Earthquake Sequences in Rate-and-State Fault Models with Thermal Pressurization

Valere R. Lambert, Stephen M. Perry, & Nadia Lapusta

Published August 7, 2018, SCEC Contribution #8308, 2018 SCEC Annual Meeting Poster #194

Theoretical studies and laboratory experiments indicate that dynamic weakening, such as thermal pressurization of pore fluids, likely acts during earthquakes on mature natural faults. At first glance, this seems incompatible with the fact that stress drops are inferred to be magnitude-invariant, since larger events may experience greater weakening, with lower final shear stresses. Through studies of long-term earthquake sequences in fault models that include standard rate-and-state friction and thermal pressurization, we show that such models do reproduce observationally inferred stress drop invariance for events that do not span the entire seismogenic segment, due to the averaged initial shear stress being lower for larger events. Stress drops for segment-spanning events depend on the properties of the arresting velocity-strengthening region at the segment edges. Furthermore, such models (1) also reproduce the inferred values of the radiation efficiency and the inferred increase of breakdown energy with event magnitude, and (2) result in ruptures with seismological estimates of fracture energy and radiation efficiency similar to values inferred directly based on the on-fault properties, making comparison to the values inferred for natural earthquakes self-consistent. However, the resulting ruptures, for the model parameters investigated, are either crack-like or mildly pulse-like, and not sharply pulse-like as suggested by some observations. Our current work is directed towards investigating parameter regimes that produce more pulse-like ruptures.

Citation
Lambert, V. R., Perry, S. M., & Lapusta, N. (2018, 08). Earthquake Sequences in Rate-and-State Fault Models with Thermal Pressurization. Poster Presentation at 2018 SCEC Annual Meeting.

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