bluuebunny/crossref_metadata_2025 huggingface dataset:
MAGNETIC WELL LOGGING
Authors: Broding R. A. , Zimmerman C. W. , Somers E. V. , Wilhelm E. S. , Stripling A. A.
Published: October 2002

The need for control data in interpretation of surface magnetometer surveys has led to the development of borehole instruments for measuring magnetic susceptibility and total magnetic field in situ. The susceptibility instrument is an alternating current induction device, and by separation of the quadrature components simultaneous recording of the magnetic susceptibility and the electrical conductivity is possible. The susceptibility log has many features that depart from ordinary electric logs. The instrument has a sensitivity of the order of [Formula: see text] cgs units and sufficient contrast has been found in the sediments to yield a log of considerable lithologic character. This magnetic character suggests the use of the susceptibility tool in the field of special well logging, particularly for geologic correlation, and for tracer studies. The general assumption that the magnetic susceptibility of the sediments is sufficiently low compared to basic igneous rocks so that sedimentary rocks have little effect on surface magnetometer measurements has been verified. Since the magnetic susceptibility and electrical conductivity logs are made with an induction instrument, an electrolyte is not required in the hole and the logs are independent of the drilling fluid, except that the conductivity log is influenced by highly conductive muds. The total field log is made with a three element self‐orientating saturable core magnetometer that has been developed for borehole use. This log has not been used extensively. In addition to reflecting changes in polarization of the formations, it is influenced by formation susceptibility. Logs have been made of the total field going into and through igneous plugs. The paper presents examples of these logs along with a brief description of the instruments developed to produce them.
A MAGNETIC STUDY OF THE SPAVINAW GRANITE AREA, OKLAHOMA
Authors: Hawes Julian
Published: October 2002

Detailed magnetic maps over three of the four Spavinaw Granite outcrops are presented. These combined with laboratory measurements of the direction and intensity of the permanent magnetization and susceptibility measurements reveal the relative importance of permanent and induced fields at short distances from the granite. An air magnetic survey at 675 feet above the granite indicates the elimination of permanent field effects at that height. The size of the air magnetic anomaly when compared with the magnitude of folding known to be present in the Spavinaw anticline suggests strongly that a petrologic contrast with accompanying susceptibility contrast exists in the basement here. This could readily be interpreted as evidence of the intrusive nature of a local igneous body forming the core of the anticline, although it does not afford evidence of the date of intrusion.
QUALITY OF GEOPHYSICAL MEASUREMENTS
Authors: McCollum E. V.
Published: October 2002

The quality of geophysical measurements may be obtained from statistical studies in which the probable error of a single observation is estimated. Since many geophysical functions, when plotted in profile form, resemble smooth mathematical curves upon which “static” caused by random errors is superimposed, it is possible to substantially remove the measured function from the errors through the construction of difference tables. Higher orders of differences consist primarily of systematic combinations of individual errors. When a function, u, is observed at equally spaced points, the probable error of a single observation may be obtained from the equation [Formula: see text] where u is the measured function, m is the order of the differences, n is the number of measurements, and the K’s are the binomial coefficients of the order, m. Application of the method to seismic and gravity profiles results in probable errors that are consistent with those obtained from the studies of basic data acquired in the field. The method may also be used in many other measurements in the field and laboratory.
ATTENUATION OF RADIO FREQUENCY WAVES THROUGH THE EARTH
Authors: Pritchett W. C.
Published: October 2002

Evidence has been presented by several investigators indicating the possibility that radio waves penetrate sufficiently deep into the earth to be useful in prospecting for oil. Conventional electromagnetic theory used with normal values of the earth constants indicates, however, that the attenuation is too great to allow the signal to be used after propagation through significant distances of shale. To settle the above question an experiment was conceived and carried out in which the signal level in the earth was measured at various distances from a battery‐operated transmitter operating at 1,652 kc suspended in an uncased, mud‐filled hole by a mud‐saturated rope. The mud resistivity was matched to that of the 40 foot thick shale section used in order that the entire immediate region would be as nearly as possibly homogeneous. The receiver was also battery‐operated and suspended by a cable in other similar mud‐filled holes at various distances from the first hole. The attenuation constant in shale was found to be 0.231 nepers/foot (2 db/foot), which is much too large to give any hope of deep penetration. A few measurements in a limestone section gave a value of 0.086 nepers/foot, which is also too large to be useful. Although these values are quite high, they are lower than theory predicts for these earth resistivities by a factor of about two.
STUDIES IN NON‐STRUCTURAL PETROLEUM PROSPECTING II. THE COMPARATIVE RESOLUTION OF PERTINENT GULF COAST REFRACTION ANOMALIES
Authors: Rosaire E. E.
Published: October 2002

