bluuebunny/crossref_metadata_2025 huggingface dataset:
ELASTIC RADIATION FROM CYLINDRICAL SOURCES
Authors: Colwell J. F.
Published: October 2002

The Green’s function is employed to find the elastic radiation in an infinite homogeneous medium generated by several different sources. These sources all have a cylindrical shape and are finite in length, but are otherwise rather distinct. They include an expanding cylinder, an explosion in a borehole, and a cylinder under torsion. It is found that in principle, an explosion in a cylindrical hole creates both shear and compressional waves. The radiation from one surface‐mounted source is also found. This is a source (the Dynagoose) in which tension is maintained between a surface plate and a long cylinder wedged in a hole.
DYNAMIC CORRELATION ANALYSIS
Authors: Schneider William A. , Backus Milo M.
Published: October 2002

A computer analysis technique is described for use in conjunction with reflection seismic data shot for conventional common‐depth‐point (CDP) stacking, with the objective of providing a space‐time variant measure of the energy relationships among CDP traces. This energy analysis may be interpreted to yield an estimate of the relative contribution of primary and multiple reflections versus record time, their velocity functions, and the fraction of uncorrelated energy which is present. These data, in addition to their interpretive value, provide a space‐time variant model of the signal and noise fields for use in the design of optimum CDP stacking filters. The heart of the method is based upon crosscorrelations computed between CDP traces from numerous sequential short data gates along the trace. These are averaged over an ensemble of like members obtained along the line of profiles and manipulated to yield a reliable estimate of the cross correlation peak amplitude and delay upon which the primary and multiple velocity and energy assignments are based. The technique is illustrated with six‐fold marine data from the Gulf of Mexico to demonstrate how it can be used in practice as a valuable analysis tool for the exploration geophysicist.
GEOPHYSICAL ACTIVITY IN 1966 APPLIED TO ENGINEERING, CONSTRUCTION, AND GROUNDWATER PROJECTS
Authors: Tucker L. R.
Published: October 2002

This is the second year in which the Society has attempted to survey the previous year’s geophysical activity applied to groundwater, engineering, and construction projects. Last year, these data were obtained from the Mining Activities Questionnaire. This year, a separate questionnaire was developed.
HIGH‐RESOLUTION SEISMIC UPHOLE SURVEYS AT THE LAWRENCE RADIATION LABORATORY
Authors: Carlson R. C. , Stearns R. T. , Berens H. B. , Hearst J. R.
Published: October 2002

Methods have been developed to measure the source and arrival times of an explosion‐induced acoustic wave to within 0.1 ms. These methods have been used to measure acoustic velocity over distances of 10 to 150 m with high accuracy. The methods are usable in dry holes. They have been used in rhyolite, tuff, dolomite, alluvium, and shale to measure velocities between 700 and 5000 m/sec. Statistical errors on the order of ±2 to 5 percent were achieved in most cases. It is concluded that the accuracy of such meaurements is limited only by the frequency transmission of the medium, not by the instrumentation.
SHEAR‐WAVE RECORDING USING CONTINUOUS SIGNAL METHODS PART I—EARLY DEVELOPMENT
Authors: Cherry J. T. , Waters K. H.
Published: October 2002

In recent years, it has been found possible to record shear‐wave reflections and horizontally traveling shear waves using continuous signal methods. Thus paper traces the equipment development and field work performed during this research. The earliest work with a version of a swinging‐weight vibrator showed that shear‐wave reflections could be recorded. This fact provided the impetus to make modifications to equipment to meet difficulties caused by lack of energy and lack of frequency bandwidth. Examples are given which show the flexibility of the system in providing comparison between the horizontally traveling surface waves induced and recorded by the various combinations of vibrator sources and geophone types and their relative orientations. Frequency selection by the different modes is well illustrated. For most of the reflection examples, the average ratio of shear‐wave velocity to compressional‐wave velocity in the first few thousands of feet is near 0.5. Finally, to complete the early development, the version of the shear‐wave vibrator and recording system which was used for most of the additional work is described. In order to make comparison of P‐wave and SH‐wave reflection records easier, this system provided for a 2:1 compression of the shear‐wave time scale as well as a 2:1 ratio of frequency output between the P‐ and SH‐vibrator systems. A few examples of SH reflection profiles achieved with this system are presented.
SEISMIC MODELS AND DETERMINISTIC OPERATORS FOR MARINE REVERBERATION
Authors: Middleton David , Whittlesey John R. B.
Published: October 2002

A phenomenological model is constructed for an extended class of multibottom configurations that incorporates in an explicit fashion the effects of marine reverberations on seismic signals sought in a background of ambient and reverberant noise. A class of dereverberation operators of increasing complexity is described, and the related effects of water ghosts for bottom cables are included. The operator formalism explicitly distinguishes between phenomena occurring in the near‐surface (water and mud) and those resulting from deep strata reflections. This formalism permits a more extensive investigation of the water‐trapped mode (j=0), which has now been found to be more significant than previously suspected. Dereverberation procedures based on both structure‐dependent and structure‐free forms of the basic models are considered and compared. The former lead to parameter‐search techniques, while the latter employ linear‐least‐squares estimation of waveform. These models and procedures are illustrated by computer‐simulated examples in the frequency domain and by analyzed seismic records.
STATIONARITY OF SEISMIC NOISE
Authors: Sax Robert L.
Published: October 2002

