Seismic evidence for megathrust fault-valve behavior during episodic tremor and slip

Gosselin, J.; Audet, Pascal; Estève, Clément; McLellan, Morgan; Mosher, Stephen; Schaeffer, A. J.

doi:10.1126/sciadv.aay5174

Cited by 54 publications

(73 citation statements)

References 39 publications

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“…Temporal changes in S wave velocity during slow slip events have been interpreted as evidence of fault-valve behaviour in the same area, i.e. where the LFEs are located at 35–45 km depth 56 . Fluid escape may be related to thinning of the E reflectors from 10 to 6 km as they extend past the corner of the mantle wedge at ~35 km depth, which reduces the thickness of the low permeability barrier, i.e.…”

Section: Discussionmentioning

confidence: 99%

“…cap rock, over the high pore pressure zone. In addition, or alternatively, the predicted onset at 40 km depth of eclogitization under equilibrium conditions as appropriate for hydrated metabasalt with its associated volume reduction and strain may disrupt the fluid seal above the LFEs, leading to fluid expulsion from the slab at this level 25 , 26 , 56 , 57 and serpentinization of the overlying mantle wedge 58 , 59 . An extensive 10–15 km thick region of anomalous mantle, which has a Poisson’s ratio of 0.26–0.28, exists between the base of the continental crust and the downgoing oceanic slab.…”

Section: Discussionmentioning

confidence: 99%

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Cascadia low frequency earthquakes at the base of an overpressured subduction shear zone

et al. 2020

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In subduction zones, landward dipping regions of low shear wave velocity and elevated Poisson’s ratio, which can extend to at least 120 km depth, are interpreted to be all or part of the subducting igneous oceanic crust. This crust is considered to be overpressured, because fluids within it are trapped beneath an impermeable seal along the overlying inter-plate boundary. Here we show that during slow slip on the plate boundary beneath southern Vancouver Island, low frequency earthquakes occur immediately below both the landward dipping region of high Poisson’s ratio and a 6–10 km thick shear zone revealed by seismic reflections. The plate boundary here either corresponds to the low frequency earthquakes or to the anomalous elastic properties in the lower 3–5 km of the shear zone immediately above them. This zone of high Poisson’s ratio, which approximately coincides with an electrically conductive layer, can be explained by slab-derived fluids trapped at near-lithostatic pore pressures.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Cascadia low frequency earthquakes at the base of an overpressured subduction shear zone

et al. 2020

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“…In the Tokai District in central Japan ( figure 4 ), Tanaka et al [ 44 , 45 ] find absolute gravity changes during two approximately 5-year-long slow-slip episodes, invoking cycles of fluid pressure and fault zone permeabilities of 10 −18 –10 −15 m 2 . In the northern Cascadia subduction zone, Gosselin et al [ 46 ] document seismic velocity changes that may reflect seal breaching and fluid flow in permeable pathways within and away from the megathrust, resulting in transient fluid pressure drops of 1–10 MPa. Nakajima et al [ 47 ] explore temporal changes in slip rate, seismicity and seismic attenuation along the approximately 50 km deep megathrust of the Philippine Sea in central Japan to infer cyclic drainage episodes from the megathrust.…”

Section: Geophysical Observations Of Sst Environment and Sourcementioning

confidence: 99%

What’s down there? The structures, materials and environment of deep-seated slow slip and tremor

Behr

Bürgmann

2021

Phil. Trans. R. Soc. A.

114

151

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Deep-seated slow slip and tremor (SST), including slow slip events, episodic tremor and slip, and low-frequency earthquakes, occur downdip of the seismogenic zone of numerous subduction megathrusts and plate boundary strike-slip faults. These events represent a fascinating and perplexing mode of fault failure that has greatly broadened our view of earthquake dynamics. In this contribution, we review constraints on SST deformation processes from both geophysical observations of active subduction zones and geological observations of exhumed field analogues. We first provide an overview of what has been learned about the environment, kinematics and dynamics of SST from geodetic and seismologic data. We then describe the materials, deformation mechanisms, and metamorphic and fluid pressure conditions that characterize exhumed rocks from SST source depths. Both the geophysical and geological records strongly suggest the importance of a fluid-rich and high fluid pressure habitat for the SST source region. Additionally, transient deformation features preserved in the rock record, involving combined frictional-viscous shear in regions of mixed lithology and near-lithostatic fluid pressures, may scale with the tremor component of SST. While several open questions remain, it is clear that improved constraints on the materials, environment, structure, and conditions of the plate interface from geophysical imaging and geologic observations will enhance model representations of the boundary conditions and geometry of the SST deformation process. This article is part of a discussion meeting issue ‘Understanding earthquakes using the geological record’.

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“…There is mounting evidence for large variations of pore pressure on the time scale of the slowearthquake cycle. During slow slip events, seismic images, geodetic load studies as well as earthquake source mechanisms indicate that pore fluid pressures around the subduction interface drop markedly [42,94,99]. The migration of LFE activity is highly suggestive of pore-pressure diffusion [26,35].…”

Section: Introductionmentioning

confidence: 99%

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

Farge¹,

Jaupart²,

Shapiro³

2021

Preprint

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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.

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Seismic evidence for megathrust fault-valve behavior during episodic tremor and slip

Cited by 54 publications

References 39 publications

Cascadia low frequency earthquakes at the base of an overpressured subduction shear zone

Cascadia low frequency earthquakes at the base of an overpressured subduction shear zone

What’s down there? The structures, materials and environment of deep-seated slow slip and tremor

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

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