- Home
- A-Z Publications
- Geophysical Prospecting
- Previous Issues
- Volume 31, Issue 5, 1983
Geophysical Prospecting - Volume 31, Issue 5, 1983
Volume 31, Issue 5, 1983
-
-
MEASURED ANISOTROPY IN PIERRE SHALE*
Authors J. E. WHITE, L. MARTINEAU‐NICOLETIS and C. MONASHAbstractThe five elastic coefficients which characterize a transversely isotropic medium have been measured for the Pierre Shale. The first‐arrival times deduced from two closely spaced vertical seismic profiles provide values of magnitude and direction of the phase velocity at a given depth for different locations of the sources. From these velocities, we can estimate the five elastic coefficients by assuming that the P‐ and SV‐wave velocities have only a small dependence on the angle of propagation. On the other hand, it is shown that the accuracy in the difference between the directions of propagation and particle motion is not sufficient to determine the anisotropy.
This work was industrially sponsored through the Integrated Geophysics Project.
-
-
-
A STATISTICAL APPROACH TO THE EXTRACTION OF THE SEISMIC PROPAGATING WAVELET*
More LessAbstractA model of the seismic trace is generally given as a convolution between the propagating wavelet and the reflectivity series of the earth and normally it is assumed that a white noise is added to the trace. The knowledge of the propagating wavelet is the basic point to estimate the reflectivity series from the seismic trace.
In this paper a statistical method of wavelet extraction from several seismic traces, assuming the wavelet to be unique, is discussed. This method allows one to obtain the propagating wavelet without any classical limitative assumptions on the phase spectrum. Furthermore, a phase unwrapping method is suggested and some statistical properties of the phase spectrum of the reflectivity traces are examined.
-
-
-
ROCK‐BURST FORECASTING AND GENETIC RESEARCH IN COAL‐MINES BY MICROGRAVITY METHOD*
More LessAbstractMicrogravity can be used for predicting rock bursts. For the first time gravity anomalies related to rock bursts have been recorded. The methodology developed has lead to the first successful predictions. The depth of the rock‐burst focus might be determined on the basis of analytical downward continuation of related gravity anomalies: the focus is treated as a singular point of the gravity potential and its derivatives.
The rock‐burst gravity anomalies might be explained on the basis of the assumed dilatancy process that causes the rock burst. The mean density change of the rock mass threatened with rock bursts can be estimated from the corresponding rock‐burst gravity anomalies.
-
-
-
THE TRANSIENT ELECTROMAGNETIC RESPONSE OF A CONDUCTING SPHERE IN AN IMPERFECTLY CONDUCTING HALF‐SPACE*
By T. LEEAbstractThe presence of a conducting environment about a spherical ore body must be considered when calculating the transient electromagnetic response of the ore body due to a step current flowing in a large circular loop at the earth's surface. Failure to do this can easily lead to errors in excess of 10% in numerical calculations. Moreover, there is only a limited time interval in which the response of the spherical conductor is easily seen.
In a poorly conducting ground the resonance response of the sphere is the first to be excited. Later, however, the non‐resonance or wave‐type response is excited. These waves destructively interfere and finally the response of the sphere decays with time as t−7/2.
For a range of times and depths the best loop for detecting the sphere has about the same radius as the sphere.
-
-
-
LINEAR FILTERING OF VLF DIP‐ANGLE MEASUREMENTS*
Authors M. KAROUS and S. E. HJELTAbstractThe suggested interpretation technique is based on discrete linear filtering of VLF data. The output of the described filtering results is expressed in terms of an equivalent current density at a specified depth that would cause the measured magnetic field. The most practical six‐point filter gives an accuracy of 8%. The filter is an extension of the commonly used Fraser filter to process VLF dip‐angle data.
Filtering the same data set for various depths gives an idea about the change of current density with depth. Areas with high current‐density correspond to good conductors. The conductor dip can also be determined.
The use of the technique is illustrated on theoretical and field examples. In all cases a good correlation with original models and other types of geophysical measurements was obtained. As shown in the last example, the filtering technique is also applicable in interpretation of other electromagnetic methods.
-
-
-
ON THE INTERPRETATION OF RESISTIVITY SOUNDINGS BY THE LEAST‐SQUARES METHOD*
By J. CHYBAAbstractAn interactive least‐squares method for the interpretation of VES curves was proposed by Johansen (1977). The method permits one to select some parameters (thicknesses and/or resistivities of individual layers) and to change the rest in such a way that the interpreted model approaches the measured data. This note suggests a modification of Johansen's method, in which not only the individual parameters can be selected but also linear combinations of parameters—in particular, the sum of thicknesses of several layers.
-
-
-
A BOREHOLE MAGNETOMETRIC RESISTIVITY EXPERIMENT*
Authors J. E. ACOSTA and M. H. WORTHINGTONAbstractA borehole magnetometric resistivity (MMR) experiment is described in which an attempt is made to determine the extent and orientation of zones of fissuring within an otherwise massive sequence of carboniferous limestone. The region under investigation lies beneath a landfill site and the main parameter of interest is the direction of flow of ground water, which will be influenced by the orientation of the faults or fissures within the rock. The MMR method possesses some extremely advantageous features for application to hydro‐geological problems of this kind. The method is sensitive to electrical current channelling within an otherwise relatively resistive medium, and the detection of the magnetic field within the borehole does not depend upon electrical contact of the receiver with the ground. Consequently, the method can be used in dry or plastic‐cased boreholes. A direction of maximum electrical current flow is deduced from the MMR data which coincides with the predominant direction of jointing within the region.
We are most grateful to the Water Research Centre, Medmenham, Berkshire, for supporting this research and particularly to Dr M. Fleet and Mr K. Beesley for their help and advice.
-
-
-
GEOELECTRICAL MODELS INVOLVING LAYERS WITH A LINEAR CHANGE IN RESISTIVITY AND THEIR USE IN THE INVESTIGATION OF CLAY DEPOSITS*
Authors E. MUNDRY and H.‐J. ZSCHAUAbstractA model has been set up for the interpretation of geoelectrical sounding data for certain kinds of clay deposits containing gradually varying amounts of sand. The model assumes that in the so‐called gradient layer, resistivity varies linearly with depth. Model calculations show how such a layer can be replaced by two homogeneous layers.
An inversion procedure using the Marquardt algorithm has been developed for the interpretation of sounding data obtained with the Schlumberger array; it assumes a gradient layer beneath several covering layers. The procedure is demonstrated on two clay deposits. A comparison is made between the newly developed interpretation, the traditional approach using model curves, and computerized inversion for a homogeneous layer model.
-
-
-
EXPLORATION OF HIGH RESISTIVITY BASEMENT USING ELECTRICAL AND MAGNETIC FIELDS OF QUASI‐STATIC POINT SOURCES*
By L. SZARKAAbstractDetermination of thickness of sediments (usually of high conductivity) overlying a high‐resistivity basement is one of the basic problems of electrical exploration methods. This paper proposes to determine horizontal electrical conductance on the basis of impedance calculated from electrical and magnetic fields of distant quasi‐static (low‐frequency) point sources. Using the proposed method, horizontal conductance of the sediments can be determined also from artificial quasi‐static noise‐impulses coming from sources of unknown position and intensity. The results of analogue modeling and field examples prove the potential of the proposed technique.
-
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)