Re-visiting the dip-slip rate of the North Tehran Fault at the northern megacity of Tehran (Iran) using luminescence dating 

Abstract

The North Tehran Fault (NTF) is the most active tectonic structure crossing the northern fringe of the densely populated megacity of Tehran (Iran). It extends over 68 km and juxtaposes the southern piedmonts of the Central Alborz Mountains (volcanic rocks associated with the Karaj Formation) from the Neogene-Quaternary Tehran Alluvium. The NTF is an oblique-slip fault in which the left-lateral strike-slip faulting accompanies the dominant reverse motion. The geomorphic features affected by the NTF’s activity appear to be limited and concealed during the past few decades due to the rapid northward expansion of the Tehran metropolitan area. Nevertheless, numerous evident fault outcrops, displaying stratigraphic offsets in various locations along the megacity, are still accessible. This study selects two fault outcrops inside the city in the western segment of the NTF and a third one in the eastern termination of the NTF close to its junction with the Mosha Fault. These sites were already studied in previous works, however, no reliable geochronological data have been available so far for them. In the first two western sites, the Eocene Karaj Formation rocks were thrust over Quaternary alluvial-colluvial deposits. The subsidiary fault is almost parallel to the main NTF in the second site at Kan, which separates the old alluvial-colluvial deposits in the hanging wall from the younger deposits in the footwall. The third site is located close to the termination of the NTF in the Kond region. Here, remnants of Quaternary fluvial terraces are uplifted by the NTF and form elevated landforms identified in its hanging wall. To estimate the dip-slip rate for the NTF, we applied luminescence dating to the alluvial-colluvial deposits and fluvial terraces to constrain the deposition time. By incorporating the measured vertical offset for each site, the dip-slip rates of the NTF were established at different locations.