Sinistral Strike Slip Faults of the Kyrgyz Tien Shan
Résumé
The Tien Shan are an intracontinental mountain belt experiencing shortening as a result of far field deformation from the ongoing India-Eurasian collision. At the longitude of Kyrgyzstan the Tien Shan accommodate ~20 mm/yr of shortening. In central Kyrgyzstan, the most well studied faults include the northwest-striking right-lateral Talas Fergana fault and the series of east-striking reverse & thrust faults that form the basins and subranges that accommodate most of this compression. Yet in satellite imagery, some of the most prominent fault ruptures appear on a series of east-northeast-striking left-lateral strike slip faults. Little is known about the paleoseismology, rate of slip, or tectonic role of these faults. Here we present new drone-based high resolution topography and imagery along with geomorphic, geochronology, paleoseismic, and slip rate data for four of these sinistral faults. The studied faults are in the Aksay, Kazarman, Issyk Kul, and Song Kol basins. These data reveal that each fault has produced Holocene surface ruptures with single event displacements as great as 5-7 m along faults as long as ~100 km, corresponding to M~7.5 earthquakes. We propose a structural model to explain how these faults may have evolved from reverse faults that have rotated about their horizontal axis and then reactivated as strike slip faults due to their optimal alignment in the current stress field. How the existence of these faults affects seismic hazards is a question of discussion, as they are currently not considered in the regional strain budget that is largely based on compression.