Oral Presentation

Earthquakes occur in fault damage zones whose structure is dynamically evolving over time. Thus, fault zone structure is highly variable along the fault and can influence the locations, magnitudes, and recurrence intervals of earthquakes. In this talk, I will discuss recent research in understanding how the source physics of earthquakes changes with the spatially and temporally varying fault zones and how seismic data recorded from these earthquakes is used to gain a better understanding of fault zone structure.

I will first present dynamic rupture simulations with spatially heterogenous fault zones to discuss how earthquake nucleation and arrest are affected by the along-strike segmentation of fault damage zones. I will then show several examples of fully dynamic earthquake cycle models in which dynamic fault zone waves that occur within seconds and earthquake cycles that span hundreds of years are simultaneously modeled. By considering the evolution of fault zone material properties over earthquake cycles, we find fault structural maturity has a primary influence on earthquake magnitudes and recurrence intervals. I will also discuss results from other research groups on incorporating an ensemble of fractures and off-fault plasticity in the simulations of earthquakes in fault zones.

With the wealth of broadband seismic data, another ongoing effort is to better understand the spatial variation and material properties of fault damage zones. By comparing the observed seismic spectra with the results from dynamic rupture simulations, we find fault damage zones can cause an additional peak in the stacked P-wave velocity spectra of small earthquakes along directions close to fault strike. Moreover, most clusters of M 1.5-3 earthquakes at Parkfield and Ridgecrest have amplified high-frequency energy at stations close to fault strike. The different frequency bands of amplification for Parkfield and Ridgecrest suggest that the Parkfield fault zone is narrower and more localized. Our results can help constrain the along-strike variation in fault zone structure, where earthquake clusters along some fault sections show greater azimuthal variation in their spectra than clusters in other sections.