bluuebunny/crossref_metadata_2025 huggingface dataset:
GRAVITY SURVEY OVER A GULF COAST CONTINENTAL SHELF MOUND
Authors: Nettleton L. L.
Published: October 2002

A gravity survey of 50 stations over one of the mounds near the edge of the Continental Shelf developed a strong, roughly circular negative anomaly. The gravity minimum is similar in magnitude and lateral extent to those over large salt domes in the on‐shore and explored offshore areas of the Gulf Coast. An approximate quantitative evaluation shows that the minimum can be accounted for quite completely by a large shallow salt dome. The shallow part of the dome is approximately co‐extensive with the topographic feature and it seems quite certain that this particular mound is genetically, related to a salt dome. If other similar mounds also are salt domes, the area of domes off the Louisiana coast is approximately doubled over that presently known from commercial geophysical exploration.
IRREGULAR MAGNETIC ACTIVITY IN NORTHERN CANADA WITH SPECIAL REFERENCE TO AEROMAGNETIC SURVEY PROBLEMS
Authors: Whitham K. , Loomer E. I.
Published: October 2002

An investigation of the diurnal and seasonal characteristics of irregular magnetic activity in northern Canada, using two indices of disturbance, shows that in general the K index provides a reliable but smoothed measure of short period activity. Two peaks of activity are evident, a day‐time peak, dominant inside the polar cap, and a night peak, dominant south of the auroral zone. The latter occurs within one hour of local geomagnetic midnight at four Canadian observatories, whereas the day‐time peak occurs progressively later at higher latitudes. The maximum activity occurs in the equinoxes at latitudes near the auroral zone, and during the summer solstice at very high latitudes. Measurements of range at the most disturbed observatory suggest that aeromagnetic surveying in high latitudes is in general feasible, but that for accurate reconnaissance work it is very advantageous to plan operations, so far as conditions permit, taking account of the systematic diurnal variation of disturbance. It is shown that errors of about one half the assumed diurnal change between base lines will occur and sufficient data is given to allow approximate predictions of the optimum length of flight lines.
PATENTS IN THE SERVICE OF GEOPHYSICS
Authors: Ritzmann O. F.
Published: October 2002

This paper presents a general discussion of the significance of patents and how they affect geophysical operations. Patents have become an important part of our technical literature. In spite of the exclusive character of the patent grant, the geophysical exploration art has been very little handicapped by patents or patent controversies. The inventions disclosed in patents have served as stepping stones for advancing the practical application of all branches of physics to exploration techniques.
A SLIDE RULE FOR NEAR‐SURFACE REFRACTION PROBLEMS
Authors: Knox W. A.
Published: October 2002

The paper describes a slide‐rule useful for determining reflection time corrections for multilayer weathering problems. It is also useful to the seismic reviewer in computing a correction factor for data which have been reduced by overly‐simplified corrections.
SOME OBSERVATIONS ON ROCK MAGNETISM
Authors: Howell Lynn G. , Martinez Joseph D. , Statham E. H.
Published: October 2002

It seems that in general the plane of maximum magnetic susceptibility lies in the bedding plane for sediments and in the plane of foliation for metamorphic rocks; there is, also, a tendency for the remanent vector to lie in the plane of foliation in the latter. In the case of chemical deposits, the question is raised as to whether the hematite crystal growth is controlled by the magnetic field. Since pure hematite crystals are paramagnetic along the ternary axis, the remanent vector lies in the basal plane perpendicular to this axis, which being the plane of ferromagnetism, is also the plane of maximum susceptibility. We have investigated chemically deposited hematite in the Clinton iron ore of Silurian Age. Although the remanent vector lies close to the plane of maximum susceptibility, this plane, unfortunately, is also the bedding plane. Several other hematite‐bearing formations show a direction of magnetization close to the bedding plane. Measurements of magnetization and susceptibility anisotropy of samples cooled below the transition temperature for hematite have been made with no conclusive results other than indications of the presence of hematite in some cases. Samples from the Hazel formation of pre‐Cambrian Age have been investigated. The planes of maximum susceptibility for this slightly metamorphosed red bed dip at various angles, and thus a system of microfractures containing magnetic material is suggested as a possible explanation. Pole locations for the Clinton iron ore and the Hazel are presented.
SEISMIC SURVEY OF SINAI AND THE GULF OF SUEZ
Authors: Masson Pierre A. A. H. , Agnich F. J.
Published: October 2002

Severe obstacles are present to increase the difficulty of seismic operations in the Gulf of Suez area. A program combining land seismic work, semi‐marine exploration over a reef zone, and rapid offshore reconnaissance is described. The results of each are illustrated, and the value of a rapid marine survey in guiding more detailed work on land is emphasized.
ELIMINATION OF SECONDARY PRESSURE PULSES IN OFFSHORE EXPLORATION (A MODEL STUDY)
Authors: Knudsen William C.
Published: October 2002

