Surface Rupture of the 2008 Mw 6.6 Nura Earthquake: Triggered Flexural‐Slip Faulting in the Pamir‐Tien Shan Collision Zone

• Published in: Tectonics (Washington, D.C.) Vol. 43; no. 9
• Main Authors: Patyniak, M., Landgraf, A., Dzhumabaeva, A., Baikulov, S., Williams, A. M., Preusser, F., Abdrakhmatov, K. E., Arrowsmith, J R., Strecker, M. R.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-09-2024
• Subjects: 2008 Nura earthquake; Age determination; Central Asia; Deformation; Earthquakes; Fault lines; Faults; Field tests; flexural‐slip faulting; Geochronology; Geological hazards; Geological time; Geomorphology; Glacial deposits; Growth rate; Holocene; Inspection; Mapping; Mountains; Paleogene; Pamir‐Tien‐Shan collision; Plate tectonics; Quaternary; Seismic activity; Seismic hazard; Structures; SURE; surface rupture; Thrust faults; Unmanned aerial vehicles; Central Asia
• ISSN: 0278-7407; 1944-9194
• DOI: 10.1029/2024TC008360

This study investigates the intricate relationship between earthquake sources and seismogenic surface ruptures in a complex tectonic setting with active faults in the continental collision zone between the southern Tien Shan and the northern Pamir Mountains in Central Asia. The study focuses on the 2008 Mw 6.6 Nura earthquake along the Pamir Frontal Thrust, where the seismogenic surface rupture occurred unexpectedly within the footwall and 10 km away from the source thrust fault. This discrepancy raises questions about the interactions and potential trigger mechanisms between tectonic structures during earthquake rupture. Using unmanned aerial vehicle photography and field inspection, our investigation integrates detailed fault‐zone mapping with tectono‐geomorphic observations to unravel potential interactions between subsurface structures and surface‐deformation phenomena. Our findings suggest that a combination of slip along deep‐seated basement faults and remotely triggered flexural slip within folded Paleogene strata led to surface rupture of overlying Quaternary glacial deposits. Geomorphological and geochronological analyses coupled with systematic displacement measurements furthermore reveal evidence of similar past ruptures within the regional fault system, suggesting a recurrence interval of 1.7 kyr and a Holocene vertical offset rate of 0.4 mm/yr. The analysis of the Nura rupture zone contributes significantly to evaluate linkages between surface and subsurface structures regarding fault‐zone behavior and seismic hazard assessments. Importantly, our results highlight the critical role of on‐site investigations in regions with poorly defined surface ruptures, where misinterpretation may lead to the underestimation of the impact of seismic events and limitations in assessing earthquake history and strain accumulation.
Plain Language Summary
This study investigates surface ruptures related to earthquakes in Central Asia, focusing on the 2008 Nura earthquake in south Kyrgyzstan, where the Tien Shan and Pamir mountains converge due to the collision between the Indian and Eurasian tectonic plates. The surface rupture during that event occurred at a different location than expected, causing us to investigate more closely the complex interactions between faults during earthquakes in this region. Based on detailed mapping on a high‐resolution digital surface model and on‐site observations, our analysis suggests that movement along hidden tectonic fault structures in the subsurface caused the bending of overlying folded sedimentary strata, which in turn resulted in the breaking of the ground. Through geomorphological analysis and geological age determination, we conclude that similar events in the regional fault system occurred in the past, in intervals of 1,700 years and with a vertical growth rate of 0.4 mm/yr within the last 12,000 years. Understanding such geotectonic processes is important for a better assessment not only of earthquake hazard in this region, but also of faulting processes elsewhere that have a similar deformation character, thus emphasizing the importance of field investigations in regions where the understanding of tectonic structures is limited.
Key Points
Field survey of the 2008 Mw 6.6 Nura earthquake surface rupture in Kyrgyz Pamir shows evidence of secondary flexural‐slip faulting
Our results suggest similar events in the eastern Pamir‐Tien Shan collision zone with a recurrence interval of approximately 1.7 kyr
We propose a rupture model where slip along deep‐seated tectonic structures remotely triggered flexural‐slip along shallow folds