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1st SAGA Biennial Conference and Exhibition
- Conference date: 29 Jun 1989 - 30 Jun 1989
- Location: Johannesburg, South Africa
- Published: 29 June 1989
49 results
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On The Agulhas Magsat Anomaly: Implications For Continental Breakup Of Gondwana
Authors L.A.G. Antoine and A.B. MoyesThe Agulhas anomaly is a prominant intense satellite magnetic anomaly situated off the southeastern coast of Africa. The anomaly is clearly identifiable on all published satellite magnetic anomely maps (Regen et al., 1975; Langel et al., 1982; Hastings, 1982; Hahn et al., 1984; Yanagisawa and Kono, 1985; Arkani-Hamed and Strangway, 1985; Kuhn and Zaaiman, 1986). Implicit in the publication of a global satellite magnetic anomaly map is that the data represent magnetic responses from magnetic mineral concentrations originating within the crust and/or upper-mantle.
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New Heatflow Estimates For Australia And South Africa
By F.W. ArnottGeothermal constraints for mapping and evolution studies of the lithosphere, fission track dating and in exploration studies of oil maturation
and exothermic deposits are limited by the distribution of heatflow data.
This is due to the time and oost required to collect data and the absence
of deep drill holes in areas where new heet flow data is required. Heet
flow data is only available for 109 sites in Australia (Cull 1982) and 112
sites in South Africa (Gough 1963; Carte and van Rooyen 1969; Jones 1987;
1988). These are mostly in mineralized terranes.
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The Bumbeni Line - An Aligned Group Of N.E. Trending Bodies In Northern Natal
More LessA characteristic of the African crust are numerous NE-SW trending
lineaments along which volcanic and sub-volcanic ring complexes, basalt
flows and acideous plutons predominantly occur.
One such lineament is the Bumbeni lineament (Fig. 1) which consists
of numerous igneous complexes and 13 can presently be identified (fig.
2). The majority of the complexes are buried and situated along a line
stretching from Sodwana Bay (northeastern Natal coast) through the
Hiuhiuwe and Umfolozi Game Reserves towards the southern boundary of
the Kaapvaal Craton (Fig. 1). The only exposed volcanic member along
the lineament is the Bumbeni Complex (Fig. 1) which can geophysicafly
be subdivided into two separate bodies namely Complex A, consisting of
acideous plutons and a ring dyke complex called Complex B.
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Seismic Stratigraphy: An Integrated Aproach To Predicting Hydrocarbon Plays
By G. BeamishThe post-rift Cretaceous sequences of the Bredasdorp Basin, offshore
South Africa, have been rigorously analyzed using the unified
application of the latest seismic-stratigraphic, sequence-stratigraphic
and depositional systems concepts. Utilizing 101 seismic profiles,
totalling 5600km, 10 cyclic depositional sequences have been identified
bounded by 9 Type 1 and 2 Type 2 unconformities.
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The Trans-Witwatersrand Basin Deep Seismic Reflection Profile:<br>Implications For Horizontal Tectonics In The<br>Early Archean Basement
Authors W.P. Colliston and W.U. ReimoldThe Trans-Witwatersrand Basin Deep Seismic Reflection profile (Geol.
Survey of Rep. of S. Africa, open file) adds a new dimension to the
Vredefort controversy (hypothesis: astrobleme, internally derived
catastrophe, tectonic origin). In principie, such a profile could
resolve this uncertainty, but the resolution is as yet not sufficient to
remove all ambiguity.
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The Beattie Anomaly And Its Significance For Crustal Evolution Within The Gondwana Framework
By B. CornerIn this study magnetic data from southern Africa and adjacent areas in
Antarctica are compared within a Gondwana framework. The results show
striking similarities in regional structural style, as interpreted from
these data, between the Namaqua-Natal Belt and the area to the east of the
present-day Lebombo margin of the Kaapvaal craton (western Dronning Maud
Land, Antarctica).
