Dynamic rupture initiation and propagation in a fluid-injection laboratory setup with diagnostics across multiple temporal scales

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 118; no. 51; pp. 1 - 12
• Main Authors: Gori, Marcello, Rubino, Vito, Rosakis, Ares J., Lapusta, Nadia
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 21.12.2021
• Subjects: Dynamic loads; Earthquakes; Fluid injection; Hydrodynamics; Injection; Interfaces; Laboratories; Mechanical loading; Models, Theoretical; Nucleation; Physical Sciences; Pressurized fluids; Rupture; Rupturing; Seismic activity; Slip; Stress propagation; earthquake source physics; nucleation length; fluid pore-pressure rate; laboratory earthquakes; fluid-induced seismicity
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2023433118

Fluids are known to trigger a broad range of slip events, from slow, creeping transients to dynamic earthquake ruptures. Yet, the detailed mechanics underlying these processes and the conditions leading to different rupture behaviors are not well understood. Here, we use a laboratory earthquake setup, capable of injecting pressurized fluids, to compare the rupture behavior for different rates of fluid injection, slow (megapascals per hour) versus fast (megapascals per second). We find that for the fast injection rates, dynamic ruptures are triggered at lower pressure levels and over spatial scales much smaller than the quasistatic theoretical estimates of nucleation sizes, suggesting that such fast injection rates constitute dynamic loading. In contrast, the relatively slow injection rates result in gradual nucleation processes, with the fluid spreading along the interface and causing stress changes consistent with gradually accelerating slow slip. The resulting dynamic ruptures propagating over wetted interfaces exhibit dynamic stress drops almost twice as large as those over the dry interfaces. These results suggest the need to take into account the rate of the pore-pressure increase when considering nucleation processes and motivate further investigation on how friction properties depend on the presence of fluids.