Lateral Heterogeneity Implications from 2-D Nuclear-Seismic Travel-Time Inversion

Abstract

Deep seismic soundings (DSS) from long-range recordings along profiles in northern Eurasia are used for the two-dimensional inversion and interpretation of lateral variations of the lithosphere-asthenosphere system. The major steps in developing a suitable model for travel-time inversion are shown. Modelling of nuclear-seismic data from the refraction - wide-angle reflection line QUARTZ in western Eurasia using a 2-D travel-time inversion method for layer boundaries and elastic wave velocities simultaneously, has quickly and efficiently resolved major structural differences between the East European Platform to the northwest of the Urals and the Siberian Platform to the southeast. Differences in Moho depths range between 36 Lm under the European platform in the northwest and about 50 km below the center of the Siberian basin. Subcrustal lithospheric velocities vary laterally from 7.90 km/s under the Altai - Sayan folded region, 8.21 km/s in the Siberian basin, 8.15 km/s southeast of and below the Urals mountain belt to an average apparent velocity of 8.24 km/s below the European platform. The type of boundary between the lithosphere and the asthenosphere, a sharp first order discontinuity in the northwest and transition zone in the southeast, and strong variations in the mantle transition zone depths have been resolved by minimizing the travel-time residuals for the model with a weighted least-squares algorithm. Nevertheless further modelling is needed to explain all structures of the two dimensional wavefield, as shown in an example for shotpoint 123 recorded to the south.