The deformation mode of the Tibetan Plateau is of crucial importance for understanding its construction and extrusion processes, as well as for the assessment of regional earthquake potential. Block motion and viscous flow models have been proposed to describe the deformation field but are not fully supported by modern geophysical observations. The 2021 Mw 7.4 Maduo earthquake, which occurred inside the Songpan-Ganzi terrane (SGT) in central-east Tibet, provides a chance to evaluate the associated deformation mode of the region. We conduct a joint inversion for this earthquake and resolve a bilateral rupture process, which is characterized by super- and subshear rupture velocities, respectively. We interpret this distinct rupture behavior to be the result of the respective slip concentration depths of the two ruptured segments. We analyze geological, seismic, and geodetic evidence and find that the SGT upper crust shows distributed shear deformation and distinct transverse anisotropy, which are associated with folded structures originating from compression of the paleo-Tethys ocean accretional prism realigned by following shear deformation. The SGT receives lateral shear loading from its NS boundary and accommodates a right-step sinistral motion across the terrane boundary faults. The unique tectonic setting of the SGT defines locations and behaviors of internal faulting and strong earthquakes such as the 2021 Maduo earthquake, with the latter occurring on slow-moving faults at intervals of several thousands of years.
Keywords: Maduo earthquake; Songpan-Ganzi terrane; Tibetan Plateau; deformation mechanism; seismic anisotropy.