A nanoindentation study of attenuation in geological materials

Viscoelastic behavior in geological materials controls a wide range of geophysical phenomena, such as mantle convection. We present a new method for measuring attenuation in single crystals of minerals and in reference materials over a frequency range of 1-1e-4 Hz via nanoindentation. In the experiments, we calculate the phase lag between a sinusoidal load applied to the tip of the nanoindenter and its displacement into and out of the tested sample, which provides a measure of the inverse quality factor 1/Q (i.e., attenuation) of the sample. Experiments were conducted on polymethyl methacrylate (PMMA), indium, halite, olivine and quartz. Attenuation spectrum from our tests on PMMA and indium are in excellent agreement with reported values from past studies. We quantified the natural damping of the nanoindenter and show that it becomes comparable to that of the samples at frequencies greater than 0.1 Hz, but is much lower at lower frequencies.