Abstract
We present a new 3-D shear-velocity model for the top 30 km of the crust in the wider Vienna Basin region based on surface waves extracted from ambient-noise cross-correlations. We use continuous seismic records of 63 broad-band stations of the AlpArray project to retrieve interstation Green’s functions from ambient-noise cross-correlations in the period range from 5 to 25 s. From these Green’s functions, we measure Rayleigh group traveltimes, utilizing all four components of the cross-correlation tensor, which are associated with Rayleigh waves (ZZ, RR, RZ and ZR), to exploit multiple measurements per station pair. A set of selection criteria is applied to ensure that we use high-quality recordings of fundamental Rayleigh modes. We regionalize the interstation group velocities in a 5 km × 5 km grid with an average path density of ∼20 paths per cell. From the resulting group-velocity maps, we extract local 1-D dispersion curves for each cell and invert all cells independently to retrieve the crustal shear-velocity structure of the study area. The resulting model provides a previously unachieved lateral resolution of seismic velocities in the region of ∼15 km. As major features, we image the Vienna Basin and Little Hungarian Plain as low-velocity anomalies, and the Bohemian Massif with high velocities. The edges of these features are marked with prominent velocity contrasts correlated with faults, such as the Alpine Front and Vienna Basin transfer fault system. The observed structures correlate well with surface geology, gravitational anomalies and the few known crystalline basement depths from boreholes. For depths larger than those reached by boreholes, the new model allows new insight into the complex structure of the Vienna Basin and surrounding areas, including deep low-velocity zones, which we image with previously unachieved detail. This model may be used in the future to interpret the deeper structures and tectonic evolution of the wider Vienna Basin region, evaluate natural resources, model wave propagation and improve earthquake locations, among others.
Highlights
Accurate seismic velocity models improve our understanding of structures and processes in the solid Earth
The new 3-D shear-wave velocity model we present in this study correlates with several previously mentioned geological features
We will not try to interpret the tectonic evolution of the Vienna Basin, surrounding region and underlying structures in detail, and wave the new insights provided by this model to be assessed by more qualified colleagues
Summary
Accurate seismic velocity models improve our understanding of structures and processes in the solid Earth. We compute a new high-resolution crustal 3-D shear-velocity model of the wider Vienna Basin region using ambient-noise tomography This method is based on the extraction of estimated Green’s functions (GFs) from interstation cross-correlations of ambient seismic noise, which allow to create virtual sources at every passive seismic station (see Campillo & Roux (2015) for a review paper). GF retrieval from ambient-noise cross-correlations has revolutionized the use of seismic arrays for imaging and monitoring purposes at various scales and is an established technique with many proven applications (e.g. Shapiro et al 2005; Nishida et al 2009; Poli et al 2011; Lin et al 2012; Ren et al 2013; Brenguier et al 2014; Molinari et al 2015; Nakata et al 2016; Kastle et al 2018) It allows to gather information about the structure of the Earth between two seismic stations without using an active or earthquake source, as the retrieved GFs contain broad-band information about dispersive surface waves in the microseism period band (Longuet-Higgings 1950; Hasselmann 1963). The available seismic records range from 0.5 up to 2 yr in length and have been recorded between February 2015 and April 2017
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