Abstract.Between 1990 tectonic observations shows that these two earthquakes occurred on low-angle (_< 35 ø) north dipping normal faults located between 4.5 and 10 km depth in the inner part of the rift. Assuming that the deformation is concentrated in relatively narrow deforming zones, we use a simple model of a dislocation in an elastic half-space to study the implication of the localization. Using the geometry of the known seismogenic faults, our observations imply continuous aseismic deformation in the uppermost crust of the inner rift. This model predicts geodetic strain rates close to seismic strain rates in opposition to previous estimates. This is because our model takes into account the activity on low-angle normal faults in the inner rift and an effective seismogenic layer of 6-7 kin, about half that usually assumed.

International audienceA 66-station GPS network spanning central Greece, first observed in 1989, has been occupied fully on three occasions: June 1989, October 1991 and May 1993. Subsets of this network bounding the Gulf of Korinthos have also been occupied in June 1995, October 1995, May 1996 and September/October 1997. The first three occupations were processed using a fiducial GPS methodology, whereas later surveys were processed using CODE precise orbits. Combination of data from different surveys to yield smooth site velocities requires global network translations at each epoch to compensate for errors in the realization of the reference frame. This method provides a posteriori estimates of the relative coordinate errors and reference frame noise. Only one earthquake, the 1995 June 15 Egion event, has caused significant local coseismic displacement, and its effects on the interseismic velocity field are removed using an elastic dislocation model.We constrain the orientation of the 100 yr triangulation–GPS velocity estimates of Davies et al. (1997) using 14 sites common to the two networks. The goodness of fit of this transformation indicates that the short-term and 100 yr geodetic estimates of deformation are highly compatible. We infer that short-term geodetic studies are capable of determining longer-term deformation rates provided that transient, local effects can be modelled. From the combined velocity field, we estimate principal strains and rigid-body rotation rates at points on a regular grid using data from neighbouring sites. Strain rates are high within the Gulf of Korinthos and much lower elsewhere. The extension rate across the Gulf of Korinthos increases from east to west. Comparison of the extension rate with historical and recent rates of seismic release of strain reveals significant medium-term seismic hazard in the western Gulf of Korinthos, and may also indicate long-term aseismic strain.

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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

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[1] A new set of geodetic velocities for Greece and the Aegean, derived from 254 surveymode and continuous GPS sites, is used to test kinematic and dynamic models for this area of rapid continental deformation. Modeling the kinematics of the Aegean by the rotation of a small number (3-6) of blocks produces RMS misfits of ∼5 mm yr −1 in the southern Aegean and western Peloponnese, indicating significant internal strain within these postulated blocks. It is possible to fit the observed velocities to within 2-3 mm yr −1 (RMS) by models that contain 10 or more blocks, but many such models can be found, with widely varying arrangements of blocks, that fit the data equally well provided that the horizontal dimension of those blocks is not larger than 100-200 km. A continuous field of velocity calculated from the GPS velocities by assuming that strain rates are homogeneous on the scale of ∼120 km fits the observed velocities to better than 2-3 mm yr −1 (RMS), with systematic misfits, representing more localized strain, confined to a region approximately 100 × 100 km in size around the western Gulf of Corinth. This velocity field accounts for the major active tectonic features of Greece and the Aegean, including the widespread north-south extensional deformation and the distributed strike-slip deformation in the NE Aegean and western Greece. The T axes of earthquakes are aligned with the principal axes of elongation in the geodetic field, major active normal fault systems are perpendicular to those axes, and ∼90% of the large earthquakes in this region during the past 120 years took place within the areas in which the geodetic strain rate exceeds 30 nanostrain yr −1 . These observations suggest that the faulting within the upper crust of the Aegean region is driven by forces that are coherent over a scale that is significantly greater than 100 km. It is likely that those forces arise primarily from differences in gravitational potential energy within the lithosphere of the region. Citation: Floyd, M. A., et al. (2010), A new velocity field for Greece: Implications for the kinematics and dynamics of the Aegean,

[1] We measure ground motion around the Lake Mead, Nevada, using synthetic aperture radar interferometry. The lake water level has fluctuated through time since impoundment in 1935. To quantify the deformation due to water level variations over the past decade, and to constrain the crust and mantle rheological parameters in the lake area, we analyze 241 interferograms based on 43 ERS images acquired between 1992 and 2002. All interferograms have a high coherence due to arid conditions. Most of them show strong atmospheric artefacts. Tropospheric phase delays are estimated and corrected for each interferogram by analyzing the phase/elevation correlation. Corrections are validated using data from the ERA40 global atmospheric reanalysis. Corrected interferograms are inverted pixel by pixel to solve for the time series of ground motion in the lake area. Temporal smoothing is added to reduce random atmospheric artefacts. The observed deformation is nonlinear in time and spreads over a 50 Â 50 km 2 area. We observe a 16 mm subsidence between 1995 and 1998 due to an 11 m water level increase, followed by an uplift due to the water level drop after 2000. We model the deformation, taking into account the loading history of the lake since 1935. A simple elastic model with parameters constrained by seismic wave velocities does not explain the amplitude of the observed motion. The two-layer viscoelastic model proposed by Kaufmann and Amelung (2000), with a mantle viscosity of 10 18 Pa s, adjusts well the data amplitude and its spatiotemporal shape.Citation: Cavalié, O., M.-P. Doin, C. Lasserre, and P. Briole (2007), Ground motion measurement in the Lake Mead area, Nevada, by differential synthetic aperture radar interferometry time series analysis: Probing the lithosphere rheological structure, J. Geophys.