clearly understood out probably involves activation of the explosive at the detonation wave front by high velocity products of the detonation which are projected forward at speeds even greater than the detonation velocity.
A PROPOSED LEAST SQUARE METHOD FOR THE DETERMINATION OF THE ELEVATION FACTOR
Authors: Legge, J. A.
Published: October 2002

The purpose of this paper is to present a least square method whereby the elevation factor is determined by fitting a polynomial to the gravity profile. The method is applicable to stations located along a straight line as well as those located at random over an area.
Education and the Petroleum Industry
Authors: Illing V. C.
Published: October 2002

At a meeting of the Institute of Petroleum held at the Royal Society of Arts in London, April 29, 1943, Professor V. C. Illing, a Vice‐President of the Institute, delivered a paper entitled Education and the Petroleum Industry which was published in the Journal of the Institute of Petroleum, Vol. 29, No. 238, pp. 259–283 (October, 1943). The section on exploration appeared to be of particular interest: consequently, permission was secured from Professor Illing and the Institute to reprint it. (Editor’s Note.)
QUANTITATIVE INTERPRETATION OF MAGNETIC AND GRAVITATIONAL ANOMALIES
Authors: Kogbetliantz Ervand G.
Published: October 2002

A new interpretation method for gravitational and magnetic anomalies based on the use of average values (integrals) of suitably chosen functions of the observed quantity is discussed and illustrated by application to the particular case of a symmetric anticline. The quantitative interpretation yields the position of the apex, the slope of the sides, the thickness, the depth of the base of the anticline, as well as the density contrast for the gravitational case and the magnitude and direction of the magnetization vector for the magnetic case.
Detection of guided waves between gas wells for reservoir characterization
Authors: Parra Jorge O. , Hackert Chris L. , Gorody Anthony W. , Korneev Valeri
Published: October 2002

Guided seismic waves can be used to predict continuity and discontinuity of reservoir structures between wells, with the low‐velocity beds acting as waveguides. We relate guided‐wave signatures to waveguide targets using experimental data acquired at the Stratton gas field in southeast Texas. The observed seismic data indicate the presence of trapped energy in low velocity shale markers between wells 145 and 151. Guided waves in the form of leaky modes are excited, transmitted, and detected in the low‐velocity shale markers at a well separation of 1730 ft (527 m). Dispersion analysis, modeling, frequency–amplitude depth curves, well logs, and lithological information all support the results. Specifically, the characterization of two low‐velocity shale markers, V2 and V5, demonstrates that V2 is more heterogeneous than V5 between the source well 151 and detector well 145. Finally, images of synthetic and real data show the potential applications of the guided‐wave technology as a tool for reservoir characterization.
Finite‐difference quasi‐P traveltimes for anisotropic media
Authors: Qian Jianliang , Symes William W.
Published: October 2002

The first‐arrival quasi‐P wave traveltime field in an anisotropic elastic solid solves a first‐order nonlinear partial differential equation, the q P eikonal equation. The difficulty in solving this eikonal equation by a finite‐difference method is that for anisotropic media the ray (group) velocity direction is not the same as the direction of the traveltime gradient, so that the traveltime gradient can no longer serve as an indicator of the group velocity direction in extrapolating the traveltime field. However, establishing an explicit relation between the ray velocity vector and the phase velocity vector overcomes this difficulty. Furthermore, the solution of the paraxial q P eikonal equation, an evolution equation in depth, gives the first‐arrival traveltime along downward propagating rays. A second‐order upwind finite‐difference scheme solves this paraxial eikonal equation in O(N) floating point operations, where N is the number of grid points. Numerical experiments using 2‐D and 3‐D transversely isotropic models demonstrate the accuracy of the scheme.
Investigating peatland stratigraphy and hydrogeology using integrated electrical geophysics
Authors: Slater Lee D. , Reeve Andrew
Published: October 2002

