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.