Stéphane Baize

Large‐scale inflation of Tungurahua volcano (Ecuador) revealed by Persistent Scatterers SAR interferometry

The Tungurahua volcano, in Ecuador, has been experiencing a substantial activity period since 1999, with several eruptions, including those of 2006 and 2008. We use a persistent scatterers approach to analyze a time series of Envisat synthetic aperture radar (SAR) data over the period 2003–2009, to investigate surface deformation in the region of the volcano. We measure a continuous large-scale uplift with a maximum line of sight displacement rate of about 8 mm/yr, which is the first evidence of a sustained inflation in the Andes for an active volcano encompassing several eruptions. We model this signal as magma emplacement in a permanent storage zone at 11.5 km below sea level, with a net inflow rate of 7 million m3/yr. The paroxysmal eruptions in 2006 and 2008 did not seem to disrupt this long-term signal. However, we observe significant deformation during the 2006 eruption consistent with an additional intrusion of 4.5 million m3 of magma.

Probing large intraplate earthquakes at the west flank of the Andes

Estimating the potential for the occurrence of large earthquakes on slow-slip-rate faults in continental interiors, away from plate boundaries, is possible only if the long-term geological record of past events is available. However, our knowledge of strong earthquakes appears to be incomplete for thrust faults flanking large actively growing mountain ranges, such as those surrounding Tibet and the Andes Mountains. We present a paleoseismic study of a prominent fault scarp at the west flank of the Andes in Santiago, Chile. The evidence demonstrates recur rent faulting with displacement of ~5 m in each event. With two large earthquake ruptures within the past 17–19 k.y., and the last event occurring ~8 k.y. ago, the fault appears to be ripe for another large earthquake (moment magnitude, M w 7.5). These results emphasize the potential danger of intraplate continental faults, particularly those associated with youthful mountain fronts.

Present-day vertical isostatic readjustment of the Western Alps revealed by numerical modelling and geodetic and seismotectonic data

Abstract The active tectonics of the Western Alps reveals contrasting regimes: ongoing extension at the heart of the chain and transpression–compression at its external sectors. The active processes currently affecting this region are still a matter of debate. The classical models proposed in the literature invoke: Eurasia–Adria plate collision, counterclockwise motion of the Adria microplate, slab retreat of the subducted continental lithosphere and slab-detachment. More recently, several authors prefer the hypothesis of tectonics driven by isostasy–buoyancy forces. To better understand the influence of these processes on the velocity, strain and stress fields at the surface and in the crust, we developed 2D viscoelastic numerical models along a vertical cross-section perpendicular to the Western Alps. We run our models with different driving forces in order to investigate, one by one, the geodynamic processes proposed in the literature. Results are compared with available geodetic, geological and seismotectonic data. In order to bring into coincidence model predictions and observations, an important vertical isostatic readjustment must be included in the modelling, together with a slight horizontal compression (0.5 mm year−1), probably due to Africa–Eurasia convergence. We show that the subduction process in this Alpine region is likely to be dead and that buoyancy forces may be dominating the present-day tectonics.

Characterization of potentially active faults in the southern Upper Rhine Graben using GPR

The Upper Rhine Graben (URG) is one of the tectonically most active regions in Europe. It is delimited by faults to both sites, which are supposed to be active especially at the eastern side. This area includes a series of critical facilities, e.g. the nuclear power plant Fessenheim, located in direct vicinity of active faults. For risk assessment, the long-term deformation rate within the eastern border fault system is an important parameter. However, no recent neotectonic studies exist for that area. To fill this gap, a geophysical survey with GPR and ERT was conducted with the goal of finding an appropriate trenching site for a detailed paleoseismic study. The results presented here from the southern part of the URG suggest that the Rhine River fault has indeed been active in relatively recent times.