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- Volume 35, Issue 7, 1987
Geophysical Prospecting - Volume 35, Issue 7, 1987
Volume 35, Issue 7, 1987
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SIGNAL ADJUSTMENT OF VIBROSEIS AND IMPULSIVE SOURCE DATA*
Authors R. BRÖTZ, R. MARSCHALL and M. KNECHTAbstractIn certain areas continuous Vibroseis profiling is not possible due to varying terrain conditions. Impulsive sources can be used to maintain continuous coverage. While this technique keeps the coverage at the desired level, for the processing of the actual data there is the problem of using different sources resulting in different source wavelets. In addition, the effect of the free surface is different for these two energy sources.
The approach to these problems consists of a minimum‐phase transformation of the two‐sided Vibroseis data by removal of the anticipation component of the autocorrelation of the filtered sweep and a minimum‐phase transformation of the impulsive source data by replacement of the recording filter operator with its minimum‐phase correspondent. Therefore, after this transformation, both datasets show causal wavelets and a conventional deconvolution (spike or predictive) may be used. After stacking, a zero‐phase transformation can be performed resulting in traces well suited for computing pseudo‐acoustic impedance logs or for application of complex seismic trace analysis. The solution is also applicable to pure Vibroseis data, thereby eliminating the need for a special Vibroseis deconvolution.
The processing steps described above are demonstrated on synthetic and actual data. The transformation operators used are two‐sided recursive (TSR) shaping filters.
After application of the above adjustment procedure, remaining signal distortions can be removed by modifying only the phase spectrum or both the amplitude and phase spectra. It can be shown that an arbitrary distortion defined in the frequency domain, i.e., a distortion of the amplitude and phase spectrum, is noticeable in the time section as a two‐sided signal.
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STUDIES OF ROADWAY MODES IN A COAL SEAM BY DISPERSION AND POLARIZATION ANALYSIS: A CASE HISTORY*
Authors P. KRAJEWSKI, L. DRESEN, W. SCHOTT and H. RÜTERAbstractField data from two‐component in‐seam seismic measurements are used to study roadway modes and their interaction with reflected seam waves. Using the multiple‐filter technique to investigate the dispersion behaviour of the different waves, it can be shown that the roadway modes disperse very similarly to the related transmitted seam waves. However, because of the free surface of the coal face, the dispersion curves of the roadway modes show a velocity reduction and a slight shift to lower frequencies compared to those of the related transmitted seam waves. Polarization analysis using hodograms, rectilinearity and polarization angle confirms these results. The parameters found by polarization analysis can be used to design polarization filters which help to separate roadway modes and reflected events in the traveltime range of superposition in the presented field case.
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LEVINSON INVERSION OF EARTHQUAKE GEOMETRY SH‐TRANSMISSION SEISMOGRAMS IN THE PRESENCE OF NOISE*
By F. SCHERBAUMAbstractThe Kunetz‐Claerbout equation for the acoustic transmission problem in a layered medium in its original form establishes the relation between the transmission and the reflec tion response for P‐waves in an horizontally layered medium and with vertical incidence. It states that the reflection seismogram due to an impulsive source at the surface, is one side of the autocorrelation of the seismogram due to an impulsive source at depth and a surface receiver.
By adapting Claerbout's formulation to the transmission of SH‐waves, the Kunetz‐Claerbout equation also holds for reflection and transmission coefficients dependent on the incident angle. Thus, earthquake geometry SH‐transmission seismograms can be used to caculate corresponding pseudoreflection seismograms which, in turn, can be inverted for the impedance structure using the Levinson algorithm. If the average incidence angle is known, a geometrical correction on the resulting impedance model can improve the resolution of layer thicknesses.
In contrast to the inversion of reflection seismograms, the Levinson algorithm is shown to yield stable results for the inversion of transmission seismograms even in the presence of additive noise. This noise stabilization is inherent to the Kunetz‐Claerbout equation.
Results of inverted SH‐wave microearthquake seismograms from the Swabian Jura, SW Germany, seismic zone obtained at recording site Hausen im Tal have been compared with sonic‐log data from nearby exploration drilling at Trochtelfingen. The agreement of the main structural elements is fair to a depth of several hundred metres.
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VERTICAL SEISMIC PROFILING—SEPARATION OF P‐ AND S‐WAVES*
More LessAbstractIn vertical seismic profile's (VSP's) shot with a large source offset, rays from shot to receiver can have large angles of incidence. Shear waves generated by the source and by conversions at interfaces are likely to be recorded by both the vertical and the horizontal geophones. Varying angles of incidence may give strong variations in the recorded amplitudes. Separation of P‐ and SV‐waves and recovery of their full amplitudes are important for proper processing and interpretation of the data. A P‐S separation filter for three‐component offset VSP data is presented which performs this operation. The separation filter is applied in the k‐f domain and needs an estimate of the P‐ and S‐velocities along the borehole as input. Implementation and stability aspects of the filter are considered. The filter was tested on an 1800 m offset VSP and appeared to be robust. Large velocity variations along the borehole could be handled and results were superior to those obtained by velocity filtering.
