The mechanical properties of fault zones and earthquake cycle dynamics along the northern margins of the Iranian Plateau

This thesis presents, in integrated format, research investigating the mechanics of the earthquake cycle and the kinematics of continental deformation along the northern margins of the Iranian Plateau. The research focuses on improving the characterisation of seismic hazard surrounding the South Caspian Basin (SCB), an aseismic block moving independently of its surroundings within the Arabia-Eurasia collision. Fault zones surrounding the basin are in proximity to numerous urban agglomerations, which have a combined population exceeding 15 million. Motivated by improving the characterisation of seismic hazard in the region, this research aims to improve our understanding of the motion of the SCB with respect to its surroundings. I measure the rate and distribution of strain accumulation on the major faults facilitating the motion of the basin with Sentinel-1 InSAR time-series. I also characterise how the resulting strain is released from earthquake ruptures preserved in the geological record, from geomorphological analysis of satellite optical imagery and paleoseismological investigation of faults. The first study presents geomorphological analysis and field observations of an estimated Mw 7.8 paleo-rupture along the Main Köpetdag fault (MKDF), Turkmenistan. The MKDF is seismically-quiescent within historical records, despite its kinematic significance facilitating the motion of the SCB. However, paleoseismological investigation brackets the timing of this rupture to 600–800 years B.P.. This indicates a major earthquake is missing from historical records in neighbouring Iran, which suggests that the paucity of historical earthquakes in Turkmenistan may be misleading. The second study presents ascending and descending Sentinel-1 InSAR time-series of surface deformation from interseismic motion along the MKDF. I model the fault-parallel motion across the MKDF, and combine this with a recent geological slip-rate to constrain 8.7 ±1.1 mm/yr right-lateral motion across the MKDF. I also measure >1 mm/yr of uplift directly to the north of the MKDF, aligning with mapped frontal thrusts to the main strike-slip fault, and model this deformation with a strain-partitioning geometry. Using these measurements, I revise velocity triangles to constrain Iran-Eurasia-SCB kinematics. The final study presents a regional-scale velocity field derived from Sentinel-1 InSAR time-series. This presents a spatially-continuous image of the lateral extrusion of the SCB facilitated by conjugate strike-slip motion along the MKDF, and Shahroud Fault Zone (SFZ) in NE Iran. The westward component is observed to start abruptly at the Bäherden-Quchan Fault Zone (BQFZ). As well as these observations, I measure the rate of motion and present observations of the distribution of deformation along numerous major active faults through the eastern Alborz and Köpetdag, including the MKDF-SFZ conjugate system, BQFZ, and thrust faults in the eastern Köpetdag. The research I present in this thesis will provide invaluable contributions to improve the characterisation of the seismic hazard posed by faults surrounding the basin. Effective communication of these hazards will allow this knowledge to be integrated into societal awareness and infrastructure developments in the rapidly growing economies in this part of the modern Silk Roads. In future, this improved understanding should enable the mitigation of the devastating hazards posed by earthquakes along the northern margins of the Iranian Plateau.

Keywords: Iran
Earthquake Geology
Earthquake Geomorphology
InSAR
Tectonics
Turkmenistan
Continental Deformation
Advisor: Walker, R
Parsons. B