摘要:

AbstractLateral inhomogeneities generate fluctuations in the traveltime of seismic waves. By evaluation of these traveltime fluctuations from different source and receiver positions, lateral inhomogeneities can be located using a pseudo inverse matrix method (Aki, Christoffersson and Husebye 1977). The formulation of the problem is possible for transmitted waves as well as for reflected and refracted waves. In reflection seismics this method is of importance, if no reflections from the inhomogeneities themselves, but only reflections from lower boundaries can be observed.The basic assumptions for the mathematical formulation are (1) the average velocities and depths of the reflecting horizons are known already from standard processing methods, and (2) the traveltime residuals are due to lateral velocity changes between different reflectors or between reflectors and the surface. The area of the earth to be considered is divided into layers and the layers into rectangular blocks. The parallel displacement of a ray after passing a disturbed block is neglected, only the traveltime residual is taken into account.In this paper the method and its application to data obtained with two‐dimensional models are describe

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1981.tb00399.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractDue to non‐linear effects, the swept frequency signals (sweeps) transmitted into the subsurface by vibrators are contaminated by harmonics. Upon correlation of the recorded seismograms, these harmonics lead to noise trains which are particularly disturbing in the case of down‐sweeps. The method described in this paper—which can be regarded as a generalization of Sorkin's approach to the suppression of even order harmonics—allows elimination, from the final vibratory source seismogram, of harmonics of the sweep up to any desired order. It requires that not one single signal but rather a series ofMsignals is employed where each signal has an initial phase differing from that of the previous one of the series by the phase angle 2πM. Prior to stacking, the seismograms generated with the different signals have to be brought into the form they would have if they had been generated with the same signal.The method seems also to be capable of reducing the correlation noise if sign‐bit recording technique

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1981.tb00400.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA type of iterative deconvolution that extracts the source waveform and reflectivity from a seismogram through the use of zero memory, non‐linear estimators of reflection coefficient amplitnde is developed. Here, we present a theory for iterative deconvolution that is based upon the specification of a stochastic model describing reflectivity. The resulting parametric algorithm deconvolves the seismogram by forcing a filtered version of the seismogram to resemble an estimated reflection coefficient sequence. This latter time series is itself obtained from the filtered seismogram, and so a degree of iteration is required. Algorithms utilizing zero memory non‐linearities (ZNLs) converge to a family of processes, which we call Bussgang, of which any colored Gaussian process and any independent process are members. The direction of convergence is controlled by the choice of ZNL used in the algorithm. Synthetic and real data show that, generally, five to ten iterations are required for acceptable deconvoluti

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1981.tb00401.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractTwo dimensional inverse modeling, a process to be applied after standard processing and interpretation, uses interfaces picked by the user. These interfaces are transformed into an approximate subsurface model.The subsurface model is represented by curved interfaces and interval velocities. The interfaces have to be unique functions of the line coordinate. Otherwise they may be arbitrarily curved and may begin or terminate anywhere along the section, e.g., at faults, pinchouts, salt domes and the like. Interval velocities may vary laterally along the section. The inverse modeling algorithm then modifies the model until traveltimes calculated from this model match the traveltimes observed as closely as possible in a least squares sense.The traveltimes corresponding to the model are obtained through ray tracing taking exact account of refraction. The traveltimes observed are the arrival times of single impulses before stacking contributing to the interfaces. These traveltimes are provided by ANAKON, a continuous interface analysis system.The comparison of INMOD results with those of well measurements and those of classical interval velocity computation from seismic data shows the accuracy of the method. Deviations of INMOD derived interface depths are within 2% of well data.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1981.tb00402.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractLaboratory studies of absorption‐frequency behavior in rocks often use spectral ratios of digitally recorded ultrasonic signals which have been transmitted through a rock sample and a reference sample of very low absorption, respectively. It is proposed to treat the digitally recorded signals as an autoregressive‐moving average (ARMA) process which, using recursive filter concepts, can be represented as a ratio of two polynomials in the z‐transform variable z. The numerator polynomial contains only that part of the signal that is modified by anelastic effects, whereas the denominator contains the elastic effects of the physical apparatus such as reverberations. Examples are given which show that this separation of the recorded signal greatly facilitates the laboratory investigation of loss mechanisms and absorption‐frequency behavior based on spectral

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1981.tb00403.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractA method is given for solving the dc electric field problem of a point current source in an anisotropic 2 1/2‐dimensional structural model. The surface integral equation of the field strength is given. Parallel to the strike the field strength is represented by a Fourier series. On the plane perpendicular to the strike each term of the field strength series is solved by means of the method of sub‐sections, where linear behaviour of field strength over the sub‐sections is assumed. Some numerical examples for different galvanic effects are

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1981.tb00404.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractThe laterites in Burundi, which are formed by weathering of ultrabasic rocks, show a complete profile with the following horizons:canga, the ferruginous crust capping,ferralite, consisting essentially of iron hydroxides, andsaprolite, which contains a large quantity of hydrosilicate minerals. Nickel bearing minerals occur in the saprolite and the lower portion of ferralite.Resistivity well‐logging and resistivity sounding indicated that the electrical properties of rocks depend upon their composition: Canga and ferralite showed high resistivities of 6,500 Ωm and 800 Ωm, respectively. The resistivity of saprolite was found to be much lower, between 10 Ωm and 20 Ωm. The laterite is underlain by resistive peridotite. The chargeability of saprolite was found to be lower than that of the upper horizons and the bedrock.Electrolytic conductivity of laterite, which depends on the geometry of the deposit, was found to be low, because the laterite contains moisture and ground water, which are highly resistive. The relatively high conductivity of saprolite is caused by nickeliferous hydrosilicates, which exhibit the electrical properties of clay minerals, with an apparent maximum conductivity of 0.25 S/m. The conductivity of saprolite corresponds to a concentration between 30% and 50% of conductive silicate minerals distributed in the pore space of deposit. A nickel enrichment of up to 6% was estimated from the resistivity of the saprolite.Prospecting for laterites by electrical sounding showed that the development of laterite horizons in a nickel deposit correlates with the surface morphology of weathered ultrabasic massif. Thus the method can be used in preliminary exploration of such dep

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1981.tb00405.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

AbstractSix thousand three hundred IP measurements made in central and southern Germany have been statistically evaluated. Shapes of IP decay curves obtained in the course of routine prospecting for sulfides were characterized in the following way: three chargeabilities were recorded during the 2 s current‐off time. By dividing the last by the first chargeability an “IP decay coefficient’ was calculated and statistically evaluated by means of histograms. When the histograms were compared with the statistics of apparent resistivity and chargeability, no relationship could be detected. Therefore, the histograms ofM3/M1values represent a characteristic property of distinct areas with certain geological features, mineral assemblage and tectonics. Weathering does not alter this geophysical “fingerprint”, which depends solely o

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1981.tb00406.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1981.tb00407.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1981.tb00408.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY