bluuebunny/crossref_metadata_2025 huggingface dataset:
AN EVALUATION OF BASEMENT DEPTH DETERMINATIONS FROM AIRBORNE MAGNETOMETER DATA
Authors: Jacobsen Peter
Published: October 2002

Four years ago Creole Petroleum Corporation submitted identical airborne magnetometer data for a portion of the Eastern Venezuela basin to two different geophysical contractors for independent, detailed analysis. These contractors offer the customary generalized basement depth maps; but they specialize in delineating areas of relatively local relief on the basement surface. Both kinds of interpretation were requested by Creole. The main purpose of the study was to evaluate the reliability of interpretations of local basement relief from magnetic data. Accordingly, the region for study was deliberately chosen to include, in part, areas for which Creole had considerable knowledge of basement depths and local basement configuration from other sources. Local basement relief shown by the two magnetic interpretations is in poor agreement with basement depth information from seismograph and well data. Moreover, the two magnetic pictures bear little resemblance one to the other. With respect to regional basement depth contours, one of the magnetic interpretations compares statisfactorily with the picture based on seismograph and well control. A tentative conclusion is that local basement relief cannot be reliably interpreted from magnetometer data alone.
A CRUSTAL STRUCTURE REFRACTION SURVEY IN SOUTH TEXAS
Authors: Cram Ira H.
Published: October 2002

On August 11, 1960, sixty oil exploration and research seismograph crews attempted to record two shots detonated in the Texas Gulf Coastal Plain. Shotpoint A was located 16 miles northwest of Cleveland, Texas. Shotpoint B was located 27 miles northwest of Victoria, Texas. The shotpoint line is approximately parallel to the strike of the Cenozoic sediments and the distance between shotpoints is 260.2. km. More than 3,000 lb of explosives were placed in five holes at each shotpoint. The top of the charge was at a depth of 95 ft and the bottom at 250 ft at each shotpoint. The regional Bouguer anomaly is −25 mgal. The shot instant was keyed to a 140 cps reference signal transmitted by radio station KTRH, Houston, Texas. First and later refracted arrivals were used to determine the velocity structure which was supported by events identified as reflections from the refractors. The results indicate the following thickness‐velocity relationships: 2.0 km of 2.3 km/sec material, 5.3 km of 3.94 km/sec material, 12.5 km of 5.38 km/sec material, and 13.2 km of 6.92 km/sec material. The Mohorovicic discontinuity is represented by a velocity of 8.18 km/sec, and the total crustal thickness is 33.0 km. Possible geologic identities of the refractors are as follows: the 2.3 km/sec and 3.9 km/sec layers represent the Cenozoic and Mesozoic sediments, the 5.4 km/sec layer represents Paleozoic and Precambrian rocks, the 6.9 km/sec layer is the high‐velocity crustal layer, and the 8.18 km/sec zone represents upper mantle material. The South Texas velocity section appears to correlate well with adjacent measurements in the Gulf of Mexico and in northeastern Arkansas.
RAPID COMPUTATION OF GRAVITY ANOMALIES FOR IRREGULARLY SHAPED THREE‐DIMENSIONAL BODIES
Authors: Roy Amalendu
Published: October 2002

So much has been written (Levine, 1941, Gassman, 1951, Baranov, 1953, Talwani and Ewing, 1960, Goguel, 1941, etc.) on the above subject that any further publication on this theme seems to be of doubtful value. The only justification of printing this note lies in the genuine simplicity of both derivation and use of the method outlined herein. While this may be of particular interest to those who have to undertake manual computation, some simple scheme of programming on digital computers may perhaps also be devised.
GEOPHYSICAL CASE HISTORY OF THE ALTURITAS CONCESSION, STATE OF ZULIA, WESTERN VENEZUELA
Authors: Stenson Harry R.
Published: October 2002

The geophysical case history of Alturitas area, western Venezuela is presented. It is unusual in that all the commonly used geophysical methods were employed. The Alturitas anomaly was discovered by the torsion balance in 1929. Subsequent surveys included the gravity meter, magnetometer, refraction and reflection seismograph. The surveys are discussed in chronological order giving the reasons for the particular surveys and results obtained. Although the geophysical results were generally good, an error correlation led to a misinterpretation of stratigraphic relations. This in turn resulted in drilling depths much deeper than anticipated. Five wells were drilled on the concession resulting in three oil wells and two dry holes. Alturitas‐1 and Alturitas‐2 are two of the deepest oil wells outside the United States. Maps are presented for the key geophysical surveys.
BENEATH THE SURFACE
Authors: Brant A. A.
Published: October 2002

One‐half score and three years ago we gathered here to see whether mining exploration might not prosper. Now we are engaged in a great test as to whether any endeavor conceived by ordinary men operating freely, can long endure.
THE SEISMOLINE, AN ANALOG COMPUTER OF THEORETICAL SEISMOGRAMS
Authors: Sherwood J. W. C.
Published: October 2002

