S U M M A R YWe investigate the depth of faulting and its connection with surface folding in the Zagros Simply Folded Belt of Iran. Our focus is a sequence of earthquakes (M w 5.7, 5.5, 5.2, 5.0, 4.9) that struck the Fin region, in the south-eastern Simply Folded Belt, on 2006 March 25. Modelling ground displacements measured with radar interferometry, we find that either N-or S-dipping model reverse faults can reproduce the observed fringe patterns. Despite the uncertainty in fault orientation, we can constrain the vertical extents of rupture to between a top depth of ∼5-6 km and a bottom depth of ∼9-10 km, consistent with the ∼8 km centroid depth of the largest earthquake. We suggest that the faulting ruptured the thick 'Competent Group' of Paleozoic and Mesozoic conglomerates and platform carbonates, which makes up the lower part of the sedimentary cover. The rupture probably terminated within the Precambrian Hormuz salt at its base, and the Cretaceous Gurpi marls at its top. These mechanically weak layers act as barriers to rupture, separating faulting within the Competent Group from deformation in the layers above and below. The pattern of coseismic surface uplift is centred on the common limb of the Fin syncline and Guniz anticline, but is oblique (by 20 • ) to the trend of these open, symmetric, 'whaleback' folds, and also overlaps a section of the Fin syncline axis. These observations suggest that locally, surface folding is decoupled from the underlying reverse faulting. Although the Fin syncline and Guniz anticline are symmetric structures, some other nearby folds show a strong asymmetry, with steep or overturned southern limbs, consistent with growth above N-dipping reverse faults. This suggests that the Simply Folded Belt contains a combination of forced folds and detachment folds. We also investigate the distribution of locally recorded aftershocks in the weeks following the main earthquakes. Most of these occurred at depths of ∼10-30 km, with a particularly high concentration of events at ∼20-25 km. These aftershocks therefore lie within the crystalline basement rather than the sedimentary cover, and are vertically separated from the main rupture. This study confirms earlier suggestions that earthquakes of M w 5-6 are capable of being generated within the thick 'Competent Group' of Paleozoic and Mesozoic sediments, as well as in the basement below the Hormuz Salt Formation.

No abstract

Emergent salt diapirs are highly mobile geological objects, kinematics of which pose essential pure and applied problems for geologists and engineers. Movement and deformation of buried salt after its ejection onto the surface is a multivariable process which is susceptible to plenty of intrinsic and ambient factors. As a result existing data acquisition approaches give extremely variable movement rates for subaerial salt extrusions. The Anguru diapir in the Zagros fold and thrust belt (ZFTB) is a typical emergent intra-anticlinal salt plug which demonstrates a very recent activity, and hence is selected to be studied for quantifying salt kinematics under relatively well-defined physical conditions. We used Interferometric Synthetic Aperture Radar (InSAR) time-series data to evaluate surface displacement over the salt dome by constructing 236 interferograms derived from 47 Envisat ASAR (time span: 2003-2010) and 12 ALOS PALSAR (time span: 2006-2010) images, which combined with other lines of evidence, suggest a very recent extrusion history. The maximum LOS (Line Of Sight) displacement rates of the diapir surface are -2.6 and +1.4 cm a-1. Modeling of the Anguru salt plug surface suggests a bilobed pattern of LOS movements which allows interpretation of the interferometric patterns observed over active upwelling (doming) or downwarping structures.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5413388