Architecture and development of (Pliocene to Holocene) faults and fissures in the East Volcanic Zone of Iceland

In Southeast Iceland, comparison between the deeply eroded off-rift and flank zones, on the one hand, and the active rift zone, on the other hand, allows us to characterize the geometry and mechanisms of faulting and fracturing since the Upper Pliocene to Holocene. We used different approaches based on the inversion of fault-slip data and of focal mechanisms of earthquakes, as well as on study of aerial photographs by means of photogrammetry. Our study reveals that about half of the past and current stress states are strike-slip whereas surface deformations are large normal faults and extensional fractures. The parallelism between the directions of extension (σ3) in both extensional and strike-slip regimes, implies a σ1/σ2 stress permutations probably due to uniaxial extensional stress (σ1 = σ2 > σ3) and fluid overpressure. In detail, the deviation of σ3 trajectories, probably relates to the presence of central volcanoes, which may locally induce perturbations of the general stress field.