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Basement-involved fault geometry and kinematics has a systematic effect on the structural style of the tectonic setting. In this study, 2D and 3D seismic datasets, well data as well as thickness and depth maps were utilized to consider and reconstruct the characteristics and effects of the wrench-dominated basement-involved fault underlying the Bahregansar anticline, which is a gentle, elongated and NW-SE-trending structure in the NW Persian Gulf, on the nature of its folded strata. Moreover, using the 2D sequential restoration, the deformation of the basement structural features was modelled and analysed for its influence on the reactivation of faulting. The results show that themajor basement-involved fault, called theHendijan-Bahregansar-Nowrooz Fault (HBNF), extends along the NE-SW-trending orientation and consist of several key anticlines. The structural evolution of the Bahregansar anticline has been deeply affected by Turonian folding phase and Pliocene Zagros orogeny associated with the HBNF. In the Upper Cretaceous, the HBNF propagated upward through the overlying sedimentary sequences when the inherited normal fault contractionally reactivated in the sinistral-reverse sense as the transpression zone in response to the Neo-Tethys oceanic plate subduction under the Eurasian plate. In this regard, the NNE-SSW-trending Bahregansar anticline (i.e., Arabian trend) formed as a forced fold. Continuing oblique convergence and associated deformation was accommodated by a change in the HBNF displacement sense from sinistral to dextral movement and buckling of the Bahregansar anticline as a result of the Pliocene Zagros orogeny. [ABSTRACT FROM AUTHOR]

Abstract: Concentric bracings composed of three members arranged in y-shaped geometry have been traditionally used to provide openings in braced bays. However, using common single gusset plates in y-braced frames leads to single curvature flexure and out of plane buckling of braces accompanied by low hysteretic energy dissipation. In order to explore and improve the behavior of y-braced frames, a research program including experimental tests was conducted at BHRC 1 [1] Building and Housing Research Center, Iran. structural engineering laboratory. Specimens presented in this paper include four full-scale frames with y-bracings of different geometries and cross sections. Quasi-static cyclic loading was increasingly applied until yielding and failure occurred in the specimens. The results show that out-of-plane buckling with single curvature in braces can be replaced by in-plane, double curvature buckling through appropriate detailing of cross sections and connections. These sections have larger radius of gyration for out of plane buckling of bracing members. Hysteretic energy dissipation and damping of y-bracing are increased due to inelastic flexural deformation of brace members. Energy dissipation capacity of y-braced frames with new details is comparable with the traditional X bracing. Based on these findings, two-bay y-braced frames were designed to carry the same lateral load as X-braced frames. The seismic performance of these frames was compared using nonlinear static procedures and found to be similar. [Copyright &y& Elsevier]

Mechanically induced calcite twins in veins and host rocks of Late Cretaceous to Miocene age in Iran have been used to determine regional Arabia-Eurasia collisional stresses. A late folding stress regime with a compression oriented 025° (±15°) has been identified across the Zagros belt and the southern Iranian Plateau. This late Neogene stress pattern agrees with the current stress field determined from the focal mechanisms of basement earthquakes and suggests that the Hormuz salt décollement poorly decouples the basement and cover stress fields. Our data show that the collisional state of stress has been relatively constant since ca. 5 Ma. The magnitudes of the stresses obtained from the twinning analysis are unexpectedly low, and, to a first approximation, they are constant across the Zagros simply folded belt. This result supports an overall mechanism of buckling of the detached Zagros cover. Internal viscous-plastic processes help to relieve stress within this cover, thus lowering its seismogenic potential. Beyond these regional implications, this study underlines the potential of paleostress analyses in constraining both the tectonics and the mechanics of ancient and active foreland fold belts. [ABSTRACT FROM AUTHOR]