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TitleCoupled evolution of deformation, pore fluid pressure, and fluid flow in shallow subduction forearcs
AuthorSun, TORCID logo; Ellis, S; Saffer, D
SourceJournal of Geophysical Research, Solid Earth vol. 125, issue 3, e2019JB019101, 2020 p. 1-25,
Alt SeriesNatural Resources Canada, Contribution Series 20200007
PublisherAmerican Geophysical Union
Mediapaper; on-line; digital
File formatpdf; html
Subjectstectonics; hydrogeology; structural geology; sedimentology; Science and Technology; Nature and Environment; plate tectonics; tectonic environments; models; subduction zones; deformation; fluid flow; pore pressures; hydrologic environment; sediment transport; dewatering; bedrock geology; structural features; faults; horsts; grabens; stress analyses; basement geology; permeability; porosity; sedimentary wedges; overburden thickness
Illustrationsschematic cross-sections; schematic representations; tables; models; flow diagrams; plots; profiles
Released2020 03 09
AbstractDeformation and fluid flow in subduction zone forearcs are dynamically coupled, but our quantitative understanding of their coupling is incomplete. In this work, we investigate the hydrological and mechanical coupling in shallow forearcs, using a Lagrangian-Eulerian finite element model that incorporates constitutive and transport properties of sediments and faults constrained by laboratory and field measurements. Wide-ranging observations show that sediment thickness and composition, plate convergence rate, basement strength and roughness, and subducting slab dip angle vary between subduction zones. We therefore systematically study their effects on forearc stress and pore fluid pressure states, consolidation and dewatering patterns, and margin morphology. Our models, with the incorporation of a simple description of permeability enhancement along fault damage zones, yield a range of fault permeability (10 to the -13th power - 10 to the -17th power m2) consistent with previous estimates and describe the important role of upper plate splay faults in causing heterogeneous dewatering and consolidation patterns and in modulating effective normal stress on the plate interface. Spatial variations in tectonic loading and sediment consolidation can also be caused by subducting basement roughness such as a horst-and-graben structure. For typically observed relief and spacing, our models predict locally enhanced porosity reduction by up to 50% at the downdip edge of the horsts and anomalously high sediment porosity above the geometrical highs. At the margin scale, our results demonstrate that sediment permeability and thickness are dominant controls on fluid overpressure, sediment compaction, and megathrust strength. Rough and frictionally strong megathrusts produce similar effects in driving high wedge tapers.

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