For the case of low‐relief structure associated with petroleum accumulation, the non‐structural working hypothesis postulates the observation of refraction fan anomalies with characteristics which are unique when compared with those of the refraction fan anomalies postulated by the geophysical structural working hypothesis generally accepted for the resolution of refraction fan anomalies. These unique characteristics are observable magnitude on depths of survey too shallow to intercept the underlying structure, double‐peaked maximum configuration, off‐structural orientation of maximum leads, and change in type of configuration as the survey depth increases to structural interception. Case treatments are shown where such structurally forbidden refraction fan anomalies were observed across low‐relief structure associated with petroleum accumulation, subsurface conditions which were revealed by subsequent development. These case treatments are substantiating evidence for the non‐structural working hypothesis in Gulf Coast refraction prospecting.
THREE DIMENSIONAL INTERPRETATION OF GRAVITATIONAL ANOMALIES
Authors: Grant Fraser S.
Published: October 2002

A method is developed for determining the approximate size and shape of the three‐dimensional mass distribution that is required to produce a given gravitational field. The first few reduced multipole moments of the distribution are calculated from the derivatives of the surface field, and the approximative structure is determined from the values of these moments and a knowledge of the density contrast between the body and its surroundings. A system of classification of problems by symmetry is introduced and its practical usage discussed. A relaxation method is described which may be used to adjust the initial solution systematically to give agreement over the whole field. A descriptive discussion is appended.
THE CYLINDRICAL ORE BODY IN THE PRESENCE OF A CABLE CARRYING AN OSCILLATING CURRENT
Authors: Wait James R.
Published: October 2002

The problem of an infinite cable carrying an oscillating current parallel to a conducting cylinder is solved. The homogeneous electrical properties of the media inside and outside the cylinder can be arbitrary. The special case is considered in detail where the exterior medium is a relatively poor conducting medium. The application to geophysical prospecting for massive sulphide ore zones is discussed.
GEOPHYSICAL EXPLORATION COMES OF AGE
Authors: Hammer Sigmund
Published: October 2002

The oil industry throughout the world last year invested about $325,000,000 in geophysical exploration for oil. This marks a phenomenal growth of the science since its inception less than three decades ago. The commercial acceptance of geophysics is justified by its success in eliminating many wasteful “dry holes” in drilling for oil. Applications in the search for other minerals show encouraging gains. The paper (1) reviews briefly the history and growth of geophysical exploration, especially as related to oil‐finding, and of the Society of Exploration Geophysicists; (2) discusses the present technical status and world‐wide industrial scope; and (3) attempts to peer into the future to catch a glimpse of future developments and prospects.
COMPARISON OF VELOCITIES OBTAINED BY DELTA‐TIME ANALYSIS AND WELL VELOCITY SURVEYS
Authors: Swan B. G. , Becker Adrian
Published: October 2002

A comparison of time‐depth curves obtained by statistical analysis of delta‐times with similar curves from well velocity surveys is presented, representative of results of a study made at a total of 21 wells located in Texas, Oklahoma, Louisiana, Mississippi, Nebraska, and North Dakota. A method applicable to routine studies of delta‐times is described. A conclusion is drawn that with average quality reflection data an accuracy of 2 to 3 percent in velocities so obtained may be expected.
CONTINUOUS VELOCITY LOGGING
Authors: Summers G. C. , Broding R. A.
Published: October 2002

A method for obtaining a continuous well log of formation acoustic compressional velocity is described. The instrument is composed of an acoustic pulse generator separated from a receiver by a five‐foot acoustic insulator. Means are provided for generating an acoustic pulse and automatically selecting and recording the first‐break travel time as detected by the receiver. The instrument has a range of 5,000 to 25,000 feet per second and an accuracy better than 5 percent. The log is taken in a conventional well logging manner at speeds of 100 to 150 feet per minute. Typical logs are illustrated along with their probable correlation to seismic reflection horizons and lithology in the borehole.
A STUDY IN INTEGRATION OF GEOLOGY AND GEOPHYSICS
Authors: Towles Henry Clay
Published: October 2002

The need for cooperation between and integration of geology and geophysics in the search for petroleum is illustrated by application and analysis in the Kilgore Area, Gregg and Rusk Counties, Texas. Independent interpretations of geologic structure from regional geology and reflection seismograph survey are presented and evaluated. The geologic interpretation is revealed to be based on accurate data of insufficient density and distribution to reveal even sizeable structural features. The reflection seismograph interpretation of structure reveals both small and large features which are of doubtful validity due to questionable time‐depth relationships over the area. An integrated interpretation utilizing the geological data to define velocity limitations for the seismic time‐depth relationship is attempted and a theoretical corrected structural interpretation is presented. The following conclusions are reached: (1) Standard methods of exploration for petroleum often produce incorrect results; the limitations of geologic and reflection seismograph methods do not overlap; therefore, it is possible to utilize the maximum interpretation of geological data as a guide to the velocity variations which affect the seismic interpretation. (2) Lack of sufficient velocity information can be a serious handicap to utilization of the reflection seismograph method; therefore, every opportunity to obtain additional velocity information should be utilized. (3) The Kilgore Area illustrates that existing seismic interpretations of structure that are in disagreement with known geologic data may often be recomputed for a correct interpretation at a small extra cost.
SOUND RANGING IN A MEDIUM HAVING AN UNKNOWN CONSTANT PHASE VELOCITY
Authors: Schriever William
Published: October 2002