Hydrology has been suggested as the mechanism controlling vegetation and related surficial pore‐water chemistry in large peatlands. Peatland hydrology influences the carbon dynamics within these large carbon reservoirs and will influence their response to global warming. A geophysical survey was completed in Caribou Bog, a large peatland in Maine, to evaluate peatland stratigraphy and hydrology. Geophysical measurements were integrated with direct measurements of peat stratigraphy from probing, fluid chemistry, and vegetation patterns in the peatland. Consistent with previous field studies, ground‐penetrating radar (GPR) was an excellent method for delineating peatland stratigraphy. Prominent reflectors from the peat‐lake sediment and lake sediment‐mineral soil contacts were precisely recorded up to 8 m deep. Two‐dimensional resistivity and induced polarization imaging were used to investigate stratigraphy beneath the mineral soil, beyond the range of GPR. We observe that the peat is chargeable, and that IP imaging is an alternative method for defining peat thickness. The chargeability of peat is attributed to the high surface‐charge density on partially decomposed organic matter. The electrical conductivity imaging resolved glaciomarine sediment thickness (a confining layer) and its variability across the basin. Comparison of the bulk conductivity images with peatland vegetation revealed a correlation between confining layer thickness and dominant vegetation type, suggesting that stratigraphy exerts a control on hydrogeology and vegetation distribution within this peatland. Terrain conductivity measured with a Geonics EM31 meter correlated with confining glaciomarine sediment thickness and was an effective method for estimating variability in glaciomarine sediment thickness over approximately 18 km2. Our understanding of the hydrogeology, stratigraphy, and controls on vegetation growth in this peatland was much enhanced from the geophysical study.
Three‐dimensional induction logging problems, Part I: An integral equation solution and model comparisons
Authors: Avdeev Dmitry B. , Kuvshinov Alexei V. , Pankratov Oleg V. , Newman Gregory A.
Published: October 2002

A 3‐D frequency‐domain solution based on a volume integral equation approach has been implemented to simulate induction log responses. In our treatment of the problem, we assume that the electrical properties of the bedding as well as the borehole and invasion zones can exhibit transverse anisotropy. The solution process uses a Krylov subspace iteration to solve the scattering equation, which is based on the modified iterative dissipative method. Internal consistency checks and comparisons with mode matching and finite‐difference solutions for vertical borehole models demonstrate the accuracy of the solution.

There are no known analytical solutions for induction log responses arising from deviated boreholes intersecting horizontal bed boundaries. To simulate such responses requires the numerical solution of Maxwell's equations in three dimensions along with independent tests to validate the solution approach and its accuracy. In this paper, we compare two independent 3‐D frequency‐domain solutions for the problem, based on finite differences and the integral equation technique. Specific examples in the quasi‐static limit are studied, including a 45° deviated borehole that intersects formation bed boundaries as well as cases where the bedding exhibits transverse anisotropy. All comparisons made in this paper show very good agreement and demonstrate, for the first time, verifiable induction log responses in the presence of deviated boreholes. We also show that responses arising from deviated boreholes can be significant and must be accounted for properly when interpreting induction logs.
Iron oxides as a cause of GPR reflections
Authors: Van Dam Remke L. , Schlager Wolfgang , Dekkers Mark J. , Huisman Johan A.
Published: October 2002

Iron oxides frequently occur as secondary precipitates in both modern and ancient sediments and may form bands or irregular patterns. We show from time-domain reflectometry (TDR) field studies that goethite iron-oxide precipitates significantly lower the electromagnetic wave velocity of sediments. Measured variations in magnetic permeability do not explain this decrease. The TDR measurements and a dielectric mixing model also show that neither electrical conductivity nor relative permittivity of the solid material are altered significantly by the iron-oxide material. From drying during all of the measurements, the amount of iron oxides appears to correlate with the volumetric water content, which is the result of differences in water retention capacity between goethite and quartz. These variations in water content control relative permittivity and explain the observed variation in electromagnetic wave velocity. Using 2-D synthetic radar sections, we show that the pattern of iron-oxide precipitation may have a profound influence on the GPR reflection configuration and can cause major difficulties in interpretation.
On: ADVERSE EFFECTS ASSOCIATED WITH VARIABLE COMPOUNDED SEISMOGRAPH RECORDS
Authors: Rieber Frank
Published: October 2002

