bluuebunny/crossref_metadata_2025 huggingface dataset:
THE USE OF A COUPLER IN THE CONVERSION OF IMPACT ENERGY INTO SEISMIC ENERGY
Authors: Mereu R. F. , Uffen R. J. , Beck A. E.
Published: October 2002

The factors which influence the efficiency of generation of seismic energy by a falling weight‐coupler system have been investigated both theoretically and experimentally using model techniques. Two media, sand and clay‐silt‐sand, were used. Source conditions were changed by (1) varying the mass of the falling weight, (2) varying the drop‐height, and (3) embedding various bodies (couplers) at the impact point. The results showed that for compressional waves: 1. [Formula: see text] where A is the amplitude of the seismic signal, M the mass of the coupler, and [Formula: see text] the maximum speed of the coupler. 2. The seismic energy is not proportional to the source energy. 3. In general, for a given source energy the larger the falling mass the more efficient is the generation of seismic energy. 4. The coefficient of restitution between the falling mass and coupler can be determined from seismic‐wave amplitudes. 5. Complex waves can be generated when the mass of the falling weight is greater than that of the product of the mass of the coupler and the coefficient of restitution. 6. The wave shape depends on the coupler mass and the elastic properties, and the degree of compaction of the medium. 7. The stacking of suitable masses on the coupler can increase the seismic efficiency by a factor of nearly four. The results of this study have important implications in the practical application of the weight‐drop method used in seismic exploration and in other related energy coupling studies.
SEISMIC AND GRAVITY STUDIES AT THE SOUTH POLE
Authors: Weihaupt John G.
Published: October 2002

Results of a seismic and gravity study at the South Pole during the 1961–62 austral summer are presented. Seismic compressional waves in the ice at the South Pole are shown to reach a maximum velocity of 3,925 m/sec at a depth of 186 m. This depth is attributed to the density profile of the ice. An ice thickness of 2,900 m is indicated from seismic reflection shooting. Gravity data reveal flat topography underlying the ice in the vicinity of the South Pole.
A DENSITY DETERMINATION BY UNDERGROUND GRAVITY MEASUREMENTS IN MICHIGAN
Authors: Secor George B. , Meyer Howard J. , Hinze William J.
Published: October 2002

The in situ density of an 1,100‐ft section of Paleozoic sedimentary rocks in the southeastern portion of the Michigan Basin was determined by the established method of observing the change in gravity over a known vertical interval within the earth. The measurements were made in and adjacent to the Detroit Mine (Sec. 33, T2S, R11E) of the International Salt Company in Detroit, Michigan, which is the only deep shaft mine in the Southern Peninsula of Michigan.
On: “INVESTIGATION OF UPWARD CONTINUATION SYSTEMS” BY L. L. NETTLETON AND J. R. CANNON (GEOPHYSICS, DECEMBER, 1962, PP. 796–806)
Authors: Roy Amalendu
Published: October 2002

(1) Earlier tests of continuation systems on fields of ideal bodies minimized errors due to finite sizes of the ring systems used for calculation. This happened because the field due to an ideal body or a group of bodies falls to zero at large lateral distances. The object of Nettleton and Cannon’s paper is to correct this situation by conducting tests on “continuous” periodic fields. However, they seem to have largely defeated the purpose by choosing periodic fields which consist of alternations (about a zero value) of positive and negative anomalies of equal magnitude and the same (but inverted) shape. As long as the ring system is not unduly small, the contribution to the upward continuation integral from the area outside the ring system will be nearly zero. This is because the positive and the negative contributions from the plus and minus anomalies in such fields will tend to cancel each other. The fields chosen by Nettleton and Cannon, therefore, are virtually equivalent to what they themselves declared as unsatisfactory.
REPLY BY AUTHORS TO DISCUSSION BY AMALENDU ROY
Authors: Nettleton L. L. , Cannon J. R.
Published: October 2002

The discussion by Roy is critical of certain choices of tests and conclusions of our paper. To a large extent, Roy’s comments apply in general to systems of calculation of other functions from measured potential fields, and to the obvious fact that any system of computation from an actual map of a potential measurement is approximate.
On: “DEEP GRAVITY INTERPRETATION BY STRIPPING” BY SIGMUND HAMMER (GEOPHYSICS, JUNE 1963, PP. 369–378)
Authors: Richards T. C.
Published: October 2002

The gravity stripping technique in extending interpretation to deep horizons is far from being new as stated by Hammer in his paper, for an important contribution to the subject was made by Evans and Crompton in 1946. These authors do not claim to be the first in this field and give several earlier references to papers on isostasy in which the need for stripping the estimated effects of “local geology” from Bouguer gravity measurements is proposed as a first step in the interpretation of the deeper horizons; some attempts to do this were, understandably, rather crude.
AEROMAGNETICS
Authors: Reford M. S. , Sumner J. S.
Published: October 2002

