bluuebunny/crossref_metadata_2025 huggingface dataset:
CRATERING EXPERIMENTS WITH LARGE HIGH‐EXPLOSIVE CHARGES
Authors: Vortman L. J.
Published: October 2002

Spherical charges of cast TNT weighing 1,000, 40,000, and 1,000,000 lb were detonated at various depths below the surface in desert alluvium soil and in basalt rock to determine variation in crater dimensions with burst depth and to define scaling laws relating the dimensions of large‐charge craters with those of small‐charge craters. Data suggest scaling as the 0.3 power of the charge weight, but consideration of gravity and overburden effects provide a variable scaling ranging from the cube root of charge weight for surface bursts or very small charges to the fourth root of charge weight for very large charges buried at relatively greater depths. Results show that, for these two media, dimensions agree if density alone is considered and strength properties are ignored. Close‐in air blast is suppressed by charge burial to a greater extent than is air blast at greater distances. Ground‐shock‐induced air shock becomes more important relative to blast from venting gas as the burst depth is increased. Suppression of close‐in air blast by charge burial is essentially the same for charges buried in basalt rock and alluvium soil. Empirical relations are derived showing the relation of the motion of the ground surface above the charge to the scaled burst depth.
THE APPLICATION OF THE MAGNETOTELLURIC AND TELLURIC METHODS IN CENTRAL ALBERTA
Authors: Srivastava S. P. , Douglass J. L. , Ward S. H.
Published: October 2002

In 1950, Tikhonov in Russia and Kato and Kikuchi in Japan showed that quantitative information concerning the electrical properties of the subsurface could be obtained from simultaneous measurements of short‐period fluctuations in the earth’s electric and magnetic fields. This appeared to amount to a significant advance from qualitative telluric field studies of Schlumberger and his followers. However, it was not until 1953, when Cagniard presented his basic paper, that the potential of the magnetotelluric method was realized.
COMMENTS ON THE DISCUSSION BY A. T. DENNISON
Authors: Szasz Stephen
Published: October 2002

Prescott’s derivation of the differential equation for θ, which describes the movement of the receptor mass with respect to the frame, is correct (equation (6)); the general solution of this equation (7) is also correct. Dennision also agrees with these equations.
On: “DIFFRACTION OF ELECTROMAGNETIC WAVES BY AN INHOMOGENEOUS SPHERE” BY. J. G. NEGI (GEOPHYSICS, AUGUST 1962, PP. 480–492)
Authors: Ben‐Menahem Ari , Cisternas Armando
Published: October 2002

In the section of the paper by Dr. Negi dealing with “The Influence of the Air‐Earth Boundary,” the author is using results given in a paper by B. P. Dyakonov (1959). Formula (28) in Dyakonov’s paper is incorrect because the spherical wave functions should be given differently.
THE MAXIMIZATION OF SENSITIVITY IN COIL‐TYPE MAGNETOMETERS FOR ROCK MAGNETISM
Authors: Hall Donald H.
Published: October 2002

A common design of magnetometers for measuring rock magnetism is based on a circular double coil which acts as a detector of magnetic flux. If the linear dimensions of the coil and the distance from coil to specimen are expressed as multiples of the inner radius of the coil, a simplified expression for the electrical output of the coil results. It is then possible to construct a single family of curves applicable to the calculation of the electrical output of double coils of all sizes and proportions. Such a family of curves is presented. There are optimum proportions for which double coils reach maximum sensitivity. These proportions lead to wider and thicker winding sections for a given inner radius than usually used in double coils, but not much so. In fact, a coil of optimum proportions can reach the same sensitivity as a coil of lower proportions and have fewer turns, larger wire, and lower resistance. Sensitivity drops off rapidly for proportions lower than optimum, but drops off slowly for proportions larger than optimum. Thus, coils of small proportions should be avoided if possible. Sensitivity is best when the specimen is placed at the center of a coil of optimum proportions and when the inner circumference of the coil encloses the specimen as tightly as possible. If the inner radius of the coil is enlarged (with optimum proportions still maintained) to accommodate a larger specimen, sensitivity is further increased. Attention to all of these factors can lead to a sensitivity of from 30 to 45 times as large as the sensitivity that would otherwise result. Tables of maximum sensitivities and minimum signal for coils of various sizes and proportions are given as an aid in the design of coils.
RESULTS AND LIMITATIONS OF MAGNETOTELLURIC SURVEYS IN SIMPLE GEOLOGIC SITUATIONS
Authors: Vozoff K. , Hasegawa H. , Ellis R. M.
Published: October 2002

Results are presented of magnetotelluric measurements near a fault and on deep horizontal sediments. These are compared with known geological and geophysical data from the same localities, and are found to be in fair agreement with predictions from existing theories. Differences are attributed to shortcomings in measurement and analysis techniques, to geological complications, and partly to possible failings in the Cagniard and d’Erceville‐Kunetz theories. Evidence is discussed indicating substantial variation of Upper‐Mantle conductivity with location.
EXPERIMENTAL GROUND AMPLITUDES FROM SMALL SURFACE EXPLOSIONS
Authors: Kovach Robert L. , Lehner Francis , Miller Ray
Published: October 2002

The ground amplitudes produced by the detonation of small untamped surface charges of Dupont’s Nitramon S Primer and EL 506 PETN flexible sheet explosive were measured on a variety of rock types. For equivalent weights, the PETN sheet explosive produced larger ground amplitudes.
MULTIPLE REFLECTION PROBLEMS IN WESTERN CANADA
Authors: Mouritsen Stanley A.
Published: October 2002

The purpose of this paper is to stimulate interest in the problems of sedimentary multiple reflections in Canada and to show examples of some of the existing types. The types considered are: Second White Specks to the Paleozoic surface, the Blairmore to the Paleozoic surface, the suspected Ireton or base of the Nisku to the Paleozoic surface, the Devonian to the Paleozoic surface, and the base‐of‐weathering to the Paleozoic surface. Record examples were contributed by oil companies in Calgary to illustrate the Cretaceous‐to‐Paleozoic surface and the base‐of‐weathering‐to‐Paleozoic‐surface types. Records showing the other types are classified as confidential and unavailable. The base‐of‐weathering‐to‐Paleozoic‐surface multiple is shown with supporting cross‐sections and record‐sections as well as the simple field procedure, based on known data, that can be used by the field interpretation staff to help confirm this type of multiple. The problem of correctly interpreting seismic records where multiple reflections are present is discussed, and the criteria for distinguishing between multiple anomalies and true structures (particularly reef structure) presented. The conclusions drawn from the discussion are that for most types of multiple reflection interference accurate interpretations can be made. However, multiple reflections in certain areas can make definite interpretive results impossible.
GEOPHYSICAL ACTIVITY IN 1962
Authors: Smith Neal J.
Published: October 2002

Petroleum geophysical exploration in the Free World, consisting of seismic, gravity, ground magnetic, and other nonairborne geophysical methods, declined 10.0 percent over 1961. This is the sharpest in the continual series of declines that began in 1957 and amounts to a loss of 1,008 crew‐months; it is 32 percent down from the peak year of 1956. Airborne magnetometer activity, on the other hand, rose from 347,841 line‐miles in 1961 to 433,473, an increase of 25 percent.
A RAPID CURVED‐PATH METHOD FOR WEATHERING AND DRIFT CORRECTIONS
Authors: Duska Leslie
Published: October 2002

For weathering and drift corrections, especially in areas where the low‐velocity material is very thick, the Blondeau method, as modified by Swartz, has proved to be not only advantageous, but the only accurate method under certain conditions. This paper presents a new procedure for applying the Blondeau‐Swartz method to the single‐layer case which achieves considerable time saving, elimination of the potential sources of errors, increased accuracy, and a final answer, or reduction value, which is rapidly checked for correctness. An example of the use of the rapid method is presented. The constants in this example are characteristic of the glacial‐drift problem in Central Alberta.
BASIC PROBABILISTIC METHODS IN GEOLOGICAL SEARCH
Authors: Kyrala A.
Published: October 2002

An exposition of the basic mathematical methods used in calculating the probability of successful search for geological structures in a discrete set of regions is given. The argument is framed without the restrictive assumption of a specific distribution for the conditional probability of discovery but is subsequently illustrated by the specific case of a Poisson distribution. The optimal allocation of search effort to the various regions is determined. The important question of how the probabilities of occurrence of deposits should be adjusted after unsuccessful search is specifically answered by calculation of the a posteriori probabilities.
ENERGY AND VECTOR RECORD‐SECTIONS
Authors: Baranov Vladimir , Picou Claude H.
Published: October 2002

It is known that seismic traces are often characterized by quasi‐periodic oscillations which are nearly sinusoidal. A comparison between these field seismic traces and the corresponding synthetic seismograms, as computed from velocity logs, shows that these continuous oscillations are due partly to secondary arrivals which are mutually interfering and partly to seismic “noise.” The main arrivals of reflected energy superimpose and interfere with these continuous oscillations; consequently, it is difficult to pick reflections accurately. This paper considers methods of eliminating these continuous oscillations from the seismic sections, and of bringing out the energy content of the seismic waves in order to outline the changes in reflection energy which are superimposed upon the common and almost constant background energy arising from secondary arrivals and from noise. From the commonly known expressions of kinetic energy and potential energy of compression in vibrating solids, it has been possible to design a suitable computer for obtaining film cross‐sections which are the energy cross‐sections, so‐called because they show the energy arrivals. Another possibility is to calculate correlations between successive seismic traces (adjacent or not) and to do this only for dips which may possibly be reflected arrivals. It has also been possible for this case to design a suitable computer and to add to the playback unit a system for presenting correlations. This system uses a cathode‐ray tube equipped with an optical projection system which gives the possibility of automatically applying small segments of a line or vector with an inclination equal to the apparent dip of the reflection and with a thickness proportional to the strength of the reflection; thence the name of “vector section” given to this section. After a short résumé of the principles which are fundamental to these processes, the practical results obtained by the two methods are described and discussed, and a comparison between their relative advantages is given.
APPLICATION OF INVERSE FILTERS TO INDUCTION LOG ANALYSIS
Authors: George C. F. , Smith H. W. , Bostick F. X.
Published: October 2002

