Thermo-poromechanics of chemically active faults—enriching Anderson’s theory of faulting in sedimentary rocks

Abstract

SUMMARY 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-viscoplastic model we are able to correlate the inclination angles of those specific faults with their dynamical response and enrich their faulting regimes with kinematic characterization. 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.