Surface Wave Tomography of the Alps Using Ambient‐Noise and Earthquake Phase Velocity Measurements

Abstract

A large data set of surface wave phase velocity measurements is compiled to study the structures of the crust and upper mantle underneath the Alpine continental collision zone. Records from both ambient‐noise and earthquake‐based methods are combined to obtain a high‐resolution 3‐D model of seismic shear velocity. The applied techniques allow us to image the shallow crust and sedimentary basins with a lateral resolution of about 25 km. We find that complex lateral variations in Moho depth as mapped in our model are highly compatible with those obtained from receiver function studies; this agreement with entirely independent data is a strong indication of the reliability of our results, and we infer that our model has the potential to serve as reference crustal map of shear velocity in the Alpine region. Mantle structures show nearly vertical subducting lithospheric slabs of the European and Adriatic plates. Pronounced differences between the western, central, and eastern Alps provide indications of the respective geodynamic evolution: we propose that in the southwestern and northeastern Alps, the European slab has broken off. The complex anomaly pattern in the upper mantle may be explained by combination of remnant European slab and Adriatic subduction. Along‐strike changes in the upper mantle structure are observed beneath the Apennines with an attached Adriatic slab in the northern Apennines and a slab window in the central Apennines. There is also evidence for subduction of Adriatic lithosphere to the east beneath the Pannonian Basin and the Dinarides down to a maximum depth of about 150 km.

Thermochemical Heterogeneity and Density of Continental and Oceanic Upper Mantle in the European‐North Atlantic Region

“…The Cenozoic orogens of Europe (Alps, Pyrenees, and Carpathians) are all associated with high-density LM anomalies, typically in the range 3.35-3.37 g/cm 3 (Figure 9). Regional tomography models with high-velocity bodies imaged down to 200-to 260-km depth suggest the presence of subducting slabs beneath these orogens (Hetenyi et al, 2018;Kastle et al, 2018;Lippitsch et al, 2003), and judging from the range of density values we do not expect slab eclogitization, which may occur locally where LM density increases to 3.39-3.40 g/cm 3 . Our results agree with a recent study for Pyrenees where the absence of a high-density anomaly in the upper mantle was interpreted as lack of eclogitization of the subducted Iberian crust (Dufrechou et al, 2018).…”

“…We do not use seismic tomography models to define the LAB for several reasons. (1) Tomography models that cover the entire region provide a significantly different images of the upper mantle velocity structure (Kustowski et al, ; Lu et al, ; Ritzwoller & Levshin, ; Schaeffer & Lebedev, ; Schivardi & Morelli, ; Villasenor et al, ; Weidle & Maupin, ; Yang et al, ; Zhu et al, ), with a significant discrepancy in tomography models for the Arctic region (Lebedev et al, ; Levshin et al, ) and for different parts of the continental Europe (Hejrani et al, ; Kastle et al, ; Lippitsch et al, ; Pedersen et al, ; Silvennoinen et al, ). (2) Upper mantle of, at least, some parts of the region is anisotropic (Eken et al, ; Fry et al, ; Kustowski et al, ; Pilidou et al, ; Plomerová & Babuška, ; Zhu et al, ), complicating interpretations of velocity anomalies in terms of the LAB.…”

“…We do not use seismic tomography models to define the LAB for several reasons. (1) Tomography models that cover the entire region provide a significantly different images of the upper mantle velocity structure (Kustowski et al, 2008;Lu et al, 2018;Ritzwoller & Levshin, 1998;Schaeffer & Lebedev, 2013;Schivardi & Morelli, 2009;Villasenor et al, 2001;Weidle & Maupin, 2008;Yang et al, 2007;Zhu et al, 2012), with a significant discrepancy in tomography models for the Arctic region (Lebedev et al, 2018;Levshin et al, 2007) and for different parts of the continental Europe (Hejrani et al, 2017;Kastle et al, 2018;Lippitsch et al, 2003;Pedersen et al, 2013;Silvennoinen et al, 2016).…”

Supplementary material to "Slab Break-offs in the Alpine Subduction Zone"

“…Map comparison of different tomographic models at 100 km depth. The colors show either shear-velocity deviations (Kästle et al, 2018) or compressional-velocity deviations (other models) of PREM (Dziewonski and Anderson, 1981, Figure S3. Map comparison of different tomographic models at 200 km depth.…”

Inferring Crustal Temperatures Beneath Italy From Joint Inversion of Receiver Functions and Surface Waves

“…The CROP project (Finetti, 2005) shed light on intracrustal features through deep seismic reflection. While these studies have mainly characterized the crust in terms of compressional-wave velocities, Verbeke et al (2012), Molinari et al (2015), and Kästle et al (2018) used ambient noise to obtain the shear velocity distribution at depth. Despite the abundance of data, interpretation is made difficult by uneven coverage, varying resolution, and sensitivity of each method.…”