Understanding the Rupture Kinematics and Slip Model of the 2021 Mw 7.4 Maduo...

Xu, L., Z. Yunjun, C. Ji, L. Meng, E. Fielding, R. Zinke, and H. Bao (2023), Understanding the Rupture Kinematics and Slip Model of the 2021 Mw 7.4 Maduo Earthquake: A Bilateral Event on Bifurcating Faults, J. Geophys. Res., 128, e2022JB025936, doi:10.1029/2022jb025936.

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. Plain Language Summary A large earthquake struck Maduo county in northeast Tibet on 21 May 2021, with a magnitude of 7.4. To better understand the earthquake rupture and its physics, we use the seismic waveforms from remote stations and surface displacement data from radar satellites to study the rupture geometry, propagation history, and the slip distribution on the fault. Our results show that the earthquake started on the near-vertical Kunlun Pass-Jiangcuo fault and propagated bilaterally both east and west along the fault. The earthquake ruptured a length of ∼160 km and moved along the fault at average speeds lower than the shear wave velocity on both sides. The eastern part of the fault included a fork with significant slip on both the north and south branches. This bifurcation behavior can be well explained by the stress direction, rupture speed, and angles between forking faults. Most slip is concentrated at shallow depth, but our estimate for the slip distribution shows that deep slip at the depth of the Tibetan middle crust is required to match all of the observations. The amount of possible deep slip is related to local crust structure and is worthy of more investigation.

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Earth Surface & Interior Program (ESI)