The aeromagnetic method of geophysical surveying has been established in less than two decades as a powerful method in mining and petroleum exploration. Many economically important discoveries can either directly or indirectly be credited to the aeromagnetometer. Magnetic methods are most important in their assistance to geological reconnaissance and mapping. Also, deep crustal and upper‐mantle studies can be made from results. New instruments, the spin‐precession magnetometers, have come into being in the past five years. Included are the proton‐precession magnetometer, the alkali‐vapor rubidium and cesium instruments, and the metastable‐helium magnetometer. All of these devices have airborne capabilities, and their future use is destined to increase. Modern navigational and interpretational techniques have improved the usefulness of aeromagnetic surveying. Diurnal effects are corrected for and their behavior is becoming understood. Data compilation, the major step in the entire process between measurement and interpretation, is an involved routine, but can be automated with the aid of Doppler navigation and statistical techniques. Interpretative systems may be divided into qualitative inspection, profile analysis, and map methods. Numerous schemes have been proposed for analytic purposes and the principal methods are reviewed. Although much of the world has been covered by surveys, the program seems less than half done. With more emphasis on detailed surveys, comprehensive interpretation, and sensitive instruments, the future of aeromagnetics seems bright.
A STATISTICAL ANALYSIS OF SOME AEROMAGNETIC MAPS FROM THE NORTHWESTERN CANADIAN SHIELD
Authors: Horton C. W. , Hempkins W. B. , Hoffman A. A. J.
Published: October 2002

Autocovariance and power‐spectral techniques are applied to aeromagnetic maps from the District of MacKenzie, Northwest Territories, Canada, to obtain trend directions and other structural information. Such trends are representative of the geologic structures creating the magnetic anomalies, and they are subjected to structural analysis. Results of computations for four maps 17×17 miles in size and one profile 185 miles long show good agreement with the known geological structure of the region. These analyses predict a dominant structural trend from S 18° W to N 18° E and two associated conjugate shear directions. In addition, an unexplained basic periodicity with a wave length of 15 miles is shown. This type of statistical analysis is suggested as a new tool for the extension of geologic data into inaccessible or covered regions.
A STUDY IN INDUCED POLARIZATION
Authors: Anderson L. A. , Keller G. V.
Published: October 2002

Induced polarization in pyritic sandstone arises in part from overvoltage effects and in part from electrolytic polarization. Because induced‐polarization measurements are commonly used to search for sulfides, the electrolytic polarization is an undesirable background effect. Pyrite in sandstone can be located only when overvoltage polarization substantially exceeds electrolytic polarization. Laboratory measurements indicate this is true only if there is ten percent or more pyrite in a rock. However, overvoltage polarization is much larger when low current densities are used, particularly if the matrix resistivity is high. Field measurements indicate that at low current densities as little as one or two percent pyrite may provide sufficient overvoltage polarization to be recognizable in the presence of electrolytic polarization.
SIGNAL‐TO‐NOISE RATIO AND RECORD QUALITY
Authors: Junger Arne
Published: October 2002

The appearance of a seismic record is a function of the signal‐to‐noise ratio. This ratio is expressed quantitatively, but it can not be measured on the record. The quality of the record is expressed by the lineup of events and constancy of character across the record, but is generally not expressed numerically. The appearance of the record is here expressed numerically by the mean phase shift from perfect lineup of various events. A statistical relationship is established between this mean phase shift and the signal‐to‐noise ratio. A seismic record may be approximated by considering the signal to have a sinusoidal waveform and the noise to be a continuous sine wave with the same frequency as the signal and with random phase shift with respect to the signal on various traces. The resulting record will show a random phase shift, the mean value of which is a function of the signal‐to‐noise ratio. A plot of these two values shows that with increasing signal‐to‐noise ratio there is very little change in the mean phase shift, and thus of the quality of the record, until a value of one‐half for the signal‐to‐noise ratio is reached, showing that the noise dominates the record up to this point. For values of the signal‐to‐noise ratio between one‐half and two, there is a large change in the mean phase shift, indicating a strong visual improvement for this range. For a signal‐to‐noise ratio larger than two, the signal predominates visually, and only a slight improvement in quality can be obtained with additional improvements in the signal‐to‐noise ratio. These conclusions are in agreement with experimental data published elsewhere.
THE REFLECTION OF LONGITUDINAL WAVE PULSES FROM PLANE PARALLEL PLATES
Authors: Muskat Morris
Published: October 2002

A wave theory treatment is given of the reflection of elastic wave pulses from plane parallel plates. The analysis automatically resolves the reflected wave system into a series of undistorted individual pulses having the same shape as that impinging on the reflecting plate, but which are characterized by varying amplitudes and phase shifts corresponding to various internal reflection and refraction processes within the plate. The numerical values for the reflection coefficients for the three most prominent longitudinal reflected pulses resulting from an incident longitudinal wave pulse are given in both tabular and graphical form, for angles of incidence between 0 and 30°, for velocity ratios between the plate and incident medium of 1.0 to 2.0, and for density ratios of 0.9 to 1.3. The actual superposition of the individual reflected waves is shown graphically for three cases where the ratio of the reflecting plate thickness to the length of the incident pulse has the values 2, 1, or 1/2.
VELOCITY DETERMINATIONS BY MEANS OF REFLECTION PROFILES
Authors: Green C. H.
Published: October 2002

