P-wave velocity anisotropy in crystalline rocks   总被引：1，自引：0，他引：1  

Vladislav Babu&#;ka 《Geophysical Journal International》1984,76(1):113-119

Summary. Compressional wave velocities and anisotropy coefficients determined at high hydrostatic pressures are compiled from the data published for the main types of crystalline rocks. The crack-free elastic anisotropy of igneous crustal rocks is generally very low, between 1 and 3 per cent on average. The anisotropy of metamorphic rocks is higher (up to 22 per cent), but very variable. The average anisotropy coefficients in schists and amphibolites are about 10 per cent, in gneisses between 3 and 7 per cent, and in granulites less than 3 per cent. The average anisotropy of olivine ultramafites is between 7 and 12 per cent, whereas in pyroxenites and eclogites it is usually less than 4 per cent. A comparison of ranges of average velocities and average anisotropies for the individual rock groups suggests that, whereas in the crust the lateral velocity variations are mainly due to compositional changes, in the olivine of the uppermost mantle the velocity variations due to anisotropic structures could be of the same magnitude as the variations due to inhomogeneities.  相似文献   

Thirty-Element Active Antenna Array as a Prototype of a Huge Low-Frequency Radio Telescope     

Alexander?Alexandrovich?KonovalenkoEmail author  Igor?Savelievich?Falkovich  Nikolay?Nikolaevich?Kalinichenko  Alexander?Alexandrovich?Gridin  Igor?Nikolaevich?Bubnov  Alain?Lecacheux  Carlo?Rosolen  Helmut?O.?Rucker 《Experimental Astronomy》2003,16(3):149-164

An effective wide-band (10 to 60 MHz) active antenna element has been developed. The cost of one short (3 m), thin dipole with built-in amplifier and metal construction is less than 45 euro. It was shown both theoretically and experimentally that the upper limiting frequency is at least 60 MHz, the dynamic range is 90 dB/V and the share of the amplifier noise to the background antenna temperature is about 10%. The developed active dipole was tested by building a 30-element antenna array and comparing its parameters with one of the subpart of the UTR-2 radio telescope having passive dipoles of 8.6 m in length and 1.8 m in diameter. The 3C461 ionospheric scintillation spectra observed in the experiments show that the sensitivities and noise-immunities of both antennas are close. This proves the availability using of a short cheap active dipole in new generation giant radio telescopes.  相似文献   

Änderung der Lage und Orientierung des netzes auf Einem Rotationsellipsoid Durch Konforme Abbildung     

Vladislav Hojovec 《Studia Geophysica et Geodaetica》1958,2(3):193-205

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Elastic anisotropy of the upper mantle and the Mohorovičić discontinuity     

Vladislav Babuška 《Studia Geophysica et Geodaetica》1970,14(3):296-309

Zusammenfassung Der Artikel macht auf die Wahrscheinlichkeit von Ver?nderungen elastischer Anisotropie der Erdkruste und des obersten Erdmantels mit der Tiefe aufmerksam und weist auf eine M?glichkeit der Entstehung von seismischen Grenzfl?chen zwischen den Medien mit verschiedener elastischer Anisotropie hin. Diskutiert wird die M?glichkeit einer Interpretation der Moho-Diskontinuit?t als einer Grenzfl?che zwischen der isotropen oder heterogen anisotropen Erdkruste und dem transversal isotropen obersten Erdmantel. In unhydrostatischem Kraftfeld mit überwiegender vertikaler Druckkomponente stellt die Moho-Diskontinuit?t eine „Isofl?che” mit gleichen physikalischen Bedingungen dar, die zur Entstehung der Vorzugsorientation von Olivin geeignet sind. Die Vorzugsorientation von Olivinfl?chen (010) in einer horizontalen Ebene (d. i. senkrecht auf die Richtung der Hauptkomponente des Drucks) würde als ein Impuls zur Entstehung laminarer Strukturen gelten, die die Anisotropie des obersten Erdmantels und seinen Kontrast gegenüber der Erdkruste erh?hen. Durch die Entstehung der überwiegend aus den vorzugsweise orientierten Olivinkristallen zusammengesetzten transversal isotropen Schicht kommt es im Vergleich mit einem isotropen oder sonst anisotropen Aggregat zu einer pl?tzlichen Erh?hung der Geschwindigkeit der Longitudinalwellen in horizontaler Ebene und umgekehrt zu ihrer Herabsetzung in der vertikalen Richtung. Dabei ist der Unterschied in der Dichte oberhalb und unterhalb der Moho-Diskontinuit?t nur durch allm?hliche Ver?nderungen der chemischen Zusammensetzung mit der Tiefe gegeben. Vom seismologischen Gesichtspunkt aus handelt es sich also um ein Gradientmedium, das im obersten Erdmantel transversal isotrop ist.

