COMPUTATION OF INTERVAL VELOCITIES FROM COMMON REFLECTION POINT MOVEOUT TIMES FOR n LAYERS WITH ARBITRARY DIPS AND CURVATURES IN THREE DIMENSIONS WHEN ASSUMING SMALL SHOT-GEOPHONE DISTANCES*     

TH. KREY 《Geophysical Prospecting》1976,24(1):91-111

It is well known that interval velocities can be determined from common-reflection-point moveout times. However, the mathematics becomes complicated in the general case of n homogeneous layers with curved interfaces dipping in three dimensions. In this paper the problem is solved by mathematical induction using the second power terms only of the Taylor series which represents the moveout time as a function of the coordinate differences between shot and geophone points. Moreover, the zero-offset reflection times of the nth interface in a certain area surrounding the point of interest have to be known. The n—I upper interfaces and interval velocities are known too on account of the mathematical induction method applied. Thus, the zero-offset reflection raypath of the nth interface can be supposed to be known down to the intersection with the (n—1)th interface. The method applied consists mainly in transforming the second power terms of the moveout time from one interface to the next one. This is accomplished by matrix algebra. Some special cases are discussed as e.g. uniform strike and small curvatures.  相似文献   

NEW POSSIBILITIES FOR REFLECTION SEISMICS BY UNDERSHOOTING BODIES WITH COMPLICATED TECTONICS *     

R. BADING  J. ECHTERHOFF  TH. KREY  R. MARSCHALL 《Geophysical Prospecting》1974,22(1):1-21

In modern oil exploration layers of prospective interest with rather simple structural features are often overlain by very complicated bodies as e.g. saltdomes or other kinds of diapirs, olistostromes, or front zones of overthrusted blankets. In all these cases normal reflection seismic investigations, where downgoing and upgoing rays are rather close to each other, mostly fail, either because no reflections from underneath the complicated bodies are obtained, or because a reliable migrated depth presentation becomes practically impossible due to the inhomogeneity of the overlying bodies. The undershooting technique avoids these difficulties by using ray paths which do not traverse the complicated bodies e.g. by shooting on one side of a saltdome and recording on the other side. On account of the large shot-geophone distances in this method special considerations and computer processes were developed concerning moveout corrections for common depth point stacking and migrated depth presentation. In many cases the location of the disturbing complicated bodies is known in advance. The shooting and recording program can then be adjusted to this knowledge and thereby kept to a minimum. If the location of the complicated bodies is unknown a more extended seismic program has to be carried out encompassing a great variety of shot-geophone distances. But in this case the approximate location of the complicated bodies can be deduced from the survey too. Results are presented in order to give an idea of the efficiency of the new seismic tool.  相似文献   

TEM and XRD determination of crystallite size and lattice strain as a function of illite crystallinity in pelitic rocks   总被引：2，自引：0，他引：2  

W.-T. JIANG  D. R. PEACOR  P. ÁRKAI  M. TÓTH  & J. W. KIM 《Journal of Metamorphic Geology》1997,15(2):267-281

Average crystallite size and mean-square strain of illite in rock specimens and clay separates were measured independently in TEM images and by single-line Fourier (Voigt method) profile analysis of the c. 1 nm peak of XRD patterns for a prograde sequence of pelitic rocks (illite crystallinity indices=0.17–0.58°Δ2θ) from the Gaspé Peninsula, Quebec. The TEM-determined crystallite sizes in clay separates approximate those determined by Fourier profile analyses and those calculated from illite crystallinity indices by the Scherrer equation, with the exception of the diagenetic sample. The crystallite sizes and mean-square strains of illite in rock samples exhibit a trend similar to that determined by profile analyses, but the average crystallite sizes are up to five times larger than those measured for clay separates. TEM images show that all rock samples have a wide range of crystallite sizes, and the proportions of larger crystallites increase with metamorphic grade. The diagenetic illite is defect-rich, fine-grained (mean thickness by volume=c. 70 nm), 1M_d material. Anchizonal illite tends to occur as separate aggregates of small 1M_d and larger 2M₁ crystals (c. 200 nm), comprising arrays of subparallel coalescing packets. The epizone sample has thick (c. 400 nm), defect-free crystals of muscovite occurring in stacks of parallel layers, or subhedral crystals intergrown with large-angle boundaries. Cleaved crystals that are free of intracrystalline layer terminations are dominant in clay separates of all samples, having ranges of smaller sizes with volume-average thicknesses of c. 43, 43, and 81 nm (c. 14, 28, 67 nm by the Voigt method), respectively, for the three zones. The results suggest that illite crystallinity indices do not provide a direct measure of a single microstructural state of illite in rocks, although they yield consistent limits for average crystallite sizes for the anchizone (23 & 48 nm here). Therefore, they serve as a general parameter of the degree of recrystallization on a relative basis, in part because the contributions of all peak-broadening variables (mixed layering, size and strain) decrease regularly with prograde regional metamorphism of pelites. The microstructural changes caused by rock disaggregation are probably a function of those variables as well. The data collectively demonstrate a trend from metastable, defect-rich, small crystals towards a stable assemblage of larger, defect-free crystals, through dissolution of strained crystals and neocrystallization, consistent with the Ostwald step rule.  相似文献   

