Modeling the earthquake cycle and fault zone evolution with the mortar finite element method
Yuval Tal, Ben-Gurion University of the Negev

Faults are zones with a complex internal structure and non-planar geometry, which affect the rupture process during the seismic cycle. Here, I study numerically the effects of fault structure on the seismic cycle at different scales, as well as how fault structure and near field stresses evolve with slip. The numerical method includes the following main features: (1) To enable slip that is comparable to minimum wavelength of roughness, friction laws are implemented into the mortar finite element method, in which non-matching meshes are allowed across the fault and the contacts are continuously updated; (2) The mesh near the fault is refined with hanging nodes to accurately represent the fault geometry; (3) The method uses variable time steps with quasi-static and fully dynamic schemes; (4) The method accounts for elastic and inelastic deformation in the form of Drucker–Prager plasticity; and (5) To model properly the evolution of stresses on the fault with slip, the method accounts for wear. In this seminar, I will briefly describe the method, then show the results from numerical modeling of stick-slip experiments on granite samples with different levels of roughness, modeling of the effect of roughness and earthquake ruptures on the evolution and scaling of damage zones near small faults, and initial results from simulations with wear.

Modeling shallow slow slip events along the Hikurangi margin: Insights into their segmentation and the effect of pore-pressure cycling
Andrea Perez-Silva, Victoria University of Wellington

Over the last two decades, geodetic observations have revealed slow slip events (SSEs) in most subduction zones worldwide. Of these, SSEs that occur along the shallow (<~15 km depth) portion of the Hikurangi margin (New Zealand) are one of the most well monitored and documented. Two intriguing and as of yet poorly understood observations of shallow Hikurangi SSEs have been made recently. First, their recurrence intervals are strongly segmented along the Hikurangi margin, varying from ~5 yrs to ~1 yr. Second, pore fluid pressure in the vicinity of the megathrust fault has been inferred to cyclically vary during these SSEs. In this seminar I will discuss how two different numerical models, both applying boundary integral element method (BIEM) and within rate-and-state framework, may give insight into the mechanisms that explain these observations. Our modeling results suggest that the geometry of the subducting plate at Hikurangi may play an important role in the segmentation of SSE recurrence interval. They also indicate that pore-pressure cycling may trigger SSEs with realistic source properties. These findings may contribute to our understanding of slow slip behavior in other subduction zones.

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