While the idea of making an indirect determination of average sub‐surface velocities by means of reflection profiles is far from new it is nevertheless considered worth reporting, inasmuch as it has been recently employed with fair success by the writer in areas beyond any wells that could be “shot” for direct velocity measurements. Two examples of such surface velocity profiles are described—one located in the Means Field area of Andrews County, West Texas, and the other about 8 miles south of the Refugio Field, in Refugio County on the Texas Gulf Coast.
ELECTRICAL PROSPECTING WITH NON‐SINUSOIDAL ALTERNATING CURRENTS
Authors: West S. S.
Published: October 2002

A method of electrical prospecting using alternating current of rectangular or other non‐sinusoidal waveform is described. The changes in waveform caused by anomalous subsurface structure are determined by a null method in which the detected electromotive force is balanced against an electromotive force produced by passing the output of a standard oscillator through an adjustable network. This process of measurement (applicable also to the transient method) makes possible a useful representation of the data in terms of two‐dimensional contours.
REFRACTION ARRIVALS THROUGH THIN HIGH‐VELOCITY LAYERS
Authors: Rosenbaum J. H.
Published: October 2002

The first significant refraction arrival through a thin high‐velocity elastic layer in an elastic medium has been investigated theoretically by means of an asymptotic theory. This first low‐frequency arrival is closely connected with the longitudinal plate wave in the thin layer. When the medium surrounding the layer is a fluid, the signal does not decay exponentially with horizontal distance; when the surrounding medium is a solid, the signal does decay exponentially. A very simple approximate formula for this exponential decay is presented and compared with numerical results of the more rigorous theory. The decay as well as the shape of the signal is dependent upon the contrast in elastic parameters between the plate and the surrounding medium. Higher‐frequency early arrivals, associated with the second symmetric mode, have also been investigated. They exhibit greater exponential decay with horizontal distance than the low‐frequency first arrivals.
CONVOLUTION FILTERING OF GRAVITY AND MAGNETIC MAPS
Authors: Byerly P. Edward
Published: October 2002

This note discusses some applications of convolution filter theory to gravity and magnetic maps. Sampling of the field is equivalent to a multiplication, and the corresponding convolution determines the sampling spectrum. If aliasing is acceptably small a specific filtering multiplication in the wavenumber domain corresponds to a convolution of a set of grid coefficients with gridded map values. The application of this theory to single‐ring residuals, certain vertical derivatives, downward continuation, and low‐pass filtering is discussed.
A GEOPHYSICAL STUDY OF A BASEMENT ANOMALY IN INDIANA
Authors: Rudman Albert J. , Blakely Robert F.
Published: October 2002

Seismic, gravity, aeromagnetic, vertical, and horizontal magnetic surveys were made in Indiana as part of a statewide effort to study the basement complex. These surveys were interpreted collectively in a prescribed sequence that led to information ordinarily not obtained individually from such surveys. Prominent seismic reflections and sharp, coincident magnetic and gravity anomalies in Pulaski County, Indiana, were interpreted to show the depth, geometry, and rock type of an anomalous body within the basement complex. Seismic reflection data show the top of the anomalous body to be at a depth of 1.4 km. Analysis of the aeromagnetic anomaly indicates that the body can be approximated by a thick, vertical prism polarized along the earth’s field. Second derivative analysis of the vertical magnetic anomaly outlines the body as roughly circular and [Formula: see text] in area. Curve‐fitting between the observed vertical magnetic anomaly and an anomaly computed for the prismatic model readily shows that the body has a vertical dimension of 2.5 km and has a magnetic susceptibility contrast of 0.0088 cgs. Similar curve‐fitting based on the observed gravity anomally shows that the body has a density contrast of [Formula: see text]. Supporting evidence for the suggested susceptibility and density contrasts was obtained by substituting these values in Poisson’s equation relating gravity and horizontal magnetic fields. Studies of basement rocks in Indiana, Illinois, and Ohio support the interpretation that the anomalous body in Pulaski County is a basaltic plug intruded into a granitic basement and may have been one of a series of vents located along the Cincinnati arch that were the source for Precambrian basalt flows in Indiana.
GEOPHYSICAL ACTIVITY IN 1964
Authors: Smith Neal J.
Published: October 2002

Certain qualifications of this report should be mentioned. In most parts of the text and tables crew‐months for quite different kinds of crews are added as though they were equivalent, i.e., conventional shooting is lumped with horizontal stacking, with nonexplosive sources, etc., digital recording is not distinguished from analog, marine crews are not separated from land crews, Sparker, Gas Gun, and explosive marine are not distinguished. No distinction is made between crews working a normal month and those, like bush and some marine, that may work a 30‐day month. A similar situation exists in the case of gravity. All this is somewhat like adding apples and oranges.
STANDING‐WAVE PHENOMENA IN SHORT‐PERIOD SEISMIC NOISE
Authors: Gupta Indra N.
Published: October 2002

