Time-lapse measurement of P-wave velocities under the freeze-thaw condition in various rocks

Global warming issues have led to pronounced cryospheric changes in mountainous areas and cold regions. Freeze-thaw weathering can alter the properties of rock masses and permafrost soils, drastically changing local environmental and geological conditions. So far, although many in-situ and laboratory tests have investigated the variation of mechanical and hydraulic properties of rock under changing temperatures, the effect of temperature variation on the rock seismic properties (e.g., elastic wave velocity, wave amplitude, wave frequency, and wave attenuation) is still insufficiently studied. In this study, we developed a laboratory setup for time-lapse measurement of ultrasonic wave propagation across rocks under freeze-thaw conditions. The P-wave velocities under changing temperature from −20 ℃ to 20 ℃ were continuously recorded for four types of rocks (i.e., granite, marble, sandstone, and gabbro) under both dry and saturated conditions. The results demonstrate that the P-wave velocity of all saturated rocks drops significantly when the temperature is above 0 ℃. Particularly, saturated sandstone was observed to have the greatest drop in wave amplitude, probably owing to the relatively high water content due to its high porosity. Also, we observe a hysteresis of wave velocity related to the rocks' temperature gradient during the freeze-thaw cycles. These findings provide new insights into rock dynamic responses related to temperature changes in the cryosphere and cold regions.