The behavior of the gas bubble generated by explosive charges fired below the ocean’s surface has been studied by means of a scale model. The motion of the bubble was recorded using a high‐speed camera. A small pressure detector was used to record the pressure variation near the bubble. The behavior of the bubble generated by the equivalent of a 15‐lb charge was studied with the bubble subjected to the following boundary conditions: a single charge at various depths below the liquid surface, two charges on a vertical axis at various separations and various depths, two charges on a horizontal axis at various separations, a single charge at various separations below a solid plate, and a single charge at various separations to the side of the solid cylinder. Of these methods, the only one which appeared promising was the location of two charges on a vertical axis with both charges within 20 ft of the surface.
SOUND VELOCITY vs. TEMPERATURE IN WATER‐SATURATED SEDIMENTS
Authors: Shumway George
Published: October 2002

Sound velocity vs. temperature was measured in a continental shelf silt, a calcareous ooze, a deep‐sea red clay, a continental slope clay, and a quartz sand using a resonant chamber technique. The temperature effect on these water‐saturated sediments was approximately the same as for water alone; this similarity to water behavior would be expected inasmuch as the compressibility of a water‐sediment mixture is dominantly due to the relatively large water compressibility.
MAXIMUM GRAVITY EFFECT OF CERTAIN SOLIDS OF REVOLUTION
Authors: Duska Leslie
Published: October 2002

This paper presents formulae for calculating the gravitational attraction, at points on their central vertical axes, of several solids of revolution. Such calculations are sometimes desirable to find the maximum anomalies which may be caused by geologic bodies which are assumed to have the approximate shape of a solid of revolution. A reasonable set of density differences must be used in such preliminary gravity calculations to find the limits of the anomalies to be expected. A table of formulae is presented.
GENERATION OF SEISMIC WAVES BY WEIGHT DROPS
Authors: Domenico S. N.
Published: October 2002

A series of experiments designed to evaluate the weight‐drop technique was conducted in West Texas. These tests demonstrated the general nature of the seismic waves generated by a weight drop and the effectiveness of compositing drops in providing useful reflection information. At the first of two test sites discrete waves from single drops consisted of a refracted wave, an air‐earth coupled wave, reflected wave segments, and fragmentary waves which were likely dispersive surface waves. A 72-seismometer array provided appreciably more reflected wave segments on records from single drops and also on records from the composite of these drops than did a single seismometer. Additional testing revealed that records prepared from weight drops along three parallel lines 100 ft apart recorded at the same seismometer station are appreciably different. Compositing of the drop lines in general did not provide reflections superior to the best on individual lines. At the second test site record quality appeared significantly superior to that at the first site. Discrete waves on records from single drops recorded by a 36-seismometer array were of the same types as those observed previously. However, the air‐earth coupled wave, prominently developed at the first site, did not appear. Compositing of drops provided two prominent reflections which were correlatable over a 5-mile traverse.
RESULTS OF AIRBORNE MAGNETOMETER PROFILE FROM BROWNSVILLE, TEXAS, TO GUATEMALA CITY
Authors: Agocs W. B.
Published: October 2002

An airborne magnetometer profile was obtained in the course of ferrying an aircraft from Brownsville, Texas, to Guatemala City, Guatemala, via Tampico, Tuxpan, Veracruz, Tuxtla, Tapachula and Tequisate, a distance of slightly over 1,000 miles. The profile indicates that the basement depth is on the order of −20,000 ft along the eastern coast of Mexico, except for the Tamualipas uplift. In southern Mexico and Guatemala the basement level rises to approximately −10,000 ft, and it is exposed in the extreme southern part of Mexico. Several major fault systems and intra‐sedimentary volcanic horizons are indicated by the profile. Bouguer anomaly data, supplied by Dr. G. P. Woollard, show surprisingly good agreement with the sub‐surface structure as determined from the magnetics. Gross errors in the depth determinations from the single profile may arise due to simplifying assumptions that the trends are transverse to the direction of the profile and that they are elongate. The excellent correlation between the structures determined from the magnetics and the Bouguer gravity anomalies lends confidence to conclusions drawn from these indications, and this should permit further analysis of the gravity.
SCATTERING OF COMPRESSION WAVES BY SPHERICAL OBSTACLES
Authors: Knopoff Leon
Published: October 2002

The scattering of plane P waves by a spherical obstacle is formulated. A calculation is given for the special case of scattering by a perfectly rigid sphere in which the medium outside has a Poisson’s ratio of [Formula: see text]. The range of sizes of obstacles used in the calculation includes radii very small compared with wave length and radii comparable to the wave length. For incident P waves, scattered P and S are computed with shifts in time phase occurring in both with respect to the incident beam. For small obstacles, the scattered S wave is generally broadside to the scattered P‐wave beam.
WATER REVERBERATIONS—THEIR NATURE AND ELIMINATION
Authors: Backus Milo M.
Published: October 2002

In offshore shooting the validity of previously recorded seismic data has been severely limited by multiple reflections within the water layer. The magnitude of this problem is dependent on the thickness and the nature of the boundaries of the water layer. The effect of the water layer is treated as a linear filtering mechanism, and it is suggested that most apparent water reverberation records probably contain some approximate subsurface structural information, even in their present form. The use of inverse filtering techniques for the removal or attenuation of the water reverberation effect is discussed. Examples show the application of the technique to conventional magnetically recorded offshore data. It has been found that the effectiveness of the method is strongly dependent on the instrumental parameters used in the recording of the original data.
SEISMIC REFLECTIONS FROM LAYERING WITHIN THE PRE‐CAMBRIAN BASEMENT COMPLEX, OKLAHOMA
Authors: Widess M. B. , Taylor G. L.
Published: October 2002

