Volcanoes are among the most dynamic geological objects and their eruptions provide a dramatic manifestation of the Earth's internal activity. However, strong eruptions are only short 1

International audienceGPS (Global Positioning System) data collected in the Corinth Rift during eleven campaigns between 1990 and 2001 provide velocities of 57 points with ∼ 1.5 mmyr−1 accuracy. Peloponnesos moves at 30 mmyr−1 to the N215◦ E with respect to a fixed Europe. Extension across the rift is accommodated in a narrow band offshore. Its rate increases from east to west and is 16 mmyr−1 near Aigion. Both sides of the rift behave as clockwise rotating blocks with rates of 7 ± 0.5◦ Myr−1 and 2.8±0.8◦ Myr−1, respectively for the northern and southern blocks. After removing block rotations, the northern block shows a north–south extension rate of 120 ± 50 nstrain yr−1, whereas the southern block indicates the internal deformation is still inside the error bar (< 20 nstrain yr−1). The strain accumulation across the major faults located along the southern coast of the Corinth Gulf is less than 1 mmyr−1. This implies long recurrence periods for large earthquakes on these faults.Analyse de onze années de mesures de deformations collectées par GPS dans la zone du laboratoire du rift de corinthe.Les données GPS collectées dans le rift de Corinthe au cours de onze campagnes de mesure entre 1990 et 2001 ontpermis d’obtenir des vitesses pour 57 points, avec une incertitude de ∼ 1,5 mma−1. Le Péloponnèse se déplace avec unevitesse de 30 mma−1 en direction N215◦ E par rapport au système de référence Europe fixe. L’extension à travers le rift est accommodéedans une bande étroite en mer, dans le golfe. Le taux d’extension augmente d’est en ouest et est de 16 mman−1 prèsd’Aigion. Les deux côtés du golfe de Corinthe se comportent comme des blocs intéressés par des rotations horaires dont les tauxsont de 7 ± 0,5◦ Ma et 2,8 ± 0, 8◦ Ma−1 respectivement pour les blocs nord et sud. Après avoir retiré les rotations des blocs,le bloc nord montre une extension nord–sud de 120 ± 50 nstrain a−1, alors que le bloc sud indique que la déformation interneest encore dans la barre d’erreur (< 20 nstrain a−1). L’accumulation de la déformation à travers les failles majeures localiséesle long de la côte sud du golfe de Corinthe est inférieure à 1 mma−1. Cela implique, pour ces failles, des temps de chargementet récurrence longs (500–1000 ans) pour les séismes de magnitude 6,5 à 7 s’y produisant

International audienceWe invert Rayleigh waves reconstructed from cross-correlations of 18 months of ambient seismic noise recorded by permanent seismological stations run by the Piton de la Fournaise Volcanological Observatory. By correlating noise records between 21 receivers, we reconstruct Rayleigh waves with sufficient signal-to-noise ratio for 210 inter-station paths. We use the reconstructed waveforms to measure group velocity dispersion curves at periods between 1.5 and 4.5 s. The obtained measurements are inverted for two-dimensional group velocity maps and finally for a 3-D S-wave velocity model of the edifice from +2 to −1 km above sea level. Our results clearly show a high velocity body spatially delimited by the borders of the active 10 km wide caldera. The preferential N30°-N130° orientations of this anomaly at −0.5 km below sea-level is an evidence of the preferential paths of magma injections associated to the NE-SE Rift Zones. This structure is surrounded by a low-velocity ring interpreted as effusive products associated to the construction of the Piton de la Fournaise volcano on the flank of the older Piton des Neiges volcano