AUTHORS:

Lepore S., Polkowski M. and Grad M.

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.

International Journal of Earth Sciences, 2018, vol. 107(6), pp 2043–2062, doi: 10.1007/s00531-018-1587-9