Two stone discs and a flywheel may sound like a Flintstonian vehicle, but in fact, it’s the recipe for a new, rather high-tech device that scientists are using to study earthquakes in the lab, described in a recent Science paper.
In an actual earthquake, two jagged rock faces slide past each other at fault lines, and the energy of that collision propagates through the earth in waves. In this experiment, the researchers simulate a fault line using two stone disks one atop the other and a 500-pound metal flywheel. In the simulated quake, the energy of the spinning flywheel is transmitted to the bottom disc through a shaft (or clutch, for those more familiar with cars), and the bottom disc starts spinning, moving past the top disc until friction brings the “slip” grinding to a halt.
Previously, scientists applied pressure to opposing rock surfaces to simulate quakes, but that pressure was not great enough to mimic large ones. This experimental setup approximates quakes of magnitudes 4 through 8, which is quite a range, since earthquakes are measured on a logarithmic scale. Magnitude 4 is considered a light quake (one struck near the California-Mexico border in May 2012), while magnitude 8, 10,000 times larger, is considered a great quake, around the size of the Sumatran earthquake of 2000 (magnitude 7.9). For more context, the Italian earthquakes in May, 2012, were around magnitude 6. In 1968, Japan had a magnitude 8.3 quake, and the 1960 Chilean earthquake, of magnitude 9.5, is the largest ever recorded.
In this new set-up, the scientists apply a defined amount of energy to the rocks and then observe how the rocks move past each other—their friction, acceleration, and so on. In the future, they think that scientists could do the reverse: use measurements from real earthquakes to estimate the quakes’ total energy, which they cannot do using the seismic data they now collect.