[S-SS10] 地震発生の物理・断層のレオロジー

[SSS10-02] Rupture kinematics of 2021 Mw7.4 Maduo, China earthquake and the implications for earthquake physics

*Gang Liu¹ (1.Institute of Seismology, China Earthquake Administration.)

キーワード：Rupture kinematics, slip mode, suerpshear, immature fault

Laboratory experiments and numerical simulations suggest that earthquake rupture can transition from self-healing pulses to self-expanding cracks and that its propagation along a fault can be accelerated from slower than the shear wave speed to faster than it. However, evidence for such an earthquake is rare in nature. Here we present a detailed, accurate description of the rupture process through the joint inversion of near-field strong motions tracked by a dense high-rate GPS network and permanent offsets observed from campaign-mode GPS sites and satellite-based InSAR imagery, for a Mw 7.4 earthquake occurred 2021 that broke a slowly-slipping strike-slip fault in the northeastern Tibet. Our preferred rupture model reveals an asymmetric bilateral bimodal rupturing ––while slip is advancing at the sub-Rayleigh speed toward the west, its eastward progression has speeded up from the sub-Rayleigh to the supershear, with slip mode transitioning simultaneously from early pulse-like to late crack-like. This supershear rupture is also imaged by the back projecting of teleseismic P-waves. The transition of slip mode may relate to a highly stressed segment where the breakdown may have facilitated the passage of rupture front to the supershear as well. These findings suggest that large earthquakes do not always propagate in a short duration of slip pulse, and the expanding crack could propagate because of the heterogeneous prestress pattern on an immature fault.