Mantle transition zone beneath Eurasia

Mantle Pds (Fig. 1) converted phases are detected in the records of 11 seismograph stations in easternmost Russia and China. These data reveal neither a strong depression on the 660-km discontinuity nor a layer of partial melting atop the 410-km discontinuity that were found previously beneath this region in studies using long-period underside SH reflections and multiple ScS reverberations. Apparently, a significant deepening of the 660-km discontinuity occurs only if the subducted plate penetrates the discontinuity, which is not the case in the study region. Most estimates of thickness of the mantle transition zone (MTZ) in Eurasia based on the Pds data are a few kilometres larger than the standard value (250 km), and suggest that the average thickness of the MTZ beneath Eurasia is about 10 kilometres more than beneath the surrounding oceans.