Shear-Wave Splitting in the Alpine Region

Abstract

<p>To constrain seismic anisotropy under and around the Alps in Europe, we study SKS shear-wave splitting from the region densely covered by the AlpArray seismic network. We apply a technique based on measuring the splitting intensity, constraining well both the fast orientation and the splitting delay. 4 years of teleseismic earthquake data were processed automatically (without human intervention), from 724 temporary and permanent broadband stations of the AlpArray deployment including ocean-bottom seismometers. We have obtained an objective image of anisotropic structure in and around the Alpine region, at a spatial resolution that is unprecedented. As in earlier studies, we observe a coherent rotation of fast axes in the western part of the Alpine chain, and a region of homogeneous fast orientation in the central Alps.  The spatial variation of splitting delay times is particularly interesting. On one hand, there is a clear positive correlation with Alpine topography, suggesting that part of the seismic anisotropy (deformation) is caused by the Alpine orogeny. On the other hand, anisotropic strength around the mountain chain shows a distinct contrast between western and eastern Alps. This difference is best explained by the more active mantle flow around the Western Alps. We discuss earlier concepts of Alpine geodynamics in the light of these new observational constraints. </p>

Two subduction-related heterogeneities beneath the Eastern Alps and the Bohemian Massif imaged by high-resolution P-wave tomography

“…In this study of the broader region around the E. Alps we have applied the isotropic mode of the code. In spite of the general good agreement with the high-resolution large-scale isotropic tomography (Paffrath et al, 2021, this issue), the images can be biased due to seismic anisotropy (Eken et al, 2012;Qorbani et al, 2015Qorbani et al, , 2016Bokelmann et al, 2021). Therefore, we consider the isotropic images of the E. Alps as the first step of our study and after collecting sufficient amount and well-distributed high-quality data we will run the coupled anisotropicisotropic mode of the code (Munzarová et al, 2018) and create an anisotropic model of the region, whose fabrics will be approximated by symmetry axes generally oriented in 3D.…”

Two subduction-related heterogeneities beneath the Eastern Alps and the Bohemian Massif imaged by high-resolution P-wave tomography

“…In this study of the broader region around the Eastern Alps we have applied the isotropic mode of a coupled anisotropic-isotropic teleseismic P-wave tomography developed by Munzarová et al (2018a). In spite of the general good agreement with the high-resolution large-scale isotropic tomography (Paffrath et al, 2021, this issue), the images can be biased due to seismic anisotropy (Eken et al, 2012;Qorbani et al, 2015Qorbani et al, , 2016Bokelmann et al, 2021;Handy et al, 2021). Laterally varying anisotropy, which correlates with tectonics of the region, has been indicated in shear-wave splitting (e.g.…”