SHEAR-WAVE VELOCITY STRUCTURE BELOW THE IBERIAN PENINSULA AS OBTAINED BY A DETAILED ANALYSIS OF SURFACE-WAVES

A tentative tomography of lberia based on broadband surface wave data is performed for the first time. In this paper we have complemented a previous study of the northern half of the lberian Peninsula with a study of the southern half of the peninsula based on a detailed analysis of Rayleigh wave dispersion. Now we present the first shear velocity contour maps at different subcrustal depths. Quality digital records provided by the NARS array have been used. Standard techniques, as multiple filtering and time-variable filtering, are employed to efficiently remove higher mode interference and improve isolation of the fundamental mode Rayleigh wave from the seismograms, and thus to calculate the interstation Rayleigh wave group velocity. Frequency-domain Wiener deconvolution is used to determine the interstation phase velocity. We perform simultaneous inversion of phase and group velocity dispersion data by means of the stochastic inverse operator. The inversion results previously reported for the northern Iberian region together with the results obtained here are used for 3-D mapping of shear wave velocity over the Iberian Peninsula. Lateral variation in velocity at five depth intervals chosen in agreement with the theoretical earth models determined by joint inversion, is displayed for the lithosphere and asthenosphere of lberia.