Thermo-poro-mechanics of chemically active faults -enriching Anderson's
theory of faulting in sedimentary rocks
Abstract
A suggested model to explain the episodic nature of slow earthquakes
involves shear zones exhibiting rate-and temperature-dependent
frictional behaviour hosting fluid-release chemical reactions. In this
work we extend the considerations of that approach, coupling the effects
of the mechanics at different faulting regimes to the chemically induced
fluid pressurization inside the fault. By introducing a pressure and
temperature dependence of the mechanical response in an
elasto-visco-plastic model we are able to correlate the inclination
angles of those specific faults with their dynamical response and enrich
their faulting regimes with kinematic characterisa-tion. We retrieve
that steeply dipping (normal) faults exhibit a simple response of either
being locked or slip at fast seismic velocities; shallow dipping
(reverse) faults on the other hand exhibit a much richer behaviour where
episodic stick-slip instabilities can be encountered. When present,
their magnitude depends on the (reverse) fault’s angle with faults
dipping at around 45 • exhibiting a maximum, whereas sub-horizontal
thrusts exhibit episodic stick-slip events as low velocities and
magnitude. These findings position slow earthquakes and episodic tremor
and slip sequences as a natural response of shallow dipping (thrust)
faults, in a regime that according to rate-and-state friction
considerations is intrinsically stable.