A method for the sound ranging of explosions is described, in which the direction‐angle of the explosion is given in terms of the ratio of the differences in the arrival times at two pairs of microphones, geophones, or hydrophones. It is unnecessary to know either the phase‐velocity in the intervening medium or the absolute values of the time differences. However, the paths and the phase‐velocities must be such that the time differences are the same as they would be for a wave‐front traveling from explosion to the microphones at some constant velocity. A rapid graphical method for determining the location of the explosion is described. The precision of the determinations is discussed. Applications of the method to the scoring of bomb hits on bombing practice areas are suggested. The effect of the motion of the medium is considered.
EXPLORATION WORK IN MEXICO
Authors: Rojas Antonio Garcia
Published: October 2002

Since 1940 Mexico has increased exploration work in search of new oil fields. Most of the exploration has been done in the Gulf Coast area where all existing Mexican oil fields are located. A brief résumé is given of the main problems of the different provinces under exploration and a list of the fields discovered by Petróleos Mexicanos in the different provinces of the country. Geophysical methods have been responsible for location of a very large percent of the new fields. To compare the intensity of exploration in the United States and Mexico, the amount of seismic and gravity‐meter work and of wildcat drilling per million barrels of production is given for both countries. The data shows that Mexico’s level of geophysical exploration, per million barrels of oil produced, is very close to that of the United States. A very marked increase in the intensity of exploration is shown for both countries. Wildcat drilling in Mexico has been less intensive than in the United States but shows a definite tendency to increase; its present level is very close to that of the United States during 1940. The writer is of the opinion that the difference in intensity of wildcat drilling shown in the data presented is actually smaller than appears as there is a certain amount of duplication in the United States because of leaseholding problems.
ON THE PROPAGATION OF RAYLEIGH WAVES ON THE SURFACE OF A VISCO‐ELASTIC SOLID
Authors: Horton C. W.
Published: October 2002

The propagation of Rayleigh waves over the surface of a visco‐elastic solid is examined. It is shown that for a Poisson solid (λ=μ), the behavior of the waves can be characterized by a dimensionless parameter δ=ωη/μ which is less than 0.1 for the frequencies and elastic parameters of interest in geophysics. In this expression ω=angular frequency, μ=shear modulus, η=viscosity. For small values of δ it is possible to modify the usual analysis of Rayleigh waves and obtain the new characteristics without much difficulty. It is shown that the motion of a particle on the earth’s surface is changed from an ellipse to a Lissajous’ figure and that the phase angle between the vertical and horizontal displacements is changed from [Formula: see text] to [Formula: see text] radians. The surface wave has an attenuation factor of [Formula: see text] where [Formula: see text] is the wave length of the Rayleigh wave in the absence of internal friction.
HISTORY OF THE IMOGENE OIL FIELD ATASCOSA COUNTY, TEXAS
Authors: Bolinger John W.
Published: October 2002

The original lease block on the area which is now the Imogene Oil Field was taken as a result of the discovery in 1935 by surface geology of a large fault, upthrown to the southeast. A general reconnaissance reflection seismograph survey followed in 1940, preceding the drilling of the discovery well by about two years. A further detailed reflection seismograph survey was made after the discovery to outline the structure more accurately.
MAGNETIC SUSCEPTIBILITY MEASUREMENTS IN MINNESOTA PART II: ANALYSIS OF FIELD RESULTS
Authors: Mooney Harold M. , Bleifuss Rodney
Published: October 2002

75 samples of 7 rock types have been analyzed for magnetite content by magnetic separation and chemical analysis, making allowance for iron which occurs as ilmenite, hematite, and silicates. Magnetic susceptibility shows a clear dependence on magnetite content but with too much scatter to permit prediction of one from the other. For small magnetite content V (in volume percent), susceptibility k is roughly given by [Formula: see text] cgs. Based on 200 outcrops of 11 rock types, the approximate mean susceptibility of basalt and diabase is [Formula: see text], of rhyolite and gabbro [Formula: see text], of acid intrusives including granite [Formula: see text], of greenstone [Formula: see text], and of slates [Formula: see text]. Variability is high for acid intrusives, intermediate for basalt, rhyolite, and greenstone, and lower for diabase, gabbro, and slate.
CONTRIBUTION TO THE METHOD OF TORSION BALANCE SURVEYING IN UNDERGROUND
Authors: Zagorac Željko
Published: October 2002

A manner of interpretation of torsion balance survey in underground is shown, when the gradients Uxz, Uyz, and the curvature value Uxy are measured. Values Uxy and Uxz are composed as vectors in the vertical plane Z‐Y; Uyz and Uxy are composed in the plane Z‐X. On various examples it is shown that the resulting vectors give a better means of determining the position of ore bodies. An example of actual torsion balance survey in an iron ore mine is given. The method of eliminating the influence of mass irregularities close to the instrument by means of parallel profiles is described and discussed.
GEOPHYSICAL PROGRESS
Authors: Cortes Henry C.
Published: October 2002

