bluuebunny/crossref_metadata_2025_split huggingface dataset:
ESTIMATES OF TERRESTRIAL THERMAL GRADIENTS AND HEAT FLOW VARIATIONS WITH DEPTH IN THE HINTON‐EDSON AREA OF THE ALBERTA BASIN DERIVED FROM PETROLEUM BOTTOM‐HOLE TEMPERATURE DATA*
Authors: KUSHIGBOR C. , LAM H. L. , MAJOROWICZ J. A. , RAHMAN M. 
Published: April 2006

AbstractThere is a significant increase in terrestrial heat flow with depth in the Hinton‐Edson area of the deep part of the western Canadian sedimentary basin in Alberta. This is especially true near the Rocky Mountain foothills which is an area of high relief, high hydraulic head and regional water recharge. Gravity‐imposed downward movement of meteoric water through the thick sedimentary strata with velocities as low as 10–10 m/s to 0.5 × 10–9 m/s may cause an increase of heat flow with depth. Such disturbance of heat flow with depth on a regional scale in the sedimentary strata means that it is not possible to determine the background conductive steady‐state heat flow associated with crustal or upper mantle heat sources in such an area from measurement of conductive heat flow in the part of the sedimentary column where water movement occurs. This is because the convective portion cannot be determined, particularly when measurements are made in only part of the regional hydrodynamic system of the basin.
ZERO—PHASE FORWARD FILTERS FOR RESISTIVITY SOUNDING*
Authors: MANSINHA L. 
Published: April 2006

AbstractForward filters to transform the apparent resistivity function over a layered half‐space into the resistivity transform have been derived for a number of sample intervals. The filters have no apparent Gibbs' oscillations and hence require no phase shift. In addition, the end points of the filter were modified to compensate for truncation. The filters were tested on simulated ascending and descending two‐layer cases. As expected, “dense” filters with sample spacing of In (10)/6 or smaller performed very well. However, even “sparse” filters with spacing of In (10)/2 and a total of nine coefficients have peak errors of less than 5% for p1:p2 ratios of 10–6 to 106. If a peak error of 5.5% is acceptable, then an even sparser filter with only seven coefficients at a spacing of 3 In (10)/5 may be used.
THE USE OF SEISMIC SHEAR WAVES AND COMPRESSIONAL WAVES FOR LITHOLOGICAL PROBLEMS OF SHALLOW SEDIMENTS*
Authors: STÜMPEL H. , KÄHLER S. , MEISSNER R. , MILKEREIT B. 
Published: April 2006

AbstractFrom a great variety of in situ shear wave experiments, i.e., reflection, refraction and borehole surveys in the shallow sediments of the north German plains, several specific properties have been derived. Shear waves (S) differ from compressional waves (P) in that:

they are not affected by the degree of water saturation. Thus, they provide a better correlation between the velocity Vs and (solid) lithology;
they generally have lower frequencies, but shorter wavelength and, hence, a better resolution of thin layers;
they have lower absorption Qs−1 and hence a better penetration in partially saturated and gas‐containing sediments than P‐waves.

Correlations have been established between Vs and the confining pressure and between reduced Vs values and several lithological parameters like the grain size of sandy material. More lithological and hydrological information is obtained by using S‐ and P‐wave surveys along the same profile. The best information on a sedimentological structure is obtained by the simultaneous observation of Vs, Vp, Qs and Qp.
INTERACTION BETWEEN AIRGUNS*
Authors: VAAGE S. , URSIN B. , HAUGLAND K. 
Published: April 2006

AbstractIn the design of linear airgun arrays the interaction between the airguns is usually neglected. We review the different formulae which have been proposed for the minimum separation between airguns at which the interaction is negligible. These formulae can all be approximated by a linear function of a single variable.We have analyzed a large number of measurements in order to establish the amount of interaction between two airguns of various volumes at different pressures and depths. The resulting far‐field signature has been measured and compared with the sum of the signatures from the two airguns measured in the same experimental situation. The changes in primary pulse amplitude, bubble period and primary/bubble peak‐to‐peak amplitude ratio were computed from the measurement data as a function of airgun separation, chamber volume, chamber pressure and airgun depth. The influence of a waveshape kit was investigated, and the effects of interaction and the effects of using a waveshape kit were compared.
EM COUPLING IN MULTIFREQUENCY IP AND A GENERALIZATION OF THE COLE‐COLE IMPEDANCE MODEL*
Authors: BROWN R. J. 
Published: April 2006