Short‐period vertical seismometers are used in deep holes at several sites to obtain the change with depth in amplitude and phase spectra of short‐period seismic noise. Although the observed spectra can be explained by an arbitrary combination of several Rayleigh modes, an alternative theory is suggested here. An attempt is made to explain both amplitude and phase spectra of observed microseisms of period less than 6 sec in terms of standing‐wave phenomena caused by steady‐state plane harmonic compressional waves propagating vertically through a horizontally stratified medium. At most sites, the observed data indicate satisfactory agreement with the expected results. A considerable fraction of the short‐period noise may, therefore, be regarded as P‐wave noise propagating vertically from below.
WAVE VELOCITIES IN ROCKS AS A FUNCTION OF CHANGES IN OVERBURDEN PRESSURE AND PORE FLUID SATURANTS
Authors: King M. S.
Published: October 2002

A system has been developed for determining precisely the dilatational and shear‐wave group velocities in rock samples subjected to hydrostatic confining and internal pore pressures independently to 10,000 psi. Pulses of polarized shear waves of 500‐kc/sec carrier frequency are produced and detected by axially polarized ceramic transducers attached to Pyrex glass prisms mounted in pressure‐sealed cells at each end of the rock sample. Complete mode conversion from dilatational waves to polarized shear waves, and vice versa, occurs at the free surfaces of the prisms. Pulses of dilatational waves of the same carrier frequency are produced and detected by axially polarized ceramic transducers mounted in a separate pair of pressure‐sealed cells which are attached at each end of the sample. Dilatational and shear‐wave velocities have been measured on three dry sandstones in directions perpendicular and parallel to the bedding plane. Two of the rocks were found to exhibit anisotropy in the form of transverse isotropy with the bedding plane as the plane of symmetry, and the third to exhibit isotropy. A reduction was noted in the degree of anisotropy for the two rocks as the hydrostatic confining pressure was increased. The influence of pore liquid saturants on the velocities of waves in several sandstones has been investigated. It has been concluded that the velocities in these rocks depend significantly on interfacial surface phenomena, relaxation behavior of the liquid saturants in small cracks, and upon interaction between the saturant and interstitial detrital material. At high hydrostatic pressures on the rock frame, the effects of interfacial surface phenomena and relaxation behavior of the liquid saturants tend to decrease. The influence of changes in pore fluid pressure on the velocities of waves has been studied. Provided the effects of mechanical hysteresis of the rock were avoided, the velocities in sandstones were found to depend on the simple difference between the hydrostatic confining and internal pore pressures.
PROPAGATOR MATRICES IN ELASTIC WAVE AND VIBRATION PROBLEMS
Authors: Gilbert Freeman , Backus George E.
Published: October 2002

The boundary value problems most frequently encountered in studies of elastic wave propagation in stratified media can be formulated in terms of a finite number of linear, first order, ordinary differential equations with variable coefficients. Volterra (1887) has shown that solutions to such a system of equations are conveniently represented by the product integral, or propagator, of the matrix of coefficients. In this paper we summarize some of the better known properties of propagators plus numerical methods for their computation. When the dispersion relation is some mth order minor of the integral matrix it is possible to deal with mth minor propagators so that the dispersion relation is a single element of the mth minor integral matrix. In this way one of the major sources of loss of numerical accuracy in computing the dispersion relation is avoided. Propagator equations for SH and for P‐SV waves are given for both isotropic and transversely isotropic media. In addition, the second minor propagator equations for P‐SV waves are given. Matrix polynomial approximations to the propagators, obtained from the method of mean coefficients by the Cayley‐Hamilton theorem and the Lagrange‐Sylvester interpolation formula, are derived.
QUANTITATIVE INTERPRETATION OF GAMMA‐RAY SPECTRAL LOGS
Authors: Rhodes D. F. , Mott W. E.
Published: October 2002

From calculations of the intensity of unscattered gamma rays inside cylindrical self‐absorbing sources, curves have been developed that aid in the application of gamma‐ray spectrometric techniques to borehole logging. Specifically, the curves provide factors which can be used to normalize spectral data to any standard set of borehole and formation conditions used for calibration. Taken into account are the effects of borehole diameter, mud density, casing and cement thickness, bed thickness, and detector eccentricity. Illustrative examples of applications of these curves depict the solutions to a variety of specific problems as well as methods for obtaining additional curves. Curves showing the portion of the log response due to gamma rays originating within specific zones of the formation provide an evaluation of the depth of investigation of the gamma‐ray spectral log.
VERTICAL GRADIENT OF GRAVITY ON AXIS FOR HOLLOW AND SOLID CYLINDERS
Authors: Elkins Thomas A.
Published: October 2002

The recent interest in borehole gravimeters and vertical gravity gradient meters makes it worthwhile to analyze the simple case of the vertical gravity gradient on the axis of a hollow cylinder, simulating a borehole. From the viewpoint of potential theory the results are interesting because of the discontinuities which may occur when a vertical gradient profile crosses a sudden change in density. Formulas for the vertical gradient effect are given for observations above, inside, and below a hollow cylinder and a solid cylinder. The special case of an infinitely large outer radius for the cylinders is also considered, leading to formulas for the vertical gradient effect inside a borehole on its axis and inside a horizontal slab. Some remarks are made on the influence of the shape of a buried vertical gradient meter on the correction factor for changing the meter reading to density.
THE APPLICATION OF FINITE FORWARD DIFFERENCES IN THE RESISTIVITY COMPUTATIONS OVER A LAYERED EARTH
Authors: Nabighian Misac N.
Published: October 2002

