Water injected into an inactive fault can cause a seismic slip along the fault - movement without detectable earthquakes - that may then indirectly lead to micro-earthquakes.

That's the result from a controlled experiment by Yves Guglielmi and colleagues, who observed these events in real time after injecting fluid into a natural fault near an underground experimental facility in southeastern France.

Researchers are intensely interested in this type of induced seismicity, especially with a rise in earthquakes caused by injections of wastewater from gas and oil exploration. The experiment by Guglielmi and colleagues offers a better look at how friction in fluid-filled faults contributes to slip along the fault.

In this case, the injected water caused very slow, four-micrometers-per-second aseismic creep on the fault before transitioning to a faster, 10-micrometers-per-second seismic slip and a series of tiny earthquakes.

As Francois Cornet notes in a related Perspective article, experiments like this could guide monitoring at injection sites by potentially keeping the injection flow rate at a level that maintains aseismic slip rather than triggering earthquakes.