ABSTRACTThe Cole‐Cole relaxation model has been found to provide good fits to multifrequency IP data and is derivable mathematically from a reasonable, albeit greatly simplified, physical model of conduction in porous rocks. However, the Cole‐Cole model is used to represent the mutual impedance due to inductive or electromagnetic coupling on an empirical basis: this use has not been similarly justified by derivation from any simple physical representation of, say, a half‐space, layered or uniform.A uniform conductive half‐space can be represented as a simple subsurface loop with particular resistive and inductive properties. Based upon this, a mathematical expression for the mutual impedance between the two pairs of electrodes of a dipole‐dipole array is derived and designated “model I”. It is seen that a degenerate case of model I is the Cole‐Cole model with frequency exponent c= 1. Model I is thus more general than the Cole‐Cole expression and must provide at least as good a fit to a set of field data. Provision for variation of c from unity could be made in model I equally well as for the Cole‐Cole model although, at present, this would be a purely empirical alteration.Model I contains four parameters, one of which is, in effect, the resistivity of the half‐space. Therefore only three parameters are involved in the model I expressions for normalized amplitude and for phase of the EM‐coupling mutual impedance. Model I is compared with previously published “standard” values for two different dipole separations. Under particular constraints, model I is shown to provide better fits than the Cole‐Cole model (with c= 1) over particular frequency ranges, specifically at very low frequencies and at moderately high frequencies where the model I phase curve follows the standard phase curve across the axis to positive values (negative coupling).
COMBINED SOUNDING‐PROFILING RESISTIVITY MEASUREMENTS WITH THE THREE‐ELECTRODE ARRAYS*
Authors: KAROUS M. , PERNU T. K. 
Published: April 2006

ABSTRACTA combination of DC‐resistivity sounding and profiling measurements can be used to obtain the maximum information about distribution of resistivities in the earth. Combined sounding‐profiling measurements with the AMN, MNB arrays are considered. The resistivity data from such measurements can be presented as: (a) normal sounding curves, (b) combined sounding‐profiling curves, (c) profiling curves, (d) pseudo‐sections, or as transformations obtained by the so‐called gradient processing, to emphasize the influence of the target objects.The examples chosen from numerical modeling and field tests show the efficiency of measurements with three‐electrode arrays to accurately locate thin conductors and contacts of lithological units of different resistivities. An interpreted cross‐section is compared with the results of other geophysical measurements (VLF‐R, dipole EM, Δ, IP) showing good correlation.
A REGIONAL GRAVITY STUDY OF THE NORTHERN NORTH SEA (56–62° N)*
Authors: HOSPERS J. , FINNSTRØM E. G. , RATHORE J. S. 
Published: April 2006

AbstractA Bouguer gravity anomaly map is presented of the North Sea and adjacent land areas in Norway and Denmark, covering an area situated between 56° and 62°N, 1°W and 10°E. The gravity data from the UK sector of the North Sea, the land and offshore areas of Denmark, and the land areas of Norway have been published before. However, the gravity data from the Norwegian sector of the North Sea are new. A large number (about 60) of individual gravity features can be defined in the mapped area. Most of those situated in the UK sector of the North Sea and on land in Norway have been discussed earlier; however, most of the anomalies found elsewhere which are qualitatively interpreted here have not been discussed before. An interpreted Bouguer anomaly map is presented which identifies all these features.The majority of the gravity anomalies encountered in the mapped area can be shown to be associated with one of the following geological features: (i) basement highs, (ii) large bodies of heavy basic or ultrabasic rock in the crystalline basement, (iii) large igneous intrusions within the sedimentary column and thick accumulations of volcanic rocks or their associated eruption centers, (iv) major basement faults.Large‐scale geological structures such as the Central, Viking and Sogn Grabens and the East Shetland, Stord, Forth Approaches and Norwegian‐Danish Basins are essentially in isostatic equilibrium and are only locally marked by relatively weak gravity minima.A residual gravity anomaly map has been produced by subtracting from the observed Bouguer anomalies the estimated gravity effect of an assumed thinned crust. This residual gravity anomaly map shows a number of features of the Bouguer anomaly field with greater clarity.
THE GRAVIMETRIC DETECTION OF MINING SUBSIDENCE*
Authors: LYNESS D. 
Published: April 2006

