Heterogeneous strong asperities and tectonic complexity control irregular cascading ruptures.

Rupture characteristics and heterogeneity of large earthquakes are essential for seismic hazard assessments. We use relocated aftershocks, geodetic measurements, and seismic waveform data to distinguish contributions from closely separated fault structures of the 2024 7.5 Noto earthquake. We find that the initial rupture triggered slip on a complex fault of a preceding swarm and led to bilateral slow rupture there. The earthquake ruptured two fault segments with contrasting dip angles along the eastern and western segments. Aftershocks continued to rupture the preexisting swarm faults. A delayed rupture occurred southwest of the hypocenter, implying that substantial resistance caused by a barrier temporally hindered rupture propagation. Additional stress from surrounding slip eventually overcame the strength of the barrier fault section, leading to a compound rupture. The mainshock triggered a small earthquake swarm, in which the relatively larger events were not followed by abundant aftershocks. Our findings demonstrate the influence of strong asperities and complex geometry in the progression of cascading ruptures.