Seismic noise has been measured in deep wells by the Geotechnical Corporation at twelve different locations and by the Shell Development Company at three deep wells. To explain the power attenuation and the coherence between vertically separated seismometers, one requires noise vibrations taken as a mixture of propagation modes, possibly surface‐wave modes and body‐wave modes. This was illustrated in observations by many authors including Archambeau et al. (1964), Douze (1964), Sax and Hartenberger (1964), Seriff et al. (1965), and Sax (1965).
MULTICHANNEL DECONVOLUTION FILTERING OF FIELD RECORDED SEISMIC DATA
Authors: Davies E. B. , Mercado E. J.
Published: October 2002

Several writers have proposed the use of multichannel filters for the elimination of coherent noise on seismic records. One filter of this type which can be constructed is a multichannel Wiener filter which has a multichannel input and a single channel output. In this form, it is applicable to data collected for vertical or horizontal common‐depth‐point stack processing. The choice of desired output characteristics for this Wiener filter is flexible and, for example, can be tuned to correspond to multichannel deconvolution. The results of the application of filters of this type to field and synthetic data, in general, show little if any advantage over single‐channel deconvolution. This failure appears to be connected with the low cross coherence of both noise and reflection signal on field‐recorded, common‐depth‐point traces.
NONLINEAR ENERGY TRANSFER IN ELASTIC WAVES
Authors: Holstrom Geoffrey
Published: October 2002

If an elastic pulse of finite amplitude propagates through a solid, the energy originally associated with one frequency is partially transferred to other frequencies. This transfer can lead, for lossless compressive pulses, to the formation of a shock wave. Changes of entropy occur in steady shocks only in terms beginning with third order in the compression, and hence a perturbation treatment neglecting heat conduction is valid to second order. The one‐dimensional mass and momentum conversation equations are solved to second order, and the solutions are used to study energy transfer. Generally speaking, transfer occurs from lows to highs, leading to apparent attentuation of frequencies in the seismic range. A drop in energy of low frequencies might occur even if the only apparent loss mechanism is high frequency scattering. Formulas are developed giving the apparent attenuation over propagation distances or oscillation times small enough that perturbation treatment remains valid. It appears that this process could be important as a loss mechanism at low frequencies if initial pulses are sufficiently sharp, or if initial free oscillations have sufficiently large high‐frequency content.
A RAPID GRAPHICAL METHOD FOR THE INTERPRETATION OF A‐ AND H‐TYPE ELECTRICAL SOUNDINGS
Authors: Zohdy Adel A. R.
Published: October 2002

Three‐layer vertical electrical sounding (VES) curves that register the effect of a highly resistive electric basement are of either the minimum (H) or the double‐ascending (A) type. The correct interpretation of these two important types of VES curves depends largely on the successful determination of the resistivity of the second layer. This resistivity can sometimes be evaluated from electric logs, from a comparative study of field VES curves, from electrical measurements on outcrops, or from parametric VES curves. A new single auxiliary curve has been devised to help interpret both these types of VES curves, provided that the resistivity of the second layer is known. The thickness of the middle layer is determined accurately and rapidly by the value of the abscissa at the intersection of the total longitudinal conductance line S with the new auxiliary curve. The auxiliary curve is used to interpret an H‐type curve, an A‐type curve, and a five‐layer (KQH‐type) parametric VES curve. Analysis of the KQH parametric curve shows that the resistivity of the third layer may vary by more than a thousandfold without affecting the shape of the curve, whereas the resistivities of the second and fourth layers may correspondingly vary by less than one order of magnitude.
CONTINUATION OF ELECTROMAGNETIC FIELDS—I
Authors: Roy Amalendu
Published: October 2002

This note examines the theoretical problem of continuation of electromagnetic fields by the method of spectral analysis and synthesis, without making any restricting assumptions in regard to the conductivity of the medium and the frequency of the field. It is found that the space frequency spectrum of the continued field at a level z is obtained by multiplying that of the observed field on z=0 by exp (±θz), where [Formula: see text], [Formula: see text] and [Formula: see text] are the spatial frequencies in two orthogonal directions and k is the propagation constant. For spherical geometry, the expansion of the observed field needs to be done in terms of spherical harmonics, and the multiplying factors for inward and outward continuation are, respectively, [Formula: see text] and [Formula: see text] where J and H are Bessel functions, r is the radius of sphere of continuation and a is the radius of the sphere of observation. While the method is valid for continuation in air or inside a homogeneous medium, it fails in the more practical case when one wants to continue inside an inhomogeneous earth. This is because, in certain regions of an in homogeneous earth, the field consists of two unknown parts, one of which increases with z or r while the other decreases.
GEOPHYSICAL ACTIVITY IN 1967 APPLIED TO PETROLEUM EXPLORATION
Authors: Tucker L. R.
Published: October 2002