AbstractA series of gravity measurements were taken over a period of time (c. 150 days each) above two adjacent working coal faces. Precise levelling and gravity measurements were taken along the same profile before, during, and after seam extraction. The observed change in gravity agrees well with the levelling data. The combined data sets illustrate the validity of a simple Bouguer relationship for the gravity gradient.The results of two‐dimensional modelling are used to estimate the gravitational effect of the extracted material. A local feature detected only on the gravity signal may be due to an outcropping limestone layer.This controlled experiment demonstrates the possibility of using high‐precision gravity measurements as a substitute for levelling, particularly in surveys of large areal extent where the cost of obtaining comprehensive coverage by levelling may be prohibitive.
CALCULATION OF DISPERSION CURVES AND AMPLITUDE‐DEPTH DISTRIBUTIONS OF LOVE CHANNEL WAVES IN HORIZONTALLY‐LAYERED MEDIA*
Authors: RÄDER D. , SCHOTT W. , DRESEN L. , RÜTER H. 
Published: April 2006

AbstractWe present dispersion curves, and amplitude‐depth distributions of the fundamental and first higher mode of Love seam waves for two characteristic seam models. The first model consists of four layers, representing a coal seam underlain by a root clay of variable thickness. The second model consists of five layers, representing coal seams containing a dirt band with variable position and thickness. The simple three‐layer model is used for reference.It is shown that at higher frequencies, depending on the thickness of the root clay and the dirt band, the coal layers alone act as a wave guide, whereas at low frequencies all layers act together as a channel. Depending on the thickness, and position of the dirt band and the root clay, in the dispersion curves of the group velocity, secondary minima grow in addition to the absolute minima. Furthermore, the dispersion curves of the group velocity of the two modes can overlap. In all these cases, wave groups in addition to the Airy phase of the fundamental mode (propagating with minimum group velocity) occur on the seismograms recorded in in‐seam seismic surveys, thus impeding their interpretation. Hence, we suggest the estimation of the dispersion characteristics of Love seam waves in coal seams under investigation preceding actual field surveys.All numerical calculations were performed using a fast and stable phase recursion algorithm.
SIMPLE DATA PROCESSING OF TRIPOTENTIAL APPARENT RESISTIVITY MEASUREMENTS AS AN AID TO THE INTERPRETATION OF SUBSURFACE STRUCTURE*
Authors: ACWORTH R. I. , GRIFFITHS D. H. 
Published: April 2006

AbstractThe advantages of the Wenner tripotential method (Carpenter 1955) for apparent resistivity profiling are described and two new data processing techniques introduced as an aid to the interpretation of apparent resistivity sections (pseudo‐sections). These techniques were developed from model data computed using a two‐dimensional finite difference method.Oscillatory components present in anomalies on tripotential profiles and related to electrode spacing are shown to be effectively removed by linear filtering that also simplifies their form and aids recognition. Furthermore, it is shown that the ratio of the beta‐ and gamma‐apparent resistivities is a good indicator of resistivity variation, and is particularly sensitive to lateral change.Model data indicates that, over a wide range of conditions, enough subsurface information can be obtained by inspection of tripotential resistivity and ratio profiles, and from space sections to make possible a useful—and sometimes semi‐quantitative—interpretation.A rationale for the general interpretation of tripotential data is developed. Field data are described from an area of weathered granite basement in Nigeria. A model of the subsurface is developed using parameters derived from the processed observations. The observed and calculated apparent resistivity space sections are very similar.
FULL WAVE EQUATION DOWNWARD CONTINUATION OF SEISMIC REFLECTION DATA*
Authors: FOSTER D. J. , CARRION Ph. M. 
Published: April 2006