The general availability of digital computing equipment has motivated the investigation of the application of filtering techniques of communication theory to the analysis of electric and induction well logs. It will be shown that, with certain assumptions, the induction log may be represented as a linear filter with an impulse response and system function. A response equalization filter, which filters a shallow investigation log for comparison with a deep investigation log, may be used to scan pairs of induction, or induction and electric logs to detect invaded formations. An iterative process may be used to obtain an approximate solution for the depth of invasion from three appropriately chosen logs. Inverse convolution filtering may be used to obtain approximate resistivity values from apparent resistivity values indicated by the logs in radial zones concentric with the borehole for induction logs with different coil spacings.
MICROSEISMS AND AN ATTEMPTED APPLICATION TO EXPLORATION
Authors: Toksöz M. Nafi
Published: October 2002

A study of microseisms is made to determine some of their statistical properties and to investigate the feasibility of their use in determining the structures in the upper several kilometers of the earth’s crust by the phase‐velocity method. It is found that the microseisms in the period range of 1 to 6 sec arrive from several directions with comparable strength and at the same time. There are occasional short intervals of 10 to 40 sec during which microseisms are mostly unidirectional. It is also found that these relatively short‐period microseisms are not stationary in the wide sense over time intervals longer than 5 or 10 minutes. The phase velocities of microseisms recorced with an array of eight instruments are measured in four different locations. The velocities, although scattered, are found to be in agreement with the computed theoretical dispersion curve for the fundamental Rayleigh mode, based on the available seismic velocity information. An error analysis is made and the confidence limits are placed within ±20 percent of the measured velocities. It is concluded that in determining shallow crustal structures the microseism‐phase‐velocity method potentially is at least as effective as the gravity method, although it is not as suitable for routine work as the gravity method.
OPERATIONAL MAGNIFICATION AND PHYSICAL ENVIRONMENT OF SEISMOGRAPH STATIONS
Authors: Alsup S. A. , Guyton J. W.
Published: October 2002

Maximum satisfactory operational magnifications of 115 standardized seismograph stations in the United States range from 30,000 to 630,000 and are used to evaluate the sites relative to one another. Grouping the sites according to physiographic province, rock type, distance from cultural features, and type of installation shows distinct correlation between physical environment and operating magnification. As composites of the sites studied, the highest magnification site is a mine in an igneous intrusive body in the Basin‐Range province; the lowest magnification site is a surface installation on poorly consolidated sedimentary rock on the Coastal Plain. Regional variations of magnification capability are closely related to physiographic provinces; local variation within a province is as great as the variation of physical environment.
GRAVITATIONAL EXPLORATION AND THE PRINCIPLE OF EQUIVALENCE
Authors: Thyssen‐Bornemisza Stephen
Published: October 2002

The equality of gravitational and inertial mass is mentioned by Einstein (1916) as an empirical principle constituting the basis of his Principle of Equivalence. The equivalence of gravitation and inertia implies that every phenomenon of gravitation can be explained as a phenomenon of inertia if observed inside an accelerated system.
A COMPARISON OF THE VARIOUS PARAMETERS EMPLOYED IN THE VARIABLE‐FREQUENCY INDUCED‐POLARIZATION METHOD
Authors: Hallof Philip G.
Published: October 2002

The increased use of the induced‐polarization method in recent years has resulted in two methods of measurement. The measurements in the frequency domain (variable‐frequency method) rely on changes in the apparent resistivities measured as the frequency of the applied current is varied. The measurement in the time domain (pulse‐transient method) detects transients in the measured potentials when the applied current is interrupted. The “chargeability” is the parameter used in the pulse‐transient method, while both the “frequency effect” and the normalized parameter “metal factor” are used in the variable‐frequency method. The most useful parameter would be the one which best indicates the amount of metallic mineralization present. Eight sets of field results from variable‐frequency field surveys are shown. The cases are shown in pairs; in each pair, the geometry of the source is much the same. By comparing the resistivity, the frequency effect (chargeability), and metal‐factor data with the amount of mineralization indicated by the drilling results, the usefulness of these parameters can be evaluated.
MAGNETIC ANOMALIES OVER THIN SHEETS
Authors: Reford M. S.
Published: October 2002

Curves are presented showing the total intensity magnetic anomalies caused by thin sheets, uniformly magnetized by induction. The purpose is to give a general picture of the changes in size and shape of the anomalies with changes of dip and strike at various latitudes.
THEORETICAL PREDICTION OF SEISMIC NOISE IN A DEEP BOREHOLE
Authors: Sax Robert L. , Hartenberger Royal A.
Published: October 2002

Seismic noise attenuation as a function of depth below the earth’s surface is described in terms of surface wave modes. The energy density of the noise, which often represents a combination of modes, is computed as the arithmetic sum of the energy densities of all contributing modes. Three models are used to determine the fractional contribution of each mode. Model A stipulates that each mode contributes equally to the energy of the noise; Model B specifies that the energy fraction contributed by each mode is dependent upon the energy in those beds in which the shear velocity of the bed exceeds the phase velocity of the mode; and Model C prescribes that all modes have equal energy density at the free surface. A comparison of observations with attenuations based on the three models reveals that Model B is the best.
RECOMMENDED EXPLOSION‐CRATER NOMENCLATURE
Authors: Hansen Spenst M. , Nordyke Milo D. , Rawson Donald E. , Sherman Walter C. , Spruill Joseph L. , Steinriede William L. , Toman John
Published: October 2002

