Geomorphology of the Doruneh Left-Lateral Strike-Slip Fault in Eastern Iran

The Doruneh left-lateral strike-slip fault is one of the longest, and most prominent active faults in Iran, stretching from the centre of the country to the Afghan border. The fault is oriented east-west, and accommodates up to 15 mm/yr of north-south right-lateral shear by vertical axis clockwise rotation. The fault shows numerous indications of cumulative left-lateral slip over a range of Quaternary time-scales. Measurements of ~26 m of left-lateral displacement in young (10-12 ka?) alluvial fan and river terrace deposits provide a slip-rate estimate of ~2.5 mm/yr. 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 a single earthquake event of unknown age. A series of small streams showing left-lateral displacements of 4 to 5.5 m record the likely magnitude of slip during this earthquake, which from scaling relationships would have had a magnitude of ~7.5, and ruptured the fault over a length of >100 km. At the estimated slip-rate of ~2.5 mm/yr, the average recurrence time between large-magnitude earthquakes on the Doruneh fault is ~2,000 years. Components of shortening are spatially separated (partitioned) onto thrusts which run parallel to the main strike-slip strand. Parts of these thrust faults have generated destructive historical earthquakes. Observations from the field and satellite imagery provide information on the structure of the folds, and examples of late Cenozoic and Holocene fault movement.