S-wave splitting from records of local micro-earthquakes in West Bohemia/Vogtland: An indicator of complex crustal anisotropy |
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Authors: | V Vavry?uk A Bou?ková |
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Institution: | (1) Institute of Geophysics, Acad. Sci. Czech Republic, Boční II/1401, 141 31 Praha 4, Czech Republic |
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Abstract: | Most S-wave particle motions of local micro-earthquakes in the West Bohemia/Vogtland region display S-wave splitting. The
split S waves are usually well defined, being separated in time and polarized in roughly perpendicular directions in the horizontal
projection. In most cases, the polarization of the fast S wave is aligned NW-SE (referred to as “normal splitting”), which
is close to the direction of the maximum horizontal compression in the region. However, for some ray directions, the polarization
of the fast S wave is aligned NE-SW (referred to as “reverse splitting”). The pattern of normal/reverse splitting on a focal
sphere is station-dependent, indicating the presence of inhomogeneities in anisotropy. For some stations, the normal/reverse
splitting pattern is asymmetric with respect to the vertical axis, indicating the symmetry axes of anisotropy are probably
inclined. The presence of inclined anisotropy is confirmed by observations of directionally dependent delay times between
split S waves. A complex and station-dependent anisotropy pattern is probably the result of a complicated anisotropic crust
characterized by diverse geological structures. The spatial variation of anisotropy probably reflects the presence of a variety
of different types of anisotropic rocks in the region. |
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Keywords: | anisotropy Earth’ s crust earthquake swarm micro-earthquakes polarization stress field S waves S-wave splitting 90°-flips West Bohemia/Vogtland |
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