A serious lack of consistency of terminology has characterized numerous articles published in recent years reporting research in the cratering field. The need for a uniform system of nomenclature to provide a common basis of expression has thus become increasingly apparent.
REFLECTION SURVEY AT BARRACUDA FAULT
Authors: Paitson L. , Savit C. H. , Blue D. M. , Knox W. A.
Published: October 2002

One of the areas selected for evaluation by Project Mohole as a potential site for drilling through crust to mantle is Barracuda Fault in the Atlantic. Reflection profiling obtained as accessory data to crustal refraction profiles reveals 5.5 kilometers of relief associated with that structure. These data also suggest three possible environments of deposition: 1. Turbidites and pelagic ooze in an environment of basin accumulation. 2. Turbidites and pelagic ooze in an environment of alternate deposition and erosion. 3. Deposition of pelagic ooze on topographic highs and possible erosion (slumping). Materials relatively transparent to the spectrum of seismic energy employed are interpreted as pelagic ooze. Finely stratified sediments are interpreted as pelagic and turbidite sequences. A zone of diffracted energy lying beneath the sediment is thought to be basement.
MAKING GEOPHYSICS MEANINGFUL TO GEOLOGISTS
Authors: Brundage Harrison T.
Published: October 2002

This has been a problem in the past, just as the converse has also. Communications barriers, however, are fading away, because at each level, educational, corporate divisional, and in operations, geologists are becoming better geophysicists and geophysicists are becoming better geologists. Their formerly discrete endeavors are becoming better coordinated and their work less separate. Geophysicists have been largely concerned with measurements of earth‐crust phenomena. Incorporation of more geology into such measurements has increased the reliability of the conclusions. As knowledge of the earth increases, the application of geology becomes less of an intuitive matter and thus more precise also. In this epoch in which oil and gas exploration proceeds to progressively greater depths, the distinction between a petroleum geologist and a petroleum geophysicist becomes more difficult to define. The time appears to be approaching when universities aiming graduates at the petroleum industry may graduate petroleum earth scientists, not geologists and geophysicists.
DISCOVERIES
Authors: Deussen Alexander
Published: October 2002

What are the reserves of oil? This question has been a serious matter of concern to us ever since oil has come to occupy the dominant position in our national economy which it now occupies.
TRANSIENTS IN ELECTRICAL PROSPECTING
Authors: Hawley Paul F.
Published: October 2002

The technique used in the older methods of electrical geophysical prospecting is well known. The measurements of current and potential drop which are made are the steady‐state values, which can be readily measured on indicating‐type meters. The factor of time is of very little importance.
THE ADJUSTMENT OF MISCLOSURES
Authors: Cowles Laurence G.
Published: October 2002

The adjustment of misclosures in slope traverses by the method of least squares is effected by solving a system of simultaneous equations which may be written by inspection of the traverse diagram. These equations can be solved by measurements of currents in an analogous electrical resistance network. This paper is devoted mainly to the development of the electrical analogy.
IMPROVEMENTS IN THE CONTINUOUS SEISMIC PROFILER
Authors: Caulfield David D. , Hoskins Hartley , Nowak Richard T.
Published: October 2002

The continuous seismic profiling system used at the Woods Hole Oceanographic Institution now has (1) an electrical spark sound source which has a maximum stored energy of 100,000 joules and can produce a variety of acoustic pulses with peak pressures of up to 134 db above [Formula: see text], at a repetition period of 10 sec, and which has a conversion efficiency (stored electrical energy to sound energy radiated) of 10 percent, (2) a streamlined and uniformly neutrally buoyant line‐hydrophone array with a band‐pass of 20 to 1,000 cps, and (3) a matched‐filter detector that measures the correlation between the reflected signal and the waveform incident on the sea floor in the same frequency range as the reflection. A source whose sonic output can be varied readily makes possible tailoring the resolution of the system for the best display of features of the oceanic crust of varying vertical size. A large reduction in the self‐noise of the detector is achieved through the use of streamlined, stable‐towing, line‐hydrophone arrays which also discriminate against the noises of the towing vessel. A matched‐filter detector gives the maximum signal‐to‐noise ratio obtainable from a linear filter, and an eight‐fold improvement over the rectified amplitude presentation formerly used has been obtained. Reflections from 0.8 sec beneath the sea floor in continental shelf areas have been obtained at ship speeds of eleven knots and from 1.8 sec beneath the sea floor in the deep sea at six knots.
RAYLEIGH‐WAVE MOTION IN AN ELASTIC HALF‐SPACE
Authors: Sorge W. A.
Published: October 2002

Measurements made on Rayleigh waves below the surface of a simulated elastic half‐space confirm in detail the behavior predicted by theory. These measurements, made by means of a two‐dimensional seismic model, show that the amplitude of the Rayleigh wave falls off rapidly with increasing depth.
MINIMUM‐PHASE AND RELATED PROPERTIES OF THE RESPONSE OF A HORIZONTALLY STRATIFIED ABSORPTIVE EARTH TO PLANE ACOUSTIC WAVES
Authors: Sherwood J. W. C. , Trorey A. W.
Published: October 2002

