INVESTIGATION OF TOPOGRAPHY ON THE UPPER MANTLE DISCONTINUITIES BENEATH EUROPE

We produced receiver functions using data from the GDSN stations in Europe, and western Asia. We used standard frequency domain deconvolution to process all events 5.5 and greater recorded between 1977 and 1998. These data were depth converted using moveout correction derived from the IASPI velocity model and stacked by bin (defined by backazimuth) to produce average receiver functions for different azimuths. The 410 and 660 km discontinuities produce strong Ps phases in receiver functions produced for all of these stations. The Ps-phases from 80, 210, and 720 are variable in strength (or in some cases nonexistent) among these stations. In general the midcrustal layer appears under stations based in Mountainous terrains or near subduction zones. The transition zone thickness (TZT) for stations with strong P410s and P660s phases tends to be between 250 and 285 km. The TZT appears to be thickest beneath stations in Southern Europe and Southern Asia and suggests a pattern related to the lower mantle temperatures expected in a subduction environment. The TZT in central Europe through central Asia has little topography and appears to be about 250 km. The TZT is extremely variable beneath Northern Europe but does not have a pattern that readily reflects surface tectonics.