Morphological and palaeoseismological analysis along the Taleghan fault (Central Alborz, Iran)

Abstract

SUMMARY The Taleghan fault (TF) is a major active fault of the Central Alborz mountain range in Iran. Located 50 km northwestwards of Tehran, this 80-km-long fault represents one of the major structures threatening 15 million people living in the capital of Iran and the surrounding cities (e.g. Karaj). The TF could be the source of some of the strongest historical earthquakes recorded in the Tehran region, notably the 958 AD event (estimated magnitude M 7.7). To characterize the kinematics and activity of the fault, we carried out a detailed morphological and palaeoseismological study combining aerial photographs, digital elevation models and fieldwork. We show that, unliked described so far, the TF is not a reverse fault but a left-lateral strike-slip fault with a normal component. Its strike, dip and rake within its eastern part are 105, 60 and –20/–40, respectively. Our palaeoseismological analysis shows that a sequence of 2–3 events with magnitudes Mw ≥ 7 occurred during the past 5300 years. If we consider a three-event scenario, the average recurrence interval is ∼2000 years, and the most recent event is younger than 80 AD. If we consider a two-event scenario, the time interval between the second and the first events ranges between 3760 and 830 years, and the elapsed time since the last event ranges between 3529 and 1599 years. Combined with morphotectonics data, our palaeoseismological analysis allows estimating a minimum horizontal slip rate of 0.6–1.6 mm yr −1 and a minimum vertical slip rate of ∼0.5 mm yr −1 . Taking the ∼450-m total vertical displacement observed across the fault, we conclude that the kinematical change along the TF (from reverse to left-lateral + normal) occurred ∼ 1M a.