Earthquakes and slip transients through multi-dimensional and multi-physics thermomechanical modeling

I study the physics and mechanics underlying seismic and aseismic slip. The slip behaviors are simulated by applying the rate and state friction formulation at steady state to 2D and 3D fault zones of finite thickness. The evolutionary frictional effect is modeled by the history-dependent stress and strain evolution in our model. The motivation of this research and summary of the rock friction laws’ development and application from a long-term tectonic (LTT) modeling point of view are covered in the first chapter. In the second chapter, I model fast and slow slip that have characteristics of earthquakes and slow slip events (SSEs) in which SSEs emerge at a critical friction-drop, ∆μ_c. The simulated earthquakes and SSEs have the same scaling as natural event for both stress and strain drop, as both type of events originate from shear failure. Co-seismic slip and moment release versus slip duration scale differently for earthquakes (cubic) and SSEs (linear), which indicate that energy is preferentially dissipated as kinetic energy for earthquakes. In my third chapter, I show that transients can arise spontaneously for mixed-brittle-ductile fault zones. Geological observations indicate that the core material composition in faults is highly heterogeneous. Brittle and ductile materials have velocity weakening and strengthening slip behaviors, respectively. Simulation results show that the semi-brittle shear zone forms complex fracture networks. Creeps and transients slip along few discrete fault surfaces. During earthquakes, both shear and tensile failures overwhelm the whole shear zone. This study confirms that fault core composition plays a critical role in determining slip behavior. In the last chapter, I investigate the effect of fault zone materials’ frictional properties on coseismic shallow slip deficit (SSD) at strike-slip faults. Our modeling approach generates coseismic slip profile that matches the SSD, the depth of peak slip, and the slip distribution below seismogenic zone that obtained from geodetic studies. Simulation results indicate that the frictional parameter distribution is the main factor controlling the fault zone coseismic slip profile. This study also shows that, contrary to the common belief, the shallow part of the strike-slip fault zone may have a velocity weakening slip behavior.