Observation of anomalous elastic behavior in rock at low temperatures

We have measured qualitative elastic properties of basalt and Berea sandstone from room temperature down to 4 K using Resonant Ultrasound Spectroscopy (RUS). A simple elastic solid should show a monotonic increase in the elastic constants as temperature decreases. The basalt samples show this gross behavior while the sandstone shows a very unexpected anomalous regime between 40 K and 200 K where the elastic constants decrease with decreasing temperature. Both rocks show temperature‐dependent structure in both the modulus and internal friction, and also significant hysteresis, indicating history and rate‐dependent properties. This data provides insight into the time and energy scales of dynamical effects observed in sandstones. The low temperature range (4K–300K) is of interest due to the renewed interest in Mars and Lunar rocks.