Fluids in the earth’s crust promote earthquakes, as well as a variety of seismic slip events, both in natural tectonic contexts and potentially due to industrial activities, such as sewage disposal, geothermal energy production and CO2 storage. To study the physical processes linking fluids and sliding motion, we designed a laboratory seismic device capable of injecting fluid over a simulated fault and monitoring the resulting slip over a wide range of temporal and spatial scales. Our results indicate that faster injection rates result in lower fluid pressure at the onset of failure, highlighting the role of the fluid injection rate in inducing seismic events or seismic slip. We also find that the presence of fluids significantly affects the dynamic propagation of failure.
Fluids are known to trigger a wide range of slip events, from slow, creeping transients to dynamic earthquake breaks. However, the detailed mechanics underlying these processes and the conditions leading to different failure behaviors are not well understood. Here, we use a seismic lab setup, capable of injecting fluids under pressure, to compare the failure behavior for different fluid injection rates, slow (megapascals per hour) versus fast (megapascals per second). We find that for rapid injection rates, dynamic ruptures are triggered at lower pressure levels and on much smaller spatial scales than quasistatic theoretical estimates of nucleation sizes, suggesting that such rapid 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 a gradual acceleration of the slow glide. The resulting dynamic ruptures propagating on wetted interfaces exhibit dynamic stress drops almost twice as large as those on dry interfaces. These results suggest the need to take into account the rate of increase in pore pressure when examining nucleation processes and motivate further investigation into how frictional properties depend on the presence of fluids.
- Accepted November 3, 2021.
Author contributions: research designed by MG, VR, AJR and NL; MG carried out research; MG analyzed the data; and MG, VR and NL wrote the article.
The authors declare no competing interests.
This article is a direct PNAS submission.
This article contains additional information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2023433118/-/DCSupplemental.