Vito Rubino

Fluids in the Earth's crust are known to trigger a variety of slip events, from slow, creeping transients to dynamic earthquake ruptures, as revealed by a wide number of observations both in tectonic settings and during human activities, such as wastewater disposal associated with oil and gas extraction, geothermal energy production, and CO₂ sequestration [1-4].

We have recently developed a highly-instrumented laboratory setup capable of injecting pressurized fluids onto a simulated fault under a wide range of pressure vs. time history in order to study the rupture behavior for different rates of fluid injection [5].

_{Laboratory setup featuring a fluid-injection circuit. The hydraulic circuit is capable of injecting pressurized fluid to the interface under a wide range of pressure vs. time histories and trigger ruptures. Credit: Gori, Rubino, Rosakis, Lapusta, Proceedings of the National Academy of Sciences, 118, 51 (2021).}

We observe a gradual nucleation process when fluid is injected at the relatively slow rates, 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.

_{Injected fluid pressure vs. time histories. The plots above show two typical pressure ramp-up profiles employed to deliver fluid onto the interface, which result in substantially different rupture behavior: (a) slow and (b) fast pressure ramp up procedures. Credit: Gori, Rubino, Rosakis, Lapusta, Proceedings of the National Academy of Sciences, 118, 51 (2021).}

In contrast, when using 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, indicating that such fast injection rates constitute dynamic loading. These findings point towards the need consider the rate of the pore-pressure increase when studying nucleation processes. The observation of different frictional behavior of wet vs. dry interfaces motivate further research to understand the role of fluids in modulating friction properties.

References

1. Ellsworth WL, Injection-induced earthquakes. Science 341, 1225942 (2013).
2. Dahm T, Hainzl S, Fischer T. Bidirectional and unidirectional fracture growth during hydrofracturing: role of driving stress gradients. Journal of Geophysical Research. 115, B12, 2010.
3. Guglielmi Y, Cappa F, Avouac JP, Henry P, Elsworth D, Seismicity triggered by fluid injection-induced aseismic slip. Science 348, 1224–1226 (2015).
4. McGarr A, Bekins B, Burkardt N, Dewey J, Earle P, Ellsworth W, Ge S, Hickman S, Holland A, Majer E, Rubinstein J. Coping with earthquakes induced by fluid injection. Science 347, 830-831 (2015).
5. Gori M, Rubino V, Rosakis AJ, Lapusta N, Dynamic rupture initiation and propagation in a fluid-injection laboratory setup with diagnostics across multiple temporal scales, Proceedings of the National Academy of Sciences, 118 (51), e2023433118 (2021).