The various categories of Geophysical Activities for 1967 covered in this or in corollary reports are Petroleum; Mining; Engineering, Construction, and Ground Water; and Oceanographic Surveys. Data are fairly complete for most groups, and reasonable reliance can be placed on the numbers. Items such as cost, though, are partly estimated. If anything, they are on the conservative side.
SEISMIC SURVEY IN THE REGION OF RECENT EARTHQUAKE ACTIVITY NEAR DENVER, COLORADO
Authors: Rummerfield Ben F. , Olson A. Peter , Hoover D. B.
Published: October 2002

A seismic‐reflection survey was carried out near Denver, Colorado, for the U. S. Geological Survey, to determine if structures exist in the 12,000‐ft sedimentary section or in the Precambrian basement that might explain the recent earthquake activity. No major faults were revealed in the sedimentary section. Reflections from a steeply dipping horizon believed to be in the basement complex may be indicative of faulting; however, the magnitude cannot be ascertained, as reflection events cannot be correlated at these depths. The results of the survey suggest the possibility of monitoring and studying subsurface structural conditions and related parameters in regions of seismic activity and/or suspected zones of tectonic instability.
THE INVERSE PROBLEM OF MAGNETOTELLURIC SOUNDING
Authors: Wu Francis T.
Published: October 2002

Based on the model of a flat layered earth, a nonlinear, least‐squares method is used to invert magnetotelluric sounding curves to obtain the layer resistivities and thicknesses. Partial derivatives of the apparent resistivity with respect to layer parameters show the manner in which the layer parameters are contrbuting to the apparent resistivities. Uniqueness of the inversion is not guaranteed, but when the partial derivatives are linearly independent and the relative magnitudes of the layer resistivities of the initial guess are not too far from the correct ones, the convergence of the method to the correct values seems to be ensured.
GEOPHYSICAL RESEARCH & PROGRESS IN EXPLORATION, 1965–1968
Authors: Wuenschel P. C. , Treitel S. , Flinn E. A. , Keller G. V. , Pickett G. R.
Published: October 2002

This is a progress report on developments in geophysical research and progress in exploration during the time interval from 1965 to 1968. It is the seventh treatment of this type prepared by the members of the society in the past 13 years.
LONG‐PERIOD SIGNAL PROCESSING RESULTS FOR THE LARGE APERTURE SEISMIC ARRAY
Authors: Capon J. , Greenfield R. J. , Lacoss R. T.
Published: October 2002

The results of a series of off‐line signal processing experiments are presented for long‐period data obtained from the Large Aperture Seismic Array (LASA) located in eastern Montana. The signal‐to‐noise ratio gains obtained with maximum‐likelihood processing, as well as other simpler forms of processing, are presented for body‐wave as well as surface‐wave phases. A discussion of the frequency‐wavenumber characteristics of the noise which led to these results is also given. On the basis of these experiments, several recommendations are made concerning optimum long‐period array configurations and on‐line or off‐line processing methods. The usefulness of maximum‐likelihood processing in suppressing an interfering teleseism is demonstrated. An experiment is given in which maximum‐likelihood processing achieved about 20 db suppression of an interfering teleseism, while simpler forms of processing such as beam‐forming obtained about 11 db. The matched filtering of surface waves using chirp waveforms is shown to be highly effective. A useful discriminant for distinguishing between natural seismic events and underground nuclear explosions, using both the long‐period and short‐period data, was found to be the relationship between the surface‐wave and body‐wave magnitudes. Measurements of this discriminant made on events from four tectonic regions of the earth are presented. It is shown that 60 and 100 percent detectability of surface waves for natural seismic events from the Central Asian‐Kurile Islands‐Kamchatka region occurs at about LASA body‐wave magnitudes 4.5 and 4.9, respectively.
A MAGNETOTELLURIC STUDY OF RESISTIVITY ANISOTROPY
Authors: Rankin D. , Reddy I. K.
Published: October 2002

The apparent resistivity curves obtained from the magnetotelluric field measurements at the University of Alberta Geophysical Observatory, near Leduc, Alberta, reveal a strong anisotropy. The significance of the direction of the incident magnetic field in interpreting the structure from the apparent resistivity curves is examined in detail for the case of a linearly polarized incident field. The tensor impedance analysis of the data indicates that the directions of the principal axes of anisotropy are aligned parallel to the north‐south and east‐west measuring axis. The high coherency between the orthogonal horizontal components of the incident magnetic field is in complete agreement with this interpretation. The two apparent resistivity curves are interpreted and an anisotropic layered model is derived. The anisotropy is found to lie in the Precambrian basement down to a depth of 14 km. The isotropic upper layer has a resistivity of 8 ohm‐m which is characteristic of the sedimentary section. The anisotropic resistivity structure proposed for the Precambrian basement may be attributed either to local lithological changes in the basement or to major but more distant structure.
A COMPARISON OF TERRESTRIAL HEAT FLOW AND TRANSIENT GEOMAGNETIC FLUCTUATIONS IN THE SOUTHWESTERN UNITED STATES
Authors: Warren Robert E. , Sclater John G. , Vacquier Victor , Roy Robert F.
Published: October 2002

