Investigating the relationship between fault damage zones and earthquakes through earthquake cycle simulations

Abstract:

Earthquake cycle simulations are powerful tools for the study of both earthquakes and interseismic deformation and provide an opportunity to reconcile seismologic, geodetic, and geologic datasets over various time scales. Here I will focus on the influence of the fault damage zone, a well-known structure of localized deformation around faults, on seismicity evolution and aseismic transients. First, I will present a suite of fully dynamic earthquake cycle simulations based on the spectral element method and rate- and state-dependent friction. I will show that fault damage zones can make a significant contribution to the spatial and temporal seismicity distribution. Fault stress heterogeneities generated by fault zone waves persist over multiple earthquake cycles that, in turn, produce small earthquakes that are absent in the homogeneous cycle simulations with the same friction conditions. Shallow fault zones can also produce a bimodal depth distribution of earthquakes with clustering of seismicity at both shallower and deeper depths. The results build new links between material properties of fault zones, which can be measured using geologic, seismic and geodetic methods, and the characteristics of earthquake sources.

Fault zone structure also evolves over time, resulting in damage accumulation and healing. In the second part, I will present fully dynamic simulations in which damage accumulation and healing are modeled as changes in seismic wave velocities of fault zones. The reduction of seismic wave velocity and rate of interseismic healing are constrained from observations in Wenchuan, Landers and Nojima. Our simulations show that faster healing lengthens the quiescence period between earthquakes while permanent damage limits the maximum sizes of earthquakes. Fault zone healing also promotes the penetration of aseismic slip into the locked region and reduces the sizes of fault asperities that host earthquakes. The results indicate that the damage and healing of fault damage zones can have a pronounced effect on the temporal evolution of locked and creeping regions. Finally, I will discuss the implications of our results on paleoseismic studies by comparing earthquake recurrence intervals inferred from slip measured at different depths in the simulated earthquake catalog.