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

Abstract

In many subduction zones, the plate interface hosts intermittent, low-frequency, low-magnitude seismic tremor and low-frequency earthquakes (LFEs). Seismic activity clusters in episodic bursts that migrate along the fault zone in complex ways. Geological structures in fossil tremor source regions testify to large and pervasive variations of fluid pressure and permeability. Here, we explore the potential of fluid pressure transients in a permeable subduction interface to trigger seismic sources and induce interactions between them. We show how variations of pore pressure and permeability can act in tandem to generate tremor-like patterns. The core feature of the model is that lowpermeability plugs behave 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 distribution. 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 occurrence 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.

Seismic tremor reveals active trans-crustal magmatic system beneath Kamchatka volcanoes

“…2, C and D). The modeling shows that in a conduit with background diffusivity of ∼100 m 2 s −1 [as previously inferred for the KVG (22)], rapid migration velocities can reach ∼10 km/hour (53), which is again close to the observations presented here.…”

“…In a conduit with multiple low permeability barriers, the overall permeability is proportional to the number of open versus closed valves ( 45 ), which, on average, increases with overall pressure gradient across the system. A recent study of dynamics of such a system ( 53 ) has shown that closely located valves can interact, which results in cascades forming very rapidly migrating pressure transients (analogous to nonlinear pressure waves) able to propagate in both upward and downward directions, similar to what we observe for the KVG tremors (Fig. 2, C and D).…”

“…We conclude, therefore, that the large trans-crustal KVG plumbing system remains in a hydraulically open state and is subject to very frequent fast fluid pressure transients emerging from a local valving behavior ( 53 ). Because pressure controls most key volcanic processes such as fluid flow rates, mineralogical reactions, and degassing, its fast migrations provide a very efficient mechanism of destabilization/activation of the system before eruptions.…”

Spatiotemporal Distribution of Shallow Tremors Along the Nankai Trough, Southwest Japan, as Determined From Waveform Amplitudes and Cross‐Correlations

“…The tremor episodes that we identified began near and downdip from the subducted seamount (except for the 2016 episode, which was induced by an M JMA 6.5 earthquake), thus suggesting that the seamount played the role of the valve in the model of Farge et al. (2021). Note that the triggering of a tremor according to the valve model of Farge et al.…”

“…Farge et al. (2021) suggested a model in which episodic activity and migration of tremor at a plate boundary was the result of a fluid valve mechanism that involves fluid clogging in regions of low permeability, which increases pore pressure. When that pore pressure reaches a threshold value, an impulsive unclogging event occurs that opens the valve and generates a rapid pressure transition accompanied by tremors.…”