A description is given of the Seismoline, an electrical analog computer of theoretical reflection seismograms involving all primary and multiple reflections. The computer utilizes an analogy between seismic wave propagation through a stratified earth and electrical wave propagation along a lumped‐parameter transmission line. A description is given of the prototype Seismoline and the experimental tests performed on it. It is concluded that it provides a convenient, speedy, and sufficiently accurate computer for the quantity production of theoretical seismograms, except possibly in cases where the acoustic impedance contrasts of the geologic section are extremely low. Changes in the velocity and thickness of the various geologic layers may be made with ease, and the resulting changes on the seismogram can be viewed almost simultaneously. This inherent flexibility introduces the possibility of a feedback process whereby an operator might modify his filter settings or the geologic model in order to effect a better match between corresponding theoretical and field seismograms.
ELECTRICAL RESISTIVITY OF ROCKS IN THE AREA 12 TUNNELS, NEVADA TEST SITE, NYE COUNTY, NEVADA
Authors: Keller George V.
Published: October 2002

Electrical resistivity measurements provide a semiquantitative method for estimating the water content of a rock. Techniques for measuring resistivity along tunnel walls and in horizontal drill holes were used in the Area 12 tunnel complex at the Nevada Test Site prior to the Atomic Energy Commission’s Hardtack Phase II test series during the fall of 1958. The results indicate that in future underground tests where the amount of water in the rock must be determined, resistivity measurements can be used to estimate water content, with only a limited number of samples needed to check the results.
SEISMIC EXPLORATION IN THE CANADIAN ARCTIC ISLANDS
Authors: Hobson George D.
Published: October 2002

The Polar Continental Shelf Project, a broad program of research in the Canadian Arctic, was started in 1959. Seismic studies were undertaken by the Geological Survey of Canada. Refraction and reflection techniques were employed in the first stages of a reconnaissance program during May, June, July, and August 1960. Certain new techniques were developed during this seismic program in the high Arctic. The crew operated from motor toboggans in 1960 but helicopters will be used more extensively in the future for a more efficient operation. Adverse weather conditions such as blizzards, low temperatures, white‐outs, wind, and rain are a hindrance to operations at various times of the year. The sea ice appears to present no great noise problem to standard recording techniques. Several air shots were recorded in direct comparison with surface shots but the gain in energy level is not enough to justify using the method. The records from various locations within the Sverdrup Basin indicate that both reflection and refraction techniques are satisfactory. A cross‐section illustrates the results of the 1960 program.
On: TUMAN’S PAPER ON “REFRACTION AND REFLECTION OF SONIC ENERGY IN VELOCITY LOGGING” (GEOPHYSICS, OCTOBER, 1961, P. 588)
Authors: Geertsma J.
Published: October 2002

In his paper, Tuman found that, surprisingly, in all cases studied the minimum travel time of acoustic waves was along a curved path in a formation surrounding a borehole. The curvature resulted from velocity variations around the borehole in formations which show a nonlinear stress‐strain relationship. However, the results of these calculations may be in error due to the use of incorrect stresses selected for the determination of the local acoustic wave velocity. In particular, the use of the radial stress distribution for this purpose is doubtful for the calculation of a curved travel path which in general does not deviate much from the vertical direction.
ELASTIC WAVES ALONG A CYLINDRICAL BORE
Authors: White J. E.
Published: October 2002

This paper concerns axially symmetric solutions for waves propagating along a cylinder in an infinite elastic solid. Solutions are presented describing unattenuated propagation along the axis at phase velocities higher than shear and compressional speeds in the solid, in contradiction to earlier publications. Special attention is given to the limiting case of phase velocity equal to compressional speed in the solid, which at low frequencies very closely approximates the coupling of a fluid‐filled borehole to a plane compressional wave in the surrounding solid. Comparison with some experiments in a uniform section of Pierre shale show excellent agreement at low frequencies. In the low‐frequency limit, these solutions reduce to an approximate expression for borehole coupling published earlier by the author.
A NOTE ON THE ELECTROMAGNETIC RESPONSE OF A STRATIFIED EARTH
Authors: Wait James R.
Published: October 2002

The response of an oscillating magnetic dipole over a continuously stratified flat earth is considered. As a result of certain simplifying approximations, which are valid at low audio frequencies, solutions for exponentially varying conductivities can be obtained in relatively simple form.
INHOMOGENEOUS CYLINDRICAL ORE BODY IN PRESENCE OF A TIME VARYING MAGNETIC FIELD
Authors: Negi Janardan G.
Published: October 2002

The secondary fields are evaluated for the case of an inhomogeneous conducting cylinder embedded in an infinite homogeneous medium under the influence of a time varying magnetic field. Both sinusoidal and step function responses are studied in detail for a practical case of interest in geophysical prospecting in which the exterior medium is relatively poorly conducting, the propagation constant in the cylinder is varying linearly across the section of the core, and the magnetic permeability is the same everywhere.
STRATIGRAPHIC TRAP STUDY IN COTTONWOOD CREEK FIELD, BIG HORN BASIN, WYOMING
Authors: Sengbush R. L.
Published: October 2002

Stratigraphic trap production in the Cottonwood Creek field is controlled by loss in porosity and facies change in the “E” zone of the Phosphoria dolomite. The edge of the field was delineated on the seismic records through loss in amplitude of the high‐frequency “E” zone reflection due to thinning and decrease in velocity contrast of the “E” zone. Variable‐area cross‐sections show vividly this stratigraphic change. This study indicates that present techniques of magnetic tape recording and processing coupled with synthetic seismograms and the attendant filter theory approach to the seismic method have increased the capability of the seismic method to find stratigraphic traps.
LOVE WAVE DISPERSION IN HETEROGENEOUS ANISOTROPIC MEDIA
Authors: Anderson Don L.
Published: October 2002