Reflections from within the pre‐Cambrian basement complex were recorded in the vicinity of the Wichita Mountains in southwestern Oklahoma. The reflections, of good quality and persistence, depict a section in excess of 20,000 ft of igneous rocks that appears like a seismic section of sedimentary formations. A well in the area drilled 4,000 ft of this pre‐Cambrian section, encountering alternating layers of silicic and gabbroic igneous rocks exhibiting high contrast in density. Pre‐Cambrian outcrops of much of the Wichita Mountains, comprising comparable types of rocks, display sheet‐like, gently dipping layers, some of which persist for several miles. The seismic reflections are thus produced by the igneous layers of differential acoustic properties. An abrupt change of direction of dip occurring at about mid‐depth of the seismic section precludes the possibility that the seismic events are multiple reflections.
THE MISSISSIPPIAN IN THE ALBERTA PLAINS AND THE REFLECTION SEISMOGRAPH
Authors: Blundun G. J.
Published: October 2002

The eroded Mississippian surface is the major unconformity in the province of Alberta. To map its erosional highs and lows is most important, because the Mississippian may be productive of hydrocarbons or may cloak the attitude of deeper sediments from which production is sought. This paper deals with the methods of presentation of reflection seismic data to that end, together with a suggested recording instrument technique. Some of the interpretive problems, and the possible significance of Mississippian porosity on the acoustic impedance of its reflection are mentioned. Maps of similar data, one geological and the other reflection seismic, are presented for comparison. The former is obtained from drilled wells and the latter from reflection shooting performed prior to drilling.
AUTHORS’ REPLY
Authors: Zietz Isidore , Peselnick Louis
Published: October 2002

We disagree with Treitel's comment that our attenuation coefficient [Formula: see text] is not the same as the attenuation coefficient, α, as used by him.
USE OF PORTABLE PLAYBACK SYSTEM EFFECTS A SAVING
Authors: Hall T. O.
Published: October 2002

Since developing and operating a portable magnetic playback system which removes electrically the static and dynamic corrections, a considerable saving in preparing corrected record sections has been effected. The field playback machine can handle only a limited number of magnetic tapes.
SEISMOGRAM SYNTHESIS INCLUDING MULTIPLES AND TRANSMISSION COEFFICIENTS
Authors: Wuenschel P. C.
Published: October 2002

Synthetic seismograms that include multiples and transmission coefficients have been obtained by solving the boundary value problem for the multilayered half‐space exactly for the plane wave case at normal incidence. The computations of four seismograms of interest have been programmed for the IBM 704. The seismograms differ in location of source and detector, i.e., whether buried or at the surface of the half‐space and whether or not this surface is a stress‐free surface. Evaluation of the computer programs prior to synthesizing seismograms is accomplished by comparing computer with analytical solutions of simple problems. The significance of multiples to the total reflected signal depends on the vertical distribution of acoustic impedance. For small contrasts in acoustic impedance distributed throughout the section, multiples are relatively insignificant. For moderate contrasts similarly distributed, multiples can produce discrete events, cause phase shifts in large amplitude direct reflections, and alter the frequency of weak direct reflected signal. If the near‐surface contrasts are large, then multiples within these layers can mask a direct reflected signal from depth by producing “ringing” or “wave training.” The present analysis gives a more reasonable explantion of “ringing” records than has been given heretofore. It is evident when comparing synthetic seismograms, including multiples with field seismograms, that the predicted multiple contribution in many cases is greater than actually present, indicating that the mathematical model on which computation is based is not yet adequately realistic.
OUTLINING OF SALT MASSES BY REFRACTION METHODS
Authors: Musgrave A. W. , Woolley W. C. , Gray Helen
Published: October 2002

Short surface‐to‐surface refraction lines define the top of a shallow salt dome previously located by reflection methods. A map is made from the results of a number of longer refraction lines radiating from the center of the dome. The increased accuracy of this system is primarily dependent upon the accurate determination of velocities and distances. Flank wells are used for further refraction shooting which yield more accurate velocity information and more detailed salt profiling. A map from this integrated information permits exploitation at a minimum risk, even though every location is essentially a wildcat.
TESTS OF AN AIRBORNE GRAVITY METER
Authors: Nettleton L. L. , LaCoste Lucien , Harrison J. C.
Published: October 2002

