Geomorphology and structure of the Jid right-lateral strike-slip fault in the Mongolian Altay mountains

Abstract We describe the late Cenozoic structure and evolution of the Jid right-lateral strike-slip fault in the northern Mongolian Altay mountain chain. Parts of the Jid fault have a vertical component of motion, introduced by bending along the fault. Some locations show additional structural complexity at the Earth's surface, with parallel strands having strike-slip, normal and reverse faulting, probably indicating a spatial separation of dip-slip and strike-slip components of motion in cross-section. The Jid fault shows indications of recent movements at scales ranging from drainage re-organisation at the kilometre scale, to ground deformations likely to result from movements during the last earthquake, which occurred ∼870–980 years ago based on OSL dating of deposits exposed in trenching. From the scale of the ruptures the earthquake would have had a magnitude of ∼7.5 with an estimated right-lateral slip of ∼5 m. Numerous horizontal offsets of about 10–15 m, and vertical scarps of ∼5 m in the youngest alluvial deposits show the likely cumulative movement over the last ∼15,000 years, and suggest a maximum slip-rate of roughly 1 mm/yr. The minimum cumulative right-lateral slip on the Jid fault is 1 km, which would accumulate in ∼1 Ma at present-day rates of slip. The relatively small vertical component of motion on the Jid fault is not sufficient to generate topography in the adjacent Kharkhiraa and Turgen Uul mountains, with relief of over 2000 m. The high mountains may therefore result from localised uplift on thrust faults rather than by oblique slip on the Jid fault.