An analysis is made of Love‐wave propagation in a medium composed of transversely isotropic layers. This is the kind of anisotropy which most commonly occurs at the surface of the earth, and in particular is displayed by bedded sediments. The exact boundary value problem is solved for a simple layer and extended to multilayered media by a generalization of Haskell’s technique. By a suitable redefinition of parameters, it is possible to cast the anisotropic problem into isotropic form so that existing programs, tables, and graphs can be used to determine the structure of layered anisotropic media. It can be shown that the Love‐wave period equation expresses the condition of constructive interference between multireflected SH waves with directionally dependent velocities. Also, it is demonstrated analytically and numerically that a restricted form of the anisotropy considered here is the limit of a finely laminated solid as the laminations become much smaller than a wave length. For long wave lengths, a multilayered structure may be replaced by an equivalent single layer.
GEOPHYSICAL DATA ON THE CLIMAX STOCK, NEVADA TEST SITE, NYE COUNTY, NEVADA
Authors: Allingham John W. , Zietz Isidore
Published: October 2002

A granitic stock at Oak Spring, Nevada, was selected in 1960 by the Atomic Energy Commission as a possible site to study the seismic effect of a deep nuclear shot contained in a large volume of rock. Geophysical surveys were conducted to determine the general configuration of the stock, particularly the thickness. The stock intrudes a sequence of carbonate and siliceous sedimentary rocks of Paleozoic age, which are overlain by Tertiary pyroclastic rocks consisting of tuff, welded tuff, and breccia. A three‐dimensional analysis of a detailed aeromagnetic survey indicates that the stock has a shape similar to a truncated cone, the diameter of which increases from about one mile at the surface to at least 6 miles near sea level, 5,000 feet beneath the surface. The stock, therefore, is much larger than indicated by the area of [Formula: see text] square miles exposed at the surface. In addition, computations show that the intrusion has a thickness of at least 13,000 ft. Much of the ambiguity of interpretation was removed from the analysis because susceptibility measurements of cores from recent drilling and remanent magnetization data from surface samples were available. Interpretation of a gravity profile over the stock gives the probable thickness of the overlying alluvial fill and buried tuff, but does not delineate the intrusive from the Paleozoic rocks.
THE MAGNETO-TELLURIC EFFECT ON A DIKE
Authors: Rankin David
Published: October 2002

The method of d’Erceville and Kunetz (1962) is applied to the solution of the magneto‐telluric effect on a vertical dike for the special case of the magnetic vector polarized parallel to the strike. The results for several frequencies have been computed and are presented graphically.
ELECTROLYTE ACTIVITY: ITS EFFECT ON INDUCED POLARIZATION
Authors: Keevil N. B. , Ward S. H.
Published: October 2002

Induced polarization (IP) occurs at metal‐solution and membrane‐solution interfaces in rock materials. Minerals producing significant IP include sulfides, magnetite (electrode polarization), and some clays (membrane polarization). In mineral exploration, one is concerned with the distinction between these two phenomena; either may be significant, but together they are confusing. While no practical means has yet been devised to do this in the field, one may exist. The present study represents the first stage in an attempt to elucidate the phenomena and to make such a distinction. There is no means of studying directly the effect of variables on polarization at a single interface or cell in a rock if those variables also affect rock resistivity. Hence, one must speak of rock IP independently of individual cell IP. Data reported herein reflect rock IP. Temperature and pressure appear to have little effect on IP of specimens studied so far; further investigation may show that they are important in some geologic environments. Changes in electrolyte activity greatly influence rock IP. Membrane and disseminated electrode polarization decrease while connected (veined) electrode IP increases with increasing activity. This fact may be useful in interpretation of depth variations of IP in the field, particularly over oxidizing sulfide bodies.
THEORETICAL SEISMOGRAMS WITH FREQUENCY AND DEPTH DEPENDENT ABSORPTION
Authors: Trorey A. W.
Published: October 2002

In the computation of conventional theoretical (or “synthetic”) seismograms, the effects of the variation of frequency‐dependent absorption with depth are presently ignored. Such absorption can produce significant differences in both the relative amplitudes and frequency spectra of primary and multiple reflections having the same arrival time. This paper describes a feasible way, using a digital computer of the IBM 7090 class, for computing theoretical seismograms which properly take into account the variation of absorption with both frequency and depth, it being assumed that the absorption coefficient varies linearly with frequency. It is pointed out that attempts to solve the problem using Fourier analysis in the frequency domain would lead to significant aliasing errors. Consequently a method borrowed from the field of network theory utilizing deconvolution is devised whereby solutions are obtained directly in the time domain. Both “primary” and “primary‐plus‐all‐multiple” traces are computed, the former including the “peg‐leg” multiples described by Anstey (1960) and Webster (1960). These calculations demonstrate that absorption can reduce the multiple content of theoretical seismograms.
NEW SP CORRECTION CHARTS
Authors: Segesman F.
Published: October 2002

For use in quantitative log analysis, SP correction charts were constructed from data taken on a resistor network analog for various cases of invaded and noninvaded thin beds. An abrupt transition was simulated between invaded and noninvaded zones. Batteries were inserted at appropriate locations in the high‐impedance network to simulate the electrochemical emf’s contribution to the SP. The correction curves are presented in a form considered to be easily usable by the working log analyst. Examples of their use are shown. Various factors to observe in the application of the charts are discussed.
ON TECHNIQUES WITH SEISMIC INTERVAL TIMERS
Authors: Hawkins L. V.
Published: October 2002