Dr. Mott‐Smith has devoted some time and thought to a consideration of the analyzer, and has stated as his conclusion that he feels that the method is applicable only to a certain narrow range of problems. He seems to have the impression that the earlier and more widely used methods are better adapted for the general run of work.
On: “THE RELATIVE PLACE OF EMPIRICAL AND ANALYTICAL METHODS OF GEOPHYSICAL INTERPRETATION”
Authors: Goldstone Frank
Published: October 2002

Mr. Weaver’s paper is a challenge to analyze our present methods of turning geophysical data into drill sites and to question whether these methods make full use of scientific knowledge. The development of most applied science has been from the empirical to the analytic. To take medicine as an example; primitive peoples had an equal faith in their witch doctors as in their herbal remedies. It required the skilled observation of the scientist to prove that the witch doctor’s dance was less curative than the quinine, and yet 400 years after Hippocrates civilized peoples were still casting out evil spirits from the sick. When and how did exploration geophysicists graduate from the necromantic era and did we leave too many Hippocrates’ unheeded?
Discussion by Leo J. Peters and Thomas A. Elkins
Authors: Peters L. J. , Elkins T. A.
Published: October 2002

We would like to call attention to a point of considerable practical importance which is neglected in this interesting and ingenious paper on the computation of the second derivative. This is the fact that gravity field data inevitably contain errors so that the second derivative values computed by coefficients from this gravity data also will contain errors, which may be of such magnitude as to mask the real effects caused by geologic structure, the finding of which was the purpose of the gravity survey.
On: “THEORY OF GRAVITY INSTABILITY WITH VARIABLE OVERBURDEN AND COMPACTION,” BY M. A. BIOT AND H. ODÉ (GEOPHYSICS, APRIL 1965, PP. 213–227)
Authors: Outmans H. D.
Published: October 2002

In a recent paper Biot and Odé (1965) analyze the Rayleigh-Taylor stability problem for two viscous (Newtonian) fluids superposed one over the other and subjected to the force of gravity.
Author’s Reply
Authors: White J. E.
Published: October 2002

Mr. Savit has sent me a copy of his letter to the editor. I suggest that the “seemingly contradictory conclusions” mentioned by Mr. Savit might largely be cleared up by repeating in their entirety the two sentences which contain the portion of a sentence quoted by Mr. Savit: “It was anticipated that for large values of Δτ, either of the last two cases would result in smaller residual signal than was obtained with the uniform distribution. This turns out to be true by a small factor, but it appears that, for small values of Δτ, the details, of the strength distribution have very little effect on the resulting waveform.”
On: “Dispersion of body waves in layered media” by I. N. Gupta (GEOPHYSICS, August, 1966, pp. 821–823)
Authors: Nakamura Yosio
Published: October 2002

In his short note, Gupta has shown that the dispersive effect of a finely layered medium may be responsible for some of the anomalous observations in explosive and earthquake investigations. In his note, the phase velocity of waves propagating perpendicular to a horizontally stratified structure at its low-frequency limit is compared with that at the high-frequency limit, and consequently a time delay for low-frequency waves has been denoted. The following discussion shows by a further calculation that a still greater time delay can be expected in other frequencies. The result will be of further help for the interpretations given in the subject note.
Reply by authors to discussion by Robert L. Sax and Paul R. Lintz
Authors: Lacoss R. T. , Kelly E. J. , Toksöz M. N.
Published: October 2002

Messrs. Sax and Lintz are entitled to their misinterpretation of our definition of [Formula: see text] and [Formula: see text]. These quantities are defined as [Formula: see text] and [Formula: see text], and are the components of the velocity vector. They are not the components of the phase velocity in x and y directions as the commonly used definition implies. With our definition all the equations in the introductory as well as the subsequent sections of our paper are correct.
Reply by Robert B. Smith and W. D. Stanley to discussion by Nelson C. Steenland
Authors: Smith Robert B. , Stanley W. D.
Published: October 2002

