Co-seismic rupture of the 2021, Mw7.4 Maduo earthquake (northern Tibet): Short-cutting of the Kunlun fault big bend

Abstract

We report detailed field measurements of the 2021, Mw7.4 Maduo earthquake surface rupture south of the Kunlun fault, near the northern boundary of Tibet's Bayan Har block. In the field, the dominantly left-lateral surface rupture length was ∼151 km, along the poorly known Jiangcuo fault, with maximum horizontal and vertical displacements of ∼2.1±0.2 to 2.9±0.2 m (up to 3.6±0.2 m at one site) and ∼1.2±0.2 to 1.8±0.2 m, respectively. The rupture, which propagated bilaterally from a roughly central epicenter, terminated in well-defined, ∼20 km-long horsetail splays, as predicted by Coulomb stress failure, consistent with the very young age of the still growing Jiangcuo fault, which may be trying to bypass the Anyemaqen restraining bend in order to connect directly the Kokoxili and Maqen segments of the main Kunlun fault. 14C dating at one site (Cuoerjiala) implies long return times (≥6500 years) for M7+, Maduo-type earthquakes, in keeping with a slow horizontal slip rate of ∼0.55±0.03 mm/yr and the subdued geomorphic expression of the fault. In the broader Tibetan tectonics framework, the Jiangcuo fault may be better interpreted as a kinematic streamlining of the Kunlun fault bend, rather than a result of diffuse deformation across the Bayan Har terrane.