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Free-surface formulation of mantle convection—II. Implication for subduction-zone observables

Gurnis, Michael and Eloy, Christophe and Zhong, Shijie (1996) Free-surface formulation of mantle convection—II. Implication for subduction-zone observables. Geophysical Journal International, 127 (3). pp. 719-727. ISSN 0956-540X. doi:10.1111/j.1365-246X.1996.tb04050.x.

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Viscous and viscoelastic models for a subduction zone with a faulted lithosphere and internal buoyancy can self-consistently and simultaneously predict long-wavelength geoid highs over slabs, short-wavelength gravity lows over trenches, trench-forebulge morphology, and explain the high apparent strength of oceanic lithosphere in trench environments. The models use two different free-surface formulations of buoyancy-driven flows (see, for example, Part I): Lagrangian viscoelastic and pseudo-free-surface viscous formulations. The lower mantle must be stronger than the upper in order to obtain geoid highs at long wavelengths. Trenches are a simple consequence of the negative buoyancy of slabs and a large thrust fault, decoupling the overriding from underthrusting plates. The lower oceanic lithosphere must have a viscosity of less than 10^(24) Pa s in order to be consistent with the flexural wavelength of forebulges. Forebulges are dynamically maintained by viscous flow in the lower lithosphere and mantle, and give rise to apparently stiffer oceanic lithosphere at trenches. With purely viscous models using a pseudo-free-surface formulation, we find that viscous relaxation of oceanic lithosphere, in the presence of rapid trench rollback, leads to wider and shallower back-arc basins when compared to cases without viscous relaxation. Moreover, in agreement with earlier studies, the stresses necessary to generate forebulges are small (~ 100 bars) compared to the unrealistically high stresses needed in classic thin elastic plate models.

Item Type:Article
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Gurnis, Michael0000-0003-1704-597X
Additional Information:© 1996 RAS. Accepted 1996 August 9. Received 1996 August 5; in original form 1995 November 22. We thank John Toth for a helpful review. This paper is contribution number 5617 of the Division of Geological and Planetary Sciences, California Institute of Technology. The TECTON finite-element software used here was provided by H. J. Melosh of The University of Arizona. The work was supported by the David and Lucile Packard Foundation and NSF grants EAR-9496185 and EAR-9417645.
Group:Seismological Laboratory
Funding AgencyGrant Number
David and Lucile Packard FoundationUNSPECIFIED
Subject Keywords:fault models, geoid, mantle convection, rheology, subduction, topography
Issue or Number:3
Record Number:CaltechAUTHORS:20130212-075733844
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36861
Deposited By: Tony Diaz
Deposited On:23 Feb 2013 00:19
Last Modified:09 Nov 2021 23:25

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