CRUSTAL REFLECTIVITY PATTERN AND ITS RELATION TO GEOLOGICAL PROVINCES1     

H. TRAPPE  TH. WEVER  R. MEISSNER 《Geophysical Prospecting》1988,36(3):265-281

The statistical treatment of deep seismic reflections from several different geological units has resulted in different reflectivity histograms. Reflectivity in old and cold shields differs significantly from that in younger, warmer areas. In the shields reflectivity is generally poor and concentrated in the upper crust whilst Caledonian and Variscan areas show strong reflecting lamellae in their lower crust. Also the length of the reflecting elements varies with age and heat flow. The lower crust in young areas is a zone of a strong viscosity minimum as derived from model studies with a temperature dependent rheology. The subhorizontal reflecting lamellae in the lower crust are considered to have been created in a large-scale high-temperature, low-viscosity ordering process whose remnants are still preserved today. Local-scale differences of reflectivity histograms define certain subprovinces which can be distinguished by their specific patterns.  相似文献   

Palaeoecology of the Quaternary     

SVEND TH. ANDERSEN 《Boreas: An International Journal of Quaternary Research》1981,10(1):132-132

Book reviewed in this article:
H. J. B. Birks & Hilary H. Birks: Quaternary Palaeoecology  相似文献   

The subdivision of the Quaternary of Norden: a comment     

SVEND TH. ANDERSEN 《Boreas: An International Journal of Quaternary Research》1979,8(1):74-75

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The luminosity index for M stars and the distance to the LMC     

TH. Schmidt-Kaler  M. O. Oestreicher 《Astronomische Nachrichten》1998,319(6):375-386

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Influence of molecular outflows from young stellar objects on molecular clouds     

TH. Henning 《Astronomische Nachrichten》1989,310(5):363-366

In this paper it is investigated whether molecular outflows can support the turbulence in molecular clouds against decay. In the momentum-driven regime of molecular flows the time scale of the replenishment of the fluctuations is longer than the dissipation time scale of pure hydrodynamical supersonic turbulence.  相似文献   

HUNGARY AFTER 1989: INSCRIBING A NEW PAST ON PLACE*     

KENNETH E. FOOTE  ATTILA TTH  ANETT RVAY 《Geographical review》2000,90(3):301-334

ABSTRACT. Since the fall of the Communist government in 1989, Hungary's political monuments and historical shrines have undergone great change. Although popular attention focused on the removal of overtly political monuments, new shrines were also created, and forgotten memorials were restored. In a departure from earlier political eras, decisions about contested places are issuing from local authorities and private citizens, rather than from the central government. The result is a sometimes subtle rearrangement of public memorials and shrines that interprets the national past by drawing symbolic and spatial parallels between some historical events while rejecting connections among others. The meanings of events and places, particularly those linked to twentieth‐century wartime and civil upheavals, remain contested.  相似文献   

ROSAT PSPC detection of soft X-ray absorption in GB 1428+4217: the most distant matter yet probed with X-ray spectroscopy     

TH. Boller  A. C. Fabian  W. N. Brandt  M. J. Freyberg 《Monthly notices of the Royal Astronomical Society》2000,315(2):L23-L28

We report on a ROSAT PSPC observation of the highly luminous z =4.72 radio-loud quasar GB 1428+4217 obtained between 1998 December 11 and 17, the final days of the ROSAT satellite. The low-energy sensitivity of the PSPC detector was employed to constrain the intrinsic X-ray absorption of the currently most distant X-ray detected object. Here we present the detection of significant soft X-ray absorption towards GB 1428+4217, making the absorbing material the most distant matter yet probed with X-ray spectroscopy. X-ray variability by 25±8 per cent is detected on a time-scale of 6500 s in the rest frame. The X-ray variation requires an unusually high radiative efficiency of at least 4.2, further supporting the blazar nature of the source.  相似文献