Understanding the factors governing the stability of fault slip is a crucial problem in fault mechanics1–3. The importance of fault geometry and roughness on fault-slip behaviour has been highlighted in recent lab experiments4–7 and numerical models8–11, and emerging evidence suggests that large-scale complexities in fault networks have a vital role in the fault-rupture process12–18. Here we present a new perspective on fault creep by investigating the link between fault-network geometry and surface creep rates in California, USA. Our analysis reveals that fault groups exhibiting creeping behaviour show smaller misalignment in their fault-network geometry. The observation indicates that the surface fault traces of creeping regions tend to be simple, whereas locked regions tend to be more complex. We propose that the presence of complex fault-network geometries results in geometric locking that promotes stick-slip behaviour characterized by earthquakes, whereas simpler geometries facilitate smooth fault creep. Our findings challenge traditional hypotheses on the physical origins of fault creep explained primarily in terms of fault friction19–21 and demonstrate the potential for a new framework in which large-scale earthquake frictional behaviour is determined by a combination of geometric factors and rheological yielding properties.
