Crustal shear-wave velocity and Poisson's ratio distribution in northwest Spain

We have modelled shear wave data from a seismic refraction experiment in the northwest of the Iberian Peninsula to derive shear-wave velocity and Poisson's ratio models in the crust and upper mantle. The models show that the uppermost crust has high Poisson's ratios, sigma It is low, 0.21-0.24, in the middle crust and high, sigma>0.25, and increasing with depth in the lower crust. Poisson's ratio is 0.27 in the uppermost mantle. These results may be interpreted in terms of high quartz content in the rocks of the upper and middle crust and of high feldspar and low quartz content in the lower crust of NW Spain. (C) 1997 Elsevier Science Ltd.