Tectonics of continental convergence in Central and West Asia

Thesis

This thesis presents three case studies of tectonically converging mountain ranges across West and Central Asia, examining how and whether this convergence is accommodated by earthquakes. In northern Tajikistan, where the Pamir and Tian Shan have fully converged, I use calibrated earthquake relocations and analysis of tectonic geomorphology to find that the 1949 Mw 7.6 Khait Earthquake occurred not on the geomorphically well expressed boundary fault, but within a previously unmapped structure in the Tian Shan basement. I show vertical axis rotations within the Tian Shan accommodate up to half the convergence rate between the Pamir and Tian Shan, demonstrating the greatest seismic hazard can lie on cryptic faults. In the Kura Basin of Azerbaijan, I use time series InSAR to reveal that the convergence between the Turkish Iranian Plateau and Greater Caucasus is accommodated by rapid creep on faults in the sedimentary cover, and hypothesise gravitational collapse of basin sediments into the South Caspian Basin as an additional driving force of this creep. Finally, I use calibrated earthquake relocation to demonstrate that the 1985 Mw 6.9 Wuqia Earthquake occurred beneath the sedimentary cover of the Tarim Basin, northwest China. I find that the earthquake occurred on a buried, slow moving transpressive strike slip fault formed during more rapid strike-slip motion between the Pamir and Tarim Basin. Overall this thesis extends our knowledge of how converging zones in continental interiors behave, and demonstrates that the greatest seismic hazard in a region is not necessarily on the most geomorphically well-expressed faults.

Authors: Johnson, B

• DOI: 10.5287/ora-kovpovwxd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: earthquakes; geodesy; insar; seismology; pamir; geomorphology; fault creep; surface rupture; tectonics; geodynamics
• Subjects: Vakhsh River Valley (Tajikistan); Synthetic aperture radar; Alai Valley (Kyrgyzstan); Neotectonics; Pamir-Alai Mountains; Surface fault ruptures; Digital elevation models; Apsheron Peninsula (Azerbaijan); Caspian Sea; Earth sciences; Photogrammetry; Asia, Central; Earthquakes; Tien Shan; Mountains--Caucasus, South