AbstractA new method for suppressing multiple reflections in seismograms is developed. It is based on a downward continuation procedure which uses the full acoustic wave equation (hyperbolic form) as a downward continuation operator. We demonstrate that the downward continuation of the recorded wave field maps a reflectivity function without multiply reflected events. The method is applied successfully to individual traces of plane‐wave decomposed (slant‐stacked) synthetic and field data.
FIRST ARRIVAL PICKING ON COMMON‐OFFSET TRACE COLLECTIONS FOR AUTOMATIC ESTIMATION OF STATIC CORRECTIONS*
Authors: COPPENS F. 
Published: April 2006

AbstractThe increase in the number of geophone groups in production records during recent years and the requirement for accurate basic static corrections for high resolution records have made it necessary to develop sufficiently accurate automatic techniques for the determination of static corrections.A fully automatic method is presented which makes use of the delay‐time method in order to compute static corrections at each shot position. Delay times, weathering and subweathering velocities are determined from automatic picks of the first arrivals on common‐offset trace collections.It is assumed that the weathering is a single layer and that the dip of the subweathering layer under the geophone groups is small.The picking routine is fully automatic and successful in most cases, provided the signal‐to‐noise ratio is sufficiently high.The subsequent filtering of erroneous values for picked times is performed by means of statistical techniques, using curves of picked times on common‐offset trace collections. If the distance between receivers and shot‐points on the profile is sufficiently short, one can expect only little change in the picked times of two contiguous traces.The method is well adapted to end‐on spreads with a great number of traces, where distances between geophone groups are short.Examples are presented showing the possibilities of the method for the determination of long wavelength as well as short wavelength components of static corrections.
ACOUSTIC MODELING OF THE SEAFLOOR*
Authors: BERGE A. M. , DRIVENES G. , KANESTRØM R. , BESKOW B. 
Published: April 2006

ABSTRACTData from routine seismic surveys contain considerable information about the geo‐acoustic properties of the seafloor. Waves are reflected at a wide range of angles of incidence from near‐vertical reflections (higher multiples) to supercritical reflections (primary and lower multiples). The reflection coefficient is approximately constant for small angles of incidence (< 10°) but varies greatly for larger angles of incidence. Near‐vertical reflections are used to determine the seafloor density. The P‐velocity in the seafloor is determined in advance from the critical distance using the amplitude variation of the primary as well as the multiples. The Vp/VS ratio is determined by modeling the amplitude variation with the angle of incidence. The primary reflection from the seafloor and the first three multiples are included in the modeling.Seismic data obtained with both conventional and superlong airgun arrays have been modeled. Data collected from the Barents Sea show that even if the P‐velocity is the same at different sites, the Vp/Vs ratio, density and Poisson's ratio vary significantly. The most extreme example shows that for a P‐velocity of 2.80 km/s the Vp/Vs ratio varies between 1.9 and 6.0. The corresponding densities vary from 2.36 g/cm3 to 1.80 g/cm3 and the Poisson's ratio varies from 0.31 to 0.49.The acoustic modeling offers a method of assessing the mean geotechnical or mechanical properties of larger volumes of marine sediments in terms of incompressibility, shear modulus and Poisson's ratio.
A NEW APPROACH TO THE INVERSION OF SEISMIC DATA*
Authors: THORNTON B. S. , SUTTON G. R. 
Published: April 2006

ABSTRACTA new inversion method for seismic reflection data is based on impedance concepts and uses transformations to reduce the essentially non‐linear problem to a linear eigenvalue formulation without approximation. A set of reflection data has been inverted using this method. The characteristic impedances of the layers so determined are compared with log data from a reference borehole.
WHY WATERGUNS?*
Authors: TREE E.L. , LUGG R.D. , BRUMMITT J.G. 
Published: April 2006