The paper describes a new method of computing the infinite series which arise in the calculation of standard graphs in the resistivity method. It is shown that, by using finite forward differences of higher orders and repeated summations by parts, the convergence of the potential and resistivity series can be improved appreciably. The procedure allows calculations with any degree of accuracy and with a substantial savings in computational labor. A correct estimate of the truncation errors involved may easily be determined.
APPLICATION OF DYNAMIC PROGRAMMING TO THE PROBLEM OF PLANE WAVE PROPAGATION IN A LAYERED MEDIUM
Authors: Darby E. K. , Neidell Norman S.
Published: October 2002

The philosophy of dynamic programming is applied to the problem of plane wave propagation at normal incidence in a layered medium. Using the intuitive concepts of reflection, transmission, and delays, the problem is reduced to a two‐stage process or a two‐layer problem where one of the layers is inhomogeneous. A solution in terms of recursive relations is obtained and a method for compactly describing complex configurations of layers is given. The recursive relations proceed forward in time.
PRACTICAL CONSIDERATIONS IN THE USE OF COMMON REFLECTION POINT TECHNIQUES
Authors: Mayne W. Harry
Published: October 2002

The effectiveness of the common‐reflection‐point horizontal stacking technique is dependent upon the accuracy with which the desired signals (primary reflections), recorded with different travel paths, can be aligned in‐phase for summation. Inaccuracies can result from the application of an incorrect moveout function, improper corrections for near‐surface effects, and variation in the signal waveform on the channels to be summed. The last effect can occur because of differences in the transmission path and/or changes introduced in processing. A typical case is described to illustrate the magnitude of errors observed in one survey and the adjustments which were required to establish time coincidence of the primary reflections. Theoretical considerations defining the maximum permissible errors in phase alignment for various numbers of channels indicate that the allowable error should not exceed one half the reflection period regardless of the number of channels, and that the required precision increases rapidly as the number of channels is decreased. For example, a twelve‐fold stack will permit nearly twice the allowable error as a three‐fold stack for the same end result.
EXPERIENCES WITH MULTIPLE COVERAGE SEISMIC METHODS
Authors: Courtier W. H. , Mendenhall H. L.
Published: October 2002

Several comparisons from current operating areas show the data enhancement of the CRP (multiple coverage) compositing process. The use of 24‐trace geophone spreads 7200—0—7200 ft has evolved for most work performed by phillips Petroleum Company, after more than 100 crew years of experience. Common section cabling, limited lead drilling and operations, ample radio communications, proper shotpoint numbering, and efficient drilling operations have produced average overall year round costs, for twelve‐fold coverage of approximately $1630 per mile (95.2 percent twelve‐fold plus 4.8 percent six‐fold). This includes all areas and all playback, processing, and interpretation costs.
AEROMAGNETIC EVIDENCE FOR HUECO MOUNTAIN WRENCH FAULT, TEXAS
Authors: Steenland Nelson C.
Published: October 2002

Several noteworthy examples of magnetic evidence of strike‐slip faults have been published in recent years, including examples in the Pacific Ocean (Vacquier et al. 1961) and the western Atlantic Ocean (Drake and Woodward, 1963). Aeromagnetic data indicate vertical and horizontal movement along the southern edge of the Hueco Mountains, El Paso and Hudspeth Counties, Texas. The amount of slip is small compared to the published examples, but displacement is of interest because it occurs at the junction of two large, vastly different geologic provinces, the Basin and Range province to the north and the thrust belt of northern Mexico to the south.
ELECTROMAGNETIC FIELDS IN AN N‐LAYER ANISOTROPIC HALF‐SPACE
Authors: O’Brien Douglas P. , Morrison H. F.
Published: October 2002

From Maxwell’s equations and Ohm’s law for a horizontally anisotropic medium, it may be shown that two independent plane wave modes propagate perpendicular to the plane of the anisotropy. Boundary conditions at the interfaces in an n‐layered model permit the calculation, through successive matrix multiplications, of the fields at the surface in terms of the fields propagated into the basal infinite half space. Specifying the magnetic field at the surface allows the calculation of the resultant electric fields, and the calculation of the entries of a tensor impedance relationship. These calculations have been programmed for the digital computer and an interpretation of impedances obtained from field measurements may thus be made in terms of the anisotropic layering. In addition, apparent resistivities in orthogonal directions have been calculated for specific models and compared to experimental data. It is apparent that the large scatter of observed resistivities can be caused by small changes in the polarization of the magnetic field.
THERMAL REGIME OF A LARGE DIAMETER BOREHOLE: INSTABILITY OF THE WATER COLUMN AND COMPARISON OF AIR‐ AND WATER‐FILLED CONDITIONS
Authors: Diment William H.
Published: October 2002