Magnetic time‐variations between Tucson, Arizona and Sweetwater, Texas indicate that a zone of high electrical conductivity underlies the southwestern United States. The interpretation of this zone by Schmucker as a rise of the isotherms in the upper mantle is supported by six heat flow observations along the line of the geomagnetic profile. These and other observations indicate a high but variable heat flow in the Basin and Range Province which contrasts strongly with the uniform values of [Formula: see text] reported for the Texas Foreland. The width of this high heat flow anomaly, which may extend across the entire Basin and Range Province, suggests anomalously high temperatures in the upper mantle. This interpretation is further supported by magnetotelluric data between Phoenix, Arizona and Roswell, New Mexico and by the low seismic [Formula: see text] velocity and negative gravity anomaly. It is suggested that the “anomalous mantle” may be related to the tectonic evolution of the western United States and the late Cenozoic fault system.
ANALYSIS OF THE RELATIONSHIP BETWEEN ACOUSTIC REFLECTIVITY AND SEDIMENT POROSITY
Authors: Faas Richard W.
Published: October 2002

Ocean‐bottom sediment porosity and acoustic reflectivity are related by a simple linear equation. The equation was derived empirically from data published by several investigators and is valid for a wide variety of sediment types and ocean conditions. The degree of validity of the relationship appears to be excellent as the correlation coefficient between the porosity and acoustic reflectivity is 0.97.
THE ECONOMICS OF MINERAL EXPLORATION
Authors: Peters W. C.
Published: October 2002

Exploration activity within a region or within a mining organization is controlled by an economic pattern based upon changing conditions in mining practice, processing technology, and marketing opportunities. Exploration programs and new developments in exploration science must be viewed in the context of the rapidly changing concept of an ore body. Any exploration effort, whether based upon a prospect examination, a programmed regional evaluation, or a task force charged with the replacement of a depleting ore body, is essentially a profit‐versus‐risk affair. Each decision to abandon or to continue and each budget allocation uses the accumulated experience from failures and successes. Quantification of the risk and of the expected ore body at each stage in the effort requires the skill of a well‐informed and competent exploration team within a parent organization which provides specific guidelines regarding its goals and capabilities. A successful exploration program under modern competitive conditions requires a long‐term commitment in which the risk factors, geology, politics, and economics for the selected region or commodity have been fully investigated. In evaluating potential profit versus risk, consideration should be given to evidence that the largest financial losses are often not in exploration but rather in the abandonment of an unprofitable mining operation after the commitment of a capital investment on the basis of incomplete geologic investigation. The decision as to when an anomaly is to be considered a target may be less critical than the decision as to when an investigated target is to be considered an ore body.
MAGNETIZATION OF A RECENTLY DISCOVERED SEAMOUNT IN THE CENTRAL PACIFIC
Authors: Francheteau Jean , Sclater John G. , Craig Harmon
Published: October 2002

From April through December 1967, the R/V ARGO of the Scripps Institution of Oceanography took part in Expedition NOVA, a detailed geological and geophysical study of the southwest Pacific. On June 23 and 24 two major seamounts, which have been named Hohnhaus and Dixon seamounts, were discovered about 104 km apart on the abyssal plains of the central Pacific. The northernmost, Hohnhaus seamount, is located at 13°30′N, 179°10′W; a single crossing was made which showed that it is at least 3780 m high with a base diameter greater than 50 km. Dixon seamount, located at 12°34′N, 179°05′W, was subjected to an extensive topographic, subbottom reflection, and magnetic survey. It is 4100 m high, 63 km wide at its base, and rises with the 20 percent slope characteristic of shield volcanoes from the surrounding abyssal plain mean depth of 5700 m to a minimum depth of 1581 m. The topography was surveyed with a standard Gifft Depth Recorder; a towed free‐precession magnetometer gave the total magnetic field intensity along the ship’s track and subbottom reflection profiles were obtained using an air gun sound source.
DYNAMIC PHOTOELASTIC STUDIES OF P AND S WAVE PROPAGATION IN PRESTRESSED MEDIA
Authors: Thomson Ker C. , Ahrens Thomas J. , Toksöz M. Nafi
Published: October 2002

The occasional existence of very pronounced, anomalous, horizontally polarized seismic waves from underground nuclear bomb blasts has been reported by several investigators. In order to further understanding of this phenomenon and the processes of mechanical radiation from explosions, particularly in prestressed media, a model study has been undertaken. Experimental apparatus has been developed which permits the generation and propagation of body waves from explosions in transparent plate models prestressed to various two‐dimensional stress configurations. High‐speed framing camera sequences are presented showing the explosion process and the resulting plate compressional and shear wave propagation in prestressed models. These are compared to theoretical calculations of isochromatic and [Formula: see text] isoclinic fringe patterns associated with the wave propagation in stressfree plates and plates prestressed in tension and shear. The following distinctive optical phenomena were predicted theoretically and observed in the high‐speed photoelastic patterns: a [Formula: see text] discontinuity between P and S wave isoclinics for the unstressed case; a tendency for the isoclinics to broaden and envelope the isochromatics in regions where the P and S waves are superimposed; development of serrations in the dynamic isoclinics in the presence of a prestressing field (yielding a pseudo‐isochromatic appearance to isoclinics when viewed monochromatically); and finally, a general similarity between the dynamic optical effects in media under tensile and shear prestress.
THEORETICAL RESPONSE OF A TIME‐DOMAIN, AIRBORNE, ELECTROMAGNETIC SYSTEM
Authors: Nelson P. H. , Morris D. B.
Published: October 2002

