SENSITIVITY OF SS PRECURSORS TO TOPOGRAPHY ON THE UPPER-MANTLE 660-KMDISCONTINUITY

The sensitivity of SS precursors to the presence of topography on the 660-km discontinuity is addressed using an axisymmetric finite differe nce approximation to the SH wave propagation in the Earth mantle. Nume rical experiments are lead to quantify the bias in both wavelength and amplitude committed in estimating depth information on the upper-mant le discontinuities from ray inversion of SdS arrival times. It is furt her shown that long period S660S arrival-times do not provide informat ion on the deepening of the '660' in presence of a velocity increase e xpected as the thermal signature of a subducting slab.