The Strength of Strike-Slip Fault Systems: Constraints from the Rock Record

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Plate boundary fault systems (where tectonic plates slide past one another) host the world's largest earthquakes and are zones of enhanced permeability and fluid flow through the crust of the Earth. My group studies the mechanics of rock and mineral deformation in fault systems (from the field- to nano-scale) to constrain models of the seismic cycle, tectonic plate motion, and the strength of the lithosphere. Understanding how rocks and minerals deform is critical because it directly controls the long term (i.e., plate tectonics) and short term (i.e., earthquake cycle) evolution of our planet, and impacts society by producing earthquakes, modifying landscapes, and forming/trapping natural resources (mineral, hydrological, and hydrocarbon). Over the next five years my group will work to determine the strengths of strike-slip fault systems in the middle to lower crust. Rocks in the middle to lower crust deform through ductile mechanisms. The ductile deformation of middle to lower crustal rocks is coupled to episodic deformation in the brittle upper crust which produces earthquakes. Understanding the strengths of ductile middle to lower crustal rocks is therefore fundamental to understanding the earthquake cycle. Despite its importance to geodynamics and earthquake physics, the strength of the middle to lower crust is poorly understood and controversial, and there are several competing conceptual models. One innovative way to assess fault system strength is to use paleopiezometric methods (i.e., measurements of paleo-stress) on rocks that deformed in the middle to lower crust and have been exhumed to Earth's surface over geologic time. The proposed research aims to critically assess piezometric methods and produce new best methods, apply these new best methods to constrain the strengths of poorly understood rock types, and to integrate observations into global compilations to determine which conceptual model of crustal strength best fits the data. The research will be completed by nine highly qualified personnel (5 undergraduates and 4 master's students), who will be trained to use modern digital field methods and high-quality microanalytical instruments, making them highly skilled assets for industry, academia, or government surveys. The work addresses several grand challenges in structural geology and tectonics, including determining fault system strength from Earth's surface to the base of the lithosphere and developing a better understanding of the relationship between stress and strain in the lithosphere.