Slip-rate estimate and past earthquakes on the Doruneh fault, eastern Iran

The Doruneh fault, with a length of similar to 600 km, is one of the longest, and most prominent, faults in Iran. It performs an important role in the regional tectonics, but has no record of large earthquakes. The geomorphology of the Doruneh fault contains numerous indications of cumulative left-lateral slip over various scales. We describe three sites where Late Quaternary landforms are displaced by the fault. (a) An incised alluvial fan near the village of Uch Palang is displaced by 800-850 m. (b) The Kuh-e Teagh-Ahmad fold is composed of folded Quaternary gravels and is displaced by similar to 200-400 m. (c) A sequence of three terraces of the Shesh-Taraz river are displaced left-laterally by a maximum of 25 m. Infrared stimulated luminescence (IRSL) dating of the uppermost Shesh-Taraz river terrace gives a deposition age of similar to 10 ka, which correlates with changes in global climate similar to 10-12 ka ago, and provides a provisional slip-rate estimate of 2.4 +/- 0.3 mm yr(-1). No major recent or historical earthquakes are recorded on the Doruneh fault. Relatively fresh scarps and partially infilled fractures appear to be the preserved surface ruptures from an earthquake event of unknown age. A series of small streams showing left-lateral displacements of 3 to 5.5 m (with an average slip of similar to 4.7 m) record the possible magnitude of slip during this earthquake, which from scaling relationships would have had an M-w of similar to 7.5, and ruptured the fault over a length of > 100 km. At the estimated slip-rate of similar to 2.5 mm yr(-1), the average recurrence time between large-magnitude earthquakes on the Doruneh fault is similar to 2000 yr.