Fault zones play a key role in shaping the deformation of the Earth’s crust. All of these zones contain fluids, which heavily influence how earthquakes propagate. In an article published today in Nature Communications, Chiara Cornelio, a Ph.D. student at EPFL’s Laboratory of Experimental Rock Mechanics (LEMR), shows how the viscosity of these fluids directly affects an earthquake’s intensity. After running a series of laboratory tests and simulations, Cornelio developed a physical model to accurately calculate variables such as how much energy an earthquake needs to propagate—and, therefore, its force—according to the viscosity of subsurface fluids.