Evolution of frictional shear resistance in response to rapid variations of normal stress

Yuval Tal, Vito Rubino, Nadia Lapusta, & Ares J. Rosakis

Published August 14, 2018, SCEC Contribution #8491, 2018 SCEC Annual Meeting Poster #174

A proper formulation of the shear-resistance evolution during rupture is essential for many earthquake source problems, including simulations of the ground motion. While the shear resistance is typically assumed to be proportional to normal stress, several studies have shown a gradual, slip-dependent, response of the frictional shear resistance to rapid variations in the normal stress. Here we use laboratory experiments to quantify normal stress variations and the corresponding evolution of the frictional shear resistance produced by the interaction of dynamic ruptures with the free surface, similarly to what occurs in natural thrust events. The experiments also enable studying the potential fault opening and ground motion of the simulated thrust faults. In order to image and quantify the full-field behavior of the ruptures near the free surface, we use an experimental technique (Rubino et al., 2017) that combines ultra-high speed photography and digital image correlation to produce maps of dynamic displacements, velocities, strains, and stresses at intervals of less than a microsecond. It allows us to image the evolution of fault-normal stress and fault-parallel shear stress, and thus to study how friction evolves under the conditions of rapid normal stress variations. We enhance the experiments with dynamic simulations, using a self-developed finite element simulator (Tal and Hager, 2017). The simulations help us to design the experiments, explore a wider range of geometries and loading conditions, constraint parameters and conditions that cannot be constraint solely by the experiment, and study how the ground motion would be affected by different assumptions about the friction evolution on the fault near the free surface.

Citation
Tal, Y., Rubino, V., Lapusta, N., & Rosakis, A. J. (2018, 08). Evolution of frictional shear resistance in response to rapid variations of normal stress. Poster Presentation at 2018 SCEC Annual Meeting.

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