In the paper by J. C. Stam (Geophysics, April, 1962, pp. 198–212) reviewing developments in shallow seismic refraction techniques, the single‐channel seismographs using a time counting circuit are discussed. I would like to take the opportunity of commenting on techniques in use with this type of instrument.
THE MEASUREMENT OF SHEAR‐WAVE VELOCITIES IN SOLIDS USING AXIALLY POLARIZED CERAMIC TRANSDUCERS
Authors: Jamieson John C. , Hoskins Hartley
Published: October 2002

A double mode conversion obtained by critical‐angle reflection allows the velocity of shear‐wave propagation to be determined using longitudinally polarized ceramic discs. This method provides a simple and convenient method of obtaining high‐frequency shear waves of predeterminable polarization in the laboratory. Elastic constants of brass and Pyrex obtained with this method are in excellent agreement with those measured by the PnSP method of Hughes. This mode conversion technique, unlike the PnSP method, can be used on anisotropic materials of noncylindrical geometries.
PROPERTIES AND DRAWING OF THE SO‐CALLED DAR ZARROUK CURVES
Authors: Orellana Ernesto
Published: October 2002

The physical significance of the so‐called Dar Zarrouk curves (Maillet) is clarified and some new conclusions are drawn. A method is described for the quick and accurate construction of these curves based on the properties cited. The author illustrates the way to use them in solving different types of problems related to electrical prospecting, such as the determination of the limits of validity of the principle of equivalence, the depth of penetration, the possibility of differentiating between similar formations, etc. Five practical examples are discussed, and a template for use in the construction of Dar Zarrouk curves is included.
NATURAL RADIOACTIVITY IN WASHINGTON COUNTY, MARYLAND
Authors: Moxham R. M.
Published: October 2002

Natural gamma‐radioactivity patterns in Washington County, Maryland, reflect the principal variations in lithology. The highest radioactivity is associated with the more argillaceous parts of the geologic section and with soils derived from high‐potassium carbonate rocks. Surface radiation intensity ranges from about 5 to 30 microroentgens per hour, of which the rocks contribute 30 to 90 percent. From the aerial survey data, the surface radiation intensity from extended sources can be estimated to within about three microroentgens per hour and the equivalent uranium content can be estimated to within approximately 5 ppm.
DEEP GRAVITY INTERPRETATION BY STRIPPING
Authors: Hammer Sigmund
Published: October 2002

“Old gravity data never die.” Review interpretations of gravity surveys can be made whenever warranted by new geological concepts, development information, or improved techniques. Important additional uses can be gained by extending the interpretation to deeper horizons by calculating and subtracting the gravity effects of overlying strata whose structure becomes known in detail from shallower development. This constitutes the new technique reported in this paper. An essential new factor which makes gravity “stripping” practicable is the advent of the gamma‐gamma density log which determines subsurface density relations in strata penetrated by development drilling. Combined stratigraphic and density information defines the mass anomalies in the upper strata. Subtracting the calculated shallower gravity influences improves the definition of the deeper gravity prospects. Applications of the method are illustrated by selected examples.
MAGNETIC ANOMALY TREND AND SPACING PATTERNS
Authors: Affleck James
Published: October 2002

Statistical studies of magnetic anomaly patterns have been made as part of a continuing investigation of anomaly characteristics and their relation to intrabasement tectonic patterns. Surveys exceeding one million square miles in area are included in the study. Anomaly trends are shown to have statistical preference for E‐W, N‐S, NW‐SE, and NE‐SW directions. In individual basement provinces definable by magnetic character, the dominant trend is most often either NS‐SE or NE‐SW. E‐W and N‐S trends are persistent throughout all surveys. Statistical treatment of distances between adjacent parallel anomalies demonstrates that the commonest spacing is approximately 4 miles. Possible relationships to crustal forces and strength are discussed.
THE NATURE OF HIGH‐FREQUENCY EARTH NOISE SPECTRA
Authors: Frantti G. E.
Published: October 2002

The spectra of earth noise in the frequency range 0.2 to 100 cps are presented for a number of widespread locations within the United States and for other selected North American and foreign sites. The data are analyzed as a function of physiographic environment. Some of the spectral anomalies are correlated with human activity and certain natural sources. The analysis suggests that a substantial portion of high‐frequency earth noise originates at the earth’s surface and follows a propagation path at, or near, the surface.
GAMMA‐RAY SPECTROSCOPY IN WELL LOGGING
Authors: Caldwell Richard L. , Baldwin Willett F. , Bargainer James D. , Berry James E. , Salaita George N. , Sloan Raymond W.
Published: October 2002

