The dynamics of multiscale, multiphysics faults: Part II - Episodic stick-slip can turn the jelly sandwich into a crème brûlée

Abstract

Incorporating coupled Thermal-Hydro-Mechanical-Chemical (THMC) processes in lithospheric deformation models is a research frontier in the study of lithosphere dynamics. In this study we present a fundamental theoretical analysis on the important lithosphere deformation mechanism of creep enhanced by fluid-release reactions. This mechanism features a surprisingly rich dynamics stemming from the feedback between deformation induced fluid release through mineral breakdown reactions (dissolution) and fluid cementation into a solid matrix (precipitation) when the tectonic forces are locally relaxed. We show that the thermal-mechanical feedback processes in the temperature and pressure evolution equations and the resulting feedback between the fluid flow and mechanical deformation result in a highly dynamic system. The feedbacks lead to an oscillatory response resulting in a stick (or slow creep)-slip (or fast slip) phenomenon. The inferred oscillatory dissolution-precipitation reaction can explain the Episodic Tremor and Slip (ETS) phenomenon frequently encountered in subduction zones and commonly attributed to the dehydration-precipitation reaction of Serpentine minerals in the fault zone. Our study reveals a complex behaviour linking short time scale pulses of deformation to long term geodynamic deformation. We present a new tool to derive a systemic map of the presence of oscillation in a wide parameter space. By upscaling the mechanics over several cycles we show here that faulted rocks with large strength can indeed behave in an equivalent manner to weaker intact rocks and lubricate important geodynamic processes. We postulate a series of verifiable predictions with the potential to link a large range of geophysical observables of short and long time scale geodynamic processes with joint geological, hydrological and geochemical studies.