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Durham University

Department of Earth Sciences


Publication details for Prof Stefan Nielsen

Nielsen, S. (2017). From slow to fast faulting: recent challenges in earthquake fault mechanics. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375(2103): 20160016.

Author(s) from Durham


Faults—thin zones of highly localized shear
deformation in the Earth—accommodate strain
on a momentous range of dimensions (millimetres to
hundreds of kilometres for major plate boundaries)
and of time intervals (from fractions of seconds
during earthquake slip, to years of slow, aseismic
slip and millions of years of intermittent activity).
Traditionally, brittle faults have been distinguished
from shear zones which deform by crystal plasticity
(e.g. mylonites). However such brittle/plastic
distinction becomes blurred when considering
(i) deep earthquakes that happen under conditions
of pressure and temperature where minerals are
clearly in the plastic deformation regime (a clue
for seismologists over several decades) and (ii) the
extreme dynamic stress drop occurring during
seismic slip acceleration on faults, requiring efficient
weakening mechanisms. High strain rates (more than
104 s−1) are accommodated within paper-thin layers
(principal slip zone), where co-seismic frictional
heating triggers non-brittle weakening mechanisms.
In addition, (iii) pervasive off-fault damage is
observed, introducing energy sinks which are not
accounted for by traditional frictional models. These
observations challenge our traditional understanding
of friction (rate-and-state laws), anelastic deformation
(creep and flow of crystalline materials) and the
scientific consensus on fault operation.
This article is part of the themed issue ‘Faulting,
friction and weakening: from slow to fast motion’.