The point of Mr. Steenland’s discussion appears that he does not consider that the computer‐generated perspective views of geophysical maps are as clear or distinct as contour maps. Further he asserts that they lack a quantitative use. On the contrary the perspective views were produced from the same data as the contoured map but in a quantitative digital form. We believe that perspective views are by no means a substitute for contour maps but provide a complementary form of three‐dimensional data.
Reply by authors to discussion by S. K. Choudhury and R. Amaravadi
Authors: Paul M. K. , Datta S. , Banerjee B.
Published: October 2002

We appreciate Messrs. Choudhury and Amaravadi’s interest in our paper and thank them for pointing out some typographical errors in the paper. In fact, we were aware of these and some other similar errors. To us, the corrections of these errors are quite obvious to any serious reader of the paper and they do not seem to deserve any special attention of the general readers of Geophysics. However, we take this opportunity to list them below.
Reply by author to Dr. Thyssen‐Bornemisza
Authors: Fajklewicz Z. J.
Published: October 2002

I am deeply grateful to Dr. Thyssen‐Bornemisza for his interest in my paper. I am glad that he has no reservations about the essence of the article but only to the suggested measurement techniques, which he finds cumbersome and costly. He is of the opinion that, in several cases, less costly microgravimetric surveys could be applied. It should be obvious that there are no universal measurement techniques in exploration geophysics.
Reply by the authors to M. H. Safar
Authors: Ziolkowski A. , Parkes G. E. , Hatton L. , Haugland T.
Published: October 2002

It is refreshing to see some of Safar’s (1976a) argument reprinted in Geophysics and to find that we did not misunderstand it the first time. There are two aspects to Safar’s first point, one concerning what he wrote in 1976 which we apparently misquoted, and another concerning the dynamic pressure across the wall of the bubble. To clear up the first aspect, we quote from p. 780 of Safar (1976a).
Reply by the authors to Richard O. Hansen
Authors: Grauch V. J. S. , Campbell D. L.
Published: October 2002

We had not attempted to show different geologic situations in our paper because there are numerous “typical” situations that we believed would only reiterate our basic conclusions. Nevertheless, because Mr. Hansen brought up a particular geologic situation, we tested it and found that our main conclusions indeed are reiterated.
Reply to F. M. Lyakhovitskiy by F. K. Levin
Authors: Levin Franklyn K.
Published: October 2002

I regret that I was unaware of the papers by Lyakhovitskiy and Nevskiy. As Dr. Lyakhovitskiy points out in his elegant discussion of my paper and that of Dr. Berryman, the work of Lyakhovitskiy and Nevskiy gives a unity to the investigation of the physical properties of thin‐layered solids that my study of a few specific cases lacked.
Reply by the authors to Timothy H. Larson and Paul C. Heigold
Authors: LeSchack Leonard A.
Published: October 2002

Drs. Larson and Heigold are quite correct; equation (1) should read [Formula: see text], and the superscript 2 of the expression [Formula: see text] was left out. Actually, on our reprint copy there appears to be an apostrophe where the superscript 2 should have been. We obviously missed this in the proofreading.
On: “Two‐dimensional joint inversion of magnetotelluric and dipole‐dipole resistivity data” by Y. Sasaki (GEOPHYSICS, 54, 254–262, February 1989)
Authors: Dodds D. J.
Published: October 2002

There appears to be an error in the formulation of the dc resistivity response in this paper. Equation (6) is valid only when the conductivity is constant, but the text and the notation imply that it is variable. Grant and West (1965) give the correct relation [their equation (14‐2)], which is restated here using Sasaki’s notation and accounting for source currents.
Reply by the authors to D. Johnson
Authors: Krail Paul M. , Brysk Henry
Published: October 2002