Temperatures were measured as a function time and depth in a borehole before and after it had been filled with water. The hole is 25 cm in diameter, 340 m deep, and effectively sealed from influx of ground water. The measurements reveal that: (1) Temperature differences between the air‐filled hole and the water‐filled hole (after dissipation of the water injection disturbance) do not exceed 0.05°C at the same depth. (2) Temperatures in the water‐filled hole exhibit oscillations at all depths where temperature increases downward but are stable at the bottom and near the surface where temperature decreases with depth. (3) The temperature oscillations have periods ranging from several minutes to several hours. (4) The amplitudes of the oscillations are several hundredths of a degree, and are roughly proportional to the geothermal gradient near the point of measurement, thus suggesting that the size of cells or eddies are rather constant and that the distance of water movement is no more than several times the inner diameter of the casing. (5) No oscillations were detected in the air‐filled hole, but because the time constants of the instrument are long in an air‐filled hole, the possibility of short period oscillations cannot be excluded.
STATISTICAL EVALUATION OF DEEP CRUSTAL REFLECTIONS IN GERMANY
Authors: Dohr Gerhard , Fuchs Karl
Published: October 2002

By a routine method of observation during exploration reflection measurements, sufficient data were compiled to allow significant statistical conclusions concerning deep crustal reflectors. The appearance of deep crustal reflections differs considerably from that of reflections from shallow sedimentary beds. They correlate only over short distances, seldom more than a few kilometers. The reflection times display quite a scatter, even over small areas. In many cases the reflected signal is typically broadened to continue over a few cycles. Following this reflection band along a profile, the main energy is frequently shifting from one phase to another until finally it disappears completely. A new method of wide angle reflection observations using a common reflection point technique was used to support and confirm results of the statistical analysis.
A STATISTICALLY OPTIMIZED DECONVOLUTION
Authors: Burns W. R.
Published: October 2002

There are many innate errors involved in the process of deconvolution. Of interest here is an analysis of one of these. In particular, the errors resulting from the pseudo randomness of the seismic records are calculated. These errors are present even assuming that the many assumptions involved in the deconvolution process are correct. Such assumptions are in themselves dangerous. The errors calculated thus represent the most optimistic conditions. A technique to calculate the useful amount of deconvolution is derived using the error information. The technique is applied, example results given, and the practical difficulties discussed. The technique is found to be of primary interest as a learning device and research tool. Its complexities at present limit its use in routine processing. It is found, however, to yield information which cannot otherwise be objectively obtained.
SYNTHESIS OF A LAYERED MEDIUM FROM ITS ACOUSTIC TRANSMISSION RESPONSE
Authors: Claerbout Jon F.
Published: October 2002

A direct (noniterative) method is presented to determine an acoustic layered medium from the seismogram due to a time‐limited plane wave incident from the lower halfspace. It is shown that one side of the autocorrelation of the seismogram due to an impulsive source at depth is the seismogram due to an impulsive source on the surface. This transforms the problem to the acoustic reflections problem as solved by Kunetz. Both the deep source time function and the layering can be determined from a surface seismogram.
EFFECTS OF STRUCTURE ON THE GRAVITY FIELD OF WYOMING
Authors: Malahoff Alexander , Moberly Ralph
Published: October 2002

A density model of the upper crust of Wyoming, computed on structural and petrographic evidence without prior reference to gravity data, when compared with the observed gravity field, demonstrates that: (1) Existing measurements and theory of change of sedimentary rock density with depth of burial are satisfactory for gravity interpretation for local rock types and the slower rates of sedimentation in the area. (2) Gravity stations established over sedimentary basins are generally as satisfactory as those on basement rock outcrops for depicting regional Bouguer gravity trends. (3) The Laramide deformation was mainly germanotype. The regional gradient in Bouguer gravity across Wyoming has increasingly negative values to the southwest. Local variation in the Bouguer anomaly field is related mainly to the low density Cretaceous and Cenozoic sediments of the basins, and to a lesser degree to the Laramide structural blocks. Interpretation of the gravity field indicates that the blocks are bounded by near‐vertical faults extending into the upper mantle, and that the uplifted blocks are undercompensated (i.e., rootless). In order to lead to a reasonable depiction of isostasy for the region, plots of mean Bouguer anomalies versus mean elevation must be made over 2°×2° squares, or larger, because of the variation in structure and composition of the crust.
THEORY OF BOREHOLE MAGNETIC SUSCEPTIBILITY MEASUREMENTS WITH COIL PAIRS
Authors: Anderson Wallace L.
Published: October 2002

The boundary value problem for an axially symmetric configuration of a transmitter‐receiver coil pair in a borehole is considered with particular attention to the “quadrature component” of voltage induced at the receiver coil. It has been known from mathematical expressions previously presented in the literature on induction logging that the quadrature voltage is dependent upon the magnetic permeabilities of the formation and borehole media. The purpose of this investigation was to explore the nature of that dependence in sufficient detail to ascertain some features of its potential usefulness for magnetic susceptibility measurements, particularly of the type contemplated in “Project Mohole.” Although that project is no longer being actively pursued, results of the study are of possible interest in magnetic susceptibility measurements for other purposes, such as geologic correlation. Numerical results from a digital computer program show that the quadrature voltage at the receiver coil is essentially independent of changes in borehole or formation conductivity under the conditions for which the computations were performed. Effects of coil size and the spacing between coils on the quadrature receiver coil voltage were used to determine optimum coil geometry. Analytical expressions valid for small ratios of coil diameter to coil spacing confirm the computer results throughout their domain of validity. An investigation of the sensitivity of the method shows that, when coil geometry is optimum, a given percentage change in κ yields a very slightly greater percentage change in receiver coil voltage. With proper coil spacing, the dependence of receiver coil voltage on κ is very well described by an equation of the form [Formula: see text] where γ is a constant nearly equal to one. This result was verified both analytically and numerically by the calculations from the full expression for voltage.
IS SEISMIC ENERGY OF DIAGNOSTIC VALUE?
Authors: Hermont A. J.
Published: October 2002

