Arantza Ugalde

Intrinsic and scattering seismic wave attenuation in the Canary Islands

The Canary Islands volcanic complex is studied in terms of coda wave attenuation. A multiple lapse time window method, based on the hypothesis of multiple isotropic scattering with uniform distribution of scatterers, is applied to the available seismic data in order to obtain the intrinsic absorption (Qi−1) and the scattering attenuation (Qs−1) in the Canarian lithosphere. The analysis is performed for two hypocentral distance ranges: from 0 to 80 km and from 0 to 140 km. Results show that in both cases and for all the studied frequency bands (1–2, 2–4,6–8 and 8–10 Hz ) intrinsic absorption dominates. The low albedos found in the region indicate the low degree of heterogeneity in the Canarian lithosphere at the scale length of the studied frequencies. On the other hand the coda attenuation (Qc−1) calculated on the basis of the single-scattering theory gives values near (Qi−1) for low frequencies and near the total attenuation (Qt−1) for high frequencies. The degree of frequency dependence of the attenuation parameters is strong in all cases. A correlation of the observed attenuation parameters with the geological evidence for a hotspot-type archipelago and with other geophysical studies is suggested.

Analysis of Rayleigh Wave Ellipticity in the Iberian Peninsula and Morocco Using Ambient Noise and Teleseismic Records

/V ratios, we use more than 250 shallow (h 6.0 recorded atmore than 450 seismic stations. We also use all the multicomponent ambient noise cross correlations computed for each station pair for the time period 2010 to 2012. Periods between 20 and 100 seconds are investigated. We observe a good agreement between the uppermost geological features of the crust and the obtained Rayleigh H/V ratios, with low values in major mountain ranges and high ratios in sedimentary basins. Combination of Rayleigh H/V ratio measurements from both earthquakes and ambient noise data with phase velocities and other types of seismic data will help to better constrain the Earth’s structure at different crustal levels.