The Tuoli Fault: Late Pleistocene Tectonics and Slip Rate of a Left‐Lateral Strike‐Slip Fault in the Western Junggar Mountains, NW China

Abstract The Western Junggar Mountains, Junggar Basin, and East Junggar ranges lie between the Tian Shan and Altai Mountains in Central Asia. Cenozoic northward subduction of the Indo Plate beneath Eurasia has reactivated these features through intense crustal shortening, driving modern topographic growth in the region. The manner in which the strain between the Tian Shan and Altai mountains is transmitted through the Western Junggar Mountains has remained unclear. The Western Junggar Fault System comprises the East Tacheng, Tuoli, and Daerbute sinistral strike‐slip faults. This study focused on the Tuoli fault. Based on the geometry and continuity of the fault traces, this fault can be divided into northern and southern branches, forming two fault segments. Paleoseismic observations have revealed two or three events since 15.4 ± 7.7 ka. Paleoseismic exposure observations and fault lengths show that the most recent event (Mw 7.1 or 7.6) ruptured the northern branch and occurred 1.5 ∼ 4.0 ka. Based on the offset geomorphological features and abandonment ages of alluvial or fluvial surfaces, the average late Pleistocene slip rate along the southern branch is 1.4 ± 0.2 mm/yr and is 0.4 ± 0.1 mm/yr along the northern branch. Slip rates derived from geological observations are consistent with those (1.7 mm/yr) obtained from the block rotation model. This consistency indicates that the Tuoli fault, along with the two other left‐lateral strike‐slip faults in the Western Junggar Mountains, forms a bookshelf structure that accommodates crustal shortening between the Tian Shan and Altai Mountains via clockwise block rotation.