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HYBRID SEISMIC MODELLING: A TECHNIQUE TO COMBINE PHYSICAL AND COMPUTER METHODS FOR VERTICAL WAVE INCIDENCE*
Authors J. MEISTER and L. DRESENAbstractA hybrid seismic modelling technique has been developed to investigate complex geological phenomena. Those parts of a geological structure which are too complicated to be treated theoretically are studied by two‐dimensional physical models; other sections of the structure which can be treated theoretically, i.e., inhomogeneities in the vertical direction, are modelled by computer methods. A feedback process is used to combine the results of both physical and computer modelling.
Horizontally layered coal‐seam models are presented to test the hybrid modelling technique for normal incidence. A comparison of the hybrid seismograms with pure synthetic seismograms shows an acceptable conformity for normal incidence. A hybrid zero‐offset section is shown to investigate a complex geological structure in the Ruhr coalfield in Germany.
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PARAMETER ESTIMATION AND FAULT DETECTION BY THREE‐COMPONENT SEISMIC AND GEOELECTRICAL SURVEYS IN A COAL MINE*
Authors M. BREITZKE, L. DRESEN, J. CSOKAS, A. GYULAI and T. ORMOSAbstractThree‐component seismic and geoelectrical in‐mine surveys were carried out in Lyukobanya colliery near Miskolc, Hungary to determine the in situ petrophysical parameter distributions and to detect inhomogeneities in the coal seam. The seismic measurements comprise an underground vertical seismic profile, using body waves, and an in‐seam seismic amplitude‐depth distribution and transmission survey, using channel waves. The geoelectrical measurements are based on the drift‐ and seam‐sounding method.
Interval traveltime‐, amplitude‐, multiple‐filter‐ and polarization analysis methods are applied to the seismic data. They lead to a five‐layer model for the strata including the coal seam. The coal seam and two underlying beds act as a seismic waveguide. The layer sequence supports the propagation of both normal and leaky mode channel waves of the Love‐ and Rayleigh type. A calculation of the total reflected energy for each interface using Knott's energy coefficients shows that the velocity ranges of high reflection energy and of normal and leaky mode wavegroups coincide. The excitation of wavegroups strongly depends on the seismic source. A simultaneous inversion of a geoelectrical drift‐ and seam‐sounding survey prevents misinterpretations of the seismic data by clearly identifying the low‐velocity coal seam as a high‐resistivity bed. Calculations of dispersion and sounding curves improve the resolution of the slowness and resistivity in each layer.
Both diminished amplitudes and distortions in the polarization of transmission seismo‐grams and decreasing resistivities in a geoelectrical pseudosection of the coal seam are related to an inhomogeneity.
A calculation of synthetic seismograms for Love and Rayleigh channel waves with the finite‐difference and the Alekseev‐Mikhailenko method agrees well with the field data for the main features, i.e., particular arrivals in the wave train, wavegroups, velocities and symmetries or asymmetries.
This in‐mine experiment demonstrates that the simultaneous acquisition, processing and interpretation of seismic and geoelectrical data improve the lithological interpretation of petrophysical parameter distributions. Coal seam inhomogeneities can also be detected more reliably by the two independent surveys than by one alone.
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Volume 72 (2023 - 2024)
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Volume 70 (2021 - 2022)
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Volume 69 (2021)
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Volume 67 (2019)
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Volume 66 (2018)
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Volume 65 (2017)
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Volume 64 (2015 - 2016)
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Volume 63 (2015)
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Volume 62 (2014)
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Volume 61 (2013)
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Volume 60 (2012)
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Volume 59 (2011)
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Volume 58 (2010)
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Volume 57 (2009)
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Volume 56 (2008)
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Volume 55 (2007)
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Volume 54 (2006)
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Volume 53 (2005)
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Volume 52 (2004)
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Volume 51 (2003)
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Volume 50 (2002)
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Volume 49 (2001)
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Volume 48 (2000)
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Volume 47 (1999)
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Volume 46 (1998)
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Volume 45 (1997)
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Volume 44 (1996)
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Volume 43 (1995)
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Volume 42 (1994)
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Volume 41 (1993)
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Volume 40 (1992)
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Volume 39 (1991)
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Volume 38 (1990)
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Volume 37 (1989)
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Volume 36 (1988)
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Volume 35 (1987)
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Volume 34 (1986)
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Volume 33 (1985)
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Volume 32 (1984)
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Volume 31 (1983)
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Volume 30 (1982)
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Volume 29 (1981)
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Volume 28 (1980)
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Volume 27 (1979)
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Volume 26 (1978)
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Volume 25 (1977)
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Volume 24 (1976)
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Volume 23 (1975)
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Volume 22 (1974)
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Volume 21 (1973)
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Volume 20 (1972)
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Volume 19 (1971)
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Volume 18 (1970)
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Volume 17 (1969)
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Volume 16 (1968)
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Volume 15 (1967)
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Volume 14 (1966)
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Volume 13 (1965)
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Volume 12 (1964)
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Volume 11 (1963)
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Volume 10 (1962)
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Volume 9 (1961)
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Volume 8 (1960)
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Volume 7 (1959)
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Volume 6 (1958)
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Volume 5 (1957)
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Volume 4 (1956)
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Volume 3 (1955)
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Volume 2 (1954)
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Volume 1 (1953)