Dynamic Weakening by Acoustic Fluidization during Stick-Slip Motion

Abstract

The unexpected weakness of some faults has been attributed to the emergence of acoustic waves that promote failure by reducing the confining pressure through a mechanism known as acoustic fluidization, also proposed to explain earthquake remote triggering. Here we validate this mechanism via the numerical investigation of a granular fault model system. We find that the stick-slip dynamics is affected only by perturbations applied at a characteristic frequency corresponding to oscillations normal to the fault, leading to gradual dynamical weakening as failure is approaching. Acoustic waves at the same frequency spontaneously emerge at the onset of failure in absence of perturbations, supporting the relevance of acoustic fluidization in earthquake triggering.

Reply to comment by Davies and McSaveney on “The reduction of friction in long runout landslides as an emergent phenomenon”

“…They then make suggestions on how these discrepancies could be remedied simply by altering some of those assumptions or changing some of the parameters in that specific model. We suggest that in addition to experiments [ Melosh and Gaffney, ], numerical models of granular flows [ Giacco et al, ; Johnson et al, ] may help to further refine the assumptions and various parameters that the acoustic fluidization model depends on [ Melosh , ]. Our simulations, for example, suggest that the wavelength‐driving acoustic fluidization is determined by the size of fragments present in the landslide [ Johnson et al, ].…”

Drop Height and Volume Control the Mobility of Long‐Runout Landslides on the Earth and Mars

“…In addition to explaining general increases in mobility with increasing slide volume, this rheology also explains the observed decrease in mobility with increasing fall height, also consistent with the predictions of acoustic fluidization (Collins & Melosh, ; Johnson et al, ; Melosh, ). Furthermore, acoustic fluidization or something similar to it may be important for understanding the movement of large rock masses during earthquakes or the collapse of impact craters (Giacco et al, ; Melosh, ).…”

The reduction of friction in long runout landslides as an emergent phenomenon

“…Even at seemingly safe distances from mountainsides, these landslides are devastating to life and property [ Erismann , ]. Understanding this puzzling process can aid in hazard mitigation and may even help us understand the apparent reduction of friction observed in other geologic processes such as earthquakes [ Melosh , ; Giacco et al ., ].…”