Tesis doctoral: Estudio de la estructura y propiedades anisotropas de la litosfera subcortical del macizo Ibérico a partir de datos sísmicos de ondas p y s

JORDI DIAZ I CUISI

Abstract


A first insight to the structure of the lithosphere beneath Iberia has been provided by a P-wave travel time residual study, carried in the center of the peninsula. Both teleseismic and regional events have been studied, showing significant variations in the relative travel time residual~b etween the stations of the array. This fact has heen interpreted as an evidence of the presence of crustal heterogeneities beneath Central Iberia at short wavelength intervals. Data from the Iberian LIthospheric Heterogeneity and Anisotropy (ILIHA) deep seismic sounding experiment have been used to study the seismic structure of the lower lithosphere beneath the Ossa-Morena zone (SW Iberia). The interpretation of the mantle phases observed in the record sections evidences a layered lower lithosphere, witb alternating high and low velocity zones. Two to three main reflectors are observed in the uppermost mantle, between 30 and 90km depth. One reversed line and two intersecting unreversed lines define an area beneath SW Iberia wbere the same lithospheric reflectors segments are sampled along different azimuths. The independent analysis of the lines has shown evidences of azimuthal P-velocity anisotropy. We have inferred a model with at least two anisotropic zones in the lower lithosphere, with a roughly NNEISSW fast velocity direction A passive seismic experiment has been carried over the same SW area of Iberia to investigate the presence of anisotropy using independent  techniques and data sets. We have used a classical cross-correlation method to interpret the splitting of shear waves as the result of their propagation through anisotropic structures. Main parameters which define the characteristics of the anisotropy pattern, such as fast velocity direction and degree of anisotropy, are recovered for each event studied. The analysis of SKS and S phases shows evidence of the presence of anisotropy. The results from the different events depict a rather consistent anisotropic structure, with a rough NEISW to EN fast velocity direction. The different hypothesis suggested to explain the origin of the continental mantle anisotropy are discussed and related to tbe anisotropic pattern derived from the two data sets (DSS crossing profiies and shear wave splitting)

 


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