Histories or reviews covering the period from 1922, the first year of petroleum geophysics in the United States, to 1940 were ably presented by Eckhardt, Macelwane and Weatherby at the Society of Exploration Geophysicists’ Annual Meeting of the latter year. This paper deals mainly with advances in geophysics since 1940. Marked progress has been made in the amount of geophysical activity, in the number of new oil fields discovered per year based wholly or partially on geophysics, in geophysical techniques, and in education. Improvements in instrumentation, field operational procedures, and interpretation methods have steadily increased the usefulness of the three major methods—seismic, gravity, and magnetic. The development of the aerial magnetometer, especially, and the underwater gravimeter represent notable achievements. These developments have made possible the extension of geophysical activity offshore, and in many other areas previously considered inaccessible. Advances have also been made in logging, particularly in the radioactivity type, geochemistry and electrical prospecting. Research, both fundamental and applied, is being conducted on a greater scale now than in 1940 or prior thereto. Increased geological‐geophysical coordination has led to better appreciation and utilization of the geophysical methods and has resulted in the discovery of important oil and gas reserves. Novel or more direct oil finding methods may possibly be discovered or perfected. It is more probable, however, that the future of exploration geophysics will be primarily in the continual refinement of the present known methods. Advances in exploration geophysics and geology, along with teamwork, should insure adequate production and reserves within the United States for a long period. This is predicated on our nation having competitive free enterprise, which has been responsible for the leadership of this country in oil finding, producing, transporting and refining techniques.
A COOPERATIVE PLAN IN STUDENT EDUCATION
Authors: Green Cecil H.
Published: October 2002

Effective exploration is a combination of well designed equipment and competent personnel. The latter factor attains special importance as exploration problems become more complex and competition increases with other industries for scientific manpower. A cooperative plan for undergraduate university students is described wherein aptitudes are measured in a guided course of actual exposure to various phases of petroleum exploration.
DETECTION OF REFLECTIONS ON SEISMIC RECORDS BY LINEAR OPERATORS
Authors: Wadsworth G. P. , Robinson E. A. , Bryan J. G. , Hurley P. M.
Published: October 2002

Linear operators are used as a statistical tool in the analysis of seismic records. It was found that when an operator is chosen for a non‐reflection interval and applied to regions during which reflections occur, the effectiveness of the operator is disturbed and large errors of prediction result. This effect provides a method for the discrimination of reflections. The technique used has its basis in the theory of time series, relevant concepts of which are reviewed. The mechanics of application are given, and illustrative examples on ten seismograms are presented.
DEEP‐HOLE GEOPHONE STUDY IN GARVIN COUNTY, OKLAHOMA
Authors: Jolly R. N.
Published: October 2002

The results of a seismic well survey made with calibrated recording equipment are presented. This survey differed from the conventional type in that a geophone which could be locked to the wall of the bore hole was used, thereby providing reliable amplitude data and permitting reflections to be recorded at depth. Consequently it was possible to observe the true shape and amplitude of the seismic pulses, both initial and reflected, over the major portion of their travel paths. Quantitative data were obtained on such factors as decrease of pulse amplitude with depth, location of reflecting horizons, and magnitude of reflection coefficients.
A UNIVERSAL SLIDE RULE FOR COMPUTING THE DIPS OF REFLECTING HORIZONS ON THE ASSUMPTION OF LINEAR INCREASE OF VELOCITY
Authors: Daly John
Published: October 2002

A slide rule is described by which the dip of reflectors can be computed rapidly and accurately for the case where instantaneous velocity can be assumed to increase linearly with depth. Values for initial velocity [Formula: see text], rate of increase of velocity, k, and the spread distance Δx, can be introduced into the device easily and changed at will. In conjunction with a previously described instrument, normal move‐out graphs and wave front charts can be constructed quickly and precisely.
DISPERSIVE PROPERTIES OF STRATIFIED ELASTIC AND LIQUID MEDIA: A RAY THEORY
Authors: Tolstoy Ivan , Usdin Eugene
Published: October 2002

The interference principle of wave guide propagation is applied to the derivation of the period equations for a number of problems involving both elastic and liquid strata. In the case of undamped steady state propagation in a solid or liquid stratum two arbitrarily chosen points at the same depth must be indistinguishable on an amplitude basis. This well known principle combined with the knowledge of the reflection coefficients enables us to derive in a few simple steps the period equations for a number of multilayer cases which heretofore had been avoided on account of algebraic difficulties. The period equations obtained by this method exhibit a singular simplicity and unity of form. As a consequence of this one may distinguish formally the [Formula: see text] and [Formula: see text] waves discovered by Sezawa and understand their physical significance.
A THEORY FOR THE REGIONAL CORRECTION OF POTENTIAL FIELD DATA
Authors: Grant Fraser S.
Published: October 2002

An analytical method based on the theory of statistical probability is developed for separating regional from local potential field effects. It is applied to an objective test on an artificial problem, as well as to a gravity survey that has already been the subject of studies of other averaging methods. It succeeds in both tests with good accuracy, and points up the danger of arbitrariness in the use of numerical methods.
TWO‐DIMENSIONAL MODEL SEISMOLOGY
Authors: Oliver Jack , Press Frank , Ewing Maurice
Published: October 2002

