Fault rheology in an aseismic fold-thrust belt (Shahdad, eastern Iran)

Copley, Alex and Jolivet, Romain (2016) Fault rheology in an aseismic fold-thrust belt (Shahdad, eastern Iran). Journal of Geophysical Research: Solid Earth, 121 (1). 2015JB012431. ISSN 2156-2202 eissn 2169-9313 DOI 10.1002/2015JB012431

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Abstract

Geodetic observations of aseismic deformation in a thrust belt near Shahdad in eastern Iran have been used to place constraints on the rheology of creeping faults in a thin-skinned thrust belt (\textless5 km thickness). Creep on shallow and high-angle thrust ramps at the range front occurs at a steady rate, in response to the topographic gradient across the thrust belt. Parts of these thrust ramps, and the low-angle basal thrust they connect to at depth in a ramp-and-flat geometry, underwent accelerated creep following the nearby Mw 6.6 Fandoqa earthquake in 1998. Estimates of the rate of fault slip and the driving stresses in these two contrasting times reveal a nonlinear relationship between the stresses and sliding velocity. The degree of nonlinearity rules out bulk shear of a weak layer in the sedimentary section (e.g., evaporites) as the deformation mechanism. Instead, we suggest that the motions are accommodated by slip on faults governed by a friction law with a highly nonlinear relationship between shear stress and slip rate (e.g., as predicted by �rate and state� models). The high-angle thrust ramps are responsible for building aspects of the geological and geomorphological signs of active shortening visible at the surface, but the folding preserved in the geology must be accomplished by other methods, possibly during the rapid transient postseismic deformation following nearby earthquakes.

Item Type: Article
Uncontrolled Keywords: 2015AREP; IA70
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
08 - Green Open Access
Journal or Publication Title: Journal of Geophysical Research: Solid Earth
Volume: 121
Page Range: 2015JB012431
Identification Number: 10.1002/2015JB012431
Depositing User: Sarah Humbert
Date Deposited: 28 Apr 2016 12:38
Last Modified: 28 Jun 2016 00:00
URI: http://eprints.esc.cam.ac.uk/id/eprint/3636

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