Gravity measurements have been made in an airplane and a contour map using 20 mg interval constructed for 12,000 ft elevation. The LaCoste and Romberg instrument used is similar to that recently tested on a surface ship. The meter was installed in a B-17 aircraft equipped with APR (precision radar altimeter) and aerial mapping cameras for the accurate navigation needed for determination of the centrifugal (Eötvös) and elevation corrections. A series of nine lines over the Imperial Valley gave results believed to be accurate to about 10 mg or better as indicated by (1) the general consistency of the contour map and its similarity to a free air gravity map drawn from ground data, (2) repeat observations over almost the same courses, (3) agreement of independent values at line crossings (with Eötvös correction differences of as much as 2,000 mg), and (4) agreement with values calculated from ground gravity stations. Short period disturbances due to accelerations of the airplane are averaged over a certain time interval. This results in an “uncertainty principle,” in that the accuracy of observation increases as this time interval is lengthened, but details of the gravity variation are lost due to the increased distance traveled during each measurement. The values reported are for an averaging time of approximately three minutes corresponding to a travel distance of about ten miles. The quality of the results is adequate for geodetic purposes and possibly for certain regional geophysical problems.
AUTHOR’S REPLY
Authors: Howell B. F.
Published: October 2002

Because Fourier analysis is so well known, no attempt was made in the paper to go into detail on its theory. Sengbush’s concept of amplitude density in the case of integral analysis is clearer than the way this process is described in the paper.
DISCUSSION ON THE ELECTROSEISMIC EFFECT
Authors: Kindij Eugene
Published: October 2002

I would like to offer the following comment on the paper The Electroseismic Effect by Martner and Sparks in the April 1959 issue of Geophysics.
PHOTOGRAMMETRIC DETERMINATION OF ELEVATIONS FOR REGIONAL GRAVITY SURVEYS
Authors: Kinoshita W. T. , Kent B. H.
Published: October 2002

Precision photogrammetric methods were used to obtain elevations of gravity stations in an area in the southern Sierra Nevada and in west‐central Idaho. In both areas, relief is more than 3,000 ft and in the Idaho area there is also a dense cover of forest and brush. In addition to photogrammetric determinations of gravity station elevations in the Idaho area, 55 photogrammetric elevations were determined for ground points that had been established previously by topographic surveys. A statistical analysis of the differences between photogrammetric and known ground elevations indicated that the mean of the errors is −0.2 ft; 71 percent of the photogrammetric errors are included within one standard deviation (3.4 ft), and 96 percent of the errors are included within twice the standard deviation (6.8 ft). The photogrammetric combination used in both areas was the multiplex stereoscopic plotting instrument and 1:49,500 scale photography taken with a 6-inch focal length lens. It is probable that smaller standard deviations can be obtained by combining larger scale photography with more precise stereoscopic plotting instruments.
PLANE COMPRESSIONAL VOIGT WAVES
Authors: Collins Francis
Published: October 2002

The Voigt wave equation, long considered a possible mathematical model for seismic waves, was extensively studied in 1943 by Norman Ricker, who developed an asymptotic solution applicable at sufficiently large distances from the shotpoint. Ricker’s solution does not agree with his field results (1953) in all respects. For example, Van Melle (1954) has shown that Ricker’s wavelets decay too rapidly with distance to be consistent with the experimental data. This particular difference between theory and observation may arise from the form of the wave source implicitly assumed by Ricker, a doublet impulse of displacement. A single impulse of pressure seems a more reasonable first approximation to the shot. For this source a complete solution for plane waves is developed, valid for all distances and times. A method similar to Ricker’s is then outlined for obtaining an asymptotic solution suitable for computations at large distances. The wavelets from the pressure impulse do not decay as rapidly as Ricker’s doublet displacement solutions. This is a move toward better agreement with experiment. On the other hand, the pressure impulse wavelets have only a single lobe, a definite move away from the observations. There is some reason to believe, however, that the corresponding spherical waves would be more oscillatory than the plane waves. More mathematical work is needed for further tests of the Voigt solid as a theoretical model for earth waves. The next step suggested is the computation of spherical waves from a pressure impulse.
SCATTERING OF ELASTIC WAVES BY SMALL INHOMOGENEITIES
Authors: Miles John W.
Published: October 2002

Rayleigh scattering theory is extended to determine the perturbation on an arbitrarily prescribed elastic wave field produced by small inhomogeneities in an otherwise homogeneous, isotropic medium. The general result is applied to the specific problems of the scattering of both plane P- and S-waves. It is found that a change in compressibility acts at a distance as a simple source and a change in density as a dipole, as in the acoustical problem, while a change in shear modulus contributes both simple‐source and quadrapole fields.
To: “LESSONS IN SEISMIC COMPUTING”
Authors: Geyer R. A.
Published: October 2002

The following errata represent the combined efforts of Messrs. William J. Zwart, John E. Owen, and Jerry Fillebrown, who gave so very generously of their time to compile this list. The Special Editor of this volume regrets that their excellent co‐operation had not been made available to him at a time when it was most needed, namely, prior to the publication.
FOREWORD
Authors: Archie G. E.
Published: October 2002

A symposium on well logging, arranged by the Program Chairman, Mr. T. H Braun, with the assistance of Mr. H. M. Johnson, was held at the 29th Annual Meeting of the Society of Exploration Geophysicists, Los Angeles, California, November 9–12, 1959.
WELL LOGS IN CARBONATE RESERVOIRS
Authors: Chombart L. G.
Published: October 2002

