Revisiting the dip-slip rate of the North Tehran Fault (Northern Iran) through studying the faulted materials and geomorphic markers

Abstract

The North Tehran Fault (NTF), located south of the Central Alborz Mountains, crosses north of the megacity of Tehran. The NTF is the principal active fault in Tehran, playing an essential role in the risk potential for the near ten million inhabitants of the capital city. Despite this risk, our knowledge about its slip rate is limited to two contradictory quantifications for the western segment of the fault. Slip rates remain unquantified towards the north and east, where it forms a transpressional duplex structure with the Mosha Fault. In this study, we combine detailed fieldwork on the previously documented outcrops of the NTF, including faulted colluvial and alluvial units in the west and uplifted remnants of the pediment surface in the east of the fault. We present new luminescence ages to temporally constrain the fault activity in the Middle-Late Pleistocene in selected sites. Our study in the western NTF reports a cumulative dip-slip rate of 0.56 ± 0.04 mm a⁻¹ for the Kan area and a minimum slip rate of 0.28 ± 0.02 mm a⁻¹ for the Hesarak area outcrops. On the hanging wall of the eastern NTF, a dated pediment surface has risen 579 m relative to the present base level of the Kond River in the footwall. Our analyses suggest that 299 m of such differential movement is thrust-related uplift, which indicates an uplift rate of 1.00 ± 0.12 mm a⁻¹. The dip-slip and shortening rates for the NTF at the Latyan Basin amounts to 1.39 ± 0.17 mm a⁻¹ and 0.97 ± 0.12 mm a⁻¹, respectively.