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The seismic component of Topo-Iberia: an example of a new generation of crustal seismology experiments.

AutorGallart Muset, Josep ; Diaz, J. ; Carbonell, Ramón ; Villaseñor, Antonio ; Schimmel, Martin ; TOPOIBERIA Seismic working group
Fecha de publicación5-jun-2015
ResumenWith the wide availability of broad-band sensors and dataloggers equipped with large storage capabilities, a new approach in crustal and lithospheric seismology has become possible. One of the best examples in Europe of such kind of new generation experiments is provided by the Iberarray observatory platform designed in the framework of the TopoIberia. The IberArray seismic pool was composed by 70+ BB stations, covering the study area in 3 deployments with a site-density of 60km x 60km. The data base holds ~300 sites, including the permanent networks in the area. Hence it forms a unique seismic database in Europe that allows for multiple analyses to constrain the complex geodinamics of the Western Mediterranean. The scientific explotation of this large database is still on progress, but the main results are already available and have lead to the publication of an Special Issue devoted to the Iberian Geodynamics in Tectonophysics. We will highlight here some of the results coming from different techniques.The SKS splitting analysis has provided a spectacular image of the rotation of the fast velocity direction along the Gibraltar Arc. In central and northern Iberia, the fast polarization directions are close to EW, consistently with global mantle flow models considering contributions of surface plate motion, density variations and net lithosphere rotation. Those results suggest an asthenospheric origin of the observed anisotropy related to present-day mantle flow. Receiver functions have revealed the crustal thickness variations beneath the Atlas, Rif and southern Iberia, evidencing a relevant crustal root beneath the Rif, in agreement with recent, high-density active seismic experiments. The Variscan Iberian massif shows a flat Moho discontinuity, while the areas reworked in the Alpine orogeny show a slightly thicker crust. Beneath N Iberia, the imbrication of the Iberian and Eurasian crusts results in complex receiver functions. Depths exceeding 45 km are observed along the Pyrenean range, while the crust thins to values of 26-28 km close to the Atlantic coasts. It is interesting to note that this Moho topography can be compared to the Moho map derived from active seismic profiling, as many deep profile are available on the area. The geometry of the 410-km and 660-km discontinuities has been investigated using novel cross- correlation/stacking techniques, which have revealed significant changes in the transition zone thickness which needs to be explained geodynamically. Ambient noise tomography has allowed to identify the main sedimentary basins and to discriminate between the Variscan and the Alpine reworked areas. Local body-wave tomography in North Morocco has improved the location of the small magnitude events on the area and the details of the crustal structure. Finally, teleseismic tomography has confirmed, using an independent data set, the presence of a high-velocity slab beneath the Gibraltar Arc. It is worthy to note that only the fruitfully collaboration of different research teams from Europe, Africa and North America has made possible to get those results
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