Frictional Control on Accelerating Creep During the Slow‐To‐Fast Transition of Rainfall‐Induced Catastrophic Landslides

Abstract Slow moving landslides regulated by precipitation/snowmelt induced subsurface pore‐pressure transients can sometimes accelerate to catastrophic failure causing loss of infrastructure and lives. Yet, unified theories of the transition of slow landslides into ultimately catastrophic ones in response to pore‐pressure changes remain relatively unexplored. Here, we use a simple gravity‐driven block‐slider model governed by laboratory‐derived rate‐and‐state friction (RSF) equations with velocity‐weakening parameters to analyze the mechanical progression of initially creeping landslides toward runaway acceleration. The rigid‐block approximation allows for exact or semi‐analytical estimates of the timescales over which such, potentially unstable, creeping landslides can be expected to transition to runaway acceleration in response to idealized pore‐pressure perturbation histories. We demonstrate that the duration of creep preceding catastrophic failure is critically sensitive to the RSF parameters, pore‐pressure variation amplitude and frequency, and background shear‐load and pore‐pressure levels through a set of non‐dimensional numbers. Our model predicts that slow landslides within velocity‐weakening clay‐rich soils can potentially creep for years to decades before transitioning to runaway failure when regulated by typical seasonal pore‐pressure transients. Remarkably, for much larger and rapid pore‐pressure changes, the same landslides can evolve to runaway failure over days to few tens of minutes. Being dependent purely on soil parameters that can be inferred from routine laboratory experiments, our model provides a theoretical framework that might be practically useful to understand the non‐linear and hysteretic response of landslide motion to pore‐pressure transients.