The Peculiar Acoustics of Rocks
For centuries, humans have used rocks as building materials. From the Parthenon of ancient Greece to the more recent Strasbourg cathedral to the Texas State capital building rock endures. Although the mechanical and acoustical properties of rocks should be very well known, it turns out that quite the opposite is true. Rocks, in fact, exhibit some very peculiar behaviors. In addition to often being nonlinear, they exhibit hysteresis when pushed and pulled and have mechanical properties that slowly vary in time. All of these behaviors may also vary in their response, depending on the stimuli. Thus, although in some ways rocks can be treated as simple solids, in other ways they behave more like fluids. The real answer, however, is somewhere in between. Because of the complexity of the behavior of rocks, our quest is for measurements and for the simplest models that can capture all the important features of the peculiar behavior of a rock. Ultimately, such models can be used to predict and better understand what goes on beneath our feet.