Active tectonics and palaeoseismicity of the Northern Tien Shan and Dzhungaria

Thesis

This thesis focuses on the active tectonics and the palaeoseismicity around the Dzhungarian Basin. The study of surface ruptures is crucial to comprehending the earthquake occurrences of faults. I investigate geomorphic displacements along the boundary strike-slip Dzhungarian Fault using high-resolution drone and Pléiades satellite imagery. The results reveal possible single-event fault slip along the Dzhungarian Fault in the most recent earthquake. I suggest this earthquake is likely linked with a previously identified palaeo-earthquake rupture on the Lepsy Fault. With a joint rupture of the two faults, it could generate an earthquake with a magnitude up to Mw 8.4, which would be amongst the largest magnitude inferred for a continental earthquake. I further use Quaternary dating techniques and InSAR time-series analysis to determine the geological and geodetic slip rates of the Dzhungarian Fault. The results show that the northern Dzhungarian Fault has a long-term uplift rate of 0.6 ± 0.2 mm/yr, whilst the southern Dzhungarian Fault has geological and geodetic strike-slip rates consistent with a range of 2.1 – 4.7 mm/yr. I also re-investigate three historical earthquakes with magnitudes greater than Mw 7.0: the 1812 Nilke, the 1906 Manas and the 1944 Xinyuan Earthquakes in the Borohoro Shan. By re-analysing source parameters and integrating published data, seismological analysis results, and remote-sensing mapping, the study demonstrates the significance of both reverse and strike-slip faulting in the regional seismotectonics, which also indicates the deformation kinematics of the Borohoro Shan as being in a transpressional zone. I collate my results with those from the literature to propose updated earthquake scaling relationships of intra-continental earthquakes. Finally, this study suggests that the Dzhungarian Basin and its surrounding tectonic units are rotating anticlockwise to accommodate both the N-S crustal shortening and the left-lateral shearing within a large-scale zone from the SW Tien Shan to the Altay Mountains.

Authors: Tsai, C-H

• DOI: 10.5287/ora-go4bzamzp
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Dzhungaria; intra-continental earthquakes; strike-slip fault; Palaeoseismicity; InSAR; Tien Shan; quaternary dating