In a horizontally stratified absorptive earth with vertically traveling plane compressional waves, denote the Fourier transforms of the reflectivity, delayed transmissivity, and the acoustic impedance by R, T, and Z, respectively. It is shown that both Z and 1±R are positive real (p‐r) functions. Although R, in general, is neither p‐r nor minimum phase, |R|<1 for real frequencies. T (the transmission function referred to a time origin [Formula: see text]—the one‐way traveltime through the section) is not, in general, p‐r. If the absorption law is a minimum‐phase function, however, then T is minimum phase. If absorption is absent, then the inverse filter for T is not only minimum phase, but is also of a finite duration equal to [Formula: see text].
DIRECTIONAL AND WIDE‐BAND VELOCITY FILTERING
Authors: Jackson Philip L.
Published: October 2002

The purpose of this note is to point out that the condition of monochromatic illumination in obtaining a two‐dimensional Fourier transform by optical means may be relaxed for wide‐band velocity filtering, and for the directional filtering of any two‐dimensional structure such as a contour map. Similar considerations hold for two‐dimensional Fourier transforms obtained by any means.
ADVICE TO A HIGH SCHOOL SENIOR
Authors: Thralls H. M.
Published: October 2002

One of the most important things in life is to choose a means of livelihood that you will sincerely enjoy. Whatever career you choose, there will be times that you will be certain that you would have fared better in another field. There are no careers, there are no industries, and there are no lives, that are free from set‐backs and ups‐and‐downs. There are no rosy paths free of thorns. No career will present a straight and narrow path to follow. There will be junctions in all roads you travel and you must make a decision at each junction. You’ll never know where the other road would have led, so always forge ahead on the chosen path without looking back. Where you’ve been is not nearly as important as where you’re going. Geophysics, as a career, will be no different in these respects than any other you might choose, but the basic thing that we need to determine to answer your question is, “Will there be a continuing demand for geophysicists during your lifetime?” Let’s try to evaluate the future by the past.
THE AUXILIARY POINT METHOD OF ELECTRICAL SOUNDING INTERPRETATION, AND ITS RELATIONSHIP TO THE DAR ZARROUK PARAMETERS
Authors: Zohdy Adel A. R.
Published: October 2002

The so‐called “auxilliary point” method for the interpretation of geoelectrical resistivity soundings has received considerable attention from the European geophysicists. However, almost no mention of it has been made in the American literature. It is the aim of this paper to introduce the method and to establish its mathematical relationship to the so‐called “Dar Zarrouk” parameters. The auxiliary point method is an empirical graphical method by which a multilayer problem is progressively reduced to the simple two‐layer case. Hence, to interpret a multilayer sounding curve, use is made of the available two‐ and three‐layer master curves in conjunction with one, or more, of four charts that represent families of auxiliary curves. The four charts are known as the Hummel (H‐chart), the Anisotropy (A‐chart), the Displaced‐Hummel (DH‐chart), and the Displaced‐Anisotropy (DA‐chart). The mathematical basis for the drawing of these charts is discussed, and furthermore the identity of the Dar Zarrouk point to the anisotropy point is shown. The relation between the various parameters of the auxiliary points and the Dar Zarrouk point is graphically illustrated. Other auxiliary methods for the interpretation of sounding curves, e.g., the Cagniard and the Ono charts are essentially the same as the auxiliary point charts. A theoretical four‐layer case illustrates the practical use of the method, its advantages, and its limitations.
RECONNAISSANCE SURVEY USING AVERAGE HORIZONTAL GRADIENTS OF GRAVITY
Authors: Thyssen‐Bornemisza Stephen
Published: October 2002

Some time ago, Romberg (1956/57) pointed out the advantage of reading horizontal gravity gradients rather than vertical gradients with the gravity meter. Several years later, in March, 1960, an experimental profile of gravity‐meter‐determined horizontal gradients was run for the author in the South Houston field by courtesy of Texas Instruments Incorporated. Since then, this gradient technique was repeatedly discussed but only very few results could be published (Thyssen‐Bornemisza et al., 1960, 1962a, 1962b). Stackler (1963) more recently pointed out again the value of the average gravity gradient for reconnaissance surveys predominantly in inaccessible areas.
A NOTE ON THE USE OF MICROSEISMS IN DETERMINING THE SHALLOW STRUCTURES OF THE EARTH’S CRUST
Authors: Aki Keiiti
Published: October 2002

In the VELA UNIFORM Special Issue I of Geophysics, M. N. Toksöz presented the result of his attempt at determining the shallow structures of the earth’s crust from the phase velocity of microseisms. He stated that his attempt resulted only in partial success on account of the fact that the microseisms arrived from more than one direction at the same time with comparable strength. He also concluded that there was no way of improving the results by the use of special arrays because, according to him, there were two unknown parameters, direction and phase velocity, and without the knowledge of one the other cannot be found. I thought this problem was already solved in my paper (Aki, 1957), in which a statistical theory of determining the phase velocity of random waves was given with a successful application to microseisms in Tokyo in the frequency range of 5 to 15 cps. Since Toksöz’s conclusion might have given a pessimistic view on the use of microseisms, I feel it is necessary to report a brief summary of my old paper published in a Japanese journal which might not be well circulated in the United States.
MAGNETIZATION OF KEWEENAWAN ROCKS NEAR DULUTH, MINNESOTA
Authors: Jahren Charles E.
Published: October 2002