The secondary magnetic field induced by a time‐domain, airborne EM system is calculated by transforming the tabulated mutual impedances of two magnetic dipoles above an earth of homogeneous or layered resistivity structure. The computational procedure is extended to produce response curves useful in interpreting data from a particular system, the Barringer Input system. It is demonstrated that the apparent resistivity can be estimated through use of the receiver channel ratios, a method which is independent of absolute system calibration. Layered earth calculations indicate to what extent conductive overburden cases can be readily distinguished, in terms of the conductivity‐thickness parameter, but separate interpretation of layer resistivity and thickness will require an amplitude‐calibrated flight system.
OPERATIONAL AIRBORNE THERMAL IMAGING SURVEYS
Authors: Stingelin Ronald W.
Published: October 2002

This paper reviews the methodology and significant parameters which experience has shown to be required in the conduct of airborne infrared imaging surveys using optical‐mechanical line scanning systems in the three to five and eight to fourteen micron spectral regions. For nonrectilinearized infrared imagery to be compatible with uncontrolled mosaicking, all flight lines should be in the same direction, flight lines must be spaced to allow matching of only the central seventy degrees of each strip, and surveys must be flown parallel to the prevailing wind direction. High‐resolution detectors are recommended for most geological terranes, and high‐sensitivity detectors for imaging hydrological and certain geothermal terranes. Nighttime data collection has proven superior to daytime data collection for most applications and little difference is found between the interpretability of imagery resulting from longwave and that from shortwave infrared detectors. Automatic gain control (AGC) and attendant ac averaging effects are minimal over homogeneous terranes exhibiting low infrared emittance variations. Amplification circuitry using dc restoration and manual level and gain controls is necessary when imaging land/water contacts or terranes with large variations in infrared emittance. A signal differentiation capability proved useful in coal fire and thermal pollution surveys.
MAGNETIC ORIENTATION OF BOREHOLE CORES
Authors: Fuller M.
Published: October 2002

The use of natural remanent magnetization (NRM) to orient boreholes was reported at least thirty years ago (e.g., Lynton, 1938). The method depends upon determining the direction of remanent magnetization of the sample and relating it to the geomagnetic field in which the rock was presumed to have been magnetized. If the NRM faithfully records the relevant geomagnetic field and the field is known, the orientation of the core sample is available. Unfortunately, the ancient geomagnetic pole positions are not, in general, sufficiently well known to make this method particularly successful for rocks that are older than late Tertiary. Moreover, the presence of a weak, viscous component of magnetization parallel to the present geomagnetic field at a given site may produce erroneous results unless it is recognized and eliminated. However, the existence of this component provides another means of orienting the core sample. Isolation of this component might initially appear to be difficult, but it is actually a standard procedure of paleomagnetism; and, in fact, many studies have implicitly demonstrated that the direction of the present geomagnetic field at the sample site is recoverable (e.g., As and Zijderveld, 1958; Zijderveld, 1967). Indeed a number of people have recognized the possibility of using this component to orient borehole samples (e.g., Hargraves, 1969—private communication). The use of this soft viscous component has been advocated recently to distinguish between normal and reversely magnetized rocks in connection with tests of the sea floor spreading hypothesis (Irving and Roy, 1968). Nevertheless, no explicit demonstration of the technique of orienting borehole cores has been published. In the course of paleomagnetic surveys, our demagnetization studies have revealed a number of examples of behavior which makes the orientation method possible. This note describes such behavior and explains how the orientation might be recovered.
On: “Estimation of Seismic Noise Structure Using Arrays” by Lacoss et al (GEOPHYSICS, February 1969, p. 21–38)
Authors: Sax Robert L. , Lintz Paul R.
Published: October 2002

There is a fundamental error in the article “Estimation of Seismic Noise Structure Using Arrays” by Lacoss et al which appeared in the February 1969 issue of Geophysics. The fundamental error is that the authors are attempting to resolve the horizontal phase velocity v into two components [Formula: see text] and [Formula: see text] where it is implied that [Formula: see text] and [Formula: see text]. This is incorrect as can be seen from Figure 1 in which d is the distance of the plane wavefront from the origin, [Formula: see text] and [Formula: see text] are the x and y components, and t is the corresponding time.
LOG EVALUATION OF NONMETALLIC MINERAL DEPOSITS
Authors: Tixier M. P. , Alger R. P.
Published: October 2002