Thermal neutron capture gamma rays have been observed in boreholes drilled in shales, sandstones, and limestones. A capsuled source of neutrons and a scintillation crystal detector, connected through 5,000 ft of logging cable to a transistorized, multichannel, pulse‐height analyzer, were used. Resolved peaks were identified on the basis of the known energies of expected gamma rays and results obtained in models where conditions of porosity, casing, and fluid were controlled. To properly interpret borehole spectral data a system with good energy resolution and an accurate means of energy calibration are necessary. This is accomplished by using hydrogen and iron to give prominent gamma‐ray peaks at opposite ends of the energy range of interest. On field spectra, identification was made of gamma rays from chlorine, silicon, calcium, hydrogen, and iron. On the basis of chlorine gamma rays, salt water can be differentiated from oil or fresh water. Gamma rays from iron casing are an undesirable background and reduce the sensitivity of the method compared to that possible in an uncased hole. Two examples of natural gamma‐ray spectra show well resolved lines from uranium‐radium and thorium.
ELASTICITY OF SELECTED ROCKS AND MINERALS
Authors: Woeber A. F. , Katz Samuel , Ahrens T. J.
Published: October 2002

Elastic constants of selected rocks and minerals are listed, as obtained from measured values of density and of compressional and rotational wave velocities along three orthogonal directions. Density‐velocity correlation and velocity‐anisotropy are discussed.
RAYLEIGH WAVE TRANSMISSION ON ELASTIC WEDGES
Authors: Kane J. , Spence J.
Published: October 2002

A method is introduced by which transmission or conversion coefficients can readily be calculated for surface‐wave action at crustal discontinuities which can be idealized as wedge‐shaped obstacles. The method, an iteration procedure, is illustrated by an application to Rayleigh‐wave propagation on elastic wedges with free boundaries. It is shown that the leading term of the iteration procedure yields an expression for the transmission coefficient which matches the experimental data for a range of wedge angles which includes the crustal wedges commonly found in seismic practice. Numerical data are presented which illustrate the transmission coefficient’s variation in terms of Poisson’s ratio and the wedge angle.
ROLL‐ALONG AND DROP‐ALONG SEISMIC TECHNIQUES
Authors: Shock Lorenz
Published: October 2002

The designation “Roll‐Along” is used to indicate the use of horizontal‐data‐stacking techniques when field data are derived by the shooting method. The term “Drop‐Along” is used for weight‐drop data. These methods have proven valuable in obtaining usable data in areas where the standard pattern techniques are ineffective, or where extreme multiplicity requirements make patterns economically impractical. Operational techniques have been developed for both Roll‐Along and Drop‐Along in which standard field recording equipment and cables are utilized. A discussion of these techniques and the associated data processing operations is presented. Record‐sections are used to illustrate the quality of data obtainable by these methods and to compare it to pattern shooting.
AN EXAMPLE OF THE USE OF SYNTHETIC SEISMOGRAMS
Authors: Delaplanche Jacques , Hagemann R. F. , Bollard Pierre G. C.
Published: October 2002

From an actual example taken from the Paris Basin, it is shown how the comparison between field records and synthetic records can be used to ascertain the existence of a potential reservoir for oil and gas. The seismic survey programmed had two main objectives: (1) to define the deep structure which could be presumed from the surface geological measurements, and (2) to obtain stratigraphic data on the structural anomalies of the existence or nonexistence of a reservoir in the Lias series. Two tests drilled independent of geological surveying had revealed a significant truncation in this series. The analysis of the recordings presented was guided by a detailed study of that stratigraphic data. The synthetic records computed for the two tests drilled formed the basis of the correlations. A third test drilled on the structure, after the geophysical survey, permitted verification of the conclusion. During the field work, a special type of recording apparatus was used, underlining the advantages of synthetic seismograms for subsurface problems of this nature.
SEISMIC DATUM CONSTRUCTION IN AREAS OF RUGGED TOPOGRAPHY
Authors: Thomas Robert P. , Morrison Robert H.
Published: October 2002

One of the steps in the reduction of seismic data is the correction for variations in surface elevation. This requires the adoption of a common reference surface, usually known as the seismic datum, but also referred to as the floating datum, the undulated or warped datum, or the datum plane. Ideally, the seismic datum should parallel the velocity layers, and in that sense it is an isovelocity surface; in practice, the datum is more often a surface of convenience. In its simplest form, the datum is a horizontal plane, but commonly it is undulated to conform to the generalized topography. While the warping of a datum surface serves to simplify and minimize the elevation corrections, it is usually done in the knowledge that the isovelocity surfaces are often similarly undulated. Such undulations of the velocity layers are generally attributed to the variations in loading caused by the irregularity of the ground surface. In an attempt to develop an objective means of constructing a satisfactory universal seismic datum, a zone chart was designed, similar to the terrain‐correction zone chart employed in gravity reductions. The compartmented transparent disk, superimposed on a topographic map and centered over the shotpoint, permits the calculation of a properly weighted, or “normalized,” elevation which serves as the basis for the undulated seismic datum. Tests of the resulting datum indicate that it will normally compensate adequately for velocity variations due to topographic loading and, consequently, insure a more accurate interpretation of the seismic data.
SHOCK DEFORMATION OF ROCKS
Authors: Ramez M. R. H. , Attewell P. B.
Published: October 2002

