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

We utilize the slowness-enhanced back projection (SEBP) and joint finite fault inversion (FFI), which combines body waves, surface waves, and 3D ground displacements to image the rupture process and slip distribution of the Mw7.4 Maduo earthquake. The results indicate a 160-km-long bilateral rupture occurring on a north-dipping fault. The WNW branch ruptures a length of ~75 km by 2.7 km/s, while the ESE branch ruptures a length of ~85 km by 3 km/s. Most slip concentrates above 10 km depth, with several major slip patches up to 5.7 m located on the east segment of the main fault and on the bifurcated branching fault. The comparison between SEBP and FFI shows the consistency between large slip pulses and high-frequency sources. We observe up to 3 m slip with large uncertainty deep beyond 15 km, which is abnormal since it requires rupture penetrating into the ductile layers. We propose that the deep slip could be an artificial compensation to match the observed moment, which indicates that the crust in the source region is more rigid than the current understanding. Or the deep creeping fault is turned into seismic ones by the strain localization and dynamic weakening. The stress analysis on the forks of the fault demonstrates that the branching behaviors on the eastern forks could be well explained by the pre-stress inclinations, rupture speeds, and branching angles.