Well logs can be used to locate and evaluate deposits of various commercially important minerals. It is only necessary that the mineral of interest represent a significant fraction of the formation bulk volume, and that it exhibit characterizing properties measurable by logs. Because modern logging methods measure electrical, density, acoustic, radioactivity, and certain nuclear characteristics of formations, they may be used to identify many minerals. For evaluation of sulfur deposits, either density or sonic logs provide good resolution when compared with porosity computed from neutron or resistivity logs. Trona beds are identified by a sonic reading of approximately 65 μsec/ft, neutron porosity index of about 40 percent, low natural radioactivity, and pronounced hole enlargement. Gamma‐ray logs provide important information in the location, identification, and evaluation of potash mineral deposits. Neutron, sonic, and density logs, in various combinations, augment the gamma‐ray data in such studies. Coal beds are characterized by high resistivities, and by high apparent porosities on sonic, neutron, and density logs. Density logs are particularly suited for evaluation of yield from oil shales. In all such explorations for nonmetallic mineral deposits, well‐logging methods provide a fast, detailed, and economical reconnaissance of the entire length of drilled hole. Results compare well with core assays.
APPLICATION OF WELL LOGGING TECHNIQUES IN METALLIC MINERAL MINING
Authors: Baltosser R. W. , Lawrence H. W.
Published: October 2002

Nearly all of the well logging devices currently used in the petroleum industry have found some limited application in metallic mineral exploration and mining. However, due to differing problems, the emphasis in the mineral industries has been on those devices regarded as “exotic” or “specialty” by the petroleum industry. These include devices to measure or determine induced polarization, magnetic susceptibility, and, hopefully, nuclear activation and the use of spectral analysis. Problems which the mining industry believes are solvable with well logging methods include bulk assay and recognition of minerals adjacent to and retired from a borehole, delineation of joint and fracture systems, leaching problems which involve porosity, permeability and groundwater movement, bank stability in open pit mines, roof and pillar loading in shaft mines, grindability, and penetration rates in drilling. Devices currently offered by the well logging industry which may be useful for these problems include those capable of measuring electrical properties, natural and induced nuclear radiation, seismic velocities of both compressional and shear modes, temperature, mechanical features of a borehole such as diameter and rugosity, and borehole photography either direct or by television.
THE ANOMALOUS VERTICAL GRADIENT OF GRAVITY
Authors: Hammer Sigmund
Published: October 2002

The behavior of the earth’s vertical gradient of gravity as observed, for example, in tall buildings or boreholes is a matter of considerable geophysical importance. The following elementary considerations may be of interest.
STATUS AND TRENDS IN LOGGING
Authors: Evans Hilton B.
Published: October 2002

Logging service companies are attempting to provide a fairly good selection of devices which have proven to be popular with the oil industry. However, the introduction of new devices or new services is being limited because oil companies are standardizing the logging‐suites run in their various geographic operating areas. Some of these new techniques appear to have significant applications. Recently, standard logging‐suites and evaluation‐techniques have evolved; these can be evaluated in terms of open‐hole and cased‐hole applications and the physical parameters of interest. Generally, these standard procedures depend on the differences in responses of multiple electrical and porosity devices. The multiple measurements are input to response equations which yield the parameters of interest. Although mining companies have been slow to adopt logging techniques, the use of logging devices and interpretation methods in nonpetroleum mineral (groundwater, nonmetals, metallic sulfides, etc.) exploration and evaluation, and in providing geophysical survey parameters is increasing. Nuclear, electrical, acoustic, and other methods are utilized, and newer applications of these to exploration, particularly in lithology determination, suggest themselves. Log digitizing and computer processing of log data have become routine in most major oil companies, but techniques, programs, and equipment vary significantly. Currently, commercial digitizing services are too expensive to be used extensively; the per‐log costs, however, are declining as more digitizing companies offer competitive services. Two basic commercial systems for transmission and computation of log data are functioning. To date, these systems yield “quicklook” reconnaissance parameter computations. Current research and development emphasis is on pulsed neutron‐spectroscopy and acoustic‐parameter measurements and on digital processing techniques.
DISCRETE TIME SOLUTION OF PLANE P‐SV WAVES IN A PLANE LAYERED MEDIUM
Authors: Frasier Clint W.
Published: October 2002

For plane waves at normal incidence to a layered elastic medium, both the forward and inverse discrete time problems have been previously solved. In this paper the forward problem of calculating the waves in a medium of plane, homogeneous, isotropic layers is extended to P and SV body waves at nonnormal incidence, where the horizontal phase velocity of each wave is greater than the shear and compressional velocities of each layer. Vertical traveltimes for P and SV waves through each layer are rounded off to unequal integer multiples of a small time increment Δτ. This gives a 4×4 layer matrix analogous to the 2×2 layer matrix for normal incidence obtained by previous authors. Reflection and transmission responses recorded at the free surface of a layered half space are derived as matrix series in integer powers of the Fourier transform variable [Formula: see text]. These responses are generated recursively by polynomial division and include all multiply reflected P and SV waves with mode conversions. It is shown that the reflection response matrix generated by a source at the free surface equals the product of a constant matrix and the positive time part of the autocorrelation matrix of the transmission response matrix due to a deep source. This is an extension to nonnormal incidence of a theorem proved by Claerbout for acoustic waves at normal incidence.
THE EFFECT OF HARMONIC DISTORTION IN THE USE OF VIBRATORY SURFACE SOURCES
Authors: Seriff A. J. , Kim W. H.
Published: October 2002

