GP 229: Earthquake Rupture Dynamics

Instructor: Eric Dunham

GEOPHYS 229 focuses on earthquake source physics and the interplay between friction and elastodynamics that governs earthquake nucleation, propagation, and arrest. The course combines lectures on theoretical concepts with numerical experiments using codes for earthquake modeling. GEOPHYS 229 introduces linear elastic fracture mechanics (LEFM) for both quasi-static and dynamic fractures/cracks, with material nonlinearities and weakening processes relegated to the stress singularity at the crack tip. This will be covered in a manner that will be accessible to anyone with a background in mechanics, with no special knowledge of earthquakes required. While the focus will be on shear cracks, the concepts are equally applicable to tensile cracks. Following this, we will explore departures from LEFM by identifying the specific processes that govern the evolution of fault strength and rupture propagation. These include friction laws such as slip-weakening friction (a cohesive zone model for shear cracks) and rate-state friction. We will study earthquake nucleation for these friction laws. We will apply concepts from dynamic fracture mechanics, in particular energy balance arguments, to write an equation of motion for the propagation of the rupture front. We will determine the factors controlling rupture velocity, the supershear transition, and ability of ruptures to propagate through fault bends and branches. Time permitting, the course may also cover additional processes governing the evolution of fault strength, including dynamic weakening mechanisms such as flash heating and thermal pressurization. Dynamic weakening can lead to the formation of slip pulses, instead of crack-like ruptures, and we will identify controls on this behavior. We will discuss earthquake scaling laws and the concept of self-similarity. We will consider inelastic response of the off-fault material, formation of damage zones, and off-fault energy dissipation—processes of relevance in the brittle upper crust. We will also examine the transition from frictional sliding on localized fault surfaces to distributed viscous shear in the lower crust and upper mantle. We will also cover earthquake cycle models with rate- state friction. These go beyond models for the rupture dynamics in a single earthquake to account for aseismic slip that occurs during the postseismic, interseismic, and nucleation periods between earthquakes. Finally, we will explore the interplay between fault zone fluid flow, pore pressure evolution, and frictional slip—a coupling of importance for induced seismicity as well as naturally occurring earthquake swarms and possibly slow slip events. Various modeling procedures, such as the approximation of inertial dynamics with the radiation-damping response, will also be covered.

Access the current syllabus here: https://syllabus.stanford.edu