Characterizing spatially restricted rupture in Nankai shallow very low-frequency earthquakes

Slow earthquakes represent a distinct class of fault slip phenomena characterized by prolonged source duration and reduced seismic radiation compared to regular earthquakes. While essential for understanding seismic cycles and megathrust earthquakes, the mechanisms governing their rupture processes remain elusive. Here we present the finite-fault inversions of very low-frequency earthquakes (VLFs) in the Nankai Trough, a subtype of slow earthquakes producing detectable seismic waves while maintaining resolvable rupture dimensions. Comparison with two nearby regular earthquakes reveals that VLFs exhibit a distinct two-stage process: (1) rapidly accelerating slip confined to hypocentral regions, and (2) progressive deceleration and spontaneous termination within the initial slip zone, without lateral propagation. Source dynamic simulations reconcile these observations through a slip-weakening friction model, suggesting that a low slip-weakening rate facilitates slow self-arresting ruptures consistent with VLFs. Our findings provide observational insights into VLFs rupture dynamics, suggesting that slow earthquakes may experience limited propagation and self-arresting evolutions.