It has been the subject of numerous Hollywood movies, and is often referred to as “the big one” — the potentially massive earthquake and resulting tsunami that will, one day, affect North America’s west coast. But how does one measure the potential impact of an earthquake?
In a new study published in the March 7 edition of Science Advances, Pascal Audet, associate professor of Earth sciences at the University of Ottawa, and Andrew Schaeffer, Banting fellow, describe how they used technology akin to ultrasonography — an imaging technique using sound waves to view an internal structure — to finally confirm how the friction responsible for earthquake rupture varies downward along the fault line. By inferring the levels of fluids in the rocks, Audet was able to determine that at shallow depth, fluids are free to circulate through the rocks and friction is higher where earthquakes occur. At greater depth, the fluids become trapped in the rocks and lubricate the fault, decreasing friction and preventing earthquake propagation.
These findings are important, as they will help scientists understand the factors responsible for earthquake ruptures at subduction zones (where oceanic plates dive under the continent), and they can be used as to help estimate the level of shaking during a large earthquake.