I would like to thank Daniel Johnson for this discussion, but we do not agree with his argument. The ship has a rudder to overcome the influence of the crosscurrent; the forces on the vessel causing it to deviate from its intended path are nullified by the rudder. The resultant direction of the ship is on its course. The streamer has no rudder, it sees the resultant velocity of the ship’s direction and the crosscurrent.
Reply by the author to Dr. Sternberg
Authors: Degroot‐Hedlin Catherine
Published: October 2002

Dr. Sternberg has raised several interesting points in his discussion on the relative merits of using a TEM survey to determine static shifts versus solving for the static shifts by means of regularized inversion. It was certainly not my intention to dismiss the TEM method as a completely impractical means of determining static shifts. Indeed, in some situations the TEM method might prove to be complementary to the method of solving for the static shifts by means of regularized inversion.
Reply to Discussion by J. R. Wait
Authors: Edwards R. Nigel
Published: October 2002

My original paper describes an analog model source suitable for obtaining MT data over a confined resistive or conductive 3‐D structure embedded in a uniform medium. I am sure Professor Wait is not questioning the validity of the source for this purpose, provided the structure does not extend outside the modeling region.
Reply by the authors to M. M. Roksandic
Authors: Hinds R. C. , Kuzminski R. , Anderson N. L. , Richards B. R.
Published: October 2002

We would like to thank Mr. Roksandic for pointing out the apparent discrepancies between Figures 14 and 15 in our paper. As he notes, the second fault to the south of the 7–36 well on the seismic section (Figure 14) is not shown on the geologic section (Figure 15). At the time that the geologic section was drafted, we felt that the magnitude of this seismically‐interpreted fault was too low to warrant inclusion in the geologic section. In retrospect, this fault should have been deleted from the seismic section in order to avoid confusion.
Reply by the author to D. J. Dodds
Authors: Sasaki Yutaka
Published: October 2002

I am grateful to Mr. Dodds for pointing out the error in my paper. Equation (6) should read [Formula: see text], and equation (7) should read [Formula: see text]
On: “SHALLOW STRATIGRAPHIC VARIATIONS OVER GULF COAST STRUCTURES”
Authors: Price W. Armstrong
Published: October 2002

The geological implications of the geophysical interpretations here presented are impressive in number and in their coordination. An important test of a scientific discovery is that it reveal a coordination of features not previously seen to be related.
Reply by author to discussion by Peter Hubral
Authors: Ursin Bjørn
Published: October 2002

I thank Peter Hubral for giving the correct formula for a point source which is mostly used in practice. His discussion shows that my results are only valid for cylindrical waves, that is, for a line source perpendicular to the line of measurement.
On: “The geomagnetic gradiometer” by H. A. Slack, V. M. Lynch, and L. Langan (GEOPHYSICS, October 1967, p. 877–892)
Authors: Steenland Nelson C.
Published: October 2002

The material in this paper was presented at the Annual Meeting in Houston in November 1966 and was enthusiastically received. Certainly many have looked forward to its publication. However, your attention is directed to some errors and subjective material which detract from the application of this new tool.
Reply by author to Discussion by William D. Hibler III
Authors: Ku C. C.
Published: October 2002

We would like to thank Dr. Hibler for clarifying several points about our paper. We also like to make the following comments.
Reply by the author to Th. Krey
Authors: Hubral Peter
Published: October 2002

I am grateful to Th. Krey for his derivation of formula (14) which is valid for the two‐dimensional case and which clearly shows what is actually obtained when subjecting primary reflections in neighbouring shot records to, what I called in the subject note, the process of normal wave stacking. Krey’s formula (14) confirms that the amplitude loss of primary shot record reflections, that is due to geometrical spreading, is removed by the normal wave stack as I stated in my short note. However, the formula also shows that the resulting event in the normal wave stack section does not, as I implied, provide a true amplitude reflection, which was correctly defined in my previous paper (Hubral, 1983) and in Krey’s short note (Krey, 1983). I am satisfied to see that Krey’s formula (14) however indicates that primary reflections in a normal wave stack section can very easily be transformed to the desired accurate true amplitude reflections with two simple corrections only.
Reply by the author to William C. Pearson
Authors: Hammer Sigmund
Published: October 2002