Since both the intensity of a seismic wave and its energy density are directly related to the square of the particle velocity, a quantity available as the output of a geophone, it is feasible to record energy density as a function of time and space. The energy recorded is a function of the spatial attenuation factors of the media traversed, the partition at reflection boundaries, and the geometric spreading. If a proper correction can be made for the latter two effects, it is possible to generate a function that is diagnostic of the attenuation properties of the geologic model and may be useful for lithologic interpretation. A quantity that is proportional to the logarithm of the peak absolute value of the square of the particle velocity, or the logarithm of the energy density, was recorded along a series of test profiles. Conventional reflection data were also recorded. The purpose of the field program was to gain preliminary experience in energy recording and to seek an answer to the query posed in the title. The main conclusion is affirmative. This, however, must be qualified. It is apparent that several serious impediments must be overcome. It is necessary to develop satisfactory techniques to remove the geometric and reflectivity effects from the recorded energy data, to eliminate measurement errors which can produce magnitude errors of several orders, and, above all, to develop a detailed and accurate set of in‐situ spatial attenuation factor data.
A DEEP SCHLUMBERGER SOUNDING TO INVESTIGATE THE ELECTRICAL STRUCTURE OF THE CRUST AND UPPER MANTLE IN SOUTH AFRICA
Authors: Van Zijl J. S. V.
Published: October 2002

A deep Schlumberger electrical sounding on the Namaqualand Granite‐Gneiss Complex has been carried out. The sounding center is situated near the middle of this body which measures approximately 500 km by 150 km. Whereas in previous investigations of a similar nature, current electrode spacings have generally been limited to less than 100 km, the use of a telephone line as an emission line has made it possible to extend the maximum current electrode separation to 270 km. Factors which may have influenced the reliability of the measurements include leakage tests, measuring accuracy, lateral effects, and surface electrode effects. The interpretation of the sounding curve which shows the existence of six layers was carried out with the aid of a computer. Some comments are made about the range of the principle of equivalence in the interpretation from the computed results. In particular the results suggest that the lower crust has an extremely high resistivity of approximately 40,000 ohm‐m supposedly due to dehydration. The final layer is conductive.
MULTIVARIATE ANALYSIS USED IN THE DETECTION OF STRATIGRAPHIC ANOMALIES FROM SEISMIC DATA
Authors: Mathieu P. G. , Rice G. W.
Published: October 2002

In attempting to interpret stratigraphic changes from seismic data, we usually try to detect quantitative changes in one or two variables: amplitude of a peak, say, or time interval between peaks. At times, we may try to detect qualitative changes in wave shape. Differentiating stratigraphic conditions from a single variable, say time interval or amplitude, is often very difficult because the observed differences within the variable may be small and within the expected range of noise. However, a linear combination of a larger number of variables can, in some cases, uniquely describe a specific stratigraphic condition. Furthermore, linear coefficients can be computed which will optimize the discrimination between stratigraphic conditions. Stratigraphic conditions such as the variation from a sand to a shale can be described by seismic measurements, say amplitudes at discrete times. For example, [Formula: see text], [Formula: see text], ⋯, [Formula: see text] can represent the digitized amplitudes of a synthetic seismogram from one sand well; [Formula: see text], [Formula: see text], ⋯, [Formula: see text] would be amplitudes from another sand well; [Formula: see text], [Formula: see text], ⋯, [Formula: see text] would be amplitudes from a shale well; and so on. Discriminants [Formula: see text], [Formula: see text], ⋯, [Formula: see text] for sand and [Formula: see text], [Formula: see text], ⋯, [Formula: see text] for shale are computed such that the several seismograms of one group are brought close together while the two groups (sand, shale) are maximally separated. This technique, known as discriminatory analysis, is familiar to the statisticians. It is shown how the technique can be used effectively with seismic data, and an example is given in which it successfully delineated a known oil‐bearing sand body directly from seismic traces.
A DEEP‐SEA ELECTRICAL RESISTIVITY PROBE FOR MEASURING POROSITY AND DENSITY OF UNCONSOLIDATED SEDIMENTS
Authors: Kermabon A. , Gehin C. , Blavier P.
Published: October 2002

