Abstract
P wave velocities of both dry and saturated rocks were measured during a slow temperature change (0.5K/min.) between 110K and 370K. Their thermal expansions were measured simultaneously. The change of P wave velocity was larger by about one or two orders than that expected from the net change of sample length due to thermal expansion. In the dry condition, hysteresis in the temperature-P wave velocity relation was observed in only granite among various kinds of rocks, which is explained by frictional sliding at the surface of microcracks and crushing of microcrack asperities. In the saturated condition, however, hysteresis was observed in all rocks due to the temperature difference between freezing and thawing of water within pores and microcracks. A large increase in P wave velocity was observed in all rocks between 273K and 230K during cooling. A sharp decrease in P wave velocity coincided with thermal cracking detected by the changes of both the activity of acoustic emission (AE) and thermal expansion. These observations suggest that the temperature effect on P wave velocity of rock is strongly affected by (1) thermal cracking, and (2) the phase change of water within pores and microcracks.