Mr. Pearson’s Discussion was received after answers by the author had been submitted to prior Discussions by Steenland and Herring. The essential criticisms of all three writers stem from two significant errors in the paper under discussion, namely (1) overstatement of the precision and resolving power of the Carson airborne gravity method based mainly on the 1981 test survey; (2) inadvertent errors in the dimensions of some of the data on Figure 8. An early attempt to publish a correction for item (1) (Hammer, 1982) has been delayed and is not yet in print. A revised Figure 8, redrawn to proper scale, is included as Figure 1 above in the Reply to Herring’s Discussion. Public criticism for my errors in this definitive paper on airborne gravity is useful.
Reply by the authors to M. Lane and T. Ulrych
Authors: Jin D. J.
Published: October 2002

We appreciate Lane and Ulrych’s interest and comments on our note and thank them for pointing out errors in our figures and subsequent interpretation of them. We reran the program that produced the original plots using identical data and found results consistent with those of Lane and Ulrych. Unfortunately, with the passage of time, many records have been discarded; we have not been able to find out what caused the results originally reported.
Reply by the authors to W. Harry Mayne
Authors: Gibson Bruce , Larner Ken
Published: October 2002

We agree that in some circumstances nonlinear sweeps can improve the signal‐to‐noise bandwidth of our processed data; a paper by Anstey (1980) gives an excellent review of what these improvements might cost. While the use of nonlinear sweeps has been advocated to combat earth attenuation, it is useful to keep in mind the limitations of its role in the battle. We can command the use of nonlinear sweeps in those situations where the source amplitude spectrum required to compensate for earth attenuation has a slope that is modest enough to be practically attainable in the field. Usually, however, that source function can be tailored to flatten spectral amplitude for only a restricted target zone. Great care is thus required in selecting the nonlinear sweep; the geophysicist must know the target zone well and must be careful not to sacrifice data quality in other time windows.
Reply by the author to F. Bryan Davies
Authors: Hammer Sigmund
Published: October 2002

Dr. Davies introduces signal‐processing theory into the argument. Although its pertinence to this discussion is quite marginal, it appears to be an interesting topic for a technical paper for publication in Geophysics. Other points by Davies call for my strong dissent.
Reply by the authors to H. W. Hardy
Authors: Snyder Donald D. , Fleming David B.
Published: October 2002

We thank Mr. Hardy for correcting us regarding the early history of the development of the continuous velocity logging method and Humble’s contribution thereto. The development of the acoustic log took place prior to the 25‐year period covered by our review. Unfortunately, the prefacing remarks regarding the early history of the acoustic tools omitted mention of the Humble developments and the paper presented by Mounce et al. (1951). We apologize for this oversight.
Reply by the authors to Peter Maliphant
Authors: Costain John K. , Çoruh Cahit
Published: October 2002

We offer the following in response to Peter Maliphant’s discussion of our paper.
Reply by the author to Colum Keith
Authors: Morsi M. H.
Published: October 2002

I would like to point out the following in reply to the discussion by Mr. Keith.
Reply by the authors to A. Walden and R. White
Authors: Ziolkowski Anton , Fokkema Jacob
Published: October 2002

We thank Andrew Walden and Roy White for their interest in our paper and their explanation of the practical whiteness assumption in deconvolution. As we understand it, what they are saying is this: True whiteness is not at issue when we are dealing with finite chunks of data. The only thing that matters is whether the statistical properties of a finite segment of the impulse response of the earth (what Walden and White call the reflection response [Formula: see text]) are those of a finite length sample from an uncorrelated sequence. Quite. And how are we going to find that out unless we first do the signature deconvolution with a known signature? In other words, we can only test this assumption in circumstances where we have no need of it.
On: “Apparent resistivity and diffusion velocity” by A. P. Raiche, and R. G. Gallagher (GEOPHYSICS, 50, 1628–1633, October 1985).
Authors: Lee Terry , Ignetik Rainer
Published: October 2002

