- Home
- A-Z Publications
- Geophysical Prospecting
- Previous Issues
- Volume 19, Issue 3, 1971
Geophysical Prospecting - Volume 19, Issue 3, 1971
Volume 19, Issue 3, 1971
-
-
REVIEW ON THE BASIC THEORETICAL ASSUMPTIONS IN SEISMIC DIGITAL FILTERING*
Authors I. FINETTI, R. NICOLICH and S. SANCINAbstractA review of the most significant mathematical properties of digital operators and an introduction to their important applications to seismic digital filtering is given.
Basic definitions in the time‐series field and the principles of digital filtering are introduced starting from the Z‐transform domain.
Predictive decomposition for stationary stochastic processes and inverse operators are also discussed.
Applications of digital filtering to seismic signal concern the predictive deconvolution, characteristics of dispersive and recursive operators, matched filters, and multichannel operators.
A brief discussion on frequency, wave number, and velocity filtering phylosophy is given at the end of the paper.
-
-
-
A SOLUTION OF THE DIPPING INTERFACE PROBLEM USING THE SQUARE ARRAY RESISTIVITY TECHNIQUE*
Authors M. BROADBENT and G. M. HABBERJAMAbstractApparent resistivity measurements with the square array technique in the vicinity of a dipping interface have the advantage over collinear array methods that they are less dependent on orientation of the array.
In order to exploit this, existing potential solutions for the dipping interface problem have been adapted for the computation of apparent resistivities over such a feature using a square array.
Comprehensive interpretation techniques covering this problem are given and the limitations imposed by residual array orientation effects are discussed.
-
-
-
COMPARISON OF “AQUAFLEX” WITH CONVENTIONAL EXPLOSIVE FOR SEISMIC REFRACTION MEASUREMENTS AT SEA*
Authors D. J. BLUNDELL and R. L. HANDLEYAbstractA seismic refraction line fired using conventional explosive charges was repeated using a seismic cord, “Aquaflex”. It was found that travel times and frequencies were the same for both kinds of source and that amplitudes from “Aquaflex” were comparable with those produced using conventional explosives more than ten times the weight. This advantage carries with it gains in cost and efficiency and reduces damage to fishing.
-
-
-
MULTICOVER MEASUREMENTS IN REFRACTION SHOOTING*
More LessAbstractMulticover measurements in refraction shooting are comparable to long‐spread reflection shooting. Of course, spread length, distance of traces and offset may be larger than in reflection shooting and depend on the, depth, the velocity and the dipping of the refractors to be detected. For later processing an equation for the refractor velocity is derived in case of flat and steep dipping refractors. The depth and the angle of dip will be computed from delay times. An outlook to digital processing is given.
-
-
-
SELECTION OF SEISMIC PICKING BASED UPON THE DIP, MOVE‐OUT AND AMPLITUDE OF EACH EVENT*
More LessAbstractThe general use of continuous CDP seismic lines means that the neighbourhood of each depth point can be considered according to two sets of co‐ordinates:
— the co‐ordinates of the abscissa on the seismic lines and the reflection time, which allow investigation of the local dip of coherent events;
— the co‐ordinates of the reflection time and the move out, which allow investigations of the average velocity for these same events.
The combination of both investigations for each coherent event is a very convenient operation for the seismologist, and can provide some useful interpretation aids such as velocity profiles, or information on the interval velocities.
The principles which we use consist in the examination of a large range of possibilities, of which only the most coherent are chosen.
Some examples are shown.
-
-
-
FIRST EXPERIENCE AND RESULTS WITH A NEW SEISMIC INTERPRETATION METHOD*
By G. DOHRAbstractAt the EAEG meeting in Venice (May 1969) Linsser presented a new method for the interpretation of seismic measurements (“Transformation of Seismic Data into Geological Models by Digital Template Analysis”). First results were presented during the S.E.G. convention in Calgary (September 1969). Meanwhile some experience concerning the possibility of the application of this method is available.
Starting from the fact that the computer is able to store several physical parameters (amplitude, wave‐length, direction of the seismic event, coincidence with a template and the beginning and the end of each reflection), the importance of these data for the investigation of special geophysical questions will be discussed.
This method has been tested with several examples on the following problems:
- 1 Proving and exact localisation of faults.
- 2 Investigation of velocities of interesting layers.
- 3 Additional information for the geological interpretation of seismic sections.
- 4 Picking of weak reflections in the “Pre‐Zechsteinian” in Northern Germany.
Finally the possibilities of further applications and developments are discussed.
-
-
-
VERTICAL MAGNETIC DIPOLE OVER TRANSITIONAL EARTH*
Authors K. MALLICK and A. ROYAbstractHarmonic steady‐state solutions for magnetic and electric vector components are obtained for a layered transitional earth in a vertical magnetic dipole field. The conduction currents dominate the displacement currents. The time factor eiωt is implied. MKS units are used.
