Active tectonics along the Khazar fault (Alborz, Iran)

The Alborz Mountain accommodates some of the convergence between Central Iran and Eurasia, ischaracterized by active range-parallel fold and thrust structures. At present, the kinematics of the rangeinvolves a strain partitioning mechanism and clockwise rotation of the South Caspian Basin. Rangeparallel,left-lateral strikeslip faulting dominates the central part of the mountain range, while reversefaulting affects its northern and southern borders. Several slip-rate studies have been carried out alongactive faults in the internal and southern parts of the range. However, the characteristics of the mainnorthern bounding fault (the Khazar [Persian: Caspian] Fault) remain poorly known. Our analysis providesnew constraints on the activity of this fault. We first show that the fault generally is a hidden thrust fault,often associated with fault-bend and fault-propagation folds (forebergs). In the central part of the fault, theradiocarbon dating of an uplifted terrace allows estimating minimum vertical and average horizontal sliprates of ۲.۰ ± ۰.۵ mm/yr and ۳ mm/yr respectively. Hence, minimum slip rate along the fault reach to ۳.۶mm/yr. About ۱۵۰ km further east, near the city of Behshahr, within the archeological site of Gohar-Tappe,a paleoseismological trench study on a young detachment fold suggests that at least ۵ events occurred inthe past ۵,۳۰۰ years, ۳ of them with surface-rupturing between ۵۳۰۰- and ۳۹۰۰-years cal BP, our resultsconfirm that the Khazar Fault is a major active structure in northern Iran, and represents a significantseismic hazard for the entire Central Alborz region.

Keywords:

Iran , Alborz , Khazar Fault Active tectonics Thrust fault Detachment fold (foreberg) Slip rate Paleoseismology