Kutschera, Fabian, Jia, Zhe, Oryan, Bar, Wong, Jeremy Wing Ching, Fan, Wenyuan, and Gabriel, Alice‐Agnes
The 1 January 2024, moment magnitude MW $\left({M}_{W}\right)$ 7.5 Noto Peninsula earthquake ruptured in complex ways, challenging analysis of its tsunami generation. We present tsunami models informed by a 6‐subevent centroid moment tensor (CMT) model obtained through Bayesian inversion of teleseismic and strong motion data. We identify two distinct bilateral rupture episodes. Initial, onshore rupture toward the southwest is followed by delayed re‐nucleation at the hypocenter, likely aided by fault weakening, causing significant seafloor uplift to the northeast. We construct a complex multi‐fault uplift model, validated against geodetic observations, that aligns with known fault system geometries and is critical in modeling the observed tsunami. The simulations can explain tsunami wave amplitude, timing, and polarity of the leading wave, which are crucial for tsunami early warning. Upon comparison with alternative source models and analysis of 2000 multi‐CMT ensemble solutions, we highlight the importance of incorporating complex source effects for realistic tsunami simulations. Plain Language Summary: The 2024 moment magnitude 7.5 New Year's Day Noto Peninsula earthquake ruptured a complex, partially offshore fault system and generated a tsunami in the Sea of Japan. We use seismic data to show that the earthquake can be characterized by six distinct subevents, with an initial predominantly onshore rupture propagation toward the southwest and a 20 s delayed second rupture onset toward the northeast, mostly offshore. This second rupture episode is critical for the generation of the tsunami. We use the information we gain from these subevents, such as location and faulting mechanism, to infer the seafloor movement, which informs tsunami simulations. The reconstruction of the earthquake rupture process is not unique. This allows us to explore the influence of source uncertainties on the modeled tsunami, highlighting the importance of complex source effects for tsunami generation. The need for complexity in the generation of the tsunami becomes further evident when we compare the solutions against other, rapidly available models of the earthquake. We find that the preferred model matches tsunami onset times, first‐motion polarities, and initial wave amplitudes, crucial aspects for tsunami early warning. Key Points: The earthquake ruptures bilaterally, including six subevents, and delayed re‐nucleation at its hypocenter, consistent with fault weakeningOur multi‐fault subevent model aligns with known fault system geometries and is critical in explaining the observed tsunamiAnalysis of alternative source models and 2000 multi‐CMT solutions shows complex source effects are important for realistic tsunami models [ABSTRACT FROM AUTHOR]