High-resolution surface wave tomography of the European crust and uppermost mantle from ambient seismic noise

Abstract

Taking advantage of the large number of seismic stations installed in Europe, in particular in the greater Alpine region with the AlpArray experiment, we derive a new high-resolution 3-D shear wave velocity model of the European crust and uppermost mantle from ambientnoise tomography. The correlation of up to 4 yr of continuous vertical-component seismic recordings from 1293 broad-band stations (10 • W-35 • E, 30 • N-75 • N) provides Rayleigh wave group velocity dispersion data in the period band 5-150 s at more than 0.8 million virtual source-receiver pairs. 2-D Rayleigh wave group velocity maps are estimated using adaptive parametrization to accommodate the strong heterogeneity of path coverage. A probabilistic 3-D shear wave velocity model, including probability densities for the depth of layer boundaries and S-wave velocity values, is obtained by nonlinear Bayesian inversion. A weighted average of the probabilistic model is then used as starting model for the linear inversion step, providing the final V s model. The resulting S-wave velocity model and Moho depth are validated by comparison with previous geophysical studies. Although surface wave tomography is weakly sensitive to layer boundaries, vertical cross-sections through our V s model and the associated probability of the presence of interfaces display striking similarities with reference controlledsource seismology (CSS) and receiver function sections across the Alpine belt. Our model even provides new structural information such as an ∼8 km Moho jump along the CSS ECORS-CROP profile that was not imaged by the reflection data due to poor penetration across a heterogeneous upper crust. Our probabilistic and final shear wave velocity models have the potential to become new reference models of the European crust, both for crustal structure probing and geophysical studies including waveform modelling or full-waveform inversion.

Crustal and uppermost mantle shear wave velocity structure beneath the Middle East from surface wave tomography

“…Our algorithm is based on that of Boschi and Dziewonski (1999). The inversion algorithm is discussed in detail by Lu et al (2018). As shown by the examples in Supplementary Figure S3, we are dealing with heterogeneous ray coverage across the study area.…”

“…As shown by the examples in Supplementary Figure S3, we are dealing with heterogeneous ray coverage across the study area. Following previous studies (Schaefer et al, 2011;Auer et al, 2014;and Lu et al, 2018) we employed the adaptive-cell version of Boschi and Dziewonski's (1999) algorithm. In this approach, the cell size in each part of the model space is adjusted according to the ray density.…”

“…We adopted a modified version of the algorithm of Lu et al (2018) to invert group-velocity dispersion data for depth-dependent models of shear-wave speed (Vs), by extracting dispersion curves at 0.25° intervals from the group-velocity maps ( Figure 3). As shown by the resolution tests (Supplementary Figure S5), resolution is best at 18 s period.…”

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

“…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).…”