Imaging the Eastern European lithosphere with ambient seismic noise

The Eastern European lithosphere is a natural laboratory to study continental formation and evolution through time. It comprises a mosaic of Archean continental remnants separated by Proterozoic rifts and belts, and younger accreted terranes to the west. The transition is marked by the Trans European Suture Zone, a continental-scale geological boundary extending from the Baltic to the Black Sea and disappearing beneath the Carpathians. To investigate the transition from Precambrian to Phanerozoic Europe and the seismic structure of the East European craton, we use ambient noise data recorded at all available broadband seismic stations that were operational in Eastern Europe and surrounding areas, between 1999 and 2020. We preprocess the data with a novel de-signaling method to eliminate high amplitude transient signals from the noise trace, using the continuous wavelet transform. We then cross-correlate hourly segments and stack them, and obtain phase velocities at discrete frequencies via an automated phase velocity picker in the frequency domain, assuming the cross-correlation can be described by a Bessel function. We then invert inter-station dispersion curves for isotropic and anisotropic phase velocity anomalies across the region, obtaining the highest-resolution anisotropic tomographic model of the Eastern European lithosphere to date. The model shows excellent correlation between known sedimentary basins and isotropic phase velocities at lower frequencies and more complex heterogeneity and layered anisotropy at deeper levels of the crust and upper mantle. Our results have fundamental implications for understanding the structure of the crust at a time when subduction processes were probably nascent or not yet operational.