Understanding the Rupture Kinematics and Slip Model of the 2021 Mw 7.4 Maduo Earthquake: A Bilateral Event on Bifurcating Faults

Abstract

We image the rupture process of the 2021 Mw 7.4 Maduo, Tibet earthquake using slowness-enhanced back-projection (BP) and joint finite fault inversion, which combines teleseismic broadband body waves, long-period (166–333 s) seismic waves, and 3D ground displacements from radar satellites. The results reveal a left-lateral strike-slip rupture, propagating bilaterally on a 160 km long north-dipping sub-vertical fault system that bifurcates near its east end. About 80% of the total seismic moment occurs on the asperities shallower than 10 km, with a peak slip of 5.7 m. To simultaneously match the observed long-period seismic waves and static displacements, potential deep slip is required, despite a tradeoff with the rigidity of the shallow crust. The deep slip existence, local crustal rigidity, and synthetic long-period Earth response for Tibet earthquakes thus deserve further investigation. The WNW branch ruptures ∼75 km at ∼2.7 km/s, while the ESE branch ruptures ∼85 km at ∼3 km/s, though super-shear rupture propagation possibly occurs during the ESE propagation from 12 to 20 s. Synthetic BP tests confirm overall sub-shear rupture speeds and reveal a previously undocumented limitation caused by the signal interference between two bilateral branches. The stress analysis on the forks of the fault demonstrates that the pre-compression inclination, rupture speed, and branching angle could explain the branching behavior on the eastern fork.