-
-
-
RECENT DEVELOPMENTS IN WELL VELOCITY SURVEYS AND THE USE OF CALIBRATED ACOUSTIC LOGS*
Authors P. KENNETT and R. L. IRESONAbstractIn recent times, velocity surveys at marine well locations have been performed using non‐explosive energy sources such as air‐guns and gas guns. In addition, surveys in land wells have been successfully carried out using a modified version of the air‐gun. This paper illustrates some of the characteristics of these devices and compares the data obtained from typical surveys with conventional dynamite surveys.
Since data obtained from well velocity surveys using non‐explosive sources are now commonly recorded on tape, they lend themself to further digital processing and interpretation techniques that were not previously so conveniently available. Some examples of these processes, e.g. the examination of attenuation, frequency and energy content of the recorded well geophone signals, are given in the paper. Examples of some other digital processes, using calibrated Acoustic logs, whether recorded digitally in the field or subsequently converted from analogue recordings, are also given in the paper. These include the construction of an Acoustic log in the vertical axis from logs obtained in deviated wells.
-
-
-
ONDE AMORTIE DE TYPE RAYLEIGH À L'INTERFACE DE DEUX MILIEUX SOLIDES À FORT CONTRAST DE DENSITÉS ET DE VITESSES*
Authors S. K. GUPTA and L. MARTELSummaryDamped Rayleigh‐type waves at the interface of two solid media with strong density and wave velocity contrast have been studied theoretically and experimentally with a two‐dimensional model; plexiglas and brass were used as model materials.
-
-
-
REFLECTIONS ON AMPLITUDES*
Authors R. F. O'DOHERTY and N. A. ANSTEYAbstractModern seismic recording instruments allow precise measurements of the amplitude of reflected signals. Intuitively we would expect that this amplitude information could be used to increase our knowledge of the physical properties of the reflecting earth.
The relevant factors defining the amplitude of a reflection signal are: spherical divergence, absorption, the reflection coefficient of the reflecting interface, the cumulative transmission loss at all interfaces above this, and the effect of multiple reflections.
Of these factors, three—spherical divergence, the reflection coefficient and the transmission loss—are reasonably clear concepts (though the estimation of transmission loss from acoustic logs caused some difficulties in the hey‐day of synthetic seismograms). Absorption still presents considerable problems of detail, but our understanding has increased significantly in recent years.
The factor least well understood is undoubtedly the effect of multiple reflections. Multiple paths having an even number of bounces can have the effect of delaying, shaping and magnifying the pulse transmitted through a layered sequence. Simple demonstations of this phenomenon can be made using elementary thin plates, and these can be presented for various synthetic and real sequences of layers. Such demonstrations lead one to explore the relation between the spectrum of the transmitted pulse and the spectrum of the reflection coefficient series.
If it were possible to isolate the amplitude and shape variations imposed by absorption within a layer, there would be a chance that this measure of absorption would be useful as a correlatable or diagnostic indication of rock properties. If it were possible to isolate the amplitude and shape variations imposed by multiple reflections, there would be a chance that this measure would be useful as an indication of cyclic sedimentation and of the dominant durations of the sedimentary cycles. However, the separation of these two effects constitutes a formidable challenge. The very difficulty of this separation suggests that it may be opportune to review the quantitative estimates of absorption made by field experiments.
-
-
-
DISCOVERY OF DIRECT‐SHIPPING IRON ORE BY GEOPHYSICAL METHODS IN THE CENTRAL PART OF THE LABRADOR TROUGH*
More LessAbstractThe deposits of the central sector of the Labrador Trough are magnetite‐rich iron ores subjected to enrichment by the process of leaching. In spite of the fact that some ore types are porous and low in density, most of the ore zones have undergone a net increase in density brought about by enrichment. In the course of their formation, the magnetic characteristics of the rocks have changed and a great deal of the magnetite was altered to relatively non‐magnetic iron oxides and hydrous iron oxides. Consequently, induced as well as remanent magnetization decreased, but the ratio of the latter with respect to the former increased substantially. All drift‐covered areas underlain with iron‐formation are potential ore producing areas. From measurements of the first two physical properties and determination of the thickness of overburden by means of a combined gravity‐magnetic‐seismic or resistivity survey, it is possible to detect and distinguish the iron formations and potential ore zones from the country rocks.
In spite of the fact that the iron formations are a complex assemblage of rock types, each having different physical and chemical properties, a qualitative and semi‐quantitative correlation between the results of the surveys and the geology as well as the structure of the area could be established. Consequently, in order to increase the chances of success, first a mathematical correlation of the amplitude of the gravity anomalies with the specific gravity, the iron content, the silica content, the porosity factors and the dimensions of the underlying orebodies, and secondly, a quantitative correlation of the ground magnetic intensity relative to the reference lithologie unit with the percentage of Fe3 O4 recovery and the volume magnetic susceptibility were done for many deposits.
