Upper mantle structure beneath central Eurasia using a source array of nuclear explosions and waveforms at regional distances

Consistent broadband, regional, three-component P waveforms from a set of 11 explosions that occurred at the former Soviet test site in Kazakhstan during 1988 and 1989 have been observed and most of the prominent features in these waveforms are modelled to determine upper mantle structure beneath central Eurasia. It is argued that most of the prominent features in these waveforms can be explained by reflections at or refractions near discontinuities or large velocity gradients in the upper mantle. A model with discontinuities of approximately 3.0% and 6.5% near 200 km and 400 km, respectively, produces a better fit to the broadband data at ARU and GAR than previous models for this region. This model also produces a good match to waveforms recorded at OBN and NORESS, however, this model is not unique. Comparison of our results with other upper mantle studies shows that the central Eurasian upper mantle is similar to the upper mantle of the central and eastern United States. -from Authors