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Book Chapter

Analogue and numerical modelling of accretionary prisms with a décollement in sediments

By
Yasuhiro Yamada
Yasuhiro Yamada
1
Department of Civil and Earth Resources Engineering, Kyoto University, Kyoto 606-8501, Japan (e-mail: yama@electra.kumst.kyoto-u.ac.jp)
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Kei Baba
Kei Baba
2
JAPEX Research Center, Chiba 261-0025, Japan
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Toshifumi Matsuoka
Toshifumi Matsuoka
1
Department of Civil and Earth Resources Engineering, Kyoto University, Kyoto 606-8501, Japan (e-mail: yama@electra.kumst.kyoto-u.ac.jp)
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Published:
January 01, 2006

Abstract

Active accretionary prisms at subduction margins generally include a horizontal detachment, décollement, within the sedimentary pile. The décollement, and its extension to undeformed regions (i.e., proto-décollement), corresponds to a layer of high fluid pressure. The deformation of the prisms, including such an anomalous layer, can be modelled and examined using analogue experiments and numerical simulations. Both these methods approximate the material under deformation as an assembly of partides (grains). The décollement layer is found to be best modelled by intercalating a layer with smaller internal frictional coefficient than the surrounding materials corresponding to the sediments. Our analogue experiments with dry sand and microglass beads reproduce structural geometry similar to that of interpreted seismic profiles at the toe of the prisms. Thrust faults originate from the horizontal beads layer and propagate upward with a constant angle of about 30°. Each of the fault bends produces a series of minor back thrusts. A particle image velocimetry (PIV) analysis revealed that the fault activity is characterized by intermittent reactivation and segmentation. The numerical simulations based on the distinct element method (DEM) were performed with similar kinematic settings and material properties as the analogue experiments. The numerical simulation results not only reproduce similar geometries as in the analogue experiments, but also show that the particle assembly experiences temporai variations in the deformation velocity and stress field as deformation propagates. This might be related to stick-slip motion of the frictional fault surfaces, which is a common feature of faulting during accretionary processes at subduction margins.

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Contents

Geological Society, London, Special Publications

Analogue and Numerical Modelling of Crustal-Scale Processes

S. J. H. Buiter
S. J. H. Buiter
Geological Survey of Norway, Trondheim, Norway
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G. Schreurs
G. Schreurs
University of Bern, Switzerland
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Geological Society of London
Volume
253
ISBN electronic:
9781862395015
Publication date:
January 01, 2006

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