Remanent magnetization measurements on 200 oriented samples from the Keweenawan gabbro, diabase, and associated rocks in the Duluth area show a clustering of directions west‐northwest and downward. Gabbro samples magnetized in this direction usually have Q, the ratio of remanent to induced magnetization, up to five, whereas other gabbro samples have larger Q. Diabase shows no such generalization. Remanent magnetization is important in all rocks studied. Q ranges from 0.3 to 75, but is less than 1.0 in only 15 samples. Volume magnetic susceptibility averages range from [Formula: see text] to [Formula: see text]. There is no apparent correlation between magnetic susceptibility and the direction of remanent magnetization. Average directions of remanent magnetization indicate a Keweenawan geomagnetic north pole at latitude 30° to 34° N, longitude 175° to 180° W.
SOME EXPERIMENTS ON MULTIPLE REFLECTION CANCELLATION
Authors: Silverman Daniel , Sparks N. R.
Published: October 2002

One of the most promising methods of identification or cancellation of multiple reflections on seismic records involves the calculation of synthetic records with all primaries and multiples, and the matching of the synthetic record with the field record. Such matching suffers today from the lack of precise information about the velocities and densities of the formations, dips of beds nonvertical transmission, etc. One possibility of improving this match involves the use of the earth itself as the “synthetic record computer.” In this process, the upcoming (or downgoing) primary signals are fed back into the earth with a vibrator in proper amplitude and phase to create a synthetic record of multiples only, which should match the multiples on the field record. Of course, only those multiple reflections which include a downward reflection from beds above the primary signal detectors will be included in the synthetic record of multiples only. The paper reports two experimental programs. One was carried out on an analog network to simulate the near‐surface and deeper formations, with means to feed back the upcoming signals in proper timing and polarity to cancel the multiples. These experiments indicated the theoretical workability of the process. The second program of experiments involved the use of a vertical spread to detect the upcoming and downgoing signals, and the use of a hydraulic vibrator to impress those signals back into the earth. These experiments were not conclusive because of insufficient power in the vibrator and high noise level. However, they indicated possible ways in which these limitations might be reduced, and the method applied to routine field operations.
FICTITIOUS ANOMALIES OF HIGHER VERTICAL DERIVATIVES OF GRAVITY
Authors: Fajklewicz Zbigniew J.
Published: October 2002

Computation of the first and second vertical derivatives of gravity gives rise to anomalies which look as though they were evidence of local geological features which, in fact, do not exist. Such anomalies are called fictitious anomalies. An average of two to four fictitious anomalies appear for every true anomaly. Fictitious anomalies are often so strongly defined as to mislead the geophysicist. In this paper an attempt is made to show how fictitious anomalies occur. This makes evident certain limitations in the method of interpreting gravity by computing derivatives.
CORRELATING VERTICAL MAGNETIC INTENSITY AND AVERAGE HORIZONTAL GRADIENTS OF GRAVlTY
Authors: Thyssen‐Bornemisza Stephen
Published: October 2002

Average horizontal gradients of gravity observed with the gravity meter may communicate more information than a corresponding number of conventional Bouguer values if local conditions are favorable (Thyssen‐Bornemisza and Stackler, 1960, 1962; Thyssen‐Bornemisza, 1965). Several small experimental profiles of average horizontal gradients of gravity were taken over an area previously surveyed with the magnetometer, as shown in Figure 1.
POSSIBLE P‐WAVE OBSERVATIONS IN SHORT‐PERIOD SEISMIC NOISE
Authors: Seriff A. J. , Velzeboer C. J. , Haase R. J.
Published: October 2002

For the past two years we have been engaged in a program of seismic noise measurements in deep boreholes; noise in a frequency range of approximately 0.2 to 5.0 cps has been studied. A special deep‐well seismometer designed by The Geotechnical Corporation has been used for recording noise at depths down to 14,000 ft in cased holes. The seismometer, which has a response almost identical to the typical short‐period Benioff, was clamped to the casing of the deep hole by a mechanical locking arm during observation periods. An identical seismometer has been used as a reference in a 500‐ft hole adjacent to the deep well. A surface array of four vertical Benioff seismometers was also recorded, with one seismometer near the well and three others at distances ranging from 0.5 to 1.0 km. Two horizontal seismometers were stationed near the wellhead.
A SELF‐ADJUSTING FILTER FOR SHALLOW SEISMIC EXPLORATION
Authors: Meyerhoff H. J.
Published: October 2002

In shallow seismic exploration, signals from repeated impacts are recorded on a geophone. These records are synchronized and added to enhance the seismic signal component relative to the uncorrelated noise that impairs reception. Linear filtering is the technique proposed in this paper to improve seismic signal detection over and above that obtained by synchronous addition. To arrive at the practical filter which best (in mean square) approximates, at its output, the seismic signal component, when fed with the geophone record, requires at least two such repeated synchronized recordings. The filter network is composed of a set of band‐pass sections with variable parameters which are automatically adjusted to optimum. The setting time for the self‐adjusting procedure may be preselected; the longer the time to set, the greater the probable accuracy of the parameter settings. Once set to optimum, the filter is fed with the synchronized sum of geophone recordings. The resulting filter output is reversed in time and played back again through the same optimum filter to yield an output which has no phase distortion introduced by linear filtering. Such a filter is being incorporated into seismic and hydrosonde equipment.
SONIC VELOCITY AND PENETRABILITY OF SIMULATED LUNAR ROCK DUST
Authors: Osgood Jack H. , Green Jack
Published: October 2002

