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Fig. 16. Initial results of the shear-wave splitting measurements evaluated from data of the RETREAT array (green diamonds), permanent observatories (yellow diamonds) and the NAP (North Apennine Profile – blue diamonds). Thick symbols are the very high quality measurements, thin symbols are fair measurements. The big arrows on the top mark the SW-NW (blue) and N-E (red) azimuths of arriving shear waves. The green dashed lines mark boundaries of domains of the mantle lithosphere with similar orientation of anisotropic structures resulting from the initial stage of our study. c) We have applied the three-dimensional analysis of anisotropic parameters of body waves to the Northern Apennines, the tectonically active region affected by a progressive collision between the Eurasian and African plates, associated with a steady growth of the mountain range. Simultaneous extension in the convergent margin of the Adriatic and Tyrrhenian domains results in a retreat of the subducting Adriatic plate from the orogenic front caused by sub-lithosphere mantle processes. The study will contribute to developing a 3D self-consistent dynamic model of the syn-convergent extension in the Northern Apennines within the multidisciplinary international project RETREAT. Shear-wave splitting evaluated from recordings of the RETREAT array, formed by the network of permanent and 35 portable stations, evidences seismic anisotropy within the upper mantle. Ten of the portables are equipped by STS2 seismometers and GAIA data acquisition systems belonging to the MOBNET of the GI. Initial analysis of the splitting reveals both distinct lateral variations of anisotropic parameters and their dependence on the direction of propagation within the upper mantle (Fig. 16). Variations of the splitting time delays and orientation of the fast shear waves exclude a simple sub-lithosphere mantle flow, associated with the Apennines subduction, as the only source of the observed effective anisotropy. A part of the anisotropic signal, observed both in the shear-wave splitting and the P-residual spheres, can be generated by a frozen-in fabric of the Adriatic and Tyrrhenian lithosphere domains (Plomerová et al., 2005c). 33
References Babuška V., Plomerová J. and BOHEMA W.G, 2003. BOHEMA seismic experiment: search for an active magmatic source in the deep lithosphere in central Europe. EOS Trans. AGU, 84, 409-417. Babuška V. and Plomerová, J., 2004. Sorgenfrei-Tornquist Zone as the mantle edge of Baltica lithosphere: new evidence from three-dimensional seismic anisotropy. Terra Nova 16, 243-249. Babuška V., Plomerová, J., Vecsey L., Jedlička P. and Růžek B., 2005. Ongoing passive seismic experiments unravel deep lithosphere structure of the Bohemian Massif. Stud. Geophys. Geod., 49, 423-430. Plomerová J., Achauer U., Babuška V., Granet M. and BOHEMA W.G., 2003. Passive seismic experiment to study lithosphere-asthenosphere system in the western part of the Bohemian Massif. Stud. Geophys. Geod., 47, 691-701. Plomerová J., Vecsey L., Babuška V., Granet M. and Achauer U., 2005a. Passive seismic experiment MOSAIC – a pilote study of mantle lithosphere of the Bohemian Massif. Stud. Geophys. Geod., 49, 541-560. Plomerová J., Babuška V., Hyvonen T., Vecsey L., Kozlovskaya E., Raita T., and SSTWG, 2006b. Proterozoic-Archean boundary in the upper mantle of eastern Fennoscandia as seen by seismic anisotropy. J. Geodyn., submitted. Plomerová J., Margheriti L., Park J., Babuška V., Pondrelli S., Vecsey L., Piccinini D., Levin V., Baccheschi P., and Salimbeni S, 2006c. Seismic Anisotropy beneath the Northern Apennines (Italy): Mantle Flow or Lithosphere Fabric? Earth Planet. Sci. Lett., submitted. SLICE: Seismic velocity models Project SLICE (Seismic Litospheric Investigations of Central Europe) was using the data of two international seismic refraction experiments ALP 2002 and SUDETES 2003 (Brückl et al. 2003, Grad et al. 2003) to study the deep structure of Central Europe. The field work for this ambitious project Fig. 17. Schematic map of profiles used in inversions: (i) measured during the Celebration 2000 experiment (in red, labeled as C09a|b and C10a|b), (ii) Alp 2002 experiment (in green, labeled as A20a|b) and (iii) Sudetes 2003 (in blue, labeled as S01a|b – S05a|b). Numbering along profiles denotes the relative in-profile distance in km. Shot positions are depicted by violet circles. 34
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