Two rocks—a sandstone and a monominerallic aggregate of calcite crystals—have been deformed by means of detonators exploded on the end faces of cylindrical specimens, and shock levels up to 7 kilobars recorded. Microscopic examination of the deformed cylinders revealed the nature of the deformation and the extent to which it had progressed along the specimen. The sensitivity of quartz to imposed stresses was used to trace the final geometrical distribution of stress in the system which was then related to the theoretical stress distribution having particular regard to the tensions induced by lateral reflections. Both rocks are shown to have accommodated the imposed stresses by separation along grain boundaries and by intergranular and intragranular tensile fractures. It was observed that calcite grains satisfying a minimum size condition dictated by a particular shock level were bent when swept by a spherical shock front.
WIDE‐BAND VELOCITY FILTERING—THE PIE‐SLICE PROCESS
Authors: Embree Peter , Burg John P. , Backus Milo M.
Published: October 2002

A new technique has been developed which makes it possible to process a seismic record‐section in such a way that all seismic events with dips in a given range are preserved with no alteration over a wide frequency band, while all seismic events with dips outside the specified range are uniformly and severely attenuated. By applying this process to a noisy record‐section, a record‐section may be obtained which has all events within a specified dip range perfectly preserved, and very high‐velocity noise essentially eliminated, a result which is impossible by simple wave‐number filtering or conventional array usage. In structurally complex areas where several steeply dipping events interfere, the technique may be applied to separate the events with different dips. In areas where a normal‐moveout contrast exists between primaries and multiples, the technique may be used for wide‐band multiple attenuation. By application of a “rotating Pie‐Slice” to micro‐spread noise data, seismic noise may be separated on the basis of propagation velocity, and a clearer picture of the seismic noise problem obtained. The “rotating Pie‐Slice” also provides a means of uncovering diffractions and other steeply‐curved events from a record section. The paper discusses the motivation and implementation of the process and its application to both synthetic and actual data.
BASEMENT DEPTHS FROM WIDELY SPACED AEROMAGNETIC PROFILES IN KANSAS AND NEBRASKA
Authors: Watkins Joel S.
Published: October 2002

Profiles of the basement surface in western Kansas and Nebraska were constructed by drawing smooth curves through the shallowest depths estimated from aeromagnetic anomalies along six widely spaced traverses. Ratios of inferred‐depth‐to‐basement to true depth along the traverses ranges from 0.7 to 1.0. Clusters of shallow depth estimates commonly yield an average estimate within 15 percent of the true depth.
THE MAGNETIZATION OF A ROCK CONTAINING MAGNETITE AND HEMOILMENITE
Authors: Carmichael Charles M.
Published: October 2002

In areas such as the Canadian Shield, rocks often contain iron and titanium oxides with a remanent magnetization. These rocks can produce aeromagnetic anomalies that are positive, negative, or nonexistent depending on the magnitude and direction of the remanent component relative to that of the induced. In the Allard Lake region of Quebec there is a deposit containing up to 20 percent oxide that produces no anomaly detectable by either the airborne or ground magnetometer. Analyses of the rock by microscopic, magnetic, and X‐ray techniques have shown that it contains separate crystals of an almost pure magnetite and of exsolved hemoilmenite. The magnetite crystals are magnetized normally and the hemoilmenite crystals inversely. They are present in quantities such that their magnetic moments cancel and so produce no anomaly. While this is probably an unusual occurrence it shows that considerable care must be taken in regions where minerals having an inverse remanent magnetization may be present.
SEISMIC PROPAGATION PATHS, REGIONAL TRAVELTIMES, AND CRUSTAL STRUCTURE IN THE WESTERN UNITED STATES
Authors: Stuart David J. , Roller John C. , Jackson Wayne H. , Mangan George B.
Published: October 2002

The U. S. Geological Survey, with VELA UNIFORM support, has recorded a network of about two thousand long‐offset refraction seismograms to provide information on the detection, location, and identification of seismic events. The measured velocities of compressional waves in upper‐mantle rocks, [Formula: see text], varies from at least 7.75 to 8.25 km/sec in the western United States. There seems to be a systematic variation of the velocity of [Formula: see text] with geologic environment and also with crustal thickness. Where the crust is thick (>35 km), measured values of the velocity of [Formula: see text] tend to be high (>8km/sec), and, where the crust is thin (<35 km), measured values of the velocity of [Formula: see text] tend to be low (<8 km/sec). The velocity of [Formula: see text] is generally low in the high mountains of the far west and generally high in the stable continental interior. The close relation between rock density and seismic velocity implies that, on a regional scale, a large part of isostatic compensation is achieved by density variations in upper‐mantle rocks.
DETECTION OF P‐WAVES FROM WEAK SOURCES AT GREAT DISTANCES
Authors: Claerbout Jon F.
Published: October 2002

Optimum (Wiener sense) filters for suppression of noise in multiple time series are computed by a new method due to E. A. Robinson. Filters for prediction error and interpolation error have been used to detect P‐wave signals from three teleseismic events. These filters facilitate detection of signals in noise with low signal‐to‐noise ratios. The instrumentation consists of short‐period Benioff seismometers, both three‐component stations and surface arrays of verticals. It was found that microseismic noise in the pass band of these instruments is more accurately termed “Brownian motion of a surface” than “random waveforms with characteristic direction(s) of propagation.” Thus, single time‐series filters work almost as well as multiple time‐series matrix filters. Prediction‐error filters gave results substantially more satisfactory than simple band‐pass filters.
GEOPHYSICAL STUDIES OF BASIN STRUCTURES ALONG THE EASTERN FRONT OF THE SIERRA NEVADA, CALIFORNIA
Authors: Healy J. H. , Press Frank
Published: October 2002