Modern well logs can play an important, often decisive role in the evaluation of carbonate reservoirs, and in well completions therein. To do so however, the logs must be selected and interpreted with due regard for the specific rock “types” and pore structures encountered by each well. Indeed, the basic condition stated applies to all evaluation and completion techniques now in use or conceivable. It becomes vitally important in carbonate reservoirs, however, because of their extraordinary heterogeneity. Characteristically, these reservoirs exhibit significant, often extreme, and always unpredictable variations in pore structure, pore size distribution and fluid content, within very short distances, in any direction. To cope with such a reservoir, an evaluation and logging program adhering to certain principles is most likely to yield valid results and insure better completions and greater ultimate recovery, at minimum cost. First, in every well, the cuttings or cores should be described precisely as to rock types and depths. Second, any techniques used should permit the largest possible number of determinations through the reservoir, so that any existing relationships between pore size distribution, porosity and water saturation may be established on a sound statistical basis. Among logging devices, “focusing” tools meet this requirement best. Third, starting very early in the development of the reservoir, the latter should be cored and logged in key wells, the cores subjected to capillary pressure and other petrophysical tests, and all potentially diagnostic logs run and analyzed in the light of all other data. Fourth, in non‐key wells, the logging program should include only those logs proved most reliable in the key wells for the pore structures encountered and the data desired (usually porosity, water saturation, net ft of pay).
On: “PHOTOMECHANICAL METHOD OF FREQUENCY ANALYSIS OF SEISMIC PULSES”
Authors: Moody Robert C.
Published: October 2002

I would like to add an observation to the paper, “Photomechanical Method of Frequency Analysis of Seismic Pulses,” Geophysics, v 24, n. 4, by B. F. Howell, et al.
A NOTE ON CHEMICAL MAGNETIZATION OF ROCKS
Authors: Howell Lynn G. , Martinez Joseph D. , Frosch Alex , Statham E. H.
Published: October 2002

Previously obtained magnetic data for Silurian samples from Alabama are presented. Both the remanent vector and the plane of maximum susceptibility lie close to the bedding plane for this ore containing chemically formed hematite. Now, X‐ray measurements show preferred crystal orientation of the hematite in agreement with the susceptibility anisotropy. On the other hand, samples from the Tertiary in Texas containing hematite resulting from chemical alteration show no appreciable preferred crystal orientation or susceptibility anisotropy. Thus, in this case there is no obvious relationship between the crystal growth of the hematite and the direction of the earth’s magnetic field. It is suggested that the stresses probably played a role in the crystal orientation in the Silurian iron ore. An interesting chemical magnetization took place in the Weches of Tertiary age in Texas. The unaltered glauconite in the Weches is reversely magnetized whereas the limonite derived from the glauconite by weathering is normally magnetized.
VARIATION OF ELECTRICAL CONDUCTIVITY WITH DEPTH BY THE MAGNETO‐TELLURIC METHOD
Authors: Niblett E. R. , Sayn‐Wittgenstein C.
Published: October 2002

Apparatus has been installed at the Dominion Observatory Research Station at Meanook, Alberta, for the continuous recording of earth potentials. The theory due to Cagniard (1953) and others, in which relative amplitudes of horizontal components of electric and magnetic fields are used to interpret the sub‐surface structure, is applied in a modified form, to data from the Meanook records. Values of electrical conductivity between depths of 10 km and 100 km are estimated, and found to vary roughly between [Formula: see text] and [Formula: see text] e.m.u.
MAGNETIC AND TELLURIC CURRENT DISTURBANCES IN ALASKA
Authors: Wescott E. M.
Published: October 2002

Much of Alaska lies in or near the auroral zone, where magnetic and telluric current disturbances are large compared to those at lower geomagnetic latitudes. Pronounced and different diurnal variations of disturbance are evident from analysis of K indices from Barrow, College, and Sitka magnetic observatories. The quietest period for magnetic or electrical surveying is the late morning and afternoon hours locally. Recordings of telluric current disturbances can be used as a sensitive indicator of ionospheric activity. The large amplitude and rich frequency spectrum of the telluric currents suggests their use as a prospecting tool in Alaska.
AN ANALYSIS OF THE OBSERVED TIME DISCREPANCIES BETWEEN CONTINUOUS AND CONVENTIONAL WELL VELOCITY SURVEYS
Authors: Gretener P. E. F.
Published: October 2002

Discrepancies between conventionally obtained times and the integrated continuous velocity curves are analyzed (Shell tool only). It is found that these discrepancies may be ascribed to a random scatter and a systematic deviation, the integrated continuous curves being short. Possible causes of these discrepancies are discussed but no final explanation can be offered.
GRAVITY PROSPECTING FOR REEFS: EFFECTS OF SEDIMENTATION AND DIFFERENTIAL COMPACTION
Authors: Yungul S. H.
Published: October 2002

