Seismic and aseismic slip in faults with rock gouge using a 3D laboratory earthquake setup: the effect of fluid injection rate

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Fluids play a key role in earthquake source processes. A large body of observations has shown the close connection between fluids and faulting. This is observed in natural events and in earthquakes induced by human activities, such as carbon sequestration, geothermal energy extraction, and wastewater disposal associated with oil and gas extraction. Here the researchers investigate the relation between fluid injection and the resulting seismic response. This response ranges from slow aseismic slip (no earthquake) to unstable seismic slip (earthquake). They use a highly instrumented laboratory setup comprising fault analogs which allow 3-D visualization of fault responses. Time sequences of unstable slips are captured by a high-speed camera. Fluid injection rate and pressures are recorded at the fault interface. The state-of-the-art bench top experiments contribute to the fundamental understanding of the role of fluids in faulting. They provide critical experimental measurements for the validation of 3-D numerical codes modeling fluid induced seismicity. The project provides support for an early-career scientist, graduate and undergraduate students, and fosters outreach toward high-school and middle-school students and their teachers. Its outcomes improve earthquake hazard assessment, notably related to human activities. The project is co-funded by both the Geophysics program and the Tectonics program. Here, the laboratory experiments produce frictional ruptures triggered by highly controlled fluid injection in 3-D specimens. The simulated fault can host a range of rupture behavior, ranging from slow slip all the way to fully dynamic response. Dynamic ruptures spontaneously propagate along a frictional interface with slip rates of the order of 0.1-10 m/s; this range is highly relevant to natural earthquakes. 3-D specimens and setup allow testing the hypothesis that low vs. fast injection rate can result in stable vs. unstable slip behavior. The experiments feature rock gouge interfaces embedded in specimens made of a polymeric material, poly-methyl-methacrylate (PMMA). This material is readily available in bulk form and makes possible the production of 3-D samples. Using polymers as analog materials yields several advantages, including their small nucleation sizes for unstable slip, and transparency, which are here essential. The ability to closely monitor the fault behavior at a high level of detail enable the team to explore and quantify the connection between slow slip and dynamic rupture.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.