P wave anisotropic tomography of the Alps

Abstract

The first tomographic images of P wave azimuthal and radial anisotropies in the crust and upper mantle beneath the Alps are determined by joint inversions of arrival time data of local earthquakes and teleseismic events. Our results show the south dipping European plate with a high‐velocity (high‐V) anomaly beneath the western central Alps and the north dipping Adriatic plate with a high‐V anomaly beneath the Eastern Alps, indicating that the subduction polarity changes along the strike of the Alps. The P wave azimuthal anisotropy is characterized by mountain chain‐parallel fast‐velocity directions (FVDs) in the western central Alps and NE‐SW FVDs in the Eastern Alps, which may be caused by mantle flow induced by the slab subductions. Our results reveal a negative radial anisotropy (i.e., Vph < Vpv) within the subducting slabs and a positive radial anisotropy (i.e., Vph > Vpv) in the low‐velocity mantle wedge, which may reflect the subvertical plate subduction and its induced mantle flow. The results of anisotropic tomography provide important new information on the complex mantle structure and dynamics of the Alps and adjacent regions.

Aseismic Deep Slab and Mantle Flow Beneath Alaska: Insight From Anisotropic Tomography

“…This feature is apparently different from the result in Japan that the subducting Pacific and Philippine Sea slabs exhibit a positive RAN (Vph > Vpv; Liu & Zhao, 2017;J. Wang & Zhao, 2013), but it is in good agreement with the Vp RAN model of Hua et al (2017) that shows a negative RAN in the subducting European and Adriatic slabs beneath the Alps. Hua et al (2017) suggested that the discrepancy in the dip angle of the subducting slabs beneath the Alps and Japan leads to the RAN difference in the slabs, because the Pacific and Philippine Sea slabs beneath Japan are subducting with a lower angle whereas the European and Adriatic slabs under the Alps have a nearly vertical angle.…”

Slab Break-offs in the Alpine Subduction Zone

“…Using the tomographic models kindly provided by their authors (Piromallo and Morelli, 2003;Lippitsch et al, 2003;Koulakov et al, 2009;Dando et al, 2011;Mitterbauer et al, 2011;Zhao et al, 2016;Hua et al, 2017), we define 4 section traces and 2016) is one of the most recent ones and was the first to propose continuous slabs all along the Alpine arc. These models also illustrate the differences between different data sets and methods (Table 1).…”

Supplementary material to &quot;Slab Break-offs in the Alpine Subduction Zone&quot;

“…Anomaly variations in vertical direction are not interpreted by the authors. The images by Hua et al (2017) show a significantly weakened anomaly in the upper 200 km. A slab window between 100-200 km is also indicated in the model of Piromallo and Morelli (2003).…”

“…∼ 250 km (Lippitsch et al, 2003) > 400 km (Koulakov et al, 2009) > 400 km (Dando et al, 2011) > 400 km (Mitterbauer et al, 2011) > 400 km (Zhao et al, 2016) > 400 km (Hua et al, 2017) (discontinuous) Slab dip All body-wave tomographic models show a vertical to subvertical, slightly northward dipping slab between 12 • and 14 • longitude, if the entire slab is taken into account (Lippitsch et al, 2003;Koulakov et al, 2009;Dando et al, 2011;Mitterbauer et al, 2011;Zhao et al, 2016;Hua et al, 2017). E-W slab continuity All models show a gap or discontinuity (northward step) between central and eastern Alpine anomalies (Piromallo and Morelli, 2003;Lippitsch et al, 2003;Koulakov et al, 2009;Mitterbauer et al, 2011;Zhao et al, 2016;Hua et al, 2017). Vertical slab continuity Lippitsch et al (2003) show a slab that is continuous from the lithosphere down to 250 km depth.…”

“…All models that cover areas east of 14 • E indicate that the slab anomaly weakens and then disappears in the upper 250 km (? Koulakov et al, 2009;Dando et al, 2011;Mitterbauer et al, 2011;Zhao et al, 2016;Hua et al, 2017). N-S shortening Total of 190 km, mostly in the southern Alps minimum 55 -75 km in the southern Alps minimum 50 km in the southern Alps (Schönborn, 1999;Nussbaum, 2000)…”