Abstract
AbstractWe 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.
Highlights
We provide the first measurement of strike-slip and shortening rates across the 200-kmlong right-lateral strike-slip Main Köpetdag Fault (MKDF) in Turkmenistan
Turkmenistan is situated at the northern edge of the belt of shortening related to the Arabia-Eurasia continental collision (Figure 1)
The relative motion between the South Caspian Basin (SCB) and surrounding parts of NE Iran and Turkmenistan is partly accommodated by the Shahroud left-lateral fault zone (SFZ, Figure 2a) in Iran and the right-lateral Main Köpetdag fault (MKDF, Figure 2a) in Turkmenistan (e.g., Hollingsworth et al, 2006, 2008, 2010)
Summary
Turkmenistan is situated at the northern edge of the belt of shortening related to the Arabia-Eurasia continental collision (Figure 1). As there is an unknown amount of deformation occurring across the Köpetdag and eastern Alborz, and in the eastern Caspian lowlands between them, the trends of the range-parallel strike-slip faults within the SFZ and MKDF do not directly constrain the direction of motion of the SCB relative to Iran and Eurasia. In the absence of GPS data, they used a value for the Iran-Eurasia shortening that is too high, and were limited by the lack of direct constraint on the rates of strike-slip within the Alborz and Köpetdag ranges They estimate 7–10 mm/yr in a direction north of 300° for the motion of the SCB relative to Eurasia and 13–17 mm/yr in direction 210° relative to Iran. The approach that we take in constructing our velocity triangle allows us to estimate the amount of shortening perpendicular to the eastern Alborz and Köpetdag, and the overall motion of the SCB
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