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Address: Boční II, Praha 4-Spořilov.  相似文献   

Cs137 gamma-ray absorption in eclogites     

Věra Vaňková  Vladislav Babuška  Reviewer J. Fiala 《Studia Geophysica et Geodaetica》1972,16(4):383-392

Summary The coefficient of the gamma-ray absorption _Cs ¹³⁷ investigated in eclogites of the Bohemian Massif varies with fresh samples from0.2477 cm ^–1 to 0.2804 cm ^–1 . Symplectite is the main factor decreasing the value of down to0.242 cm ^–1 . On the contrary, the coefficient increases with the increasing content of clinopyroxene and especially of garnet. The linear dependence of the coefficient on the density may be expressed by the equation =0.0682+0.028.  相似文献   

Elastic anisotropy of igneous and metamorphic rocks     

Vladislav Babuška 《Studia Geophysica et Geodaetica》1968,12(3):291-303

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East-alpine earthquake of 2nd December 1963     

Vladislav Babuška  Libuše Ruprechtová  Olga Zenklová 《Studia Geophysica et Geodaetica》1965,9(3):302-305

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Velocities of seismic waves propagating through the Bohemian massif from foci in Poland     

Jaroslava Plomerová  Vladislav Babuška  Libuše Ruprechtová  Reviewer A. Zátopek 《Studia Geophysica et Geodaetica》1984,28(1):56-66

mam mm ua a na Pn, Pg, Sn u Sg nu¶rt;u u au -ma. aa, m ¶rt; amu 5° m numa ua¶rt;a ¶rt;am mu a na n au ma¶rt;amu u mu anmau , uu m n u ma¶rt;am¶rt;a. am nmau a uu m anmau mmu aua.  相似文献   

Upper mantle beneath the Eger Rift (Central Europe): plume or asthenosphere upwelling?   总被引：4，自引：0，他引：4  

Jaroslava Plomerová  Ulrich Achauer  Vladislav Babu&#;ka  Lud&#;k Vecsey  BOHEMA working group 《Geophysical Journal International》2007,169(2):675-682

We present the first results of a high-resolution teleseismic traveltime tomography and seismic anisotropy study of the lithosphere–asthenosphere system beneath the western Bohemian Massif. The initial high-resolution tomography down to a depth of 250 km did not image any columnar low-velocity anomaly which could be interpreted as a mantle plume anticipated beneath the Eger Rift, similar to recent findings of small plumes beneath the French Massif Central and the Eifel in Germany. Alternatively, we interpret the broad low-velocity anomaly beneath the Eger Rift by an upwelling of the lithosphere–asthenosphere transition. We also map lateral variations of seismic anisotropy of the mantle lithosphere from spatial variations of P -wave delay times and the shear wave splitting. Three major domains characterised by different orientations of seismic anisotropy correspond to the major tectonic units—Saxothuringian, Moldanubian and the Teplá-Barrandian—and their fabrics fit to those found in our previous studies of mantle anisotropy on large European scales.  相似文献   

Artificial screen for reducing seismic vibration generated by blasting     

Dragan Bogunovic  Vladislav Kecojevic 《Environmental Geology》2007,53(3):517-525

The purpose of blasting operations is rock fragmentation. Blasting is a key component in the overall rock fragmentation system - the first element of the ore extraction process. It provides appropriate rock material granulation or size that is suitable for loading and transportation. However, in spite of many advantages explosives have, their usage may cause environmental problem such as seismic vibration. One of the solutions to this particular problem may be application of an artificial screen as a barrier to the seismic wave path. The results of experimental research on the artificial screen concept, its characteristics and role in attenuation of seismic effects generated by blasting are presented. The experiment is based on two physical phenomena: (1) the size and degree of discontinuity and (2) the reflection and refraction of seismic waves. More than 1,500 laboratory measurements were conducted with different combinations of screen sizes, positions of the screen to blasting source, and intensities of blasting impulses. The results of the study show reduction of generated vibrations up to 58% by employment of artificial screens.  相似文献