A syn-eruptive ground deformation episode measured by GPS,during the 2001 eruption on the upper southern flank of Mt Etna

Ground deformation occurring on the southern flank of Mt Etna volcano during the July–August 2001 eruption was monitored by GPS measurements along an E–W profile crossing the fissure system. This profile was measured eight times during the eruption, using the 'stop and go' semi-kinematic technique. Horizontal and vertical displacements between GPS surveys are reported for each station. The most significant event is a deformation episode occurring during the first week of the eruption, between 25–27 July. Displacements were measured on benchmarks close to the eruptive fissure and the tensile 1989 fracture. Data inversions for measured displacements were performed using the Okada model. The model shows the narrowing of the 2001 dyke accompanied by a dextral dislocation along an east-dipping fault, parallel to the 1989 fracture.Editorial responsibility: T. Druitt     

Strain and stress fields along the Gibraltar Orogenic Arc: Constraints on active geodynamics

The Gibraltar Orogenic Arc, in the Western Mediterranean, represents a complex region of active deformation related to the oblique Nubia–Eurasia convergence process. To increase the knowledge on the ongoing active processes in this region, we have used the most up-to-date and comprehensive geodetic crustal motion and stress fields. To this end, we analyzed both continuous and campaign-mode GPS data collected between 1999.00 and 2011.00 across the area and compiled a multidisciplinary dataset of well-constrained stress indicators to be compared with the geodetic results. The main results highlight the oblique nature of the Nubia–Eurasia convergence, which provides the largest component of the observed stress-pattern and is responsible for a significant strain-rate field along the Gibraltar Orogenic Arc. We discuss our findings with respect to available geological, seismological and geophysical data in order to verify their coherency compared to more relevant geodynamical models proposed in literature. According to previous studies, we confirmed how much of the secondary stress-pattern can be related to the gravitational potential energy field, which may also be responsible for some 2D stress–strain-rate angular discrepancies observed in large areas of the Betics. In addition, taking into account the sub-orthogonal azimuthal relationship between the S_Hmax and ε_hmin directions and the Fast Polarization Directions, we conjectured a deep dynamic process controlling both the crustal stress field and the surface deformation on large areas of the orogenic arc. Finally, although the models proposed to explain the geodynamic pattern of the Gibraltar Orogenic Arc are supported by a discrete number of geological and geophysical observations, it is only the back-arc extension and westward rollback model that is able to adequately account for the vast majority of the observations. Based on our findings and other evidences, we retain that this process could still be active beneath the Gibraltar Orogenic Arc.