Record details

Title
    Zur Erklärung der seismischen Anisotropie im oberen Erdmantel unter Mitteleuropa
Statement of responsibility
    Peter Bormann
Author
    Bormann, Peter
Language
    anglicky
Source title - serial
    Zeitschrift für geologische Wissenschaften
Vol./nr.
    Vol. 24, no. 3-4
Pages
    p. 411-419
Year
    1996
Notes
    2 obr., 3 s.bibl.
    Anglické resumé
    Zkr. název ser.: Z. geol. Wiss.
Subject group
    anizotropie
    Český masiv
    diskontinuita Mohorovičičova
    plášť svrchní
    seizmická vlna
    seizmologie
Geographical name
    Česká republika
    Evropa střední
Keyword
    Anisotropie
    Erdmantel
    Erklärung
    Mitteleuropa
    Oberen
    Seismischen
    Unter
Abstract (in english)
   eleseismic recordings of SKS waves at 15 stations in Central Europe revealed shear-wave splitting indicative for seismic anisotropy. The polarization direction of the fast split wave varies between N40 E in the west and N120 E in the east. The avage delay-time between the two split waves is t=0.83+-0.31 a. This is too large to explain the splitting as an effect of crustal anisotropy only. On the other hand the trend of follows closely that of Hercynian fold axes. But even when assuming the preservation of frozen Hercynian rock fabric and structural trends throughout the whole lithosphere the latter is not thick enough beneath Central Europe to explain delay-times 0.4 s. Therefore, lattice-preffered horizontal orientation (LPO) of the a-axis of olivin in the asthenospeher is assumed to be the prime or even sole cause of the observed anisotropy parameters. LPO may be caused by drag-induced shear flow below the Westeuropean Plate. According to the model GFZ95 (MONTAG et al.
   1995) the latter moves with absolut velocities between about 2 to 3 cm/y towards roughly N57 E +-5. This direction is close to the average =62 observed at the western seismic stations, i.e. for areas charcterized by low topography of the Moho and lithosphere-astenosphere boundary. But the latter deepens down to 150-200 km benetah the Alps and the western boundary of the East European Platform. These "roots" border the relatively thin lithosphere beneath Central Europe. They trend with about N40 E to N100 E in the south and about N110 - 130 E in the north and east. This corresponds to the observed variations in a. We hypothesize, therefore, that the observed anisotropy is mainly due to plate-drag induced LPO in the asthenosphere. The latter follows closely the direction of absolute plate motion in areas of low topography of the lithosphere-asthenosphere boundary but more closely the trend of the latter in case of strong topography
Contributor
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
    U
Entered date
    20. 2. 2008
Import date
    8. 8. 2012