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Fault rheology in an aseismic fold‐thrust belt (Shahdad, eastern Iran)
Author(s) -
Copley Alex,
Jolivet Romain
Publication year - 2016
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2015jb012431
Subject(s) - geology , thrust , slip (aerodynamics) , thrust fault , seismology , creep , shear (geology) , fold and thrust belt , sedimentary rock , fold (higher order function) , fault (geology) , geotechnical engineering , petrology , tectonics , engineering , paleontology , materials science , aerospace engineering , composite material , foreland basin , mechanical engineering
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 (<5 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 M w 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.