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A Geophysical Case Study Of A Nickel Sulphide Occurrence Situated In The Western Portion Of The Bushveld Complex
Authors B. Corner, E.C. Wedepohl and R.J. DurrheimIn this study, a nickel sulphide occurrence, situated in the western
Transvaal some 150 km to the northwest of Pretoria, was investigated
geophysically. The geophysical surveys were conducted as part of field
schools held, in 1985 and 1986, for the third-year and honours students of
the Department of Geophysics, University of the Witwatersrand.
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Seismic Raytracing Of An Overturn Structure
By G.E. DavisonSeismic exploration of the Witwatersrand Basin has greatly increased our
understanding of the structures within the basin over the last several
years. In most of our surveys, the seismic data have been sufficiently clear to determine the structures within the basin and the position of the
Central Rand Group. However, in several areas around the basin, complex
structures (such as overturn structures) exist. Where seismic profile lines
cross these structures, the seismic data become very confused, and
interpretation becomes very difficult. This is especially true of overturn
structures. In an attempt to better understand what happens seismically at
overturn structures, 2-D and 3-D raytracing were performed on a computer
model of an overturn structure within the Witwatersrand Basin. This
experiment was also an attempt to image such a structure.
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Seismic Raytracing As An Aid To Seismic Interpretation
By G.E. DavisonOften times, seismic profiles run oblique to structures, causing sideswipe
and confusing reflector patterns. Seismic Raytracing can be very helpful in
distinguishing structures that are profiled at an oblique angle. The
procedure would be to create an interpretive model, raytrace it, create a
synthetic seismogram from the raytracing data, and compare it to the actual
seismic data to see if the model is indeed representative of the actual
structure.
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Pleistocene Estuary Of The Orange River
Authors R.W. Day, A.J. Franzsen and J. RogersPalaeochannels are widely distributed along the inner
and middle shelf of the west coast of Southern Africa, but
of particular interest is a set of channels off the southern
Namibian coast (Fig 1). This article describes the mapping
of these channels using seismic records, and offers a model
for their formation.
Two types of seismic data are presented - one using
Boomer (Marine Diamond Corporation) and the other using a
lower frequency airgun (Geological Survey of South Africa).
The Boomer penetrated 20 metres or more into the inshore
sediment wedge and its records often show details within the
Cretaceous and Tertiary bedrock (Fig 2). The airgun
generally achieved better penetration into bedrock but at
the expense of resolution. For both surveys, Decca Navigator
was used for position fixing (Foster 1973; Birch 1979).
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A New Approach To Velocity Filtering
More LessThere are two very important considerations when deciding on or evaluating
velocity filtering (also known as dip filtering) of reflection seismic shot records:
1. Are relative amplitude strengths preserved ?
2. Is there sufficient discrimination on the basis of slope
between primary reflections and coherent noise ?
The first issue is very important when any AVO (amplitude variation with
offset) processing is done, and the second issue determines how effective
the filtering process will be.
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Coherent Noise On Marine Seismic Data - Its Causes And Cures
Authors A.T. Dippenaar and P.R. LevittDuring recent years SOEKOR bas been plagued by linear coherent noise on
stacked seismic sections. The dips of these coherent events are mainly in
the negative direction with velocities varying between 2200 and 3500 m/s.
Many theories have been forwarded to explain the origin of these linear
events and just as many solutions offered to solve the problem. SOEKOR's
increased reliance on seismic stratigraphic (as opposed to structural)
interpretation, which requires good signal-to-noise and high resolution
seismic sections, has made it imperative that solutions for this problem
be found.
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Numerical Modelling Of Dc Resistivity Problems
More LessNumerical methods for solving the DC geoelectrical problem can
be divided into two groups : domain methods and boundary
methods. In domain methods the whole of the domain is
discretized while in the boundary methods only the boundaries
of domains are discretized.Under domain methods one would find
amongst others the finite difference method and the finite
element method. A popular boundary technique is the boundary
element method.
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Significance Of Seismically Reflective Layering Within The Basement To The Witwatersrand Basin
Authors R.J. Durrheim, B. Corner and G.R.J. CooperDuring the past decade deep seismic reflection profiling in
Europe, north America and Australia has produced new, insights into
continental structure and evolution. However, very few profiles have been
acquired over Archaean rocks. There are several fundamental guestions
regarding the evolution of the earth which seismic studies of the Archaean
crust may help to answer. These include:
- Have tectonic styles evolved with time?