Hankel transforms with simple integrands can be evaluated very efficiently without using Bessel functions. However, if simple closed forms exist, then direct numerical integration should be avoided. In general, the simple closed forms improve the accuracy and readily yield approximations at early and late stages of the transient. We draw attention to one such result, which is well known and would have facilitated the computation in this paper.
Response by D. M. Pai to the Reply by the authors
Authors: Pai D. M.
Published: October 2002

In consideration of the authors’ reply, I must clarify the following: This discussion is solely concerned with pointing out that the eigenstate expansion method in the first 4 pages of their paper [the material encompassing equations (1) to (17)] is essentially identical to my GHM/LEP method; this discussion is not at all concerned with the Chebychev expansion method in the latter part of their paper [the material following equation (18)], nor is this discussion concerned with advocating one method over another.
Discussion on the paper by A. Ziolkowski
Authors: Warwick John W.
Published: October 2002

I refer to A. Ziolkowski’s paper Why don’t we measure seismic signatures? (Geophysics, February 1991). It is evident that Ziolkowski does not have a very high opinion of the professional standards of his fellow, practicing exploration geophysicists.
Reply by the authors to B. Zhou
Authors: Saatcilar R. , Ergintav S. , Canitez N.
Published: October 2002

The algorithm for fast computation of numerical derivatives using real FFT is a brilliant idea. Due to the halving, it is certainly possible to compute the derivatives of real signals almost twice as fast as the conventional procedure. However, we do not agree with Zhou about the achievement of the same performance of the fast Hartley transform.
Reply by author to D. Blair
Authors: Tang Xiao‐Ming
Published: October 2002

I welcome the comments of Dane Blair to my paper on waveform inversion of bar waves. These comments certainly point out the complexity of wave propagation in bars. In the development of the inversion technique, I had performed waveform analyses for cylindrical bars. It is worthwhile to present some results of these analyses in order to emphasize the condition under which the inversion technique is applicable.
Response by Mark Graebner to the reply by the author
Authors: Graebner Mark
Published: October 2002

I thank Dr. Hale for his response. I would like to make an additional comment in order to remove any remaining ambiguity. Dr. Hale is correct in stating that in the descriptive text of their paper, the authors never explicitly claimed that the diving wave had a frequency independent π/2 phase shift. I should have been more precise in stating that my observation about the frequency independent phase π/2 shift was a deduction based on equation (1). Since Dr. Hale has stated that the omission of sgn ω in equation (1) is the result of an oversight, then my deduction and speculation are invalid. I hope that this discussion will keep equation (1) from leading others astray.
Reply by the author to N. C. Steenland
Authors: Skilbrei Jan R.
Published: October 2002

Steenland writes that my statement in paragraph three of my Introduction is not correct. My statement is, “In most geological situations, and particular over sedimentary basins, the interpreter is unable to recognize bodies with limited depth extents.” It was implicit that I meant bodies within the basement with limited depth extents because the title of the short note is: “The straight‐slope method for basement depth determination revisited.” I believe that most interpreters agree with my statement. However, when it comes to recognizing intrasedimentary volcanics, I agree that it is often easy to distinguish these types of anomalies from those anomalies that are due to sources which exist within the basement when the volcanic rocks within the sediments are far removed above the basement.
On: “Regularizing 3‐D data sets with DMO” (A. Canning and G. H. F. Gardner, July–August 1996 GEOPHYSICS, 61, p. 1103–1114)
Authors: Mohan N. L.
Published: October 2002

It is quite interesting indeed to learn Canning and Gardner’s (1996) mathematical approach to 3‐D DMO processing, which I believe essentially deals with scaling in every aspect of the migration process.
Reply by the authors to N. L. Mohan
Authors: Gardner Gerald H. F.
Published: October 2002

We can honestly say that we inadvertently missed the papers by Mohan et al. cited in the discussion and assure the correspondents that there was no intention to deny them credit for their work.
Reply by the authors to the discussion by K. Wapenaar
Authors: Ehinger Andreas , Lailly Patrick , Marfurt Kurt J.
Published: October 2002