The solutions of many problems in seismology may be obtained by means of ultrasonic pulses propagating in small scale models. Thin sheets, serving as two dimensional models, are particularly advantageous because of their low cost, availability, ease of fabrication into various configurations, lower energy requirements, and appropriate dilatational‐to‐shear‐velocity ratios. Four examples are presented: flexural waves in a sheet, Rayleigh waves in a low velocity layer overlying a semi‐infinite high velocity layer, Rayleigh waves in a high velocity layer overlying a semi‐infinite low velocity layer, and body and surface waves in a disk.
FILTERING ASSOCIATED WITH SELECTIVE SAMPLING OF GEOPHYSICAL DATA
Authors: Swartz C. A. , Sokoloff V. M.
Published: October 2002

Geophysical data are often subjected to a variety of selective sampling operations in order to render their interpretation easier. The filtering effects of a number of commonly employed selective sampling procedures are discussed in detail in this paper. Curves are given showing the frequency selectivity characteristics of several arithmetic sampling processes including simple averaging, successive differences, and residual curves and maps. Instrumental sampling such as geophone mixing and electric filtering is also considered. The equivalence of electric filtering to an arithmetic sampling process is pointed out and illustrated by an example. A recently developed statistical method of detecting seismic reflections is discussed as a sampling procedure and curves are presented to show the filtering action for two special cases under restricted conditions.
EARTHQUAKE INVESTIGATIONS
Authors: Gilmore Marion H.
Published: October 2002

Earthquakes are a menace to life and property, but they are also a source of important scientific knowledge, for they give us information about the interior of the earth which we can obtain in no other way. The United States Coast and Geodetic Survey has developed instruments for the recording of strong earth motions; has recorded tilt of large areas; has determined dominant periods of buildings, of water towers, of dams and of the ground; and has made special studies of a statistical nature about these phenomena.
A NOTE ON THE PROPAGATION OF SEISMIC WAVES
Authors: Muskat Morris
Published: October 2002

It is suggested that in the computation of theoretical time‐distance curves for seismic wave propagation a more tractable form of analysis is obtained if the depth is expressed as a power series in the velocity than when the converse but more conventional method is used. Several illustrations of this procedure are given.
GEOPHYSICAL AND GEOLOGICAL INVESTIGATIONS IN THE GULF OF MEXICO, PART I
Authors: Ewing Maurice , Worzel J. L. , Ericson D. B. , Heezen Bruce C.
Published: October 2002

In 1953 the research vessels vema and atlantis spent about three weeks in the Gulf of Mexico. Coring, seismic refraction, and topographic studies were undertaken. The topography in the various physiographic provinces is illustrated by reproductions of precision depth records from the continental shelf, continental slope, continental rise, and abyssal plain areas. Many sediment cores longer than 30 ft were taken in the Gulf. An abrupt change separates approximately three feet of Recent sediments from Wisconsin in all cores taken in depths greater than 1700 fathoms. This change is very similar to one found in many Atlantic and Caribbean cores indicating an abrupt termination of the Wisconsin glacial epoch. Abundant evidence of turbidity current deposition was found in all cores from the abyssal plain and the continental rise. Deposition of sediments in the unusually rough and broad continental slope area is apparently very rapid in the depressions and very slow on the elevations. The seismic results point to the southern half of the Gulf of Mexico as a typical oceanic area, modified by an increased load of sediments. A profound change near the continental slope is required for connecting this structure to typical continental structures.
THE SUDBURY AEROMAGNETIC MAP AS A TEST OF INTERPRETATION METHODS
Authors: Zietz Isidore , Henderson Roland G.
Published: October 2002

The method of interpretation of aeromagnetic maps described by Vacquier, Steenland, Henderson, and Zietz (1951) is applied to several anomalies on the aeromagnetic map of part of Sudbury, Ontario. The resulting average computed depths deviate from the known depths by less than 10 percent. The aeromagnetic map is described and compared with the known surface geology.
THE FUTURE OF GEOPHYSICS
Authors: Lyons Paul L.
Published: October 2002

The year 1955 marks a continued decline in exploration for oil in the United States and in the world as judged from the employment of seismograph parties. The decline indicates that in the United States we have passed an upper limit of action within the framework of exploration practices as they have existed. The precipitate rise of geophysical exploration was due to the effort of exploration companies to be “firstest with the mostest.” The rapid coverage of prospective oil areas in the United States and in world, however, has not resulted in a complete exploration of the sedimentary areas. Many areas may be considered virtually unexplored. In addition, frontiers exist in the search for very‐small‐relief structures and stratigraphic traps by geophysical methods. Application of improved instruments, techniques, and interpretations to these problems will result in a new phase of sustained exploration with successes going to those with the most complete information and the best ideas. A changing geophysics will occupy an important place in the world petroleum economy, with at least 450 billion barrels of oil yet to be found.
THE SYNTHESIS OF SEISMOGRAMS FROM WELL LOG DATA
Authors: Peterson R. A. , Fillippone W. R. , Coker F. B.
Published: October 2002

