Absolute stress levels on numerically simulated faults: definitions, links to seismological observables, and differences for crack-like vs. pulse-like ruptures

Valere R. Lambert, & Nadia Lapusta

In Preparation September 8, 2020, SCEC Contribution #10799

Determining absolute stress levels on faults has profound implications for fault mechanics and earthquake physics. Recent studies have shown that average measures of shear stress can depend on both the style of motion along the interface and scale at which stress is inferred, posing challenges for comparing notions of fault strength from laboratory to field scales. In this study, we investigate the similarities and differences among three measures of average shear stress on faults; 1) the spatially-averaged stress, 2) the dissipation-based stress, and 3) the energy-based stress, as well as their relation to notions of average fault strength. Using numerical simulations of earthquake sequences and aseismic slip on rate-and-state faults with enhanced dynamic weakening from the thermal pressurization of pore fluids, we examine the scaling of average stress measures related to dynamic rupture with overall rupture size and weakening behavior, as well as their relationship with seismologically inferable quantities. Energy-based average stress measures are likely the most useful as they can in principle be inferred from thermal constraints and seismic observations of apparent stress and static stress drop. Our models also demonstrate the significance of both rapid dynamic weakening and healing of shear resistance within the duration of dynamic ruptures, as exhibited by self-healing pulse-like ruptures, for facilitating strong faults with low dynamic resistance and moderate static stress drops. Our results suggest that re-examining seismological estimates of radiated energy and static stress drop from large earthquake ruptures may improve constraints on average absolute stress levels on seismogenic faults.

Citation
Lambert, V. R., & Lapusta, N. (2020). Absolute stress levels on numerically simulated faults: definitions, links to seismological observables, and differences for crack-like vs. pulse-like ruptures. Journal of Geophysical Research: Solid Earth, (in preparation).