- Is the type of upper crust related to the type of lower crust ?
- Why does Proterozoic crust seem to have a greater tendency to be covered
by Phanerozoic sediments than Archaean crust?
- Has there been significant overprinting of early tectonic features in the
lower crust ?
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Seismic Velocity Structure Of The Central Kaapvaal Craton
Authors R.J. Durrheim and R.W.E. GreenDuring the 1950’s several investigations made use of
Witwatersrand mine tremors in order to study the seismic velocity structure
of the Kaapvaal Craton, and derived simple one- or two-layered models
[Wilmore et al.., 1952; Gane et al., 1956; Hales and Sacks, 1959]. In this
study we take advantage of the advances in seismograph design, signal
processing and seismic interpretation techniques to derive a substantially
more detailed crustal model.
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Non-Hyperbolic Moveout Correction Of Reflection Seismic Records
More LessFor a horizontally layered earth the exact two-way travel time equation
is:
T2 = T02 + x2 / V2 + C3 X4 + C4 X5 + - - - (1).
(Taner and Koehler, 1969).
T = two-way time from source to receiver; T0 = vertical two-way time;
X = source to receiver distance (offset); V, c3, c4, = constants
which depend on the interval velocities (V1) thicknesses of the
individual layers (Fig. 1).
The terms in X4 and X5 are small for low and medium angles of
incidence, and these terms are normally ignored in seimic processing.
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Vertical Seismic Profiles - The Heard Rock Environment
By A.M. FRANCISIt is now some years since the first Vertical Seismic Profile (VSP) data
was acquired in South Africa in the so-called “hard rock” mineral
exploration environnent. In the intervening period to date, although use
has been made of the technique, most noticeably for seismic correlation,
the VSP in hard rock has not been utilized to quite the same extent as in
the oil industry.
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Preliminary Results Of Potential Field Studies Of The Kaapvaal Craton - Kheis Subprovince - Gordonia Subprovince Transitions
Authors K. Geerthsen and M.J. MaherAs part of the National Geophysics Programme (NCpP) a study of the geo-
physical signature of the transition from the Kaapvaal Craton to the Kheis
Province and from the Kheis Province to the Nemaqua Metamorphic Complex was
undertaken. Previous geophysical work on these features includes the
modelling of long gravity profiles by De Beer and Meyer (1984), a detailed
gravity survey by Maher (1980) and natural remanent magnetisation (NRM)
studies by Onstott et. al. (1986).
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New Developments In Underground Microgravity
Authors Christian Gram and Dr. Uwe CastenUnderground gravity observations in deep coal mines using the conventional
gravity meter LaCoste-Romberg Model D which has been adapted to the fire
damp regulations, can be accurate to ± 3 ugal. For underground
determination of the vertical gradient of gravity the LaCoste-Romberg meter
is used together with a specially designed measuring tower. Using this
equipment an accuracy in tower gradient observations of ± 30E was obtained.
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A Geophysical Case Study Of A Copper-Zinc Sulphide Deposit In The Northern Cape
Authors E. Groenewald, E. Gurria, J. King, V. Nooko and C. RedekoppThe 1989 Wits University Geophysics Field School was held at
Copperton, 60km southwest of Prieska, northern Cape. With the
permission of Anglovaal Ltd., an intensive geophysical study was
carried out over the annex to the main sulphide ore body. The
geology of the deposit is described in detail by Wagener and Van
Schaikwyk (1986). At the site of the Annex sulphide body, the host
rocks are overlain by a thin layer of tillite of the Dwyka Formation.
Calcrete is locally developed. On the basis of previous work
(Anglovaal Ltd.), two lines on the existing survey grid ware chosen
for detailed study. Various techniques were used, and instrument
responses were compared over these two lines, each 500m long and 200m
apart. We present data from one of these lines (Fig. 1). The
techniques used ware EM (Geonics EM-34, Crone Pulse EM, Scintrex
Genie), time domain IP (gradient array), SP, resistivity sounding
(Schlumberger array) and profiling (gradient array), gravity,
magnetics and hammer refraction seismics. The results and a
qualitative interpretation follow.