Theoretical considerations are given for the design of an ultrasonic pulsing system for noncohesive dusts. In addition, measurements of less than one percent error of sonic velocity were made in volcanic rocks of different textures. Pumice containing elongate vesicles exhibits marked sonic anisotropy. In contrast, basaltic scoria with approximately equidimensional vesicles exhibits sonic isotropy. These anisotropy contrasts may be significant in interpreting Surveyor return data and in evaluating lunar base requirements. Sonic velocity with a simultaneous recording of porosity in rock dusts under ambient conditions ranges from 150 m/sec (500 ft/sec) to 700 m/sec (2,100 ft/sec). Absolute measurements of shear strength, using the vane‐type shear tester, were made at critical density obtained by vibrating the simulated lunar dust samples for specified time periods. Relative shear strengths were also compared at maximum density obtained by long‐period vibration of dust samples. Comparson of stress curves of dusts of different grain shapes indicates that relatively little strain occurs before the plastic zone of the stress curve is reached for volcanic dust consisting of angular glass shards. For purpose of shear strength analysis, grain shapes may be grouped as spherical, prismatic, and vesiculate. Shearing resistance curves are analyzed for each of these groups, and the vesiculate shapes have the highest shear strengths at critical density. Moreover, the sliding habit during shear appears to reflect the shape of the grains. Grain shape is apparently a first‐order parameter affecting shear strength of dust particles >0.1 mm in diameter. Adhesion effects due to hard vacuum ([Formula: see text] to [Formula: see text] torr) are small but measurable for the grain sizes considered. At equivalent porosities, vacuum at [Formula: see text] torr apparently does not markedly influence the peak shear strength of dust composed of vesiculate particles greater than 0.1 mm in diameter. Once sonic velocity and shear strength data are obtained by a lunar probe or astronaut, practical studies can be made on bearing capacity, trafficability, and lunar base construction.
ANOMALOUS MAGNETIZATION IN TRIASSIC DIABASE NEAR LEESBURG, LOUDOUN COUNTY, VIRGINIA
Authors: Toewe E. Clayton , Le Van D. C.
Published: October 2002

A 3,000‐gamma closed negative anomaly, approximately 15 ft in diameter and roughly circular in outline, was found during a total intensity magnetic survey in the Leesburg quadrangle, Loudoun County, Virginia. This anomaly is on the farm of C. R. Tillett near Waxpool, 7.75 miles south‐southeast of Leesburg, at latitude 39°00′39″N and longitude 77°31′51″W (Figure 1). The area surveyed exhibits essentially no topographic relief. It is underlain by a diabase sill of Triassic age that dips 20–30 degrees to the west. Fairly fresh diabase outcrops are randomly scattered throughout the area.
A PROPOSED STANDARD FORMAT FOR NINE‐TRACK DIGITAL TAPE
Authors: Savit Carl H.
Published: October 2002

Digital seismic tapes have, to the present time, been prepared in a great variety of formats. With the rapid growth of digital recording and the strong likelihood that tapes will be exchanged among the various oil companies and contractors, an urgent need for standardization has become apparent.
On: “OIL FIELDS AND AEROMAGNETIC ANOMALIES,” BY NELSON C. STEENLAND; “INSTRUMENT DETAILS AND APPLICATIONS OF A NEW AIRBORNE MAGNETOMETER,” BY HOMER JENSEN; AND “SOME RESULTS OF AEROMAGNETIC SURVEYING WITH A DIGITAL CESIUM VAPOR MAGNETOMETER” BY RAOUL I. GIRET (GEOPHYSICS, OCTOBER 1965)
Authors: Kellogo William C.
Published: October 2002

Three articles appearing in the October 1965 edition of Geophysics, which was devoted to magnetic methods, deserve comment. These are papers by Steenland, Jensen, and Giret. Perhaps the following remarks will lead to better understanding of certain concepts in aerial magnetic surveying. All three authors discuss (and presumably advocate) the use of “high sensitivity magnetometers”. This advocation has considerable merit in certain instances of petroleum exploration. However, each paper has certain oversights or omissions to which I will draw attention. I will also discuss certain other related subjects which seem pertinent.
On: “THE GRAVITATIONAL ATTRACTION OF A RIGHT RECTANGULAR PRISM,” BY DEZSÖ NAGY (GEOPHYSICS, APRIL, 1966, PP. 362–371)
Authors: Corbató Charles E.
Published: October 2002

You might be interested to note that the results obtained by Nagy (1966) and published in Geophysics concerning the vertical component of the gravitational attraction of a right rectangular prism not only had been published previously by Sorokin and Haáz but also were derived and published (in English) 136 years ago by Everest (1830, p. 94–97). Everest calculated closed expressions which are equivalent to that of Nagy for the horizontal and vertical gravitational effects of a rectangular parallelopiped and used these equations to estimate the topographic deflection of the plumb bob due to the Satpura Range in India.
RADIATION OF BODY WAVES FROM NEAR‐SURFACE EXPLOSIVE SOURCES
Authors: Gupta I. N. , Kisslinger C.
Published: October 2002

