Improvements in the knowledge of the anelastic structure of the Iberian Peninsula from seismic data of the ILIHA project

Abstract

Attenuation coefficients of Rayleigh waves propagating across the Iberian Peninsula, and quality factor models were obtained for different two-station great-circle paths. The data used were long-period wave trains contained in the seismograms provided by the ILIHA array installed in the peninsula in the 1980s. More than 300 seismograms were analysed to obtain 14 sets of similar paths, consisting of either paths totally included in one of the four pure tectonic regions or mixed paths crossing several regions. We used the two-station method to determine attenuation parameters (γR) and then an inversion method to derive Qβ-1 models. The attenuation coefficients of seismic energy in the 10-120 s range are in the range 2.8 × 10-3-0.1 × 10-3 km-1, and correlate well with both previous results obtained from analogue WWSSN and most seismogeotectonic characteristics of Iberia. The Qβ models obtained also agree with a few models for Iberia determined earlier, and they show significant variations from one region to another. As a general feature, the γ-values are higher in the active seismotectonic regions (typical maximum of 2.6 × 10-3 km-1) than in the more stable ones (typical maximum of 1.4 × 10-3). Moreover, the maximum of Qβ-1 in the active regions (145× 10-3-120 × 10-3) is higher than in the stable ones (40 × 10-3-100 × 10-3). In general, both the regionalized attenuation coefficients of Rayleigh waves and the quality factor models exhibit a good agreement with previously published Lg wave attenuation and coda Q distribution patterns in Iberia.