Issyk-Ata fault and its two strong Holocene paleoearthquakes records near densely populated Chui basin: focus on Dzhal area of Kyrgyz Range, Tien Shan

Geodetic observations over the past several decades identify the Tien Shan as a prominent and active intracontinental mountain belt, characterized by a meridional shortening rate of up to 20 mm/a. The region has experienced significant seismic events, particularly along its northern boundary, highlighting the recurrent seismic activity in the Kyrgyz Republic. The Issyk-Ata fault, stretching 120 km from west to east in the northern Tien Shan, bounds from the north a young, growing anticline demarcating the foothills of the Kyrgyz Range and the Chui depression. This region is susceptible to strong earthquakes, posing a significant threat to the Chui region and Bishkek, the capital city with over a million residents. The youngest fault in the area is the Issyk-Ata fault, traversing the southern part of Bishkek, where modern construction has obscured its features. This study integrates remote sensing, detailed fieldwork, and paleoseismological investigations to map and analyze surface ruptures, quantify vertical displacements, and assess seismic hazards along the Issyk-Ata fault. Using optically stimulated luminescence and radiocarbon dating, we determined ages for documented paleoseismic events, placing two ancient earthquakes in the Holocene. Magnitude estimates suggest seismic events with magnitudes ranging from 6.6 to 7.1. In the Dzhal area, geological and geomorphological analysis yielded a long-term fault-slip rate of 1.15 mm/a. The Issyk-Ata fault shows variable rupture behavior, with distinct segments demonstrating different seismic characteristics and histories of activity. This variability necessitates comprehensive seismic hazard modeling to better understand and mitigate potential risks in the region.