Holocene slip-rate on the Sabzevar thrust fault, NE Iran, determined using optically stimulated luminescence (OSL)

Fault slip-rates and the recurrence interval between earthquakes can be determined from reliable dating of deformed sediments. We report optically stimulated luminescence (OSL) ages of alluvial gravels, fine-grained sediments and colluvial deposits associated with the Sabzevar thrust fault in northeastern Iran. Six samples of the late Quaternary deposits were dated by OSL using the single aliquot regenerative-dose (SAR) protocol. The OSL ages indicate deposition of alluvial gravels in the study region between ∼ 30 and ∼ 9-13 ka, followed by a period of fluvial incision which is ongoing at the present day. The alluvial deposits have been uplifted by ∼ 9.5 m relative to the river level, indicating a Holocene slip-rate of ∼ 1 mm/yr and a rate of convergence across the fault of 0.4-0.6 mm/yr assuming a maximum fault dip of 60°. The average interval between large earthquakes on the Sabzevar fault will be ∼ 3000 years if the fault dips ∼ 60°, and less if the fault dip is less. The last earthquake to destroy Sabzevar was in 1052 A.D.