Exploring feedbacks between subduction-zone seismicity, mineral reactions, and fluid pressure using an integrated numerical model: MEFISTO

Abstract:

Abundant structural and geochemical evidence supports dynamic links between earthquakes, fluid flow, and mineral reactions at subduction zones. However, the behavior of this dynamic system is difficult to predict, because of the interaction of multiple simultaneous feedback loops. To make progress in understanding how these factors influence the behavior of subduction zones, we present a numerical model, the Mineralization, Earthquake, and Fluid-flow Integrated SimulaTOr (MEFISTO). The model incorporates four key hypothetical process couplings. (1) Mineral precipitation, which is rate-limited by temperature, increases shear strength across the subduction interface, suppressing small ruptures. (2) Mineral precipitation also occludes porosity and permeability, suppressing fluid flow and promoting fluid overpressure. (3) Fluid pressure increase, which arises from subsurface fluid generation and porosity reduction, reduces interfacial strength and promotes earthquake rupture. (4) Earthquake rupture increases porosity and permeability, promoting fluid flow and reducing fluid pressure. Preliminary simulation results reproduce a variety of observed phenomena, including populations of earthquakes whose magnitudes increase with temperature; cycles of the buildup and release of seismic energy having decade- to century-scale periodicity; clusters of small events that follow large events in time and are located upon the previous rupture surface; and differences in the depth of the brittle-ductile transition that are imparted by changes in fluid pressure.