Crustal structure of the Iberian Peninsula and surrounding regions from ambient noise tomography

Abstract:

We present new high-resolution images of the crust in the Iberian Peninsula and surrounding regions using seismic ambient noise. We have compiled continuous recordings of all permanent broadband stations and temporary experiments in the region (IberArray, WILAS, PYROPE, PICASSO) from 2007 to 2014. This dataset consists of more than 400 broadband stations, although not all of them were operating simultaneously. We cross-correlate the three components these continuous recordings between all station pairs to obtain empirical Green’s functions (EFGs). From these EGFs we measure group and phase velocities of the fundamental mode Rayleigh and Love waves, and also obtain estimates of Rayleigh wave ellipticity. We then perform a 2D tomographic inversion of the dispersion measurements to obtain phase and group velocity maps of Rayleigh and Love waves for periods from 4 to 40 seconds. The short period dispersion and ellipticity maps show excellent correlation with surface features (i.e. sedimentary basins, internal zones of mountain ranges, and stable regions), while maps for longer periods are a good proxy for crustal thickness. Due to the high station density of the dataset used we are able to image the entire Iberian Peninsula with unprecedented resolution, resolving small scale structures such as the West Alboran and Lower Tagus basins, the high anomaly associated with the Ronda-Beni Bousera peridotites, etc. We also investigate the existence of azimuthal anisotropy of Rayleigh wave velocities as a function of period (i.e. depth) . Given the good correlation of the new dispersion maps with gravity anomalies, estimates of crustal thickness from receiver functions, and P-wave velocities from local earthquake tomography, our ultimate objective is to obtain an integrated model of shear-wave structure that fits all these datasets.