Understanding Local-Scale Fault Interaction Through Seismological Observation and Numerical Earthquake Simulation

A number of outstanding questions in earthquake physics revolve around under-standing the relationships among local-scale stress changes, fault interactions (i.e. how stresses are transferred) and earthquake response to stress changes. Here, I employ seismological observations and numerical simulation tools to investigate how stress changes from a mainshock, or by fluid injection, can either aid or hinder further earthquake activity. Chapter 2.2 couples Coulomb stress change models with rate- and state-dependent friction to model the time-dependent evolution of complex aftershock activity following the 2010 El Mayor-Cucapah earthquake. Part III focuses on numerical simulations of earthquake sequences with the multi-cycle earthquake simulator, RSQSim. I use RSQSim in two applications; 1) multi-cycle simulation of processes that controlling earthquake rupture along parallel, but discontinuous, offset faults (Chapter 3), and 2) investigation of relationships between injection of fluids into the subsurface and the characteristics of the resulting induced seismicity (Chapter 4).Results presented in Chapter 2.2 demonstrate that both increases and decreases in seismicity rate are correlated with regions of positive and negative Coulomb stress change, respectively. We show that the stress shadow effect can be delayed in time when two faulting populations are active within the same region. In Chapter 3, we show that the pre-rupture stress distribution on faults governs the location of rupture re-nucleation on the receiver fault strand. Additionally, through analysis of long-term multi-cycle simulations, we find that ruptures can jump larger offsets more frequently when source and receiver fault ruptures are delayed in time. Results presented in Chapter 4 demonstrate that induced earthquake sequences are sensitive to the constitutive parameters, a and b, of the rate-state formulation. Finally, we find the rate of induced earthquakes decreases for increasing values of hydraulic diffusivity