Role of fluids in rock deformation and the earthquake cycle

Introduction

The dynamics of the solid Earth, e.g., the initiation of plate tectonics, the strength of plate boundaries, and the formation and evolution of mountains, is directly controlled by the chemical and physical action of water. In the shallow (brittle) part of the lithosphere, fluid pressure counteracts the lithostatic pressure and weakens faults.

Chemical Activity and Rock Weakening

At greater depth, the chemical activity of water makes rocks plastically weaker and is also responsible for metamorphic reactions that induce weakening. Fluids have been invoked to explain observations of tremor and slow slip at depth, and a large fraction of crustal seismicity is attributed to upward fluid flow, inducing earthquake swarms.

Knowledge Gaps

Yet we still have very few quantitative constraints on either fluid pressure or chemical activity of water at depth in the lithosphere. In addition, fluid pressure and transport are coupled to deformation, and the mechanisms by which fluids induce fault slip and seismicity are not well understood. Crustal fluids are very mobile, and rock physical properties evolve in response to both fluid-rock interactions and deformation.

Project Aim

The aim of this project is to identify and quantify the coupled mechanical, hydraulic, and chemical processes occurring across the lithosphere, from slow creep to rapid earthquake slip. We will determine the role played by fluids on:

1. Deep and shallow seismicity
2. Slow slip
3. Long-term evolution of plate boundaries

Methodology

I propose to conduct laboratory rock deformation experiments with state-of-the-art instrumentation and data processing methods to:

• Determine the spatio-temporal evolution of fluid flow and seismicity during faulting
• Quantify the evolution of rock physical and transport properties during long-term "healing"
• Test how chemical water activity and metamorphic hydration reactions impact deep fault rheology

The laboratory data will allow us to establish the geophysical signature of fluids in the lithosphere and how they impact the dynamics of faults.