The classical questions are: “Do reefs create recognizable gravity anomalies?” “If and when they do, then what causes these anomalies?” To find the answers to these questions, first a study of the case histories was made. It indicated that deeply buried, “isolated,” organic reefs frequently create recognizable but “mysterious” gravity anomalies, and that there is no evident direct relation between the reef mass and the gravity anomaly. To find out the causes of these anomalies, the field of investigation proved to be so large that this paper could be entitled “a tentative density analysis of the sedimentary subsurface.” The reef mechanism and the depositional processes are such that there is a concentration of sand in the over‐reef section. Densities in clay and sand mixtures were investigated in terms of composition and depth of burial. The sand concentration alone is capable of creating shallow positive and deep negative density contrasts sufficient to account for the major part of the gravity anomaly. The gravity effect of a hypothetical reef was calculated. The result was very much like those actually observed. The gravity anomaly depends mainly on what has happened after the reef was buried, and not on the contrast at the reef level.
EFFECT OF POROSITY, GRAIN CONTACTS, AND CEMENT ON COMPRESSIONAL WAVE VELOCITY THROUGH SYNTHETIC SANDSTONES
Authors: Viksne Andris , Berg Joseph W. , Cook Kenneth L.
Published: October 2002

Compressional wave velocities through 36 synthetic sandstone cores were measured and related to several of their physical properties, namely, porosity, manufacturing pressure, grain contacts, and amount of cement. The cores were composed of Ottawa sand grains averaging 0.12 mm in diameter and commercial Grefco cement; the manufacturing pressure was varied from 4,000 to 10,000 psi; the cement content by volume was varied from 10 to 100 percent; the effective porosities ranged between 2.1 and 30.4 percent; and the compressional wave velocities ranged between 9,170 and 17,420 ft.sec. All velocity measurements were taken at room temperature and atmospheric pressure using cores that contained only air in the pore space. The results are presented in graphic form, showing the relationship between the compressional wave velocity and manufacturing pressure, porosity, and cement content. For Grefco cement contents between 10.0 and 17.5 percent, the compressional wave velocity is controlled by the manufacturing pressure and the porosity. A change in manufacturing pressure of 1,000 psi changed the compressional wave velocity by one percent for cores having porosities of about 23 percent and by about 3 percent for cores having porosities of about 28 percent. A decrease in porosity of one percent increased the velocity by an average of 1.4 percent for effective porosities between 23 and 26 percent. The velocity is also dependent, to a great extent, on the number of grain contacts which is intimately associated with the manufacturing pressure, and the cement content which is intimately associated with the porosity. For cement contents greater than 17.5 percent by volume, the sand grains float in the cement, and the analogy between the synthetic sandstone cores and natural sandstones is questionable.
INDUCED POLARIZATION IN ELECTROLYTE SATURATED EARTH PLUGS
Authors: Henkel J. H. , Collins T. C.
Published: October 2002

This paper describes the results of some studies of the dependence of induced polarization and of the formation resistivity factor upon solution concentration in saturated porous plugs. Two theories based upon two different simple models are developed. The first treats induced polarization as an electric dipole polarization occurring at the surface of clay particles. It is a relaxation theory that does not lead to results agreeable with experiments. The second theory treats induced polarization as a concentration polarization which is induced at solution‐clay surfaces when current flows across the surfaces. The second theory is more successful than the first in two ways: (1) it leads to a time dependence more consistent with the experimental decays; (2) it leads to equations involving the resistivity of the saturating solution [Formula: see text] which are also more consistent with experiments.
A SIMPLE INTEGRAL TRANSFORM AND ITS APPLICATIONS TO SOME PROBLEMS IN GEOPHYSICAL INTERPRETATION
Authors: Roy A. , Jain S.
Published: October 2002

A simple integral transform, defined by [Formula: see text], where F(x, y) represents the measured geophysical field and x and y are suitably chosen directions, has been used for formulating convenient interpretation techniques to some geophysical problems that are normally not amenable to easy quantitative interpretation. Some synthetic numerical examples are given.
AN ANALOG SEISMlC CORRELATOR
Authors: Tullos F. N. , Cummings L. C.
Published: October 2002

An analog computer has been built to compute the cross‐correlation coefficients of multi‐trace seismograms. The evaluation program has shown that the computer has greater accuracy than is normally required to compute the cross‐correlation functions of short samples of data. Points on the correlation curves are computed and plotted at the rate of approximately 50 points per minute. Scanning is in difference of arrival times (Δt) across the record, with increments of [Formula: see text] to 16 millisecond. The correlation process is completely automatic with the exception of normalization, which is approximated by holding the total average signal power constant with a ganged attenuator. Analysis of synthetic and actual seismic data indicates that the correlation will be an interpretational aid in areas where the data are poor.
SPACE EXPLORATION, A CONTINUING EFFORT
Authors: McMahon Allen J.
Published: October 2002

Space exploration is carried on for political, scientific, military, economic, and psychological reasons. Today, sound, practical reasons exist to continue and extend the use of satellites to improve methods of meterology, communications and navigation; to name only a few. Scientific discoveries accruing from sound, well-planned space exploration, and their influence on American industries, can only dimly be forseen. Further exploration effort promises to increase and emphasize the role played by the sun in a wide variety of human activities. The satellite Explorer VI and the space probe Pioneer V have extended communications to ranges of 20,000,000 miles; have increased scientific‐knowledge of the properties of the exosphere with respect to magnetic fields and energetic charged particles. The space between the planets, far from being empty, is repeatedly being disturbed by great clouds of ionized gas called plasma. These are examples of the unusual and intriguing problems awaiting space exploration. Solution of these and unknown problems can best be achieved by continuous and diligent effort. The part played by the United States in space exploration has been excellent to date. The long range pay‐off of such superb effort can scarcely fail to enrich this country, initially, militarily and eventually economicallly.
ELIMINATION OF SECONDARY PRESSURE PULSES IN OFFSHORE EXPLORATION
Authors: Knudsen William C.
Published: October 2002

