Coulomb-like creeping segment acts as a stress sensor in Northern Sumatra

Abstract

Understanding how fault creep evolves in space and time is essential for identifying zones of aseismic stress release and stress accumulation. Creeping faults typically exhibit rate-strengthening friction, in which frictional resistance increases with sliding velocity and promotes stable slip. The northern Aceh segment of the Sumatran Fault Zone is a notable exception, hosting active creep yet rupturing in a Mw 6.1 strike-slip earthquake in 2013. Here we show, using satellite observations, that creep rates decreased by ~60% from 2007–2010 to 2017–2023. Numerical models constrained by these observations reveal two creep events: one triggered by stress transfer from the distant 2004 Mw 9.2 megathrust earthquake, and a second re-acceleration driven by nearby continental earthquakes. These results suggest that the Aceh fault exhibits emergent, nearly velocity-neutral behaviour at the segment scale. In this regime, the fault behaves like a brittle Coulomb surface lacking the self-stabilizing influence of velocity- and slip-history-dependent friction, enabling long-range triggering and the coexistence of creep and earthquakes. The fault can thus act as a natural stress gauge in a region of significant seismic hazard.