Harmonic distortion apparently arising from nonlinear processes, especially coupling of the vibrator to the ground, has often been observed in land seismic operations utilizing a frequency‐modulated mechanical vibrator as a surface source. The effect of harmonic distortion is to add a long oscillatory tail to the correlogram of a single sweep for the case in which the sweep frequency decreases with time. For up‐sweeps the distortion effect appears as a forerunner. It is shown analytically that for kth harmonic distortion, the zero‐to‐peak amplitude of the distortion tail (or forerunner) relative to the autocorrelation peak when the seismogram is crosscorrelated with, the undistorted outgoing signal is given approximately by √1/(k−1)TW times the amplitude ratio of harmonic to fundamental. W is the frequency range of the fundamental sweep and T is its length. Some examples computed by crosscorrelating a fundamental sweep (generated artificially) with its harmonic components are shown to demonstrate the effect of harmonic distortion. Some results on harmonic distortion observed in field seismograms recorded in the Val Verde basin of West Texas are presented. Second harmonic distortion of the order of 30 to 100 percent of the fundamental was observed.
THEORETICAL STUDIES ON THE ROTARY FIELD ELECTROMAGNETIC METHOD OF PROSPECTING
Authors: Sinha Ajit K.
Published: October 2002

The electromagnetic response of a sphere and of a two‐layer conducting earth placed in a rotating electromagnetic field is considered. A rotating electromagnetic field is generated by passing alternating currents of equal strength and frequency that are out of phase by 90 degrees through two identical, orthogonal coils, one horizontal and the other vertical. The resultant elliptically polarized primary field, whose ellipticity is a function of the spatial location, seems to have several advantages over the linearly polarized field ordinarily employed in the slingram method of airborne electromagnetic prospecting. The responses of the two models have been obtained under certain simplifying assumptions which hold in some cases of airborne electromagnetic prospecting. Based on the theoretical results, several master‐charts have been plotted which may be used for the determination of parameters such as the shape, size, depth, and conductivity of the inhomogeneities from the field data. The principal advantages of the rotary field method over the conventional electromagnetic methods, such as its insensitivity to small variations in the separation between the transmitters and the receivers, and to small rotations along the direction of the flight path, and automatic cancellation of the primary fields at the receivers, make it possible to measure the “pure anomaly,” and to use much greater transmitter‐receiver separation than in the conventional methods. The main disadvantages of this system are noise and the inability to map closely spaced anomalous bodies.
On: “IP and Resistivity Type Curves for Three‐dimensional Bodies” by K. Dieter, N. R. Paterson, and F. S. Grant (GEOPHYSICS, Vol. 34, no. 4, August, 1969, p.615–632).
Authors: Roy Amalendu
Published: October 2002

All boundary conditions of the problem discussed by Dieter et al cannot be satisfied by the solution given in equations (8) and (9). It is not adequate to consider just one image in the manner illustrated by Figure 2. There will be a series of higher order images: [Formula: see text] and [Formula: see text] will be reflected on S giving the next image. This image in turn will be reflected on [Formula: see text]; and so on. Equations (8) and (9), therefore, represent an approximation—not a very good one—and will hold approximately only under very restricted conditions (see, for instance, “Interpretation Theory in Applied Geophysics” by F. S. Grant & G. F. West, p. 425, McGraw‐Hill Book Company, N. Y.). They do not constitute “a perfectly suitable form” for the potential due to a closed conducting body in a half‐space.
EMISSION BY UNDERWATER EXPLOSIONS
Authors: Lavergne M.
Published: October 2002

Theoretical and experimental investigations of the seismic effects of underwater explosions of dynamite charges are described. We investigate the acoustic efficiency in a broad frequency band and in the seismic frequency band, the partition of energy between the shock wave and bubble pulses, the seismic effects of cavitation due to ghost reflection at the air‐water interface, and the damage caused to marine life. Results concerning the variation of the seismic efficiency with shot conditions are given: the conclusion is that the seismic efficiency of charges of the order of 100 gm can be considerably increased by dividing the charges and by shooting at depth. Experiments show that two or three properly spaced 50 gm charges of dynamite, shot at a depth of about 12 m, give the same result as a single charge of about 5 to 15 kg shot at a depth of 1 m. CDP marine sections comparing caged charge shooting with conventional shooting in the same area are shown.
STATISTICALLY OPTIMAL STACKING OF SEISMIC DATA
Authors: Robinson John C.
Published: October 2002

A theory for weighting seismic records in the stacking process has been developed from a statistical seismic model. The model applies to common‐depth‐point seismic records which have been statically and dynamically corrected; the same model applies to an ordinary stacking procedure. The model stipulates for the signal and noise components, respectively, of a seismic record that (1) the signal is coincident with and similarly shaped to the signal on other records, and (2) the noise is statistically independent of that on any other record and of the signal and has zero mean value. In accord with the model, a seismic record is completely described for the purpose of weighting by its signal scale and its signal‐to‐noise energy ratio. Several statistical procedures for evaluating these parameters for seismic field data are presented. The most favorable procedure is demonstrated with both synthetic and field seismic records.
THE POTENTIAL OF DIGITAL SEISMIC RECORDINGS FOR MULTICHANNEL PROCESSING
Authors: Lindsey J. P.
Published: October 2002