The behavior of a gas bubble generated by detonating an explosive below the surface of the ocean and located centrally in a perforated sphere, perforated pipe, and solid‐walled pipe has been studied by means of a scale model. The motion of the bubble was recorded using a high speed camera, and the pressure variations were recorded using a small pressure detector. The behavior of the gas bubble when surrounded by a perforated sphere has also been analyzed numerically. The model results showed that significant reduction in secondary pressure pulse amplitude was effected by all three devices, but the perforated sphere was the most effective. That enclosing the gas bubble in a perforated sphere would effectively eliminate the secondary pressure pulses was also verified by the numerical solution of the motion. Design criteria for a perforated sphere are presented.
GRAVITY SURVEYS IN HEAVY SAND DUNES
Authors: Colley G. C.
Published: October 2002

The paper discusses the problems involved in desert surveys under the headings of “Access” and “Correction of Gravity Data.” The types of sand formation are described. In planning a survey the importance of reconnaissance, aerial photographs, and the provision of suitable equipment are stressed. The advantages and disadvantages of motor transport, light aircraft, helicopters, and the operational procedures used with each are discussed. Terrain corrections are necessary on most stations and suggestions are given for their determination. The different densities of the dune sand and the “floor” introduce a problem in the determination of the Bouguer Correction. A method is given whereby close estimates of the sand thickness can be found by contouring on the “floor” or on minimum elevations. The resulting Bouguer values after computation are as regular as those found in areas of small elevational changes.
THE USE OF PHOTO‐RESISTIVE CELLS AS LOSSER ELEMENTS IN A TRANSISTORIZED SEISMIC AMPLIFIER
Authors: Hefer Fred W.
Published: October 2002

The usual advantages of transistorized amplifiers—lowered power consumption, lighter weight, improved compactness, and increased reliability—are often cited. A fifth consideration is improved performance. One of the elements previously limiting amplifier performance is the AGC losser device. A photo‐resistive device can approach five idealized requirements quite closely. The amplifier described uses four cells of photo‐resistive material mounted in a common configuration. The four cells are illuminated from a common miniature lamp. Voltage for the lamp is derived from AGC control circuits. Resistance of the cells, and hence loss across them, depends on the level of illumination. Temperature compensation is achieved for the entire amplifier by use of a “fifth” stage with current derived from it being fed back to the other four primary amplifying stages. Amplifier performance and stability are illustrated by graphs of pertinent data.
MINIMUM STATISTICAL UNCERTAINTY OF THE SEISMIC REFRACTION PROFILE
Authors: Steinhart John S. , Meyer Robert P.
Published: October 2002

Interpretation of refraction results resolves in finding a model that fits the data as closely as possible. In many cases several plausible models may be postulated. Criteria are then required to evaluate the uncertainty of these models especially to determine if the data are sufficiently good to distinguish among the models. By expanding the depth function in a Taylor series, a straightforward evaluation of statistical uncertainty may be made. The problems of obtaining estimates of uncertainty for the parameters are discussed, and the method is outlined for estimating uncertainty of the depths. This estimate of the statistical uncertainty is shown to be a minimum in the sense that it may be said that the uncertainty is at least as large as the estimate. Finally, the applicability of least squares procedures to refraction work is discussed, and it is shown that the method of least squares is preferred for the purpose of the minimum estimate.
GHOST ELIMINATION FROM REFLECTION RECORDS
Authors: Hammond J. W.
Published: October 2002

A method is described for the elimination of ghost energy from reflection records. Two or more shots at different depths are recorded on magnetic tapes. The magnetic tapes are then composited in groups of two or more. The formula is derived for the calculations of shot depth separation and the relative displacements of the magnetic tapes on replay. The application of the method to an everyday field technique is illustrated with examples.
GRAVITY AND AEROMAGNETIC EXPLORATION IN THE PARADOX BASIN
Authors: Steenland Nelson C.
Published: October 2002

Aeromagnetic data are analyzed to study the configuration of the Precambrian rocks in the eastern Paradox basin, principally in the vicinity of the Gypsum and Dolores structures. The analysis shows that the Precambrian surface is uplifted several thousand feet on the southwestern flanks of the surface structures and that the uplifted Precambrian blocks are strongly mineralized ferromagnetically. It is postulated that this mineralization is contemporaneous with deformation that, in turn, resulted in the formation of the “salt anticlines” in the adjacent deep basement areas to the northeast. Gravity anomalies in the area are found to be entirely minimal and attributable to the masses of the salt “bulges” within the surface anticlines. These masses are quite well defined in the instances of these structures from the width of outcrop at Gypsum and from the depth to the Precambrian computed from the aeromagnetic data, the pre‐salt Paleozoic interval being quite uniform.
DIFFRACTION OF ELECTROMAGNETIC WAVES BY AN INHOMOGENEOUS SPHERE
Authors: Negi Janardan G.
Published: October 2002

