In the biaxial friction apparatus above, two wedges of natural rock are loaded horizontally and vertically until the stresses resemble a fault in the earth. Then the vertical load is increased until the rocks begin to slide. As the normal stress increases, the fault will transition from smoothly creeping to stick-slipping. Stick-slip events are like mini-earthquakes and can be heard as little cracks and pops. We use transducers, which act like mini-seismometers, to measure waves (below) that come from the slip events.
