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Slab detachment under the Eastern Alps seen by seismic anisotropy.

Qorbani E, Bianchi I, Bokelmann G - Earth Planet. Sci. Lett. (2015)

Bottom Line: We attribute the deeper layer to a detached slab from the European plate.On the other hand, the upper layer has NW-SE fast orientations coinciding with a low-velocity layer which is found above a more-or-less eastward dipping high-velocity body.The anisotropy of the upper layer shows large-scale NW-SE fast orientation, which is consistent with the presence of asthenospheric flow above the detached slab foundering into the deeper mantle.

View Article: PubMed Central - PubMed

Affiliation: Department of Meteorology and Geophysics, University of Vienna, Austria.

ABSTRACT

We analyze seismic anisotropy for the Eastern Alpine region by inspecting shear-wave splitting from SKS and SKKS phases. The Eastern Alpine region is characterized by a breakdown of the clear mountain-chain-parallel fast orientation pattern that has been previously documented for the Western Alps and for the western part of the Eastern Alps. The main interest of this paper is a more detailed analysis of the anisotropic character of the Eastern Alps, and the transition to the Carpathian-Pannonian region. SK(K)S splitting measurements reveal a rather remarkable lateral change in the anisotropy pattern from the west to the east of the Eastern Alps with a transition area at about 12°E. We also model the backazimuthal variation of the measurements by a vertical change of anisotropy. We find that the eastern part of the study area is characterized by the presence of two layers of anisotropy, where the deeper layer has characteristics similar to those of the Central Alps, in particular SW-NE fast orientations of anisotropic axes. We attribute the deeper layer to a detached slab from the European plate. Comparison with tomographic studies of the area indicates that the detached slab might possibly connect with the lithosphere that is still in place to the west of our study area, and may also connect with the slab graveyard to the East, at the depth of the upper mantle transition zone. On the other hand, the upper layer has NW-SE fast orientations coinciding with a low-velocity layer which is found above a more-or-less eastward dipping high-velocity body. The anisotropy of the upper layer shows large-scale NW-SE fast orientation, which is consistent with the presence of asthenospheric flow above the detached slab foundering into the deeper mantle.

No MeSH data available.


Related in: MedlinePlus

Map of average SKS splitting parameters calculated over the good quality measurements. Thick white lines represent average fast orientation (ϕ) at each station from this study and Bokelmann et al. (2013). Splitting delays (δt) are shown by the length of the line (see scale on lower left). Black lines display measurements from previous studies (Barruol et al., 2011; Kummerow and Kind, 2006), and stations located in the Southern Alps and Po-plain, marked by triangles, Salimbeni et al. (2013). For discussion see the text. (For interpretation of the colors in this figure, the reader is referred to the web version of this article.)
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fg0020: Map of average SKS splitting parameters calculated over the good quality measurements. Thick white lines represent average fast orientation (ϕ) at each station from this study and Bokelmann et al. (2013). Splitting delays (δt) are shown by the length of the line (see scale on lower left). Black lines display measurements from previous studies (Barruol et al., 2011; Kummerow and Kind, 2006), and stations located in the Southern Alps and Po-plain, marked by triangles, Salimbeni et al. (2013). For discussion see the text. (For interpretation of the colors in this figure, the reader is referred to the web version of this article.)

Mentions: The average values of splitting pairs are displayed in Fig. 2. The line's orientation presents the average fast orientation azimuth for each station and the line's length indicates the average splitting delay. The stations DAVA, FETA, RETA, WTTA, ABSI, ROSI, MOSI, and KOSI which are located in longitude range between 9°E and 12°E show fast azimuths at about N60° (azimuth from North). These azimuths are in good agreement with the results of previous studies for the Western Alps presented by Barruol et al. (2011) and the Central Alps by Kummerow and Kind (2006) (black lines in Fig. 2). The NE–SW fast orientation detected for the western stations turns gradually to nearly East–West at the stations RISI, ABTA, CLUD, and ZOU2 (located at longitudes between 12°E and 13°E). The station FVI is an exception, with a fast azimuth oriented N72°. East–West fast orientation are detected for station KBA, JAVS and CEY as well (Fig. 2). Further to the East, the fast orientations turn from E–W to NW–SE, where the fast azimuth are predominantly N115° oriented. This is observed for the stations located at longitudes greater than 13°E.


