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Kinematics of fault-related folding derived from a sandbox experiment

Bernard, Sylvain and Avouac, Jean-Philippe and Dominguez, Stéphane and Simoes, Martine (2007) Kinematics of fault-related folding derived from a sandbox experiment. Journal of Geophysical Research B, 112 (B3). Art. No. B03S12 . ISSN 0148-0227. doi:10.1029/2005JB004149.

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We analyze the kinematics of fault tip folding at the front of a fold-and-thrust wedge using a sandbox experiment. The analog model consists of sand layers intercalated with low-friction glass bead layers, deposited in a glass-sided experimental device and with a total thickness h = 4.8 cm. A computerized mobile backstop induces progressive horizontal shortening of the sand layers and therefore thrust fault propagation. Active deformation at the tip of the forward propagating basal décollement is monitored along the cross section with a high-resolution CCD camera, and the displacement field between pairs of images is measured from the optical flow technique. In the early stage, when cumulative shortening is less than about h/10, slip along the décollement tapers gradually to zero and the displacement gradient is absorbed by distributed deformation of the overlying medium. In this stage of detachment tip folding, horizontal displacements decrease linearly with distance toward the foreland. Vertical displacements reflect a nearly symmetrical mode of folding, with displacements varying linearly between relatively well defined axial surfaces. When the cumulative slip on the décollement exceeds about h/10, deformation tends to localize on a few discrete shear bands at the front of the system, until shortening exceeds h/8 and deformation gets fully localized on a single emergent frontal ramp. The fault geometry subsequently evolves to a sigmoid shape and the hanging wall deforms by simple shear as it overthrusts the flat ramp system. As long as strain localization is not fully established, the sand layers experience a combination of thickening and horizontal shortening, which induces gradual limb rotation. The observed kinematics can be reduced to simple analytical expressions that can be used to restore fault tip folds, relate finite deformation to incremental folding, and derive shortening rates from deformed geomorphic markers or growth strata.

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Avouac, Jean-Philippe0000-0002-3060-8442
Additional Information:© 2007 American Geophysical Union. Received 8 November 2005; revised 14 September 2006; accepted 6 October 2006; published 17 February 2007. We are grateful to Remi Michel for his help in the design of the optical monitoring system. We also thank Jacques Malavieille, Rick Allmendinger, and John Suppe for fruitful discussions. The manuscript has benefited from thorough reviews and helpful suggestions by Hemin Koyi, Jurgen Adam, Mark Fisher, and the Associate Editor Wouter Schellart. The analogue experiments were initiated thanks to a grant by CNRS/INSU to S.D. This study was partly funded by the Gordon and Betty Moore Foundation. This is Caltech Tectonics Observatory contribution 45.
Group:Caltech Tectonics Observatory, Seismological Laboratory
Funding AgencyGrant Number
Gordon and Betty Moore FoundationUNSPECIFIED
Subject Keywords:fault-related folding; sandbox experiment; kinematic modeling
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Caltech Tectonics Observatory 45
Issue or Number:B3
Record Number:CaltechAUTHORS:20101115-153513150
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Official Citation:Bernard, S., J.-P. Avouac, S. Dominguez, and M. Simoes (2007), Kinematics of fault-related folding derived from a sandbox experiment, J. Geophys. Res., 112, B03S12, doi:10.1029/2005JB004149
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20818
Deposited By: Tony Diaz
Deposited On:15 Nov 2010 23:46
Last Modified:09 Nov 2021 00:03

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