Velocity structure of upper-mantle transition zones beneath central Eurasia from seismic inversion using genetic algorithms

Abstract

We present velocity constraints for the upper-mantle transition zones beneath Central Siberia based on observations of the 1982 RIFT Deep Seismic Sounding (DSS) profile. The data consist of seismic recordings of a nuclear explosion in north-western Siberia along a 2600 km long seismic profile extending from the Yamal Peninsula to Lake Baikal. We invert seismic data from the mantle transition zones using a non-linear inversion scheme using a genetic algorithm for optimization and the WKBJ method to compute the synthetic seismograms. A statistical error analysis using a graph-binning technique was performed to provide uncertainty values in the velocity models. Our best model for the upper-mantle velocity discontinuity near 410 km depth has a two-stage velocity-gradient structure, with velocities increasing from 8.70-9.25 km s-1 over a depth range of 400-415 km, a gradient of 0.0433 s-1, and from 9.25-9.60 km s-1 over a depth range of 415-435 km, a gradient of 0.0175 s-1. This derived model is consistent with other seismological observations and mineral-physics models. The model for the velocity discontinuity near 660 km depth is simple, sharp and includes velocities increasing from 10.15 km s-1 at 655 km depth to 10.70 km s-1 at 660 km depth, a gradient of 0.055 s-1.