TY - JOUR A1 - Ghods, Abdolreza A1 - Shabanian, Esmaeil A1 - Bergman, Eric A1 - Faridi, Mohammad A1 - Donner, Stefanie A1 - Mortezanejad, Gholamreza A1 - Aziz-Zanjani, Asiyeh T1 - The Varzaghan-Ahar, Iran, Earthquake Doublet (M-w 6.4, 6.2): implications for the geodynamics of northwest Iran JF - Geophysical journal international N2 - On 2012 August 11, a pair of large, damaging earthquakes struck the Varzaghan-Ahar region in northwest Iran, in a region where there was no major mapped fault or any well-documented historical seismicity. To investigate the active tectonics of the source region we applied a combination of seismological methods (local aftershock network, calibrated multiple event relocation and focal mechanism studies), field observations (structural geology and geomorphological) and inversions for the regional stress field. The epicentral region is north of the North Tabriz Fault. The first main shock is characterized by right-lateral strike-slip motion on an almost E-W fault plane of about 23 km length extending from the surface to a depth of about 14 km. The second main shock occurred on an ENE-striking fault that dips at 60-70A degrees to the NW. Independent inversions of focal mechanisms and geologically determined fault kinematic data for the active stress state yield a transpressional tectonic regime with sigma(1) oriented N132E. For the region northeast of the North Tabriz Fault, the presence of rigid lithosphere of the South Caspian Basin implies the kinematic adjustment by northward transferring of the contracted masses through both distributed deformation and structural deflections. Our results suggest that the kinematic adjustment inside a contracting wedge may occur along interacting crosswise or conjugate faults to accommodate low rates of internal deformation. At a global scale, our results indicate that despite the basic assumption of 'rigid blocks' in geodetic plate modelling, internal deformation of block-like regions could control the kinematics of deformation and the level of seismic hazard within and around such regions of low deformation rate. KW - Earthquake source observations KW - Seismicity and tectonics KW - Continental neotectonics KW - Continental tectonics: compressional KW - Dynamics: seismotectonics KW - Asia Y1 - 2015 U6 - https://doi.org/10.1093/gji/ggv306 SN - 0956-540X SN - 1365-246X VL - 203 IS - 1 SP - 522 EP - 540 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Haghipour, Negar A1 - Burg, Jean-Pierre A1 - Kober, Florian A1 - Zeilinger, Gerold A1 - Ivy-Ochs, Susan A1 - Kubik, Peter W. A1 - Faridi, Mohammad T1 - Rate of crustal shortening and non-Coulomb behaviour of an active accretionary wedge - the folded fluvial terraces in Makran (SE, Iran) JF - Earth & planetary science letters N2 - We surveyed fluvial terraces to decipher the Quaternary increment of crustal shortening and shortening rate in the on-shore Makran Accretionary Wedge. We focused on three major catchment basins and associated fold systems. Terrace profiles reconstructed from differential GPS measurements combined with DEM revealed two regional dominant wavelengths, about 5 km in the northern part of the study area and about 15 km to the south. These two wavelengths suggest the existence of two active decollement layers at two rooting depths. The average shortening rate due to folding is estimated at 0.8-1.2 mm/a over the last 130 ka. This accounts for 10-15% of the shortening rate (similar to 8 mm/a) given by kinematic GPS measurements between Chabahar and Bazman and 3% of the convergence between Arabia and Eurasia, across the Makran subduction zone. Despite active deformation and a relatively high shortening rate, the geophysical record shows nearly absent seismic activity in Makran. We propose that strain accumulated in folds over intermediate decollement levels within a thick, incompletely lithified sedimentary cover explains the essentially aseismic, recent tectonics in this region. The importance of folds points to imperfect Coulomb behaviour of the wedge. (C) 2012 Elsevier B.V. All rights reserved. KW - fluvial terraces KW - Be-10 dating KW - accretionary wedge KW - shortening rate Y1 - 2012 U6 - https://doi.org/10.1016/j.epsl.2012.09.001 SN - 0012-821X VL - 355 SP - 187 EP - 198 PB - Elsevier CY - Amsterdam ER -