Interaction of earthquake rupture with idealized fault inhomogeneities: Effects on rupture speed, slip, and seismic radiation

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This study will advance our fundamental understanding of the dynamics and physics of earthquake-producing faults, focusing on the relation between fault features and seismic radiation, with applications to seismic hazard mitigation. One key question this project aims to answer is if the presence of fault inhomogeneities may cause earthquake ruptures to accelerate and propagate at supershear speeds. It is important to understand the conditions under which supershear earthquakes occur, since supershear ruptures can cause much stronger shaking farther from the fault than subshear ones. Can such destructive earthquakes occur on faults in the US, for example, on the San Andreas fault, some parts of which are locked and loaded for the new big one?According to well-established theories, homogeneous faults require a high level of shear stress to propagate at supershear speeds. Yet numerous field observations reveal that supershear earthquakes occur on mature strike-slip faults that operate at low overall levels of shear prestress. Recently, numerical simulations have shown that heterogeneous faults with patches of higher stress or lower strength can transition to supershear speeds under a much wider range of prestress conditions than what is obtained in models with homogeneous strength. Motivated by these findings, we plan to carry out a combined laboratory and numerical study of how the speed of earthquake ruptures, as well as their accumulated slip and resulting seismic radiation, are affected by several fault inhomogeneity features likely to be present on natural faults. We will also investigate the complimentary question of what the radiated wave fields can tell us about the variations in fault properties. In addition to clarifying the dynamics and physics of earthquakes, the developed well-characterized experiments on faults with inhomogeneity can serve as benchmarks for validation of kinematic inversion models and dynamic rupture codes. The new proposed experimental technique for the enhanced characterization of dynamic rupture processes by coupling digital image correlation and high speed photography can become an invaluable tool for studies of transient phenomena in earthquake science and solid mechanics.