OBSERVATION OF CONVERTED MOHO REFLECTIONS IN THE NORTH-WEST OF THE IBERIAN PENINSULA

Converted Moho phases are observed in several seismic refraction recor ds in the northwest of the Iberian Peninsula. The converted Moho waves have amplitudes as large as subcritical PMP and SMS at some offsets. The amplitude analysis of the converted Moho waves indicates that they comprise predominantly P-to-S reflections (PMS) rather than S-to-P (S MP). Synthetic seismograms have been computed to study the influence o f different values of Poisson's ratio in the uppermost mantle on the a mplitude of converted Moho waves. The interpretation of the converted reflections leads to a Poisson's ratio of 0.27 in the uppermost mantle and a model of the crust-mantle boundary with a first-order discontin uity.