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Data-Adaptive, Robust, Non-Linear Algorithms For Noise Removal On Stationary Or Non—Stationary Time Or Space Series Data
By M. HattinghBasically all geophysical data consist of readings made in a time and/or
space series manner. The general problem is to separate the noise
components from the signal components. To succeed, some knowledge of what
is noise and what is signal are necessary. Unfortunately most methods
break down when the data are not stationary and contain spurious peaks or
outliers. Sometimes no information of the noise can be obtained. In
this paper the results of some new algorithms will be shown that was
developed to tackle the problem in these circumstances. Four methods were
developed. The basic concepts of each method is outlined and examples on
synthetic and real data are given.
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Interpretational Processing Of Lateral. Seismic Profiles (Lsp)
Authors R.C. Hinds and W.J. BothaIn most presented cases, the development of LSP processing has followed the scenario of surface seismic processing, namely that one pseudo-migrated finished LSP section was the result given to the interpreter. The interpreter of the surface seismic data only occasionally had the desire or felt the need to re-examine the individual. results from the various processing steps that the input data had gone through. In surface seismic processing today, where so much averaging is taking place through stacking, signal enhancement and horizontal correlation methods, ïnterpreters are becoming very involved in the processing that has been done to the data and, consequently, are demanding to see the effect that various processes have on their data through intermediate data displays.
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Interpretational Processing Of Vertical Seismic Profiles (Vsp)
Authors R.C. Hinds and W.J. BothaIn most presented cases, the development of VSP processing has followed the scenario of surface seismic processing, namely that one finished section was the result given to the interpreter. The interpreter of the surface seismic data only occasionally had the desire or felt the need to re-examine the individual results from the various processing steps that the input data had gone through. In surface seismic processing today where so much averaging is taking place through stacking, signal enhancement and through horizontal correlation methods, interpreters are becoming very involved in the processing that has been done to the data and, consequently, are demanding to see the effect that various processes have on their data through intermediate data displays. In the interpretation of VSP datasets where the limited quantity data contains much information about the subsurface on or about the borehole, it has become imperative to design data presentation systems that allows one to fully examine the effect of the processing stages on the VSP data.
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Palaeomagnetic Studies In Western Dronning Maud Land, Antarctica
More LessSampling for palaeomagnetic purposes has been undertaken in the western part of Dronning Maud Land, Antarctica. The study area comprises three mountain ranges bounded by latitudes 72° S to 73° S and longitudes 4° W to 2° E (Fig 1). The fieldwork has been completed over three consecutive summer seasons starting in 1986/87. A total of 170 sites have been sampled covering most of the rock types in the two primary geological terrains.
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Application Of Seismic Sequence Concepts To Basin Evolution And Petroleum Exploration, Pletm0S Basin
By A. JollandsAs a result of shallow burial depths and slow subsidence rates, a total of 67 Type-1 and Type-2 unconformities were identified in the post-rift Cretaceous section of the Pletmos Basin, (figure 1). Purpose of this study was to develop a seismic sequence stratigraphic framework for the mid-Valanginian to mid-Campanian sequences as a basis for future petroleum exploration. The study further developed the recent stratigraphic techniques proposed by Exxon.
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Modelling The Deep Temperature Structure Of Witwatersrand Gold Mining Areas
Authors M.Q.W. Jones and P. BottomleyUnderground workings in Witwatersrand gold mines are likely to exceed depths of 4000 in. An important consideration in planning of deep mining is the refrigeration cost which depends on rock temperatures. Temperature measurements made during the past 50 years have resulted in a know-ledge of regional rock temperature variations (Jones and Bottomley, 1986; Jones, 1988), but the temperature structure of most goldfields is not well determined. Temperatures may be predicted using one-dimensional (vertical.) analysis where strata are horizontal, but structural complexities involving rocks of different thermal conductivity and radioactive heat production may result in non-vertical heat conduction. This paper discusses a numerical
technique that permits computation of the temperature field in such areas.