Amplitude distributions obtained from field observations of the azimuthal distribution of motion from cratering shots near a vertical face in a limestone section yielded data on radiation into a half‐space. These effects have been approximately reproduced in the laboratory by means of two‐dimensional seismic models. Small chemical explosions were fired on or near the edge of a large plexiglas sheet and the radiation of both P and S waves observed. Shots on the edge of the model sheet produce P and S radiation patterns expected from a normal downward impulse on the free surface. The radiation patterns from cratering shots may be qualitatively explained by the combined action on the free surface of a normal downward stress and a pair of horizontal stresses (dipole without moment) at the source point. The observed data are not sufficient for verifying theoretical S wave distributions. Observations of SV amplitudes from nuclear explosions could yield useful information concerning the relation between the angle at which the waves leave the source and the distance at which the wave emerges.
MAGNETOTELLURIC MEASUREMENTS IN SOUTHERN ALBERTA
Authors: Vozoff K. , Ellis Robert M.
Published: October 2002

Results are presented of magnetotelluric measurements at three locations in southern Alberta. At two stations interpretations using Cagniard’s theory are consistent with other measurements which show a conductivity discontinuity near 80 km. However, at the station closest to the Rocky Mountains, the conductivity increase appears at approximately 35 km. In this case, it is unlikely that the long period decrease in the apparent resistivity curves is due to source effects.
GEOPHYSICAL ACTIVITY IN 1965
Authors: Smith Neal J.
Published: October 2002

The report on 1965 geophysical activities in the Free World includes, as usual, petroleum and mining. In addition, activities for engineering purposes and ground water exploration have been included for the first time. This has been talked about for many years, but the diverse, widespread nature of these usages made the task seem very difficult. The trial has borne out the difficulties, but a reasonable measure of success has been achieved and as experience with collecting these data expands the value of the report will increase. The inclusion of engineering and ground water activities serves to show the breadth as well as the depth of geophysical importance to the economic community.
MODERN SEISMIC EXPLORATION OF THE GULF COAST SMACKOVER TREND
Authors: Rosenkrans R. R. , Marr John D.
Published: October 2002

Modern seismic methods, which attenuate multiple reflections, demonstrate the existence of consistent diagnostic primary reflections from the deep Lower Cretaceous formations, from key Jurassic formation boundaries and from the base of the salt along the Smackover trend across Texas, Louisiana, and Mississippi. These data make feasible, for the first time, realistic delineation of deep subsurface structure. Typical seismic data along the trend are shown and related to subsurface geology. Certain new concepts in salt tectonics along this trend are indicated. The end of Smackover time was the beginning of the first major period of salt flow with related folding and faulting. The Buckner formation, up to possibly 5000 ft thick, represents backfill and base‐leveling material deposited around Smackover mantles over the pre‐Cotton Valley salt swells. Evidence exists of a mother salt bed up to 6000 ft thick. The possibility exists of Buckner reef growth on top of some Smackover lime highs over salt swells. Salt flow tectonics created rim synclines which tend to preclude migration of hydrocarbons into salt‐generated Smackover closures. Optimum evaluation of Smackover prospects requires determination of age, cause, and magnitude of Smackover closures (including rim synclines if present) plus, if possible, detection of reef buildups.
APPLICATIONS OF GREEN’S THEOREM IN TWO‐DIMENSIONAL FILTERING
Authors: Ford Wayne T.
Published: October 2002

There seems to be considerable interest in the design of a discrete two‐dimensional filter from band‐pass and band‐reject area specification in the ω‐k plane. The calculation of such a filter requires the evaluation of a double integral for each filter point. Considerable effort has been expended in efforts to give the results of these integrations in closed form for special cases. The present note was written to point out that a rather general class of filters can be calculated from a single computer program. The simplicity of this program is a result of an elementary application of Green’s Theorem in the plane.
On: “Gradient Measurements in Ground Magnetic Prospecting,” by Peter Hood and D. J. McClure (GEOPHYSICS, June 1965, p. 403–410)
Authors: Rowan Irwin
Published: October 2002

This paper has prompted me to supply some unpublished information and to make several comments. The paper (Roman and Sermon, 1934) mentioned by these authors described a magnetic gradiometer designed and constructed at Michigan College of Mining and Technology (now Michigan Technological University) at Houghton, Michigan, in 1933. At that time, we were not familiar with Haalck’s paper of 1925 nor with the previous work mentioned below. As stated, materials and design details were based on supplies locally available, and the development was to test the feasibility of using paired earth inductors to measure directly the earth’s magnetic gradient. Field tests indicated that the instrument held promise and justified plans for improvement. Readings seemed reliable and repeatable, and the instrument proved to be more sensitive than had been expected.
EVIDENCE FOR A LINEAR ATTENUATION MECHANISM
Authors: Savage James C. , Hasegawa Henry S.
Published: October 2002

Comparison of the attenuation of the Fourier components of an elastic pulse with the attenuation of sinusoidal waves of the same frequencies constitutes a test whether the attenuation mechanism is linear. As an example of this linearity test, attenuation by the nonlinear, variable‐friction mechanism proposed by Knopoff and MacDonald has been examined. The Q spectrums obtained from the Fourier components of several pulses calculated from the equations governing that attenuation mechanism differ radically from the flat spectrum expected for sinusoidal waves. Thus the mechanism could readily be identified as nonlinear by the linearity test. The test was applied to experimental observations of attenuation in metals, and it is found that the attenuation mechanism is linear. The same result is suggested by existing observations of the attenuation in Pierre shale and Westerly granite, as well as other independent evidence. Thus mechanisms involving nonlinear processes, including all those mechanisms which depend on ordinary friction, are not likely to be important sources of loss.