Fluid viscosity impact on earthquake's intensity

According to a research conducted by a PhD candidate at EPFL, the viscosity of fluids affects the intensity of earthquakes.

The study, which was recently published in Nature, was carried out by Chiara Cornelio, PhD student at EPFL's Laboratory of Experimental Rock Mechanics (LEMR). It showed that viscosity of fluids that exist in fault zones affect the magnitude of seismic events.

Cornelio simulated earthquakes with different intensities and propagating speeds with 4 fluids with different viscosity. The experiments were performed with SHIVA (slow to high velocity apparatus), a rotary shear machine, on full cylinder samples of Westerly granite and Carrara marble. The results of 36 laboratory tests showed that there is a clear correlation between earthquake intensity and fluid viscosity. In particular, the tests showed that both static and dynamic friction coefficients decrease with viscosity.

"Imagine these fluids working like soap, reducing the friction between your hands when you wash them, or like the oil you spray on mechanical parts to get them moving again. Moreover, naturally occurring earthquakes produce heat when the two plates rub together. That heat melts the rock, creating a lubricating film that causes the fault to slip even further. Our study also gives us a clearer picture of how that natural process works," Assistant Professor and head of LEMR, Marie Violay, stated.

The study is part of a wider research program which includes geothermal energy projects that can trigger seismic events (induced seismicity). "Subsurface exploration projects such as geothermal power, injection wells and mining all involve injecting pressurized fluids into fractures in the rock. Studies like this show how a better understanding of the properties and effects of fluids is vital to preventing or attenuating induced earthquakes. Companies should factor these properties into their thinking, rather than focusing solely on volume and pressure considerations," Cornelio stated.