Under certain simplified but realistic physical assumptions, the basic data from continuous velocity surveys in wells can be used to simulate the variations in acoustic impedance in the ground which give rise to seismic reflections. An analogue computer is described which makes use of the basic well data to produce synthetic seismic records which resemble actual seismograms from shothole explosions. This process provides an interesting insight into the requisite physical conditions, as well as the physical processes, whereby seismic reflections are set up in the earth. The close relationship between seismograms and well logs is brought out. Illustrations are given of field results.
A NEW METHOD OF PATTERN SHOOTING
Authors: Parr J. O. , Mayne W. H.
Published: October 2002

In areas where reflection shooting is difficult, it is often necessary to attenuate the energy in a broad continuous band of disturbing wavelengths to less than a few hundredths of what would be recorded if all units were bunched together. The wavelength band of the attenuated energy should be adjacent to the band of reflection wavelengths received. Attenuation of the undesired energy is best accomplished with multiple detectors or charges. In many areas the pattern should attenuate energy horizontally propagated in all directions, not just in the direction of the detector line. Neither a finite number of uniformly effective, uniformly spaced units in line nor a uniformly effective sheet of finite length will accomplish this result. A system for gradation of the effectiveness of units described in this paper does produce this result (not only for in‐line disturbances but also for disturbances coming in from the side of the line). The attenuation band can be made broad with good attenuation or narrower with still better attenuation, as desired. The variation of effectiveness can be applied to detectors or charges arranged in a horizontal line, over a horizontal area, in a vertical line, or over a vertical area. The principle of varying effectiveness can also be applied to reversed‐polarity detectors in order to accentuate certain apparent wavelengths.
ELECTRIC ANALOGUE OF RESISTIVITY LOGGING
Authors: Guyod Hubert
Published: October 2002

The electric analogue device described below was designed to determine the relationship between the true resistivity of a ground formation and the apparent resistivities obtained by various electrode arrangements. This analogue is a network model which simulates properties of the formations and other pertinent variables encountered in actual logging.
DISCUSSION OF PAPER BY G. P. WOOLLARD ENTITLED “AN EDUCATIONAL PROGRAM IN GEOPHYSICS”
Authors: Hubbert M. King
Published: October 2002

As this commentator pointed out originally in 1938, and at various times subsequently (Hubbert, 1938, 1946), the teaching of geophysics in the departments of geology as these were constituted up until 15 or 20 years ago was an almost impossible task. This was because it was then the custom, with few exceptions, for geology students to terminate their mathematical training at about trigonometry or college algebra, their physics either with no college physics at all or at most one year, and their chemistry after qualitative or quantitative analysis.
MINIMUM VARIANCE IN GRAVITY ANALYSIS PART 1: ONE‐DIMENSIONAL
Authors: Brown William Fuller
Published: October 2002

Suppose that we have measurements of the vertical intensity of gravity or the magnetic field at n points; we wish to estimate a second derivative or the like at a specified point. If there were no experimental error, we could interpolate and differentiate well enough with a polynomial of degree k−1 <n−1. What shall we do when experimental error is present? The minimum‐variance principle says: adjust the n−k arbitrary constants of the polynomial formula so as to minimize the mean square error (variance) of the estimated quantity. By applying this principle directly, we can get “best” estimation formulas of specified degree k. We can also get “best” formulas by a least‐squares method; it gives the same results as the minimum‐variance method, by a theorem of mathematical statistics. The theorem furthermore enables us to estimate the variance and to choose a satisfactory value of k. For shortening the calculations, orthogonal polynomials are useful; tables of them are available in several places, and tables of their derivatives are given here. The methods are illustrated by applying them to several made‐up examples of data with known random errors.
REFLECTION OF AN ACOUSTICAL PRESSURE PULSE FROM A LIQUID‐SOLID PLANE BOUNDARY
Authors: Spencer T. W.
Published: October 2002

The problem treated is concerned with predicting the transient response of a system composed of a liquid layer, bounded above by a vacuum and below by a perfectly elastic solid, when excited by an arbitrary pressure applied uniformly over the surface of a spherical cavity located in the fluid. The Laplace transform of the displacement response is expressed in terms of an integral which is expanded in such a way that each term describes the contribution from one of the image sources. Each term may be evaluated exactly at points located on a vertical axis passing through the source. The final expression for the vertical displacement at axial points is composed of the acoustic, after‐flow, and correction terms. In solids for which Poisson’s ratio is greater than one third the initial variation of the correction is toward positive values (corresponding to motion directed toward the interface). For Poisson’s ratio less than one third the initial variation may be either positive or negative depending on the magnitude of the compressional velocity ratio. A surface wave is shown to exist regardless of the choice of parameters. The surface wave velocity is always less than it would be in the absence of the liquid.
MUTUAL ELECTROMAGNETIC COUPLING OF LOOPS OVER A HOMOGENEOUS GROUND—AN ADDITIONAL NOTE
Authors: Wait James R.
Published: October 2002

