Slip-rate on the Main Köpetdag (Kopeh Dagh) strike-slip fault, Turkmenistan, and the active tectonics of the South Caspian

We provide the first measurement of strike-slip and shortening rates across the 200-km-long right-lateral strike-slip Main Köpetdag Fault (MKDF) in Turkmenistan. Strike-slip and shortening components are accommodated on parallel structures separated by ∼10 km. Using Infra-red-stimulated luminescence and reconstruction of offset alluvial fans we find a right-lateral rate of 9.1 ± 1.3 mm/yr averaged over 100 ± 5 ka, and a shortening rate of only ∼0.3 mm/yr averaged over 35 ± 4 ka across the frontal thrust, though additional shortening is likely to be accommodated locally by folding and faulting, and regionally within the eastern Caspian lowlands to its south. The MKDF is estimated to have ∼35 km of cumulative right-lateral slip which, if these geological measurements are correct, would accumulate in only 3–5 Ma at the rate we have determined, suggesting that the present tectonic configuration started within that time period. We use the MKDF slip-rate to form a velocity triangle, from which we estimate the Iran-South Caspian and Eurasia-South Caspian shortening rates, and show that the South Caspian Basin moves at 10.4 ± 1.1 mm/yr in direction 333° ± 5 relative to Eurasia and at 4.8 ± 0.8 mm/yr in direction 236° ± 14 relative to Iran. In contrast to both the eastern Köpetdag and the Caspian lowlands the MKDF has little recent or historical seismicity. The rapid slip-rate estimated here suggests that it is a zone of high earthquake hazard.