A few discoveries were made with this method. Finally, a fully quantitative interpretation of the geophysical data using a multimodeling analysis led to the discovery of additional direct‐shipping iron ore deposits in the Schefferville mining district of Canada.
-
-
-
POSITIONING OF MARINE SURVEYS WITH AN INTEGRATED SATELLITE NAVIGATION SYSTEM*
Authors F. P. KRONBERGER and D. W. FRYEAbstractFor almost two years, satellite navigation has been used in reconnaissance exploration. However, only in the last six months has it been demonstrated that an “integrated” system provides navigational accuracy for all geophysical prospecting. This paper describes the accuracy of the integrated system and illustrates its merits.
The primary objective of the integrated system is to provide continuous, accurate, geodetic position information. This is accomplished by integrating instantaneous position, velocity and heading from outputs of the Doppler sonar, gyrocompass, velocimeter, vertical references with periodic updates obtained from the Navy Navigation Satellite System. Each of the subsystems, their operations and functions will be discussed.
Satellite navigation offers many advantages for marine surveys. Features for point‐to‐point automatic steering, onboard plotting of shotpoint data, firing of seismic energy source as a function of exact distance and real‐time data logging onto digital tape have been implemented. With the onboard computer all navigation, gravity and magnetic information is recorded on tape and some preprocessing and filtering of gravity and magnetic data may be accomplished.
-
-
-
MODÈLES ANALOGIQUES ÉLECTRONIQUES DU PROCESSUS D'EXPLOSION DANS LES ROCHES*
More LessAbstractThe first part of the contribution deals with the generalization of the solution given by Sharpe and states the elements of the mathematical model of the explosion generating longitudinal waves. The generalization of Sharpe's solution consists in finding out the response of the medium to a pressure p(t) applied at the source, for any value of the ratio K=Vp/Vs covering the range √2 ÷∞.
The second part contains the results of the calculation and design of three electronic analog models of the explosion process in rocks. The first is represented by electrical circuits separated by emitter follower circuits. The scheme of the second model has electrical circuits and elements of operational calculus (integrator, summation instrument). The electrical circuits are represented by the two filters simulating the selective effect of the explosion in rocks. The third model is a logical programming scheme of the problem on an analog computer.
For the calculus of the electrical parameters of the three schemes we have taken into account scaling of the physical and geometrical parameters of the medium and of the explosion which should ensure the simulation of the explosion process in rocks of all kinds of importance in seismic prospecting.
-
Volumes & issues
-
Volume 72 (2023 - 2024)
-
Volume 71 (2022 - 2023)
-
Volume 70 (2021 - 2022)
-
Volume 69 (2021)
-
Volume 68 (2020)
-
Volume 67 (2019)
-
Volume 66 (2018)
-
Volume 65 (2017)
-
Volume 64 (2015 - 2016)
-
Volume 63 (2015)
-
Volume 62 (2014)
-
Volume 61 (2013)
-
Volume 60 (2012)
-
Volume 59 (2011)
-
Volume 58 (2010)
-
Volume 57 (2009)
-
Volume 56 (2008)
-
Volume 55 (2007)
-
Volume 54 (2006)
-
Volume 53 (2005)
-
Volume 52 (2004)
-
Volume 51 (2003)
-
Volume 50 (2002)
-
Volume 49 (2001)
-
Volume 48 (2000)
-
Volume 47 (1999)
-
Volume 46 (1998)
-
Volume 45 (1997)
-
Volume 44 (1996)
-
Volume 43 (1995)
-
Volume 42 (1994)
-
Volume 41 (1993)
-
Volume 40 (1992)
-
Volume 39 (1991)
-
Volume 38 (1990)
-
Volume 37 (1989)
-
Volume 36 (1988)
-
Volume 35 (1987)
-
Volume 34 (1986)
-
Volume 33 (1985)
-
Volume 32 (1984)
-
Volume 31 (1983)
-
Volume 30 (1982)
-
Volume 29 (1981)
-
Volume 28 (1980)
-
Volume 27 (1979)
-
Volume 26 (1978)
-
Volume 25 (1977)
-
Volume 24 (1976)
-
Volume 23 (1975)
-
Volume 22 (1974)
-
Volume 21 (1973)
-
Volume 20 (1972)
-
Volume 19 (1971)
-
Volume 18 (1970)
-
Volume 17 (1969)
-
Volume 16 (1968)
-
Volume 15 (1967)
-
Volume 14 (1966)
-
Volume 13 (1965)
-
Volume 12 (1964)
-
Volume 11 (1963)
-
Volume 10 (1962)
-
Volume 9 (1961)
-
Volume 8 (1960)
-
Volume 7 (1959)
-
Volume 6 (1958)
-
Volume 5 (1957)
-
Volume 4 (1956)
-
Volume 3 (1955)
-
Volume 2 (1954)
-
Volume 1 (1953)