A study has been made of the mass physical properties and electrical resistivity of marine sediments. The well‐known linear correlation of density with porosity was confirmed. A third‐degree polynomial curve was found to be the best fit for our data relating porosity and the formation factor, which is the ratio of the bulk resistivity of marine sediments, to the resistivity of interstitial water. An electrical resistivity probe has been devised to obtain “in‐situ” profiles of resistivity versus depth. The instrument is 13 m long and weighs 700 kg in water. About thirty rapid measurements on the sea floor can be made in one lowering. Good correlation was obtained between electrical probe measurements and direct porosity measurements made on cores taken nearby.
APPLICATION OF DEEP ELECTRICAL SOUNDINGS FOR GROUNDWATER EXPLORATION IN HAWAII
Authors: Zohdy Adel A. R. , Jackson Dallas B.
Published: October 2002

Forty‐five resistivity soundings, using Schlumberger and equatorial dipole electrode configurations, were made on the islands of Oahu and Hawaii to determine the applicability of direct current resistivity methods for locating freshwater aquifers in the State of Hawaii. The soundings were made on the northwestern part of the island of Oahu near the town of Waialua and on the island of Hawaii on the “saddle” area near Pohakuloa and Humuula. Interpretation of 32 sounding curves obtained on the island of Oahu indicates that it is possible to correlate five stratigraphic units underlain by a vesicular basalt basement and that the determination of the approximate depth to the fresh‐water‐saline‐water interface within the basalt is feasible. Two of these Schlumberger soundings with electrode spacings [Formula: see text] reaching 6000 ft yielded sounding curves of the maximum and minimum types whose terminal branches asymptotically approach a resistivity of about 30 ohm‐m, which is believed to be the true resistivity of basalt saturated with sea water. Near the town of Waialua the aquifer is a coral zone as well as parts of the weathered vesicular basalt basement. On the island of Hawaii, near Pohakuloa, an exploratory well drilled in basalt to a depth of 1001 ft (prior to the resistivity survey) proved to be dry. Interpretation of thirteen deep soundings made with Schlumberger and equatorial arrays suggests that the minimum depth to a conductive layer, which may represent basalt saturated with fresh water, is about 2700 ft below land surface. The groundwater appears to be dike impounded.
IP AND RESISTIVITY TYPE CURVES FOR THREE‐DIMENSIONAL BODIES
Authors: Dieter K. , Paterson N. R. , Grant F. S.
Published: October 2002

A new method for calculating anomaly patterns and type curves of apparent resistivity and apparent chargeability over three‐dimensional bodies imbedded in a half‐space is practicable. The solution of the boundary‐value problem for a point source of current near a body of arbitrary shape in the form of an inhomogeneous integral equation is solved numerically by the method of least squares. The solution is then used to construct the apparent resistivity and apparent chargeability functions for three and four‐electrode arrays in the vicinity of the body in a straightforward manner. Type curves show the application to an actual field example. Finally, some simple, direct aids for interpreting anomalies over mineralized zones of compact (i.e. roughly spherical) shape result. This study represents the results of the first phase of a continuing program of research into resistivity and IP interpretation theory.
On: “The Coefficient of Coherence: Its Estimation and Use in Geophysical Data Processing,” by M. R. Foster and N. J. Guinzy (GEOPHYSICS, August 1967, p. 602–616)
Authors: Colligan J. A.
Published: October 2002

This note is to point out an error in the article by Foster and Guinzy. The error occurs in equation (11) (p. 604) which should read [Formula: see text].
SIMULATION OF TIME‐DOMAIN, AIRBORNE, ELECTROMAGNETIC SYSTEM RESPONSE
Authors: Becker A.
Published: October 2002

The response of a time‐domain electromagnetic system over a thin conducting sheet may be simulated by purely electronic means and without recourse to scale model experiments. The simulation is based on the similarity between the frequency domain response function for a thin sheet and the transfer function of certain RC active networks. Since this type of experiment employs actual field equipment, the proposed technique also constitutes a valid means of data quality control. It is difficult to carry out an analog simulation for conductors which do not resemble a thin sheet. If, however, the frequency domain response function for the situation in question is known, the simulation may be carried out on a digital computer. The digital simulation process involves a numerical Fourier decomposition of the primary field waveform (as seen by the receiver), the calculation of the effect of the ground on each harmonic component, and the recombination of the secondary field harmonics to form the observed transient. The technique is illustrated with some calculations of theoretical responses for an EM system over a homogeneous ground and over a thin horizontal conducting sheet. The digital simulation technique is more useful than the analog.
GRAVIMETER FILTERS
Authors: Floyd George F.
Published: October 2002

In order to obtain accurate gravity measurements from ships or aircraft, it is necessary to remove the “noise” effects of platform accelerations by filtering. At the same time, the filter must track the changing gravitational field, the “signal,” or signal errors will result. Thus, there is the optimization problem of designing filters which maximize noise reduction without introducing signal tracking errors. The best class of filters for this purpose is defined in terms of what is called a zero signal‐error constraint, which specifies that the filter must track any parabolic input with no error except a known time delay. Since the noise to be eliminated is such that a low‐pass filter is required, study of the transfer functions was restricted to that type filter in light of this constraint. It was found that only the Butterworth filter with n⩾2 is satisfactory. The problem of physical realization of an optimum filter was investigated by setting appropriate constraints on attenuation at the cut‐off frequency and the envelope at the impulse response.