Using new methods to understand how fault properties influence earthquake properties

In this thesis, I investigate the interaction of aseismic slip with earthquake stress drops and the interaction of fault properties with properties of repeating earthquakes. I use and develop a new inter-station phase coherence-based approach to estimate the rupture extents and stress drops of earthquakes. This new method is sensitive to different properties than spectral corner frequency approaches, and may be useful for examining properties such as rupture velocity. I use the phase coherence method to examine how stress drops vary with aseismic slip. The seismic coupling, and thus aseismic slip, varies along the Blanco fault. I find that the stress drops of earthquakes in areas with more aseismic slip are lower than earthquakes in areas with less aseismic slip, which may be caused by a shortened seismic cycle on the hotter, more aseismic section of the fault. I also examine stress drops of aftershocks of the 2010 M_W 7.2 El Mayor-Cucapah earthquake to test whether changes in post-seismic slip rate cause changes in stress drops of aftershocks. The result of this comparison is unclear, but I find that the phase coherence method can be applied to the P wave and S wave which is useful for noisy datasets. Finally, I examine repeating earthquakes in Parkfield, California to test whether the observed recurrence interval-moment scaling M_0^1/6 is due to spatially variable slip rates on a fault. In this hypothesis, repeating earthquakes occur on smaller faults with lower slip rates and recurrence interval-moment scaling reflects the scaling of slip rate with fault length. I find that the recurrence interval-moment scaling of repeating earthquakes varies with the distance between sequences, which suggests that repeating earthquakes occur on smaller, lower slip rate faults. This result suggests that repeating earthquake properties may reflect fault properties rather than the amount of aseismic slip.