Three-dimensional shear velocity structure of the Mauléon and Arzacq Basins (Western Pyrenees)

We present a 3-D shear wave velocity model of the Mauléon and Arzacq Basins from the surface down to 10 km depth, inverted from phase velocity maps at periods between 2 and 9 s. These phase velocity maps were obtained by analyzing coherent surface wave fronts extracted from ambient seismic noise recorded by the large-N Maupasacq seismic array with a matched filtering approach. This new model is in good agreement with a local earthquake tomography study performed on the same acquisition dataset. Our passive imaging models reveal the upper crustal architecture of the Mauléon and Arzacq Basins, with new details on the basement and its relationship with the overlying sedimentary cover. Combining these new tomographic images with surface and subsurface geological information allows us to trace major orogenic structures from the surface down to the basement. In the basin, the models image the first-order basin architecture with a kilometric resolution. At depth, high velocity anomalies suggest the presence of dense deep crustal and mantle rocks in the hanging wall of north-vergent Pyrenean Thrusts. These high velocity anomalies spatially coincide with a positive gravity anomaly in the western Mauléon Basin. In addition, our models reveal major changes from the Chaînons Béarnais to the western Mauléon Basin across a set of orogen-perpendicular structures, the Saison and the Barlanès transfer zones. These changes reflect the along-strike variation of the orogenic evolution that led to the preservation of the former rifted domain and its underlying mantle in the orogenic wedge of the Western Pyrenees. We discuss the implications of these results for the 3-D architecture of the Mauléon Basin and its underlying basement. Nous présentons un modèle 3-D de vitesse des ondes de cisaillement des bassins de Mauléon et d’Arzacq de la surface jusqu’à 10 km de profondeur inversé à partir de cartes de vitesse de phase pour des périodes entre 2 et 9 s. Ces cartes ont été obtenues à partir de l’analyse de fronts d’onde de surface cohérents extraits du bruit sismique ambiant enregistré par le réseau Maupasacq par filtrage adaptatif. Ce nouveau modèle est en bon accord avec la tomographie locale réalisée sur ce même jeu de données. Nos nouvelles images tomographiques révèlent l’architecture supra-crustale des bassins de Mauléon et d’Arzacq, avec des informations nouvelles sur la nature du socle et sa relation à la couverture sédimentaire. En combinant ces nouvelles images tomograp