Active tectonics of NE Iran

• Main Author: Hollingsworth, J.
• Published: University of Cambridge 2008
• Subjects: 551.4
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604169

In this dissertation I use historical and instrumental seismicity, along with observations from satellite imagery, topographic data and field observations of the geomorphology to clarify the active tectonics of NE Iran. The aim is to better understand the deformation occurring within NE Iran in the context of the Arabia-Eurasia collision. In the Central Kopeh Dagh, an array of active right-lateral strike-slip faults cut obliquely across the range, and which are almost certainly responsible for a number of destructive earthquakes. These faults have identifiable ends, where they turn into thrusts, which indicate that they are restricted to the Kopeh Dagh range and do not continue beyond it. Their significance to the regional tectonics appears to be in achieving an across-strike shortening and along-strike elongation by rotating about vertical axes. Simple calculations using the cumulative offset between faults, and their associated rotation, can account for ~30 km of along-strike elongation and ~50 km across-strike shortening in the Central Kopeh Dagh, since the onset of strike-slip faulting. Along-strike elongation in the Central Kopeh Dagh is taken up by the westward component of motion between the NW Kopeh Dagh-South Caspian block, relative to both Eurasia and Central Iran. From the limited GPS data currently available, ~50% of the shortening across NE Iran (i.e. ~6 mm/yr) is accommodated in the Kopeh Dagh. Estimates of the total deformation across this range could be achieved in ~10 Ma, at present-day rates. The remaining 50% of shortening across NE Iran is accommodated south of the Kopeh Dagh, across the sub-parallel East Alborz, Sabzevar (Siah Kuh) and Kuh-e-Sorkh mountain ranges. The active tectonics of the East Alborz vary significantly along strike. East of 57°E, regional shortening is accommodated on thrust faults bounding the southern margin of the range. OSL dating of displaced geomorphology indicates <1 mm/yr (i.e. <20% OF NE Iran shortening) across this range, at longitude of Neyshabur. The remaining 30% of shortening across NE Iran is probably accommodated across the Sabzevar and Kuh-e-Sorkh mountain ranges, south of the East Alborz.