A seismic cross-section through the east European continent

Abstract

S U M M A RYA 2-D pro¢le for the shear wave velocity and anisotropy between Egypt and Spitsbergen is presented. The pro¢le is constructed using fundamental-and higher-mode Love and Rayleigh waves recorded by stations of the NARS-DEEP, IRIS and GEOFON networks. The surface wave data have been inverted for shear velocity and anisotropy using a waveform inversion. In the eastern Mediterranean lithosphere we observe a large di¡erence (7 per cent) between SH and SV velocities. We interpret this anomaly as an anisotropic oceanic lithosphere beneath the eastern Mediterranean, an interpretation which is consistent with tectonic reconstructions of the region. The east European continent is imaged as a high-velocity body whose thickness increases with the estimated age of the lithosphere. The continental root of the Ukrainian and Baltic shields and east European platform extends to a depth of 200 km. This is in contrast to the surrounding younger continental regions which appear to be less than 100 km thick. We further studied the structure of the continental lithosphere by investigating a possible relation between seismic velocities and tectonic age. Both a logarithmic and a square root relation have been ¢tted to the average seismic velocities in each tectonic region. The data slightly favour a logarithmic relation but a square root relation cannot be excluded.

Shallow anisotropy in the Mediterranean mantle from surface waves

“…and inversion of Pn travel times [e.g., Hearn , 1999]. Information on polarization anisotropy is available only for the easternmost Mediterranean basin [ Muyzert et al , 1999], where up to 7% anisotropy is observed in the lithosphere, and for the Iberian Peninsula [ Maupin and Cara , 1992], where anisotropy is required only below 100 km.…”

Theory and Observations - Seismic Anisotropy

“…It is absent from some regions, for example, northern Europe (Muyzert et al, 1999). The values of x $ 1.08, corresponding to 4% difference in SH and SV velocity, are however very common below the Moho and down to at least 200 km depth (Freybourger et al, 2001;Gaherty, 2007;Marone et al, 2004;Panning and Romanowicz, 2006) (see Figure 19 for some examples).…”

The anisotropic seismic structure of the East European platform

“…Similarly both the Australian and Kaapvaal cratons were found to have a uniform 4–5% shear anisotropy in the lid extending to 250 km depth with a sharp transition to an isotropic mantle regime below that [ Gaherty et al , 1999; Simons et al , 1999; Jordan et al , 1999]. Significantly, however, the results of the NARS profile through the east European continent identified large shear anisotropy (7%) beneath the Mediterranean, but no clear pattern in shear anisotropy beneath the EEP [ Muyzert et al , 1999]. …”

“… Marquering and Snieder [1996] found a relatively laterally homogenous, fast S wave velocity structure beneath the platform extending to 300 km depth. This is also apparent in the 2‐D profile from the NARS experiment which shows a sharp transition in the thickness of the lithospheric root between the EEP (200 km) and younger continental regions (100 km) [ Muyzert et al , 1999; Paulssen et al , 1999]. …”

“…This study focuses on the seismic structure of the East European platform, a Precambrian age structure that comprises most of Russia west of the Urals (Figure 2) that has remained relatively undeformed since 1.6 Ga. [ Glebovitsky , 1997; Zonenshain et al , 1990]. This area has been studied in part by several groups [ Marquering and Snieder , 1996; Zielhuis and Nolet , 1994; Vinnik and Ryaboy , 1981; Ryberg et al , 1995; Paulssen et al , 1999; Muyzert et al , 1999]. P wave structure appears particularly heterogeneous in the upper 100 km.…”