Slab detachment under the Eastern Alps seen by seismic anisotropy.

Qorbani E, Bianchi I, Bokelmann G - Earth Planet. Sci. Lett. (2015)

Map of average SKS splitting parameters calculated over the good quality measurements. Thick white lines represent average fast orientation (ϕ) at each station from this study and Bokelmann et al. (2013). Splitting delays (δt) are shown by the length of the line (see scale on lower left). Black lines display measurements from previous studies (Barruol et al., 2011; Kummerow and Kind, 2006), and stations located in the Southern Alps and Po-plain, marked by triangles, Salimbeni et al. (2013). For discussion see the text. (For interpretation of the colors in this figure, the reader is referred to the web version of this article.)
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4376057&req=5

fg0020: Map of average SKS splitting parameters calculated over the good quality measurements. Thick white lines represent average fast orientation (ϕ) at each station from this study and Bokelmann et al. (2013). Splitting delays (δt) are shown by the length of the line (see scale on lower left). Black lines display measurements from previous studies (Barruol et al., 2011; Kummerow and Kind, 2006), and stations located in the Southern Alps and Po-plain, marked by triangles, Salimbeni et al. (2013). For discussion see the text. (For interpretation of the colors in this figure, the reader is referred to the web version of this article.)
Mentions: The average values of splitting pairs are displayed in Fig. 2. The line's orientation presents the average fast orientation azimuth for each station and the line's length indicates the average splitting delay. The stations DAVA, FETA, RETA, WTTA, ABSI, ROSI, MOSI, and KOSI which are located in longitude range between 9°E and 12°E show fast azimuths at about N60° (azimuth from North). These azimuths are in good agreement with the results of previous studies for the Western Alps presented by Barruol et al. (2011) and the Central Alps by Kummerow and Kind (2006) (black lines in Fig. 2). The NE–SW fast orientation detected for the western stations turns gradually to nearly East–West at the stations RISI, ABTA, CLUD, and ZOU2 (located at longitudes between 12°E and 13°E). The station FVI is an exception, with a fast azimuth oriented N72°. East–West fast orientation are detected for station KBA, JAVS and CEY as well (Fig. 2). Further to the East, the fast orientations turn from E–W to NW–SE, where the fast azimuth are predominantly N115° oriented. This is observed for the stations located at longitudes greater than 13°E.

Bottom Line: We attribute the deeper layer to a detached slab from the European plate.On the other hand, the upper layer has NW-SE fast orientations coinciding with a low-velocity layer which is found above a more-or-less eastward dipping high-velocity body.The anisotropy of the upper layer shows large-scale NW-SE fast orientation, which is consistent with the presence of asthenospheric flow above the detached slab foundering into the deeper mantle.

View Article: PubMed Central - PubMed

Affiliation: Department of Meteorology and Geophysics, University of Vienna, Austria.

ABSTRACT

We analyze seismic anisotropy for the Eastern Alpine region by inspecting shear-wave splitting from SKS and SKKS phases. The Eastern Alpine region is characterized by a breakdown of the clear mountain-chain-parallel fast orientation pattern that has been previously documented for the Western Alps and for the western part of the Eastern Alps. The main interest of this paper is a more detailed analysis of the anisotropic character of the Eastern Alps, and the transition to the Carpathian-Pannonian region. SK(K)S splitting measurements reveal a rather remarkable lateral change in the anisotropy pattern from the west to the east of the Eastern Alps with a transition area at about 12°E. We also model the backazimuthal variation of the measurements by a vertical change of anisotropy. We find that the eastern part of the study area is characterized by the presence of two layers of anisotropy, where the deeper layer has characteristics similar to those of the Central Alps, in particular SW-NE fast orientations of anisotropic axes. We attribute the deeper layer to a detached slab from the European plate. Comparison with tomographic studies of the area indicates that the detached slab might possibly connect with the lithosphere that is still in place to the west of our study area, and may also connect with the slab graveyard to the East, at the depth of the upper mantle transition zone. On the other hand, the upper layer has NW-SE fast orientations coinciding with a low-velocity layer which is found above a more-or-less eastward dipping high-velocity body. The anisotropy of the upper layer shows large-scale NW-SE fast orientation, which is consistent with the presence of asthenospheric flow above the detached slab foundering into the deeper mantle.

No MeSH data available.


Related in: MedlinePlus