ABSTRACTA single watergun generates a ‘stand‐alone’ narrow pulse of acceptable energy content and broad‐band spectrum.When multiple units of equal volume are fired simultaneously and are accurately synchronized, carefully depth‐controlled and spaced beyond their near‐field interactive distance, the energy measured in the far‐field increases proportional to the square of the number of individual units employed.When these multiple units are configured in areal array designs based on distance weighting or varying density distribution of the equal elements, further gains in downward directivity and attenuation of horizontally traveling interference accrue. Such pattern designs take account of the spectral content of the particular watergun used, while the wavenumber response is concentrated to attenuate the dominant interference at water velocity.Finally, the high‐frequency content, and high repeatability and synchronizing accuracy of the new generation of waterguns improves the high resolution potential to help combat natural earth absorption losses. We should, therefore, keep the ‘in‐line’ dimensions at both source and receiver as short as possible. Unacceptable interference that persists during subsequent processing can be controlled by the long‐array simulation technique.
A COMPARISON OF STATISTICAL AND DETERMINISTIC WIENER DECONVOLUTION OF DEEP‐TOW SEISMIC DATA*
Authors: BOWEN A. N. 
Published: April 2006

ABSTRACTWiener ‘spiking’ deconvolution of seismic traces in the absence of a known source wavelet relies upon the use of digital filters, which are optimum in a least‐squares error sense only if the wavelet to be deconvolved is minimum phase. In the marine environment in particular this condition is frequently violated, since bubble pulse oscillations result in source signatures which deviate significantly from minimum phase. The degree to which the deconvolution is impaired by such violation is generally difficult to assess, since without a measured source signature there is no optimally deconvolved trace with which the spiked trace may be compared.A recently developed near‐bottom seismic profiler used in conjunction with a surface air gun source produces traces which contain the far‐field source signature as the first arrival. Knowledge of this characteristic wavelet permits the design of two‐sided Wiener spiking and shaping filters which can be used to accurately deconvolve the remainder of the trace. In this paper the performance of such optimum‐lag filters is compared with that of the zero‐lag (one‐sided) operators which can be evaluated from the reflected arrival sequence alone by assuming a minimum phase source wavelet. Results indicate that the use of zero‐lag operators on traces containing non‐minimum phase wavelets introduces significant quantities of noise energy into the seismic record. Signal to noise ratios may however be preserved or even increased during deconvolution by the use of optimum‐lag spiking or shaping filters.A debubbling technique involving matched filtering of the trace with the source wavelet followed by optimum‐lag Wiener deconvolution did not give a higher quality result than can be obtained simply by the application of a suitably chosen Wiener shaping filter. However, cross correlation of an optimum‐lag spike filtered trace with the known ‘actual output’ of the filter when presented with the source signature is found to enhance signal‐to‐noise ratio whilst maintaining improved resolution.
THE SCALING OF AIRGUN ARRAYS, INCLUDING DEPTH DEPENDENCE AND INTERACTIONS*
Authors: ZIOLKOWSKI A.M. 
Published: April 2006

ABSTRACTThe article provides a theoretical basis for the extension of the method of scaling law deconvolution to three dimensions using airgun arrays as a sound source.Earlier papers by the author required the dimensions of the scaled sources to be different while the depths and firing pressures were maintained the same in order to preserve the same dynamics of the scaled sources at scaled time. However, this forces the source ghost to be considered as part of the impulse response of the earth rather than as part of the downgoing source wave. And, in fact, the dynamics of the scaled sources are not the same at the same depth because the ghost reflection modulates the behaviour of the oscillating bubbles generated by the airguns, and this modulation does not scale.To force the sources to scale properly, including the ghost interaction, the larger source must be put at greater depth, where hydrostatic pressure is greater, and the initial firing pressure must be adjusted accordingly. Thus, the depth, initial firing pressure and gun volume are all variables. The interaction among guns in scaled airgun arrays also scales exactly if the geometry of an array and the depth of its deployment are scaled by the same factor.
REFLECTION‐WINDOW MAPPING OF SHALLOW BEDROCK*
Authors: SINGH S. 
Published: April 2006

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 operations.