In our paper, the equalities [Formula: see text] (1) [Formula: see text] are of central importance for the mathematical correctness of our proposed common offset wave‐equation migration algorithm. In his comment, Kees Wapenaar outlines two “concerns” regarding these equalities.
Reply by the authors to the discussion by C. E. Corry
Authors: Livelybrooks Dean , Smith J. T.
Published: October 2002

We would like to thank Dr. Corry for his provocative comments on our paper written with the late Marianne Mareschal (Livelybrooks et al., 1996). The problem of spatial aliasing addressed by Corry is, indeed, a very serious concern, as small‐scale inhomogeneities can result in real multiplicative shifts (“statics”) in measured apparent resistivities (Larsen, 1977). For this reason, we have concentrated our efforts on modeling and presenting results based on the magnetotelluric (MT) impedance phases ϕ, which are unaffected by such static shifts. However, the mapping of frequency onto Schmucker’s (1970) effective depth z*, used in our phase “pseudosections” (Figure 7) does depend on our estimates of the individual site statics.
Reply by the authors to the discussion by Gijs J. O. Vermeer
Authors: Sun Y. , Schuster G. T. , Sikorski K.
Published: October 2002

The authors appreciate O. Vermeer’s interest in our paper. Issue: The dimensionality is low when fold is taken into account: “For N‐fold data, the actual effort consists of N 2‐D integrations,…, followed by simple summations of the single‐fold results.”
Reply by the author to the discussion by Hualin Zeng and Deshu Xu
Authors: Pawlowski Robert
Published: October 2002

I am gratified by the interest of Hualin Zeng and Deshu Xu in my work on preferential continuation. I should mention that the method owes its origin to concepts related to the subject of Wiener regional‐residual separation filtering — ideas and theory that were first introduced to me years ago by Richard O. Hansen.
Electromagnetic induction in a layered earth with arbitrary anisotropy
Authors: Yin C. , Maurer H.‐M.
Published: October 2002

The traditional model for interpreting geoelectromagnetic data is a layered isotropic earth, but in regions with distinct dipping stratification, this model is inadequate. In this case, it is useful to extend the model to a layered earth with general anisotropy, assigning each layer a symmetrical [Formula: see text] resistivity tensor. The electromagnetic (EM) field is presented by two scalar potentials which describe the poloidal and toroidal part of the magnetic field. After stripping off the horizontal coordinates by a 2‐D Fourier transform, we obtain two coupled ordinary differential equations in the vertical coordinate. To stabilize the numerical calculation, the wavenumber domain is divided into two parts. For small wavenumbers, the EM field is calculated through continuation from layer to layer, where the tranverse isotropy requires an extra treatment because the two potentials are in this case uncoupled and the requirement for the field continuation is not satisfied. To calculate the EM field for greater wavenumbers, a Green’s function is applied. The apparent resistivities in the controlled source audio‐magnetotellurics (CSAMT) method and the EM field in the earth are calculated for this model. From both EM fields and the apparent resistivities, one can clearly recognize the effect of the electrical anisotropy of the earth on the CSAMT measurements.
Unification of Euler and Werner deconvolution in three dimensions via the generalized Hilbert transform
Authors: Nabighian Misac N. , Hansen R. O.
Published: October 2002

The extended Euler deconvolution algorithm is shown to be a generalization and unification of 2‐D Euler deconvolution and Werner deconvolution. After recasting the extended Euler algorithm in a way that suggests a natural generalization to three dimensions, we show that the 3‐D extension can be realized using generalized Hilbert transforms. The resulting algorithm is both a generalization of extended Euler deconvolution to three dimensions and a 3‐D extension of Werner deconvolution. At a practical level, the new algorithm helps stabilize the Euler algorithm by providing at each point three equations rather than one. We illustrate the algorithm by explicit calculation for the potential of a vertical magnetic dipole.