Supershear transition of earthquake rupture on 3D faults with compact heterogeneity

Mary Agajanian, & Nadia Lapusta

Published September 10, 2023, SCEC Contribution #13034, 2023 SCEC Annual Meeting Poster #110

Ruptures with intersonic speeds (“supershear”) have been observed both experimentally and in the field. Supershear ruptures have characteristic Mach fronts that may carry large shaking velocities far from the fault. Thus, such ruptures can have more devastating economic and societal consequences. The traditional Burridge-Andrews mechanism of supershear transition (Andrews, 1976) requires faults to be sufficiently prestressed to transition to intersonic rupture speed. However, mature faults may have relatively low stresses (e.g., Jiang and Lapusta, 2016; Lambert et al., 2021) and also support intersonic rupture speeds.

Here, we show that the contradiction may be resolved by favorable fault heterogeneity. In fully-dynamic modeling of a single 1D rupture in a 2D inplane elastic medium, Liu and Lapusta (2008) showed that supershear transition can be triggered by favorable fault heterogeneity even when shear stresses are lower than required by the Burridge-Andrews mechanism. Building on an earlier exploration (Yi Liu, PhD thesis, Caltech), our study extends their work to 2D faults governed by rate and state friction in 3D elastic media in the context of sequences of dynamic events. We find that the interaction of a weaker patch with the rupture leads to supershear transition in the long-term under lower prestress than would be required on a uniform fault. We also show that quasi-dynamic formulations do not reproduce the long-term supershear behavior, as supershear transition is a wave-mediated mechanism and stress transfer on the fault through waves is ignored in the quasi-dynamic formulation. In summary, we find that favorable heterogeneity can reconcile observations of low-stress faults and supershear ruptures, and that quasi-dynamic formulations can produce qualitatively different outcomes.

Citation
Agajanian, M., & Lapusta, N. (2023, 09). Supershear transition of earthquake rupture on 3D faults with compact heterogeneity. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)