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A Theory Of Seismic-Wave Propagation In Porous Rocks Çontaining Clays - Interrelation Between Seismic-Wave Attenuation And Permeability
More LessKlimentos and McCann (1988) have shown experimentally that clays increase the attenuation of seismic waves in porous rocks (see figure 1). They demonstrated that the attenuation of compressional. waves is directly proportional. to day content and inversely proportional to permeability (see Figure 2).
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Evaluation Of Prediction Ahead Of The Bit By Inversion Of Vsp Data
Authors S. Kuhlmann, H. Pferdekämper J. Fatti and M. GidlowOne of the applications of VSP surveys is to predict acoustic impedance
variations in a well ahead of the bit. The up going wave traces
obtained from the VSP processing are inverted to produce a pseudo-
acoustic impedance log for the sediments below T.D. This type of
inversion is expected to be more precise than the inversion of surface
seismic data for two reasons: a) An accurate estimation of the seismic
wavelet is obtained from the deconvolved down going waves. b) The
bandwidth of the VSP traces is wider than that of surface seismic data
and the signal/noise ratio is generally better in VSP data than in
surface seismic data.
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External Geomagnetic Field Variations And Magnetic Surveys
Authors G.J. Kühn and L. LoubserThe magnetic storm which started al 01h25 on the 131h of March 1989, was probably the largest event of its kind to be recorded in South Africa since magnetic held recordings began in 1932. Soon after its commencement, the Magnetic Observatory started receiving enquiries about the anticipated development of the storm from a few exploration groups who were doing aeromagnetic surveys al the time.
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Rock Mechanics And Seismological Research In A Deep South African Gold Mine
More LessA. summary of the mines rock mechanics related research is given, covering the period 1985 until present.
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Deep Grounded Source Tem Soundings In The Limpopo Belt Area
By C.L. Le RouxDuring 1988 deep Transient Electromagnetic (TEM) soundings were carried out
using a controlled grounded source, in the Limpopo Belt area of the Northern
Kaapvaal craton. This forms part of a National Geophysics Programme and CSIR
project to develop a grounded source TEM system suitable for South African
conditions. The purpose of this talk is to present results of the test survey
conducted jointly with scientists from the Exploration Geophysics group of
Dr. K.-M. Strack of the 1GM, University of Cologne, FRG. More technical
details and experimental research results will be covered in a talk for SAGA
later in 1989.
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The Electromagnetic Response Of Magnetically Permeabie Non-Conductors
By M.J. MaherElectromagnetic prospecting has been carried out for many years using
various field systems. In the past the targets of concern were assumed to
have high conductivities and to be located in resistive or mildly conductive-
host rocks. Generally it was further assumed that the magnetic
permeability was constant throughout the region and had the same value as
that of free space (411 x io-7 h/m). Electromagnetic systems using a magnetic field as a source will also produce induced magnetizations in
magnetically susceptible parts of the earth in the area of investigation.
These magnetizations will affect the primary field and produce observable
responses under certain conditions.
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Interpretation Of A Potential Field Profile Over The Cape Fold Belt
Authors M.J. Maher and B.E. PittsPrevious studies (Beattie, 1909, Hales and Cough, 1960, 1961 and De Beer,1983) have outlined major geophysical features associated with the Cape old Belt. These are the Beattie Magnetic Anomaly, the Southern Cape Conductive Belt and en isostatic gravity anomaly. In en attempt to Further elucidate the sources of the magnetic and gravity features over the Cape
Fold Belt interpretation of data along a north striking profile has been carried out. Magnetic and gravity data for this profile which is located along longitude 22 ° 32 E between 31 °S and 34 °S were extracted from aeromagnetic maps end a digital gravity data base.
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Determination Of Hydraulic Aquifer Characteristics From Resistivity Sounding Parameters
Authors R. Meyer and V. d A. CoetseeGeophysical techniques, and geoelectrical techniques in
particular, have been employed in geohydrological studies for
many years. Apart from determining layer thicknesses and
resistivities, and linear features with which ground water is
often associated, geoelectrical parameters can also be applied to
approximate geohydrological parameters such as hydraulic
conductivity, porosity, transmissivity, specific capacity, etc.
The geohydrological parameters are traditionally derived from
pumping tests and are expensive and time consuming.