A seismic and gravity survey along the eastern front of the Sierra Nevada, California, between southern Owens Valley and the Garlock fault, outlines a series of basins with maximum depths ranging from 5,000 to 9,000 ft. These basins follow the front of the Sierra Nevada in a continuous chain with one interruption of about 10 miles near Little Lake. The gravity anomalies indicate that the basins are bounded by a series of high‐angle faults rather than a single large fault. The seismic velocities in the basin deposits appear to correlate with the stratigraphy of the section exposed in the El Paso Mountains. A comparison of Bouguer anomalies with seismic depths indicates a density contrast of 0.35 g/cc in basins less than 3,000 ft deep, and an average but widely varying density contrast of 0.25 g/cc in basins 4,000 to 8,000 ft deep. A digital‐computer program for automatic computation of basin depths from gravity anomalies was evaluated and found to be useful in this type of analysis. Changes in the depth to the Mohorovičič discontinuity cannot produce regional gradients as large as the regional gradients observed in the area of the survey. Either structure on an intermediate crustal boundary or lateral changes in crustal densities, or a combination of these, is required to explain the gravity data.
MATHEMATICAL FORMULATION OF SALT‐DOME DYNAMICS
Authors: Daneš Z. F.
Published: October 2002

The development of salt domes is formulated as a case of Taylor instability in the salt‐sediment system. It is assumed that the salt layer rests on a rigid substratum, while the upper surface of the sediment is free. Both salt and sediment are assumed to behave as highly viscous media. Of the entire spectrum of infinitesimal perturbations the component of the fastest growth is assumed to become dominant and to determine the spacing of domes. Exact solutions are derived for the linear theory in equations (3.7) and (4.24). Corrections due to the nonlinear terms are analyzed qualitatively in (5.8) and (5.9).
LOW‐AMPLITUDE AEROMAGNETIC ANOMALIES IN SOUTHEASTERN MISSOURI
Authors: Allingham John W.
Published: October 2002

This study shows that aeromagnetic anomalies of less than 200 gammas are associated with topographic relief of exposed Precambrian granitic and volcanic rocks of the St. François Mountains. Anomalies resulting from hills coarsely crystalline granite are as high as 100 gammas in amplitude, whereas anomalies over comparable hills of fine‐grained rocks, such as granophyre or devitrified volcanic rock, are as much as 200 gammas. Anomalies caused by normal faulting or shearing of igneous rocks have amplitudes of less than 100 gammas; they are observed best in profile. These anomalies are superposed on larger magnetic features related to pendants of volcanic rock in the roof of a granite batholith and are distinguished from large lateral variations in magnetic intensity by their low amplitude and small areal extent. Analyses of the compound anomalies yielded the subsurface configuration of isolated roof pendants of resistant extrusive rock in some areas. As many of these pendants have negligible remanent magnetization, induction theory was used in the analyses. Application of these results to the lead‐mining areas shows that aeromagnetic patterns of low amplitude can guide mineral exploration in the region flanking the Ozark uplift, where isolated, buried hills of Precambrian igneous rocks controlled the development of some lead‐bearing sedimentary structures in the overlying Cambrian carbonate strata.
SIGNAL AND NOISE IN DEEP WELLS
Authors: Douze Eduard J.
Published: October 2002

Deep‐well measurements at Grapevine, Texas; Hobart, Oklahoma; and Orlando, Florida, show that the noise is composed of surface waves that decrease in amplitude with depth. At Hobart, a low‐velocity wave guide contains wave‐guided noise. Fundamental and higher mode Rayleigh waves appear to be present in the noise at each site. The amplitudes of incident P waves depend on the depth at which the deep‐well seismometer is operated. High‐frequency P waves from quarry blasts are clearly visible in recordings from the deep‐well seismometer because the high‐frequency noise is suppressed at depth.
THE CAUSES OF NOISE IN SEISMIC REFLECTION AND REFRACTION WORK
Authors: Olhovich V. A.
Published: October 2002

This paper describes the causes of the noise observed in seismograms and examines its nature. The following noises have been analyzed: (a) Surface waves, (b) Secondary impulses, (c) Dispersed energy, (d) Multiples, (e) Ghosts, (f) Reverberations, (g) Diffractions, (h) Filtering effects, (i) Direct waves, (j) Sound waves, (k) Repeated impulses, (l) Microseisms. Methods for elimination of noise are not mentioned as this constitutes material to be treated in a separate paper.
METHOD USING ELLIPSES TO INTERPRET SEISMIC REFLECTION DATA
Authors: Gassaway Gary S.
Published: October 2002