Further computations are presented for the mutual impedance between small wire loops over a semi‐infinite conductor. The cases considered are where the axes of the loops are parallel to the interface.
THE LONG INTERVAL METHOD OF MEASURING SEISMIC VELOCITY
Authors: Kokesh F. P.
Published: October 2002

The reverse method of seismic velocity determination, wherein the shot is detonated in the bore hole, has been extended to operate in deep wells. This has been accomplished by the use of a long interval arrangement of a multi‐shot selective firing sound source gun and one or more geophones separated vertically by a cable several hundred feet long. A series of a relatively few such intervals can “strap” a bore hole travel‐time‐wise with good accuracy. Travel time measurements over the cased portion of the hole can generally be accomplished by means of geophones placed at or near the surface. Velocity surveys conducted in this manner become a routine well logging service, in conjunction with other services such as electrical logs. The paper describes in a general way the necessary field equipment, and field examples of surveys are presented.
POTENTIAL AND APPARENT RESISTIVITY OVER DIPPING BEDS
Authors: De Gery Jerome Chastenet , Kunetz Geza
Published: October 2002

The potential field due to a point source of current, located on the surface of the earth near a dipping bed, is given in an exact expression and modified expressions are developed for computations. These expressions lead to graphs of the potential field and to apparent resistivity vertical profiles which are presented. The Schlumberger electrode configuration is used. This configuration consists of two current electrodes and two potential electrodes, the latter placed close enough together that the current density between them can be considered to be uniform. With this configuration oriented perpendicular to the strike of the dipping bed, the apparent resistivity is paradoxical in that it approaches either zero or infinity as the electrode separation increases without limit.
AN ELECTRICAL CREVASSE DETECTOR
Authors: Cook John C.
Published: October 2002

Numerous fatal encounters with large crevasses concealed by bridges of drifted snow have occurred on the Greenland icecap and elsewhere. In response to an urgent need for rapid and reliable means of crevasse detection, a promising geophysical method has now been developed for the Department of Defense. This method is analogous to the four‐electrode method of measuring earth resistivities. It is different in that an alternating dielectric displacement‐current field is employed rather than a field of conduction current since the ice medium is essentially a nonconductor. As a result, basic differences in technique are necessary. The systems tested in Greenland and Antarctica, to date, which employ this method, continuously indicate or record the capacitive transfer reactance between pairs of electrode sleds or vehicles. Systems have been operated successfully while in motion at surface speeds up to 20 miles per hour. Pronounced and distinctive electrical anomalies have been obtained at every crevasse tested to date. Typical crevasse‐detector recordings and details of the equipment and techniques used are presented. Some potential applications of the mutual‐capacitance method in mineral prospecting and other fields are suggested.
MAGNETIC PROPERTIES OF MAGNETITE
Authors: Rao V. Bhaskara
Published: October 2002

Hysteresis characteristics of a magnetite sample from Gudur area in South India have been studied up to a maximum magnetizing field of 375 oersteds. The apparatus used was the same as developed by Bruckshaw and Rao. The studies have shown that the susceptibilities of rocks are mainly dependent on the magnetite contained in them. Variations of susceptibility of magnetite with its grain size, its purity and its distribution in an inert matrix provide the explanation for the enormous range of rock susceptibilities usually encountered.
CHARACTERISTICS OF EXPLOSIVES FOR MARINE SEISMIC EXPLORATION
Authors: Jakosky J. J. , Jakosky John
Published: October 2002

This paper describes the results of preliminary studies which were conducted at San Diego, California early in 1953, and detailed large scale field tests conducted during the later months of 1953 and the early part of 1954, chiefly near Santa Barbara, California. These studies are part of an investigation to develop an explosive which would overcome some of the disadvantages of black powder, which now is the only explosive permissible for offshore exploration in California. Special instrumentation was developed for recording the pressure‐time curves from underwater explosions. The predominant characteristics of these curves have been related to seismic record quality and the destruction of fishes and other marine life. The experimental studies have shown that non‐lethal explosives are available which will give record quality and operating costs comparable to the conventional dynamites and which are superior to the black powders.
RELATION BETWEEN REFLECTION TIME INCREMENT, INCLINATION OF REFLECTING LAYER AND INTEGRATION COVERAGE
Authors: Grunebaum Bernard
Published: October 2002

The purpose of this paper is the establishment of a criterion to ascertain the amount of compositing (or integration) which may be applied to a sequence of seismic traces without producing distortion or cancellation. The subject has been treated primarily from the standpoint of weight dropping technique, but it applies unchanged to standard seismic procedures. The mathematical treatment is based on certain restrictive assumptions which, it is believed, are sufficiently approximate for the purpose intended.
NOTE ON AN APPLICATION OF SONAR TO THE SHALLOW REFLECTION PROBLEM
Authors: Zietz Isidore , Pakiser L. C.
Published: October 2002