The electromagnetic response of an inhomogeneous conducting sphere (having radial conductivity distribution) embedded in an infinite homogeneous medium is investigated. The effect of linear conductivity variation and magnetic contrast between the two media is discussed in detail and relevant curves are presented. Analytical results are further extended to a more general situation in which this sphere is located in a half‐space and the influence of air‐earth boundary is calculated. These results may be applied to geoelectrical interpretation.
INTERPRETATION TECHNIQUES FOR A SINGLE FREQUENCY AIRBORNE ELECTROMAGNETIC DEVICE
Authors: Wieduwilt W. Gordon
Published: October 2002

An airborne electromagnetic device, designed to measure electromagnetic anomalies in a manner that readily lends itself to the interpretation of conductivity and type‐body, led to the Aero‐Newmont vertical coaxial coil EM system. This mining prospecting device, applicable chiefly in Canadian‐type mineral environment, is rigidly mounted on an S-55 helicopter. Continued studies in the theory of interpretation for such a device, plus an accumulation of over five years of field experience, have provided a knowledge of the limitations which compliment the interpretation procedure to produce a surprisingly accurate and useful exploration tool.
THE AVERAGE HORIZONTAL GRAVITY GRADIENT
Authors: Thyssen‐Bornemisza Stephen , Stackler W. F.
Published: October 2002

The authors reported experiments of making measurements with the gravity meter at close spacings (Geophysics, 1956, 1958; Journal ASPG, 1960, 1962) for the purpose of obtaining gravity gradients and micro‐gravimetric maps. Since the average horizontal gradient seems to be of some interest for geophysical exploration, a brief theoretical discussion is presented.
REPLY TO DISCUSSION BY J. GEERTSMA ON “REFRACTION AND REFLECTION OF SONIC ENERGY IN VELOCITY LOGGING”
Authors: Tuman V. S.
Published: October 2002

The aim of my paper on “Refraction and Reflection of Sonic Energy in Velocity Logging” was to show the following pertinent points which hitherto were not considered in velocity log interpretation. 1. In general, the underground formations display nonisotropic elastic properties (generally transverse isotropy). 2. When a well is drilled in these formations they become nonhomogeneous due to stress relief. This occurs in shales and in porous formations. 3. The established nonhomogeneity is such that velocity of the elastic waves increases radially from the well‐bore. 4. The nonhomogeneity in the porous and permeable beds can be increased artificially by applying a well‐head pressure (below the fracturing point).
INVESTIGATION OF UPWARD CONTINUATION SYSTEMS
Authors: Nettleton L. L. , Cannon J. R.
Published: October 2002

Recent development of a system of gravity measurement in an airplane requires the determination of gravity values in the air from ground surveys to provide values with which airborne values can be compared. Calculation of such values involves an upward continuation operation. A test of the several published continuation systems was carried out by applying them to two theoretical doubly periodic fields for which a theoretically continued value can be calculated. An important consideration is to determine a minimum practical value for R/h, or the ratio of the radius of the field covered to the height of continuation, as this ratio determines the width of the belt of ground data required to calculate comparison data for a test flight line. From tests of continuation coefficients by Peters, by Henderson, and by Tsuboi with various values for R/h, the minimum R/h value is indicated to be about 6. Consideration is given to the “truncation” error which results from the necessarily finite limit of the field of calculation. No clear preference for the different empirical treatments of this error can be made on theoretical grounds, but an arbitrary adjustment to make the coefficients sum to unity is not required.
GEOPHYSICAL CASE HISTORY—BLACK HOLLOW FIELD, WELD COUNTY, COLORADO
Authors: Northwood E. J.
Published: October 2002

The Black Hollow Field is located in Weld County, Colorado, on the west flank of the Denver‐Cheyenne Basin. The producing reservoir is the Lyons sandstone of Permian age. Seismic work was begun in the area in 1944, following up gravity leads resulting from a gravity survey done in 1943. A minor lead resulted, but it was not until 1949 when The California Company moved in a Western Geophysical crew for additional seismic work that structural closure was recognized. This led to the drilling of a well to test the Lower Cretaceous Dakota and Lakota sands, which were then the major objective. The well was abandoned in 1952. During the next year, interest increased in Permian objectives and the well was re‐entered and deepened to the Lyons, thereby becoming the discovery well at Black Hollow. Subsequent development drilling indicated anomalous thickening and stratigraphy on the west flank which led to more seismic work. Results indicated that this could be mapped. Furthermore, a velocity gradient across the area was recognized, and applying this, the possibility of extending the field to the east was recognized. More seismic work was done in an attempt to confirm this prior to additional drilling.
PROBABILITY STUDIES IN THREE VARIANTS: SEISMIC VELOCITY, DEPTH, AND LITHOLOGY
Authors: McLemore Ethel Ward
Published: October 2002

In an effort to determine if lithology—shales, sands, or a mixture of both—can be inferred from interval seismic velocity values, probability theories of statistical inference were applied to data from 16 wells shot for velocity information and from electric logs of the wells in the San Joaquin Valley, California, area. Average velocities, velocity functions, and probability ratios were derived for the three classes of lithology, for all data, for the two general areas, and for three individual oil fields: Wasco, Rio Bravo, and Coalinga.