Episodicity and Migration of Low Frequency Earthquakes modeled with Fast Fluid Pressure Transients in the Permeable Subduction Interface

In many subduction zones, the plate interface hosts intermittent, low-frequency, low-magnitude seismic tremor and low-frequency earthquakes (LFEs). Episodically, activity clusters in bursts that migrate along the fault zone in complex ways. Geological observations report a pervasive imprint of intense fluid pressure and permeability variations in the tremor source region. The dynamics of such permeable networks in the fault zone can trigger seismic sources and shape how they interact. In order to understand further how the hydraulic system of faults shape the seismicity they produce, we propose a simple model of how fluid pressure and permeability can interact within the subduction interface, and generate tremor-like patterns. Its core feature is that low-permeability plugs act as elementary fault-valves. In a mechanism akin to erosive bursts and deposition events documented in porous media, valve permeability opens and closes in response to the local fluid pressure. The rapid pressure release and/or mechanical fracturing associated with valve opening acts as the source of an LFE-like event. Valves interact constructively, leading to realistic, tremor-like patterns: cascades, synchronized bursts and migrations of activity along the channel, on both short and long time and space scales. Our model predicts that the input fluid flux is a key control on activity occurence and behavior. Depending on its value, the subduction interface can be seismically quiescent or active, and seismicity can be strongly time-clustered, quasi-periodic or almost random in time. This model allows new interpretations of low frequency seismic activity in terms of effective fluid flux and fault-zone permeability.