Introduction
Fault bends, branches, and step-overs play critical roles in the nucleation, propagation, and termination of earthquake ruptures [Ji et al. , 2003; King and Nábělek , 1985; Qiu et al. , 2016; Wesnousky , 2006]. Fault branching and bifurcation are commonly observed for strike-slip earthquakes in fault mapping [e.g. Sieh et al. , 1993] and more recently in high-resolution space geodesy images [e.g. Wei et al. , 2011]. To explain these observations, structure evolution models [Wesnousky , 1988; 2008], theorical analysis [Poliakov et al. , 2002], dynamic simulation models [Kame et al. , 2003], as well as lab experiments[Templeton et al. , 2009] have been proposed. It has been shown that prestress conditions, rupture speed, and bifurcation angle all impact rupture evolution through fault branching and bifurcation [Aochi et al. , 2002; Douilly et al. , 2020;Duan and Oglesby , 2007; Kame et al. , 2003; Poliakov et al. , 2002]. These theorical and numerical modeling results show a wide spectrum of rupture scenarios. However, to date, to the best of our knowledge, the details of kinematic rupture processes of such fault bifurcation and branching have not been reported. This may be partially accounted for by the fact that the slip on these faults is relatively small compared with the largest slip patches of the rupture, and seismological inversions are usually dominated by the larger slip patches, unless very near-fault seismic observations are available [Ji et al. , 2003].
The left-lateral strike-slip Mw7.4 Maduo earthquake occurred on May 21st, 2021, rupturing the near E-W oriented JiangCuo fault, which is located within the Bayan Har block [Zhan et al. , 2021] in the northeastern Tibetan Plateau (Fig.1b). The earthquake was well-recorded in space geodetic images [He et al. , 2022; J Liu et al. , 2022] and nearby static [M Wang et al. , 2022a] and high-rate GPS offsets [Gao et al. , 2021]. Earlier reports of the earthquake show that this was a bilateral rupture, which propagated ~80 km to both sides of the epicenter [He et al. , 2022; Ren et al. , 2022;S Wang et al. , 2022b]. While [K Chen et al. , 2022] derived a stable rupture speed of ~2.5km/s for the entire rupture, [Zhang et al. , 2022] and [Yue et al. , 2022] reported a supershear speed for rupture towards the east. Although various analyses have been reported for the earthquake, a comprehensive investigation of the rupture process is still missing to resolve the kinematic rupture details of the earthquake, especially at its eastern end that shows clear fault bifurcation but reported with different rupture speeds. To constrain the rupture details of the earthquake, here we adopt various data processing techniques and kinematic inversion methods that cover a wide range of observations. We pay special attention to the fault bifurcation and its seismic wave radiation, thus aiming to shed new light on earthquake physics.