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Moho Depth And Crüst-Mantle Velocity Contrast Determinations For South Africa From Teleseismic P-Wave Spectral Ratios
By K.R. MüllerTeleseismic events, recorded on long period or broadband seismometers at three component stations, m y be used to model crustal and upper mantle ]layering beneath the stations. The
method used in this study is referred to as the spectral ratio or crustal transfer ratio technique (Phinney, 1964), this involves the analysis of the ratios of the Fourier spectra of the vertical and radial components of the P-wave.
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Coda Q And Site Effect Of Mine Tremors
Authors E. Peberdy and R.W.E. GreenRecordings of mining induced tremors at increasing distances from the gold
mining region south of Carletonville were used to determine the seismic
quality factor Q.
This Q, used as a measure of attenuatlon, was determined independently for
a number of seismic stations along two azimuths, traversing vastly
different geologies. The small tremors that were used (ML<3,0) were all
observed at distances of less than 80 km and the Q was determined using a
version of the coda delay technique proposed by Aki (1969).
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Computer Plotting Software Applications Within Anglo American
By M.D.P. ReedRadian Corporation in Texas market contour plotting software (CPS)
which is mainly directed at the oil industry. Anglo American has
owned a mainframe version of this software for sate time, and after
sate market investigation Ma purchased several copies of CPSPC, the
personal computer product.
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Evidence For Velocity Anisotropy In Sediments Of The Central Bredasdorp Basin
Authors G.C. Smith and R.W. DworschakOil exploration boreholes drilled in the central part of the offshore
Bredasdorp basin (fig. 1) revealed systematic errors in the prediction
of depths to target horizons.
Initially, in the absence of borehole data, depth conversions from
seismic reflection time measurements were made using stacking
velocities. Because of the very small dips present in the central
Bredasdorp basin down to horizons of interest, stacking velocity was
assumed to be equal to root-mean-square (ns) velocity without any
correction for dip.
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Integrated Geophysical Interpretation On A Complex Structure
More LessIn 1986 Verwoerd et al published the discovery of a carbonatite on the farm
Stukpan east of Bothaville in the Orange Free State (figure 1). The
intrusive was initially outlined by an interpretation of gravity data.
Subsequent drilling of 2 boreholes (ZL1, RP2) intersected this intrusive and
also intersected shallow Central Rand Group rooks, thus implying a horst in
the Witwatersrand Super-group. Seismic data in the vicinity of the intrusive
are poor and difficult to interpret (figure 2). The deterioration of the
data is thought to be caused by the intrusive. Since the intrusive contains
magnetite, the aeromagnetic data provides a means by which its position and
shape along the seismic section can be determined.
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Automatic 3D Modelling Of Gravity And Aeromagnetic Data In The Witwatersrand Basin - A Poster Presentation
More LessThe usefulness of the magnetic and gravity methods in the total exploration
effort and the tact that these methods are relatively cheap, warrant
extensive research into the development of new interpretation techniques.
Since most of the gold bearing reefs in the Witwatersrand basin are covered
by younger, transgressive geological units, magnetic and gravity data are
particularly useful for determining depths to these reefs and for resolving
large structural features. The presented here bas been developed to
automatically invert digital magnetic and gravity maps. The resulting depth
maps can be used to indirectly estimate depths to target horizons.
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Geophysical Investigation Into The Entabeni And Palmietfontein Granites, And The Schiel Alkaline Complex In The Northern Transvaal And Venda
Authors E.H. Stettler, J.H. de Beer and R.J. KleywegtThe late Precambrian and early Protozoic was an important period in the history of the Kaapvaal Craton since it not only represents the final episode of the Limpopo metamorphic event at 2670 Ma (Van Reenen et al., 1988) but also the intrusion of large volumes of alkaline granite magmas, the so called “young granites” took place between 2650-2400 Ma, represented by the Turfloop, Da Maranda (± 2650 Ma); Moletsi, Lunsklip, Uitloop Shamiriri (± 2600 Ma); Smitskraal, Matlala (2500 Ma) and the youngest ones Palmietfontein (± 2456 Ma) and Entabeni (±2000 Barton pers. comm.) (Barton et al., 1983; Van Reenen et al., 1988).
