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

Abstract

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.

The Role of Background Stress State in Fluid‐Induced Aseismic Slip and Dynamic Rupture on a 3‐m Laboratory Fault

“…During all experiments the top, bottom, and sides ( z = 0 m, z = 0.3 m, x = 0 m, and x = 3.1 m) of the fault interface were left open to atmospheric pressure similar to previous cm‐to m‐scale laboratory experiments (Cebry & McLaskey, 2021; Gori et al., 2021; Lockner et al., 1982), since common methods of jacketing and adding confining pressure are not feasible for 3 m long samples.…”

High‐Rate Fluid Injection Reduces the Nucleation Length of Laboratory Earthquakes on Critically Stressed Faults in Granite

“…Fault reactivation induced by local fluid pressure perturbation has been reported over a wide range of spatial scales from lab (centimeters to meters), mine (decameters) to reservoir (kilometers) faults. In laboratory samples, fault slip induced by elevated and heterogeneous fluid pressure has been studied by regulating the injection rate, the prestresses applied to faults, and fault roughness (Cebry & McLaskey, 2021; Gori et al., 2021; Ji & Wu, 2020; Passelègue et al., 2018). Local fluid pressure perturbations due to fluid injection may directly induce aseismic slow slip, and then trigger seismic events, as has been observed for the induced seismic slip of a carbonate fault zone at mine scale in the Low Noise Underground Laboratory in France (Cappa et al., 2018, 2019; Guglielmi et al., 2015), and the 2016 M w 4.1 earthquake initiated in the Duvernay shale's caprock at field scale in Canada (Eyre et al., 2019).…”

“…More recently, Gori et al. (2021) demonstrated for the first time that the nucleation length of laboratory earthquakes on plastic polymers induced by high‐rate local fluid injection is smaller than that in the low‐rate cases, suggesting that higher injection rates may constitute dynamic loading and reduce the nucleation length. However, a systematic laboratory study characterizing the injection‐rate dependence of earthquake nucleation length of faults in rock samples and its implications for injection‐induced seismicity are lacking.…”

“…Similarly, the nucleation length calculated from rate-and-state frictional parameters obtained from velocity-stepping tests on wet fault gouges under a variety of boundary conditions is smaller at lower fluid pressures and higher slip rates (Cappa et al, 2019). More recently, Gori et al (2021) demonstrated for the first time that the nucleation length of laboratory earthquakes on plastic polymers induced by high-rate local fluid injection is smaller than that in the low-rate cases, suggesting that higher injection rates may constitute dynamic loading and reduce the nucleation length. However, a systematic laboratory study characterizing the injection-rate dependence of earthquake nucleation length of faults in rock samples and its implications for injection-induced seismicity are lacking.…”

A Spectral Boundary‐Integral Method for Faults and Fractures in a Poroelastic Solid: Simulations of a Rate‐and‐State Fault With Dilatancy, Compaction, and Fluid Injection

“…We emphasize that selecting γ = 1.7 · 10 −4 does not generally mean unconditionally stable ruptures. One could achieve seismic rupture by choosing a more rate‐weakening (and hence instability‐promoting) friction properties or by altering the injection strategy; for example, injecting at a higher rate may lead to a seismic event (Gori et al., 2021).…”