Applying optically stimulated luminescence to determine the slip rate of part of the Baatar Hyarhan fault in Mongolia (Central Asia)



Optically Stimulated Luminescence (OSL) is currently one of the most important dating methods. It dates the last exposure to sunlight. Natural hazard evidences such as colluvial wedges, alluvial and fluvial sediments can be dated by OSL. Therefore, OSL plays an important role in studies related to Paleoseismology and tectonic activity, particularly in arid and semi- arid regions. The Altai Mountains in western Mongolia are an arid zone. Baatar Hyarhan, a thrust- bounded massif, is situated in the south- eastern part of Altai. According to the geomorphology and seismicity of Mongolia, Altai is active and its activity is the response to the convergence between the Eurasian and Indian plates. Therefore, slip rate estimation is essential for investigating the activity of this mountain. There are two basins in both margins of Baatar Hyarhan. Geomorphology markers implicate low progress of Baatar Hyarhan through these basins. Faulting has uplifted ridges of folded sediment, known locally as forebergs, close to the range- front. In this article, the slip rate of Baatar Hyarhan is calculated. The eastern Zereg Basin, North- East of Baatar Hyarhan and South- West of Baatar Hyarhan forebergs are the three areas considered for sampling. Scarp heights were estimated using differential GPS (Nissen et al. 2009). Optically Stimulated Luminescence (OSL) dating was used to estimate the deposition age of these three areas. Equivalent dose (De) is measured by the analyst program and histogram method. The age at which this sediment was last exposed to light is determined by dividing the amount of radiation required to produce natural luminescence (known as the equivalent dose, De) by the dose rate. Vertical and horizontal displacement rates are determined by dividing the average of the offset by the age of each sample which are 0.07 - 0.53 mmyr -1, 0.03- 0.44 mmyr -1, respectively. The slip rate of 0.10-0.69 mmyr -1 was calculated by employing shortening rates and approximate slope of each area.