The availability of seismic digital field recording equipment has made possible new processing techniques which achieve significant reflection data enhancement. Typical of the processes that are now used routinely are deconvolution, autocorrelation and crosscorrelation, Fourier transformation, and spectral alteration. A recording fidelity that reduces errors to 1 part in 10,000 has provided the motive for developing and using these techniques. An additional capability of digital field equipment is the recording of amplifier gain information to a precision of 0.1 percent. This appears to provide a motive for developing multichannel processes which expand further our processing capabilities beyond the essentially single channel ones now in use. The present study evaluates the multichannel processing potential afforded by present day seismic digital field recording systems. The evaluation is based on measurement and computation of the effects of channel performance deviations. Each component of the field recording system (geophone, cable, amplifier, filters, sampling skew) separately, and the system as a whole, are evaluated in this context. Results of the study indicate that whereas any given channel possesses a dynamic range of 80 db, channel‐to‐channel variations establish a dynamic range of only 15 db. The 15 db range sets a serious limit on the performance of multichannel processes and points up the need for additional improvements in field hardware capabilities.
RESULTS OF A DIFFERENTIAL OMEGA TEST IN THE MACKENZIE RIVER DELTA
Authors: Sobczak L. W. , Taylor G. J.
Published: October 2002

In 1969 the Gravity Division of the Observatories Branch, Department of Energy, Mines and Resources, Ottawa, in cooperation with the Research, Development, and Programming Division of the Telecommunications and Electronics Branch of the Department of Transport, undertook an evaluation of the worldwide Omega Navigation System in the Arctic for the Polar Continental Shelf Project. Omega is a long‐range, very low frequency radio navigation system. It consists of 4 (Norway, Trinidad, Hawaii, and New York) of the planned 8 transmitters and provides navigational coverage for the North Atlantic area, North America, and parts of South America (Scull, 1969 and Dick‐Peddie, 1968). These stations presently transmit two frequencies (10.2 kHz and 13.6 kHz) in a sequential pattern synchronized in phase by means of atomic clocks (Tracor, 1968 and Findlay, 1968). The Omega receiver measures the difference of phase of received signals from a pair of transmitters. This measurement defines one line of position (LOP) in a family of hyperbolic lines. Lines of positions defined by the zero phase difference are the lines of position that are numbered on an Omega chart, and the distance between two such lines is known as a lane. A position is determined by the intersection of two lines of position within known lanes.
EVALUATION OF THE MEASUREMENT OF INDUCED ELECTRICAL POLARIZATION WITH AN INDUCTIVE SYSTEM
Authors: Hohmann Gerald W. , Kintzinger Paul R. , Van Voorhis Gerald D. , Ward Stanley H.
Published: October 2002

The induced polarization (IP) technique is based on the observation that variations of earth conductivity with frequency may be indicative of buried metallic mineralization. Conventional IP involves the use of grounded electrodes, the installation of which can be quite time consuming. However, the electromagnetic fields about an oscillating magnetic dipole also depend on ground conductivity. Thus, it is conceivable that we might be able to detect IP anomalies with an inductive system, thereby eliminating the need for grounded electrodes. An airborne induced polarization method is a theoretical possibility. Theoretical calculations based on a conductivity model determined experimentally at frequencies less than 30 hz suggest that the effect of polarizable material on electromagnetic response is quite small. In order to check the theory and to determine experimentally whether inductive IP is feasible, field tests were conducted in two areas in Nevada which exhibit strong conventional IP anomalies. The field tests consisted of measurements of the amplitudes of the electric and magnetic fields about a horizontal loop of wire carrying current at frequencies ranging from 15 hz to 1500 hz. The presence of the polarizable material is not evident in the inductive data; in fact, the observations can be fitted to theoretical curves for nonpolarizable models. Hence, on the basis of both theory and field tests, it is concluded that inductive IP based on amplitude measurements is not a practical exploration tool for environments such as that of the southwestern United States.
ON THE VALIDITY OF THE USE OF THE UPWARD CONTINUATION INTEGRAL FOR TOTAL MAGNETIC INTENSITY DATA
Authors: Henderson Roland G.
Published: October 2002

The integral solving the Dirichlet problem for a plane, known as the “upward continuation integral” to exploration geophysicists working with magnetic and gravity fields, is sometimes misunderstood. Recently, some geophysicists have commented that its use in continuing ΔT, the component of the total intensity anomaly in the direction of the earth’s normal field, is suspect, the thought being that only components normal to the surface can be so continued. The integral in question is [Formula: see text]where ΔT(α, β) represents measured total intensity values on the plane of observations z=0, in a right handed rectangular coordinate system in which the z axis is positive vertically downward.
DIRECT DESIGN OF TWO‐DIMENSIONAL DIGITAL WAVENUMBER FILTERS
Authors: Lavin Peter M. , Devane John F.
Published: October 2002

A closed form solution is derived for generating the space domain weighting coefficients for phase‐distortionless low‐pass filters with flat pass regions, variable cutoff wavenumbers [Formula: see text] and variable cutoff rates (Δk). High‐pass and bandpass filters can be designed using the same basic algorithm. The error in the spectrum of the filters, due to truncation of the weighting coefficient set, depends on both Δk and [Formula: see text]. An empirical error analysis yielded criteria for estimating the size of the coefficient array for an acceptable error level in the spectrum.