The properties of an ellipse can be used to interpret seismic reflection data by using the positions in a vertical section of a shot and a geophone as the foci of an ellipse. With the shot and geophone as the foci, the total time of travel of a reflected seismic wave serves as the constant necessary to define the ellipse. The reflecting surface then is tangent to this ellipse. Therefore, if many ellipses are plotted, the reflecting surfaces may be found by drawing smooth curves that are tangent in common to closely intersecting families of arcs. This basic principle is extended to the interpretation of complex structures that are not perpendicular to the line of traverse and to areas where the seismic velocity changes with depth by the following steps: The shots and geophones are plotted on a graph where the units along both the ordinate and the abscissa are virtual seismic traveltimes. These positions of the shots and geophones are then used as the foci of the ellipses as above. The reflecting surfaces are then drawn tangent to the dark bands of closely intersecting elliptical arcs. From this graph the one‐way time from a shot to a point of reflection, and from the point of reflection to a geophone may be scaled off; this is done by drawing the elliptical radii from the shot and geophone to the point of tangency between the ellipse and reflecting surface. The lengths of these radii are the one‐way times at the time scale of the graph. With the attitude of the wavefront as it returned to the surface at a geophone determined by a spread of three parallel geophone lines, and the one‐way time from the reflection point, one has the necessary and sufficient data to find the point of reflection in space coordinates for the assumed velocity function. Using the ray paths from the shot and geophone to this reflection point, the dip and strike of the reflecting surface at this point are found. This process is then repeated for every shot‐geophone combination for each reflecting surface.
AN EXAMPLE OF PRAIRIE‐EVAPORITE MAPPING IN THE MINTON AREA OF SASKATCHEWAN EMPLOYING THE SEISMIC METHOD
Authors: Surjik D. L. , Hobson George D.
Published: October 2002

In July, 1961, a Geological Survey of Canada seismic crew ran a continuous reflection survey in the Minton (Saskatchewan) area at the request of the Saskatchewan Department of Mineral Resources, to better delimit the edge of the Devonian Prairie Evaporite and also to determine whether structural conditions causing solution exist in the area. A density‐galvo section of a portion of the reconnaissance line runs from the Imperial Herald well (lsd.1-31-1-20 W2) to the Imperial Hummingbird well (lsd.6-13-2-19 W2) was prepared. Interpretation of the seismic section indicates that solution of the salt took place mainly in lower Gravelbourg (Jurassic) to Nisku (Devonian) time. This is confirmed by the fact that the Mississippian (carbonate) and Jurassic (Watrous Red Beds) formations thicken at the Hummingbird well. Reflections from the Prairie Evaporite are not continuously correlative. The edge of the Prairie Evaporite is predictable indirectly from reflections originating above and below it in the section. Pre‐Devonian reflectors appear below a portion of the no‐salt area. This condition cannot be attributed to spurious events. A probable relation between early solution and basement disturbance is supported by borehole evidence.
SOUTHWESTERN OKLAHOMA—A GEOPHYSICAL CASE HISTORY OF A BASIN
Authors: Laing William E.
Published: October 2002

The Eastern Palo Duro Basin, also known as the Hollis, Harmon, or Hardeman Basin, covers approximately 100 townships in southwestern Oklahoma. Approximately 18 million barrels of oil have been produced from the Altus and West Frederick trends in Jackson and Tillman Counties. The basin’s structure has been influenced by three orogenic movements: the Acadian, Wichita, and Arbuckle. Dips associated with the main Wichita structures show displacements up to 2,500 ft. Seismograph surveys have played a major part in the development of the basin. The main problems encountered are related to the surface and near‐surface material of the Quaternary deposits and the Permian Blaine Formation. The unconsolidated sands and gravels of the Quaternary deposits are particularly troublesome along the main branches of the Red River. Generally, record quality can be improved with two‐ and three‐hole patterns. The Blaine gypsum and Dog Creek shale, considered as a single unit, outcrop in the western half of the basin. Difficult drilling problems require two or three combination air‐water drills for efficient field operations. Correction problems are compounded by variations in the weathering velocity from 2,000 ft/sec to 3,850 ft/sec and in the near‐surface velocity from 8,000 ft/sec to 12,500 ft/sec. Record quality can be improved in the western area by using multiple geophone coverage, by placing the charge entirely within a shale zone, by using patterns, and by careful selection of the surface traverse to avoid gypsum outcrops. The “VIBROSEIS” system produces better data than the conventional method. Other advantages of the “VIBROSEIS” system are easier permitting and a great reduction of explosives and shothole drilling. While it is unlikely that major producing trends comparable to Altus and West Frederick remain to be found, it is concluded that adequate reservoirs are present and that there is ample room for structures comparable to Conley field in adjacent Hardeman County, Texas. By careful application of suitable seismic field techniques such structures can be reliably mapped.
CONTINUOUS ELECTRICAL PROFILING
Authors: Jakosky J. J.
Published: October 2002

Various electrical methods now used fall under two general headings—inductive and conductive. By use of the latter methods, any theoretical depth of current penetration may be obtained by employing a sufficiently great electrode separation. However, masking effects are usually present, due both to polarization and to electrolysis. These factors may be minimized by use of a “pulse” of current having a predetermined time‐current relationship; also bothersome inductive effects are minimized by employing a slow‐rising wave‐front. The pulse is of long time interval to avoid any appreciable phase shift between the currents flowing along the surface (where the potential measurements are being made) and those flowing at depth (where the desired structural effect is to be obtained). Contrast and comparison is made between refraction seismic work and conductive methods of geoelectrical prospecting, with particular attention to the method of determining intensity‐distance curves using a moving electrode. Optimum electrode configurations are described and briefly analyzed, as are the electrolytic temperature effects. The theory, operating technique, and interpretative technique of the continuous profiling method are given in detail. Diagrams and discussions illustrate the application of the method to detailed structural mapping, reconnaissance structural mapping, and fault location work. In some cases the method described is yielding satisfactory results in areas where other geophysical methods have failed to give interpretable data. The paper also presents a brief summary of the commercial work done during 1937 with the Jakosky pulse method.