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A Slide Show To Cultivate An Interest In Geophysics In School Children
Authors E.H. Stettler, J.C. Slee and A. du PlessisIn order to make school children more aware of geophysics as an
occupation a slide show was prepared on behalf of SAGA that consists
of humoristic cartoons and real life situations that explain geophysics as
a science and also as a rewarding career. The duration of the slide
sequence Is 20 minutes and is available in both official languages. The
approach of intermingling cartoons with slides depicting real
geophysics at work was chosen to keep the attention of children and to
counter the traditional negative view school children have about the
natural sciences (See SACN March 1989 first article).
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Comparison Of Seismic Acquisition Systems From Repeated Recording Experiments
By P.J. VailFor the last eight years SOEKOR bas conducted a repeated recording experiment on a test line over the FA structure on the eastern flank of the Bredasdorp basin in the southern offshore area of South Africa. The primary purpose of the project was to acquire data using different seismic sources and acquisition systems so that comparisons of these systems and of the quality of the final stacked seismic section could be made. Of particular interest was the comparison of data acquired with air guns and water guns. The project involves two phases. The initial phase, discussed in this presentation involves the comparison of different seismic sources. The second phase will involve the determination of the optimum processing parameters for each data set and a comparison of these parameters.
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Including Absorption Into The Convolutional Model Of The Seismic Trace
More LessHigher frequency seismic signals travel faster than lower frequency
signals. Thus it can be expected that some component of the differences
observed between velocities calculated from check shots (signal frequency
50 hz.) and sonic logs (signal frequency 12000-30000 Hz) would be due to
dispersive effects. In fact it has been stated (GSI 1983) that with modern
sonic tools most of this difference can be ascribed to dispersive
effects. Thus using a properly edited sonic log and calculating the
synthetic with accurate absorption should remove the need for check shot
calibration of the sonic log to obtain accurate ties to the seismic
section.
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The Magnetic Vertical Gradient: A Study To Quantify Filter Parameters
Authors P.A. Versnel and L.A.G. AntoineWith the advent of the Image Processor, large regional magnetic data sets are now routinely being processed. Linear and non-linear transformations are commonly applied to the data in order to enhance various aspects of the image. The magnetic vertical gradient is one such transformation. Although employed for many decades on potential field data, it bas in general been used in a qualitative sense. For example, in the form of a high-pass filter. The vertical gradient is not necessarily restricted to qualitative applications, many automated depth estimation techniques make use of the vertical gradient.
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Current Filament Modelling Of Transient Electromagnetic Data
More LessA PC based Transient Electromagnetic (TEM) data processing system based on Barnett current filament modelling has been developed at CSTR, to process profiling data.
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Tem Profiling In Conductive Environments - A Case Study On The Vlakfontein Shear Zone Near Pilanesberg
More LessHost TEM profiling interpretation techniques assume the host rock
response is negligible, i.e. the host rock is highly resistive
relative to the ore body under investigation, and may be
neglected at sufficiently late times. Sometimes it is assumed
that the host rock response approximates that of a homogeneous,
isotropic half-space or of a conductive overburden which may be
subtracted directly from the data (linear superposition). In
complex conductive environments such as shear zones these
assumptions may be invalid, and no existing interpretation
techniques will be successful.
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A Geophysical Investigation Of The Rodium Reefs Project
By E.E.W. WederGeophysics played an important role in the exploration of the
Rhodium Reefs Project. A detailed helicopter-borne survey was
conducted at 100 metres flight line spacing to delineate faults,
dykes and iron pegmatites. This information was crucial in
planning the drilling programme. The Kennedy’s Vale vanadiferous
magnetite plug was well delineated on the aeromagnetic map.
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Depth Imaging In The Karoo By Simple Processing Of Transient Electromagnetic Data
By M.W. ZangA UTEM (University of Toronto Electromagnetic) survey has been
carried Out in the Orange Free State to help define the pre-Karoo
basement topography and thus search for geologic structures that
may host a gas reservoir. This survey has been done by
collecting an 8 km line of vertical-component magnetic UTEM data
which have been processed by the Depth Image Processing, or DIP,
technique.
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