Modified sonar transducers have been successfully used in water‐covered areas to determine depths to the water bottom, layers within the bottom sediments, and depth to bedrock (Smith and Nichols, 1953). The possibility of detecting shallow horizontal beds by placing a sonar transducer directly on the ground is particularly attractive. Velocity discontinuities at depths of several hundred or more feet have long been successfully mapped by means of conventional seismic reflection methods. Recently, reflections from much shallower, closely spaced horizons have been recorded by increasing the filtered frequency range of the amplifiers to an upper limit of 300 to 500 cycles per second, and by other instrumental modifications (Pakiser, Mabey, and Warrick, 1954; Olson, 1955). Evison has recorded still shallower reflections by using an electromechanical vibrator that generates a square‐enveloped pulse of sine waves at frequencies of 100 to 800 cycles per second and pulse widths of from 5 to 100 milliseconds (Evison, 1954).
GEOPHYSICAL RESEARCH AND PROGRESS IN EXPLORATION
Authors: Dobrin Milton B. , Dunlap Henry F.
Published: October 2002

This paper, the SEG Research Committee’s second annual review of current developments in exploration geophysics, will emphasize research activities at universities and other non‐commercial institutions which relate closely to geophysical exploration. Industry developments worth noting in the seismic field include the considerable increase in use of magnetic recording, use of pressure‐sensitive geophones with preamplifiers in the bay and marsh areas of the Gulf Coast, use of fathometer‐type instruments to obtain near bottom layering in marine areas, and use of nonphotographic methods of reproducing seismic data. Considerable experimentation with weight dropping techniques, and with use of higher frequencies to get better resolution has continued during the past year. Use of models, particularly two dimensional models, is increasing. There have been significant innovations in logging techniques, particularly in the use of in‐hole accelerators for neutron generation, and in the development of in‐hole equipment for measuring gamma ray spectra. The use of continuous velocity logs is increasing. Academic research has been of two kinds. First, there are studies of basic physical principles underlying current or prospective exploration methods which could lead to improvements and new applications. Secondly, geophysical methods originally developed for petroleum exploration are being employed for large‐scale investigations of the earth’s crustal structure. These studies should contribute important information on the geology of such features as continental shelves, geosynclines, and mountain systems, information potentially useful to geologists for developing new concepts in exploration thinking. The two kinds of research illustrate the current interdependence between “pure” and “applied” geophysics. Important research projects on scattering, statistical improvement of signal‐to‐noise, explosionwave generation in the earth, and surface waves exemplify the activity going on in university laboratories today which may result in improved seismic exploration techniques tomorrow. Conversely, university‐sponsored seismic and gravity investigations of the deep oceans, the continental margins and various western mountain chains illustrate how geophysics is contributing basic geologic information on a regional to global scale.
MULTIPLE SIGNAL CORRELATORS
Authors: Melton Ben S. , Bailey Leslie F.
Published: October 2002

Methods of correlation of any number of input functions or signals to be compared are discussed. It is shown that correlation values can be obtained from any one of several arithmetic processes which measure the degree of similarity of the inputs, and that these processes can be mechanized. Included are a simple addition, a sign‐coincidence scheme, and two processes based on analysis of variance. The discussion of analysis of variance procedures as applied to signals shows that the answers can be interpreted in terms of statistical significance, that measurements of coherent signal power can be made, and that the accuracy of such measurements is greatly improved as the number of input signals is increased. Signal‐to‐noise ratio is shown to be uniquely related to statistical significance, and signal detectability is plotted as a function of number of inputs and signal duration. Several means of presentation of data are suggested and illustrated.
ORGANIC REEFS OF PENNSYLVANIAN AGE IN HASKELL COUNTY, TEXAS
Authors: Van Siclen De Witt C.
Published: October 2002

The reflection seismograph was used to map a prominent organic reef in the Pennsylvanian system near Stamford in central northern Texas, and the results were checked by drilling. Since seismic wave velocity in the limestone comprising the reef is the nearly twice that in the enclosing shale, distinctive reflections from beds below the base of the reef were mapped above their true position by an amount equal to almost half the reef limestone thickness. The false structure so mapped has been interpreted as showing the topography of the upper surface of the reef. As such, it is a mound 3 miles long and half as wide, with a corrected height of 1,000 feet and a central depression 300 feet deep, resembling a present‐day atoll. Numerous wells confirm the presence of this reef, but cast serious doubt upon the simple topographic interpretation of the seismic map. The atoll‐like central depression appears to be an illusion, caused by the reef having a relatively high‐velocity shell and a lower velocity center. The Stamford reef is an exceptional development along a seemingly continuous reef belt mapped similarly with refection seismograph for 25 miles. Where reef development is less extreme along this belt, and along two others of a closely related type, the reef trends show as long, as gently curving, somewhat irregular seismic “highs” with many small contours closures. Detailed seismic interpretation of these reefs, and of the structure underlying horizons which they obscure, must await improved geologic understanding of the reefs and of the subtle changes in lithology that modify seismic wave velocity. Stamford reef illustrates also what a difference there can be between seismic closure, an obvious trap by subsurface mapping, and the location of a good oil field.