摘要:

AbstractContrasting resistivity, temperature, pressure, porosity and fluid migrations are the main causes of ion accumulations along the discontinuities which create coupling‐induced natural current flow which is observed as the Natural Polarization Potential (NPP) on the surface. Natural Polarization Electric Field (NPE) variations were recorded along 13 profiles about 2.5 km each in a north‐south direction. Interpretation of the coincident anomalies of the NPP and the NPE field resulted in determination of the polarization angle, polarization focal depth and the azimuths of the polarized interfaces. Considerable agreement between faults delineated by previous geological and geophysical investigations and polarization discontinuities was observed. The polarization plane was observed to be horizontal in high temperature areas but steepened gradually in relatively colder regions in the northern coastal area. From the polarization depth distribution two depression zones were observed, separated by an uplifted section elongated in a north‐south direction. The basin at the eastern side had an estimated polarization depth of 1.1 km and was limited by the Agamemnon‐2 and ‐1 faults, while the western basin had an estimated depth of 1.3 km and extended in the east‐west direction not previously reported. The eastern basin extends on the north side around the town of Inciralti, the western basin appeared to be elongated towards the to

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00477.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTA field study was undertaken to evaluate the effectiveness of the high frequency seismic reflection technique for mapping of shallow and irregular bedrock. Bedrock reflections were obtained using a hammer source with both in‐line and common offset field layouts. The recording equipment included 12‐channel enhancement seismographs, 28 Hz vertical geo‐phones and a microcomputer. The latter increased the overall versatility of the seismic system.Field sites for this study are typical of the geological settings of the tin mining areas of Malaysia. The topographical ‘lows’ of the irregular bedrock control the localization of tin ore. The subsurface geology consists of a thin low velocity layer (± 300 m/s) overlying the compact overburden (± 1700 m/s) which in turn lies on bedrock.This paper discusses various criteria for designing an optimum window for obtaining usable reflections between the first arrival and the leading edge of the ground roll cone.Detailed mapping of the overburden and the bedrock interface by the reflection method can be useful in delineating areas for exploratory drilling and for optimum planning of mining

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00478.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTInterpretation problems are discussed for a new class of models for complex seismic media, called heterogeneous models formed by inclusions (HMI). Examples of such models in geology are destructive deformation zones, tectonic raptures, complex folds, magmatogene formations, fronts of metamorphism and of phase transition, etc., which are of importance in interpretation of seismic data. The wavefields in such media have a complicated interferential character and should be considered as complex wave groups characterized by their phase and group properties.To study the phase and group characteristics of such wavefields, a method of construction and comparative analysis of so‐called phase and group sections is introduced. This method is based on a transformation of the wavefield (seismogram) into a normalized seismogram (cos of the phase) and a perigram (a low cut version of the trace envelope). The group sections obtained on the perigrams represent zones of energy concentration and give stable estimates of the average characteristics of model structure. The phase sections are obtained on the normalized seismograms and represent primarily, the inner structure of the model.The method was applied to both synthetic and field data. The results of the combined analysis of the phase and group sections show that in many cases there are significant differences between them. On the basis of this analysis, several types of seismic objects may be distinguished which can serve as a basis for seismic interpretatio

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00479.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTFor amplitude and phase response calibration of moving‐coil electromagnetic geophones two parameters are needed, namely, the geophone natural frequency,f0, and the geophone upper resonance frequencyfu. The phase‐ellipse method is commonly used for the in situ determination of these parameters. For a given signal‐to‐noise ratio, the precision of the measurement off0andfudepends on the phase sensitivity,f(δφ/δf)For some commercial geophonesf(δφ/δf)atfucan be an order of magnitude less than the sensitivity atf0. In this paper we present an improved phase‐ellipse method with increased precision. Compared to measurements made with the existing phase‐ellipse methods, our method shows a 6‐ and 3‐fold improvement in the precision, respectively, on measurements off0andfuon

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00480.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe formal equivalency between a Hankel transform and an Abel transform followed by a Fourier transform is used as a basis for the computation of synthetic seismograms and for performing plane‐wave decomposition of both synthetic and field seismograms. The Abel‐Fourier method performs better for near‐offset or small ray‐parameter, although at greater computational effort than calculations based upon the asymptotic Hankel tr

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00481.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTBorehole surveys are usually commissioned to provide structural details as a guide to further drilling. Conductors remote from the hole are readily detected using EM probes. Vectors can be established by noting variations in wavelength, particularly for reversals of polarity. However, several holes in the same area are required to remove rotational ambiguities, and single axis systems may generate spurious anomalies related to errors in alignment. Consequently, a three‐component sensor has been designed to compare the orthogonal response at each depth. Data are expressed in terms of the invariant parameters of the polarization ellipse, and secondary fields are readily identifie

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00482.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTIn the Kapurdi block of the Barmer lignite field in western Rajasthan, India, lignite occurs as a number of discontinuous seams of varying thickness up to a few m. The country rock is a succession of clay, sand and various members of the clay‐sand family. The overburden, comprising sand, Fuller's earth, bentonitic clay, clayey sand/sandy clay and clay, is thick and, electrically, highly conductive. Both its thickness (40–90 m) and conductivity (0.5–1.0 S/m) are highly variable. The lignite seams may occur anywhere in the clay‐sand sequence below this overburden.A ten‐layered electrical model of the Kapurdi area was parameterized on the basis of galvanic resistivity sounding and core drilling results. This model was then validated by electromagnetic sounding measurements made with a 200 × 200 m square loop transmitter and energizing current of variable frequency (80 Hz to 11 kHz), using central induction sounding techniques. With a loop of this size, only formations in the overburden could be mapped. Subsequent computer modeling has shown that a larger loop of size, say, 800 m and a frequency band of 30–500 Hz are required to map formations below–as well as those within–the overburden. Even then only various clay‐sand interfaces can be mapped, i.e., only over‐burden thickness and the likely depth range of lignite seams (if they occur) can be estimated. Direct mapping of lignite seams is not feasible in practice. This is true of loop‐dipole, as well as central induction sounding. It is interesting that skin depth need not always be a factor limiting depth of exploration in elect

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00483.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTSlant stacking transforms seismic data, recorded as a function of source‐receiver offset and traveltime, into the domain of intercept time τ and ray parameterp. The shape of the τ‐p‐curves thus obtained is closely related to the slowness surfaces of the layers. A layer‐stripping operation in the τ‐p‐domain removes all effects of the layers above the target layer. The resulting curve is equal to the slowness surface of the layer except for a scaling factor containing the thickness and dip of the layer. The slowness surface is a characteristic surface for anisotropic media. This makes the τ‐p‐domain very suitable for detecting and describing anisotropic layers. The relationship between the shape of τ‐p‐curves, the slowness surfaces, and the geometry of the layers is derived. Synthetic τ‐p‐curves calculated with the reflectivity method show some difficulties that can arise in determining the shape of the curves and in applying the stripping operation. It is shown that the effects of vertical inhomogeneity on the interpretation of τ‐p‐curve

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00484.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY