Crustal and uppermost mantle S-wave velocity below the East European Craton in northern Poland from the inversion of ambient-noise records

Abstract

The P-wave velocities (V p ) within the East European Craton in Poland are well known through several seismic experiments which permitted to build a high-resolution 3D model down to 60 km depth. However, these seismic data do not provide sufficient information about the S-wave velocities (V s ). For this reason, this paper presents the values of lithospheric V s and P-wave-to-S-wave velocity ratios (V p /V s ) calculated from the ambient noise recorded during 2014 at "13 BB star" seismic array (13 stations, 78 midpoints) located in northern Poland. The 3D V p model in the area of the array consists of six sedimentary layers having total thickness within 3-7 km and V p in the range 1.85.3 km/s, a three-layer crystalline crust of total thickness ~ 40 km and V p within 6.15-7.15 km/s, and the uppermost mantle, where V p is about 8.25 km/s. The V s and V p /V s values are calculated by the inversion of the surface-wave dispersion curves extracted from the noise cross correlation between all the station pairs. Due to the strong velocity differences among the layers, several modes are recognized in the 0.021 Hz frequency band: therefore, multimodal Monte Carlo inversions are applied. The calculated V s and V p /V s values in the sedimentary cover range within 0.992.66 km/s and 1.751.97 as expected. In the upper crust, the V s value (3.48 ± 0.10 km/s) is very low compared to the starting value of 3.75 ± 0.10 km/s. Consequently, the V p /V s value is very large (1.81 ± 0.03). To explain that the calculated values are compared with the ones for other old cratonic areas.

Analysis of the primary and secondary microseisms in the wavefield of the ambient noise recorded in northern Poland

“…In September, representing the transition between summer and autumn, both the faster and the slower arrivals are again detectable. The dispersion of the surface waves has been discussed in detail by Lepore et al (2018). It must be underlined that the primary microseism was not investigated by the SI because of the very low amplitudes of surface waves at frequencies lower than 0.1 Hz, especially for weak noise sources (Ardhuin et al 2012).…”

“…Consequently, the empirical Green's function (EGF) is usually retrieved from the CC traces (Stehly et al 2006;Yang and Ritzwoller 2008;Yao and van der Hilst 2009). Afterwards, surface waves can be extracted from the EGF (Halliday and Curtis 2008;Lepore et al 2016) and the group velocity of the surface-wave arrivals can be estimated (Shapiro and Campillo 2004;Lepore et al 2018). As in most situations (e.g.…”

The geophysical characteristic of the lower lithosphere and asthenosphere in the marginal zone of the East European Craton

“…• The Monte Carlo Neighborhood Algorithm (MCNA) inversion described by Sambridge (1999), Mordret et al (2014) and Lepore et al (2018) was applied to the starting Rayleigh-wave phase velocity dispersion curve. As a starting model, we chose a layered 1D profile considering the thickness, the S-wave velocity, the density and the Poisson's ratio as parameters.…”