Theoretical and experimental analyses of the temperature responses of
water-saturated rocks to changes in confining pressure
Abstract
The temperature response of water-saturated rocks to stress changes is
critical for understanding thermal anomalies in the crust, because most
porous rocks are saturated with groundwater. In this study, we establish
a theoretical basis of the adiabatic pressure derivative of the
temperature of water-saturated rocks under both undrained (βwet_U) and
drained (βwet_D) conditions. The value of βwet_U is linearly
correlated with Skempton’s coefficient (B) and βwet_D increases
nonlinearly as the pore water volume per unit volume of rock (ξ)
increases. The theoretical calculations demonstrate that the thermal
effects of pore water predominate in water-saturated rocks with medium
to high porosity, especially under undrained conditions. In most cases,
the temperature response of rocks with a porosity of ϕ >
0.05 under water-saturated and undrained conditions is greater than that
under dry conditions. Experiments were also carried out on a
water-saturated typical medium porosity sandstone (sample RJS, ϕ =
0.102) and on a compact limestone (sample L27, ϕ = 0.003) using an
improved hydrostatic compression system. The experimental results
confirm that the theoretical derivation is correct, and the calculated
ranges of βwet_U and βwet_D are reliable for all 15 rocks.
Consequently, this study increases our understanding of the thermal
anomalies that occur after huge earthquakes, including the negative
thermal anomalies, which are probably induced by co-seismic stress
release, that were observed in the boreholes that penetrate seismic
faults after the Chi-Chi Earthquake, the Wenchuan Earthquake, and the
Tohoku Earthquake.