From Foreshocks to Rupture: Transient Slip Controls on Nucleation

Foreshocks are occasionally detected prior to earthquakes, but their influence on rupture nucleation is still poorly understood. Standard nucleation models generally attribute earthquake initiation to slow, quasi-static slip driven by fault weakening, and often disregard impulsive precursory slip events. In contrast, we demonstrate through laboratory experiments combined with a rate-and-state, Griffith-type rupture framework that foreshocks can exert a first-order control on earthquake initiation when they occur at, or during, the nucleation phase. Our results show that foreshock-induced slip bursts impose a transient sliding velocity, denoted Vmin​, whose amplitude depends on foreshock size and systematically governs both the duration and spatial extent of nucleation. Larger foreshocks produce higher Vmin​ values and promote a rapid progression toward dynamic rupture, whereas smaller foreshocks lead to prolonged quasi-static nucleation, and sufficiently weak perturbations result in complete rupture arrest. When extrapolated to tectonic fault conditions, the framework predicts that foreshock sequences and accompanying slow slip preceding natural earthquakes obey similar scaling relationships. These findings constrain characteristic nucleation slip distances to approximately 0.3–3 mm, substantially smaller than those typically inferred for dynamic rupture. Overall, our study indicates that transient slip induced by foreshocks controls the timing, evolution, and observability of earthquake nucleation.