Paleoseismology of the Kokonadyr-Tegerek Adyr Thrust Fault, Kyrgyzstan, and Implications for Seismic Hazard in the South Issyk-Kul Region

Alex Travers, Richard Walker, Ian Pierce, Neill Marshall, & Rich D. Koehler

Published September 10, 2023, SCEC Contribution #13260, 2023 SCEC Annual Meeting Poster #087

The Kyrgyz Tien Shan is a region of active intra-continental deformation characterized by multiple parallel thrust fault belts. Evidence for paleoearthquake ruptures are well preserved in the landscape, providing a unique environment to compare patterns of earthquake occurrence. Devastating earthquakes with Mw >7 have been instrumentally recorded in the North Issyk-Kul region of the Kyrgyz Tien Shan. In the South Issyk-Kul region, no large earthquakes have been instrumentally recorded. Paleoearthquakes have been documented in a few studies in the South Issyk-Kul region, however these studies generally lack thorough geomorphic surveying. Thus, seismic hazard is poorly characterized in the South-Issyk Kul region.

This poster presents the results of a paleoseismic and geomorphic study along the Kokonadyr-Tegerek Adyr thrust fault (KTAF), at a site north of Ala-Bash within the South Issyk-Kul region. Paleoseismic results from the Ala-Bash trench site reveal that the KTAF produced at least two surface-rupturing earthquakes in the Holocene. Radiocarbon results demonstrate that these two events occurred in the last ~10,000 years. Diffusion modelling places the most recent event (MRE) at ~3850-5990 years ago. Geomorphic mapping and scarp displacement analysis provide evidence for an earlier third event. A loose recurrence interval between large earthquakes can be estimated ~5,000 years at Ala-Bash.

Empirical scaling relationships and geomorphic mapping provide evidence to suggest that the MRE did not rupture the entire fault, though further study would be required to validate this speculation. Using kinematic scaling relationships, full length rupture of the 91±10km KTAF could generate an earthquake with Mw 6.94-7.63. Partial ruptures of the KTAF could generate earthquakes on the order of Mw 6.46-7.40, dependant on the rupture length.

The results of this study support Korzhenkov and Deev (2017), that the seismic hazard model for the South Issyk-Kul region needs re-assessment.

Key Words
Paleoseismology

Citation
Travers, A., Walker, R., Pierce, I., Marshall, N., & Koehler, R. D. (2023, 09). Paleoseismology of the Kokonadyr-Tegerek Adyr Thrust Fault, Kyrgyzstan, and Implications for Seismic Hazard in the South Issyk-Kul Region. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology