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The Effect of Stress and Friction Heterogeneity on Complexity of Seismic and Aseismic Slip on Strike-Slip Faults

Jeena Yun, Yuri Fialko, & Alice-Agnes Gabriel

Submitted September 10, 2023, SCEC Contribution #13035, 2023 SCEC Annual Meeting Poster #046

Numerical and laboratory models of earthquake cycles on faults governed by rate and state friction typically show a cycle-invariant behavior, while natural fault slip exhibits considerable variability. Possible explanations include heterogeneities in fault stress and/or frictional properties. We explore to what extent earthquake rupture complexity, size-frequency distribution, hypocenter location, and aseismic transients arise from various types of heterogeneity in simulations of quasi-dynamic sequences of earthquakes and aseismic slip. We model a 2D vertical strike-slip fault using Tandem (Uphoff et al., 2023) and ​​study the effects of self-affine fractal distribution of the effective normal stress, velocity-dependent parameter (a-b), and characteristic slip-weakening distance (Dc), as well as the presence of a low-rigidity damage zone. We find that characteristic earthquake sequences are insensitive to heterogeneities in any single model parameter. Only a combination of heterogeneous model parameters introduces realistic variability in the modeled earthquake sequences. In particular, variable hypocenter depths require velocity-strengthening patches inside the velocity-weakening seismogenic zone, and small Dc on the order of 1-2 mm. The primary control on hypocenter locations is the transitions from velocity-weakening to velocity-strengthening friction where the stressing rate is increased. In our most complex model, system-size events are always preceded by a cascade of partial ruptures, following a Gutenberg-Richter-type power law. Deep and shallow slow slip events (SSEs) occur after system-size and partial ruptures. The recurrence interval of the deep SSEs shows dependency on the size of the preceding earthquake, being shorter after larger events. Our simulation results emphasize the importance of the variability of frictional properties along the fault in reproducing realistic earthquake characteristics and suggest that deep SSEs on strike-slip faults may be ubiquitous.

Key Words
SEAS, Earthquake cycle simulation, fault heterogeneity, fault damage zone

Yun, J., Fialko, Y., & Gabriel, A. (2023, 09). The Effect of Stress and Friction Heterogeneity on Complexity of Seismic and Aseismic Slip on Strike-Slip Faults. Poster Presentation at 2023 SCEC Annual Meeting.

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